Naked-Eye Coulometric Sensor Using a Longitudinally Oriented Ag Band Electrode in a Microfluidic Channel

Efficient Nanozyme-Triggered Pressure Sensor for Point-of-Care Immunoassay: Visual Sensing and Time Readout Device

Point-of-care testing (POCT), with its portability and high sensitivity, is an analytical device for rapid on-site sensing and detection. In this study, a POCT device was designed for the portable detection of illegal additives by integrating a coil device that can visually sense color distance and a two-electrode electrochemical system. Real-time monitoring of pressure changes was achieved by driving CeO₂@Pt/Au nanoparticle (NP)-labeled antibodies into a competitive immunoreaction, in which CeO₂ and Pt/Au synergistically catalyzed the production of large amounts of O₂ from H₂O₂, leading to a significant increase in gas within the closed chamber. Attractively, the coil device converted the pressure stimulus into visually readable change in distance for semi-quantitative detection of the target substance, while the electrical signal output caused by the changes of the solution around the electrodes achieved accurate and reliable quantification of the target. In addition, the proposed dual-mode pressure immunoassay device has acceptable selectivity, stability, and reproducibility. Herein, this portable device, which enables target concentration readings by converting pressure into multiple signals, provides an effective way to visualize POCT assays in resource-limited areas.

Platinum Nanozyme-Triggered Pressure-Based Immunoassay Using a Three-Dimensional Polypyrrole Foam-Based Flexible Pressure Sensor

This work describes a novel and portable pressure-based point-of-care (POC) testing strategy for the sensitive and rapid detection of carcinoembryonic antigen (CEA) via a flexible pressure sensor constructed by three-dimensional (3D) polypyrrole (PPy) foam. Initially, platinum nanoparticles (PtNPs) were conjugated to the detection antibodies, which were used to form sandwich-type immunocomplexes with targets and capture antibodies in the reaction cell. Then, the carried PtNPs catalyzed the dissociation of hydrogen peroxide (H₂O₂) for the generation of oxygen (O₂) in a sealed device, translating the biomolecule recognition event into gas pressure. With the increase of pressure, a flexible pressure sensor with 3D polypyrrole foam as the sensing layer was used to sensitively monitor the pressure variations in this system. Thus, the concentration of the target could be quantitatively determined by the pressure response. Under optimal conditions, the pressure-based immunosensor showed good sensing performance for CEA in the dynamic working range from 0.2 to 60 ng/mL with a detection limit of 0.13 ng/mL. The reproducibility, specificity, and accuracy compared with commercial enzyme-linked immunosorbent assay (ELISA) kit were also acceptable. Therefore, this work provides a promising approach for developing portable and sensitive POC testing in the future.

Integrating Electrochemical and Colorimetric Sensors with a Webcam Readout for Multiple Gas Detection

Multisensor detectors have merits of low cost, compact size, and capability of supplying accurate and reliable information otherwise hard to obtain by any single sensors. They are therefore highly desired in various applications. Despite the advantages and needs, they face great challenges in technique especially when integrating sensors with different sensing principles. To bridge the gap between the demand and technique, we here demonstrated an integration of electrochemical and colorimetric sensors with a webcam readout for multiple gas detection. Designed with two parallel gas channels but independent sensor cells, the dual-sensor detector could simultaneously detect each gas from their gas mixture by analysis of the group photo of the two sensors. Using Ag electro-dissolution as reporter, the bipolar electrochemical sensor achieved quantitative analysis for the first time thanks to application of pulse voltage. The sacrificed Ag layer used in the bipolar electrochemical (EC) sensor was recycled from CD, which further decreased the sensor cost and supplied a new way of CD recycling. The EC O₂ sensor response, edge displacement of Ag layer due to electrochemical dissolution, has a linear relationship with O₂ concentration ranging from 0 to 30% and has good selectivity to common oxidative gases. The colorimetric NO₂ sensor linearly responded to NO₂ concentrations ranging from 0 to 230 ppb with low detection limit of 10 ppb, good selectivity, and humidity tolerance. This integration method could be extended to integrating other gas sensors.

Electrochemiluminescence bipolar electrode array for the multiplexed detection of glucose, lactate and choline based on a versatile enzymatic approach

A simple, efficient and versatile biosensing platform capable of the multiplexed detection for glucose, lactate and choline was developed by the integration of bipolar electrochemistry and electrochemiluminescence (ECL) imaging. The sensing bipolar electrodes (BPEs) were simply modified via a one-step method adaptable to different enzymes. The biorecognition event happening between the substrate and the corresponding enzyme could be directly reported by the ECL emitted on the same pole from luminol and in situ generated H₂O₂. Under optimized conditions, the BPEs array was successfully applied for the determination of glucose, lactate and choline in the ranges of 0.01-1mM, 0.01-1mM and 0.02-5mM, with the LOD of 7.57μM, 8.25μM and 43.19μM, respectively. Owing to the improved stability of in situ generated H₂O₂, a whole series of analytes testing could be completed in the same BPE biochip. Subsequently, an array chip consisting of nine BPEs enabled the concomitant detection of glucose, lactate and choline, demonstrating the capability for multifunctional detection of biomolecules. This versatile analytical system could be easily extended to sensitive screening in a miniaturized device and point of care testing.