Graphene Quantum Dots (GQDs) are low dimensional carbon based materials with interesting physical, chemical and biological properties that enable their applications in numerous fields. GQDs possess unique electronic structures that impart special functional attributes such as tunable optical/electrical properties in addition to heteroatom-doping and more importantly a propensity for surface functionalization for applications in biosensing and bioimaging. Herein, we review the recent advancements in the top-down and bottom-up approaches for the synthesis of GQDs. Following this, we present a detailed review of the various surface properties of GQDs and their applications in bioimaging and biosensing. GQDs have been used for fluorescence imaging for visualizing tumours and monitoring the therapeutic responses in addition to magnetic resonance imaging applications. Similarly, the photoluminescence based biosensing applications of GQDs for the detection of hydrogen peroxide, micro RNA, DNA, horse radish peroxidase, heavy metal ions, negatively charged ions, cardiac troponin, etc. are discussed in this review. Finally, we conclude the review with a discussion on future prospects.

Poly(ethylene oxide) (PEO)-based composite polymer electrolytes (CPEs) containing the amine-functionalized, zirconium-based metal–organic framework @silica (UiO-66-NH₂@SiO₂) and lithium, LiN(CF₃SO₂)₂ salt (LiTFSI) are prepared using a simple hot press method. The electrochemical properties such as compatibility of the electrolyte with the Li metal anode, Li transference number, and ionic conductivity are investigated for the different systems containing different relative concentrations of the additives. The incorporation of UiO-66-NH₂@SiO₂ in the PEO-LiTFSI matrix not only enhanced ionic conductivity by one order of magnitude but also offered better compatibility and suppressed the formation of lithium dendrites appreciably. X-ray photoelectron spectroscopy studies on post-cycled materials revealed the formation of lithium alkoxide (RO–Li) on the cathode and Li₂O on the anode. The coin cell (2032-type) consisting of LiFePO₄/CPE/Li with UiO-66-NH₂@SiO₂ as filler provided a discharge capacity of 151 mA h g^–1 at 0.1 C-rate at 60 °C, measurably higher than control experiments utilizing SiO₂ and UiO-66-NH₂. The notable enhancement of electrochemical properties when incorporating the UiO-66-NH₂@SiO₂ at the CPE was attributed to formation of more uniform ion conduction pockets and channels within the PEO matrix, facilitated by the presence of the microporous UiO-66-NH₂@SiO₂. The enhanced distribution of microporous channels, where Li ions are assumed to percolate through within the matrix, is assumed to desirably reduce formation of Li dendrites by increasing diffusion channels and therefore reducing crystallization and growth of dendrites at the electrode surface.