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Plasma-assisted ignition and combustion are promising approaches for controlling ignition enhancement and flame stabilization. The global loosely coupled plasma-assisted combustion kinetic model has been established by combining the ZDPlasKin and ChemKin codes, which is employed to numerically investigate the effects of the inert gas-diluted methane-air nanosecond repetitively pulsed (NRP) plasma on the ignition process. The results indicate that addition of the inert gas is conducive to increasing the chemical reactive species densities in the methane-air NRP discharge plasma. The addition of inert gases affects the generation pathways of plasma species and their corresponding contribution rates. Compared with the methane-air plasma, the dilution of inert gases shows obvious effects on reducing ignition delays, and the dilution of He and Ar decreases the ignition delays by 58.0 and 84.0%, respectively. CH3 + O2 = CH3O + O and H + O2 = O + OH are the dominant conducive reactions in the methane-air ignition chemistry. Moreover, the dilution of inert gases has considerable influences on the normalization sensitivity coefficients, especially for the reaction of H + O2 = O + OH.

Three-dimensional (3D) SERS substrate with the denser “hotspots” is synthesized by the constriction of PDMS film decorated with sandwiched graphene@AgNPs@graphene (G@AgNPs@G) nanostructure. Graphene layers above and below the AgNPs are used to absorb molecules onto the “hotspots”, and prevent the oxidation of AgNPs in our design. PDMS films can be easily shrunk for 3D structures, causing advantages in enhancement ability and light-matter interaction. Benefiting from the above advantages, a detection limit of 10−14 M (CV) and enhancement factor (EF) of 3.9 × 109 were obtained in our experiment. Theoretical analyses (FDTD) were also used to study the enhancement mechanism. For practical purposes, in-situ detection of MG molecules on the fish surface and the label-free detection of DNA base of adenine (A) and cytosine (C) were also studied. The high enhancement factor, great sensitivity, reliability, and stability of substrate reasonably proved that it can be used as an excellent SERS substrate for biomolecular detection.

Compared to conventional chemical sensors, this paper presented a chemical sensor system with broad selectivity for a variety of molecules without any surface modification. The system consisted of an unmodified graphene foam as sensing element, an electrical resistance time domain detection system and a Support Vector Machine (SVM) identification system. The chemical sensor adopted 3D graphene foam to increase the reaction area and improve the sensitivity for detecting target molecules. The electrical resistance time domain detection system was constructed to record the graphene resistance curve in real time with different molecules. Based on the diverse shapes of the electrical resistance curves, SVM was used to extract features of each resistance curve and discriminate the corresponding molecules via pattern recognition of each resistance curve without any graphene modification. As validation experiments, six kinds of chemical molecules (chloroform, acetone, ether, toluene, ethyl benzene and methanol) have been tested. The discrimination accuracy for each molecule could be above 98% which showed a broad selectivity for a variety of molecules. Furthermore, through theoretical calculation with the first principle, we concluded that different band structures of the graphene caused by different molecules were the mechanism for the graphene chemical sensor system to discriminate chemical molecules with selectivity. This work may present a new strategy for research and application for graphene chemical sensors.

In this paper, the study of an electricity-fluorescence double-checking biosensor and detection system has been presented. The fabrication of the double-checking biosensor was performed by integrating graphene field effect transistors (GFETs) and biosensors based on fluorescence resonance energy transfer (FRET). For the construction of the GFETs as an electrical detection channel, graphene films grown by chemical vapour deposition (CVD) were transferred onto glass substrates. A probe aptamer modified with 6′-carboxy-fluorescein (6′-FAM) was immobilized on the graphene film of the GFETs via 1-pyrenebutanoic acid succinimidyl ester (PBASE) following which graphene oxide (GO) was used to quench the 6′-FAM on the probe aptamer to form the fluorescence detection channel. When the complementary target DNA (tDNA) was introduced into the GFETs, it replaced the GO and was hybridized with the probe aptamer leading to restoration of the fluorescence of the probe aptamer. At the same time, the tDNA hybridized with the probe aptamer leading to the formation of a new double conductive layer of the GFETs, which could change the conductivity of the GFETs. With a home-made double channel detection system, the dynamic hybridization process of the tDNA with the probe aptamer was achieved simultaneously through the electrical and fluorescence channels. Compared with conventional biosensors that are equipped with a single detection mode, this double-checking biosensor could be used to monitor the time and concentration-dependent DNA hybridization kinetics in a reliable and sensitive manner. Furthermore, this work also provides a new strategy for designing biosensors integrated with multiple sensing techniques.

