Acid/base Micropatterned Devices for pH-Dependent Biosensors

Abstract

Micropatterned surfaces of poly(acrylic acid) (PAA) and poly(allylamine) (PAL) were prepared by the combination of plasma enhanced chemical vapour deposition (PE-CVD) and physical masking techniques. The deposition process for both polymers was optimized in order to obtain a good compromise between the stability and the specific chemical functionality of the surface. X-ray photoelectron spectroscopy, and secondary ion mass spectrometry were used to determine the chemical characteristics of the surfaces. The use of the imaging mode provided a determination of the chemical contrasts at the micrometre scale. The evaluation of the specific interaction forces, acting between the surfaces and the COOH-functionalized tips, as a function of the pH, was performed by chemical force microscopy. The force-distance curves provided the basis for a semi-quantitative calculation of the interaction forces between the tip and the surfaces. The repulsive or attractive nature of the interaction forces is due to the variation in the charge concentration on the surfaces. This allowed the determination of pH-dependent force maps where the PAA and PAL show a contrast in the adhesion force.