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Electroanalytical and optical techniques are widely used in the development of nanomaterials-based sensor platforms. These techniques have a quick response, high sensitivity, and selectivity. Electroanalytical and optical techniques are widely used in the development of nanomaterial-based sensor platforms. These sensors must be able to detect biomarkers, pathogens, toxins, and pharmaceuticals in biological matrices associated with cardiovascular disease, cancer, and neurodegenerative diseases. Considering these pathophysiologies, numerous investigations have been undertaken to develop sensors for early diagnosis and treatment, utilizing nanomaterials such as quantum dots. Graphene quantum dots (GQDs), which are ideally nanometer-sized graphene fragments, have recently received increased attention due to their excellent physicochemical properties such as fast electron mobility, photostability, water solubility, biocompatibility, high specific surface area, and nontoxicity. Apart from the properties mentioned above, GQDs provide π–π interactions, electrostatic, and covalent interactions with an analyte, and ease of synthesis as well as the ability to combine with other nanomaterials, which have enabled their use in various sensing platforms. This review summarizes recent advances in GQDs-based nanocomposites for sensor applications, with a focus on electroanalytical and optical techniques, as well as current challenges and future prospects. [ABSTRACT FROM AUTHOR]

A simple and cost-effective electrochemical synthesis of carbon-based nanomaterials for electrochemical biosensor is of great challenge these days. Our study describes a single-step electrochemical deposition strategy to prepare a nanocomposite of electrochemically reduced graphene oxide (ErGO), multi-walled carbon nanotubes (MWCNTs), and polypyrrole (PPy) in an aqueous solution of pH 7.0 for dopamine (DA) detection. The ErGO/MWCNTs/PPy nanocomposites show enhanced electrochemical performance due to the strong π–π* stacking interactions among ErGO, MWCNTs, and PPy. The efficient interaction of the nanocomposites is confirmed by evaluating its physical and electrochemical characteristics using field-emission scanning electron microscopy, Raman spectroscopy, electrochemical impedance spectroscopy, cyclic voltammetry, and amperometry. The deposited nanocomposites are highly stable on the substrates and possess high surface areas, which is vital to improve the sensitivity and selectivity for DA detection. The controlled deposition of the ErGO/MWCNTs/PPy nanocomposites can provide enhanced electrochemical detection of DA. The sensor demonstrates a short time response within 2 s and is a highly sensitive approach for DA detection with a dynamic linear range of 25–1000 nM (R2 = 0.999). The detection limit is estimated to be 2.3 nM, and the sensor sensitivity is calculated to be 8.96 μA μM−1 cm−2, with no distinct responses observed for other biological molecules. [ABSTRACT FROM AUTHOR]