The detected signal corresponds to a gas molecule layer adsorbed on the graphene surface with a concentration of 800 zeptomole per μm2, which is made possible by the strong field confinement of graphene plasmons and high physisorption of gas molecules on the graphene nanoribbons. We further demonstrate a fast response time (<1 min) of our devices, which enables real-time monitoring of gaseous chemical reactions. The demonstration and understanding of gas molecule identification using graphene plasmonic nanostructures open the door to various emerging applications, including in-breath diagnostics and monitoring of volatile organic compounds.Identification of gas molecules plays a key role a wide range of applications extending from healthcare to security. However, the most widely used gas nano-sensors are based on electrical approaches or refractive index sensing, which typically are unable to identify molecular species. Here, we report label-free identification of gas molecules SO 2, NO2, N2O, and NO gas molecules by detecting their rotational-vibrational modes using graphene nanoribbon plasmons.Identification of gas molecules is crucial in healthcare and security applications. Here the authors achieve label-free identification of SO For example, for diagnostics, the presence of NO in the breath of patients is typically associated with chronic obstructive pulmonary disease6, while isopropanol8 and ammonia10 in the breath of patients are normally linked to lung cancer and renal failure disease, respectively. Recently, the sensitivity of electrical devices has been improved to the single-molecule level using nanomaterials17. In addition, refractive-index sensing of gas molecules using plasmons are also approaching very high sensitivity21. However, the identification of trace gases has been fundamentally hindered. This is mainly due to the fact that the intrinsic detection variations  in these devices are not directly correlated with the components and structures of the gas molecules26, and therefore, these methods are unable to identify molecular species without molecular labels  and a chemical bond vibration in acetone and hexane vapor32. However, there is a technologically important challenge to extend solid-sample sensing to gas sensing with SEIRA:35 the dielectric response of gases at ambient pressure is >4 orders of magnitude weaker than that of solid molecular layers due to the difference in density19. For example, a 500-μm-thick NO2 layer with a concentration of 1000 ppm has the same optical density (~0.25%) as an ~10-nm-thick poly(methyl methacrylate) layer30. Furthermore, the large spatial mismatch between the evanescent plasmon field (~tens of nanometers) and dispersed gas molecules limits the detection region to the immediate surroundings of the graphene layer, thus imposing another serious constraint to the applicability of graphene plasmons to gas sensing. However, if one could redistribute these gas molecules closer to the graphene surface , it might be possible that the additional enhancement due to plasmonic light confinement can reveal the molecule vibrational modes.Recently, graphene-plasmon-based surface-enhanced infrared absorption (SEIRA) spectroscopy2, N2O, NO, and SO2, which are generally important in environmental and military monitoring applications, as well as in medical diagnostics, are unambiguously detected and identified using the designed graphene nanostructures. This result relies on the adsorptive redistribution of the gas molecules on the graphene surface , hence facilitating the interaction between ultra-confined graphene plasmons and gas molecules. Our theoretical analysis reveals that the adsorbed gas-molecule layer (about 800 zeptomole per μm2 for <1 nm thickness) on the graphene structure, in conjunction with the strong field confinement associated with the plasmons, is critical for effectively detecting and identifying gas molecules. In addition, our graphene plasmonic sensors also successfully perform real-time monitoring of gas molecules during chemical reactions with a fast response time (<1 min).In the present study, we identify gas molecules using graphene plasmons. The rotational-vibrational modes of the gas molecules NO30. The graphene nanoribbon arrays were designed to have widths (W) in the 25–100 nm range with a high filling fraction of up to 90% to achieve strong plasmon-field enhancement over a broad mid-IR spectral range , where λp is the plasmon wavelength in extended graphene. And for ribbons we have approximately λp = ~2×width , so the plasmon intensity extends a distance ~0.2×width, and ~60% of the plasmon energy is confined to a ~5-nm distance from the graphene surface  of the graphene nanoribbons, respectively . The obtained extinction spectra −1 spectral range by varying the ribbon width or Vg  and a low-energy branch 37.When the chamber did not contain gases , there was only one prominent plasmonic peak in each extinction spectrum of our plasmonic devices. The resonance peaks could be tuned within the 900–2000 cm39, and an optical-effective ribbon width (Weff) is introduced to account for pressumably inactive edges40. The dielectric permittivities of gases were retrieved from the experiments and fitted to a good approximation as the sum of Lorentzian P and R modes37 contributions,i runs over the P and R pairs of spectral positions C. This yielded absorption spectra that can be well described by d = 7 mm is the gas chamber height, λ0 is the free-space wavelength. The extracted values of 2 gas molecules are distributed uniformly in the chamber. However, there are no noticeable dips in the calculated extinction spectra if this is the case, which indicates negligible electromagnetic interaction between the SO2 gas molecules and graphene plasmons due to the extremely small gas dielectric function for the tested concentrations. To achieve the dip strength observed in the experimental spectrum  , which produces an increase in image attraction comparable to that of water (permanent dipole 1.85 D), thus permitting nearly full monolayer coverage of the surface. Furthermore, besides the above-mentioned adsorption mechanism related to polar molecules, the large amount of edge defects and dangling bonds in the graphene nanoribbons could also help to trap gas molecules, as the adsorption energy of graphene with divacancy defects is about one order of magnitude higher than that of unpatterned graphene44. Through the mapping of the Raman D peaks, we estimated a defect density of 105 μm−2 . The integrated areas of these plasmon response signals are recorded as a function of SO2 concentration. The devices had a near-linear response when monitoring the gas concentration, as shown in Supplementary Figure 2 molecules on the graphene surface at these gas concentrations was below the saturation threshold for graphene gas adsorption as previously discussed.We also measured the extinction spectra of SO2, and N2O) were employed to show the key advantage of using graphene plasmons for identification of similar gas molecules, which still remains a challenge for sensors based on electrical methods, as the adsorption of these molecules results in similar changes in resistance . Then O2 was injected into the chamber. As shown in the extinction spectrum recorded after 1 min, the signal intensity of NO decreased to ~60%, while a new pair of peaks appeared at 1590 and 1610 cm−1  (950 K) film was spin-coated onto the sample. The nanoribbon arrays were patterned in graphene using electron-beam lithography  and oxygen plasma-etching at 5 Pa and 80 W for 10 s . Two Cr (5 nm)/Au (60 nm) electrode patterns were fabricated using a second electron-beam lithography cycle combined with electron beam evaporation . The growth rate of CaF2 film was 0.5 Å/s at 100 °C in the a high vacuum of ~10–6 Torr. The graphene device on SiO2 was transferred onto the CaF2/Si substrate and then annealed at 200 °C for 5 h.Chemical vapor deposition graphene was first transferred onto a 300-nm SiOThe morphologies and thicknesses of the fabricated graphene nanoribbons were characterized by scanning electron microscopy (Hitachi S-4800) and atomic force microscopy (Neaspec s-SNOM). The quality of the graphene and defect density of the nanoribbons were measured by Raman spectroscopy (Horiba Jobin Yvon LabRAM HR800) with a laser excitation at 514 nm. Electrical properties were determined using a semiconductor parameter analyser (Agilent 4294 A).TCNP of the graphene array at the CNP, and then the extinction spectra η for in situ nanoribbon doping at EF were calculated as 1-TVg/TCNP.A home-made gas chamber was designed to meet the requirements for electrical measurements and transmission spectrum detection simultaneously. A high-precision piezometer and mass-flow controller with a 50–400 sccm flow at different times (in minutes) were used to control the partial pressure of the analyte gases. For the transmission measurements (Thermo Fisher Nicolet iN10), the excitation light was broadband. For all the extinction spectra in this work, we first recorded the transmission spectrum Electromagnetic simulations were conducted using the commercial field solver, COMSOL Multiphysics, RF module. The graphene optical response is described via the Drude model. The gas parameters including oscillator strength and broadening corresponding to each FTIR peak for the gas molecules were extracted from fitting to the measured data.Supplementary Information


