Wide-Range SPRi Sensors Based on Aptamer/sPD-L1/anti–PD-L1 Sandwich and AuNPs Enhancement for Ultrasensitive Detection of sPD-L1

Soluble programmed death-ligand 1 (sPD-L1) levels vary widely among different stages of tumor development, so the direct quantification of sPD-L1 as a cancer biomarker is useful in cancer diagnosis, prognosis and therapeutic assessment. There is an urgent need for an sPD-L1 detection method with a broad detection range and high sensitivity for monitoring cancer progression and evaluating the effectiveness of immunotherapy in real time. Herein, we have reported an enzyme-free, label-free surface plasmon resonance imaging (SPRi) sensor based on an aptamer/sPD-L1/anti–PD-L1 sandwich structure with gold nanoparticle (AuNP) signal enhancement for the ultrasensitive quantitative measurement of sPD-L1 for the first time. The gold chip of the SPRi sensing platform was modified by DNA aptamers, sPD-L1 was specifically adsorbed on the surface of a DNA aptamer-modified gold chip and then coupled with anti–PD-L1. Thus, the detection of sPD-L1 at different concentrations was realized through the formation of an aptamer/sPD-L1/anti–PD-L1 sandwich structure. We also enhanced the SPR signal via AuNPs to further improve sensor sensitivity. The SPRi sensor is able to measure sPD-L1 within a linear range of 50 pM–10 nM and 100 fM–50 pM, and the minimum detection limit is 19 fM. The sensor is designed to be widely applicable, with better accuracy and reliability for more application scenarios. The prepared SPRi sensor shows great potential in improving the sensitivity of detecting sPD-L1. The proposed method demonstrates the excellent performance of the SPRi sensor and provides a possibility for the establishment of effective clinical assay methods in the future.