Alcohol selectivity and measurement of ethanol concentrations in liquors using Teflon® AF2400-coated gold-deposited surface plasmon resonance-based glass rod sensor

Abstract

Abstract A gold (Au)-deposited surface plasmon resonance (SPR)-based glass rod sensor coated with an α-mercaptoethyl-ω-methoxy polyoxyethylene (PEG thiol) layer and a Teflon AF2400 overlayer with high selectivity for small molecules contained in aqueous solutions was developed. The PEG thiol layer forms a space (approximately 13 nm wide) for the analytes to accumulate between the Au film (45 nm thick) and the Teflon layer (approximately 12 μm thick). The water and alcohol content in the sample solutions pass selectively through the porous Teflon overlayer, accumulate in the PEG thiol spacer layer and are then detected through the SPR phenomenon. Cross-sectional scanning electron microscope imaging of the sensor was used to measure the thickness of the Teflon overlayer on the Au film. The sensor selectivity was then evaluated using aqueous solutions of various alcohols. The sensor responds reversibly to the concentrations of only monohydric alcohols. The response is faster than that of the Teflon AF1600-coated sensor as a result of the increased permeability and the reduced thickness of the Teflon AF2400 overlayer. The sensor maintains both its sensitivity and its selectivity for as long as 6 months. Direct measurement of the ethanol concentrations of aqueous ethanol solutions that were mixed with interference compounds is possible using this sensor. The ethanol concentrations of various liquors were measured directly. This sensor is a unique device with functions for both separation and detection of the analytes.