We suggest that binding to TRKB and allosteric facilitation of BDNF signaling is the common mechanism for antidepressant action, which may explain why typical antidepressants act slowly and how molecular effects of antidepressants are translated into clinical mood recovery.It is unclear how binding of antidepressant drugs to their targets gives rise to the clinical antidepressant effect. We discovered that the transmembrane domain of tyrosine kinase receptor 2 (TRKB), the brain-derived neurotrophic factor (BDNF) receptor that promotes neuronal plasticity and antidepressant responses, has a cholesterol-sensing function that mediates synaptic effects of cholesterol. We then found that both typical and fast-acting antidepressants directly bind to TRKB, thereby facilitating synaptic localization of TRKB and its activation by BDNF. Extensive computational approaches including atomistic molecular dynamics simulations revealed a binding site at the transmembrane region of TRKB dimers. Mutation of the TRKB antidepressant-binding motif impaired cellular, behavioral, and plasticity-promoting responses to antidepressants   •Several antidepressants, including SSRIs and ketamine, directly bind to TRKB•TRKB dimerization at transmembrane region forms a binding pocket for fluoxetine•Antidepressant binding to TRKB facilitates BDNF action and plasticity•Point mutation in TRKB transmembrane region blocks the effects of antidepressants Direct binding of both typical and fast-acting antidepressants to the BDNF receptor TRKB accounts for cell biological and behavioral actions of antidepressants. This mechanism directly connects antidepressant action to neuronal plasticity and may explain the slow action of typical antidepressants. Several targets for antidepressant (AD) drug action have been identified, but it is not clear how binding to these targets translates into clinical effects. Typical ADs such as tricyclic ADs (TCA), serotonin selective reuptake inhibitors (SSRI), and monoamine oxidase inhibitors (MAOI), increase the synaptic levels of monoamines by inhibiting their reuptake or metabolism, but it is unclear why their clinical effects are delayed, while the effects on monoamines are fast . The rapEssentially all ADs, including KET and R,R-HNK, increase the expression and signaling of brain-derived neurotrophic factor (BDNF) through neurotrophic tyrosine kinase receptor 2 (TRKB) . The effrd postnatal week in mice  metabolism. BDNF promotes production of CHOL in neurons  and CHOL in mice , which c in mice . Many AD in mice .These data prompted us to investigate the potential interactions between TRKB, CHOL, and ADs. We found that the TRKB transmembrane domain (TMD) senses changes in the cell membrane CHOL levels, and we elucidated its mechanism. Furthermore, we found that different AD drugs directly bind to a site formed by a dimer of TRKB TMDs, thereby facilitating cell surface expression of TRKB and promoting BDNF signaling. These data suggest that direct binding to TRKB and promotion of BDNF-mediated plasticity is a mechanism of action for AD drugs.CHOL is known to promote neuronal maturation and plasticity, but how it exerts these effects is unclear . CHOL isTRKB mostly resides in intracellular vesicles not accessible to BDNF . We founMutation of TRKB tyrosine 433, a predicted key residue in the CARC motif  to pheny439AXXXG443 (We next used atomistic molecular dynamics (MD) simulations to investigate the organization of TRKB TMD dimers . Using aAXXXG443 G–1I, a GAXXXG443 G  (i = 1.69 μM)  C, but no2.42 μM) L and S4M2.42 μM) . Binding1.69 μM) B, indica1.69 μM)  also dem1.69 μM) N, wherea1.69 μM) D, which in situ proximity ligation assay (PLA). A robust PLA signal was observed when N2A cells transfected to express TRKB were exposed to biotinylated FLX   F, similaectively C–S4G. Byectively H and S4Iectively J, which d = 1.82 μM)  E, and S,1.82 μM) K. R,R-HN1.82 μM) , 2018, b1.82 μM) H and 2I.These acute effects of ADs are not mediated by functional inhibition of acid sphingomyelinase (FIASMA) or sphingolipid metabolism , becauseDocking followed by an extensive set of 120 1-μs-long MD simulations suggested a binding site and mode for FLX in the crevice facing the extracellular side of the crossed TRKB TMD dimer A. This bAs shown above, the stable configuration of TRKB TM dimers at 20 mol % of CHOL is destabilized by increased membrane thickness at 40 mol % of CHOL G,H. RemaWe used fluorescence recovery after photobleaching (FRAP) assay in primary hippocampal neurons (DIV14) to evaluate the mobility of TRKB in neuronal spines. In neurons transfected to express GFP-tagged TRKB, the fluorescence was rapidly recovered in dendritic shafts, but not in spines after bleaching A and S6ASuper-resolution microscopy (dSTORM/TIRF) revealed that BDNF, FLX, KET, and CHOL all increased the size of clusters formed by wild-type GFP-TRKB, but not clusters of GFP-TRKB.Y433F mutants at the plasma membrane of fibroblast cell line, indicating that the increased trafficking may lead to increased cell surface expression and clustering of TRKB K–4P. TheADs are known to increase the cell surface expression of AMPA glutamate receptors and the blockade of AMPA receptors prevents the behavioral effects of KET and R,R-HNK . We confin vivo, and these effects are mediated by TRKB  in slices as well as  by TRKB . Theta-b by TRKB F. Howeve by TRKB G, consis by TRKB .Infusion of BDNF into the dentate gyrus of anesthetized rats significantly increased synaptic strength, as previously reported . HoweverADs increase the proliferation and survival of newly born dentate granule neurons . We confChronic FLX treatment reactivates critical period-like plasticity in the visual cortex of adult mice, allowing an ocular dominance (OD) shift in response to monocular deprivation, which normally only happens during a developmental critical period . In miceWe next investigated whether AD interaction with TRKB influences neuronal plasticity-dependent learning and behavior. FLX (15 mg/kg/day) for 7 days facilitated long-term memory in object location memory (OLM) test in TRKB.wt mice, but not in TRKB.Y433F mice, although the behavior of vehicle-treated TRKB.Y433F mice was similar to their vehicle-treated wild-type littermates A. A simiBDNF-TRKB signaling is known to be sufficient and necessary for the effects of ADs in the forced swimming test (FST) . FLX 15D and 6E.FLX promotes extinction of conditioned fear in a BDNF-dependent manner . The freTogether, these data demonstrate that the behavioral effects produced by different ADs were lost in TRKB.Y433F mutant mice, consistently with AD binding to TRKB. Moreover, we observed that many of these behavioral effects were also lost when ADs were co-administered with pravastatin .Further information and requests for resources and reagents should be directed to Eero Castren . This study did not generate new code.Experimental data generated in the present study is available in FigShare (in vitro assays (The cell line NIH 3T3 (mouse fibroblasts) stably transfected to express TRKB or TRKA  were used for o assays , N2A and6 cells/ml density at 5% CO2, 37°C in Neurobasal medium as described in detail  and HDR (homology directed repair) oligonucleotide (GCAAGGTCATCAGACCTGGCTCTTTCTCTCTCCTCAGGTCTTCGCCGTGGTGGTGATTGCATCTGTGGTGGGATTCTGCCTGC). Introduction of the point mutation generates a restriction site for the BbsI restriction enzyme. The targeting strategy was based on NCBI transcript NM_001025074.2.C57BL/6NTac-Ntrk2em6006(Y433F)Tac (TRKB.Y433F) mice were generated by introducing the Y433F point mutation into exon 12 of the After the administration of hormones, superovulated C57BL/6NTac females were mated with C57BL/6NTac males. One cell stage fertilized embryos were isolated from the oviducts at dpc 0.5. For microinjection, the one cell stage embryos were placed in a drop of M2 medium under mineral oil. A microinjection pipette with an approximate internal diameter of 0.5 μm (at tip) was used to inject the mixed nucleotide preparation  into the pronucleus of each embryo. After recovery, 25-35 injected one cell stage embryos were transferred to one of the oviducts of 0.5 dpc, pseudopregnant NMRI females.The genomic DNA was extracted from biopsies and analyzed by PCR. The following templates were used as controls: H2O (ctrl1), wild-type genomic DNA (ctrl2). A two primer PCR  detects the CRISPR/Cas9-induced constitutive knock-in allele as well as potential indel modifications and the unmodified wild-type allele. To distinguish indel modifications from unmodified wild-type sequences, heteroduplex analysis  has to be performed. The PCR amplicons were analyzed using a Caliper LabChip GX device. An aliquot of the PCR reaction was used to validate the presence or absence of the restriction site introduced via homology directed repair. 