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

Abstract

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 biotin-terminated 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.

Formation and electrochemical desorption of self‐assembled monolayers as studied by ToF‐SIMS

“…In this sensor design, the two Au arms are chemically differentiated by depositing different SAMs on each such that the analyte binds selectively to one arm only thus producing a phase shift. Such differentiation can be achieved by selective electrochemical desorption of a SAM from one arm only 19, 20. After the selective desorption, the second arm is incubated with another thiol of different properties vs the analyte.…”

Chip-Scale Electrochemical Differentiation of SAM-Coated Gold Features Using a Probe Array

“…The electrical resistance between any two parallel metal traces through an electrolyte with the specific resistance ρ can be estimated as 3,14,15 …”

“…The selective electrochemistry approach is based on reductive desorption of a SAM [4][5][6][7][8][9][10][11] and was demonstrated on electrically isolated arms of a single plasmonic gold interferometer. 3 Alternative techniques for "microspotting", such as contact microprinting 12 and dip-pen lithography, 13 may also be viable for this purpose but require specialized, dedicated equipment and/or processes.…”

“…The purpose of this paper is to resolve scaling issues related to toposelective electrochemistry 3,4 and to demonstrate the approach at the die level by simultaneously differentiating several Au features defined lithographically on a sensor chip. We apply time-of flight secondary ion mass spectrometry (ToF-SIMS) to identify thiol molecules deposited on Au features by detecting characteristic ion fragments from the surface (following previous work 3 ), thereby validating the process.…”

“…We apply time-of flight secondary ion mass spectrometry (ToF-SIMS) to identify thiol molecules deposited on Au features by detecting characteristic ion fragments from the surface (following previous work 3 ), thereby validating the process.…”