Rapid solid-phase microProbing of soil and groundwater lead and cadmium by tuning hydrophilic and hydrophobic microenvironments

Soil and groundwater contamination by lead and cadmium poses significant environmental and health risks, necessitating the development of rapid and accurate field monitoring techniques, which are currently lacking. Although solid-phase colorimetric microProbing imaging offers a promising solution, fine-tuning the hydrophilic/hydrophobic microenvironment of lead or cadmium molecular sensors within the microProbing material is essential for achieving rapid and accurate detection. Here, we report a method to covalently bond xylenol orange (a lead sensor) or physically adsorb dithizone (a cadmium sensor) onto the hydrophilic or hydrophobic entities of TentaGel resins, enabling uniform sensor loading, selective sequestration, and rapid microProbing of soil and groundwater lead or cadmium. Through microenvironment fine-tuning, the method achieved high sensitivity, with detection limits of 28 ppm and 9.9 ppb for soil and groundwater lead, and 50 ppb and 6.8 ppb for soil and groundwater cadmium, respectively. It accurately detected soil and groundwater lead from an economic development zone in Shenzhou (Hebei Province) and cadmium from a mine in Daye (Hubei Province), China. A portable microProbing device was also custom-designed and fabricated. With this device, the microProbing method shows great promise for field monitoring of other heavy metals in contaminated lands.