10U of BbsI enzyme was pipetted into the PCR reaction aliquot and incubated at the appropriate temperature. BbsI digest results in cleavage of the 493bp PCR product (HDR) in two fragments (362bp and 131bp).The PCR product of the positive animals from the restriction analysis was subcloned for further characterization of the founder animals. 12 subclones have been prescreened for the integration of the HDR oligonucleotide by restriction with BbsI. The ratio between the total number of analyzed clones and a positive restriction result allows an estimation of the HDR mosaicism of the founder animals. Subsequently, up to 4 clones were sequenced to confirm correct integration of the HDR oligo and presence of the Y433F point mutation. Finally, the TRKB.Y433F mice were crossed with C57BL6-RccHsd , in the University of Helsinki. All animals used from this strain were heterozygous for the Y433F mutation (TRKB.Y433F) or wild-type littermates, and genotyped after weaning.in vivo electrophysiology, male adult Sprague-Dawley rats were used.The SERT-KO mice [line B6.129(Cg)-Slc6atm1Kpl/J] on a C57BL/6 background were purchased from Taconic  and bred at the Biomedical Center, University of Freiburg. In every animal, tail biopsies were genotyped with PCR using primers from the Jackson Laboratory database to confirm homozygous knock-out. The SERT-KO mice showed bands at 210 bp, whereas the wild-type mice showed bands at 318 bp, which confirmed the gene disruption at the SERT locus. Finally, for in vivo experiments, fluoxetine and pravastatin were dissolved in the drinking water (0.08 or 0.1mg/l for fluoxetine and 0.08mg/l for pravastatin) and the volume consumed per cage was monitored every 3 days. R,R-HNK and ketamine were diluted in sterile saline for intraperitoneal injections.The present study used males and female mice (18-22 weeks old at the beginning of the experiments), and male Sprague-Dawley rats (15 weeks old at the beginning of the experiments). All animals used in the present study were experimentally naive before the beginning of the described experimental procedures. The animals were group housed  and randomly allocated into the experimental groups, except when the drug administration was performed in the drinking water. All behavioral experiments were conducted in at least two separated cohorts and analyzed automatically or by experienced observers blind to the treatment/genotype conditions. The number of animals in each experiment was based on previous studies from the literature cited in the correspondent section. For All experimental protocols were approved by the local ethics committees in Finland (#ESAVI/10300/04.10.07/2016), Norway (#6159) and Germany (#G-18-88).The protein simulated in this work included the transmembrane (TM) domains of a TRKB dimer (residues 427-459). For comparison, we also studied a TRKA dimer (residues 410-443). The lipid membranes considered were two-component bilayers composed of varying concentrations of palmitoyl-oleoyl-phosphatidylcholine (POPC) and cholesterol (CHOL). Drug binding studies in the case of TRKB were performed for fluoxetine (FLX). The effects of drugs on the physical properties of lipid membranes were studied for FLX, ketamine, and R,R-HNK. The Charmm36/m force field was used for proteins  and lipi-helical TM segment.The 3D structure for a segment of mouse TRKB containing its TM domain (residues 427-459) in its monomeric form was generated using the FMAP (Folding of Membrane-Associated Peptides) server . The serRosettaMP docking framework  was used2N90). The initial position of the TRKA TM region in the lipid bilayers was determined using the PPM Server  dimer was adapted from the NMR structure  in a membrane environment (POPC:CHOL = 100:0 and POPC:CHOL = 60:40) at 363 K to assess the stability of the selected TRKB TM dimers, and to obtain relaxed structures. The temperature was chosen based on an objective to foster sampling and to find the thermally most stable dimer structures. These exploratory simulations revealed that the only stable dimer model is centrally-coupled (A439-G443) in a cross-like configuration. The simulations of TRKB presented in this study were all started from conformations sampled from the simulations of these dimers. All membrane-protein systems considered in this study were constructed using CHARMM-GUI .The drug-binding pocket in the TRKB TM helix dimer was characterized by locally docking FLX to the TRKB TM dimers using RosettaScripts . 30 diffOne hundred and twenty independent MD simulations  were initiated by randomly repositioning and reorienting the drug in the vicinity of the aforementioned TRKB binding pocket by perturbing it from its docked mode. The effect of net positive charge on the stability of FLX binding was assessed by protonation of FLX in place (6 repeats × 500 ns).The details of the simulation systems reported in this study are given in As to the Y433F mutation, the results discussed in this paper refer to the heterozygous variant. Additional simulations for the homozygous variant (not discussed here) revealed similar behavior.Systems 9-14  were preSimulations of the TRKA TM region  method with Hamiltonian replica exchange  exchang were empPositional and orientational restraints in the harmonic form were employed to improve phase space overlap in the case of protein-binding calculations, except for the fully coupled state . Half haThe free energies and their statistical errors were estimated with the Multistate Bennett Acceptance Ratio (BAR) method  using AlTo test the possibility that drug-induced modulation of lipid bilayer properties could indirectly activate or contribute to the activation of TRKB, we performed additional protein-free simulations of POPC-cholesterol bilayers with varying CHOL concentration  (Systems 21-50). We used drug-to-lipid ratios of 1:20, 1:10, and 1:5.All simulations were carried out using GROMACS 2018 . The equBefore the production runs, all protein-membrane systems were equilibrated in stages with the protein heavy atoms kept restrained, at 310 K and 1 atm pressure using the Berendsen thermostat and barostat .−5 bar−1 on the xy-plane (membrane plane).All production simulations  were perThe simulation time for systems discussed in this work  was over 295 μs. Including a large variety of test simulations (∼330 μs) the total simulation time adds up to more than 625 μs.The cell viability assay was performed using CellTiterGlo  according to manufacturer’s instructions. Briefly, equal amounts of medium and the mixture of regents A and B were added to the E18 cortical cells (DIV8) cultivated in clear bottom 96-well plates and incubated for 40min. The luminescence was analyzed in a plate reader.The TRKB:pY (phosphorylated TRKB), TRKB:PLC-γ1, PLC-γ1:pTRKB.Y816 interactions and were determined by ELISA, based on the general method described in literature , with miThe surface levels of TRKB were also determined by ELISA . BrieflyGaussia princeps luciferase (GLuc) following the direct interaction of the proteins of interest in white 96-well plates. Two complementary fragments of the luciferase reporter protein were fused to the intracellular C terminus domain of TrkB or mutant TrkB(Y433F) to produce the PCA pairs GLuc1C-TRKB.wt/GLuc2C-TRKB.wt and GLuc1C-TRKB.Y433F/GLuc2C-TRKB.Y433F. Alternatively, the GLuc1C-TRKB.wt/GLuc2C-FYN or GLuc1C-TRKB.Y433F/GLuc2C-FYN pairs were used The GLuc2C-FYN construct expresses a lipid-raft enriched fragment of Src-family kinase FYN (Protein-fragment complementation assay  (PCA) wanase FYN . The GLuThe levels of total and phosphorylated TRKB at Y515 or Y816 in MG87.TRKB cells, challenged with BDNF, as well as the levels of PLCg1 and pTRKB.Y816 were measured by western-blotting .For the analysis of TRKB migration to lipid rafts, the samples from transfected N2A cells to express GFP-tagged TRKB.wt or TRKB.Y433F, challenged with BDNF, were processed to isolate detergent-resistant membrane (DRM) fractions in sucrose gradient . N2A celThe samples were centrifuged at 52000 x g for 18 hours at +4°C with a TLS-55 rotor in a Beckman Coulter XP Optima ultracentrifuge. Finally, 12 fractions per sample, collected from the top of the tube, were transferred to clean tubes, sonicated for 10 minutes in 0.25% SDS and prepared for western blotting, where the levels of GFP-tagged TRKB and flotillin-2 were analyzed.The cell-free assays (binding assays) were performed in white 96-well plates, based on the protocol used for western-blotting or ELISA . The plaMicroscale Thermophoresis - MST - experiments were performed using Monolith NT.115 (Blue/Red) instrument . The cell lysates of HEK293T cells expressing GFP-TRKB were used as a source of fluorescently labeled TRKB. HEK293T cells were transfected with GFP-fused TRKB as described and lysed 24h after transfection. To evaluate binding of