An Alternating Modification Strategy for Constructing l -Cys–Au Functional Interfaces in Nanochannels for Highly Selective Copper Ion Analysis

Nanochannel-based sensors offer exceptional sensitivity, selectivity, and real-time response for ionic analysis, yet achieving advanced recognition of heavy metal ions remains challenging due to the limitations of conventional single-layer surface modification. In this work, we investigate the ion transport and sensing behavior of l-cysteine (l-Cys)-modified nanochannels and further propose an alternating surface engineering strategy based on this chemically active interface. Initially, l-Cys-modified nanochannels are constructed, serving both as an effective Cu²⁺ sensor (detection limit: 10⁻¹⁵ M) and as a reactive platform that enables uniform in situ gold deposition via thiol-mediated reduction. This process yields a continuous gold nanolayer, which subsequently acts as a versatile substrate for secondary self-assembly. Through Au-S anchoring, a second l-Cys layer is introduced, forming a well-defined l-Cys-Au-l-Cys composite interface, which enables highly sensitive and selective detection of both Cu⁺ and Cu²⁺ ions. Notably, the engineered interface achieves clear and reliable discrimination between Cu⁺ and Cu²⁺. This alternating modification strategy provides a robust, modular, and scalable approach for constructing multifunctional nanochannel sensing platforms, offering broad potential for precise heavy metal ion monitoring in environmental and biosensing applications.