Hao Zhang

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.

A convenient one-pot strategy was adopted to fabricate Cu-4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) nanosheets through the coordination of HEPES with copper ions under alkaline conditions, and the obtained nanosheets possessed dual laccase-mimetic and oxidase-mimetic activities for phenolic pollutant analysis and show potential for dye decolorization/removal. The Cu-HEPES nanosheets displayed significant dual enzyme-mimetic activities, effectively catalyzing the oxidation conversion for phenolic compounds, specifically 2,4-dichlorophenol (2,4-DCP), to yield quinone imine products characterized by a unique absorption signal at 500 nm. Meanwhile, Cu-HEPES nanosheets also facilitated the conversion of 3,3′,5,5′-tetramethylbenzidine to yield a yellow-green substance with a distinctive absorption signal at 458 nm. The Cu-HEPES nanosheets displayed a satisfactory affinity (K_m = 23.2 μM) for 2,4-DCP, facilitating its use in accurately detecting 2,4-DCP (linear range from 3.3 to 16.6 µM) with a detection limit of 0.3 µM. Subsequently, the devised colorimetric sensing platform was applied to measure 2,4-DCP levels in real tap water samples, yielding satisfactory spiked recoveries ranging from 92.7% to 106.9%. Finally, the synthesized Cu-HEPES nanosheets were preliminarily evaluated for the simultaneous decolorization/removal of malachite green and Congo red, suggesting their potential applicability in aqueous systems containing multiple organic dyes.

A novel, cost-effective, label-free biosensing strategy has been established for real-time quantification of alkaline phosphatase (ALP) activity, integrating the Tyndall effect with smartphone imaging technology. This method utilizes a handheld laser diode to probe the enzyme-triggered in situ assembly of Cu-guanosine monophosphate (Cu-GMP) coordination polymers, which exhibit tunable Tyndall scattering properties. In the absence of ALP, Cu²⁺ ions chelate with GMP to form Cu-GMP coordination polymers, generating an intense Tyndall effect. Conversely, ALP-mediated hydrolysis of GMP disrupts the formation of Cu-GMP coordination polymers, resulting in diminished light scattering. The intensity of the Tyndall effect is directly proportional to the concentration of Cu-GMP coordination polymers, which in turn correlates with ALP activity levels. A comprehensive investigation of experimental parameters was conducted, including pH, incubation temperature, GMP concentration, incubation time, synthesis duration, and CuSO₄ concentration. Under optimized conditions, the developed smartphone-assisted colorimetric assay enables the detection of ALP activity within the range of 0.375–3.75 U/mL, with a limit of detection of 0.184 U/mL. The application of this method to serum samples yielded recovery rates ranging from 102.6% to 109.0%. In summary, this smartphone-based colorimetric platform offers a portable and versatile approach for instrument-free detection of ALP activity, with potential applications in point-of-care diagnostics and resource-limited settings.

Point-of-care testing (POCT) is a contemporary diagnostic approach characterized by its user-friendly nature, cost efficiency, environmental compatibility, and lack of reliance on professional experts. Therefore, it is widely used in clinical diagnosis and other analytical testing fields to meet the demand for rapid and convenient testing. The application of POCT technology not only improves testing efficiency, but also brings convenience and benefits to the healthcare industry. The personal glucose meter (PGM) is a highly successful commercial POCT tool that has been widely used not only for glucose analysis, but also for non-glucose target detection. In this review, the recent advances from 2020 to 2024 in non-glucose target analysis for PGMs as POCT devices are summarized. The signal transduction strategies for non-glucose target analysis based on PGMs, including enzymatic transduction, nanocarrier transduction (enzyme or glucose), and glucose consumption transduction are briefly introduced. Meanwhile, the applications of PGMs in non-glucose target analysis are outlined, encompassing biomedical, environmental, and food analysis, along with other diverse applications. Finally, the prospects of and obstacles to employing PGMs as POCT tools for non-glucose target analysis are discussed.

As one of the biomarkers of coagulation system-related diseases, the detection of thrombin is of practical importance. Thus, this study developed a portable biosensor based on a personal glucometer for rapid detection of thrombin activity. Fibrinogen was used for the detection of thrombin, and the assay principle was inspired by the blood coagulation process, where thrombin hydrolyzes fibrinogen to produce a fibrin hydrogel, and the amount of invertase encapsulated in the fibrin hydrogel fluctuates in accordance with the activity of thrombin in the sample solution. The quantitative assay is conducted by measuring the amount of unencapsulated invertase available to hydrolyze the substrate sucrose, and the signal readout is recorded using a personal glucometer. A linear detection range of 0–0.8 U/mL of thrombin with a limit of detection of 0.04 U/mL was obtained based on the personal glucometer sensing platform. The results of the selectivity and interference experiments showed that the developed personal glucometer sensing platform is highly selective and accurate for thrombin activity. Finally, the reliability of the portable glucometer method for rapid thrombin detection in serum samples was investigated by measuring the recovery rate, which ranged from 92.8% to 107.7%. In summary, the fibrin hydrogel sensing platform proposed in this study offers a portable and versatile means for detecting thrombin using a personal glucometer. This approach not only simplifies the detection process, but also eliminates the need for large instruments and skilled operators, and substantially reduces detection costs.