An automated scanning contactless conductivity detection device for microfluidic isoelectric focusing

Isoelectric focusing (IEF) is widely used for protein separation and enrichment, with various methods available for detecting focused protein bands. While conventional capacitively coupled contactless conductivity detection (C4D) reduced costs and enhanced portability by eliminating optical equipment, it still required an additional mobilization step due to its single-point detection method. To address this limitation, herein we designed a novel device of scanning C4D (sC4D) for microfluidic IEF. At first, we developed an automated device of sC4D which was integrated with IEF chip for protein separation. Second, we designed the relevant software for system control and real-time conductivity measurement. Third, by using equine myoglobin as a model protein we achieved quantitative detection with a linear range of 0.2-2.5 mg/mL and a limit of detection (LOD) of 0.05 mg/mL, demonstrating the feasibility of the method and platform. In contrast to the conventional C4D with single-point detection, the developed sC4D could reduce the detection time of protein band from 760 sec to 25 sec without chemical or pressure mobilization of pH gradient, and without significant deterioration of resolution, and particularly could monitor the dynamic process of IEF and cathode drift of pH gradient. These results indicate that the designed sC4D device might serve as a reliable alternative for microfluidic IEF detection and holds significant potential for applications in various electrophoretic analysis fields in the future.