Probing Charge Reversal of Zwitterion at Defects on Self-Assembled Monolayers by Scanning Electrochemical Microscopy

Defects on self-assembled monolayers (SAMs) could have detrimental impact on their functionalities; thus, to optimize performances, researchers seek to manipulate the defects of SAMs. In this work, we functionalized the defects of 1-undecanethiol SAMs using a zwitterion, cysteine. This modification with cysteine endowed the defects with a specific behavior of charge reversal. Scanning electrochemical microscopy and cyclic voltammetry both fully exhibited this charge reversal behavior. This peculiar ability of charge reversal at the defects would endow the SAMs specific functions: the SAMs have reversible electrochemical response to charged molecules. On the basis of this principle, the functionalized SAMs could be applied in specific amino acids recognition. This work supplied a practical way to take advantage of the defects of SAMs and offers some contribution to the fields of defect engineering and molecular recognition.