fluoxetine to TRKB, cell lysates were diluted 1.5x times with MST buffer  to provide optimal level of fluorescence. The lysates of non-transfected HEK293T cells were used to evaluate background fluorescence, which appeared to be undetectable in current MST set up. Titration series of fluoxetine (0-100μM) were incubated with diluted cell lysates. The measurements were done in premium coated capillaries  using LED source with 470nm and 50% infrared-laser power at 25°C. Hill model was used to evaluate binding affinity, each data point represents mean ΔFnorm values from four independent experiments. The bound fraction of the GFP-TRKB was determined and the fitting was performed using the Hill model method incorporated by the MO Affinity Analysis v2.3 software (NanoTemper Technologies).In Situ Red Starter Kit Mouse/Goat , following manufacturer’s instructions. Briefly, N2A cells  were co-transfected by lipofectamine 2000 (ThermoFisher) to express TRKB and farnesylated EGFP and, 24h later, were treated with biotinylated fluoxetine (10 μM/15min). Cells were fixed with PFA 4% for 15 min, washed, and incubated in Duolink blocking buffer for 1h at 37°C. Then, the coverslips were incubated with streptavidin-conjugated HRP (1:5000 in Duolink antibody diluent) for 45 min at room temperature. After washing twice in Duolink washing buffer A, samples were incubated overnight at 4°C with a mix of goat anti-TRKB  and mouse anti-HRP  diluted in Duolink antibody diluent. After washing in Duolink washing buffer A, samples were incubated for 1h at 37°C with a mix of minus and plus probes diluted 1:5 in Duolink antibody diluent. Then, ligation of probes with connector oligo was done by washing the samples in washing buffer A, and incubating for 30min at 37°C with ligase (25 U/ml) diluted in the Duolink ligation buffer. Amplification was done by washing the samples in the washing buffer A, and incubating for 100min at 37°C with polymerase (125 U/ml) diluted in the amplification buffer. Coverslips were washed in buffer B, then in buffer B diluted 1:100 in milliQ water, and mounted in Duolink in situ mounting medium with DAPI. All incubation steps were done in a humidified chamber.Proximity ligation assay was done with Duolink Images were acquired in z stacks  with a Zeiss LSM 710 confocal microscope .For the fluorescence recovery after photobleaching (FRAP) experiments, E18 rat embryo hippocampal cells were plated onto glass coverslips coated with poly-L-lysine (Sigma-Aldrich) in 4-well cell culture plates at a density of 200.000 cells/well. The cultures were incubated at +37°C in serum-free Neurobasal medium  for approximately 2 weeks (DIV 14-16), renewing half of the growth media weekly. Then, they were transfected with Lipofectamine 2000 (Invitrogen) in order to overexpress GFP-tagged TRKB constructs (TRKB.WT or TRKB.Y433F). The cultures were incubated with the transfection mix  in serum-free media for 1.5 hours, followed by 3x medium washes and returned to the original growth medium after that. The cells were left at +37°C o/n to overexpress the constructs . Next daMG87.TRKB or primary cultured cortical cells were fixed with 4% paraformaldehyde in PBS, and unspecific binding sites were blocked with a blocking buffer . The MG87.TRKB cells were stained with anti-GFP, while primary cultures were incubated with anti-actin. The fluorescence was obtained following incubation with secondary antibodies. The coverslips were mounted with Dako Fluorescence Mounting Medium (#S3023). Images were acquired with Zeiss LSM710 confocal microscope (63x oil objective).For Sholl analysis of cultured hippocampal cells, confocal images were processed using FIJI ImageJ (NIH software), and the number of branches in the 80-μm range from the cell soma were counted using FIJI plugin.For direct stochastic optical reconstruction microscopy (dSTORM) MG87.TRKB cells were grown on cell view 35mm dishes with glass bottom (Greiner) coated with poly-L-lysine (Sigma). Cells were transfected to overexpress TRKB.wt or TRKB.Y433F, and 24h later treated with BDNF (10 ng/ml), fluoxetine (10 μM), cholesterol (20 μM) or ketamine (10 μM) for 15 minutes and fixed as for regular immunofluorescence imaging. Briefly, cells were fixed 24 hours post transfection with 4% PFA for 20 minutes, washed three times for 5 min with 1x PBS and incubated in blocking buffer  for 1 hour. The primary antibody against GFP  was diluted 1:100 and incubated overnight at +4°C, while the secondary antibody Alexa Fluor-conjugated goat-anti-rabbit 647 (Invitrogen) was diluted 1:500 and incubated at room temperature for 1 hour. The dishes were stored in +4°C in 1x PBS no longer than 48 hours before imaging.During imaging, cells were maintained in blinking buffer , which was freshly prepared and changed every hour. Imaging was performed in TIRF mode  to specifically image the fluorophores at the plasma membrane. A GE DeltaVision OMX SR system  equipped with an Apo N 60x/1.49 oil objective and a sCMOS camera was used to acquire the images. The 640 nm diode laser was used at 100% of power to excite the Alexa 647 fluorophores while the 405 nm laser was adjusted until approximately 50% of power in order to maintain the blinking throughout the imaging session. For each cell, 35000 frames were acquired, and the localization map of single fluorophores was reconstructed with SoftWoRx 7.0 software . For the localization map, the first 1000 frames approximately were discarded and the reconstruction parameters were maintained identical for all the samples.Reconstruction parameters: For the localization of all the blinking events in the dataset, the point spread function size factor was set at 1.550 with a local maximum factor of 0.05. Drift correction was adjusted dividing the frames into 20 groups. Tracking of the fluorophores was performed with a maximum localization precision of 100 nm without fiducial markers. The final localization map of the fluorophores identified was built with a reconstruction pixel size of 10 nm and localization precision set at 5 and 100 nm respectively for the minimum and the maximum, and a fluorophore persistence threshold set at 3 frames.The analysis of the reconstructed images was performed in Fiji. Depending on the size of picture, 5 or 10 representative regions of interest (ROIs) of 2x1 μm were blindly chosen per cell and used for particle analysis of the TRKB-positive clusters. The images acquired were from three independent experiments .In vivo electrophysiology. Intrahippocampal BDNF infusion was performed as described previously  1.5 g/kg body weight, positioned in a stereotaxic frame. The body temperature was constantly monitored and maintained at 37°C with an electric heating pad. Holes were drilled in the skull and a concentric bipolar stimulating electrode  was positioned in the angular bundle for stimulation of the medial perforant path  was glued to the infusion cannula (30 gauge). The electrode was then cut so that it extended 800 μm from the end of the cannula. The recording electrode was placed in the dentate hilus . The recording electrode was slowly lowered into the brain with 0.1 mm increment while monitoring response waveform evoked at 400 μA with biphasic rectangular test pulse of 0.033 Hz (pulse-width 0.15 ms). The tip of the infusion cannula was located in the deep stratum lacunosum-moleculare of field CA1, 800 μm above the hilar recording site and 300-400 μm above the medial perforant synapse. The infusion cannula was connected via a polyethylene (PE50) tube to a 10μl Hamilton syringe and infusion pump.Responses were allowed to stabilize for 1 hour at a stimulation intensity that produced a population spike 30% of maximum. After baseline recording for 20 min, infusion of 2μl of 1 ug/ul BDNF over 30 min at a rate of 0.067μl/min. Evoked responses were recorded for 120 min post infusion. Recorded field potentials were amplified, filtered (0.1 Hz to 10 kHz), and digitized (25 kHz). Electrophysiological data was analyzed using Datawave Technologies Software company. Changes in the fEPSP slope were expressed in percent of baseline. After recordings rats were decapitated and dentate gyri were dissected and immediately frozen on dry ice and stored at −80°C until use.Ex vivo electrophysiology. Extracellular field potentials (fEPSP) were recorded in acute slices of adult mouse hippocampus (pocampus . Adult mField excitatory postsynaptic currents (EPSPs) were recorded in an interface chamber using ACSF-filled glass microelectrodes (2-4 MΩ) positioned in the stratum radiatum of the CA1 region and amplified an Axopatch 200B amplifier. Electric stimulation (100 μsec duration) was delivered with a bipolar concentric stimulation electrode placed at the Schaffer collateral. Baseline synaptic responses were evoked every 20 s with a stimulation intensity that yielded a