A Novel Approach to Detect Protein Utilizing the Microfluidic Pre-Concentrator Based on The Impedance Measurement Method

Protein pre-concentration is an important part of the protein quantification systems. The pre-concentration step facilitates increasing the detection limit of biosensors, particularly following multiple separation and preparation steps. In this study, a protein pre-concentration microfluidic chip has been proposed based on the dual-gate configuration and ion-selective membrane. The chip design included a sample channel connected electrically to two buffer channels through the Nafion membrane. Besides, two gold microelectrodes were integrated into the sample channel to measure the impedance of the protein sample after the pre-concentration stage. The proposed chip was fabricated utilizing the soft photolithography technique and casting process. Albumin-fluorescein isothiocyanate conjugate (BSA-FITC) was employed to evaluate the performance of the proposed chip. The results show that proteins were successfully concentrated after applying the potentials of 25 V, 30 V, and 0 V to the two terminals of the sample channel and buffer channels, respectively. Under the impact of electrophoretic force and electroosmotic flow, proteins were manipulated to the sensing area, i.e., the electrode region. The protein concentration increased about 1000 times after 50 seconds at the initial protein concentration of 5 µM. The impedance of the electrode region in the sample channel decreased after the proteins were concentrated there because the concentration of proteins and ions increased the conductivity leading to the decrease of the impedance between sensing microelectrodes. Furthermore, the Randles circuit model was also used to explain the impedance change of the protein concentration zone. With the achieved results, the protein concentration region can be recognized through the impedance measurement method. Furthermore, the proposed chip can potentially be applied to Lab on a chip system to detect proteins and biomolecules in future research.