Aegilops tauschii, the D-genome donor of bread wheat, Triticum aestivum, is a storehouse of genetic diversity, and an important resource for future wheat improvement. Genomic and population analysis of 549 Ae. tauschii and 103 wheat accessions was performed by using 13,135 high quality SNPs. Population structure, principal component, and cluster analysis confirmed the differentiation of Ae. tauschii into two lineages; lineage 1 (L1) and lineage 2 (L2), the latter being the wheat D-genome donor. Lineage L1 contributes only 2.7% of the total introgression from Ae. tauschii for a set of United States winter wheat lines, confirming the great amount of untapped genetic diversity in L1. Lineage L2 accessions had overall greater allelic diversity and wheat accessions had the least allelic diversity. Both lineages also showed intra-lineage differentiation with L1 being driven by longitudinal gradient and L2 differentiated by altitude. There has previously been little reported on natural hybridization between L1 and L2. We found nine putative inter-lineage hybrids in the population structure analysis, each containing numerous lineage-specific private alleles from both lineages. One hybrid was confirmed as a recombinant inbred between the two lineages, likely artificially post collection. Of the remaining eight putative hybrids, a group of seven from Georgia carry 713 SNPs with private alleles, which points to the possibility of a novel L1–L2 hybrid lineage. To facilitate the use of Ae. tauschii in wheat improvement, a MiniCore consisting of 29 L1 and 11 L2 accessions, has been developed based on genotypic, phenotypic and geographical data. MiniCore reduces the collection size by over 10-fold and captures 84% of the total allelic diversity in the whole collection. Ae. tauschii Coss.), presents a promising solution and the best resource.World population is projected to reach 9.7 billion by 2050, increasing pressure on the food system and challenging food security . Wheat, Aegilops tauschii originated as the result of hybridization between diploid A and B genome progenitors (Triticum aestivum L.). Ae. tauschii is native throughout the Caspian Sea region and into central Asia and China. Natural hybridization of tetraploid wheat and Ae. tauschii about 8,000–10,000 years ago  and ssp. strangulata . The L2 ssp. strangulata is known to be the D-genome donor  at Kansas State University (K-State) in Manhattan, KS, United States. Most of the Ae. tauschii accessions were collected in 1950s and 1960s from 15 different countries by several explorers, however, a recent exploration was carried out by WGRC scientists in 2012 in Azerbaijan to fill the geographical gaps in the collection and sample more genetic diversity , 103 wheat varieties from a panel of diverse United States winter wheat accessions were also included in the study . One random well per plate was left blank for quality control and library integrity. DNA samples were genotyping using genotyping-by-sequencing (GBS) (PstI (5′-CTGCAG-3′), and a frequent cutter MspI (5′-CCGG-3′) with a common reverse adapter ligated. Full protocol is available at the KSU Wheat Genetics website1. GBS libraries were sequenced on 10 lanes on Illumina HiSeq2000  platform at University of Missouri  or McGill University-Génome Quebec Innovation Centre  facility.A single plant for each accession was grown in 2″ × 2″ pots in the greenhouse. About five centimeter of leaf tissue from single 2–3 weeks old seedlings were collected in 96-well tissue collection box and stored at −80°C until DNA extraction. Tissues were lyophilized in the lab for 24–36 h, followed by genomic DNA extraction using Qiagen BioSprint 96 DNA Plant Kit . Extracted DNA was quantified with Quant-iTng (GBS) . GBS libAe. tauschii genome assembly  as the reference. Tassel was run with bowtie2 aligner for tags mapping in Linux HPC environment via shell script. Genotypic data were processed in R statistical programming language  discovery and genotyping was performed in single step with Tassel 5 GBSv2 pipeline , using Alanguage  using cuK = 2 using ‘simple’ prior to partition all Ae. tauschii accessions into L1 and L2 lineages. Per the developer recommendation for computational efficiency, fastSTRUCTURE was run with ‘simple’ prior and random seed for K = 2 to K = 8 with three replications each to detect the optimum values of K. Once the optimum K was determined, final fastSTRUCTURE analysis was performed using ‘logistic’ prior with all the SNPs. Only those accessions with available passport information were used in this analysis, and passport information was used to group and order accessions. To ensure the label collinearity for multiple iterations of each K run, fastSTRUCTURE results were processed using CLUMPAK package  were computed and plotted using custom R scripts. Pairwise FST were computed among L1, L2, and wheat in all combinations. MAF plots were plotted separately for L1 and L2.As a measure of average heterozygosity over multiple SNPs in a given population, Nei’s diversity index  was compLineage specific private alleles are the ones that are segregating in one lineage but fixed in the other. To determine a lineage specific allele at a SNP site, dataset was split into L1 and L2 accessions. SNP sites where MAF was zero in one lineage but greater than zero in the other lineage, were filtered and the segregating lineage specific allele identified. L1 and L2 private alleles were assigned different colors and plotted for each putative hybrid separately. For each hybrid, lineage specific contribution was determined as percentage of alleles contributed by specific lineage. Using private allele SNPs, allele matching was performed as described in Ae. tauschii collection. The core-set was selected in two steps. First, software package PowerCore was used with default settings  and as far East as eastern China . Geographical origin data was known for most of the accessions  generated 318,639 putative single nucleotide polymorphisms (SNPs) from a total of 672 samples consisting of 569 Ae. tauschii and wheat together for K ranging from two to eight with three iterations for each K . PC3 vs. altitude plot also shows a clear trend with PC3 separating the accessions according to their altitude, however, there are few outliers present on the both ends , in which the chromosomal segments from L1 and L2 were clearly demarcated without any overlap . Only 110 SNPs were segregating mostly from the one accession from Turkmenistan  alleles from L1 and 2,406 (97.3%) alleles from L2. Two chromosomes, 1D and 6D, carried 54% of the total L1 alleles with majority of the introgressions present in the distal regions , therefore, to determine the lineage-specific contribution of Ae. tauschii L1, L2, possible hybrids, wheat and Ae. tauschii collection combined. Highest Nei’s diversity index was observed for L2 = 0.1326 followed by L1 = 0.0872, and wheat of 0.0158. Higher values of the Nei’s index indicates greater allelic diversity in a given population. Combined Nei’s index for Ae. tauschii was 0.2382 and the whole dataset including wheat was 0.2597.Nei’s diversity index was computed using all SNPs separately for Ae. tauschii lineages and wheat, pairwise FST statistics were computed. Highest FST were observed between L1 and wheat, followed by wheat and L1–L2 hybrids, and wheat and L2  strategy to select diverse accession by reducing allelic redundancy and keeping the allele frequency spectrum similar. Initially 107 Ae. tauschii. Most of the accessions in our collection were also sampled from this region  represents Ae. tauschii ssp. strangulata. However, as we did not use any prior SNP information to call SNPs, we expect the ascertainment bias be minimal. Splitting two lineages and computing MAF separately revealed that both lineages had about similar distribution of MAF  with each having two subgroups, and wheat D-genome forming a third group which was most closely clustered to L2. These findings are largely in agreement with known population structure of Ae. tauschii, confirming the utility of our genotyping approach. In addition to these five groups, we unexpectedly found putative hybrids clustered together  consisting of 29 L1 and 11 L2 accessions to facilitate wheat improvement.We assayed wheat D-genome chromosomes for lineage specific introgressions from Ae. tauschii accessions in wheat breeding, we selected only 40 accessions to develop a small MiniCore set that captures 84% of the segregating alleles from the whole collection. MiniCore was carefully selected from both the lineages of Ae. tauschii but the main focus was to target more from L1. This is because L1 is a reservoir of untapped genetic diversity that has not been leveraged by the breeders. L2 accessions were chosen because this lineage is the source for many of the diseases and insect resistance. These accessions can be utilized to bring in novel genetic variation for wheat rusts, insect resistance, heat and drought tolerance to produce climate resilient wheat varieties. This MiniCore consisting of genetically diverse accessions was selected with an objective to broaden the genetic base of wheat D-genome. However, in future, the selection can be optimized based on the recombination rate and the distribution of Ae. tauschii regions that are already introgressed in the wheat D-genome.Accessing the genetic diversity present in wild relatives can be a challenging task for breeders due to the large number of accessions and confounding physiology of the wild plants. Wild accessions with overall poor phenotype could be the source of agronomically important alleles. Efficient use of germplasm collections can often be facilitated through a targeted subset of the total accession that is optimized to capture a maximum amount of the total diversity in a minimum number of accessions. To facilitate the use of Ae. tauschii is of great interest to breeders and geneticists for wheat improvement and broadening the narrow D-genome   with a desired gene introgressed in it  Figure . This oc) Figure . HoweverAe. tauschii is very important to wheat improvement in the wake of unpredictable climate and evolving biotic stresses. In this study, we confirmed that Ae. tauschii L1 has immense amount of untapped genetic diversity that can be used for wheat improvement. We also provided the evidence of natural Ae. tauschii L1–L2 hybrids, which opens the door to the possibility of new genetic variation. Finally, selection of forty genetically diverse accessions will facilitate the use of Ae. tauschii for wheat improvement for abiotic and biotic stresses via octo-amphiploid mediated bridge crossing, which will ultimately result in higher genetic gains and faster wheat improvement.Studying genetic diversity in https://github.com/nsinghs/Code_Ae_tauschiiDiversity.Sequence reads generated using genotyping-by-sequencing are available from NCBI SRA under accession SRP141206. R-code and other scripts are available at GitHub repository Ae. tauschii accessions. DW collected and provided phenotypic data. MA provided Ae. tauschii accessions. BG and JP conceived and developed the idea. JP wrote the manuscript.NS analyzed the data and wrote the manuscript. SW performed the GBS. VT and SS developed and contributed to the idea. JR acquired, managed, and provided The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


