Analyte discrimination by SAW sensor variable loop amplification probing

Abstract

A Surface Acoustic Wave (SAW) sensor with an ‘acoustically thick’ (average 0.5 µm) polyethyleneimine (PEI) chemo-selective active layer is used to demonstrate analyte-specific response for two closely related volatile organic compounds (VOC): ethanol and methanol. By means of variable amplification, we modified the SAW resonant oscillator frequency, allowing a ~ 3 MHz frequency scan. Sets of data consisting in gain-frequency values were further acquired for six analyte concentrations for each of the VOCs, while baselines were acquired for 0 analyte concentration. Following measurements, the frequency vs. gain curves were fitted using an analytical model based on the acoustic response of a visco-elastic thick layer. The variations of the fitting parameters upon sensor exposure to analyte proved highly non-linear and distinct variations for the two analytes, supporting amplificator gain based frequency scan of the SAW sensor as a functional method for analyte discrimination using a single SAW sensor.