Design and Characterization of Poly(dimethylsiloxane)-Based Valves for Interfacing Continuous-Flow Sampling to Microchip Electrophoresis

Abstract

This work describes the fabrication and evaluation of a poly(dimethyl)siloxane (PDMS)-based device that enables the discrete injection of a sample plug from a continuous-flow stream into a microchannel for subsequent analysis by electrophoresis. Devices were fabricated by aligning valving and flow channel layers followed by plasma sealing the combined layers onto a glass plate that contained fittings for the introduction of liquid sample and nitrogen gas. The design incorporates a reduced-volume pneumatic valve that actuates (on the order of hundreds of milliseconds) to allow analyte from a continuously flowing sampling channel to be injected into a separation channel for electrophoresis. The injector design was optimized to include a pushback channel to flush away stagnant sample associated with the injector dead volume. The effect of the valve actuation time, the pushback voltage, and the sampling stream flow rate on the performance of the device was characterized. Using the optimized design and an injection frequency of 0.64 Hz showed that the injection process is reproducible (RSD of 1.77%, n = 15). Concentration change experiments using fluorescein as the analyte showed that the device could achieve a lag time as small as 14 s. Finally, to demonstrate the potential uses of this device, the microchip was coupled to a microdialysis probe to monitor a concentration change and sample a fluorescein dye mixture.

Use of micromolded carbon dual electrodes with a palladium decoupler for amperometric detection in microchip electrophoresis

“…The performance of the microelectrodes was demonstrated by the separation and dual electrode detection of neurotransmitters and it was found that addition of SDS to the buffer system significantly improved detection limits and collection efficiencies. Future work will involve coupling these dual microelectrodes with PDMS-based valving schemes that interface continuous-flow sampling with microchip electrophoresis [8], with the long-term goal of monitoring the stimulated release of dopamine and norepinephrine from PC 12 cells on-chip [32].…”

“…There are many advantages in utilizing this technique, including the ability to perform high-throughput screening [5], use of minute amounts of reagent and sample [6], fast analysis times [7], and the ability to integrate multiple processes [8]. Although much progress has been made in this area, there is still a need for the development of sensitive and selective detectors for bioanalytical applications.…”

Microssistemas de análises químicas: introdução, tecnologias de fabricação, instrumentação e aplicações

“…De acordo com a complexidade das conexões entre os canais, os esquemas de mobilização dos fluídos podem envolver diversas concepções e estratégias para o controle seletivo do fluxo, desde a introdução de válvulas integradas 57,58 , ou simplesmente usar uma bomba pneumática posicionada externamente para a mobilização dos fluídos 59 .…”

“…Embora em sistemas convencionais a introdução da amostra seja realizada por ações eletrocinéticas e/ou hidrodinâmicas, em sistemas miniaturizados, devido à maior facilidade de implementação, esta etapa se faz predominantemente por processos eletrociné-ticos 70,71 . No entanto, alguns artigos relacionados à injeção hidrodinâmica em microchips podem ser encontrados na literatura 57,72,73 . A importância da introdução de amostra deve-se ao fato de que as características da zona de amostra determinam a qualidade da separação analítica.…”

New analytical portable instrument for microchip electrophoresis with electrochemical detection

“…Nowadays, various polymeric materials [16] are used such as PDMS [17,18], PMMA [19,20], polycarbonate [21], poly(ethylenterephthalate) [22,23], thermoset polyester [24,25], and polyester toner [26,27], Zeonix/ Zeonor [28,29] or thermoplastic olefin polymer of amorphous structure [7,30,31].…”