A Novel Planar Grounded Capacitively Coupled Contactless Conductivity Detector for Microchip Electrophoresis

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.

A pH-mediated field amplification sample stacking technique based on portable microchip electrophoresis heavy metal ion detection system

We built a portable microchip electrophoresis heavy metal ion detection system and proposed a pH-mediated field amplified sample stacking (pH-mediated FASS) online preconcentration method. The pH-mediated FASS focuses and stacks heavy metal cations by controlling electrophoretic mobilities with a pH change between the analyte and the background electrolyte (BGE) in solution to improve the detection sensitivity of the system. We optimized and adjusted sample matrix solution (SMS) ratios and pH to create concentration and pH gradients for SMS and BGE. Furthermore, we optimize the microchannel width to improve the preconcentration effect further. The system and method analyzed soil leachates polluted with heavy metals and separated Pb2+ and Cd2+ within 90 s, obtaining their levels at 58.01 mg/L and 4.91 mg/L with sensitivity enhancement factors (SEF) of 26.40 and 43.73. Compared with inductively coupled plasma atomic emission spectrometry (ICP-AES), the detection error of the system was less than 8.80%.

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

The conductivity detector is a broadly used device that allows for the highly efficient detection of analytes, and continuous efforts have been directed toward lowering the limit of detection. In this study, a five-electrode capacitively coupled contactless conductivity detector (TIC⁴D) is proposed, which uses copper mesh between the electrodes for a grounding shield to reduce the interference of stray capacitance and noise. After adding the copper mesh shield, the difference value between the response signal and baseline at low KCl concentration is effectively increased, achieving 33 mV for 10^-9 M KCl solution. Meanwhile, for the unshielded detector, the difference is only 18 mV for the KCl solution at the same concentration. The response signal shows a linear function of the logarithm at the range of 10^-4 M to 10^-5 M KCl solution, and the TIC⁴D detector displays a higher slope (0.8448) than the conventional single-input capacitively coupled contactless conductivity detector (C⁴D: 0.5579) and dual-input capacitively coupled contactless conductivity detectors (DIC⁴D: 0.6173). Moreover, two TIC⁴D detectors are combined to achieve a dual-channel six-input differential capacitively coupled contactless conductivity detector (SIDC⁴D), reducing the high baseline levels caused by the multi-signal input. By differentially amplifying the output signal, the high baseline levels and noise interference can be effectively reduced. For the 10^-3 M KCl solution, the ratio of the response signal to baseline for SIDC⁴D can reach 8.500, almost 7 times that of TIC⁴D, and a lower limit of detection (LOD) of 3 × 10^-10 M is also achieved. This work may open a new door based on coupled contactless conductivity for detection performance.

A Novel Symmetrical Peak Fitting Method Based on Improved WOA Algorithm for the Analysis of Microchip Electrophoresis Signals

The problem of overlapping peaks has been a challenge in microchip electrophoresis (ME) signal analysis. However, traditional peak fitting algorithms have difficulty analyzing overlapping peaks due to the high dependence on the starting point. In this study, we propose a symmetrical peak fitting method named the tent-mapped whale optimization algorithm and Levenberg–Marquardt (TWOALM), which combines a whale optimization algorithm (WOA) improved by one of the most commonly used chaotic maps, the tent map and the Levenberg–Marquardt (LM) algorithm. Specifically, we first derive the fitted model for the overlapping peaks, showing that it is separable nonlinear least squares, significantly reducing the number of parameters to be optimized. Second, we integrate the tent map into the WOA, which improves the convergence speed of the peak fitting algorithm. Finally, we propose an efficient peak-fitting algorithm that combines the improved WOA and LM. The advantage of the proposed algorithm is that it is significantly faster than WOA and significantly more accurate than the LM algorithm. The results of fitting the synthetic peaks and ME signals showed that the combination of the chaotic map-based WOA algorithm and the LM algorithm can significantly improve the peak fitting performance and provide an effective solution for the analysis of overlapping peaks.

Novel microchip electrophoresis-contactless conductivity method for detection and characterization of extracellular vesicles enriched for exosomes and microvesicles

Background: Extracellular vesicles (EVs) are important carriers of intercellular communication, used in disease diagnosis and as prognostic circulating biomarkers, and their identification and quantitative analysis are important prerequisites for their clinical application. Methods & results: A method using microchip electrophoresis with contactless conductivity detection was developed for the concentration assay of EVs. This method showed good sensitivity, reproducibility and accuracy, with good linear correlation with conventional methods (nanoparticle tracking analysis and bicinchoninic acid assay). The application to the detection of mesenchymal stem cell-derived EVs proved its applicability to clinical samples. Conclusion: This is the first study to apply this method for the detection of EVs, achieving quantitative analysis of EVs enriched in exosomes and microvesicles, and initially demonstrating the potential to separate different EV subpopulations.