In situ resistometry as a novel tool for monitoring adsorption and desorption process of self-assembled monolayers on nanoporous gold

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Nanoporous metals are produced by electrochemically controlled etching, also known as dealloying, of the less noble component of a binary master alloy. Due to their high surface-to-volume ratio and electrical conductivity, they exhibit great potential for biotechnological application such as enzyme immobilization and development of biosensors. For biofunctionalization, surface modifications are essential and self-assembled monolayers are the most promising approach [1]. However, only few techniques are capable of characterizing the formation of these monolayers on porous substrates.
Here, we present a method to in situ monitor the ad- and desorption of self-assembled monolayers on nanoporous gold by resistometry, using L-cysteine [2] and mercaptoethane-sulfonic acid as model systems. After dealloying, the nanoporous gold was immersed in an aqueous solution of the respective molecules and the relative change in resistance was monitored with a four-point resistance measurement [3].
During adsorption a pronounced resistance increase was detected, occurring in three different stages which can be attributed to the different stages in the adsorption process: First, adsorption takes places at the easily accessible outer surface and in the second stage at the internal surface. In the third stage, the reordering phase occurs, which takes several days. The total change in resistance as well as the temporal evolution depend on the substance used for adsorption. The deviations can be attributed to the inherent differences of the structure of the molecules. After adsorption, a significant decrease of the double-layer capacitance was detected, which proves the successful binding on the gold surface. Electrochemical desorption was done by cyclic voltammetry and concomitant resistometry. Simultaneous to a pronounced reductive desorption peak occurring in the first cycle, a resistance decrease was detected. By correlating the resistance change per transferred charge during desorption to the resistance change during adsorption, the initial surface coverage can be estimated.
Hence, we could show that in situ resistometry is a sensitive technique to dynamically monitor the adsorption and desorption of self-assembled monolayers on nanoporous substrates. This enables precise control of the surface modification process which is essential for development of biosensors.

[1] Hengge, E.; Hirber, M.; Steyskal, E.-M..; Nidetzky, B.; Würschum, R. submitted.
[2] Hengge, E.; Steyskal, E.-M.; Bachler, R.; Dennig, A.; Nidetzky, B.; Würschum, R. Beilstein J. Nanotechnol. 2019, 10, 2275
[3] Steyskal, E.-M.; Qi, Z.; Pölt, P.; Albu, M.; Weissmüller, J.; Würschum, R. Langmuir 2016, 32, 7757
Period23 Nov 2020
Event title9th Elecnano conference
Event typeConference
LocationParis, FranceShow on map
Degree of RecognitionInternational

Fields of Expertise

  • Advanced Materials Science