Sarcoidosis is a systemic granulomatous disease of unknown etiology. Hypergammaglobulinemia and the presence of autoantibodies in sarcoidosis suggest active humoral immunity to unknown antigen(s). We developed a complex cDNA library derived from tissues of sarcoidosis patients. Using a high throughput method, we constructed a microarray platform from this cDNA library containing large numbers of sarcoidosis clones. After selective biopanning, 1070 sarcoidosis-specifc clones were arrayed and immunoscreend with 152 sera from patients with sarcoidosis and other pulmonary diseases. To identify the sarcoidosis classifiers two statistical approaches were conducted: First, we identified significant biomarkers between sarcoidosis and healthy controls, and second identified markers comparing sarcoidosis to all other groups. At the threshold of an False Discovery Rate (FDR) < 0.01, we identified 14 clones in the first approach and 12 clones in the second approach discriminating sarcoidosis from other groups. We used the classifiers to build a naïve Bayes model on the training-set and validated it on an independent test-set. The first approach yielded an AUC of 0.947 using 14 significant clones with a sensitivity of 0.93 and specificity of 0.88, whereas the AUC of the second option was 0.92 with a sensitivity of 0.96 and specificity of 0.83. These results suggest robust classifier performance. Furthermore, we characterized the informative phage clones by sequencing and homology searches. Large numbers of classifier-clones were peptides involved in cellular trafficking and cytoskeletons. These results show that sarcoidosis is associated with a specific pattern of immunoreactivity that can discriminate it from other diseases.The online version contains supplementary material available at 10.1186/s43556-021-00064-x. Sarcoidosis is a granulomatous disease of unknown etiology , yet theSarcoidosis often coincides with other autoimmune disorders such as lupus erythematosus, vitiligo , autoimmmycobacterium tuberculosis and propionibacterium acne) [Hypergammaglobulinemia, widely regarded as non-specific, is a frequent finding in sarcoidosis that may suggest active humoral immunity to unknown antigen(s) . Targeteum acne) , 20, as um acne) –23. ThesThe prevalence of sarcoidosis is higher in the northern hemisphere. Furthermore, it has been reported that the incidence of sarcoidosis is increasing in the developing world and China , 25. Then = 45); sarcoidosis (n = 52), smear-positive TB patients (n = 24), and lung adenocancer (LC) patients (n = 31). The demographics of the study subjects are shown in  sarcoidosis training samples vs. healthy control training samples (option 1), and ii) sarcoidosis training samples vs. the rest . Two options resulted in two sets of differentially expressed clones. The first approach (option 1) at the threshold of False Discovery Rate (FDR) < 0.05 identifies 132 and at the threshold of FDR (< 0.01) identifies 14 significantly different clones between sarcoidosis and healthy controls.Two PCA plots were constructed to determine if the 132 significant clones (FDR < 0.05) and 14 clones (FDR < 0.01) from option1 can improve the class separation of sarcoidosis immune reactivity from healthy controls, TB and lung cancer samples. As shown in Fig. p-values and chose top 12 reactive clones in option 2 to construct PCA plot and hierarchical clustering. As shown in Fig. The statistical approach in option 2 yielded in 221 significant clones (FDR < 0.01) differentiating sarcoidosis from all other conditions. To demonstrate the performance of the clones identified through option 2 , we applied PCA and hierarchical clustering. As shown in Fig. Venn diagram illustrates the significant clones yielded through two different statistical approaches as well as their intersection Fig. a and b. A heatmap plot Fig.  displaysTo determine the classification performance of the identified clones using option 1 and 2, we applied the naïve Bayes classification method using option 1 and option 2 significant clones. We also assessed the classification performance of the top 14 clones from option1 and the top 12 clones from option 2. The classification models were trained on the training set and tested to classify sarcoidosis samples from other  on the testing set. As shown in Fig. p-values.Based on the results of training and test sets, we characterized the sarcoidosis classifier clones through sequencing. We sequenced classifiers’ clones and applied Expasy program to translate the cDNA sequences to peptide/protein sequences. Protein blast using algorithms of the BLAST program was applied to identify the highest homology to identified peptides , 27. Furpropionibacterium acnes and Mycobacterium tuberculosis in sarcoidosis tissues [Patients with sarcoidosis exhibit various immunological features including, a shift towards T helper type 1 response , lymphop tissues , 30–32.  tissues . Sarcoid tissues , and aut tissues , 12–14.  tissues .Using the serological analysis of antigens by recombinant expression cloning (SEREX) as a basis for autoantibody discovery, we critically examined the relevant methods of biomarker discovery and developed an innovative immunoscreening to optimize the identification of specific autoantibodies , 34, 35.Previously, we have shown that our complex antigen library detects autoantibodies as biomarkers in sera of sarcoidosis, cystic fibrosis and MTB patients with high sensitivity and specificity as compared to healthy subjects , 26, 27.Among 18 classifier clones, one clone  was repeated in both approaches. Importantly, in our previous published work, this sequence was also identified as sarcoidosis specific clone . Human merbB-4 gene. This gene is a member of the tyrosine protein kinase family and the epidermal growth factor receptor subfamily and is one of the four members in the EGFR subfamily of receptor tyrosine kinases. Three important antigen clones were related to cytoskeleton. We identified an antigenic peptide with 23 AA, which has homology to Cofilin 1. Cofilin family promotes actin filament disassembly and has been shown to be involved in myofibroblast differentiation [PATJ) protein has multiple PDZ domains. PDZ domains interact as scaffold protein to organize multimeric protein complexes at the cell membrane and are involved in signaling, trafficking, and function of G protein-coupled receptors [A relatively large peptide sequence (43AA) was identified with sequence homology to transformation related protein 10. This gene encodes a member of the bone morphogenetic protein (BMP) receptor family of transmembrane serine/threonine kinases. The ligands of this receptor are members of the TGF-beta superfamily. BMPs are involved in endochondral bone formation and embryogenesis. These proteins transduce their signals through the formation of heteromeric complexes of two different types of serine/ threonine kinase receptors: type I receptors of about 50–55 kD and type II receptors of about 70–80 kD . For insntiation . Interesntiation . The thintiation . Two relntiation . It has ntiation . Dysreguntiation . IL-17R ntiation . Recent ntiation . We idenntiation . The corntiation . A sequentiation . Two difntiation . Previountiation . This waeceptors . INADL peceptors . FurtherBecause various drugs may affect the autoantibody production, in current study, we performed immunoscreening using a set of sera from sarcoidosis subjects with no prior treatment. In spite of this, we found several shared antigenic clones between non-treated subjects (current study) and our previous study, in which samples derived from subjects, who were treated with immunosuppressive medication. We found a sets of classifiers with different sensitivity and specificity, some show increased expression and others showed decreased expression. Because sarcoidosis is a chronic disease involving many organs, the variation of autoantibodies expression profile may differ in early stages versus later stages or in various organ involvement. Although natural antibodies may also be beneficial to remove and neutralize pathogens, autoantibodies can directly interact with FCγ receptors or Toll- like receptors to initiate or amplify inflammation and perpetuate autoantibody production. Pathogenic autoantibodies can protect or cause diseases via neutralization of self-antigens, opsonization, antibody-dependent cellular cytotoxicity, activation of the complement system, pro-inflammatory and anti-inflammatory effect. Because of their broad reactivity for a wide variety of microbial components, natural antibodies have a major role in the defense against infections. Because some IgG autoantibodies may function as neutralization of pathogenic processes, the identification of decreased autoantibodies may be useful as therapeutics. Severel studies, including our study indicate that FCγ receptors play a role in sarcoidosis . The ideAll chemicals were purchased from Sigma-Aldrich  unless specified otherwise. LeukoLOCK filters and RNAlater were purchased from Life Technologies . The RNeasy Midi kit was obtained from Qiagen, . The T7 mouse monoclonal antibody was purchased from Novagen . Alexa Fluor 647 goat anti-human IgG and Alex Fluor goat anti-mouse IgG antibodies were purchased from Life Technologies .Mycobacterium Tuberculosis .This study was approved by the institutional review board at Wayne State University, and the Detroit Medical Center. Sera from four groups wereincluded in this study: 1) healthy volunteers; 2) sarcoidosis subjects, 3) patients with adenocarcinoma of the lungs; and 4) smear positive pulmonary TB patients. All study subjects signed a written informed consent. All methods were performed in accordance with the human investigation guidelines and regulations by the IRB (protocol No = 055208MP4E) at Wayne State University. Sera from patients with Tuberculosis were obtained from the Foundation for Innovative New Diagnostics . All TB patients had smear positive sputum for C as previously described [Blood samples were collected and stored at − 80°escribed .T7 phage display libraries from BALs, WBCs, EL-1 and MRC5 were combined to generate a complex sarcoid library (CSL) . DiffereInformative phage clones were randomly selected and amplified after four rounds of biopannings and lysates were arrayed in quintuplicates onto nitrocellulose FAST slides  using the ProSys 5510TL robot . The nitrocellulose slides were hybridized with sera and processed as described previously .Individual phage clones were PCR amplified using T7 phage forward primer 5′ GTTCTATCCGCAACGTTATGG 3′ and reverse primer 5′ GGAGGAAAGTCGTTTTTTGGGG 3′ and sequenced by Genwiz , using T7 phage sequence primer TGCTAAGGACAACGTTATCGG.log2 (red/green) fluorescent intensities. These data were pre-processed using the limma package in the R language environment [LOESS method was used for within array normalization [After hybridization, the microarrays were scanned in an Axon Laboratories 4100 scanner  using 532 and 647 nm lasers to produce a red (Alexa Fluor 647) and green (Alexa Fluor 532) composite image. Cy5 (red dye) labeled anti-human antibody was used to detect human serum IgGs were reactive to peptide clones, and a Cy3 (green dye) labeled antibody was used to detect the phage capsid protein . Using tironment , 74, 75 ironment , 76. Thelization , 76, 77.t-test correcting for multiple comparisons using the false discovery rate (FDR) algorithm with a threshold of either 0.05 or 0.01 FDR [Option 1, we applied a t-test between sarcoidosis training samples versus healthy controls training samples. Out of the 52 sarcoidosis samples, 26 samples were randomly assigned to the training set and the other 26 samples to the testing set. The training and testing set for the 45 healthy controls were randomly assigned to 23 samples in training and 22 samples in test sets. In the testing set, we added 24 tuberculosis samples and 31 lung cancer samples.To detect differentially expressed antigens for sarcoidosis, we applied a two-tailed option 2, we randomly split the samples from all groups in half. We assigned the first half of 23 control, 26 sarcoidoses, 16 lung cancer, and 12 tuberculosis samples to the training set. We assigned the second half of 22 healthy controls, 26 sarcoidosis, 16 lung cancer, and 12 tuberculosis samples to the testing set. We applied a t-test between sarcoidosis training samples versus healthy controls, lung cancer, and tuberculosis training samples to identify significant clones. For both options, we assessed the performance of classifiers clones, by applying principal component analysis (PCA), agglomerative hierarchal clustering (HC), heatmap, and naïve Bayes classifier. The naïve Bayes classifier model was built on the training samples to predict sarcoidosis samples from others  samples and tested the classification model on the testing set (samples not used in the training set).In Additional file 1. Supplementary Table 1. Clone ranking, clone ID, sequence of peptides, NCBI protein names, region of peptide similarity and % sequence coverage.