This article demonstrates a dispersed-monolayer graphene-doped polymer/silica hybrid Mach–Zehnder interferometer (MZI) thermal optical switch with low-power consumption and fast response. The polymer/silica hybrid MZI structure reduces the power consumption of the device as a result of the large thermal optical coefficient of the polymer material. To further decrease the response time of the thermal optical switch device, a polymethyl methacrylate, doped with monolayer graphene as a cladding material, has been synthesized. Our study theoretically analyzed the thermal conductivity of composites using the Lewis–Nielsen model. The predicted thermal conductivity of the composites increased by 133.16% at a graphene volume fraction of 0.263 vol %, due to the large thermal conductivity of graphene. Measurements taken of the fabricated thermal optical switch exhibited a power consumption of 7.68 mW, a rise time of 40 μs, and a fall time of 80 μs at a wavelength of 1550 nm.  High-speed optical switch chips are core components in optical switching systems, meeting the requirements of being high speed, large capacity, and low delay ,2,3. Opt2−TiO2 waveguide [According to the structure of the device, TO switches can be categorized into X-junction TO switches  and Machaveguide . A switcaveguide ,17,18. HIn this research, to solve the problems of the graphene film being uneven and fragile during the fabrication of the TO switch, a graphene-dispersed N-Methyl pyrrolidone (NMP) material was synthesized and doped into polymethyl methacrylate (PMMA). This composite material not only guaranteed the large thermal optical coefficient of the polymer, but also an improved thermal conductivity, due to the large thermal conductivity of graphene . TherefoKp and Kg are the thermal conductivities of the PMMA matrix and graphene filler [Kp = 0.19 W/mk; Kg = 5300 W/mk). However, the limitation of the model is that the interfacial thermal resistance between the fillers and the polymer is not considered.The thermal conductivity of the material significantly affects the performance of TO switches. The thermal conductivity of the composite material has been analyzed and calculated using the Bruggeman  and Lewie filler ,22, respD and L represent the diameter and thickness of the filler, respectively . A and B depend on the filler dimensions and the thermal conductivity of each component, respectively, and V is the volume fraction of filler. Vm is the maximum packing fraction of the filler (Vm = 0.673).In the Lewis–Nielsen model, the effects of particle morphology, aggregation method, and orientation on the thermal conductivity of the composites are considered, and the thermal conductivity is calculated by the expression:The thermal conductivity of composites as a function of the volume fraction of filler, calculated using MATLAB software , is shown in a = 5.3 μm and b = 3 μm, respectively. The distance between the electrode and the top of the core was h1 = 1.2 μm, and the thickness of the cladding was h2 = 2 μm. The refractive indexes of the imaginary and real parts of the graphene material are 2.79 and 2.97, respectively [ectively ,24. The ectively . Figure ectively ,24,26. AThe calculated response times and the thermal field distribution of the arc cladding structure for the GD-TO and ND-TO switches are shown in 2, using spin-coating and photolithography processes . The width of the core was 5.3 μm. Next, a graphene-dispersed NMP material was synthesized and doped with 0.263 vol % into PMMA . The composites were spin-coated on the core layer as a waveguide cladding. The arc cladding structure was realized by optimizing the viscosity of the cladding material and the spin rate of the spin coater . Lastly, a 0.1 μm thick Al electrode was fabricated with a width and length of 6 μm and 1.5 cm, respectively. According to the Lewis–Nielsen model, the calculated thermal conductivity of the composites was increased by 133.16%.Following the previous simulation, the polymer/silica hybrid MZI TO switch was fabricated using doped dispersed-monolayer graphene NMP material . In conclusion, we proposed a polymer/silica hybrid MZI TO switch. The predicted thermal conductivity of the composites was then increased by 133.16% for the composites doped with graphene (0.263 vol %). The fabricated TO switch exhibited a power consumption of 7.68 mW, a rise time of 40 μs, and a fall time of 80 μs at a wavelength of 1550 nm. The doped graphene material was not sensitive to the absorption of various polarized modes. In future research, the application of graphene in the all-optical switch field will be studied according to the photothermal efficiency characteristics of graphene at different wavelengths. Moreover, graphene-doped materials have potential applications in both flexible thermal optical switches and wearable fields.


A chemical-sensitive semiconductor film based on graphene has been achieved, being decorated with CH3NH3PbBr3 perovskite (MAPbBr3) nanocrystals (NCs) synthesized, and characterized by several techniques, such as field emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Reversible responses were obtained towards NO2 and NH3 at room temperature, demonstrating an enhanced sensitivity when the graphene is decorated by MAPbBr3 NCs. Furthermore, the effect of ambient moisture was extensively studied, showing that the use of perovskite NCs in gas sensors can become a promising alternative to other gas sensitive materials, due to the protective character of graphene, resulting from its high hydrophobicity. Besides, a gas sensing mechanism is proposed to understand the effects of MAPbBr3 sensing properties.This paper explores the gas sensing properties of graphene nanolayers decorated with lead halide perovskite (CH Nitrogen dioxide (NO2) and ammonia (NH3) are two examples of these harmful species. For these reasons, the in-field monitoring of harmful gases is a mandatory goal to control dangerous levels of contaminants. Above the threshold limits, when human health is at risk, gas sensors can be the last wall to start actions like reducing the access of cars to city centers, to mitigate the impact on the public health.Atmospheric contamination is one of the most important environmental issues in current societies. According to the World Health Organization (WHO), air pollution is linked to 7 million premature deaths in 2012 [Among the different types of gas sensors, chemoresistive sensors have been attracting great interest due to their high sensitivity, low cost, reproducibility and simplicity . Other tMany authors have developed chemoresistive gas sensors employing graphene semiconductors, however the use of pristine graphene for developing gas sensors still presents many intrinsic problems, including low gas sensitivity and complicated processability into devices . On the 3 [2 [Unlike metal oxides based sensors, which usually require high working temperatures to activate the oxidation-reduction processes and achieve the required electron mobility involved in gas sensing , graphen3 , acetone3 , oxygen 3 , and NO23 [2 . However3 [2 .3NH3PbI3 (MAPbI3) usually shows a fast degradation, in most cases attributed to their hygroscopic properties [3), which has been proved to be more resilient to the presence of ambient moisture [3 stability and increasing the sensor time-life, via limiting perovskite degradation. Moreover, the nanocomposite was characterized by several techniques, such as X-Ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), Field Emission Scanning Electron Microscope (FESEM), and Raman spectroscopy. In consequence, this paper shows the results with graphene decorated by MAPbBr3 NCs, registering higher sensitivities and detecting lower concentrations than other gas sensors based on perovskite thin films or similar approaches  and TWA (Time-Weighted Average) by the European Agency for Safety and Health at Work (EU-OSHA) [3 limits. Thus, the development of sensor networks able to detect these trace concentration levels in a wide range of locations would be highly advisable. In consequence, sensors should offer reversible interaction with gas molecules for allowing the continuous monitoring of these species at an affordable cost.Threshold limit values (TLV) to 1-h exposure to NOan Union  and the an Union , respectEU-OSHA)  and by t3) nanocrystals, the method proposed by Schmidt, et al. [2) were mixed in the same solvent. Subsequently, these two solutions were added to the main solution and was cooled to 60 °C. Finally, 5 mL of acetone was added to the final solution to create precipitates of perovskite nanocrystals, which were separated from the unreactive solution by using a centrifugation technique at 6000 rpm during 10 min. Afterwards, the nanocrystals obtained were suspended in toluene.To synthesize lead halide perovskite  dispersed in 1 mL of toluene. Then, graphene nanoplatelets were sonicated employing