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.Keywords:programmed death-ligand 1;surface sandwich assay;DNA aptamer/antibody bioreceptor pair;surface plasmon resonance;tumor biomarker
An automated FO-SPR method is established for sPD-L1 quantification. • The EMP interface self-assembles on FO-probes via terminal cysteines. • The functionalized probes retained > 90% of their initial response after 4 weeks at 4 °C. • sPD-L1 detection is achieved in diluted human serum via Ab-AuNP amplification. An automated dip-probe fiber-optic surface plasmon resonance (FO-SPR) method was developed for soluble programmed death-ligand 1 (sPD-L1) quantification. The system employs a one-step self-assembled epitope-mimicking peptide (EMP) as the capture element. Through a terminal cysteine, the EMP binds directly onto the gold probe to form a capture interface, eliminating the need for chemical cross-linking. Coupled with an antibody-conjugated gold nanoparticle (Ab-AuNP) sandwich assay, the FO-SPR platform achieved a limit of detection of 20.5 ng/mL in diluted human serum with recoveries ranging from 93.7% to 106.6%. Independently prepared probes yielded intra- and inter-assay relative standard deviations below 6%, and EMP-functionalized probes retained more than 90% of their initial response after four weeks of storage at 4 °C. By pairing this peptide interface with a direct-immersion format that avoids fluidic clogging, this work delivers a practical and automated FO-SPR methodology for diverse bioanalytical applications. Download: Download high-res image (122KB) Download: Download full-size image
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