Fluorescent carbon dots for therapeutic drug monitoring: advances in sensing methotrexate and 6-mercaptopurine

Carbon dots (CDs) are an emerging class of nanomaterials distinguished by excitation-dependent photoluminescence, tunable surface chemistry, excellent biocompatibility, and scalable green synthesis. Advances in precursor design and single-step heteroatom doping have produced CDs with enhanced quantum yields and tailored electronic structures, expanding their use in bioanalytical applications, particularly sensing. A key application is therapeutic drug monitoring (TDM) of chemotherapeutics such as methotrexate (MTX) and 6-mercaptopurine (6-MP), which have narrow therapeutic windows and high interpatient pharmacokinetic variability, making precise monitoring essential to prevent toxicity or therapeutic failure. Conventional method, including HPLC, LC-MS, and immunoassays, are robust but costly, complex, and non-portable. CD-based fluorescent sensors, using quenching and enhancement mechanisms, offer low toxicity, facile functionalization, and tunable emission. These features support their potential integration with portable and point-of-care platforms, including smartphone-assisted systems, real-time, personalized TDM. By bridging nanomaterial innovation with clinical diagnostics, CDs provide a promising platform for next-generation, sensitive, and patient-centric TDM.