Sensitive Detection of Biomarker Using Multifunctional Aptamer-Modified Fluorescent E. coli O157:H7.

Highly sensitive quantification of biomarkers is essential for disease diagnosis, treatment monitoring, and prognosis evaluation. Recently, nanomaterial-based immunosensors have attracted increasing attention due to their high sensitivity. However, the preparation of nanomaterials is often complex, costly, and environmentally unfriendly. Here, we employed Escherichia coli O157:H7 as a nanoreporting probe, leveraging its dyeable genomic DNA to achieve direct signal amplification of target biomarkers. A multifunctional hairpin-shaped aptamer was designed to convert the target into measurable fluorescence signals from E. coli O157:H7 through bispecific binding and allosteric effects of the aptamer. Under optimized conditions, the E. coli O157:H7-based biosensor could detect 0.05 pg/mL prostate-specific antigen (PSA), with a linear relationship ranging from 0.1 to 50 pg/mL (correlation coefficient R2 = 0.988). The method also demonstrated excellent specificity and recovery rates (93-107%), confirming its applicability for real-sample detection. A small-scale clinical study illustrated that the serum PSA levels were significantly elevated in patients with polycystic ovary syndrome compared to healthy controls. Hence, low-abundance PSA analysis may expand the utility of PSA in female-related diseases.