Controlling copper ion detection by modulating the deacetylation degree of chitosan in carboxymethyl cellulose/chitosan-based sensors

In this study, we report sensors with interdigitated electrodes functionalized with layer-by-layer (LbL) films of carboxymethyl cellulose (CMC) and chitosan (CHI) for copper ion detection. Variations in CMC/CHI bilayers (1, 3, and 5) and the degree of deacetylation (DD ≈ 95%, 75%, 55%) of high molecular weight chitosans (approx. 10⁶ g/mol) were explored for their impact on electrode sensitivity using anodic stripping voltammetry. Sensors made with 95% deacetylated chitosan exhibited nearly double the current intensity compared to those prepared with lower DD, highlighting the crucial role of amino groups in sensitivity. Rougher films enhanced copper detection, and optimal performance was achieved with three bilayers, demonstrating excellent reproducibility (2% standard deviation). The linear detection range was from 0.5 to 2.5 ppm, with a detection limit of 0.05 ppm. Validation with another analytical technique revealed relative errors ranging from 2.1% to 4.6%, confirming the method’s accuracy. The enhancement mechanism is linked to the physical-chemical characteristics of the CMC/CHI films, where the amino groups of CHI assist in copper ion complexation, improving sensor effectiveness. The control of chitosan’s DD provides a new level of customization in the properties of LbL films, enhancing the sensor’s analytical capability for highly sensitive metal ion detection.