a Sonic Tip (FisherbrandTM Model 705) at 40% of 700W for 1 h and 30 min using a 1 s on −2 s off pulsed sonication.The exfoliated graphene and the lead halide perovskite were characterized by several techniques such as XPS, HRTEM, FESEM and Raman spectroscopy.The chemical composition of the nanomaterials obtained was studied via XPS, using a SPECS spectrometer  equipped with a Phoibos 150 MCD detector, using a non-monochromatic X-ray source (Al) operating at 200 W. The intensity ratios of the different components were calculated from the area peak after a correction by the transition function of the spectrometer and a non-linear Shirley-type background subtraction. Additionally, graphene crystallinity was evaluated employing a Raman spectrometer from Renishaw, plc. , coupled to a confocal Leica DM2500 microscope. The laser used had a wavelength of 514 nm.The morphology was studied employing a JEOL JEM 2100F  HRTEM, at an operating voltage of 200 kV. Nanomaterials were ultrasonically dispersed in toluene and a drop of dispersion was deposited onto a carbon-coated copper grid, drying it at room temperature. Graphene porosity and perovskites NCs distribution were analyzed by Carl Zeiss AG - ULTRA 55  Field Emission Scanning Electron Microscope.2 quartz substrates previously cleaned in an ultrasonic bath, using an anionic detergent (Alconox) and miliQ water. Afterwards, a 1M solution of hydrochloric acid was employed in order to increase the surface hydrophilicity. Finally, the substrates were cleaned and dried several times with ethanol. Then, a film of graphene nanoplatelets was deposited onto quartz substrates by drop casting method, and subsequently, perovskite nanocrystals (5% wt solution) were deposited by spin coating at 1000 rpm for 120 s. The materials obtained were deposited onto 1.5 cmOnce the hybrid material film was deposited onto quartz substrate, its backside was glued with a thermally conducting epoxy from Heraeus, Inc.  to an alumina hotplate that comprised a screen-printed platinum heater. Then, the samples were placed on a 20 × 30 mm printed circuit board (PCB) to be connected to an airtight test chamber. Finally, two-wire contacts were made on the sensor surface employing a conductive silver paste and platinum wires  mass-flows controllers. The sensors were stabilized under synthetic dry air for 60 min before the application of the desired gas concentration during 30 min of exposure. Besides, a controller evaporator mixer (CEM) from Bronkhorst High-Tech B.V.  was used to humidify the gas mixture and thus, analyze the effect of ambient moisture on the sensing properties  and different dilutions of gases tested to achieve the target concentration. In order to reproduce real atmospheric conditions, NOties see . The relA high-resolution transmission electron microscopy (HR-TEM) analysis was conducted to characterize graphene and perovskite nanocrystals independently. 3 NCs. Additionally, FESEM images were obtained for both, bare and graphene decorated with MAPbBr2 carbon systems in the “graphite-like” [2 carbon systems, but in this case due to the π-π* interactions and π plasmon, which is derived from the energy loss due to the excitation of π electrons [3 configuration appear at 285.0 eV [According to the XPS elemental quantification, the graphene used presents a 7.8% content of oxygen and 92.2% of carbon. The results of the XPS fitting analysis are represented in te-like” . The pealectrons . Compone285.0 eV , and def285.0 eV . Meanwhi285.0 eV . Peak quThe O 1s spectrum is reproduced employing three components centered at different binding energies, which are 531.3 eV, 532.6 eV and 533.9 eV b. The fiTwo different gases, nitrogen dioxide and ammonia, with high interest to be monitored due to the danger to human health derived from their exposure at certain levels were measured. Several dilutions were performed in order to apply different concentrations, especially under the threshold limits. Due to the different baseline levels of the two films studied, normalized responses are show for better comparison in 2. Nitrogen dioxide detection was performed by applying repeated exposure and recovery cycles to increasing concentrations of the analyte considered. 0)/R0, Where R0 is the resistance value immediately before gas exposure , and R is the resistance immediately before the start of a new cleaning step . 2 concentrations measured. Graphene doped with perovskite nanocrystals presents a higher response (up to 3-fold) than bare graphene, even under a hundred ppb of NO2 exposure. Additionally, bare graphene presents a slight saturation above 500 ppb, decreasing the slope obtained and, in consequence, reducing sensitivity. 2 after six months of sensor operation. This result confirms the high stability of MAPbBr3 under ambient moisture and reactive gases, probably due to the nanocrystal structure of the perovskite. Zhu et al. [A stability study of graphene loaded with perovskite nanocrystals was conducted b, revealu et al.  report t2 detection, were applied as well for NH3 detection at ppm range  when moisture is present. However, graphene decorated with perovskite nanocrystals shows a very stable response with only a slight decrease (about 5%) when under humid conditions.Additionally, the sensitivity under dry and humid conditions was evaluated to both, bare and perovskite loaded graphene. 2 leads to a lower sensor resistance. Conversely, an electron-donating gas, such as NH3, decreases the hole concentration resulting in a higher sensor resistance. In films decorated with perovskite nanocrystals, the p-type behavior of the sensor is defined as well by the graphene nanolayers , meanwhile the MAPbBr3 NCs are ambipolar charge transporters [Graphene with oxygen-containing functional groups such as carbonyl, hydroxyl, epoxy, and ether groups exhibited enhanced hole transport characteristics due to its suitable work function ,49. In asporters . In othe2 and NH3, due to the interaction of these gases with the oxygenated defects and functional groups located on the graphene nanosheets. However, all the measurements were done at room temperature, obtaining limited sensitivity derived from the small transfer of electronic charge between graphene and adsorbed gas molecules. Nevertheless, from the gas sensing tests, it was derived that the presence of MAPbBr3 NCs decorating the graphene nanolayers was advantageous for detecting NO2 and NH3 at room temperature. In addition, surface trap sites at the perovskite have been demonstrated to act as active sites for the gas sensing process. It is reported that a net positive charge is formed at the surface of the perovskite due to the loss of bromine and undercoordination of the Pb atom, favouring the perovskite to be sensitive to the environmental gases [3 NCs. Upon the formation of the hybrid perovskite the overall resistance of hybrid films is higher than that of bare graphene due to the intrinsic electrical properties of the perovskite nanocrystals.Bare graphene samples offer a response to both, NOal gases . Regardi3 NCs is associated to the creation of electron-hole pairs by the perovskites, once these are exposed to the gases  generated at perovskite NCs are transferred from the perovskite to the graphene sheet [3, an excess of negative charges (electrons) are generated. As a consequence, perovskite NCs transfer electrons to graphene (and this is associated to an increase in resistivity), enhancing the response of the film to NH3 due to the higher concentration of electrons. This enhancement in the response when graphene is decorated with MAPbBrhe gases . On the ne sheet . Therefo3 NCs and slow down their degradation, due to the limited interaction with ambient moisture [One of the main drawbacks of the sensors based on perovskites films is the fast degradation derived from the exposure to ambient moisture. For that reason, a lead halide perovskite with bromide was chosen, due to the well-known stability over other perovskites based in halides like iodine . Additiomoisture . 2 in humid conditions can be favored by a water-mediated adsorption, as reported in chemoresistive sensors [Considering the effect of ambient moisture in the sensing mechanism, higher sensitivity under humid conditions can be observed for bare graphene. This is in agreement with other works that report the use of graphene as humidity sensors . Normall sensors .2 in the presence of ambient moisture for MAPbBr3 decorated graphene shows interesting characteristics. 2 is achieved for hybrid sensors under dry and humid conditions. The response is only slightly lower in the presence of ambient moisture. Probably water molecules partly passivate the charge transport and the creation of electron-hole pairs of perovskite nanocrystals [3 under dry conditions. The hydrophilic properties of perovskite decorated graphene were further studied by contact angle measurements (see Nevertheless, the detection of NOcrystals , slightlents see .The gas-sensitive layer developed shows its potential for detecting concentrations of nitrogen dioxide and ammonia at trace levels, even below their threshold limit values. These results are a promising beginning for the use of perovskite nanocrystal decorated graphene in gas sensing applications. However, selectivity should be further studied before their use under real conditions. One reasonable approach could be the development of multi-sensor arrays employing decorated graphene with different types of perovskite nanocrystals.2 and NH3 was achieved at room temperature, enabling the integration of these hybrid films in low-power gas sensing devices. In summary, perovskites can constitute an alternative to metals, metal oxides, polymers or other molecules commonly used in the modification of the surface of carbon nanomaterials such as graphene in view of tuning sensitivity and selectivity. This work reports the first use of graphene loaded with perovskite nanocrystals as a chemoresistive sensor. This nanocomposite material has been shown to be a good option to obtain gas sensors with high stability over time, avoiding the main problem associated with perovskites, which is their degradation in contact with ambient moisture. Decorated graphene nanolayers show enhanced nitrogen dioxide and ammonia sensitivity in comparison to their bare graphene counterparts and much reduced cross-sensitivity to the ambient moisture. Furthermore, a reversible response to NO


