Label- and Redox Probe-Free Bioelectronic Chip for Monitoring Vitamins C and the 25-Hydroxyvitamin D3 Metabolite

Monitoring immune-supporting micronutrients such as vitamins C and D is relevant as these nutrients are involved in metabolic pathways to fight against viruses and bacteria. The simultaneous determination of these biomarkers in the same sample volume is challenging, with multistep protocols if labels and redox probes are required. In this paper, we report on a flexible bioelectronic chip combining a 25-hydroxyvitamin D3 metabolite (25(OH)D3) immunoassay with an electrocatalytic assay for vitamin C. One of the sensors in the chip was made with graphitic carbon nitride modified with the electroactive dye toluidine blue, decorated with electrodeposited 6.5 nm gold nanoparticles, and coated with a layer of anti-25(OH)D3 antibodies. With this sensor, 25(OH)D3 could be detected via chronoamperometry at concentrations ranging from 0.1 to 700 ng mL^–1 with a limit of detection (LOD) of 0.01 ng mL^–1. The other sensor had 24.7 nm Pearls carbon nanoparticles whose electroactivity permitted vitamin C detection in the range from 1 to 140 μM, with an LOD of 0.12 μM. Since the chip is flexible and does not contain labels or redox probes, it has the potential for use in wearable devices to track vitamins in bodily fluids, aiding personalized nutrition by preventing deficiencies and toxicity.