The Effect of Channel Metal Coating and Surface Electric Charge on the Selectivity of a Microfluidic-Based Gas Analyzer

Microchannels have shown promise in enhancing the selectivity of generic gas sensors by modulating gas flow, resulting in transient responses that vary based on the diffusivity and adsorption rates of different gases. To further improve the selectivity of microfluidic channels, this study introduces the concept of active gas modulation using channels with charged metal coating. To explore this concept, a miniature gas analyzer is developed by integrating a metal oxide gas sensor with a microfluidic channel made of polymethyl methacrylate (PMMA) through laser ablation. The top and bottom surfaces of each channel are coated with gold, silver, and copper nanoparticles using RF sputtering to induce varying levels of electric charge by applying appropriate electrical potential to the metal electrodes. The sensor’s transient response is recorded for various target gases and gas mixtures. Experimental results reveal distinct transient responses for channels with different coatings in the absence of an electric charge. Furthermore, the presence of an electric charge on the channel wall significantly affects the sensor’s response to ethanol. To gain further insights into the effect of the electric field on gas flow within the microfluidic channel, the sensor’s response is examined when a pulsed electric field is applied. The impact of toggling the bias voltage on and off is clearly evident in the resulting graphs, illustrating its role in affecting the sensor’s response. Finally, the efficacy of this method in detecting the presence of ethanol vapor in binary and ternary gas mixtures is demonstrated, further highlighting its potential applications.