A Portable Personal Glucometer-Based Immunoassay Platform for Horseradish Peroxidase-Related Biomarker Detection

Given the prevalent use of horseradish peroxidase (HRP) as an enzyme label in immunoassays, the practical importance of point-of-care testing for the portable identification of HRP-related biomarkers is evident. Accordingly, this study devised a portable immunoassay platform using a personal glucometer (PGM) to achieve rapid detection of HRP-related biomarkers. 3,3',5,5'-tetramethylbenzidine (TMB) and dopamine (DA) were used as signal-regulating substrates, and the assay principle was based on the HRP-mediated redox reaction. In the absence of HRP, TMB and DA directly reacted with [Fe(CN)₆]^3- on commercial glucose test strips, producing a strong PGM response. When HRP and H₂O₂ were present, HRP facilitated the oxidation of TMB to generate oxidized TMB, which further reacted with DA to produce oxidized products with weak reactivity toward [Fe(CN)₆]^3-, resulting in a decreased PGM signal. Conducting the quantitative assay involved measuring the HRP-dependent change in the PGM readout. Unlike many PGM immunoassays that rely on additional glucose-producing enzyme labels or amplified nanomaterial tags, the proposed method directly converts the signal of the conventional HRP label into a PGM-readable response. The sensing platform demonstrated a good linear response to HRP concentrations ranging from 156 to 625 ng/mL, with a low detection limit of 26 ng/mL. Interference experiments indicated good tolerance to the tested nonspecific proteins. The preliminary applicability of the platform was further evaluated by detecting cardiac troponin I (cTnI) and heparin-binding protein (HBP) in spiked serum samples, with recoveries ranging from 93.0% to 117.1% for cTnI and from 88.3% to 112.5% for HBP. In summary, the proposed platform provides a portable digital readout for HRP-linked immunoassays and reduces the dependence on dedicated readout instruments.