Optimization and application of normally closed microvalves in microfluidics

Microvalves;soft lithography;actuation pressure;hysteresis;normally closed valves;antibiotics;Green Fluorescent Protein (GFP);isopropyl β-D-1-thiogalactopyranoside (IPTG)

Mohan, Ritika ; Kenis ; Paul J.A.

关键词: Microvalves;    soft lithography;    actuation pressure;    hysteresis;    normally closed valves;    antibiotics;    Green Fluorescent Protein (GFP);    isopropyl β-D-1-thiogalactopyranoside (IPTG);   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/29458/Mohan_Ritika.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The ease of fabrication and integration of pneumatic microvalves has enabled extensiveminiaturization of microfluidic devices that are capable of performing massively paralleloperations. These valves in their typical open configuration, also known as normally open (NO)valves, require to be actuated to remain closed. As a result, devices employing these valves havelimited portability in applications that require valves to be closed continuously. Normally closed(NC) valves based on pneumatic actuation not only address the above issue of portability, butalso retain the ease of integrating massively parallel networks of microfluidic elements. In thisthesis, I report the design, fabrication, and application of elastomeric NC microvalves, alongwith systematic experimental characterization of NC valve operation. Geometrical parameters of the valve, including shape, fluid channel width, membrane thickness, and valve asymmetry wereexamined with the objective of minimizing actuation pressures and ensuring reliable operation. Iobserved that introduction of asymmetry in the valve geometry created points of weak adhesionbetween the valve and the substrate, which facilitated opening of the valve at lower actuation pressures. Specifically, valves with a sharp corner feature (v-shaped) actuated at lower pressures (1.5 psi) compared to straight-shaped valves (3 psi). I also observed that membrane thickness does not significantly influence the actuation pressures. An important requirement formicrofluidic devices using NC valves is selective irreversible bonding of the fluid layer to thesubstrate, which I achieved by plasma sealing of the fluid layer to the substrate whilesimultaneously actuating the valves. Based on our experimental observations, I formulated a setof design considerations with the objective of minimizing actuation pressures, ensuring reliableoperation, and facilitating convenient integration into complex microfluidic devices. These NC valves have significant potential in applications where portability is highly desired, such as inon-chip analysis, crystallization screening, and in the study of chemical or biological processesover long durations of time. I utilized these optimized design considerations to fabricate a 4x6multiplexed microfluidic platform capable of combinatorial exposure of bacterial cells (E. coli)to diverse metabolites such as toxins, hormones, and antibiotics. I validated these chips forbiological applications first by studying cell growth, and then demonstrated the multiplexingcapabilities with inducible expression of the Green Florescent Protein (GFP) gene in E. coli cellson-chip using different concentrations of isopropyl β-D-1-thiogalactopyranoside (IPTG). Thekey application of the platform is its utilization in antibiotic susceptibility screening.