Fabrication Of Microfluidic Chip For Electrochemical Detection Of Dopamine

Neurodegenerative diseases, such as Parkinson’s disease, primarily results from the loss of dopaminergic neuron. Neural Stem Cells (NSCs) can be differentiated into dopaminergic neuron after stimulating, therefore, the transplantation of Neural Stem Cells is considered to be an ideal choice. To simulate the real environment in vivo, a three-dimensional culture micro environment of NSCs can be built by integrating microfluidic chip with collagen hydrogel. Electrochemical detection has the advantages of high detection sensitivity, miniaturization and integration, which has been a major detection method of microfluidic chip.In this paper, a novel microfluidic chip was designed and fabricated, which consisted of one main channel for cell chamber, two lateral channel for transporting cell medium and 3 groups of three-electrodes setup for dopamine electrochemical detection. In the future, the microfluidic chip can be not only used for culturing NSCs but also accomplish the detection of dopamine released from dopaminergic neuron. The microfluidic chip consists of one Polydimethylsiloxane (PDMS) microchannel plate and one glass electrodes plate. The fabrication of microchannel plate was achieved by using cast molding. Two rows of high depth-width ratio (3:1) micropillars arrays were designed in the intermediate region of PDMS cover plate, which resulted in the difficulty of PDMS microchannel plate demolding. To address the problem, a new method for demolding was presented. Firstly, the mixing ratio of PDMS prepolymer and curing agent was adjusted to 15:1. Then, demolding was performed by putting PDMS microchannel plate and silicon mold into ethyl alcohol.Finally, the surface of silicon mold was treated by using dimethyldichlorosilane. To test the surface effect of silicon treated with dimethyldichlorosilane, the experiment of contact angle measurement was performed. The results showed that the variation of contact angle from the first day to seventh day was only 2.8°, moreover, the cast molded PDMS micropillares were not broken, which shows that the surface of silicon mold treated by dimethyldichlorosilane and could meet the long term use of silicon mold. The common reference electrode in the electrochemical detection is Ag/AgCl. However, Ag/AgCl will be degradable in the biological environment. Therefore, the Au-Au-Au three electrodes setups were fabricated.The detection performance of microfluidic chip were studied. Firstly, the cyclic voltammetry curve was achieved by adopting H2SO4 as test sample, which was consistent with the cures achieved with Au-Ag-Au and Au-Ag-Pt reported previously. The results demonstrated that the built three electrodes setups could be used for the detection of dopamine. Besides, the setups also illustrated good stability and repeatability. Then, the dopamine were detected. To mimic the future application environment of microfluidic chip, the dopamine used in this paper were dissolved into the medium culturing for NSCs. The detection limit was 3.92μM and the linear detection range was 10μM～500μM.To improve the detection sensitivity of microfluidic chip, the working electrodes were modified with polypyrrole/poly (sodium 4-styrenesulfonate) (PPy/PSS). Dopamine were detected by using modified microfluidic chip. The detection of limit were 0.69μM, which decreased by an order of magnitude compared to the unmodified one. Therefore, the modification treatment have improved the detection sensitivity of microfluidic chip greatly.