Upconversion luminescence nanosensor based on the inner filter effect for rapid detection of the anticancer drug 6-mercaptopurine

An upconversion luminescence (UCL) nanosensor was developed based on the inner filter effect (IFE) mechanism. This involved the interaction between polyacrylic acid (PAA)-coated NaYF₄:Yb/Er upconversion nanoparticles (UCNPs) and the oxidation product (oxDPD) of N, N-diethyl-p-phenylenediamine (DPD). DPD was oxidized to oxDPD through the combined action of H₂O₂ and horseradish peroxidase (HRP). As a result, there was a large overlap between the UCL spectrum (545 nm) of Er-doped UCNPs and the UV-Vis absorption spectrum (552 nm) of oxDPD, which subsequently caused the quenching of UCL via the IFE. When 6-mercaptopurine (6-MP) reacted with oxDPD, the absorption intensity of the resulting product at 552 nm decreased, thereby restoring the intensity of UCL. Therefore, 6-MP can be sensitively detected according to the intensity change of UCL. The resulting detection range and the limit of detection (LOD) were 0-15 μg·mL^-1 and 0.56 μg·mL^-1, respectively. The "off-on" UCL nanosensor designed for the detection of 6-MP exhibits the advantages of easy operation, rapid response time, and high sensitivity, demonstrating promising potential for application in clinical monitoring.