QZ

	Qiyang Zhang
	Major: Analytical Chemistry
	Office: 329 McKinley Hall Phone: (316)978-7366 E-mail: qxzhang2@wichita.edu

Research Description

My research project is to develop integrated microfluidic systems and technologies to perform in vivo measurements of neurotransmitters in rat brain. Neurotransmitters play a major role in neuronal communication between neurons. This signalling process involves presynaptic release of neurotransmitters into the synapses, diffusion towards and binding to postsynaptic neurons. The concentration variations of neurotransmitters in the extracellular space indicate the activity of the neurons involved and thus the central nervous system. On the other hand, abnormal concentrations of specific neurotransmitters may provide information of diseases such as drug addiction and Parkinson’s. Therefore, rapid and accurate determination of neurotransmitters in vivo is valuable for disease diagnosis and drug discovery. Current techniques available often depend on electrochemistry or HPLC-based separations, which have limitations. Integrated microfluidic systems that I am focusing on will integrate sequential and parallel processes to enhance analysis throughput, improve temporal and spatial resolution, and simultaneously perform multiple-region monitoring. Upon the success of this research, we will provide robust and powerful tools to neuroscience research and pharmaceutical industry thus facilitating drug discovery and treatment of neurodegenerative diseases.

Figure 1. Schematic diagram of the CE-LIF system (see details in the text).

Capillary electrophoresis with laser-induced fluorescence (CE-LIF) is used as the separation and detection methods, respectively. CE-LIF is a rapid separation technique with great detection power, which allows to detect neurotransmitters at nano or even pico molar levels. My current research focuses on optimization of the CE-LIF system (shown in schematic diagram Fig. 1), aiming to yield the best outcome in research applications. This CE-LIF system we build in our lab is robust and reliable. In figure 2A, to test its long-term performance, more than 300 consecutive injections were performed and the results were plotted (Fig. 2A), and an excellent reproducibility in peak height was demonstrated by the %RSD (relative standard deviation) of 1.6. Figure 2B shows a typical electropherogram showing glutamate and aspartate at 5.0 µM each with overlap injection. Another work had been done to demonstrate this CE system is the separation of 19 basic amino acids with micellar electrokinetic chromatography (MEKC) (Fig. 3). Even more, the small diameter of capillary column improves the separation efficiency and short response time (250k theoretical plates obtained and 18 response time achieved in our lab).

Figure 2. (A) Glutamate peak heights of repeated overlap injections. Glutamate and aspartate at 5.0 µM each in aCSF (artificial cerebrospinal fluid) mixed online with the derivatization reagents KCN at 10 mM and NDA at 5 mM. (B) A typical electropherogram of glutamate and aspartate at 5.0 µM each with overlap injections; Glu and Asp peaks shown are from the immediate former injection. Small peaks are derivatization by-products.

To simplify the fabrication process and interconnection, we develop a rapid prototyping method to fabricate poly (dimethylsiloxane) (PDMS) interconnectors in integrated CE system. Our studies have shown that these miniaturized interconnectors accommodated tubing connection and provided visible trouble shooting. In particular, the needle-to-capillary connection tolerated up to 200 psi in back pressure. According to dynamic tests, a response time of 18 seconds was achieved in a two-branch CE system. Therefore, these robust interconnectors are suitable for rapid separations in microfluidic systems and could be further miniaturized in an integrated device. Other works including LabVIEW program development. We already developed two programs for our research applications. One can control high voltage power supply and valve of gating flow and sampler switch, meanwhile, acquires data from detector and records readings of power supply. All data is automatically logged on hard drive, and shown as plots on the computer screen. The other program is designed to control pneumatic pumps for microfluidics devices. These two programs are constantly modified to fit our interests of research.

By using two branches of sample supply, this CE system can be further improved for simultaneous two point detection. In the future, by employing integrated microfluidics systems, the CE systems could be miniaturized on an integrated device, which is suitable for in vivo sample extraction and analysis. With these advantages, it is achievable that to qualitatively and quantitatively detect important neurotransmitters as part of brain activity in vivo, and thus allows us to further investigate neuron cells and brain functions.

Figure 3. Electropherogram of 19 basic amino acids. Separations were obtained by using 15 cm effective separation length at an electric field of 1000 V/cm. The separation buffer consisted of 20 mM LiTB (lithium tetraborate) and 10 mM SDS (sodium dodecyl sulfate) at pH 9.26. Peak assignments are: Asp, Gln, Gly, Glu, Arg, Ala, His Met, Phe, Thr, Ser, Asn, Lys, Tyr, Val, Ile, Leu, Trp, Pro. Un-marked peaks are un-identified ones. Standard amino acids 2 µM each in aCSF.