Functionalized Mn2+ Doped Zinc Sulfide Quantum Dots as a Metal Ion Sensor for Industrial Wastes

L-cysteine capped Mn2+-doped ZnS quantum dots are prepared as a fluorescence probe for the detection of heavy metal contaminants, such as As2O42-, Cd2+, CrO42-, Ni2+, Zn2+, Ca2+, Fe2+, Cu2+, Pb2+, Co2+ and Mn2+ ions. The results show L-cysteine capped Mn2+-doped ZnS quantum dots exhibit good sensitivity and selectivity for the detection of copper ions. The relationship between the detection limit, linear range and the concentration of quantum dots are examined. The optimum fluorescence sensor is obtained at the L-cysteine-ZnS QDs concentration of 2 mg/mL and pH 7.0 in phosphate buffer. The limit of detection for this sensor system is 0.2 ppm with the linear range between 0.5 and 20 ppm. The effect of foreign ions from Mn2+, Fe2+, Co2+ and Ni2+ for the detection of Cu2+ solution is also evaluated. The results show there is no significant difference on the measurement of quenching effect.