Monitoring of Cobalt and Cadmium in Daily Cosmetics Using Powder and Paper Optical Chemosensors

Daily used cosmetics may contain high levels of heavy metals which are added to improve the quality and shine of cosmetics but represent a threat to human health. In this report, powder- and paper-based optical nanosensors using mesoporous silica nanospheres as carriers were designed for determination of Co2+ and Cd2+ in commonly used cosmetics. Powder optical chemosensors (POCs) were prepared via direct decoration of optical probes into a porous carrier. Paper-based chemosensors (PBCs) were designed via adsorbing the organic chromophore onto filter papers treated with mesoporous silica. POCs and PBCs were constructed with thick decoration of optical probes, leading to the formation of active surface centers for monitoring of Co2+ and Cd2+ in cosmetic products. The uniform structures of POCs and PBCs have resulted in selective sensing and low detection limits up to parts per billion, wide detection range determination, and fast response (on the order of seconds). Digital image colorimetric analysis (DICA) was used to quantify the color of PBCs and deduce the corresponding concentrations of Co2+ and Cd2+ using calibration curves. DICA data correlated well with that obtained from UV–vis spectrophotometry. The developed POCs and PBCs showed wide detection ranges of metal ions and a considerably low detection limit under optimal analysis conditions. The low limit of detection of Co2+ and Cd2+ ions using POCs was 6.7 × 10–9 and 3.5 × 10–9 M, respectively. To the best of our knowledge, this is the first time simple PBCs have been designed for monitoring Co2+ and Cd2+ with detection limits of 2.2 × 10–7 and 1.3 × 10–7 M. A limited amount of manufactured POCs (about 20 mg) were used for all measurements, and commercial filter paper treated with mesoporous nanosphere silica was used for sensing Co2+ and Cd2+ ions. The developed optical chemosensors had short regeneration times and exhibited high stability and surface functionality and are capable of monitoring Co2+ and Cd2+ in various cosmetic products.