Miniaturization, portability and lab-on-chip devices, like many features of the sensor, are perceived areas of work by researchers. Advanced nanomaterials like graphene, graphene oxide, reduced graphene oxide and their different forms, such as nanosheet, nanorods, nanotubes, nanoflower, nanodots, have the potential to demonstrate high-performance electrochemical sensitivity and selectivity. In theranostic (diagnostics and biomedicine) and disease monitoring, graphene and composite-based sensors have transformed these areas with new techniques and approaches. It will not be an exaggeration to include graphene as a prominent nanomaterial, which changes the view of nano techniques in sensing. The unique physicochemical properties of graphene have made it worthy of use for nanosensor technology. In this review, the authors inspected recent developments in graphene-based sensing performance and progress in its commercial validations. Herein, we also inculcate some basic aspects of sensors such as biosensors, chemisensor, and physical sensors with their recent developments and critical analysis. We also included the progress in biosensors in health monitoring, care management and prepared a consolidated framework.

Current developments in the emerging field of nanotechnology enables researchers to synthesize different types of quantum dots for biomedical applications. Carbon quantum dots (CQDs) has gained special attention due to their unique physicochemical properties, like high quantum yield and electron density. Doping of CQDs with nitrogen is a way forward to enhance their properties, which can be achieved by various approaches using wide range of nitrogen sources. The surface state of CQDs can be passivated by the nitrogen doping, which changes their energy gap width and electron density that aids in modulating their quantum yield to the higher level than without doping. The nitrogen-doped CQDs (N-CQDs) exhibit a broad range of properties, such as fluorescence, high quantum yield, easily accessibility and low cytotoxicity etc., that make them a suitable agent for variety of applications in the field of medical sciences. Due to these outstanding features of N-CQDs, it can be used for various purposes such as imaging, sensing, photocatalysis, solar cells, etc. In this review, a comprehensive synthesis methodology of N-CQDs is provided, along with its in-vitro and in-vivo bioimaging applications. This review will help in analysis of contemporary advances in the development of N-CQDs as unique and versatile nanomaterial so as to derive fruitful result for further improvement of the properties of N-CQDs for futuristic exploration in nanoscience. In this review, the recent progress in N-CQDs-based bioimaging has been summarized during the last 5 years.