Screen-printed electrodes modified with functionalized mesoporous silica for voltammetric analysis of toxic metal ions

Mercury-free sensors for lead (Pb²⁺) assay based on chemical modification of screen-printed carbon electrodes (SPCEs) with acetamide phosphonic acid self-assembled monolayer on mesoporous silica (Ac-Phos SAMMS) have been developed. The analysis of Pb using SPCEs-based adsorptive stripping voltammetry (AdSV) includes two steps. Pb²⁺ ions are firstly adsorbed on electrode surface in a Pb²⁺ solution (15 ml) during a preconcentration step, followed by a measurement step using one drop of acidic solution (50 μl) as medium for stripping voltammetry. The preconcentration of Pb²⁺ at SAMMS-based sensors utilize the binding affinity of the acetamide phosphonic acid and Pb²⁺, which can be accomplished at open circuit potential without electrolyte and solution degassing. Due to the strong covalent bonding of the functional groups on mesoporous silica, the SAMMS-based sensors with a built-in three electrode system can be reused for tens of measurements with minimal degradation, enabling the establishment of the calibration curve and lowering the costs. Linear calibration curve was found in the range of 0 to at least 100 ppb Pb²⁺ after 5 min of preconcentration. The detection limit was calculated from 3S/N to be 0.91 ppb of Pb²⁺. Reproducibilty (%RSD) was found to be 5% for a single sensor (six measurements) and 10% for five sensors. The reproducibility can be improved through the precision of manufacturing of the sensors, in which SAMMS modification can be done in situ, increasing the user-friendliness of the sensors. Cadmium, lead, and copper can also be detected simultaneously at the SAMMS modified screen-printed sensors.