Rapid self-assembly and signal amplification based on photoactive Z907 for detecting colorectal cancer biomarker vascular endothelial growth factor.

This paper introduces a continuous transient photoelectrochemical (PEC) biosensing strategy for rapid anti-vascular endothelial growth factor (VEGF) immobilization and quantification of VEGF in serum for colorectal cancer (CRC) diagnosis. A gold electrode modified with cis-bis(isothiocyanato) (2,2'-bipyridyl-4,4'-dicarboxylato) (4,4'-di-nonyl-2'-bipyridyl)ruthenium (II) (Z907) (Au/Z907) was used. By optimizing the electrolyte composition and applied potential under continuous high-frequency light switching, stable transient photocurrent bands were produced, enabling real-time sensing with intrinsic signal amplification and improved precision. Under optimized conditions (1 mM phosphate-buffered saline, 0.15 V bias, 25 W white-light illumination, and 2 Hz modulation for 4 min), anti-VEGF antibodies were rapidly immobilized on the Au/Z907 electrode. After blocking nonspecific binding sites with bovine serum albumin, the biosensor was used to quantify serum VEGF in clinical samples obtained in Taiwan from healthy donors (n = 11) and patients with tubular adenoma (n = 12), serrated adenoma (n = 11), untreated CRC (n = 11), and treated CRC (n = 3). Comparison with a commercial enzyme-linked immunosorbent assay kit revealed no significant differences among the five groups (p > 0.05, Student's t-test), validating the accuracy of the proposed platform. Receiver operating characteristic analysis further demonstrated excellent diagnostic performance. Overall, this work presents a cost-effective and instrumentation-light PEC biosensing platform capable of rapid antibody immobilization, calibration, and serum analysis on a single electrode, with potential applications in point-of-care testing in community hospitals and resource-limited settings.