Graphene quantum dots (GQDs) and carbon dots (CDs) are among the latest research frontiers in carbon-based nanomaterials. They provide interesting attributes to current electrochemical biosensing due to their intrinsic low toxicity, high solubility in many solvents, excellent electronic properties, robust chemical inertness, large specific surface area, abundant edge sites for functionalization, great biocompatibility, low cost, and versatility, as well as their ability for modification with attractive surface chemistries and other modifiers/nanomaterials. In this review article, the use of GQDs and CDs as signal tags or electrode surface modifiers to develop electrochemical biosensing strategies is critically discussed through the consideration of representative approaches reported in the last five years. The advantages and disadvantages arising from the use of GQDs and CDs in this context are outlined together with the still required work to fulfil the characteristics needed to achieve suitable electrochemical enzymatic and affinity biosensors with applications in the real world.

Novel core–shell Fe₃O₄@poly(dopamine) magnetic nanoparticles were prepared through an in situ self-polymerization method. The hybrid nanomaterial showed an average core diameter of 11 ± 3 nm and a polymer thin film thickness of 1.8 ± 0.2 nm. The core–shell nanoparticles were employed as solid supports for the covalent immobilization of horseradish peroxidase (HRP), and the resulting biofunctionalized magnetic nanoparticles were employed to construct an amperometric biosensor for H₂O₂. The enzyme biosensor showed a high sensitivity of 442.14 mA M⁻¹ cm⁻², a low limit of detection of 182 nM, a wide linear range from 6.0 × 10⁻⁷ to 8.0 × 10⁻⁴ M and high stability for 1 month.