Perioperative myocardial infarction (PMI) is a common complication of non-cardiac surgery and monitoring a PMI marker, cardiac troponin I (cTnI), is helpful for the early detection of PMI. However, there is no existing biosensor for continuous measurement of cTnI. Addressing this challenge, we developed a surface plasmon-enhanced fluorescence (SPF) immunosensor for the semi-continuous measurement of cTnI. The sensor system relied on attenuated total reflection with Kretschmann configuration at the wavelength of 633 nm. An Au substrate was modified with a robust scaffold protein fused with protein G that enabled immobilization and repeated use of a capture antibody. The cTnI was measured by a sandwich assay with a fluoresce-labeled detection antibody. We also fabricated a light pipe flow-cell to collect the fluorescence efficiently. As a result, the dynamic range of the SPF immunosensor to cTnI was 3.9–100 ng/mL, and the LOD was 0.98 ng/mL. The sensor showed output only from samples containing cTnI, indicating the high selectivity. The sensor surface was regenerated by glycine-HCl (pH 2) solution, and the high reproducibility of the output (C.V. = 1.8%) was obtained in five repeated measurements of cTnI. These results indicated the potential of the SPF immunosensor for cTnI monitoring.
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