Not All Heroes Wear Capes—Some Just Glow: Exploring Carbon Dots as Nanoagents Against COVID-19

The coronavirus disease (COVID-19) pandemic highlighted critical limitations in ongoing diagnostic and therapeutic strategies, underscoring the urgent need for alternative and complementary approaches. Carbon dots (CDs) represent a novel class of fluorescent carbon-based nanomaterials with increased research interest owing to their enhanced biocompatibility, tunable photoluminescence, aqueous solubility, and rich surface chemistry. This review outlines current approaches in the diagnosis and treatment of COVID-19, along with the main structural, physicochemical, and biological features of CDs. Recent advances in the application of CDs as biosensing and antiviral nanomaterials against SARS-CoV-2 are critically discussed with an emphasis on the influence of synthetic routes, precursor compounds, heteroatom doping, surface functionalization, and purification strategies on their optical behavior and biological performance. CD-based biosensors mainly rely on fluorescence-sensing strategies, exploiting changes in photoluminescence intensity or energy-transfer processes upon recognition of viral targets. Electrochemical approaches are also investigated, highlighting the role of CDs as electrode modifiers to enable sensitive immunodetection in complex biological samples. Apart from diagnosis, the therapeutic potential of CDs is underscored by inhibiting viral entry, replication, disrupting cell membranes, or modulating oxidative stress. Finally, current limitations, challenges, and future perspectives regarding mechanistic understanding, synthesis parameters, biodistribution, and clinical translation are discussed, demonstrating the potential of CDs as novel “shiny weapons” against COVID-19, combining therapeutic and diagnostic functions.