Fluorescence Probe for the Detection of Programmed Death-Ligand 1 (PD-L1) Using Antibody-Conjugated Silver Nanoclusters and MnO₂ Nanosheets

In this study, a dual-mode fluorescence sensing platform was developed for the ultrasensitive and noninvasive detection of programmed death-ligand 1 (PD-L1), an important biomarker in cancer immunotherapy. The system integrates antibody-conjugated bovine serum albumin-stabilized silver nanoclusters (PD-L1 Ab@AgNCs) with manganese dioxide (MnO2) nanosheets as an effective quencher. The bioconjugate exhibits red fluorescence with a quantum yield of 1.85%. MnO2 nanosheets possess a high surface area and strong absorbance within the excitation and emission range of AgNCs, enabling fluorescence quenching through both the inner filter effect (IFE) and Förster resonance energy transfer (FRET), with an energy transfer efficiency of 62.7%. Upon PD-L1 recognition, the fluorescence is selectively restored due to displacement of MnO2, resulting in a turn-on signal proportional to the target concentration. The probe achieved a limit of detection of 0.44 pg/mL and a linear range of 1.98–196.78 pg/mL. The probe maintained accuracy in complex biological matrices, including saliva, serum and urine, with recovery values ranging from 96% to 108%. High specificity was confirmed by minimal interference from coexisting biomolecules. This approach offers a robust, label-free and noninvasive method for PD-L1 detection with potential for clinical diagnostics and point-of-care applications.