The obtained results reveal the importance of defects in graphene structure, which play a key role in wetting mechanism and the formation of AgCu alloy. As a consequence, we observe a change of the wetting behavior and topology of both bulk and adsorbed Ag atoms by using Voronoi analysis (VA). Despite the differences in time scale, atomistic simulations allowed us to catch the early stages of wetting, which are important for explaining the final stage of wetting delivered from experiment. Our findings reveal also graphene translucency to metal-metal interactions, observed in previous papers.Understanding the atomic-level phenomena occurring upon the wetting of graphene-coated Cu with liquid Ag is pivotal for the description of the wetting phenomenon and the role of graphene as a diffusion barrier. We have performed molecular dynamics (MD) simulations and confronted with our present experimental results to characterize wetting behavior of graphene coated Cu surfaces. Perfect and defected graphene layers covering Cu surface were wetted with liquid Ag droplet at 1273 K. Structural and topological aspects are discussed to characterize structure of the liquid Ag droplet and a product of wetting reaction occurring on Cu/Gn and Cu/Gn Graphene is known from its extraordinary properties, which have allowed it to find a broad spectrum of applications ranging from electronics to medicine as well as gain significant research interests . Potential applications include sensors, capacitors, energy storage devices, solar cells, transparent conductive coatings, and tissue engineering applications ,2,3. GraDiffusion at the solid/liquid interface plays a huge role in electronic packaging industry, where tin-silver-copper (SAC) solders are mostly used as joints. They form intermetallic compounds (IMCs) with substrates like Cu or Ni. The extensive growth of IMCs is unwanted due to worsening joint properties and enhancing the risk of fracture, which is dangerous for electronic devices ,13. As yIn this context, there is a gap in the knowledge about the structure and properties of metal/graphene interfaces as well as wetting of graphene-coated metallic substrates with a metal droplet. So far, few papers exist which provide knowledge about graphene layer and metal/graphene interface wetted with water requiring a further explanation ,15,16. LAtomic-scale physical models, such as molecular dynamics and Monte Carlo methods, offer a possibility of gaining insight into the wetting phenomenon, interface structure, and kinetics of potential reactions on atomic level. They involve physical and chemical equations for describing interatomic interactions, which are then pivotal for a proper description of the wetting reaction on metal and metal/graphene substrates. Only a few computational papers can be found for graphene-coated substrates as compared to a graphene layer wetted by liquid metal droplets. Caccia et al. performed ab initio calculations for a study of wetting translucency in Au droplet on a pure and graphene-supported 4H-SiC substrate as well as graphene substrate with variable layer number . As a reIn this work, we provide the first atomic level insight into a wetting mechanism, structure, and topology of a silver droplet wetting graphene-coated Cu substrate at 1273 K. The aim of our paper is to unveil the mechanism of graphene wetting with liquid Ag droplet, and the structure of both Cu/graphene interface and the liquid droplet. For comparison, pure Cu substrate and a graphene layer are also considered. Here we present molecular dynamics simulation results and experimental observations. To get a more detailed insight into the mechanism of graphene wetting and its better understanding, we monitored changes of contact angle with time and provided information on structural and topological aspects to better understand the behavior of liquid droplet and the wetting phenomenon. def). In the last case, two atomic columns in the center of the graphene layer were removed. Depending on the interaction type, we used charge-optimized many body potential (COMB3) formalism [Molecular dynamics simulations have been performed for the study of structure, wetting properties and spreading mechanism of silver droplet on Cu/graphene substrate at 1273 K. We have considered four different substrate variants wetted with a silver droplet. They are pure Cu, graphene layer (Gn), Cu substrate covered by both a perfect graphene (Cu/Gn) and defect containing graphene layers  potential for describing the van der Waals interaction between liquid Ag droplet and graphene layer:For describing metal-metal interaction (Ag-Ag and Cu-Ag), the embedded atom model (EAM) potential was used , with paAg-Cε) and interatomic distance (Ag-Cσ) between Ag and C were 0.0301 eV and 3.006 Å, respectively, as standard numerical values reported in the literature [The interaction energy  until a droplet was formed. In the second step, the Ag droplet was placed about 7 Å over the four different substrate variants. MD simulations with canonical ensemble (NVT) were performed at 1273 K for three substrate variants with maximum simulation time up to 0.5 ns, and 1 ns for Cu/Gndef/Ag system. In the case of variant of graphene substrate with Ag droplet, rigid body assumption was made for graphene layer during whole simulation time. Nose-Hoover thermostat, implemented in LAMMPS code, was used for maintaining a target temperature during whole simulation. The visualization of wetting phenomenon occurring for four substrates variants was made by using Visual Molecular Dynamics (VMD) package [In the first step of our MD simulation procedure, both Cu matrix and graphene (Gn) layer were separately heated from 0 K to 1273 K before wetting studies, and then both were thermalized during 20,000 ps with 0.5 fs time step. Cu matrix with approximately 100 Å × 100 Å × 30 Å dimensions was tightly covered by a graphene layer of similar dimensions in the xy plane on which periodic boundary conditions were imposed. The Cu substrate contained 20,000 atoms, the Gn layer 7500 atoms, the Gn package .Selected atomic structures of each considered substrate variant wetted with Ag droplet were minimized using conjugated gradient method, as implemented in LAMMPS, before performing structural and topological analyses as well as calculating wettability. Time dependence of contact angles (CA) was computed for four configuration variants used to describe wetting properties of Cu matrix covered by a graphene and a single graphene substrate. Spreading area and the height of droplet on a substrate were also determined using MD simulation derived structures and compared with experimental data. Procedure of CA determination is described in the modelling section of the n3, n4, n5, n6, n7) is used to differentiate the types of VC, where ni is the number of i-edged sides in the polyhedron. This tool allows to recognize body- and face-centered cubic structures (bcc and fcc), as well as hexagonal close-packing (h.c.p).Voronoi analysis is based on three dimensional Voronoi tessellation, which provides a detailed description of atom linkage in 3-dimensional space. It gives an deep insight into local atom changes through a complete geometrical construction of atom to its neighbor atoms. More details about VA can be found in papers ,45,46. VavP, and its coefficient pK, according to a formulation proposed by Pstruś et al. [P0 was needed, which is a projection of a sphere on the surface, to compute pK coefficient. We considered atomic structure of Ag droplet in Gn/Ag variant at 1 ps, and then computed the mean value of sphere area by using the formula: pK coefficient as follows:Wettability was measured by determining spreading area ś et al. . For thihK coefficient, where the radius of the sphere was already known (D0). The height of the droplets on considered variants were calculated based on maximum and minimum value of Z for Ag atoms of geometries at 1200 ps. hK coefficient was computed using formula:Similar methodology was used to calculate pK coefficient.A Chemical Vapour Deposition method was used for graphene growth on Cu foil with the dimensions of 30 × 30 × 0.25 mm and its purity of 99.999% . We followed step-by-step a procedure of graphene deposition as it is described by Pstruś et al. . Ag sampdef) is presented in def substrates.Molecular dynamics simulations results obtained at 1273 K for Ag droplet wetting graphene-coated Cu substrates are discussed below. For clarity of the presentation, we present MD results for Ag droplet wetting a graphene layer and a pure Cu substrate in In case of perfect graphene-coated Cu substrate, silver droplet slowly spreads on Cu/Gn surface and its shape also slowly changes, which is associated with simultaneous diffusion of silver atoms on the top surface of Ag drop. Such behavior illustrates a non-reactive wetting for which a stronger interaction between droplet atoms dominate over the weaker ones between Ag and C. Similar spreading mechanism occurs for Ag wetting a perfect graphene layer as presented in def substrate wetted with liquid silver differs from the simple case described above. A mixture of non-reactive wetting and a reactive wetting is observed. To get deeper insight into these phenomena, we present in def wetting with liquid Ag droplet by combining atomistic simulations with experiment. At 1st stage, liquid Ag droplet is approaching Cu/Gndef substrate and Ag atoms are getting to interact with Cu atoms through the defect. Simultaneously, an impairment of graphene layers between part A and part B, and surface diffusion of Ag atoms on graphene layer occur at 2nd stage. The bottom part of def interface and then move on Cu substrate before its dissolution. Consequently, the Cu-graphene distance increases and graphene layer  climbs al stage . The plaDue to the dissolution of carbon in silver, based on the phase diagram for Ag-C  and defedef/Ag systems, we computed radial distribution functions (gij(r)) for each respective atomic pair contributing to the considered substrate variants with Ag droplet. The pair distribution function of the Ag-Cu pair is presented in ij(r) are illustrated in Ag-Cu(r) for Cu/Gndef/Ag system exhibits three peaks of relatively low intensity as compared to that computed for Ag-Cu pair of AgCu alloy formed upon reactive wetting of a pure Cu substrate  for the latter systems was rescaled by 0.1 to be able to make a reliable comparison because of high intensity of the first pronounced peak of gCu-C(r) for Cu/Ag system. Two features require more explanation, namely the positions of the first and third peak of gAg-Cu(r). The first peak of gAg-Cu(r) allocates around 2.9 Å similarly to the position of the first pronounced peak of gAg-Cu(r) for the AgCu alloy  in crystalline-to-amorphous transformation of the Cu substrate as showed snapshot of