Jason Shih

Integrated surface-micromachined mass flow controller

An integrated surface-micromachined mass flow controller (MFC) that consists of an electrostatically actuated microvalve and a thermal flow sensor is presented here. With a unique design and utilizing a multilayer Parylene process, the active microvalve and the flow sensor are integrated onto a single chip to perform closed-loop flow control. Sensitivity of the flow sensor is 55 PV/(/spl mu/L/min) for airflow and 12.2 pV/(nL/min) for water. The valve is actuated with a 10 kHz AC signal and an applied pressure of 21 kPa can be sealed with an actuation voltage of 200 V/sub peak/ (/spl plusmn/200 V). For flow control, both Pulse Width Modulation (PWM) and actuation voltage adjustment are demonstrated. PWM shows better performance in terms of controllability and linearity.

Surface micromachined and integrated capacitive sensors for microfluidic applications

We have demonstrated an entire series of capacitive sensors using a multi-layer parylene/photoresist surface micromachining technology. The developed sensors are designed for total integration into parylene-based microfluidic systems for real-time system monitoring. Sensors have been demonstrated for the following applications: in-line pressure sensing (range: 0-35 kPa, resolution: 0.03 kPa); liquid front position and/or volumetric measurements (range: 0->50 pL, resolution: <5 pL); and dielectric measurements, which can be used to deduce fluid properties such as liquid composition. The reported sensor technology demonstrates versatility, high sensitivity, small footprints, and easy integration.

An integrated LC-ESI chip with electrochemical-based gradient generation

This work reports the first on-chip generation of gradient elution using electrochemical pumping, for application in Liquid Chromatography-Electrospray Ionization (LC-ESI). The system consists of Parylene, SU-8 and PDMS parts to create two 3 /spl mu/L on-chip solvent reservoirs, two electrochemical pumps and an ESI nozzle. Pumping is controlled galvanostatically (i.e., through electrolysis current). At low back pressures, pumping rate can reach 200 nL/min using just 40 /spl mu/A (power consumption <100 /spl mu/W). At 80 psi, 200 /spl mu/A (power consumption <1 mW) is sufficient to deliver fluid at 75 nL/min. Higher electrical currents have been used to increase the flow rate or to achieve pumping at higher back pressures. For example, pumping at 200 psi back pressure has been demonstrated using a current of 800 /spl mu/A. Electrically controlled on-chip gradient generation is achieved without any external fluidic connections to the chip. Continuous generation of gradients for 30 minutes at a total flow rate of /spl sim/100 nL/min is also realized and confirmed with mass spectroscopy (MS) measurements. The developed on-chip gradient generation system meets the general requirements of LC applications.

Complete gradient-LC-ESI system on a chip for protein analysis

This paper presents the first fully integrated gradient-elution liquid chromatography-electrospray ionization (LC-ESI) system on a chip. This chip integrates a pair of high-pressure gradient pumps, a sample injection pump, a passive mixer, a packed separation column, and an ESI nozzle. We also present the successful on-chip separation of protein digests by reverse phase (RP)-LC coupled with online mass spectrometer (MS) analysis.

Microfabricated Platform for Nanoscale Flow Sensing and Control

In this paper we describe a microfabricated platform for nanoscale flow sensing and control. Two custom-built pneumatically-driven pumps were used to deliver two different fluids into our microfluidic chip. The two liquids were mixed on-chip and the flow rate and composition of the resulting liquid was measured. Flow rate measurements were accurate within a few nL/min and the composition within 0.2%. In this paper, composition is defined as the makeup (by volume and expressed as a percentage) of a binary mixture. Feedback from the sensors was used to control the pumps in order to produce the desired flow profiles.