Highly selective simultaneous Cu(II), Co(II), Ni(II), Hg(II), Mn(II) determination in water samples on microfluidic paper-based analytical devices

A new paper-based analytical device design was fabricated by a wax printing method for simultaneous Cu(II), Co(II), Ni(II), Hg(II), and Mn(II) determination. Colorimetry was used to quantify the heavy metal ions, using bathocuproine (Bc), dimethylglyoxime (DMG), dithizone (DTZ), and 4-(2-pyridylazo) resorcinol (PAR) as complexing agents. The affinity of the complexing agent to the heavy metal ion is dependent on the formation constant (K f ). To enhance the selectivity for heavy metal ion determination, the new device was designed with two pretreatment zones, where masking agents remove interfering ions. It was found that two pretreatment zones worked better than a single pretreatment zone at removing interferences. The reaction time, sample and complexing agent volumes, and complexing agent concentrations were optimized. The analytical results were achieved with the lowest detectable concentration of 0.32, 0.59, 5.87, 0.20, and 0.11 mg L −1 for Cu(II), Co(II), Ni(II), Hg(II), and Mn(II), respectively. The linear range was found to be in the range of 0.32–63.55 mg L −1 (Cu(II)), 0.59–4.71 mg L −1 (Co(II)), 5.87–352.16 mg L −1 (Ni(II)), 0.20–12.04 mg L −1 (Hg(II)), and 0.11–0.55 mg L −1 (Mn(II)). The lowest detectable concentration and linearity for five metal ions allow it to be applied in various water samples. The sensor provided highly selective and efficient for simultaneous Cu(II), Co(II), Ni(II), Hg(II), and Mn(II) determination in drinking, tap, and pond water samples on a single device and detection by naked eye. The results illustrated that the proposed sensor showed good accuracy and precision agreement with a standard ICP-OES method. We present a high-throughput study of the steady state Stokes shifts of > 300 fluorescent DNA-stabilized silver clusters and the correlations of DNA sequence with the optical properties of these fluorophores.