The transition was accompanied by an electron density redistribution within the molecule, sensed by atomic force microscopy with CO-functionalized tip. This demonstrates the unique capability of the high-resolution imaging technique to discriminate between different spin states of single molecules. Moreover, we present a method for triggering spin state transitions and tuning the electronic properties of molecules through weak non-covalent interaction with suitably functionalized graphene.Nitrogen doping of graphene significantly affects its chemical properties, which is particularly important in molecular sensing and electrocatalysis applications. However, detailed insight into interaction between N-dopant and molecules at the atomic scale is currently lacking. Here we demonstrate control over the spin state of a single iron(II) phthalocyanine molecule by its positioning on N-doped graphene. The spin transition was driven by weak intermixing between orbitals with  Molecules can change their electronic properties when they are adsorbed on substrates, which can be useful for sensing and catalysis. Here, the authors use atomic force microscopy to show that the spin state of an iron complex can be changed upon displacing the molecule to different sites of a nitrogen-doped graphene It shows remarkable physical characteristics, such as large values of intrinsic mobility, Young’s modulus, surface area, thermal and electric conductivity, and optical transmittance6. Hence, both pristine and chemically functionalized graphene have been found to be effective in a broad portfolio of applications, including electronics/optoelectronics, energy generation and storage, and various medical, chemical, catalytic, and environmental processes8.Graphene, a two-dimensional nanoallotrope of carbon, is currently at the forefront of scientific interest owing to its unique electronic, mechanical, optical, and transport properties13. Importantly, the performance of graphene in these technologies is governed by the nitrogen concentration and its local environment in the graphene lattice , which determine its electronic features, including the closed or open electron shell arrangement.Doping of the graphene with foreign elements has been identified as an emerging strategy to open the zero band gap and tune its electronic, magnetic, and optical properties. Nitrogen in various structural configurations is the most frequently studied n-type dopant for improving the conductivity, transport features and magnetic properties of graphene, offering a multitude of applications in related fields like spintronics, energy generation/storage and nanoelectronics16. Thus, graphene and its derivatives are attractive materials for sensing a vast variety of chemicals, (bio)molecules, and gases19. It is well accepted that adsorption of gas molecules onto the surface of graphene can be enhanced by nitrogen doping, causing changes in the local carrier concentration. Such graphene-based sensors can detect even a single gas molecule attached to or detached from the surface of graphene20. Similarly, N-doped carbon allotropes, including graphene, have been shown to act as superior electrocatalysts, establishing the emerging field of metal-free catalysis, with enormous prospects for fuel cells, metal-air batteries and oxygen-reduction reactions21.In addition to allowing control over the intrinsic physicochemical properties of graphene, nitrogen doping can significantly affect its interaction with molecular species, as well as phenomena at the phase boundary of the graphene-molecule, which are particularly important in sensing and electrocatalysis applications22. This work indicated direct relevance of the graphene-molecule interaction for advanced organic electronics22. However, owing to the absence of a central metal atom, the possibility of discriminating or even controlling the spin state of a metal ion has remained challenging.Moreover, very recent work using scanning probe microscopy (SPM) imaging techniques has demonstrated that N-doping of graphene can even tune the physicochemical properties of molecules adsorbed on its surface via non-covalent interactions. In particular, it was shown that 5,10,15,20-tetraphenyl-21H,23H-porphyrin molecules adsorbed on N-doped graphene undergo a downshift of their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) states if these molecules are located near to nitrogen defects25 and atomic clusters26, bond order analysis27, molecular electrostatic field28 or identification of different products of on-surface synthesis29. Here, we demonstrate that high-resolution images can also be used to discriminate different spin states of iron(II) phthalocyanine (FePc) molecules immobilized on N-doped graphene. The spin crossover was confirmed independently by inelastic spin excitation spectroscopy and theoretical quantum calculations. Importantly, we were able to control the spin state by changing the molecular positioning on N-doped graphene. This is the first example, to the best of our knowledge, of a spin transition induced by non-covalent interaction of a molecule with doped graphene caused by reordering of iron d-orbitals without the use of an external stimulus, such as an external magnetic field, electric field, light, pressure, or temperature. Hence, we show the unique capability of doped graphene to behave as a non-covalent tuner of the electronic and spin properties of molecules.In the present work, we used high-resolution atomic force microscopy (AFM) with a non-magnetic CO-functionalized tip and inelastic spin excitation spectroscopy to characterize molecular electronic states. This state-of-the-art AFM technique has been shown to offer unprecedented spatial resolution, allowing investigation of the chemical structure of molecules30 to prepare N-doped graphene grown on a SiC(0001) surface with the majority of nitrogen defects in the substitutional positions. Hence, the term N-dopant refers to the substitutional (graphitic) variant in the following discussion, unless stated otherwise.We investigated the possibility of tuning the electronic and magnetic properties of iron(II) phthalocyanine molecules via non-covalent interaction with single nitrogen dopants in graphene. We used ion implantation followed by a thermal annealing procedure31 and G/Pt(111)32. On the other hand, deposition of FePc onto N-doped graphene resulted in strikingly different features. The large-scale STM image obtained at 5 K in Fig. We found that the behavior of FePc was very specific depending on whether it was adsorbed on pristine or N-doped graphene. Submonolayer amounts of FePc deposited onto pristine graphene formed large and well-ordered flat islands, which were stabilized by intermolecular non-covalent interactions, as shown in the detailed scanning tunneling microscopy (STM) image in Fig. 34. By comparing the pairs of images acquired before and after the FePc lateral movement, we could precisely determine the register of the FePc molecules with respect to the N-dopants beneath  spectra. Figure I/dV spectra acquired from over the centers of two FePc molecules, one located on graphene and the other above an N-dopant. The FePc adsorbed on graphene exhibited two resonances, at –1.9 and 0.5 V, whereas the spectrum of the molecule adsorbed above the N-dopant showed shifts of the resonances to –1.2 and 0.3 V, effectively lowering the molecular gap by ~0.9 eV. This trend was very reproducible, as we observed it repeatedly during more than ten sessions with different tips on several molecules  and the electrostatic Hartree potential obtained from DFT calculations. Indeed, the electrostatic potential over the N-dopant obtained from DFT calculations . Figure dz2 Fe orbital, as shown in Fig. 42. Indeed, simulated AFM images with the electron density of the triplet and singlet states of FePc reproduced the experimental images obtained for molecules on graphene and the N-dopant, respectively  and E is in-plane magnetic anisotropy, which for planar molecules typically vanishes. Consequently, the Hamiltonian reduces to S = 1 state should show a single inelastic signal symmetric in bias voltage of the magnitude D. Indeed, we observe a symmetric step-wise increase of the conductance at bias voltages approximately ±7 meV. Consequently, we interpret this feature as inelastic spin excitations of the S = 1 spin multiplet (ms = 0 and ms = ±1) due to the zero field splitting driven spin–orbit interaction44. We would like to stress, that very similar spectra were also obtained for Fe-tetraphenyl-porphyrin molecule52, which were also attributed to inelastic spin excitation the S = 1 spin state. Therefore, we believe that the additional inelastic spin excitation measurements fully support the scenario of the spin transition of FePc from triplet (pristine graphene) to singlet (on N-dopant) state.To reinforce our interpretation of the spin transition, we carried out inelastic spin excitation spectroscopysee Fig.  acquiredz-component, i.e., pz of the N-dopant points outward from the surface and the  and dz2-like molecular orbitals of Fe. This causes an upward energy shift of the dz2-orbital with respect to , which promotes electron transfer from dz2 to , leaving the dz2 orbital empty with a closed shell electron configuration, as shown in Fig. z-component d-orbitals is facilitated by the fact they are very close