Upconversion luminescence nanosensor based on the inner filter effect for rapid detection of the anticancer drug...

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.