spreading evolution for Cu/Ag systems (see Cu-Cu(r) drawn in For a deeper insight into the impact of wetting on the structure of Cu/Gn/Ag and Cu/Gntems see  and gCu-def/Ag systems, we have also inspected time evolution of Cu-C bond length. Due to the gap dividing the “defected” graphene layer (Gndef) into two parts , whose abundance is drawn in def substrate. Moreover, 5 digit VC indices are also common for both Gn and Cu/Gndef, which are of similar abundance to VC indices of 1st group. When analyzing VC types present in one substrate variant presented in def/Ag. There is no VC types which would occur only for the Cu/Gn substrate. An abundance graph of VC types detected for Ag atoms forming an AgCu alloy in place of the structural defect in the graphene layer deposited on Cu substrate is presented in def substrate leading to alloy formation.Looking deeper into the wetting phenomenon, we performed a Voronoi analysis (VA) to characterize the topology of Ag atoms adsorbed on two considered graphene-coated Cu substrates and of Ag atoms in the bulk liquid phase. Abundance graphs of Voronoi cell (VC) types for Ag atoms being in contact with the graphene layer is presented in def substrate to those wetting Gn layer, which could not have been caught by visual perception and even from chemical analysis (In a view of the performed Voronoi analysis for Ag atoms adsorbed on a graphene layer, we can observe a similarity in behavior of Ag atoms adsorbed on Cu/Gnanalysis . This redef substrates at 450 ps is drawn in Abundance of 15 most representative VC topologies for bulk liquid Ag droplets wetting Cu/Gn and Cu/GnWe have performed molecular dynamics simulations to unveil the mechanism of liquid Ag wetting Cu substrate covered with perfect graphene layer and defect containing one at 1273 K, which is supported with our present experimental result. We have also discussed structural and topological aspects to correctly describe the impact of wetting phenomenon, occurring on different types of substrates. The results clearly show, that the presence of defect in graphene structure affects wettability behavior, and is a pivotal for the occurrence of diffusion as well. Moreover, introducing graphene at the Cu/Ag interface, allows to observe graphene translucency to metal-metal interactions.Our work shows, that with molecular dynamics we were able to simulate the early stages of wetting of Cu/Gn structure with a silver droplet, observed experimentally. It was achieved mainly due to implementing a defect in graphene in the simulations. Combination of those two approaches allows us to propose a mechanism of wetting, as well as graphene detachment from the substrate, resulting in slowing down the diffusion process in the system. However, several aspects still remain to be considered for a complete description of the wetting process, such as longer simulation time parallel with shortening of the wetting time in the experimental studies. They also concern a consideration of more complex graphene models to MD simulations, including the experimentally-observed defects for CVD-grown graphene layers. Nevertheless, despite the rather simple simulation setup, we were able to obtain consistent results.


Graphene-related materials (GRMs) such as graphene quantum dots (GQDs), graphene oxide (GO), reduced graphene oxide (rGO), graphene nanoribbons (GNRs), and so forth have recently emerged as photovoltaic (PV) materials due to their nanodimensional structure and outstanding properties such as high electrical and thermal conductivity, large specific surface, and unique combination of mechanical strength and flexibility. They can be a crucial part of transparent electrodes, hole/electron transport materials, and active layers in organic solar cells (OSCs). Besides their role in charge extraction and transport, GRMs act as device protectors against environmental degradation through their compact bidimensional structure and offer good durability. This review briefly presents the synthesis methods of GRMs and describes the current progress in GRM-based OSCs. PV parameters  are summarized and comparatively discussed for the different structures. The efficiency recently surpassed 15% for an OSC incorporating polymer-modified graphene as a transparent electrode. The long-term stability of OSCs incorporating GRMs is also discussed. Finally, conclusions and the outlook for future investigation into GRM-based devices for PVs are presented. The conversion of solar power into electrical energy is a clean, scalable, and environmentally friendly means of energy production. Organic solar cells (OSCs) are photovoltaic devices that use organic molecules or conducting polymers to generate electricity via absorption of sunlight through the photovoltaic effect . They har) of the material. The value of εr is a measure of the exciton binding energy, which also depends on temperature. OSCs comprise electron donor and electron acceptor materials. These are semiconductors and have a band gap that can be overcome by the electrons if they are provided with enough energy. When an electron of the donor material leaves the valence band, an unoccupied state  is generated, which acts as a positively charged particle. The electron and the hole are bound together, forming a state called an “exciton”, which is explained by the Coulomb interactions between both particles. This exciton must be dissociated in order to collect the charge carries and produce an electrical current. However, this dissociation requires a specific amount of energy, which depends on the dielectric constant  photoactive layers comprise a blend of at least two semiconductors creating a bicontinuous network of a donor (hole-transporting) and an acceptor (electron-transporting). This architecture allows a close mixing of both phases that favors exciton dissociation. The most common OSC device architectures are the “conventional” and “inverted” ones . In a tyIn initial BHJ-OSCs, a conjugated polymer with a low band gap and a soluble molecule were used as the donor and acceptor, respectively, the most common being poly[2-methoxy-5-(2j-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) polymer and fullerene derivatives such as ,6-phenylJ) and voltage (V) in the device. By measuring these two variables, a curve such as the one depicted in -scJ): current when the voltage in the cell terminals is equal to 0 (V = 0). This parameter depends on the absorption of light, charge generation, transport, and extraction. These processes are temperature-dependent. scJ increases with the illumination intensity as exciton generation from absorbed phonons increase.Short-circuit current (-ocV): voltage between the terminals when no current flows across the cell (J = 0). This parameter is influenced by the recombination rate of charge carriers, the work functions of the electrodes, and the energy levels of the photoactive materials employed.Open-circuit voltage (-mpJ).Current at maximum power value (-mpV).Voltage at maximum power value (-maxP).Maximum power (The current–voltage characteristic of OSCs relates the current intensity (-Power conversion efficiency (PCE): ratio between the maximum power output of the cell and the incoming light power under standard test conditions (STC). Its value ranges from 0 to 100.-Fill factor (FF): ratio of the device maximum power to the product of the short-circuit current and open-circuit voltage. It is an indication of the efficiency of a PVC, and its value ranges from 0 to 1. In fact, FF values exceeding 0.75 can be considered outstanding in OSCs.Two parameters are frequently used to compare the performance of OVCs:Herein, we first discuss the characteristics and synthesis methods of GRMs, indicating the advantages and disadvantages of the different approaches in terms of yield, scalability, and performance. Next, the recent progress of GRMs in OSCs is discussed and device performances are compared. GRMs can be used as electrodes, active layers, and transport layers, and the role of the carbon nanomaterial is discussed. Finally, up-to-date matters and potential trends for future investigation of GRMs-based materials in this field are presented. 2 carbon atoms settled in a two-dimensional honey-comb structure. It is regarded as the “mother” of other graphitic materials since other C-based nanomaterials with different dimensionality can be constructed based on this building block [5 cm2/(V·s) and high electrical conductivity [3 GPa [Graphene is a carbon nanomaterial containing of a monolayer of spng block . It has uctivity . It is suctivity , and an y [3 GPa . It dispy [3 GPa , higher y [3 GPa . In addiy [3 GPa , has optGraphene synthesis can be carried out following two main procedures, namely, bottom-up and top-down, as displayed in On the other hand, the bottom-up approach  starts fEpitaxial growth is typically performed on a semi-insulating SiC substrate that is graphitized via heating under vacuum conditions, leading to graphene formation at the outer surface of the substrate. This technique enables one to control the thickness by controlling the time and/or the temperature and is a promising route to synthesize high-quality large flakes with homogeneous thickness. One of its benefits is that the graphene layer is not transferred to another substrate, thus enabling the direct manufacturing of electronic devices . Both seMany efforts have been devoted to grow monolayer graphene samples with large domains and reduced grain boundaries. Following the first synthesis of a graphene single crystal by Ruoff et al. , differeOn the other hand, the CVD of C precursors on Cu substrates is the most popular method to produce large-area graphene films. To date, precise control of the number of graphene layers as well as the uniformity over a large area is still very challenging. Several parameters including gas partial pressures, ratio, and temperature are crucial. A high growth temperature and low carbon precursor concentration are beneficial for film growth. In addition, a pulsed-CVD approach can be used for film growth by exposing Cu to methane in an intermittent fashion during the growth steps. Graphene nanoribbons (GNRs) are planar, finite, 1D materials with a graphitic lattice structure. They can be regarded as thin graphene stripes (narrower than 10 nm) but maintain a length-to-width ratio higher than 10 . They arGNRs can be synthesized by top-down or bottom-up approaches. Top-down approaches include nanolithography patterning methods, unzipping of carbon nanotubes (CNTs) via an oxidative process or cutting of graphene or graphite precursors into thin graphene stripes via plasma etching . HoweverGraphene quantum dots (GQDs) are 0D carbon-based nanomaterials comprising one or a few graphene layers with sizes ranging from several to 100 nm . GQDs coThe synthesis methods of