half-maximum response. After obtaining a 15 min stable baseline theta burst stimulation  or tetanic stimulation  was delivered and field potentials were recorded for 45 min.Input/output (I/O) curves were constructed using gradually increased stimulation intensities of 5, 10, 20, 30, 40 and 50 mV until the fEPSP reached plateau or visible population spike was seen.https://www.winltp.com) was used for data acquisition.To examine short term plasticity, we performed paired-pulse-facilitation (PPF) experiments using interpulse intervals (IPIs) of 20, 50, 100, and 200 ms and stimulation intensity evoking half-maximal fEPSP slopes were used. WinLTP  was applied on the left eye, the eyelashes were cut and the eye was sutured shut with 3 mattress sutures. At the end, antibiotic ointment  was applied on the sutured eye and Carprofen (5 mg/kg) was injected s.c. for postoperative analgesia. The monocular deprivation lasted 8 days and during that period, all animals were checked daily and resutured when showed a sign of the thread loss to prevent reopening of the eyes.Optical imaging. The saturation of haemoglobin in the primary visual cortex of the right hemisphere was measured to assess cortical activity  in order to preferentially stimulate the binocular part of the visual field. First, a green light (540 ± 20 nm) was used to illuminate the skull surface in order to find the region of interest and acquire a map of the surface vascular pattern, then the camera was focused 600 μm below the pial surface and the green light switched with a red light (625 ± 10 nm), to record the intrinsic signal. A longpass red filter (590 nm) was put between the skull surface and the camera to avoid that light from the stimulus monitor could affect the intrinsic signal acquisition. When the signal from one eye was being recorded, the other eye was protected with viscotears and covered with a patch. The continuous-periodic stimulation was synchronized with a continuous frame acquisition, frames were collected independently for each eye at a rate of 30 fps for 5 minutes and stored as a 512 × 512 pixel image, after spatial binning of the camera images.Data analysis. An analysis software package designed by Kalatsky et al. was used to perform Fourier decomposition on the cortical maps, that allowed to extract the intrinsic signal from the biological noise : this test was performed in a square arena (28cm side) with opaque walls containing cues (black stripes or spots). The adult male and female mice (18-22 weeks old) were placed for 3 consecutive days (15min per session) in the arena with two identical objects  in the same position throughout the sessions (pretest). At the test session one of the objects is moved to a different position and the number of visits (counted as sniffing or interacting with the object) to the old (A) or newly located (A’) object was determined by an observer bling to the conditions .Contextual fear conditioning: this test was modified from previous studies . BrieflyForced swimming test: animals  were placed in 5l glass beaker cylinders  for 6min. The immobility was assessed in the last 4min of the session . The watAnimals: both males and females were used in this experiment. The Bromodeoxyuridine (BrdU) (Sigma) was administered intraperitoneally at the dose of 75 mg/kg four times every 2 hr to reach 300 mg/kg total for each animal. The injection procedure was carried out at the start of the treatment . On day 21 of the drug treatment, the animals were euthanized by CO2, brains were quickly removed, followed by hippocampus dissection on ice, instantly frozen on dry ice and stored at −80°C until further use.A semiquantitative dot-blot method was performed as previously described with minor modifications . To isolThe brain samples were homogenized in 200 μL of 100% methanol  with an ultrasound sonicator  continuously for at least 30 s. The homogenates were centrifuged at 20800 g for 35 min at 4°C. The supernatant was then removed to 0.5 mL Vivaspin filter concentrators  and centrifuged at 8600 x g at 4°C for 35 min.The HPLC system for determination of the concentration of fluoxetine consisted of a solvent delivery pump  connected to an online degasser  and a ternary gradient unit (Jasco LG-1580-02), an analytical column  protected by a 0.5-mm inlet filter and thermostated by a column heater , and a fluorescence detector (Jasco Intelligent Fluorescence Detector model FP-1520). The wavelengths of the fluorescence detector were set to 290 (excitation) and 230 (emission), which have been found to be optimized for fluoxetine . The mobpost hoc test using GraphPad Prism (https://www.graphpad.com/) v6.01; or multivariate ANOVA using JASP (https://jasp-stats.org/) v.0.14.1. The F and p values are indicated in the figure legends. All experimental data used in the present study are available in FigShare under CC-BY license (https://doi.org/10.6084/m9.figshare.12698012).The data in the present study was analyzed by Student’s t test ; one- or two-way ANOVA were also applied, followed by Fisher’s LSD


The sensing behavior has been investigated in the relative humidity (RH) range of 2–99%. The observed results reveal a remarkable response and ultrafast detection even with zero applied bias (self-powered mode), with response and recovery times of ~ 10 and ~ 0.7 s, respectively. The self-powered behavior has been attributed to the inhomogeneities and the asymmetry in the contact electrodes. The highest sensitivity of ~ 5.64 × 106% can be achieved at an applied bias of 5 V. This approach of fabricating such highly responsive, self-powered and ultrafast sensors with simple device architectures will be useful for designing futuristic sensing devices.Humidity monitoring has become extremely vital in various technological fields such as environment control, biomedical engineering, and so on. Therefore, a substantial interest lies in the development of fast and highly sensitive devices with high figures of merit. Self-powered and ultrasensitive humidity sensors based on SnS In recent years, many efforts have been made to develop humidity sensors based on various transduction principles such as capacitive, resistive, acoustic and optical detection3. Nanoscale materials have been investigated for further improvement in sensing performance in terms of higher sensitivities, and faster response and recovery times. However, all these sensors require a power supply and therefore, in a device which involves a number of such sensors, power supply becomes a huge concern which can lead to incredible cost and complexity. In the current energy scenario, considerable efforts are being made in the fields of energy storage and energy generating devices11. Hence, low cost and self-powered nano-devices are desperately in demand.Humidity monitoring and control plays an essential role in maintaining the safety and quality of day-to-day life as it has applications in many fields, including environmental control, industrial production, medical and chemical monitoring, and so on16. Among these MDCs, earth abundant layered SnS2 is being extensively investigated due to its additional advantages such as non-toxicity, high stability, and most importantly, low fabrication costs17. Therefore, in recent times, SnS2 based devices have become potential and important candidates for gas and humidity sensing. Bharatula et al. have synthesized nanofilms of SnS2, which can effectively detect humidity with response and recovery times of ~ 85 and ~ 6 s, respectively18. Qin et al. have demonstrated SnS2 nanosheets prepared by chemical exfoliation, which exhibit rapid response and high sensitivity to NH3 at room temperature19. Zhang et al. have demonstrated a self-assembled SnS2 nanoflower/Zn2SnO4 hollow sphere nanohybrid device, exhibiting excellent humidity sensing properties20. Recently, Yan et al. fabricated NO2 gas sensor based on CVD grown SnS2 with ultra-high sensitivity by utilizing inherent defects under photoillumination21. Although, there are many reports on SnS2 based devices for humidity and gas sensing, the quest is always on for fabrication of devices with properties such as large area with simple designs, self-powered, ultrasensitive and room temperature humidity sensing.It is well established that metal dichalcogenides (MDCs) have been widely investigated for various applications such as photocatalysis, optoelectronics, solar cells, sensors, etc. due to their extraordinary properties and performance in nano-electromechanical devices2 thin films. Exfoliation, chemical vapour deposition (CVD), hydrothermal and solvothermal synthesis, and sputtering have been extensively used for fabricating nanofilm based devices24. However, exfoliation of nanoflakes and growth of thin films by CVD result in thin films whose sizes are in the range of few μm, thus hindering the