A five-electrode capacitively coupled contactless conductivity detector with a low limit of detection

Minute level ultra-rapid and thousand copies level high-sensitive pathogen nucleic acid identification based on contactless impedance detection microsensor

Early screening for pathogens is crucial during pandemic outbreaks. Nucleic acid testing (NAT) is a valuable method for keeping pathogens from spreading. However, the long detection time and large size of the instruments involved significantly limited the efficiency of detection. This work described an integrated NAT microsensor that facilitated rapid and extremely sensitive detection based on nucleic acid amplification (NAA) on a chip. The biochip consisted of two layers incorporating a heater, a thermometer, an interdigital electrode (IDE) and a reaction chamber. The Pt electrode based heater and thermometer were utilized to maintain a specific temperature for the sample in the chamber. The thermometer exhibited a good linear correlation with a sensitivity of 9.36 Ω/°C and the heater achieved a heating efficiency of approximately 6.5 °C/s. Multiple ions were released during NAA, resulting in a decrease in the impedance of the amplification system solution. A large signal of impedance was generated by the released ions due to its linear correlation with the logarithm of the ion concentration. With this detection principle, IDE was employed for real-time monitoring of the in-chip reaction system impedance and NAA process. Specific nucleic acids from two pathogens (SARS-CoV-2, Vibrio vulnificus) were detected with this microsensor. The samples were qualitatively analyzed on microchip within 3 min, with a limit of detection (LOD) of 103 copies/μL. The proposed sensor presented several advantages, including reduced NAT time and increased sensitivity. Consequently, it has shown significant potential in rapid and high-quality nucleic acid testing for the field of epidemic prevention.

PCB-C4D coupled with paper-based microfluidic sampling for the rapid detection of liquid conductivity

The detection of liquid electrical conductivity has board applications in food safety testing, water quality monitoring, and agricultural soil analysis. Electrodes used in traditional liquid electrical conductivity detection come into direct contact with liquid, leading to electrode contamination and affecting the accuracy of the detection results. The capacitively coupled contactless conductivity detection (C4D) method effectively addresses this issue. However, impurity particles present in the solution can compromise the consistency and repeatability of detection results. This study combines paper-based microfluidic technology with printed circuit board-capacitively coupled contactless conductivity detection (PCB-C4D) to address this issue. Prior to sample detection, in situ rapid filtration is employed to remove impurity particles from the raw solution sample, significantly enhancing detection consistency and reliability. Simultaneously, Optimization of PCB-C4D parameters, channel size, filtration time, and solution drop rate ensures optimal detection conditions. A compact kit design facilitates reliable assembly of the PCB-C4D electrodes and paper-based channel, enhancing practicality. Practical measurements on the conductivity of orange juice, cucumber, and soil solution further validate the method's accuracy, rapidity, and effectiveness in in situ conductivity detection. This work advances the practical application of PCB-C4D technology.

Contactless conductivity detector as a tool for improving universality and sensitivity of capillary electrophoresis-frontal analysis: Proof of concept

Drug binding to plasma proteins influences processes such as liberation, adsorption, disposition, metabolism, and elimination of drugs, which are thus one of the key steps of a new drug development. As a result, the characterization of drug-protein interactions is an essential part of these time- and money-consuming processes. It is important to determine not only the binding strength and the stoichiometry of interaction, but also the binding site of a drug on a protein molecule, because two drugs with the same binding site can mutually affect free drug concentration. Capillary electrophoresis-frontal analysis with mobility shift affinity capillary electrophoresis is one of the most used affinity capillary electrophoresis methods for the characterization of these interactions. In this study, a well-known sensitivity problem of most capillary electrophoresis-frontal analyses using ultraviolet detection is solved by its combination with contactless conductivity detection, which provided sixfold lower limits of quantitation and detection. Binding parameters of the human serum albumin-salicylic acid model affinity pair were evaluated by this newly developed approach and by the classical approach with ultraviolet detection primarily used for their mutual comparison. The results of both approaches agreed well and are also in agreement with literature data obtained using different techniques.