GQDs can also be divided into top–down and bottom–up approaches . In the 3 hybridization of some carbon atoms. Thus, it has much lower electron mobility, and its electrical conductivity is typically lower than 10−10 S cm−1. It also displays lower mechanical strength and thermal stability, albeit the presence of oxygenated groups opens the way for a wide range of covalent and non-covalent functionalizations [2) and subsequent addition of amines, hydroxyls or isocyanates enables the covalent attachment of various functional groups to GO sheets [Graphene oxide (GO) is an oxidated form of graphene, and therefore its properties (which depend on the level of oxidation) are different from those of pristine graphene. GO nanosheets are amphiphilic and can be dispersed in aqueous solutions over a long period, displaying aqueous processability, which is critical for large-scale uses. They also form stable dispersions in many common organic solvents, which allows making films on numerous substrates via a simple drop-casting method, making it a suitable candidate for PV cells. Nonetheless, this nanomaterial behaves such as a wide-band–gap insulator due to spizations . In partO sheets . On the O sheets .3 and HNO3. Later, Staudenmaier and Hofmann used concentrated H2SO4, HNO3, and KClO3 to make highly oxidized graphite. However, these methods were time-consuming, and unsafe since toxic gases (ClO2 and NOx) evolved. Later, Hummers developed an innovative route by substituting HNO3 and KClO3 with NaNO3 and KMnO4, and this has been the most widely employed method since the first exfoliation of graphene in 2004. Numerous investigators have tried to enhance Hummers’ method to make it more effective and/or sustainable. Some methods prevent the evolution of toxic gases by substituting NaNO3 by other oxidizing agents [GO can be synthesized from graphite by means of different methods , namely,g agents . Anotherg agents , and thi2–103 times lower than that of pristine graphene. Reduced graphene oxide (rGO) is derived from GO by chemical, thermal, and other methods in order to lower the oxygen content. The aim is to achieve nanomaterials analogous to pristine graphene. Nevertheless, defects and remaining functional groups markedly change the arrangement of the hexagonal lattice; consequently, the characteristics of rGO are intermediate between those of graphene and GO. Thus, rGO has an electrical conductivity about 103-sp2 rehybridization of C atoms during the thermal annealing. The main disadvantage is the difficulty to use it in aqueous medium or for layers grown on substrates; therefore, it is not appropriate for OSCs. Other routes are microwave radiation or reduction with an arc-discharge lamp or a pulsed laser [The approaches of converting GO into graphene can be classified into three types : chemicaed laser , which l2H4) [4), hydroquinone, and hexamethylenetetramine [The chemical route relies on the reaction of different chemicals with GO and can be performed uner ambient conditions or with mild heating. The chemical most widely employed is hydrazine (N2H4) . Howeveretramine . The degetramine . This meetramine  with higGRMs have been applied in different parts of OSCs, mainly as transparent electrodes, hole/electron transport materials, and in active layers. The number of literature articles on OSCs containing GRMs is huge. The following sections summarize some of the most illustrative examples dealing with this topic. −1 conductivity on a glass substrate [A prerequisite for front electrodes (the one exposed to the light) of OSCs is to have elevated conductivity and high transparency. In this regard, the most common electrodes are indium and fluorine doped tin oxide (ITO and FTO). ITO has more than 80% transmittance in the visible range and about 0.1 S cmubstrate , but it ubstrate ,38. In pubstrate . Overall71BM). The hole transport layer was PEDOT:PSS, which was modified with isopropyl alcohol to guarantee homogeneous coating on the graphene electrode. An additional layer of MoO3 was deposited onto the graphene/PEDOT:PSS in order to block electrons and prevent charge recombination at the interface between the polymer and the nanomaterial. This graphene-based OSC showed comparable performance to that of an equivalent ITO-based cell under identical conditions  were reported for OSCs with CVD-graphene as the anode . The devnditions d. These 61BM as an active layer, CVD-single-layer graphene doped with Au nanoparticles, PEDOT:PSS as the top electrode, and ITO as the bottom electrode have also been manufactured, as depicted in Incorporation of foreign atoms/molecules into graphene is a worthy path to increase its conductivity and simultaneously control the work function of the modified graphene. For instance, the doping of graphene with bromine under an inert atmosphere led to transparent electrodes with high stability and a nearly 5-fold increase in conductivity with only 2–3% loss of transmittance. This was ascribed to the encapsulation of bromine by intercalation between the graphene sheets. Semitransparent OSCs with a blend of poly(3-hexylthiophene) (P3HT):PCocV of about 0.59 V. In order to attain better cell properties, novel materials such as indene-C60 bisadduct (ICBA) with a higher LUMO energy level have been employed. Thus, the cell with P3HT:ICBA as an active layer, graphene doped with bromine, PEDOT:PSS as the upper electrode, and Al as the bottom electrode attained a ocV of 0.76 V, albeit only 2.10% PCE was reached [The performance of OSCs incorporating the P3HT:PCBM active layer is restricted due to the little difference in energy between the LUMO of PCBM and the HOMO of P3HT that yields a low  reached . This co71BM as the active layer led to an efficiency of 4.23% that was preserved upon application of hundreds of bending cycles. This EG-based electrode showed a low sheet resistance, high toughness, and a transparency of 70% combined with good solution processability Conversely, very low PCE values have been attained using rGO-based electrodes due to the presence of numerous defects, which significantly restrict the cell efficiency. Thus, thermally annealed thin rGO films (about 20 nm) with 65% transparency deposited onto a PET substrate by spin coating only led to a PCE of 0.78% [ocV of 0.56 V. Remarkably, the cell obtained could resist more than 1000 cycles upon bending, whereas conventional ITO-based cells typically deteriorate and fail. Exfoliated graphene synthesized via electrochemical exfoliation of graphite was deposited onto a polymeric substrate, poly (PEN), and the mixture was used as the anode in OSCs. The cell comprising PTB7:PCof 0.78%  and Voc 3 as electron blocking and the optimization of the doping concentration. Thus, as this concentration increased up to 3 mM, the conductivity increased, but above 5 mM it started to decrease. These results suggest that by controlling the doping concentration, the conductivity values and hence the device performance can be optimized. Besides, the processing conditions and the thickness of the ETL, HTL, as well as the active layer were optimized to prevent exciton recombination and the probability of losing charge at the anode and cathode.Higher PCE 8.48%) has been reported for cells incorporating Au-doped GNRs as the anode [% has bee71BM active layer on graphene-AgNWs [ocV of 0.83 V, scJ of 23.20 mA cm−2, and FF of 69.8% was reported by Zhang and coworkers [The encapsulation of a silver nanowire (Ag NW)-based electrode with graphene is another method recently suggested to improve the durability of OSCs. Thus, AgNWs were covered on both sides with a GO layer using scalable and solution-compatible processes, resulting in a sandwich-like structure . The GO ne-AgNWs . The higoworkers  via the Hybrid transparent electrodes based on Cu-grid and graphene film have also been developed as bottom electrodes in conventional and inverted OSCs . The add4 S cm−1, a transmittance in the VIS region higher than 82%, and a PCE of 4.63% were reported [Films of Cu-based Al-doped ZnO (AZO) were prepared and incorporated as electrodes in OSCs with a structure of PEDOT:PSS/P3HT:PCBM/PCBM/Ca/Al. A graphene layer between the AZO and Cu layers was added that prevented the contact between Cu and oxygen during the preparation process of AZO, thus reducing the system transmittance. A conductivity of 2.5 × 10reported , yieldin3 S cm−1, and high thermal stability. It also showed exceptional mechanical strength up to thousands of bending cycles with an efficiency comparable to that of an ITO-based reference device (15.7%). Larger cells were manufactured to investigate their scalability, although a slight worsening in the cell performance was found upon increasing the size of the device. The cell with an active area of 0.5 cm2 showed an efficiency of 12.7%, better than the PCE of a cell with similar configuration but incorporating ITO as the electrode, irrespective of its larger active area.The highest PCE for cells incorporating graphene-based electrodes (15.2%) has been recently reported by Koo and coworkers . In such70BM as the acceptor. However, their efficiency does not exceed 5%. Hence, innovative materials for both the donor and acceptor that absorb light more efficiently, with improved HOMO/LUMO matching, more effective exciton dissociation, and enhanced charge mobility with good stability are sought. In this regard, GRMs show great potential due to their huge specific surface area and 2D structure at the nanoscale. In this section, the use of GRMs as acceptor materials is discussed, and the efficiency along with the cell configuration are summarized in As mentioned earlier, most OSCs are based on the BHJ architecture , which cocV. A similar type of OSC has been developed by other authors [In 2008, Liu and coworkers  were pio authors ,68,69,70scJ. At higher concentrations, the PCE decreased due to graphene agglomeration.Solution-processable functionalized graphene (SPFG) has been integrated as an additional constituent in a PTB7:PCBM active layer, leading to a cell with structure of ITO/PEDOT:PSS/PTB7:PCBM:SPFG/PFN/FM , onto GO followed by hydrazine reduction to improve its processability and optical transmittance without sacrificing the conductivity . Thus, PGO/GO/Ag , showed Non-covalent functionalization has also been explored as an easy alternative to improve PCE. Thus, Lyu and coworkers  developescJ with reduced conductivity. On the other hand, reduced GQDs had improved FF, attributed to the improved carrier conduction. Therefore, an intermediate degree of reduction of the GQDs is desired. GNRs, which are highly soluble and easily processable into thin films, have also been tested as electron acceptors in OSCs with PTB7-Th as the electron donor . The mixThe doping of graphene has also been tested in order to modulate the band–gap structure. Thus, N-doped graphene