We report results of studies relating to development of an ultrasensitive, rapid, and label-free biosensor based on molybdenum trioxide (MoO3) anchored onto the reduced graphene oxide (RGO) for breast cancer detection. The human epidermal growth factor receptor-2 (HER-2) secreted in the serum of breast cancer patients was used as an analyte for the detection. The in situ growth of 1D MoO3 onto reduced graphene oxide (RGO), a 2D carbon substrate, was carried out via one-pot low-temperature hydrothermal synthesis. Subsequently, the surface conjugation of the monoclonal antibodies (anti-HER-2) onto the APTES/MoO3@RGO/ITO electrode was conducted via EDC-NHS covalent chemistry. The structural and morphological properties of the MoO3@RGO nanohybrid were investigated using electron microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopic techniques. The surface area of the MoO3@RGO nanohybrid determined via Brauner–Emmett–Teller analysis was found to be 14 times greater than that of the pristine MoO3. The binding kinetics and the electrochemical activity of the developed platform were determined by cyclic voltammetry, differential pulse voltammetry, and impedance spectroscopic techniques. This nanohybrid based immunosensor exhibited improved sensitivity (13 uA mLng–1cm–2) in a broad concentration range (0.001–500 ng mL–1) with a correlation coefficient of 0.98. The limit of detection of this MoO3@RGO nanohybrid based immunosensor was found to be 0.001 ng mL–1. The results obtained via the developed immunosensor for the quantification of serum HER-2 were validated using ELISA.

Nanotwin structures are observed in high-resolution transmission electron microscopy studies of cubic phase CdS quantum dots in powder form by chemical co-precipitation method. The deposition of thin films of nanocrystalline CdS is carried out on silicon, glass, and TEM grids keeping the substrates at room temperature (RT) and 200°C by pulsed laser ablation. These films are then subjected to thermal annealing at different temperatures. Glancing angle X-ray diffraction results confirm structural phase transitions after thermal annealing of films deposited at RT and 200°C. The variation of average particle size and ratio of intensities in Raman peaks I2LO/I1LO with annealing temperature are studied. It is found that electron-phonon interaction is a function of temperature and particle size and is independent of the structure. Besides Raman modes LO, 2LO and 3LO of CdS at approximately 302, 603, and 903 cm−1 respectively, two extra Raman modes at approximately 390 and 690 cm−1 are studied for the first time. The green and orange emissions observed in photoluminescence are correlated with phase transition.

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Gas sensor technology is widely utilized in various areas ranging from home security, environment and air pollution, to industrial production. It also hold great promise in non-invasive exhaled breath detection and an essential device in future internet of things. The past decade has witnessed giant advance in both fundamental research and industrial development of gas sensors, yet current efforts are being explored to achieve better selectivity, higher sensitivity and lower power consumption. The sensing layer in gas sensors have attracted dominant attention in the past research. In addition to the conventional metal oxide semiconductors, emerging nanocomposites and graphene-like two-dimensional materials also have drawn considerable research interest. This inspires us to organize this comprehensive 2020 gas sensing materials roadmap to discuss the current status, state-of-the-art progress, and present and future challenges in various materials that is potentially useful for gas sensors.

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