Label-Free Electrochemical Immunosensor Made with Tree-like Gold Dendrites for Monitoring 25-Hydroxyvitamin D3 Metabolite

Flexible, fully printed immunosensors can meet the requirements of precision nutrition, but this demands optimized molecular architectures to reach the necessary sensitivity. Herein, we report on flexible and label-free immunosensor chips made with tree-like gold dendrites (AuDdrites) electrochemically formed by selective desorption of l-cysteine (L-cys) on (111) gold planes. Electrodeposition was used because it is scalable and cost-effective for a rapid, direct growth of Au hyperbranched dendritic structures. The 25-hydroxyvitamin D3 (25(OH)D3) metabolite was detected within 15 min with a limit of detection (LOD) of 0.03 ng mL–1. This high performance was possible due to the careful optimization of the electroactive layer and working conditions for square wave voltammetry (SWV). Electrocrystallization was manipulated by controlling the deposition potential and the molar ratio between HAuCl4 and L-cys. Metabolite detection was performed on human serum and saliva samples with adequate recovery between 97% and 100%. The immunosensors were stable and reproducible, unresponsive to interference from other molecules in human serum and saliva. They can be extended for use as wearable sensors with their mechanical flexibility and possible customization.