Plasma assisted combustion provides possibilities for reducing ignition delays and controlling pollutant emissions. The zero-dimensional plasma and combustion models have been built up to numerically investigate the effects of the synergistic nanosecond repetitive pulsed (NRP) and DC discharge on the methane/air plasma assisted ignition. The synergistic discharge means exerting the low voltage DC discharge after the NRP discharge in one period of the discharge plasma. The simulation results indicate that the selective excitation of the vibrationally excited species N2(v), O2(v) and CH4(v) as well as the electronically excited species O2(a1Δg) and O2(b1Σg +) by the synergistic discharge is superior to that by the NRP discharge when the electron energy has been deposited into different molecular degrees of freedom. The plasma kinetic effect on the ignition enhancement is highly efficient since it can break though the threshold of the thermal effect. Both the kinetic effect and the thermal effect of the NRP discharge on ignition enhancement are relatively weaker than those of the synergistic discharge. Besides, reactions involved the N2 electronically excited species produce abundant O and H, which is conducive to the formation of the methane oxidation intermediates. e + O2 = e + O + O(1D) in the NRP discharge and e + O2 = e + O2(a1Δg) in the synergistic discharge play the crucial roles in the methane/air plasma enhance ignition, respectively.

Based on the fact that graphene films grown by Chemical Vapor Deposition (CVD) have unique electronic and optical properties concurrently, a Graphene Field-Effect Transistor (GFET) which combined electronics and fluorescence was proposed and fabricated in this work. Comparing conventional GFETs, fluorescent probes were dissolved in the electrolyte of GFETs. Consequently, the combined GFETs could not only be detected by common electrical method but also be detected by fluorescent method. A Double Read-Out System (DROS) was constructed to monitor the combined GFETs by electrical method and fluorescent method synchronously. The combined GFETs and DROS have been evaluated by sensing pH value of a Phosphate Buffered Solution (PBS). Both the electrical signal and the fluorescence intensity of the combined GFETs were recorded in real-time and synchronously. Through data processing, the combined effect of electrical signal and fluorescence intensity lead to a combined sensitivity that is higher than each isolate method. These results may provide a new feasible direction for CVD graphene FETs research.

Based on large-area multilayer graphene produced by chemical vapor deposition, an integrated field-effect transistor was fabricated in this work. A planar Au electrode was used as gate electrode integrated with graphene field-effect transistors (FETs) to generate perpendicular electrical fields between the gate and the graphene substrate. Graphene film was then transferred to cover indium tin oxide films which were used as drain and source electrodes. Via this process, the contact resistance between graphene and electrodes which were caused by polymethylmethacrylate (PMMA) residues in chemical vapor deposition process was almost eliminated. An electrical detecting system was designed to detect equivalent resistance of the FETs, which indicated that the performance of the FETs was associated with the width of conducting channel, the electrical field intensity between gate and graphene, and the ion concentration of electrolyte. Adenosine triphosphate (ATP) was selected as model electrolyte to verify the detecting system in this study. It was demonstrated that the integrated FETs could achieve high sensitivity to detect ATP as low as 10 pM and the equivalent resistance of the FETs showed a good correlation with ATP concentration from 10 pM to 10 μM. These results may provide a better direction and a common detecting platform for the design of integrated graphene FETs biosensors.

A portable and modularized fluorometer based on optical fiber was proposed in this work. The fluorometer included a light emitter diode (LED) light source module (LSM), a sample cell module (SCM), an optical-electrical converter module (OCM) and a signal process module (SAM). The LEDs in LSM were driven by a constant current source to provide stable exciting light with different wavelength. The OCM included a modularized optical filter and used a photomultiplier tube (PMT) to detect fluorescence signal. The SCM was used to locate sample cuvette and could be connected by optical fibers with the LSM and OCM. Via modularized design, the LSM and OCM could both selected and replaced based on different fluorescence dyes. In order to improve the detecting dynamic range of the fluorometer, the SAM could control the light intensity of LED source in LSM, to control the gain of PMT in OCM, and particularly, four channel signal acquisition circuits with different gain were constructed to collect fluorescence signal simultaneously. Fluorescein isothiocyanate (FITC) was selected as sample to test the fluorometer. The fluorometer has shown a high sensitivity with FITC concentration of 10ng/mL and presented a good linearity from 10 ng/mL to 10 μg/mL.