in energies  state. Strikingly, in the proximity of the N-dopant, the low-spin (singlet) state was found to be about 5 kcal/mol more stable than the triplet state. We attributed this effect to weak intermixing between orbitals with para configuration, which has an even stronger local electrostatic field. Supplementary Figure para N-defect. When the molecule was located near the para N-defect, it exhibited a similar STM contrast and dI/dV spectrum to those of molecules located on pristine graphene. However, the contrast and dI/dV spectrum significantly changed when the molecule was manipulated onto a single N-defect due to the spin crossover. Again, this scenario was supported by our DFT calculations, which predicted that the molecule would be in the triplet state when located over the para N-defect. These results also strongly support the role of an open-shell like character of the single substitutional N-defect. The para N-defect has a closed-shell electronic structure which is more stable than the biradical one. The unique chemical activity of graphitic N-defects for spin crossover was further supported by theoretical analysis with different model cases, including a closed-shell pyridinic defect , for which proximity to the molecule again stabilized FePc in the triplet state.The possibility that the spin crossover was due to the local electrostatic field of the N-dopant was ruled out by analysis of a double substitutional nitrogen defect in the 54 in classical coordination chemistry. In our case, we demonstrated that such a transition can be achieved just by sliding the molecule over the surface of N-doped graphene. Thus, the electronic states of FePc molecules on graphene can be tuned locally by means of weak non-covalent interaction with N-dopants causing reordering of the selected iron d-orbitals driven by their weak hybridization with the pz orbital of a single graphitic nitrogen defect. This offers a way for controlling the spin state of a molecular system by simple positioning of the molecule onto a suitably functionalized graphene substrate. We also showed that high-resolution AFM using a non-magnetic CO-functionalized tip can distinguish between different spin states of molecules on a surface. This extends further the outstanding capabilities of the technique and opens new possibilities for studying magnetic properties at the single molecule level.These results demonstrate the diverse chemical activity of nitrogen impurities incorporated into graphene, opening a new way for not only tuning the electronic properties of molecules but also chemical functionalization of graphene. The unique character of the substitutional N-defect allows not only stabilization of the FePc molecule in its vicinity but is also responsible for the spin crossover of FePc. For comparison, such spin crossover of FePc is usually triggered by strong ligands or ligands with unpaired electrons forming covalent dative bondsI/dV measurements were acquired with the conventional lock-in technique with an amplitude modulation of 20 mV at 960 Hz. The metallic tip for dI/dV spectroscopy was formed by repeated indentations into a Au(111) surface until the surface state was clearly visible. Inelastic spin excitation spectroscopies were acquired at 500 MΩ of tunnel resistance with voltage modulation of 0.5 mV at 170 Hz. A graphene sample was prepared on a SiC(0001) substrate by annealing in Ar and was degassed in a UHV system at ≈800 °C55. N atom implantation was achieved by sputtering the graphene sample with N atoms accelerated at 120 eV and subsequent annealing to ≈800 °C. Iron(II) phthalocyanine (FePc) was thermally evaporated from a Ta pocket in UHV onto the graphene surface, which was kept at RT. After deposition, the sample was briefly annealed at temperatures below 200 °C to increase the surface mobility. STM/AFM images were analyzed using WSxM and WSPA software56.STM/AFM measurements were carried out in a UHV chamber equipped with a low-temperature STM/AFM with qPlus tuning fork sensor operated at 5 K (Createc GmbH). During the AFM measurements, a Pt/Ir tip mounted onto the sensor  was oscillated with a constant amplitude of 50 pm. To obtain high-resolution AFM/STM images, prior to the experiment, the tip was functionalized with a CO molecule gathered from a Au(111) surface. dOptimized structures of FePc molecules on N-doped and pristine graphene were calculated using both the cluster and slab models in the Turbomole, Gaussian, and VASP program packages based on ab initio density functional theory (DFT) .Theoretical AFM images were calculated using a probe particle AFM simulator . Further details about the Methods can be found in the Supplementary Methods.The data that support the findings of this study are available from the corresponding authors on request.Supplementary InformationPeer Review File


These two terminal electronic devices can be easily fabricated by forming a Van der Waals contact between large area chemical vapor deposited graphene and CdTe substrates in air and at room temperature. This approach significantly reduces the fabrication cost and improves the reproducibility and stability of electrical properties. A detailed analysis of their AC and DC electrical properties was carried out in order to determine the width of the space charge region and dominant charge transport mechanisms at reverse bias. The unoptimized graphene/CdTe heterojunction detectors exhibited a promising spectral resolution of  Owing to large atomic numbers of the compound components (48 for Cd and 52 for Te), the operation range of CdTe detectors extends to a higher photon energy region (up to 1 MeV) in comparison to Si detectors, and its wider band gap (1.46 eV at 300 K) results in a broad temperature operating range of CdTe detectors without intentional cooling5. Despite significant technical successes, some problems concerning physical properties of Schottky diodes based on high-resistivity materials have not yet been solved. High-resistivity CdTe single crystals suffer from significant temperature instabilities and uncontrollable time fluctuations of electrical characteristics due to polarization and compensation processes12.Graphene is a promising candidate for applications in the form of the front electrical contact for radiation detectors widely employed in science, engineering, medicine, and other fields. An atomically thin layer of graphene would not disturb low energy X-rays on their way to the active layer. Moreover, the relatively high sheet resistance of pristine single-layer graphene will not be a drawback due to the low electrical signal currents generated in radiation detectors or photodiodes13. However, best to our knowledge, there are no reports on two-terminal graphene/single crystal CdTe Schottky-type heterojunction X/γ-ray detectors.Recently, gated graphene field effect transistors, fabricated on intrinsic CdTe were proposed as sensors of ionizing radiationThis study aims to prepare novel graphene/single crystal CdTe heterojunction radiation detectors excluding undesirable vacuum deposition processes and technological heat treatments that may induce surface defects and modify the compensation level in the bulk of the CdTe active layer. Features of their impedance spectra and DC current-voltage characteristics were analyzed in details. Also, their spectroscopic detecting characteristics were measured at different reverse bias and room temperature.The schematic representation and AC equivalent circuit of the graphene/CdTe/Au Schottky-type heterojunction are shown in Fig. Ci is the insulator capacitance, Cb is the barrier capacitance of the graphene/CdTe region, Cb′ is the barrier capacitance of the graphene/insulator/CdTe region.εі = 3 is the dielectric constant of the organic dielectric layer; di = 20 μm is the thickness of the insulator layer; Ас = 0.14 cm2 is the area of the insulator layer under graphene.εCdTe = 10.2 is the dielectric constant of CdTe, W is the width of the space charge region that is one of the key parameters of the Schottky-type semiconductor detectors.Ab = 0.09 cm2 is the area of the graphene/CdTe region.Taking into account the device architecture of the detectors the following capacitances should be considered: Cm = Cb + C′  and imaginary (reactive) parts of the impedance, respectively:Therefore, the measured equivalent capacitance Rs is not included in equation 11) the mRd = 2|Z″min| = 94 ΜΩ and the barrier capacitance Cm = 7.3 × 10−12 F were determined from the analysis of the spectral distribution of the imaginary part of the measured impedance of the graphene/CdTe/Au devices.Values of the depletion region resistance A = Ab + Ac = 0.25 cm2. Equation , , 5), theW can be found as:The physically based solution for WV=0 = 0.18 mm.The calculated width of the space charge region at zero bias W is governed by equation  a small leakage current determines the I–V curve. This is clearly demonstrated by the reverse I–V characteristic presented in double logarithmic (log-log) coordinates in Fig. At small bias (I ~ V1/2) that is determined by the voltage dependence of the width of the depletion region (W ~ V1/2). This type of I–V characteristics is described by the generation-recombination mechanism in the scope of the Sah-Noyce-Shockley model, adapted for a metal-semiconductor contact21. It should be noted that the square root I–V dependence dominates only up to 7 V. This feature of the I–V characteristic well correlates with the previously analyzed AC characteristic which predicts that the CdTe substrate is wholly depleted at reverse bias ≥5.4 V.With increasing reverse bias, the current transport is determined by the generation current within the depletion region in the CdTe substrate. The reverse current exhibits a square root dependence on the applied bias 22. We have already shown that the graphene/CdTe interface is of high quality in comparison to other