large-scale growth optimum for industrial scale applications. Additionally, absence of ultrahigh vacuum during fabrication can often lead to unclean and contaminated interfaces. Therefore, magnetron sputtering has emerged as a perfect tool for deposition of large-scale thin films, involving ultra-high vacuum, which helps in controlling the thin film properties during deposition.There are several techniques to obtain low-dimensional SnS2 nanofilms and the effect of thickness modulation on the sensing behavior. The concept of self-powered detection lies with the presence of an internal electric field, which is strong enough to separate the charge carriers11. This phenomenon has been utilized in the designing of sensing devices. The self-powered detection can be realized by several approaches such as fabricating hybrids with piezoelectric materials, or depositing asymmetrical contact electrodes of different materials26. The most convenient way for realizing self-powered response is by introducing asymmetry in the contact electrodes of same material27, and this property has been exploited in the present study. The nanofilms have been prepared by a two-step growth process: deposition of Sn thin films on soda lime glass (SLG) substrates by dc magnetron sputtering followed by their sulfurization. Humidity sensing have been carried out at room temperature and the devices exhibit excellent detection even at zero bias, with ultrafast response. The sensitivity is found to be optimum for a film thickness of 262 nm. A possible mechanism based on charge hopping has been proposed to have an understanding about the detection phenomenon.Herein, we demonstrate self-powered humidity sensing based on SnS2 based humidity sensor. For investigation of the crystalline nature and phase purity of the thin films, X-ray diffraction (XRD) patterns were recorded and the patterns are shown in Fig. 2 with space group P3m128. The peak corresponding to (001) is found to be the most intense peak, thereby indicating z-direction oriented growth. As the thickness of the film increases, the intensity of the (001) peak becomes stronger. Moreover, the hump observed ~ 25° corresponds to the amorphous nature of SLG and decreases with increasing film thickness. The crystalline nature of the films is confirmed by Raman spectroscopy and the spectra have been presented in Fig. 1g (~ 312 cm−1) and Eg (~ 224 cm−1) can be clearly seen for all the three samples, which correspond to the vertical out of plane vibrations and the non-degenerate in-plane vibrations, respectively18. Thus, the formation of crystalline SnS2 thin films on SLG substrate is confirmed.Figure 2 thin films are shown in Fig. The surface morphology and the cross-sectional scanning electron microscopy (SEM) images of the SnS2 environment)–99% (highly humid atmosphere) with the help of a lab-built setup  curves of the devices under the influence of different biasing conditions (0–2 V) were recorded to examine the response/recovery times and the cyclic stability of the devices. It was observed that the current increases as the humidity level is increased and gradually saturates. However, there was a rapid drop in the current as the humidity is lowered by flushing the chamber with dry nitrogen. The sensors were tested with different biases and similar kind of behavior was observed.The humidity sensing behavior (at room temperature) of the devices has been investigated in the range of 2%  graphs of the three devices at two different humidity levels (85% and 99% RH). The I–V characteristics of all the devices have been shown with respect to the same values of the negative and positive voltage  and recovery (tf) times have been evaluated by estimating the difference in time for the signal to rise or fall from 10 to 90% or 90% to 10% of the final value, respectively and have been presented in Table 2 films may not be much favorable at room temperature, therefore leading to a larger response time. Moreover, limited by our experimental setup, the introduction of humidity into the test chamber is very gradual. Therefore, the saturation of humidity (99% RH) takes a considerable time, which is reflected by the response times of our devices. On the other hand, during the recovery time, water molecules might be easily getting desorbed due to lower adsorption and the external flushing by dry nitrogen gas, resulting in a very fast recovery time18.The response  roughness of the samples  leads to the slower recovery as compared to the other samples. Figure + ions) cannot move freely in the immobile chemisorbed and the first physisorbed layers of water molecules3. With increase in humidity levels (> 70% RH), the H+ ions can move freely in higher-level layers of physisorbed water molecules according to the Grotthuss reaction  by gently exhaling on the sample, kept ~ 4.02 nanofilms devices is extremely well compared to other 2D materials-based humidity sensors reported in literature41. A comparison of the sensing characteristics of our devices with other reported devices has been presented in Table 2-based ultrafast and self-powered humidity sensors are robust and low cost that might open routes for novel applications such as in breath monitoring. The self-powered behavior of our sensors can be extremely useful in systems which involve an array of such sensors, and therefore, the operational cost and the heavy circuitry becomes a big concern in the current scenario of energy crisis. Our findings may also enable nano-porous thin film-based sensors to exploit the unique advantages unveiled from the ultrathin nature of the constituent sheets and the facile synthesis processes, suitable for applications in fields such as consumer’s electronics, environmental and health monitoring.The performance of these SnS2 thin films on soda lime glass substrates by a two-step synthesis process—dc sputtering of Sn films followed by their sulfurization. XRD and Raman spectra confirmed the hexagonal crystal structure and SEM–EDS micrographs confirmed homogeneity and uniformity of SnS2 films over a large area. Humidity sensing measurements of SnS2 thin film-based devices of different thicknesses exhibit a highly responsive detection at 0 V for all the devices, showing self-powered nature of the devices. Temporal response was done at different bias voltages (0–2 V) and it is observed that the devices show high electrical stability and repeatability in ambient conditions. From the transient response curves, ultrafast response and recovery times of ~ 10 s and ~ 0.7 s, respectively, have been estimated for the self-powered detection of the sensor with optimum film thickness. Furthermore, a maximum sensitivity of ~ 5.64 × 106% in 99% RH at an applied bias of 5 V can be achieved. These results could pave a way for designing self-powered and ultrafast humidity sensors with simple architectures through easy approaches.We have successfully fabricated 2D SnS42. All the deposition parameters were optimized to obtain best conditions for continuous thin film and pure phase.SLG substrates were first sonicated for 15 min in iso-propyl alcohol followed by sonication in deionized water for 10 min. The substrates were then purged with nitrogen gas to remove any residuals before being loaded into the sputtering chamber (Excel Instruments). The thin films were prepared by a two-step process which involved: (i) deposition of Sn thin films on SLG by dc magnetron sputtering of Sn target (3 inch in diameter) at 45 W—15 min (sample A), 5 min (sample B), 1 min (sample C) and (ii) sulfurization  at 450 °C for 1 h in a tube furnace with continuous Ar gas flow. The sulfurization process has been explained in our previous reportThe crystal structure of the prepared films was examined by X-ray diffraction (XRD)—X’pert-PRO PANalytical with Cu Kα radiations (1.5418 Å). The surface morphology and compositional analysis of the films were determined using a scanning electron microscope (SEM)—Ultra55 FE-SEM Karl Zeiss—EDS. Thickness of the films were measured by cross-sectional SEM. Atomic force microscopy (AFM) was carried out using A.P.E. Research A100-AFM. Raman analysis was done using LabRAM HR equipped with a 532 nm laser.2 films to make metal–semiconductor–metal type contacts. A very simple computer-controlled setup which consisted of a test chamber, a mass flow controller, a source for humid air, and a data acquisition system was employed for humidity sensing measurements. During measurements, humid air was obtained by passing nitrogen gas through water and the flow was controlled with a mass flow controller. The conductivity of the samples was then measured with a Keithley 2400 source measuring unit, in different RH conditions.For humidity sensing measurements, 120 nm thick Cr/Au (10 nm/110 nm) contacts were deposited on the SnSSupplementary Information.


