Fabrication of a multichannel PDMS/glass analytical microsystem with integrated electrodes for amperometric detection

Abstract

The fabrication process of novel multichannel microfluidic devices with integrated electrodes for amperometric detection is described. Soft-lithography, lift-off and O₂ plasma surface activation sealing techniques were employed for rapid prototyping of cost effective PDMS/glass microchips. The capabilities of the proposed microdevices were demonstrated by the electrooxidation of hydroquinone and N-acetyl-p-aminophenol (APAP) on a Au working electrode at +800 mV and +700 mV, respectively, against a Au pseudo reference electrode, and of thiocyanate on a Cu working electrode at +700 mV against a Ag/AgCl (KCl saturated) reference electrode. Linear response over the range up to 1.0 mmol L⁻¹ for APAP and up to 4.0 mmol L⁻¹ for hydroquinone and thiocyanate were verified through calibration curves with correlation coefficients greater than 0.97 (minimum of five data points). The sensitivities for hydroquinone, thiocyanate, and APAP were 28, 19, and 78 μA mol⁻¹ L, respectively. Under the experimental conditions used, the estimated limits of detection were 0.21, 0.95, and 0.12 mmol L⁻¹ for hydroquinone, thiocyanate and APAP, respectively. The geometries of the devices were designed to allow fast calibration procedures and reliable results for in-field applications. Exerting a strong influence over the device performance, the sealing process was greatly enhanced by depositing auxiliary TiSiO₂ thin-films. The general performance of the system was verified by amperometric assays of N-acetyl-p-aminophenol standard solutions, and the influences exerted by the present fabrication methods regarding reproducibility and reliability are addressed. The proposed device was successfully applied in the determination of the concentration of APAP in two commercial formulations.