blended with P3HT:PCBM as an active layer provided transport paths specific for certain charge carriers, resulting in a moderate PCE (4.48%) . In anotIn order to attain effective OSCs, the work functions of the anode and the cathode should match the HOMO of the donor and the LUMO of the acceptor, respectively, to reduce electron- and hole-extraction barriers. In addition, these barriers can be decreased by placing a hole-transport layer (HTL) within the anode and the active layer, as well as an electron-transport layer (ETL) in the middle of the cathode and the active layer. The main roles of these layers are as follows : (a) redOC of 0.64, FF of 64%, and PCE of 3.60%. These authors reported that GO could dope P3HT at the surface of the active layer because of its large number of oxygenated groups with high H+ concentration. The doped P3HT thin layer enabled a good Ohmic contact between the active layer and the top metal electrode. Nonetheless, to attain better performance, the conductivity of the GO acting as the HTL should be improved. The work function of GO is about −4.8 eV that matches P3HT as a donor for effective hole extraction . In 20103H) prepared by functionalizing GO with H2SO4 has also been used as the HTL in similar P3HT:PCBM-based cells  p71BM as the active layer. Blending GO and PEDOT:PSS in aqueous medium significantly increased the viscosity of the solution, making a uniform film that could be directly deposited onto ITO by an adhesive lamination procedure. The resulting cell had an efficiency of 4.28% [Blending with polymers is another path to improve device performance. For instance, a GO/PEDOT:PSS composite was incorporated as an HTL in a device with PCDTBT:PCof 4.28% , much beMetal nanostructures are often incorporated in OSCs to expand their light-harvesting capability. These nanostructures can be incorporated at the active layer–electrode interfaces. In this regard, a novel amphiphilic nanocomposite (Au@PEG–GO) comprising gold nanoparticles (Au NPs), GO, and poly(ethylene glycol) (PEG) to improve solubility was developed , and it −1), high work function (4.9 eV), and outstanding environmental stability. PRGO was incorporated as the HTL in a cell with configuration of ITO/PRGO/PEDOT:PSS/PTB7-th:PBCM/Al, which exhibited an efficiency of 7.24% and an FF of 64%, values similar to those of a reference device with PEDOT:PSS (PCE of 7.17% and FF of 66%). Besides, the cell based on PRGO displayed higher durability.In order to enhance the electrical conductivity, rGO has also been tested as the HTL. Thus, a solution-processable reduced graphene oxide (spr-GO) was developed via reduction with a hydrazine derivative in aqueous medium . For comIn addition to the above-mentioned methods, thermal annealing of GO has been shown to be demonstrated to be effective to attain highly conductive rGO. Throughout thermal annealing, oxygenated groups are decomposed and detached as gas molecules. Nevertheless, this method is restricted to OSCs on glass substrates. OSCs with thermally annealed GO for 10 min in air at 150, 250, and 350 ºC have been developed  have been mixed with GO via sonication in aqueous solution combined with spin coating to produce a homogeneous GO:SWCNT nanocomposite. OSCs with P3HT:PCBM as the active layer showed an efficiency of 4.1%. The same nanocomposite was subsequently used as the connection layer for building series of tandem OSCs in order to improve light absorption.Graphene oxide nanoribbons (GONR) synthesized via oxidative unzipping of SWCNTs combined with an additional oxidation stage were fabricated and used as the HTL . The GON71BM as the active layer and the field’s metal (Bi/In/Sn: 32.5/51/16.5 wt%) as the top electrode, leading to a PCE of 5.73% [The doping of rGO with heteroatoms is another strategy that can result in improved performance. Thus, GO was simultaneously functionalized and reduced with a hydrazine derivative incorporating fluorine atoms, and the resulting fluorinated-reduced graphene oxide (F-rGO) was deposited via spin-casting. Due to the high electronegativity of the doping atoms, F-rGO has a work function of 5.1 eV and was used as the HTL in an OSC with PTB7:PCof 5.73% . An improf 5.73% , using aof 5.73% . The inhThe work function of electron transport layer (ETL) materials needs to be low enough to match the LUMO of the acceptor in the active layer; this promotes electron extraction and subsequent mobility, thus minimizing series resistance of the OSCs. GRMs with tailorable energy levels via chemical modification can be employed as the ETL too, as summarized in In 2012, Liu and coworkers  used ces−2, one of the highest for OSCs based on GRMs. A novel ETL based on ZnO nanostructures embedded in a graphene matrix with ethyl cellulose (EC) as the stabilizing agent has also been developed [61BM as the active layer, with an architecture of ITO/ZnO@G:EC/P3HT:PC61BM/MoO3/Ag, exhibited a PCE of 3.9%, around 18 and 27% higher than that with rGO or pristine graphene alone, respectively. By substituting the active layer by PTB7:PC71BM, the efficiency increased up to 8.4%, the highest reported for GRMs as the ETL. This easy and versatile strategy can result in highly conductive electron-transport layers for OSCs.Another strategy is the doping of graphene with zinc nanorods (ZnR ), which eveloped . The ZnOFor commercial applications, the long-term stability of OSCs against air, humidity, temperature, and light illumination has a huge implication because these cells are damaged more rapidly under atmospheric conditions than the corresponding inorganic counterparts . The dur71BM OSCs with conventional PEDOT:PSS and GO interfacial layers in terms of changes of normalized PCE due to thermal (a) and environmental (b) degradation, with and without encapsulation [PEDOT:PSS has been widely used as interfacial material in OSCs. However, its acidity, morphological phase segregation, and hygroscopic character provoke low stability or even full cell failure. Thus, reduction efficiencies ranging from about 60%  to almossulation . Clearly2CO3)-functionalized GQDs as the ETL and investigated their durability. The Voc of the GQDs–Cs2CO3 device was 99.4% of its initial value after 1200 h under atmospheric conditions, whereas the Voc of cells comprising only Cs2CO3 dropped quickly with time. Both types of devices showed a similar degradation trend of Jsc. The GQDs–Cs2CO3-based solar cells showed a 56% higher PCE and 200% improvement in stability compared to those comprising only Cs2CO3. The PCE of GQDs–Cs2CO3 cells was 70% of its initial value upon 450 h under air at RT and 60% RH; the stability was improved 2-fold compared to Cs2CO3-based devices, since the GQDs provide hole-blocking ability and electron transfer capability, hence preventing the diffusion of the Cs+ ion into the active layer/polymer interface. The stability of GONR-based OSCs compared to a reference PEDOT:PSS device after storage under nitrogen atmosphere was also compared [Other authors  used cescompared . The PCEIn this review, the most representative advances using GRMs as electrodes, active layers, and transport layers in OSCs have been summarized. Graphene and its derivatives, GO, rGO, GNRs, GQDs, etc., have arisen as ideal nanomaterials for OSCs due to their nanoscale dimensions, large specific surface area, and superior stiffness combined with flexibility, exceptional electrical conductivity, and high transparency. Despite that the PCEs obtained in GRM-based devices have not gone beyond cells using conventional materials, researchers in the field have already recognized the key features to increase their performance. Lowering GRM sheet resistance, for instance, by increasing the film thickness, would increase the overall PCE. Thickness adjustment also has an important effect on the film transparency. Improved transparency would result in enhanced light transmission and better efficiency. Thus, an optimal equilibrium between transparency and conductivity has to be attained. Thermal treatments  are also crucial for the final efficiency; through this easy means, noteworthy PCE increases have been attained. Numerous routes to synthesize GRMs have been proposed . In particular, devices with CVD graphene show improved properties ascribed to its homogeneity and high electronic quality, while graphene produced by exfoliation with solvents has poorer properties. Nevertheless, most of these approaches are not appropriate for cost effective industrial applications. The cell manufacture is another issue. Thus, the development of uniform films as well as the complete control over the interfacial properties between the materials applied in the cell is crucial. In this regard, solution-processable GRMs are preferred due to their solubility in common solvents. In particular, functionalized graphene is the most used GRM material in OSC devices due to its improved processability in solution. A better solubility would guarantee a good interfacial contact that would promote electronic interactions, fostering charge generation. Besides, the graphene concentration is a crucial parameter to take into account, which has to be sufficiently high to develop an interpenetrating donor/acceptor interface and an effective carriage path for the active layer. However, high graphene concentrations typically lead to agglomerates that result in detrimental performance. GO-based materials are amongst the best alternatives for PEDOT: PSS, the most common HTL material in spite of its acidic and hygroscopic characteristics that strongly limit the cell durability. A foremost benefit of GO-based materials is that they can be directly assembled from aqueous dispersions and lead to PCE data equivalent to those of cells manufactured with PEDOT: PSS; besides, they show significantly improved long term stability. Thus, the GO layer can act as a barrier, preventing the diffusion of oxygen and water molecules from the ITO electrode to the active layers. In addition, the release of oxygen from the GO sheet promotes the conversion from insulator to semiconducting behavior. Therefore, approaches to obtain functionalized GO using non-toxic chemicals is one of the chief tendencies in this research arena. Regarding ETL materials, one of the key aims is to attain highly conductive materials with a low work function to enhance electron mobility, which can be achieved by doping graphene with different atoms. The highest PCE (about 15%) has been recently attained via a combination of a polymer with CVD-graphene as the transparent electrode. Novel functionalized GRMs should be developed to match the energy levels of traditional donor and acceptor materials in the active layer and the transparent electrodes. It is expected that constant investigation struggles in this emergent area would result in a flourishing field of photovoltaic technologies.


