Carbon Quantum Dots: Green Nanobiomaterials in the Future of Biosensing

Since their casual discovery in 2004, carbon quantum dots (CDs), a new class of fluorescent carbonaceous nanomaterials, have become object of great research interest in the scientific community because of their peculiar properties, which make them suitable materials for application in numerous fields, including chemo- and biosensing, fluorescence imaging, and drug delivery. In fact, they exhibit an excellent intrinsic fluorescence, which can be tuned from the visible to NIR, their surface is rich in functional groups, which enable their functionalization with various receptor and functionalities (i.e., enzymes, etc.); they are also characterized by extremely low toxicity and excellent biocompatibility useful for biological applications in the real world. On the other hand, CDs are also expected to reduce the cost of biosensors by replacing both the noble metal substrates and the well-known quantum dots based on metal calcogenides. In fact, their synthesis is based on simple and sustainable approaches that could employ cheap and "greener" starting materials coming from biomass or agro-industrial waste. In this context, the present chapter will focus on CDs as new sustainable nano-materials for biosensors applications, with a particular care to optical and electrochemical biosensors. A short overview on the green synthesis strategies of CDs and on their optical properties is also presented.