Graphene-based gas/vapor sensors have attracted much attention in recent years due to their variety of structures, unique sensing performances, room-temperature working conditions, and tremendous application prospects, etc. Herein, we summarize recent advantages in graphene preparation, sensor construction, and sensing properties of various graphene-based gas/vapor sensors, such as NH3, NO2, H2, CO, SO2, H2S, as well as vapor of volatile organic compounds. The detection mechanisms pertaining to various gases are also discussed. In conclusion part, some existing problems which may hinder the sensor applications are presented. Several possible methods to solve these problems are proposed, for example, conceived solutions, hybrid nanostructures, multiple sensor arrays, and new recognition algorithm.

Molybdenum disulfide (MoS), as a promising gas-sensing material, has gained intense interest because of its large surface-to-volume ratio, air stability, and various active sites for functionalization. However, MoS-based gas sensors still suffer from low sensitivity, slow response, and weak recovery at room temperature, especially for NO. Fabrication of heterostructures may be an effective way to modulate the intrinsic electronic properties of MoS nanosheets (NSs), thereby achieving high sensitivity and excellent recovery properties. In this work, we design a novel p-n hetero-nanostructure on MoS NSs using interface engineering via a simple wet chemical method. After surface modification with zinc oxide nanoparticles (ZnO NPs), the MoS/ZnO hetero-nanostructure is endowed with an excellent response (5 ppm nitrogen dioxide, 3050%), which is 11 times greater than that of pure MoS NSs. To the best of our knowledge, such a response value is much higher than the response values reported for MoS gas sensors. Moreover, the fabricated hetero-nanostructure also improves recoverability to more than 90%, which is rare for room-temperature gas sensors. Our optimal sensor also possesses the characteristics of an ultrafast response time of 40 s, a reliable long-term stability within 10 weeks, an excellent selectivity, and a low detection concentration of 50 ppb. The enhanced sensing performances of the MoS/ZnO hetero-nanostructure can be ascribed to unique 2D/0D hetero-nanostructures, synergistic effects, and p-n heterojunctions between ZnO NPs and MoS NSs. Such achievements of MoS/ZnO hetero-nanostructure sensors imply that it is possible to use this novel nanostructure in ultrasensitive sensor applications.

Graphene is an ideal candidate for gas sensing due to its excellent conductivity and large specific surface areas. However, it usually suffers from sheet stacking, which seriously debilitates its sensing performance. Herein, we demonstrate a three-dimensional conductive network based on stacked SiO@graphene core-shell hybrid frameworks for enhanced gas sensing. SiO spheres are uniformly encapsulated by graphene oxide (GO) through an electrostatic self-assembly approach to form SiO@GO core-shell hybrid frameworks, which are reduced through thermal annealing to establish three-dimensional (3D) conductive sensing networks. The SiO supported 3D conductive graphene frameworks reveal superior sensing performance to bare reduced graphene oxide (RGO) films, which can be attributed to their less agglomeration and larger surface area. The response value of the 3D framework based sensor for 50 ppm NH and 50 ppm NO increased 8 times and 5 times, respectively. Additionally, the sensing performance degradation caused by the stacking of the sensing materials is significantly suppressed because the graphene layers are separated by the SiO spheres. The sensing performance decays by 92% for the bare RGO films when the concentration of the sensing material increases 8 times, while there is only a decay of 25% for that of the SiO@graphene core-shell hybrid frameworks. This work provides an insight into 3D frameworks of hybrid materials for effectively improving gas sensing performance.

Autism spectrum disorder (ASD) is a neuro-developmental disorder, which has been associated with atypical neural synchronization. In this study, functional near infrared spectroscopy (fNIRS) was used to study the differences in functional connectivity in bilateral inferior frontal cortices (IFC) and bilateral temporal cortices (TC) between ASD and typically developing (TD) children between 8 and 11 years of age. As the first report of fNIRS study on the resting state functional connectivity (RSFC) in children with ASD, ten children with ASD and ten TD children were recruited in this study for 8 minute resting state measurement. Compared to TD children, children with ASD showed reduced interhemispheric connectivity in TC. Children with ASD also showed significantly lower local connectivity in bilateral temporal cortices. In contrast to TD children, children with ASD did not show typical patterns of symmetry in functional connectivity in temporal cortex. These results support the feasibility of using the fNIRS method to assess atypical functional connectivity of cortical responses of ASD and its potential application in diagnosis.

There has been considerable controversy regarding whether children with autism spectrum disorder (ASD) and typically developing children (TD) show different eye movement patterns when processing faces. We investigated ASD and age- and IQ-matched TD children's scanning of faces using a novel multi-method approach. We found that ASD children spent less time looking at the whole face generally. After controlling for this difference, ASD children's fixations of the other face parts, except for the eye region, and their scanning paths between face parts were comparable either to the age-matched or IQ-matched TD groups. In contrast, in the eye region, ASD children's scanning differed significantly from that of both TD groups: (a) ASD children fixated significantly less on the right eye (from the observer's view); (b) ASD children's fixations were more biased towards the left eye region; and (c) ASD children fixated below the left eye, whereas TD children fixated on the pupil region of the eye. Thus, ASD children do not have a general abnormality in face scanning. Rather, their abnormality is limited to the eye region, likely due to their strong tendency to avoid eye contact.

The present study investigated pitch processing in Mandarin-speaking children with autism using event-related potential measures. Two experiments were designed to test how acoustic, phonetic and semantic properties of the stimuli contributed to the neural responses for pitch change detection and involuntary attentional orienting. In comparison with age-matched (6-12 years) typically developing controls (16 participants in Experiment 1, 18 in Experiment 2), children with autism (18 participants in Experiment 1, 16 in Experiment 2) showed enhanced neural discriminatory sensitivity in the nonspeech conditions but not for speech stimuli. The results indicate domain specificity of enhanced pitch processing in autism, which may interfere with lexical tone acquisition and language development for children who speak a tonal language.

Here we present a strategy for the fabrication of biomimetic nanoarrays, based on the use of DNA origami, that permit the multivalent investigation of ligand-receptor molecule interactions in cancer cell spreading, with nanoscale spatial resolution and single-molecule control. We employed DNA-origami to control the nanoscale spatial organization of integrin-and epidermal growth factor (EGF)-binding ligands that modulate epidermal cancer cell behaviour. By organizing these multivalent DNA nanostructures in nanoarray configurations on nanopatterned surfaces, we demonstrated the cooperative behaviour of integrin-and EGF-ligands in the spreading of human cutaneous melanoma cells: this cooperation was shown to depend on both the number and ratio of the selective ligands employed. Notably, the multivalent biochips we have developed allowed for this cooperative effect to be demonstrated with single-molecule control and nanoscale spatial resolution. By and large, the platform presented here is of general applicability for the study, with molecular control, of different multivalent interactions governing biological processes, from the function of cell-surface receptors, to protein-ligand binding and pathogen inhibition.

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