Our study opens an avenue for the controllable growth of tBLGs for both fundamental research and practical applications.Twisted bilayer graphene (tBLG) has recently attracted growing interest due to its unique twist-angle-dependent electronic properties. The preparation of high-quality large-area bilayer graphene with rich rotation angles would be important for the investigation of angle-dependent physics and applications, which, however, is still challenging. Here, we demonstrate a chemical vapor deposition (CVD) approach for growing high-quality tBLG using a hetero-site nucleation strategy, which enables the nucleation of the second layer at a different site from that of the first layer. The fraction of tBLGs in bilayer graphene domains with twist angles ranging from 0° to 30° was found to be improved to 88%, which is significantly higher than those reported previously. The hetero-site nucleation behavior was carefully investigated using an isotope-labeling technique. Furthermore, the clear Moiré patterns and ultrahigh room-temperature carrier mobility of 68,000 cm The synthesis of twisted bilayer graphene with controllable angles is challenging. Here, the authors devise a chemical vapor deposition approach using a hetero-site nucleation strategy that affords twist angles ranging from 0° to 30°. Specifically, the presence of twist angle causes van Hove singularities (vHSs) to emerge in the electronic density of states, resulting in an enhanced optical absorption4 and photocurrent generation at certain wavelengths6. Furthermore, the realization of a correlated Mott-insulator and super-conductivity, at the magic angle (tBLG with θ of 1.1°), has attracted worldwide interest8. Consequently, an approach for producing large-area, high-quality tBLG, with a full range of θ from 0° to 30° would significantly improve the ability to investigate its unique physical properties and applications. To achieve this, artificially stacking methods have been developed, but suffers from unavoidable interlayer contamination which affects the interlayer coupling9. Prior investigations also indicated that azimuthally disordered multilayer graphene could be grown on C-terminated SiC10. Recently, 30°-tBLG was obtained by using a sacrificial hexagonal boron nitride (hBN) layer on Si-terminated SiC11. However, study and applications of the SiC-epitaxial tBLG are currently limited by the tedious transfer process and the relatively high price of SiC single crystal. In addition, the intermediate layer could also enable the formation of twist angle when growing the other two-dimensional (2D) materials12.Recently, twisted bilayer graphene (tBLG), which is composed of two graphene layers with an interlayer twist angle  is currently considered one of the most promising methods, due to the high scalability and the excellent quality of CVD graphene26. However, during the high-temperature CVD growth, the energetically favorable bilayer graphene structure is the non-twisted one, i.e., AB-stacked bilayer graphene (AB-BLG), whereas any rotation between the two layers would need to overcome a high energy barrier28. Thus, compared to AB-BLG, the fraction of tBLG were limited to around 50% in previous reports29. Thus, an efficient approach for growing tBLGs, especially in high fraction of twisted graphene and with a full range of twist angles, is still highly desirable.Direct growth of bilayer graphene on transition metal substrates such as Cuθ from 0° to 30°. As proven by using a carbon-isotope-labeling technique, the gas-flow perturbation was capable of controllably initiating this hetero-site nucleation. The high crystalline quality of the as-grown tBLGs was confirmed by the clear Moiré patterns in high-resolution (HR)-transmission electron microscopy (TEM), and by the ultrahigh carrier mobility of 68,000 cm2 V−1 s−1 at room temperature. This synthesis strategy by the intentional design of nucleation sites would bring more inspiration for the controlled growth of graphene and other 2D materials with precise control over interlayer twist in the near future.In CVD approach, since the microscopic environment surrounding the nucleation site determines the orientation of graphene, two layers in bilayer graphene sharing the same nucleation center would preferentially grow with either the same orientation or solely with a twist angle of 30°. Therefore, in this study, a hetero-site nucleation strategy, where the two graphene layers nucleate at different sites, is developed to significantly enhance the fraction of tBLGs in bilayer graphene domains to 88%, with the range of 2 results in the H-terminated edges of graphene and therefore reduces interaction with Cu substrate, which promotes the diffusion of the carbon species beneath the first layer to fuel the growth of the second layer graphene30. In the common bilayer graphene growth results without introducing the gas-flow perturbation, the two graphene layers would share the same nucleation site and grow simultaneously16. In this case, the same surrounding microscopic environment, including Cu steps and particles, would result in the same crystalline orientation of the two layers, thus AB-BLG with no interlayer rotation is preferentially formed  was used to measure the resulting θ of the tBLG, based on the sharp edges of the hexagonal tBLG domains  matches the energy between vHSs of the tBLG34.Raman spectra were acquired to characterize their crystalline quality and interlayer coupling of the as-grown tBLGs, which exhibit strong des Fig. . At a lo12C-labeled and 13C-labeled methane (12CH4/13CH4) were sequentially introduced to the CVD chamber in alternating 5 min periods over a total of four cycles. To confirm its contribution to the hetero-site nucleation behavior, the flow perturbation was introduced, by increasing the flow rates of H2 and CH4, after either 5 or 10 min  is required for the first layer, after dosing of 13CH4 or 12CH4, because it must overcome an energy barrier to form a stable nucleus32. The twist angles of tBLGs in Fig. 12C-13C-labeled AB-BLG grown without flow perturbation  simulations were conducted to investigate the dynamics of the gas flow during the perturbation. After the sudden increase of flow rate of H36. However, because the partial pressure of H2 is greatly enhanced simultaneously, the graphene edges would be terminated by hydrogen, which hinders the attachment of active carbon species to the edge of the first layer37. According to the theoretical calculation, only carbon atoms can diffuse under the first layer to fuel the growth of the second layer graphene30. Thus, if the nucleation of the second layer graphene occurs at the same site with that of the first layer, several energy barriers must be overcome  of the substrate in the presence of steps, kinks, and particles would capture the C atoms and result in the nucleation of the second layer, consistent with the reported literature38. Therefore, when gas-flow perturbation is introduced, the second layer preferentially nucleates near the edge of the first layer, rather than at the original nucleation center, and the local environments near the nucleation sites of the two graphene layers are therefore different, which is responsible for the formation of interlayer twist  as functions of the H2 and CH4 (carbon-source supply) flow rates reveal the presence of two regions, as separated by green dash line  that are suitable for growing second-layer-free graphene domains, which was chosen during the first nucleation step (step I). The other region (top right) is composed of the parameters for growing second-layer-rich graphene domains, which was used during the second layer growth step (step II).To achieve hetero-site nucleation for tBLG growth, three key conditions are required: (1) no second layer can form during the nucleation stage of the first layer; (2) the second hetero-site nucleation must be triggered by a perturbation; and (3) carbon source must be sufficient for the growth of second layer. A series of experiments were conducted to improve the growth controllability with respect to the three conditions. The ratio of MLG domains (second-layer-free domains) to all graphene domains  as a function of the ratio of H2 flow rate in step II to that in step I (H2 step II/step I) is displayed in Fig. 2 step II/step I in the flow perturbation is beneficial for increasing RBLG, highlighting the importance of increase the H2 partial pressure in step II. High H2 partial pressure enables H-termination of the graphene edge, which allows more active carbon species to diffuse beneath the first layer of graphene to fuel the growth of the second layer graphene30. Meanwhile, at the same partial pressure of hydrogen, RBLG would be higher when the flow rate of CH4 in step II is higher than that in step I  would induce undesirable few-layer graphene (FLG) formation, and therefore slightly reduce the RBLG  is lower than unity  is difficult to grow because of the relatively higher stability of AB-BLG and27. The fraction of twist angles near 30° is significantly higher than the other tBLGs.The twist angles of the as-grown tBLGs were further characterized by TEM and selective-area electron diffraction (SAED). Note that, for a vivid evaluation, SAED was conducted on suspended graphene, spread over 600 holes of Quantifoil substrate  (PMMA). The selected tBLG domain was then picked up from the SiO2 substrate using an hBN flake, denoted as top hBN or t-hBN, and subsequently dropped down onto another hBN flake, denoted as bottom hBN or b-hBN, on SiO2, to form an hBN/tBLG/hBN sandwich structure  is ~1587 cm−1, with a full-width at half-maximum (FWHM) of the G peak (ΓG) of 11 cm−1, while the 2D peak position (ω2D) is ~2700 cm−1, with the FWHM (Γ2D) of 34 cm−1. The high IG/I2D peak ratio of ~20, together with the R peak at 1493 cm−1, indicate an interlayer twist angle of ~12° (laser wavelength λ = 532 nm). For the tBLG encapsulated in hBN  and performing a linear fit near the charge neutrality point  by using the angle-resolved photoemission electron spectroscopy with submicrometer spatial resolution (micro-ARPES). The θ-dependent vHSs are clearly observed in the energy–momentum–dispersion diagrams along with the corresponding integrated energy distribution curves (EDCs) .This work describes a hetero-site nucleation strategy for successfully growing the tBLG with the fraction of tBLG as high as 88%, and a wide range of twist angle from 0° to 30°. By employing the gas-flow perturbation after the nucleation of the first layer, the second layer nucleation could be initiated at a different location, which was investigated by isotope labeling in conjunction with micro-Raman spectroscopy. The sudden increase of carbon-source supply would drive the system out of equilibrium, and allow the formation of the second-layer nuclei without the preferred equilibrium stacking order. In this work, since the second layer graphene locates underneath the first layer, substrate plays crucial roles in determining the crystal orientation of graphene. The interaction between Cu substrate and the second layer graphene is much stronger than the interlayer interaction of bilayer graphene during the nucleation stage, which would suppress the equilibrium of AB-stacking configuration2), and annealed for 30 min at 1020 °C (500 sccm H2). Graphene growth proceeded by introducing 12CH4 or 13CH4  after