What works and what doesn’t when graphene quantum dots are functionalized for contemporary applications?

Graphene Quantum Dots (GQDs) is the breakthrough and the most known material for their optoelectronic properties. The richness of electrons promotes the GQDs to the next level in a wide variety of applications. An extensive array of domains includes GQDs for several applications such as agriculture, bio-medical, device fabrication, sensor, energy storage, water desalination, environmental remediation, and many more. The functionalization of GQDs enhances their biocompatibility, which can be a substitute for many traditionally available materials which are toxic and hazardous like metal quantum dots and dyes in myriad fields such as biotechnology, immunology, biochemistry, analytical, and diagnostic departments. The nanoscale morphology of the GQDs can alter the device structure and simplify functionality. Functionalized GQDs offer higher efficiency within a time which aids their potential usage in wearable and portable sensor developments. Though GQDs are functionalized with numerous functional materials, biomolecules (carbohydrates, lipids, nucleic acids, and proteins), heteroatoms (S, N, B, Cl, F, etc.,), metals (Au, Ag, metal oxides (copper oxide, iron oxide, bismuth oxide, etc.,), amino acids (glycine, histidine, cysteine, valine, etc.,), polymers (polyaniline, polypyrene, polypyrrole, poly arginine), drugs (penicillamine, folic acid, dopamine, glucose, ascorbic acid), dyes (rhodamine, methylene blue) and many more, the strategies of functionalization are unspoken and need to explore in detail to choose them for the desired applications. Functionalization strategies could be the major factor in altering the resultant functionalized GQDs and their properties. In this review, we have explored several functionalization strategies of GQDs and elucidated their applications in different domains. The elucidation of the functionalization strategies will enlighten the young researchers in availing the correct functionalization method for the opted functional group elements. This will lead to achieving the resultant material with enhanced and tuned properties for the anticipated applications in prevalent fields.