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In this paper, ultra-low level selective detection of bovine serum albumin (BSA) has been demonstrated, based on chemically derived graphene i.e., reduced graphene oxide (RGO) nanosheets. The working principle of the sensor is based upon change in conductance of the RGO nanosheets with different concentration of BSA. The change in conductance is based on the charge transfer between BSA and functional groups of RGO. The morphological and structural characterizations of RGO nanosheets were carried out by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Raman spectroscopy is performed to further validate the interaction between RGO sensing layer and BSA molecules. Electrical impedance spectroscopy is performed to observe the impedance variation when BSA interacts with RGO. The sensor device exhibits sensitivity of 10 nA/pM. The lower limit of detection (LOD) of the sensor is found to be 1 pM and response time around 35 s, confirming very high sensitivity for BSA. All electrical (current-voltage) measurements were carried out at 2 V bias for low power operation. The sensor exhibits highest sensitivity at 30 °C and for RGO thickness ~4 nm. The RGO based sensor device is selective towards BSA when compared to proteins like L-Histidine, HSA, BHB and Biotin. Our results suggest that RGO based devices are promising for low-cost, portable and real time detection of BSA at room temperature. [ABSTRACT FROM AUTHOR]

A flexible room temperature ammonia gas sensor based on reduced graphene oxide (RGO) nanosheets has been fabricated on a transparent sheet using photolithography. The structural, morphological, and chemical properties of RGO sensing layer have been analyzed. The higher binding energy of hydroxyl groups with ammonia is utilized for ammonia adsorption, and the groups are tuned at low temperatures by processing graphene oxide. Charge transfer from ammonia to the hydroxyl groups in the RGO sheets is responsible for high response and selectivity of the sensor toward ammonia. Gas sensing characteristics of the sensor was analyzed at various temperatures and humidity levels. The sensor exhibited a selective response toward ammonia vapors among seven volatile organic compounds. The sensor showed a very high response of 930% toward 400-ppm ammonia at 25 °C and 45% relative humidity (RH) level. A quick response of 31 s and full recovery of the sensor after 500 s were recorded when exposed to 400-ppm ammonia. The operation of the sensor at only 1 V facilitates its usage in low-power applications. The sensor exhibited almost negligible deviation in response in the presence of humidity, making it humidity resistant. The flexibility of the sensor was tested by bending the sensor over the range 0°–120°, where the sensor performance started deteriorating after 90 bending. The sensor showed very high stability when tested for 75 days. Therefore, the RGO-based flexible device shows potential toward future commercial room temperature ammonia gas sensors. [ABSTRACT FROM AUTHOR]

Functionalized gold nanoparticles decorated reduced graphene oxide (RGO) sheets were used as an electrical sensing platform for highly selective and sensitive Hg2+ detection. RGO sheets were synthesized by reduction of graphene oxide (GO) produced by well-known Hummer’s method. RGO sheets were further decorated with thioglycolic acid (TGA) functionalized gold nanoparticles (GNPs) by simple chemical approach. Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Ultraviolet-visible (UV-Vis) absorbance analysis were done to confirm the presence of gold nanoparticles being attached to the RGO sheets. Transmission electron microscopy (TEM) was performed to analyze the shape and size distribution of gold nanoparticles on RGO sheets. TGA functionalization of GNPs was confirmed by Fourier transform infrared (FTIR) spectroscopic analysis. The RGO sheets as fabricated were observed to impart n-type nature to the sensing characteristics which was supported by Hall measurements. The sensor performance towards Hg2+ was investigated electrically in presence of other competitive contaminants. The sensor was found to be highly selective towards Hg2+ in presence of Pb2+, Cd2+ and As5+. The interaction of Hg2+ with the sensing layer was also studied using UV-Vis spectrophotometer. Our work suggests that RGO-GNP-TGA (RGT) hybrid structures are promising for low-cost, portable and real-time room temperature heavy metal ion detectors. [ABSTRACT FROM AUTHOR]

In this work, we report the performance of graphene oxide (GO) and Nafion composite as highly responsive humidity sensor. GO was synthesized using modified Hummers and Offeman method and was mixed with Nafion ionomer. The hybrid sensing layer was characterized using atomic force microscopy, field emission scanning electron microscopy, energy dispersive X-ray analysis and Fourier transform infrared spectroscopy. GO/Nafion composite solution was drop-casted on patterned gold electrodes on Si/SiO2 substrate to fabricate the sensor. GO/Nafion-based sensor was exposed to six different humidity level (40%–88%) and large response was obtained due to high proton conductivity of GO and Nafion. The sensor response varied from ∼1400 times (40% RH) to ∼18 000 times (88% RH). Our GO/Nafion based humidity sensor also exhibited very fast response and recovery times with excellent reproducibility and stability. The reported work shows that GO/Nafion is a promising candidate to be used in development of a modern highly sensitive humidity sensor. [ABSTRACT FROM PUBLISHER]

This paper explores the performance of graphene oxide (GO) as humidity sensor. GO was synthesized using modified Hummers and Offeman method, and the sensing layer was characterized using optical microscope, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The sensor devices were fabricated by drop-casting of GO on patterned gold electrodes on Si/SiO2 substrate. GO-based sensor was exposed to six different relative humidity (RH%), and the response of our sensor was found to be excellent due to large proton conduction. The sensor response varied from ∼180 times (40% RH) to ∼1200 times (88% RH). Our GO-based humidity sensor also showed ultrafast response and recovery times with extremely good repeatability. Also, the role of functional groups in humidity sensing was explored by fabricating the sensor devices by thermally reducing GO for different time durations. We believe GO could potentially be used to develop new-generation ultrasensitive humidity sensor. [ABSTRACT FROM PUBLISHER]

Successful isolation of single-layer graphene, the two-dimensional allotrope of carbon from graphite, has fuelled a lot of interest in exploring the feasibility of using it for fabrication of various electronic devices, particularly because of its exceptional electronic properties. Graphene is poised to save Moore's law by acting as a successor of silicon-based electronics. This article reviews the success story of this allotrope with a focus on the structure, properties and preparation of graphene as well as its various device applications. [ABSTRACT FROM AUTHOR]