the flow of H2 was stable at the appropriate value  in a low-pressure CVD system. Cu-foil pieces were placed in a quartz-tube furnace  and sequentially heated to 800 °C for 30 min (500 sccm Ar), annealed for 10 min at 800 °C (500 sccm Ar), heated to 1020 °C for 10 min (500 sccm H2 with the assistance of PMMA. The tBLG/Cu sample was spin-coated with PMMA (2000 rpm) and baked at 170 °C (3 min), followed by the removal of the Cu foil by etching in 1 M Na2S2O8 solution. After being washed with deionized water, the PMMA/graphene was subsequently placed onto SiO2 and the PMMA was dissolved with acetone. The graphene was transferred onto a TEM grid using a non-polymer-assisted method, as reported previously51.tBLGs were transferred onto SiO2/Si substrates (SiO2 thickness: 90 or 285 nm) were obtained by OM (Nikon LV100ND equipped with DS-Ri2 camera). Raman spectra and maps were obtained using a Horiba HR800 instrument with a 532 nm laser or a Witech Alpha RSA300+ instrument with a 488 nm laser. TEM images, SAED patterns and Moiré pattern images were collected using the instrument of FEI Tecnai F30 (at 300 keV electron energy) and an aberration-corrected TEM . SEM images were acquired on the instrument of Hitachi S-4800 and Thermo Scientific Quattro S (at 2 keV electron energy). AFM images of tBLG on Cu foil is characterized by using Bruker Dimension Icon with ScanAsyst mode. ARPES experiment was performed on the Spectromicroscopy beamline, Elettra Synchrotron . Before the measurement, tBLG samples was in situ annealed at 300 °C for 3 h. The measurement was performed in the high vacuum (better than 5 × 10-10 mbar) at 80 K. All the data were collected with an incident photon energy of 74 eV.OM images of tBLGs on SiO2/Si at 55 °C, because the van der Waals forces between hBN and the tBLG are relatively stronger than those between SiO2 and the tBLG. Consequently, the tBLG/hBN/PPC/PDMS stack was brought into contact with another hBN flake, after which the tBLG/hBN was released from the PPC at 70 °C, yielding an hBN/tBLG/hBN heterostructure. Annealing (350 °C in air) was necessary following the construction of hBN/tBLG/hBN, which helped to clean the interfaces between hBN and tBLG43. The contamination might come from the transfer step and high-temperature growth step52, thus, using the strategies for growing clean tBLGs or no polymer transfer would contribute to the removal of contamination. The Hall bar device was fabricated with alignments marks. To pattern graphene into a Hall bar geometry, electron-beam lithography and reactive ion etching (RIE) were employed. Cr/Au (3/50 nm) electrodes were deposited by electron-beam evaporation.An hBN flake was picked up at 55 °C by a PPC/ PDMS stack on a glass slide, which was attached to a micromanipulator. The as-formed hBN/PPC/PDMS stack was then used to pick up the tBLG from the SiO53. CFD code ANSYS FLUENT is used here, and the computational mesh arrangement of over 200,000 cells is developed with fine mesh near the sample surface to guarantee the convergence. The geometry and boundary conditions of gas inlet and temperature are set as shown in Supplementary Fig. The CFD model here is based on laminar compressible flow with surface chemical reaction. Settings on gas mixture, chemical reactions are based on the previous reported literatureSupplementary InformationPeer Review File


Therefore, we propose doping sufficient cations to counter p-doping of GFETs prior to the measurements. For the pre-treatment, GFETs were immersed in a 15 mM sodium chloride aqueous solution for 25 h. The pretreated GFETs showed that the charge neutrality point (CNP) drifted by less than 3 mV during 1 h of measurement in a phosphate buffer, while the non-treated GFETs showed that the CNP was severely drifted by approximately 50 mV, demonstrating a 96% reduction of the drift by the pre-treatment. X-ray photoelectron spectroscopy analysis revealed the accumulation of sodium ions in the GFETs through pre-treatment. Our method is useful for suppressing drift, thus allowing accurate estimation of the target analyte concentration.Solution-gated graphene field-effect transistors (SG-GFETs) provide an ideal platform for sensing biomolecules owing to their high electron/hole mobilities and 2D nature. However, the transfer curve often drifts in an electrolyte solution during measurements, making it difficult to accurately estimate the analyte concentration. One possible reason for this drift is that p-doping of GFETs is gradually countered by cations in the solution, because the cations can permeate into the polymer residue and/or between graphene and SiO Here, we propose a method to suppress the drift, in which sufficient cations are doped to counter the p-doping of GFETs prior to the measurements, as shown in The demand for sensing analytes in aqueous environments is rapidly increasing in various fields, including life sciences , environ2 substrates with a thickness of 525 μm/290 nm. A source/drain electrode of 10 nm Ti and 90 nm Au was formed using electron-beam physical vapor deposition. Graphene channels were formed by oxygen plasma etching. After etching, the PMMA coat on the graphene was removed using an organic solvent. Thereafter, the graphene was annealed at 300 °C in an Ar/H2 atmosphere for 1 h to reduce organic residue.Graphene films were grown on Cu foils using a CVD method. A poly(methyl methacrylate) (PMMA) solution was coated onto the graphene/Cu foils. The Cu foils were etched away using an ammonium persulfate solution. The graphene films were transferred onto Si/SiOVDS) of 0.1 V was applied between a source/drain electrode, and a top-gate voltage (VGS) was applied through the electrolyte solution using an Ag/AgCl electrode. While sweeping the VGS in the positive direction, the drain current (IDS) was measured using a semiconductor parameter analyzer . The CNP, where VGS was applied at the minimum IDS in the transfer curve, was calculated using polynomial fitting. We selected D-PBS(-) as the electrolyte owing to its suitability for biological applications.The electrical measurements were conducted as follows: The GFET arrays were immersed in 0.1× D-PBS(-) . A bias voltage (Measurement with X-ray photoelectron spectroscopy (XPS)  was used to verify the permeation of cations to the GFETs. The measurement spot is located at the center of the channel region. The Na1s and C1s peaks were analyzed to assess the cation accumulation and graphene quality, respectively. The baseline was subtracted, and the signal intensity was normalized to the peak area of C1s.2 substrate have a p-doping effect on graphene [graphene ,24,25. Mgraphene . TherefoWe used CNP as a representative feature value for a GFET because the sensing mechanism in GFETs is often demonstrated by the gating effect, which appears as the CNP shift . Each CNWe found that the transfer curve was not stable but rather changed during the measurements. Because the CNP drift was observed during the electrical measurements performed in an electrolyte solution containing D-PBS(-), it was expected that the drift was derived from electrical effects and/or surrounding effects induced by water molecules or ions. To clarify whether the CNP drift was induced by electrical effects, we conducted electrical measurements of the GFETs with a time interval. First, the GFETs were immersed in 0.1× D-PBS(-), and then the electrical measurements were conducted for 1 h. Subsequently, the GFETs were left electrically floated for 1.5 h; that is, all the input voltages from the gate and source/drain electrodes were stopped. Thereafter, the measurements were conducted again for 1 h; in the same manner, the GFETs were electrically floated for 1.5 h. Finally, the measurements were performed for 1 h. The average CNP was calculated from the data acquired from several GFETs on the same chip.Because the drift was not affected by the electrical effects, we inferred that the electrolyte solutions were responsible for the drift. Put simply, the water molecules and/or ions in contact with the graphene were attributed to the drift. As the effect may differ depending on the solution, we immersed the GFETs into two different solutions, with and without ions, prior to the electrical measurements. The experimental procedure is illustrated in Based on these results, we developed a method to suppress CNP drift. If the CNP drift arises from gradual ion penetration, the GFETs, where ions are sufficiently penetrated prior to the measurements, should be stable during long-term electrical measurements. To verify this concept, we evaluated the CNP drift of GFETs immersed in 0.1× D-PBS(-) for 25 h and compared it with that of the non-treated samples. +, Na+, and Ca2+, are adsorbed onto graphene via cation-π interactions, leading to the same n-doping effect on graphene [Although we demonstrated that pre-immersion in the electrolyte solution suppressed the CNP drift, it still remains unclear which ions in D-PBS(-) account for drift suppression. It is known that cations, including Kgraphene ,34. Ther2 gas and removed on a hot plate at 120 °C.Based on the effect of pre-treatment on the CNP drift, it was expected that cations would permeate the GFETs. To determine whether cations accumulated around the graphene, an XPS analysis was performed on the graphene before and after immersion in the electrolyte solution. Two GFET substrates were prepared as samples for the XPS evaluation. After the GFETs were fabricated, one substrate was immersed in 0.1× D-PBS(-) for 25 h, while the other was not. Finally, both substrates were rinsed with deionized water, and the water was blown with N+ onto the graphene’s surface [+ as well as other cations, such as K+, should be adsorbed. surface ,34. Furt2 C–C bonding in graphene is assigned at approximately 285 eV, and some other tails appearing on the high-energy side correspond to the binding energy of species in PMMA or functional groups on graphene [graphene . In the graphene . Consequ2 were highly p-doped, which was confirmed by the positive values of CNP. There are two main origins of p-doping: (i) PMMA residue and (ii) SiO2 substrates. The p-doping seemed to be gradually countered; that is, the CNP became close to zero during the electrical measurements over time. We proposed a possible mechanism for the drift, in which the two origins of p-doping were gradually countered by cations, such as the K+ and Na+ included in the D-PBS(-). This mechanism was supported by the experimental results: (i) when the GFETs were sufficiently countered with cations, which are known as n-dopants to graphene, the transfer curves were stable during long-term electrical measurements, and (ii) cations were detected in the GFETs after immersion in the electrolyte solution. Finally, by countering the GFETs with cations prior to evaluation, the CNP drift was suppressed by 96%. Our method should produce a stable GFET sensor platform.We developed GFETs and evaluated the changes in their electrical characteristics. The GFETs using CVD graphene sheets and fabricated on SiOFurther experiments are needed to comprehensively understand the mechanism of cation accumulation in graphene. It might be possible to discover a more effective pre-treatment method by studying the mechanism in more detail. Furthermore, the functionalization of graphene sensors is possible by controlling the amount of accumulated cations.