TG′=G″. The modification mechanisms are different before and after percolation. Before the percolation threshold, graphene which has a molecular structure similar to asphaltene enhances asphalt, like increasing asphaltene components, and after threshold, graphene improves asphalt because of the formed graphene networks. Rotational viscosities test results show that the higher the GC is, the higher the operating temperatures are, but the operating temperatures are higher than 200 °C when GC is above 4%. The percolation helps to further develop conductive asphalt concrete for intelligence pavement, but the operating properties of GMAs need to be improved.Recently, low-cost, high-quality graphene can be obtained readily, so it is potential to prepare conductive graphene modified asphalts (GMAs). In this paper, GMAs were prepared with 0%, 2%, 4%, 6%, 8%, and 10% of graphene by weight of composites. Dynamic shear rheological experiments conducted from −30 to 120 °C illustrate that elasticity at above ambient temperatures and rutting resistance at higher temperatures are enhanced and, especially, the conceived percolation of GMAs occurs at graphene contents (GC) above 8% which were verified from three changes as GC increases, i.e., the curve characteristics of complex moduli, storage moduli at temperatures over 100 °C, temperatures when the phase angle reaches 90° and the trend of  Graphene is a kind of magic nano-material. No matter what material it is added to, it seems to have a positive impact on the properties of the material ,9,10,11.Moreno-Navarro, F. et al. , Yang, QIt is noteworthy that the modification effect of low-content GMAs is not as good as that of polymers. According to the percolation theory, when the concentration of graphene exceeds a certain value, the GMAs’ system performance will take place with an abrupt change. Perhaps, graphene will present its magic properties when it is added with a higher content. However, previous studies of GMAs have not dealt with the performances of higher-content GMAs. The reason for this may be that the price of graphene was too expensive in the near past. To our excitement, Luong, D.X. et al. obtained high-quality and low-defect graphene through fast Joule heating , which iThis paper aims to characterize the application potential of high-content GMAs in a wider temperature range, including mechanical properties, working performances, and the relationship between the microstructure of GMAs and the graphene content. For this purpose, strain sweeps, temperature sweeps and the rotational viscosity tests were conducted by dynamic shear rheometer (DSR) to comprehensively evaluate the different graphene content of GMAs. By analyzing the above results, the influence of graphene on the viscoelasticity, the mixing and compaction temperature of GMAs were determined, based on which the application potential of GMAs in engineering was evaluated, which laid a solid foundation for the future intelligent pavement application of GMAs.Graphene was purchased from Zhongke Time Nano , which is in powder form. The relevant parameters are listed in Firstly, the calculated and weighed control asphalt  was put into the oven at 120 °C for preheating. After that, it was quickly transferred to a constant temperature silicon oil bath at 145 °C for heating to make it reach the melting state. Then, the corresponding proportion of graphene was slowly added into the molten control asphalt in batches, while the graphene and asphalt were stirred at low speed. For 0%, 2% and 4% content of GMAs, they were stirred at 300 rpm for 20 min, 500 rpm for 20 min, 1000 rpm for 20 min, 2000 rpm for 20 min, and 2500 rpm for 40 min in a silicone oil bath at 145 °C to ensure it was homogeneous. For 6%, 8% and 10% content of GMAs, it was kept at constant temperature in a 150 °C silicone oil bath , the stirring process was the same as above, and, finally they were kept at high temperature until the bubbles disappeared, and then cooled to room temperature.The linear viscoelastic regions (LVEs) of GMAs were determined by using DSR, MCR 302 . For asphalt, the higher the temperature is, the longer the LVE plateau is . In viewIn order to explore the mechanical properties of asphalt at high and low temperatures, the temperature sweeps of GMAs were carried out by DSR, MCR 302. Temperature sweeps were performed with strain of 0.01%, oscillation frequency of 10 rad/s, and the temperature range reduced at the interval of 1 °C/min from −30 to 120 °C. A 25 mm parallel plate (PP25) was used to determine the overall trend of GMAs in the temperature range of −30–120 °C. In order to further analyze the results, in the temperature range from −30 to 35 °C, an 8 mm parallel plate with 1 mm gap was used, and when the temperature range was from 35–120 °C, a 25 mm parallel plate with 1 mm gap was used. Checking time continued for 10 min to eliminate thermal history and attain an equilibrium state at each measurement.In order to determine the suitable construction temperature of asphalts and explore the engineering feasibility of GMAs, the rotational viscosities of different content of GMAs were measured by MCR 302. As is known to all, asphalt is a kind of viscoelastic material. There is a glass-forming process of Newtonian fluid state to glassy state, which is shown in θ, Φ, Ψ) describe the random orientation of the platelets. Thus, the percolation threshold of nanocomposites, containing 3D, random-distributed, disc-shaped nanoparticles based on the average interparticle distance approach, can be calculated by the following formulatrV is the threshold of volume fraction of particle, d is the diameter of the graphene disk, t is the thickness of the packed graphene disk, and ipS is the maximum spacing that allows electron-hopping to take place between adjacent conductive fillers owing to quantum-mechanical tunneling. The ipS is expected to be in the order of 10 nm. For the graphene and asphalt binder used in this paper, . A is a regression constant, aE is the visco-flow activation energy (kJ·mol−1), R is the universal gas constant (8.314 J·mol−1·K−1), T is temperature in degrees K.According to the fragile liquid theory, asphalt binders are of typical fragile liquids. Thus, their temperature dependences of viscosity satisfy the Vogel–Fulcher–Tammann (VFT) equationequation . When inequation (4)η=Ae−η) and the reciprocal of the temperature 1/T, we can obtainT coefficient value, that is, Ea can be acquired, which can characterize the thermal susceptibility of asphalt in the corresponding temperature ranges.Take the logarithm from both sides of Equation (4) that is transformed into a linear relationship between the logarithmic value of the viscosity lg  with the increasing of graphene content is in concert with that of the glass transition temperature, and this temperature is much easier accurately verify. As shown in TG′=G″ with graphene content can be obviously divided into three domains. In domain I, graphene, which has a molecular structure similar to asphaltene, enhances the asphalt to some extent, like increasing asphaltene to the asphalt, thus, when graphene content is from 0% to 4%, TG′=G″ rises about 4 °C with every 2% graphene increase. In domain II, at the graphene content from 4–6%, there is a plateau of TG′=G″ at about 18 °C. This is a strong implication that there is the percolation threshold at graphene content about 8%, which is in accord with the inferred result from TG′=G″ in the same content step increasing, i.e., when graphene content increases from 8% to 10%, TG′=G″ improves about by 10 °C, that is, GMAs enter another phase, in which graphene structure plays a crucial role. Similar to the classical percolation theory equation introduced in TG′=G″ versus graphene content after percolation threshold are fitted, as shown in T is TG′=G″, 18 is the base value of transition temperature TG′=G″ as shown in TG′=G″ will be higher than 50 °C. However, due to the viscosity of GMA with high-content graphene is too large to stir homogenously, thus, the content of graphene in this study is limited to 10%.As shown in η) of all asphalt falls with the increase in temperature. Besides, at the same temperature, in comparison to the control asphalt, the viscosity of GMAs comes up along with the increase in graphene content. However, the viscosity of all asphalts is close at 180 °C, which may be due to the weakening of the influence of nanoparticles on the viscosity at higher temperature.The viscosity of an asphalt binder at high temperature is considered to be a significant characteristic to affirm the working temperature. For the sake of ensuring that the asphalt has sufficient mobility in the process of pumping and mixing, the mixing and compaction temperature were determined by measuring the rotational viscosities of control asphalt and GMAs ,33,34. A2 are shown in From the construction point of view, the most suitable viscosity range for asphalt mixing and compaction is (0.17 ± 0.02) Pa·s, (0.28 ± 0.03) Pa·s . In acco(1)At graphene content above 8%, the |G*| of GMAs at above 100 °C remains stable, which differs from those of graphene content below 8%. This implies that the percolation of GMAs occurs and graphene networks form at graphene content above 8%, which means that it is possible to make conductive asphalt concrete when the graphene content is higher than 8%;(2)The GMAs’ modification mechanisms are different before and after the percolation point, i.e., before the percolation threshold, graphene, which has a molecular structure similar to asphaltene, enhances asphalt to some extent, like increasing asphaltene, and after the percolation threshold, graphene improves asphalt because of the formed graphene networks;(3)In the temperature section of −30–120 °C, in comparison to control asphalt, as the graphene content increases, the moduli of GMAs rises gradually, and the phase angle and damping factor decrease. This illustrates that graphene boosts the elasticity and the high-temperature rutting resistance of asphalt;(4)The differences of moduli at higher temperatures between the GMAs and the control asphalt are greater than those at lower temperatures, predicting that the modification effect of graphene at higher temperatures is superior than those at lower temperatures, which is because the temperature susceptibility of graphene is much lower than that of control asphalt, and the rigid molecular structure of graphene frames GMAs at higher temperatures;(5)The temperature at δ reaching 90° rises gradually as a result of the increase in graphene content, indicating that the temperature of asphalt from viscoelastic fluid to Newtonian fluid is on the increase. When GMAs’ contents are 8% and 10%, they do not even reach 90° in the experimental temperature range. From this perspective, graphene enhances the strength and the high-temperature rutting resistance. This is also evidence that there is a percolation threshold at graphene content above 8%;(6)In terms of viscosity properties, it has been shown that adding graphene promotes the viscosity of all asphalt. The higher the content of graphene is, the bigger the viscosity is. The higher the temperature is, the closer the viscosity of different graphene content of GMAs is. Obviously, graphene improves the mixing temperature and compaction temperature of asphalts, which should be improved in the future to facilitate the pavement construction.To evaluate the potential for the intelligent pavement and modification effect of high-content graphene on asphalts, rheological experiments and rotational viscosity tests were carried out on the control asphalt and GMAs with 2%, 4%, 6%, 8% and 10% of graphene by weight. On this basis, we conclude that:


The two Dimensional (2D) materials such as MXene and graphene, are most promising materials, as they have attractive properties and attract numerous application areas like sensors, supper capacitors, displays, wearable devices, batteries, and Electromagnetic Interference (EMI) shielding. The proliferation of wireless communication and smart electronic systems urge the world to develop light weight, flexible, cost effective EMI shielding materials. The MXene and graphene mixed with polymers, nanoparticles, carbon nanomaterial, nanowires, and ions are used to create materials with different structural features under different fabrication techniques. The aerogel based hybrid composites of MXene and graphene are critically reviewed and correlate with structure, role of size, thickness, effect of processing technique, and interfacial interaction in shielding efficiency. Further, freeze drying, pyrolysis and hydrothermal treatment is a powerful tool to create excellent EMI shielding aerogels. We present here a review of MXene and graphene with various polymers and nanomaterials and their EMI shielding performances. This will help to develop a more suitable composite for modern electronic systems. The proliferation of smart electronic devices and wireless communication in the artificial intelligent age are a source of electromagnetic pollution (EMP) which is a serious universal problem. The EMP creates complexities in the natural electromagnetic environment, and is unwanted radiation which not only disturbs the general function of surrounding electronic systems but also threatens the well−being of humans ,5,6,7,8.In 2020, the world utilizes electromagnetic radiation as a jamming tool or weapon in battlefields or to destroy electronic components of the ships, radars, and flights, and destroy security of the countries. Hence, electromagnetic interference shielding is the inevitable choice around the globe ,13,14,15A), reflection (SER), and multiple reflection (SEMR). SER occurs on the surface whereas SEA and SEMR are happening within the shielding material. The wave propagating on the other side of the shielding materials is called the transmittance (T), the magnitude of which is lower than that of incident wave (I) and value of SEA, SER, and SEMR is smaller than that of I (EMI shielding can be achieved by absorption (SEhat of I . The eleWe focused on a different synthetic route of graphene (GN), MXene, and composites. GN and MXene structural features and synthesis are discussed in detail. In addition, different composite preparation methods are listed, and its effect is discussed in detail with proper comparison in the discussion. In general, aerogel or foam based composite are most attractive to scientists and have excellent EMI shielding with excellent absorption ability. 2 hybridized carbon network formed graphene. In addition, burning the dry ice by using magnesium followed by acid treatment produces GN , electrochemical exfoliation, sonication, radiation based method, and ball−milling are being used to produce GN while bottom–up follows the strategy that those are grown from metal−carbon melt, epitaxial growth on silicon carbide (SiC), dry ice method, and deposition . Multiladuces GN  . Huhickness  .,61.45,61ficantly . Wan et ficantly ,62,63. The MXene ,65.3·g−1, 0.0042 g·cm−3, respectively . The Zhu et al. study just used an electrostatic assemble of nanomaterials on the porous structure that has less effect on EMI SE and CVD, or a hydro thermal process improved porous geometry and minimized the defect of fillers [In addition, the SEed above . Thus, p fillers ,73.−3 of density, 2.4 mm of thickness, and 92.78 (vol.%) loading rate annealed at 1400 °C gave rise to 54.43 dB of highest EMI SE and the corresponding EC is 0.2012 S·cm−1. The higher annealing temperature (2800 °C) destroys EMI shielding of the composite, whereas the higher temperature repairs the defects by removing functional groups, reduced polarization loss, lessens the amorphous nature (higher amorphous nature at 1400 °C) and enhances the ohmic loss. Further, the introduction of the CNT prevents the agglomeration of GN and enhance the electric channels in the 3D network [−1 of EC while GN/PANI, Ni decorated GN/PANI and Ag decorated GN/PANI (5 wt.%) show EMI SE of 24.85, 29.33, and 24.93 dB, respectively. Therefore, metal nanoparticle decoration with GN in PANI matrix improved EMI SE compared to the GN/PANI in polyimide matrix [The many studies use PDMS as a binder to make GN-based EMI shielding materials. The 3D graphene/carbon nanotubes/polydimethylsiloxane composites (GC) was prepared by using freeze drying followed by annealing at a high temperature (2800 °C) and this is similar to the Song et al. study where they used the HC template to create the aerogel ,74. GC w network ,74. Chene matrix ,75,76. The electrical conductivity of the pure materials is high compared to the composite made from corresponding pure materials. Further, MXene based composition showed excellent EC compared to the GN. This is because of the functional group present in the MXene gave rise to a better arrangement in the polymer matrix which promoted a good electron flow path. Due to this, MXene is one of the most attractive materials in the modern electronic world. The SSE and SSE/t is depend on the density and thickness of the composite. Further, proper geometrical arrangement of the fillers is a crucial factor for better EMI shielding. In this review, we have highlighted recent progress in EMI shielding of MXene and graphene composite with different fabrication technique. The global requirement is a lightweight, flexible, cost−effective, and thinner EMI shielding material and EMI shielding over 20 dB, which is the basic requirement for the EMI shielding application in electronic devices. The graphene is synthesized by various methods in which radiative and chemical vapor deposition gives rise to good quality graphene and utilization of other methods is dependent on the types of applications. MXene synthesis also adapts various techniques and the lithium fluoride/hydrochloric acid etching is the most desirable etching method. The 2D MXene and graphene play a major role in creating different structures, especially aerogel. The freezing and freeze-drying process is used to prepare different geometric composite with excellent EMI shielding is a new approach. Further, the pyrolysis and hydrothermal process are important techniques used to achieve higher EMI shielding of the aerogel hybrid structure. The pyrolysis process of MXene created with surface titanium oxide, induces the EMI shielding while annealing of the MXene/polymer composite forms an internal conductive carbon network is another approach for excellent EMI shielding. The high temperature pyrolysis process of MXene or graphene polymer composite destroyed the EMI shielding function. The EMI shielding of graphene can be improved further by doping, decoration, oxidation, reduction, encapsulation, type of polymer, and processing technique. Thus, the proper geometrical arrangement of the fillers is a crucial factor for better EMI shielding and can be tuned by changing thickness, porosity, dielectric loss range, and complex permeability. The addition of inorganic nano composition like nanowire, ions, and nanoparticle further enhances EMI shielding and are being used to make the most powerful EMI shielding composites. The polymer/filler composites are explored to fulfil recent demand in EMI shielding in electronic devices. We hope, we have provided the fundamental understanding of MXene, graphene, and its corresponding composites to achieve a modern electronic goal in the near future.


It was found that the doping site right above C atom (T) was the most stable structure by studying three potential doping positions of the Ge and Cr atom on the graphene surface. Then, the structural parameters, density of states, and difference state density of these adsorption systems were calculated and analyzed based on the density functional calculations. The results show that the adsorption properties of GeG and CrG systems for H2 and C2H2 are obviously better than the IG system. Furthermore, by comparing the two doping systems, CrG system exhibits more outstanding adsorption performances to H2 and C2H2, especially for C2H2 gas. Finally, the highest adsorption energy (−1.436 eV) and the shortest adsorption distance (1.981 Å) indicate that Cr-doped graphene is promising in the field of C2H2 gas-sensing detection. In order to find an excellent sensing material for dissolved gases in transformer oil, the adsorption structures of intrinsic graphene (IG), Ge-doped graphene (GeG), and Cr-doped graphene (CrG) to H The oil-immersed transformer, as the key hub of a power system, undertakes the task of power transmission and transformation of the whole power grid, and its operation condition will directly affect the safety of the power network and users ,2,3,4. H2 , CH4 [10 [4 [2H2 , etc. Th [4 [2H2 ,13,14.2 adsorption behavior on doped  graphene by density functional theory (DFT) calculations and indicated that metal doping can be an ideal method to enhance the performances of a graphene-based gas sensor [2 molecule on intrinsic graphene and transition metal  -doped graphene, suggesting that the latter exhibits stronger adsorption [With the discovery of two-dimensional materials, graphene material has captured widespread attention for its excellent performances and considerable applications ,16,17. Ns sensor . Gao et sorption . Hence, 2CO) molecule in the aspect of atmospheric environment [2 and C2H2 molecules based on density functional theory (DFT). To analyze and compare the sensing mechanism and adsorption capacity of three kinds of graphene models, their geometric structures, adsorption distances, bond lengths, adsorption energies (2 and C2H2 gas molecules.Chromium (Cr) has received considerable investigation with its high electrical conductivity and excellent ductility as a transition metal (TM) atom . Germaniironment . Wang etironment . Gecim eironment . However−5 Ha, 2 × 10−3 Ha/Å, and 5 × 10−3 Ha were set for energy convergence accuracy, maximum displacement, and stress, respectively. The convergence accuracy of the Self-Consistent Field (SCF) and the k-points of the Brillouin zone were set to 1 × 10−6 Ha and 6 × 6 × 1. The setting of density of state (DOS) in Dmol3 calculation properties was selected to qualitatively analyze the electronic structure of the material by outputting the charts of the total density of state (TDOS) and partial density of state (PDOS). All of the above calculations were considered Spin polarization effect [Density functional calculations between gas molecules and three graphene-based materials were carried out in Dmol3 module of Materials Studio (MS) ,39,40. Tn effect .2 and C2H2) on three kinds of graphene-based material is defined in Equation (1).The adsorption energy  supercell with the vacuum slab of 20 Å to avoid layer interaction and the slab position of 10 Å to build a two-dimensional graphene monolayer. The models of GeG or CrG were constructed by different sites doping with a Ge or Cr atom. To obtain the steadiest doped structure, the three potential sites of metal-doped graphene structure are discussed, including the doping site right above C atom (T), the hollow site in the positive center of graphene lattice (H), and the bridge site at midpoint the two C atoms (B), which are shown in The models of Hgraphene , and Equgraphene . In whicT doping structure, while the charge transfers in GH and GB doping structures are 0.135 e and 0.032 e, respectively. The C atom of graphene and the Ge atom form the C-Ge bond by the shortest length of 1.865 Å in the GT doping structure, which is much shorter than that in GH (2.119 Å) and GB (2.279 Å) doping structures. Remarkably, the larger bind energy of 4.725 eV is consumable to form new Ge-C bonds, because the substitution doping of the T site destroys the internal structure of graphene.By comparing the detailed calculated parameters information in T doping structure are shown in The total density of state (TDOS) and partial density of state (PDOS) of GeG in GH and GB show that the tQ is 0.211 e and 0.236 e, while the charge transfer value in the GT doping structure is −0.252 e, which is higher than that of other structures. Moreover, the Cr-C bond (1.856 Å) of the GT doping structure is shortest compared with that of GH (2.031 Å) and GB (1.386 Å), but the consumable bind energy (4.732 eV) of the GT site is larger to form the new Cr-C bonds. The most stable doping configurations obtained by comparing various geometric parameters are depicted in As shown in T doping structure is depicted in Spin-polarized total DOS for IG and CrG in G2 and C2H2 molecules.According to the above analysis results, the most stable structures of doped graphene-based materials are doped by T sites, which are C atoms of the graphene structure substituted with Ge or Cr atoms. The metals doping has a strong effect on the electronic structural performances of graphene. Then, the adsorption effects of the three materials of graphene-based to oil-dissolved gas molecules are investigated based on the stable doped structures, especially the adsorption effects of H2 on intrinsic graphene, Ge-graphene, and Cr-graphene have been established, and the structures after optimization are exhibited in Figure 7. Comparing the three adsorption models, a H2 molecule tends to vertically close to the surface of IG and GeG systems, to form a stable adsorption structure, while H2 molecule adsorbs parallelly on Cr atom in CrG system. 2 molecule have small change in IG and GeG systems. Nevertheless, there are distinct variations of structural parameters in the CrG system, as the adsorption distance is obviously smaller between a H2 molecule and graphene-based material than that in IG (3.026 Å), and the H2-adsorbed Cr-graphene exits significant charge transfer (0.052 e). Therefore, these findings suggest that the CrG system is the steadiest adsorption structure to H2 molecule in metal-doped graphene.The adsorption models of H2 on IG, GeG, and CrG systems, the DOS diagrams of various systems are analyzed. According to the TDOS and PDOS of IG system displayed in 2 adsorption has a small influence on the DOS curve due to less hybridization between H-1s orbital and C-2p orbital. 2 adsorption, while the other distribution of TDOS diagram is almost unchanged in GeG system, and the varied DOS mainly caused by the 1s orbital of H atoms. As for H2 adsorption, the total DOS of the adsorption system does not change distinctly near the Fermi level in the IG and GeG system. Thus, the introduction of H2 molecules has little effect on electron properties of intrinsic graphene and Ge-graphene. As the TDOS of CrG depicted in 2 molecule and Cr-graphene mainly contributes by the hybridization of H-1s and Cr-4s orbitals, while Cr-3d orbital may be main reason for the alpha-spin and beta-spin asymmetry of TDOS. In brief, CrG system shows a stronger adsorption to a H2 molecule than that of IG and GeG systems, because of the clearly varied DOS of CrG system during the adsorption process.To further investigate the adsorption behavior of H2 molecule and Cr atom are surrounded by blue and red, respectively, which indicates that Cr atom obtains electrons from the H2 molecule. This phenomenon further confirms that charges transfer from H2 molecule to CrG, which is uniform with the results of the tQ (0.052 e). In addition, a certain amount of interaction exists because of the continuous electron area between H atom and Cr atom.2H2 in top and side views are shown in 2H2.The adsorption structures of IG, GeG, and CrG systems to C2H2 adsorption on the IG system, the C2H2 molecule is far from the graphene surface because of the weak interaction. adsE and tQ of the IG system are only −0.066 eV and −0.008 e, which are far smaller than those of GeG and CrG systems. For C2H2 adsorption on the GeG system, the C2H2 molecule is distinctly deformed after the captured C atom of C2H2 molecule by the Ge atom, while C2H2 is adsorbed on the top site of the C atom by an H atom in the IG system. It is notable that the C2H2 molecule still exhibits a planar configuration after capturing by graphene monolayer, indicating the nonactivation of C2H2 molecule during the adsorption. By comparing the adsorption parameters of GeG structures in 2H2 molecule and Ge-graphene is shorter, which indicates that the C2H2 molecule is more likely to be absorbed on Ge-graphene surface by C atom. For C2H2 adsorption on Cr-graphene, a C2H2 molecule adsorbs on Cr atom with C-Cr bond, and the bond angle of the C2H2 molecule changes significantly in the adsorption process. The C-H band was a little elongated from 1.071 Å to 1.089 Å, resulting from the impact of strong adsorption of Cr-C bonds. The adsorption energy of Cr-graphene reaches −1.436 eV, the charge transfer amounts 0.079 e, and the distance is 1.981 Å. Comparing to intrinsic graphene and Ge-graphene, Cr-graphene has the best adsorption energy, largest charge transfer, and shortest distance.For C2H2 molecule on the intrinsic graphene and Ge-graphene is relatively weaker, while Cr-graphene exhibits strong adsorption capacity owing to the huge adsorption energy (−1.436 eV). Furthermore, CrG system should be the most stable structure due to the excellent adsorption properties.In conclusion, considering the energy and structures of IG, GeG, and CrG adsorption systems, the adsorption of C2H2 system are displayed in 2H2 molecule and intrinsic graphene and the few charge transfers of adsorption. For the GeG system depicted in 2H2 molecule adsorption, suggesting the notable change of charge density and the easy transfer of electron distribution from valence to conduction band. 2H2 near −7 eV, −3 eV, and 3 eV imply that the appearance of the new peak of TDOS at these place may be caused by C2H2 adsorption. 2H2 adsorption turns magnetic Cr-graphene into a non-magnetic system. From The TDOS and PDOS distributions for C2H2 molecule and Ge atom, which infers a strong interaction between them because of a certain amount of transferred electron. A direct continuous electron region is found in 2H2 is surrounded by blue areas. This phenomenon suggests that a mass of electrons transfer from the C2H2 molecule to CrG system. The findings show that a strong chemical interaction appears between C2H2 and CrG, and results in the appearance of a new Cr-C bond. The above conclusions are uniform with the consequences of the Mulliken analysis.By analyzing the charge density difference as shown in 2 and C2H2) were investigated via a detailed DFT study. The most stable structure was explored by studying structural and electronic properties of various adsorption models. The adsorption energy, charge transfer, density of state, and other structural parameters have been employed to discuss the adsorption mechanism. It is found that both Ge doping and Cr doping by T site have most stable doping structure through researching three typical doping structures. By constructing and optimizing different adsorption models of gas molecules to IG, GeG, and CrG systems, H2 closes to Ge and Cr atom through H atom, but C atom of C2H2 directly adsorbs above Ge and Cr atom. The adsorption energies of H2 and C2H2 molecules absorbed on GeG system are −0.117 eV and −0.287 eV, and those of the CrG system are −0.390 eV and −1.436 eV, respectively. The results show that CrG system has strong adsorption abilities to H2 and C2H2 molecules, while GeG system is relatively weaker. For CrG system, the charge transfer value of Cr-graphene to C2H2 (0.079 e) is distinctly higher than that of H2 (0.052 e), confirming that the interaction between C2H2 molecule and Cr-graphene is stronger. In addition, the strong hybridization between atomic orbitals results in the more excellent adsorption performances of CrG to C2H2. Therefore, the Cr-graphene is expected to be an ideal gas-sensing material for detecting C2H2 gas.In this paper, the adsorption abilities of IG, GeG, and CrG systems towards two oil-dissolved gases (H