Multi-responsive paper chemosensors based on mesoporous silica nanospheres for quantitative sensing of heavy metals in water†

Exposure to low concentrations of heavy metal cations seriously harms living organisms, hence they are considered environmental toxins. Portable simple detection systems are required for field monitoring of multiple metal ions. In this report, paper-based chemosensors (PBCs) were prepared by adsorbing 1-(pyridin-2-yl diazenyl) naphthalen-2-ol (chromophore), which recognizes heavy metals, onto filter papers coated with mesoporous silica nano spheres (MSNs). The high density of the chromophore probe on the surface of PBCs resulted in ultra-sensitive optical detection of heavy metal ions and short response time. The concentration of metal ions was determined using digital image-based colorimetric analysis (DICA) and compared to spectrophotometry under optimal sensing conditions. The PBCs exhibited stability and short recovery times. The detection limits determined using DICA of Cd2+, Co2+, Ni2+ and Fe3+ were 0.22, 0.28, 0.44, and 0.54 mM; respectively. Additionally, the linear ranges for monitoring Cd2+, Co2+, Ni2+ and Fe3+ were 0.44–4.4, 0.16–4.2, 0.8–8.5, and 0.002–5.2 mM; respectively. The developed chemosensors showed high stability, selectivity, and sensitivity for sensing of Cd2+, Co2+, Ni2+ and Fe3+ in water under optimum conditions and hold potential for low cost, onsite sensing of toxic metals in water.