Fluorescence Label‐Free Doxorubicin Sensor Using Polystyrene Sulfonate as a Synthetic Receptor in Whispering Gallery Mode Microresonators

Abstract The conventional quantification of Doxorubicin (DXR), a crucial anticancer drug, typically relies on complex and expensive techniques, limiting measurements beyond hospital settings and at different time intervals. Here, a label‐free fluorescence sensor is presented for DXR utilizing Whispering Gallery Mode (WGM) resonators. The resonators are based on fluorescent microparticles coated with a nanometer‐thick polystyrene sulfonate (PSS) layer serving as a synthetic receptor. The sensor demonstrates linear response for both position and width of the resonance peaks within the concentration range of 1–10 µg mL −1 of DXR of clinical interest. It also exhibits good selectivity against other chemotherapy drugs and can operate in complex biological fluids. The findings underscore the potential of WGM resonators as versatile multiparameter sensors for the sensitive and selective detection of small molecules, also in complex biological media.