interfaces formed by the vacuum deposition of metal oxide or nitride films on CdTe substrates . However, the signal from 137Cs isotope (662 keV) is measured with a very promising resolution of 6.1% at the same reverse bias  of detectors strongly depends on the applied voltage. The voltage dependences of FWHM slightly vary for different detectors. Many parameters determine the energy resolution of X- and γ-ray semiconductor detectors: the attenuation length of X-rays with a given energy, the background electrical noise (dark background current) and the charge collecting efficiency. In their turn, the dominant charge transport mechanisms and charge collection efficiency depend on active material, electrical contacts (surface recombination), recombination lifetime, electron and hole mobility, and strength of the internal electrical field (applied bias divided by the active layer thickness)27. The thermoelectric cooler cools both the CdTe detector and the input field effect transistor (FET) of the charge sensitive preamplifier improving its noise-to-signal ratio. All measurements in our study were carried out at 300 K. Our detectors were not optimized, and we did not use a photolithography prepared guard ring protection against the surface leakage. Therefore, the measured relatively low energy resolution is quite reasonable and almost identical to that of wider band gap CdZnTe-based detectors, operated at the same temperature, but much higher DC bias of 450 V28.State-of-the-art commercial CdTe X-ray detectors (Ametek) with an energy resolution in the range of FWHM = 1% operate under a two-stage thermoelectric cooling that significantly reduces electrical noise and allows to increase operating voltages up to 500 VWe proposed a new concept of a Schottky-type semiconductor heterojunction detectors based on a Van der Waals contact between large area CVD-grown graphene and semi-insulating single crystal CdTe. The proposed low-cost and vacuum-free device fabrication process was tailored to skip the undesirable technological heat, which may detrimentally affect the electrical properties and level of compensation in semi-insulating CdTe single crystals leading to uncontrollable and irreproducible characteristics of the detectors based on them.WV=0 = 0.18 mm and the concentration of uncompensated acceptors NA−ND = 2.89 × 1010 cm−3 in the semi-insulating CdTe active material. Also, the dominant charge transport mechanisms through the detectors were determined at a wide range of reverse bias, which are in good correlation with the previously determined AC characteristics.There was developed a quantitative model for the AC characteristics of proposed graphene/CdTe/Au detectors in the scope of the equivalent circuit, which takes into account the features of their device architecture. The developed model was successfully employed to determine the real values of the crucial parameters relevant to Schottky diode-type semiconductor detectors: the width of the space charge region at zero bias 137Cs (662 keV) isotope with the FWHM of about 6% at the reverse bias of 100 V and room temperature.Even the unoptimized graphene/CdTe detectors exhibited a promising spectral resolution, specifically, for a 4) was added to the hydrogen gas flow to start growing graphene. The graphene was deposited at a temperature of 1050 °C. After cooling down, the graphene layers were transferred to the prepared CdTe substrates. For this purpose, the graphene layer was protected with a thin polymer layer, which was spin-coated on top of the graphene-Cu stack. Then, the Cu substrate was etched off using a concentrated ammonium persulfate ((NH4)2S2O8) water solution. The remaining polymer-graphene layer stack was rinsed several times using deionized water to remove residual impurities resulting from the etching procedure. Afterword, the polymer protected graphene layer was transferred onto the CdTe substrate, and the polymer layer was dissolved by rinsing in ethyl acetate  × 109 Ω cm at room temperature that is close to the resistivity of the intrinsic CdTe ρi = 4 × 109 Ω cm, i.e., the semi-insulating CdTe material under investigation can be considered as an almost intrinsic semiconductor.High quality and large area graphene was grown by the chemical vapor deposition (CVD) technique on copper foil. After mechanical polishing, the Cu foil was cleaned in an ultrasonic bath of acetone, and isopropyl alcohol etched in acetic acid and rinsed in deionized water. Then, the Cu foil was transferred to a growth furnace. The native oxide layer of the Cu foil was removed by annealing the substrates to high temperatures and exposing the surface to a flow of ultra-pure hydrogen gas. In a second step, methane  and 241Am (59 keV) X-ray sources by a charge-sensitive amplifier AMPTEK A250 in combination with a multichannel analyzer MCA8000A. The measurements were carried out at different biases and with the shaping time of 1 μs.The detecting properties of the graphene/7CdTe heterojunctions were measured at room temperature using Supporting Information-R1


Methods: MMP-mediated activation of PA-L1 was correlated to anthrax receptor expression and MMP activity in a panel of cancer cells . Uptake of 111In-radiolabeled PA-L1, 111In-PA-WTK563C, or 111In-LFE687A  in tumor and normal tissues was measured using SPECT/CT imaging in vivo. Results: Activation of PA-L1 in vitro correlated with anthrax receptor expression and MMP activity (HT1080 > MDA-MB-231 > B8484 > MCF7). PA-L1–mediated delivery of 111In-LFE687A was demonstrated and was corroborated using confocal microscopy with fluorescently labeled LFE687A. Uptake was blocked by the broad-spectrum MMP inhibitor GM6001. In vivo imaging showed selective accumulation of 111In-PA-L1 in MDA-MB-231 tumor xenografts (5.7 ± 0.9 percentage injected dose [%ID]/g) at 3 h after intravenous administration. 111In-LFE687A was selectively delivered to MMP-positive MDA-MB-231 tumor tissue by MMP-activatable PA-L1 (5.98 ± 0.62 %ID/g) but not by furin-cleavable PA-WT (1.05 ± 0.21 %ID/g) or a noncleavable PA variant control, PA-U7 (2.74 ± 0.24 %ID/g). Conclusion: Taken together, our results indicate that radiolabeled forms of mutated anthrax lethal toxin hold promise for noninvasive imaging of MMP activity in tumor tissue.Increased activity of matrix metalloproteinases (MMPs) is associated with worse prognosis in different cancer types. The wild-type protective antigen (PA-WT) of the binary anthrax lethal toxin was modified to form a pore in cell membranes only when cleaved by MMPs (to form PA-L1). Anthrax lethal factor (LF) is then able to translocate through these pores. Here, we used a  Matrix metalloproteinases (MMPs) are a family of zinc‐dependent proteases that together can degrade most components of the extracellular matrix. MMP activity is essential for tumor growth, allowing cancer cells to invade surrounding tissues and metastasize, as well as interact with the local tumor immune environment . The rolA molecular imaging agent that allows noninvasive imaging of MMP activity and related proteins would allow visualization of these disease processes in vivo, permitting early detection, prognosis, and measurement of therapy efficacy. A diverse range of molecular imaging agents has been developed over the past few years, expertly summarized in a previous publication . This raBacillus anthracis is a spore-forming bacterium that causes anthrax. As a means of suppressing its host’s immune response, the bacterium produces a set of toxins to promote its own survival: protective antigen (PA), lethal factor (LF), and edema factor. After binding to the ubiquitous anthrax receptors (CMG2 and TEM8), full-length PA (83 kDa) is cleaved by furin or furinlike proteases to a 63-kDa isoform  system to visualize MMP activity in tumor tissue using an adapted pretargeting system  9). Bac. Bac9). 168–P176 of the original PA . PA-L1 allows MMP-selective intoxication of tumor cells in vitro, as well as tumor xenografts grown in mice, with a modified LF fusion toxin, incorporating the adenosine diphosphate ribosylation domain of Pseudomonas exotoxin A (FP59)  .E687A, in combination with MMP-activatable PA-L1. In this report, we show that this novel pretargeted imaging system is selective for MMP-expressing cancer cell lines in vitro, and we show selective, noninvasive, in vivo imaging in MMP-expressing tumor xenografts grown in mice.Here, we expand the use of this MMP-activatable system to allow molecular imaging of MMP activity in mouse models of cancer, by SPECT imaging, using a radiolabeled catalytically inactive version of LF, LFB. anthracis LT were expressed and purified as previously described  whenever radiolabeled PA-WT is used  (E687A (90 kDa) containing a defective catalytic domain .PA-WT (83 kDa) is cleavable by furin and other furinlike enzymes . Here, w is used . PA-L1 h is used , whereas is used . LF vari 53 kDa) , LFn mod 53 kDa) , and fulc domain . CleavagK563C were site-specifically conjugated to the metal ion chelator diethylenetriamine pentaacetic acid (DTPA), using the bifunctional agent maleimide-DTPA -13--10-oxo-2,5,8,11-tetraazatridecane-5,8-diyl)diacetic acid) to allow radiolabeling with 111In, whereas PA-L1 or LFE687A was conjugated to p-SCN-benzyl-DTPA (S-2-(4-isothiocyanatobenzyl)-DTPA) before radiolabeling with 111In, using previously described methods -2,5-diphenyltetrazolium bromide) after exposure of cells to PA-WT, PA-WTith FP59 . To inveE687A was added to HT1080 or MCF7 cells growing on glass cover slides, in combination with PA-WT, PA-L1, or a vehicle control. After 3 h, cells were washed, fixed, and mounted with 4′,6-diamidino-2-phenylindole, and images were acquired using a confocal microscope . Full experimental details are laid out in the supplemental materials.Cy3-LFD) and number of binding sites for 111In-PA-WTK563C or 111In-PA-L1. In vitro assays were performed to evaluate the capacity of 