Electrochemical Differentiation and TOF-SIMS Characterization of Thiol-Coated Gold Features for (Bio)chemical Sensor Applications

A method to chemically differentiate small closely spaced lithographically defined Au features with different thiol-based self-assembled monolayers (SAMs) was developed. The key step in the method is the reductive electrochemical desorption of a SAM from a specific Au feature without affecting SAMs on neighboring Au features by simultaneously controlling their potentials with a multichannel potentiostat. The method is demonstrated by chemically differentiating the arms of a Au plasmonic Mach-Zehnder interferometer such that the arms have different affinities toward an analyte, thus rendering the interferometer useful for (bio)chemical sensing. The simultaneous presence of a poly(ethylene glycol)-terminated SAM on one arm, and of a biotinterminated SAM on the other, was verified by imaging with time-of-flight secondary ion mass spectrometry (TOF-SIMS) and phase-shift atomic force microscopy. The method can be applied generally to chemically differentiate a large number of electrically isolated Au features simultaneously, leading to low cost wafer-scale functionalization of (bio)chemical sensors and other devices. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3242308] All rights reserved.