Electrochemical strategies for decoding serotonin using advanced carbonaceous and 5(th) generation materials: A comprehensive review.

Carbonaceous materials are placed in the category of advanced and future materials for their very unique physicochemical attributes like tuneable electronic, electrical and optical properties associated with good chemical reactivity, biocompatibility and high surface to volume ratio that make them good candidates for various device applications including biosensors. Recently, such carbonaceous materials and their composites are being widely used as the electrode materials for enzyme-free electrochemical detection of various bioanalytes. Among the bioanalytes, the neurotransmitters are known to play crucial roles in maintaining proper balance in the human nervous systems. However, there are many challenges like selectivity, sensitivity and rapidity; that are normally faced during the detection of such neurotransmitters using the conventional enzymatic way. Electrochemical biosensors made up of advanced carbonaceous materials could be a single-key answer to all such challenges. Serotonin, a catecholamine group neurotransmitter, also known as the "happy hormone", is known to control human emotions. So, real-time monitoring of its level in human serum carries immense importance, however; it comes with various challenges. This review article covers the developments of advanced carbonaceous, as well as, the 5th generation materials like Mxenes and related composites in the enzyme-free electrochemical sensing of serotonin since the inception of such materials in electrochemical biosensing. A detailed literature review exhibited that, impressive results, like very low limit of detection (LoD) of 8.0 nM could be achieved using multiwalled carbon nanotube (MWCNT) based electrodes, whereas, nitrogen incorporated graphene quantum dot (N-GQD) modified electrodes can help to reach a notably high sensitivity of 24.0 μAμM.cm. Again, carbon spheres (CS) have been established as a good candidate to bring a balance between LoD (4.0 nM) and sensitivity (5.5 μAμM.cm) in combination with metal oxide electrode.