111In-LFE687A or 111In-LFn to interact with PA pores and to be delivered into cells after radiolabeling. Full experimental details are laid out in the supplemental materials.Saturation cell binding experiments were performed to determine the apparent dissociation constant  Act of 1986 and with local ethical committee approval. Animals were housed in individually ventilated cages in sex-matched groups of up to 6 per cage in an artificial day–night cycle facility with ad libitum access to food and water. No animals were euthanized for welfare reasons. All analyses were performed masked to experimental group assignment.111In-LFn  or 111In-LFE687E  through a cannula inserted in the tail vein. SPECT/CT images were acquired for up to 3 h in list mode using a VECTor4CT scanner (MILabs). Three mice were used per group. Additional experimental detail is provided in the supplemental materials.To measure plasma clearance, dynamic SPECT/CT imaging of tumor-naïve SCID mice was performed after intravenous administration of 111In-PA-L1 or 111In-PA-WTK563C . Three mice were used per group.To determine the pharmacokinetics of PA-L1 in vivo, dynamic SPECT images were acquired in MDA-MB-231 tumor–bearing mice over 3 h after intravenous injection of 111In-LFE687E  by intravenous injection, together with PA-L1 . To determine the PA-L1 selectivity of tumor uptake, and thus of MMP-mediated uptake, groups of control animals were administered 111In-LFE687A alone or in combination with PA-WT , PA-U7 , or PA-L1 and an excess of unlabeled LFE687A . SPECT imaging was performed 24 h after administration of the 111In-LF/PA combinations. Three mice were used per group.MMP-activatable, PA-L1–mediated uptake of radiolabeled LF was evaluated in a pretargeting-inspired setup. MDA-MB-231 tumor xenograft–bearing mice were administered 111In was determined per gram of tissue, normalized by the administered amount of 111In (expressed as percentage injected dose per gram [%ID/g]). Tumor tissues were stored in 30% sucrose and, after 24 h, flash-frozen with dry ice and stored at −80°C until required for further processing.After imaging, the mice were euthanized by cervical dislocation, and selected organs, tissues, and blood were removed. The amount of t test with the Welch correction for nonequal variances to compare 2 groups. One-way ANOVA followed by Dunnett posttests were used to compare multiple groups. Two-way ANOVA was used to analyze grouped data. All results are reported as mean ± SD of at least 3 independent replicates, unless otherwise indicated.All statistical and regression analyses were performed using GraphPad Prism, version 7 (GraphPad Software). Linear regression was used to test for correlations between measurements. After testing for normality using a Shapiro–Wilk test, means were compared using a In a cell-free setting, recombinant human MMP2 and furin-activated MMP14, but not furin alone, were able to cleave PA-L1. Furin, but not MMP2, was able to cleave PA-WT . Cleavage of PA-L1 by MMP2 and MMP14 at the intended site was further confirmed by mass spectrometry .Bacillus anthracis MMP-activatable LT system. All cell lines, except for HT1080, expressed relatively high levels of furin  was determined for the PA-WT/FP59 and PA-L1/FP59 combinations. Whereas HT1080, MDA-MB-231, and B8484 cells were sensitive to both PA-WT/FP59  and PA-L1/FP59 , MCF7 cells were not . Quality control using instant thin-layer chromatography showed incorporation yields and radiochemical purities of more than 95% . The molar activity of the radiolabeled compounds was 8–15, 8–15, 10, and 5 MBq/nmol for 111In-PA-WTK563C, 111In-PA-L1, 111In-LFE687A, and 111In-LFn, respectively, for in vitro studies. The molar activity of all compounds for in vivo studies is as indicated. All labeled compounds demonstrated satisfactory stability in mouse serum, although a small degree of transchelation could be observed , attributable to transferrin or albumin.The PA/LF variants were conjugated to bifunctional chelator agents, which allowed radiolabeling using 111In-labeled PA-WTK563C showed various levels of binding sites . Affinity of 111In-PA-WTK563C for CMG2 and TEM8 was confirmed by a saturation binding assay on CHO cells that were stably transfected to express CMG2 or TEM8 . The overall affinity of 111In-PA-WTK563C was measured as KD = 4.0 ± 1.2 nM and was not significantly different in any of the cell lines (P = 0.09) , confirming specific binding  . Similar31 cells . Using t111In-LFE678E, demonstrated the selectivity and specificity of the LT system (111In-LFE678E with MDA-MB-231 cells after treatment with the broad-spectrum MMP inhibitor GM6001 demonstrated MMP-mediated PA-L1 activation (P = 0.0003). 111In-LFE678E was also taken up by MDA-MB-231 cells when administered in combination with furin-cleavable PA-WT or MMP-cleavable PA-L1 but not in combination with vehicle control or nonactivatable PA-U7 (P < 0.0001) . Similar results were obtained using a labeled LFn, 111In-LFn, or using HT1080 and B8484 cells . Saturation binding studies of 111In-LFE687A using fixed prepores in MDA-MB-231 cells revealed a binding constant of KD = 0.9 ± 0.09 nM .In a separate series of measurements, exposure of the panel of cancer cells to a radiolabeled full-length catalytically inactive variant of LF, T system . A signi 0.0001) . Additio111In-LFn and 111In-LFE687A was compared in vivo. Dynamic SPECT scans were performed after intravenous bolus injection of either 111In-LFn or 111In-LFE687A in naïve SCID mice . In contrast, the radiolabeled full-length protein, 111In-LFE687A, presented a significantly slower plasma clearance (P < 0.0001) than the truncated protein, maintaining a significant amount in the blood circulation 3 h after administration (35 ± 2.6 %ID/mL). In this case, a monoexponential decay described the radiotracer pharmacokinetic, with a blood half-life of 33 min. Ex vivo biodistribution studies confirmed the in vivo imaging results, revealing low blood signal, yet high kidney uptake (29 ± 1.0 %ID/g), after administration of 111In-LFn, possibly because of glomerular filtration .The pharmacokinetic behavior of CID mice . ImagingK563C and MMP-cleavable PA-L1 were also compared, with a view to optimizing the time of injection in a 111In-LF pretargeting system. Dynamic SPECT imaging after intravenous injection of 111In-PA-L1 or 111In-PA-WTK563C in MDA-MB-231 tumor–bearing mice revealed a distinct pharmacokinetic profile for 111In-PA-WTK563C compared with 111In-PA-L1 (111In-PA-L1 (5.7 ± 1.7 %ID/g) in MDA-MB-231 tumor tissue, compared with 111In-PA-WTK563C , at 3 h after administration of the labeled compound (111In-PA-WTK563C than for 111In-PA-L1 (P < 0.05). All in vivo SPECT and ex vivo biodistribution results were confirmed by autoradiography .The pharmacokinetics of radiolabeled furin–cleavable PA-WTIn-PA-L1 . Both pr111In-LFE687A was considered to be the more appropriate variant to image MMP-mediated PA-L1 pore formation in tumor tissue in vivo, given the extremely fast clearance of 111In-LFn. In addition, the slow but steady increase in tumor uptake of PA-L1 over time indicated that a coinjection of PA-L1 with 111In-LFE687A would be advantageous. The delivery of 111In-LFE678E by PA-L1 was evaluated in mice bearing MDA-MB-231 xenografts (111In-LFE678E to tumor tissue (5.98 ± 0.62 %ID/g), compared with control animals that were not coinjected with PA-L1 , indicating PA-L1–specific delivery. Imaging data at 3 h after injection showed similar results . When animals were also administered noncleavable PA-U7, instead of PA-L1, tumor uptake was significantly reduced , indicating MMP activity–specific targeting of PA-L1 in vivo. Additionally, when the interaction between PA-L1 pores or prepores and 111In-LFE678E was blocked by coadministration of an excess of unlabeled LFE678E, tumor uptake was significantly reduced to nonspecific uptake levels . 111In-LFE678E delivery to tumor tissue was significantly lower when coadministered with furin-cleavable PA-WT . This finding was in line with the rapid plasma clearance, activation by proteases in plasma (P < 0.0001). Contrastingly, PA-WT–mediated delivery of 111In-LFE678E resulted in significantly higher delivery to spleen , again consistent with PA-WT cleavage and activation in blood plasma.On the basis of its pharmacokinetic profile, nografts . Full ex111In-LFE678E by PA-L1 via binding to anthrax receptors, MMP-activation of PA-L1, and LF binding to its de novo receptor site on PA pores.Taken together, our results indicate the selective delivery to tumor tissue of B. anthracis LT system. Previous work by Liu et al. showed in detail that PA-L1, an MMP-cleavable PA variant, allows for selective delivery of LF and related fusion toxins such as FP59 to tumor tissue in vivo for therapeutic gain  did not show the necessary tumor-to-background ratios compared with the longer interval. In contrast, the smaller size of 111In-LFn resulted in renal clearance and therefore negligible liver uptake. 111In-LFn performed equally well in in vitro assays but, in vivo, was cleared from the blood so fast that PA-L1–mediated tumor uptake could not be observed . It may be possible that variants of intermediate size may be cleared more slowly yet are still renally cleared, in analogy with radiolabeled antibody fragments and derivatives, and thus will result in more optimal imaging characteristics  grant. Julia Baguña Torres is funded through a grant from the Pancreatic Cancer Research Fund. Thomas Bugge is funded by the NIDCR, NIH Intramural Research Program, and Samantha Hopkins is funded by the NIAID, NIH Intramural Research Program. Mass spectrometry analysis was performed at the Discovery Proteomics Facility (headed by Roman Fischer), which is part of the TDI MS Laboratory led by Professor Benedikt Kessler. No other potential conflict of interest relevant to this article was reported.Click here for additional data file.