Abstract
We report the design, fabrication and characterization of a microelectromechanical systems (MEMS) flow control device for gas chromatography (GC) with the capability of sustaining high-temperature environments. We further demonstrate the use of this new device in a novel MEMS chopper-modulated gas chromatography-electroantennography (MEMS-GC-EAG) system to identify specific volatile organic compounds (VOCs) at extremely low concentrations. The device integrates four pneumatically actuated microvalves constructed via thermocompression bonding of the polyimide membrane between two glass substrates with microstructures. The overall size of the device is 32 mm×32 mm, and it is packaged in a 50 mm×50 mm aluminum housing that provides access to the fluidic connections and allows thermal control. The characterization reveals that each microvalve in the flow control chip provides an ON to OFF ratio as high as 1000:1. The device can operate reliably for more than 1 million switching cycles at a working temperature of 300 °C. Using the MEMS-GC-EAG system, we demonstrate the successful detection of cis-11-hexadecenal with a concentration as low as 1 pg at a demodulation frequency of 2 Hz by using an antenna harvested from the male Helicoverpa Virescens moth. In addition, 1 μg of a green leafy volatile (GLV) is barely detected using the conventional GC-EAG, while MEMS-GC-EAG can readily detect the same amount of GLV, with an improvement in the signal-to-noise ratio (SNR) of ~22 times. We expect that the flow control device presented in this report will allow researchers to explore new applications and make new discoveries in entomology and other fields that require high-temperature flow control at the microscale.
Highlights
Gas chromatography (GC) is one of the most widely used technologies around the world for the identification of volatile organic compounds (VOCs)
In addition to pheromone detection, we further investigated the advantage of MEMS-GC-EAG technology in detecting a generic, natural VOC, that is, green leafy volatile (GLV) (Z3-6 Ac)
Respectively. These times correspond to a 108.9% and 13.9% increase could be detected using the MEMS-GC-EAG, chopping at 8 Hz and in comparison to the values at room temperature, respectively
Summary
Gas chromatography (GC) is one of the most widely used technologies around the world for the identification of volatile organic compounds (VOCs). Similar to the optical and electrical implementation of signal chopping, the input waveform of a chopper-modulated GC-EAG is rapidly multiplied mechanically by a square wave using the MEMS flow control device, amplified and demodulated by multiplying the amplifier output by another square wave of the same frequency (Figure 1). In this way, VOCs from the GC column are directed to the FID and EAG alternately at a frequency that is controlled by the switching of the solenoid valves. Both the FID and EAG receive chopped VOC signals
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