Metal-Organic Framework-Mediated Bioorthogonal Reaction to Immobilize Bacteria for Ultrasensitive Fluorescence Counting Immunoassays

Ultrasensitive quantification of protein biomarkers has significant implications in disease diagnosis. Herein, we report a fluorescent bacteria counting immunoassay (FBCIA) strategy for protein biomarker detection based on a cascade signal conversion and amplification strategy including the copper metal-organic framework (Cu-MOF)-mediated Cu(I)- catalyzed azide-alkyne cycloaddition (CuAAC) for fluorescent bacteria immobilization that converted the concentration of target protein to countable bacterial number and the further self-proliferation of bacteria to amplify the detectable bacterial number. The developed low-background and enzyme-free cascade methodology achieved highly sensitive detection of carcinoembryonic antigen (CEA) and prostate-specific antigen (PSA) with detection limits down to 0.8 pg/mL and 64.5 fg/mL, respectively. On top of that, we also developed a smartphone device for visualizing individual bacteria and point-of-care counting of the resulting bacteria for the detection of clinical samples. The good consistency between FBCIA and clinical enzyme-linked immunosorbent assay (ELISA) validated the high reliability and promising potential of our developed platform in clinical applications.

Automated summary

In this study, a fluorescent bacteria counting immunoassay (FBCIA) strategy was developed for ultrasensitive quantification of protein biomarkers. The strategy involved a cascade signal conversion and amplification strategy, which enabled the conversion of target protein concentration to countable bacterial number. The developed platform demonstrated highly sensitive detection of CEA and PSA with low detection limits, and a smartphone device was also developed for point-of-care counting. The good consistency between FBCIA and clinical ELISA validated the high reliability and promising potential of the platform in clinical applications.