Graphene quantum dots (GQDs) have been widely investigated in recent years due to their outstanding physicochemical properties. Their remarkable characteristics allied to their capability of being easily synthesized and combined with other materials have allowed their use as electrochemical sensing platforms. In this work, we survey recent applications of GQDs-based nanocomposites in electrochemical sensors and biosensors. Firstly, the main characteristics and synthesis methods of GQDs are addressed. Next, the strategies generally used to obtain the GQDs nanocomposites are discussed. Emphasis is given on the applications of GQDs combined with distinct 0D, 1D, 2D nanomaterials, metal-organic frameworks (MOFs), molecularly imprinted polymers (MIPs), ionic liquids, as well as other types of materials, in varied electrochemical sensors and biosensors for detecting analytes of environmental, medical, and agricultural interest. We also discuss the current trends and challenges towards real applications of GQDs in electrochemical sensors.

Mesoporous silicas have properties that allow their wide chemical application, due to the large amount of silanol groups on their walls. The possibility of introducing functional groups inside and on the surface of their pores becomes viable the use of these functionalized mesoporous materials for the adsorption of metal ions. Cooper ions are essential for vital functions, but in high concentrations, they are responsible for causing problems to the human organism. Therefore, it is important to monitor the species in different media, such as sugar cane spirit. Mesoporous materials type MCM-41 functionalized were obtained by three different methods using direct (in situ) and indirect (post-synthesis) routes. The mesoporous materials have exhibited properties according to the IUPAC classification. Modified carbon paste electrodes (MCPEs) were prepared by immobilizing the synthesized materials for Cu2+ analysis. The modified electrode obtained by the immobilization of functionalized mesoporous R2 (MCPE/R2) presented the best sensitivity for Cu2+ detection. Under optimum experimental conditions, the MCPE/R2 exhibited a linear range in between 0.99 and 11.80 μmol L-1, a sensitivity based on the Limit of Detection (LOD) of 0.50 μmol L-1and Limit of Quantification (LOQ) of 0.99 μmol L-1, precision (DPRmáx) equals to 10.6% and recovery of 92.2%. The developed method proved to be efficient for Cu2+ determination in sugar cane spirit and the accuracy of the results were comparable to those obtained by AAS.