D and G peaks, dominating the spectrum from room temperature down to ≃153 K. Despite the high C:O ratio, the graphene sponge exhibits an insulating electrical behavior, with a raise of the resistance value at ≃6 K up to 5 orders of magnitude with respect to the room temperature value. A variable range hopping (VRH) conduction, with a strong 2D character, dominates the charge carriers transport, from 300 K down to 20 K. At T < 20 K, graphene sponge resistance tends to saturate, suggesting a temperature-independent quantum tunnelling. The 2D-VRH conduction originates from structural disorder and is consistent with hopping of charge carriers between We report morpho-structural properties and charge conduction mechanisms of a foamy “graphene sponge”, having a density as low as ≈0.07 kg/m Graphene-based compounds, such as graphene sponge (GS), are monolithic three-dimensional 3D) graphene-like structures that are gaining interest for their use in a variety of applications such as absorbers of pollutant liquids , due to their super hydrophobicity , or as bD graphenmentally . Energy mentally ,7,8, batmentally ,7,9, supmentally ,10,11 anmentally ,12,13. Omentally ,15.To date, graphene sponges have been synthesised by a variety of well-developed methods such as chemical vapour deposition (CVD), self-assembly of graphene-oxide sheets with different reduction methods and freeze drying , all showww.hygraner.it (accessed on 8 May 2012); product code: HYf-SG VW). All the technical information about the fabrication process here reported, has been taken from the Italian patent  with the addition of further details provided by the company. The material is synthesised by a solvo-thermal process starting from organic precursors based mainly on carbons, oxygen and hydrogen. Precursors have undergone a solvo-thermal process for more than 3 days at 250 The graphene sponge investigated in this work has been purchased by Hygraner srl  Zeiss Sigma-300 equipped with a Bruker Quantax energy dispersive (EDX) detector in order to collect x-rays for the micro-analysis of the elemental composition. Analysed samples have been fixed on aluminum sample holder (stubs) by using self-adhesive carbon conductive tabs. Up to 500,000× magnification scale has been achieved, allowing resolution down to few nanometers.G-band for which a Voigt function has been used.Raman spectroscopy of the GS has been carried out by a micro-Raman apparatus (Horiba mod. iHR320) including a Czerny-Turner spectrometer. The laser source Morphology of the GS has been investigated both by optical microscopy and by scanning electron microscopy (SEM), while homogeneity and local chemical composition has been probed by EDX analysis. On sight, the whole block of GS reveals continuous yet uneven surface, resembling a crumpled paper sheet A. Flakes10÷20 nm B. MorphoEDX micro-analysis, averaged on a millimetre sized area of a GS sample, has detected see  carbon aIn what follows, we employ Raman spectroscopy to yield information on the quality of the GS material, average size of the crystallites, and the defect density. Information extracted from Raman spectra analysis will be correlated to features observed by SEM and to the electronic transport properties.G-peak and D-peak, respectively, next to a smaller peak seen at 1112 cmD and G-peaks has revealed narrow components at 1217 cmRaman spectrum of our GS at 293 K is shown in G-peak is the dominant signature for G-band appears blue-shifted with respect to the expected 1593 cmG-peak is broadened  of the D-peak can range from D-peak exhibits a rather large FWHM  conduction ,41 usuald = 1, 2 and 3 , is to define a reduced activation energy, w, for p value can be determined from the slope of w vs. log T plot, yields The problem with identification of the correct Equation  is obeye vs. logT,51. This vs. logT. A leasteratures . The T−1 and rGO ,44. A leEquation  has enabEquation  suggestsHaving established that the VRH conduction occurs in 2D, it is now possible to use the appropriate expression for Equation  40,47]:,47:T0 ape for 1/α, consideon of GO ,40. La mnm at RT  and the  the fit , using Equation .On the basis of the above considerations, the detected VRH conduction is, at least in part, the electrical manifestation of the presence of defects and high disorder in the GS lattice matrix, as Raman investigation has clearly shown. However, for the assumptions above regarding For the further explanation of carrier conduction mechanisms occurring in the GS, we look deeper in the morphology of the investigated material. SEM observations and micro-analysis have revealed a morphology consisting of partially overlapped small flakes of rGO. These comprise conducting graphene-like  regions , as sugg regions ,57, withThe insulating character of the rGO will depend on the fraction of oxidised disordered regions, forming clusters of nduction . A stronnduction  as well nduction . In any T, the hopping conduction is ‘frozen’, explaining the deviation from the T range, a different conduction mechanism sets in, with a weak T dependence or completely T-independent. Considering the local structural features of our GS and the large defect density, the presence of small (thin) disordered regions, such as point and line defects, appears reasonable. Under these hypotheses, charge carriers can move throughout the material by quantum tunnelling, through thin barriers formed by the defects [As known in literature and mentioned above, a widespread defect is related to oxygen functional groups . The studied material showed a visible foamy or spongy texture and an irregular morphology, formed by large and randomly oriented small flakes of graphene oxide, few millimetres in size. The composition analysis has proven carbon and oxygen as far dominant elements, in a C:O ratio close to 13:1, corresponding to that of a highly reduced graphene oxide. The Raman To conclude, our experimental findings demonstrate a complex foamy and low density three dimensional graphene-like material, in which the interplay between the composition, the defected/irregular structure, and the random orientation of large flakes of graphene oxide, determine unconventional structural and electronic transport properties of interest for several technological applications.Outcomes of the present study and the main conclusions here derived exclusively refer to the electrical behavior of the graphene sponge purchased from Hygraner srl. The sponge used for this study is produced for other uses (filtration). The material synthesis and the whole fabrication process reported in


The etiology and pathophysiology of sarcoidosis remains unclear, with epidemiologic studies limited by its relatively low prevalence. The internet has prompted patients to seek information about medical diagnoses online; Google Trends provides access to an anonymized version of this data, which has a new role in epidemiology. We hypothesize that there is seasonal variation in the relative search interest of sarcoidosis, which would suggest seasonal variation in the incidence of sarcoidosis.p-value less than 0.05 indicating statistical significance.Google Trends was used to assess the relative search volume from 2010 to 2020 for “sarcoidosis” and “sarcoid” in 7 countries. ANOVA with multiple comparisons was performed to compare the mean relative search volume by month and by season for each country, with a Our analysis revealed a significant seasonal variation in search popularity in 4 of the 7 countries and in the Northern Hemispheric countries combined. Direct comparison showed search terms to be more popular in spring, specifically March & April, than in the winter. Southern Hemisphere data was not statistically significant but showed a trend towards a nadir in December and a peak in September and October.Overall, these findings suggest seasonal variation with a possible peak in spring and nadir in winter. This supports the hypothesis that sarcoidosis has seasonal variation and is more commonly diagnosed in spring, but more evidence is needed to support this, as well as investigation into the pathophysiology of sarcoidosis to explain this phenomenon.The online version contains supplementary material available at 10.1186/s12890-021-01602-7. Sarcoidosis is an inflammatory condition of unknown etiology, characterized by non-caseating granulomas. More than 90% of patients will have pulmonary involvement, but sarcoidosis can manifest in almost any body system, including the lymph nodes, joints, skin, heart, and GI tract . Most inWith improving access to information through the Internet, patients commonly seek answers to their medical questions online . Google The term “infodemiology” encompasses the use of information obtained online “in the analysis, detection, and forecasting of diseases and epidemics, and in predicting human behaviour” in health . InfodemThe manuscript does not contain clinical studies or patient data. Google Trends data was extracted for each of the terms “Sarcoid” and “Sarcoidosis”, using filters for “Web Searches”, “All Categories”, “Worldwide” and from January 2010 to July 2020 , and the United States (USA). The relative search volume for “sarcoid” and “sarcoidosis” for these countries is found in Table Figures Of note, December–February, summer months, were significantly less popular than both winter  and spring  in Australia. None of the results from the other southern countries analyzed were statistically significant, but there was a trend toward lower search volume in December, and, less markedly, July–August. Overall, September and October, spring months, were relatively popular in the southern countries.With respect to monthly data, there was a statistically significant difference between months for the term “sarcoidosis” in Australia, the UK, and the USA. “Sarcoidosis” was more popular in March and April compared to the month of December in the USA and the UK. Furthermore, data for all three datasets from the UK strongly indicated overall variation (p = 0.0001–0.001), with relative search volume lowest in December and significantly different compared to the months of March to May. In addition, volume in December was significantly less than that of the months of June and July for “sarcoid” and both search terms combined.The results of this analysis indicate that searches for sarcoidosis are higher in the spring months, and significantly less so in the winter, particularly in the Northern Hemisphere. This suggests that the condition may be more commonly diagnosed in the spring. Overall, this seems to support findings of higher incidence in winter-spring, as observed in previous studies. Both the Minnesota and the Taiwanese studies showed lowest incidence in autumn, which was statistically significant , 7. The Our study assumes that patients only search for sarcoidosis online after contact with the healthcare system and when they are most unfamiliar with the term, that is, when they are first diagnosed. In addition, there is often a delay between when patients develop symptoms and diagnosis; a delay would systematically skew results. If sarcoidosis truly is most common in the winter-spring and least common in autumn, a few weeks’ delay would shift search patterns forward in time, making winter appear to be less popular, reflecting lower incidence in autumn, followed by the spring peak, corresponding to incidence in winter-early spring. Once they have been diagnosed, we expect that patients would preferably consult other sources, such as their physician, or resources provided to them by their physician, when their disease relapses. There are cases of seasonal variation in hypercalcemia in sarcoidosis patients, so it is plausible that this could also impact Google search trends in a similar fashion .Another important assumption was that the countries included follow a traditional four-season structure. We would expect opposing results when comparing southern hemisphere countries to those in the northern hemisphere; that is, that June–August would have the least search term popularity and September–November, the most. The results of the comparison of means in the southern countries showed mixed trends, none of which met statistical significance. December was less popular overall, but a smaller peak in interest was observed in September and October. The December phenomenon suggests that the variation may be due, in part, to a non-weather-related factor, but the latter peak is more consistent with the pattern observed in the Northern Hemispheric countries and true seasonal variation.The main limitation of our study was the nature of the data obtained from Google Trends. In the interest of maintaining privacy, Google Trends only provides relative search volume, and it is not possible to obtain absolute values. This makes it difficult to ascertain that the data is sufficient to make valid conclusions. Other countries with less access to internet or using search engines other than Google would be excluded, despite a relatively high prevalence of sarcoidosis. Lastly, the search terms used in this study were English words, which probably limited non-Anglophone countries from fulfilling the inclusion criteria.As mentioned earlier, the results obtained from Google Trends varies day-by-day; this is because Google Trends only analyzes a sample of the total searches . With biIn Moccia et al.’s study on trends in Multiple Sclerosis, the country selection criteria were more stringent, with a minimum relative search volume of 70 and population of 20 million to avoid “noise” from areas of less search interest . This waThe strongest data to support the overall results was obtained from the United Kingdom, which showed very significant data in every data set. This probably swayed the overall statistics for the Northern Hemisphere countries towards significance. The incidence of sarcoidosis is about to 11.5/100,000 in Sweden , but onlOur study adds evidence to the hypothesis that the incidence of sarcoidosis exhibits seasonal variation and is more commonly diagnosed in the winter & spring. It is expected that future work will be needed in determining how to best incorporate “infodemiology” and the wealth of Internet-based data into future medical research. Hopefully, the results of this study lead to more investigation into the etiology behind this seasonal phenomenon and better understanding of the pathogenesis of sarcoidosis.Additional file 1. Raw search results for term "Sarcoidosis" by month and country.Additional file 2. Raw search results for term "Sarcoid" by month and country.