A step towards mobile arsenic measurement for surface waters.

Surface modified quantum dots (QDs) are studied using a bio-inspired cysteine rich ligand (glutathione, GSH) and their quenching response and selectivity to arsenic examined. As predicted from As(3+) binding with highly crosslinked phytochelatin-(PCn)-like molecules, better arsenic selectivity is obtained for a thicker more 3-dimensional GSH surface layer, with exposed sulfhydryl groups. A detection limit of at least 10 μM can be achieved using CdSe/ZnS core-shell QDs capped with this GSH structure. The system is also demonstrated using a mobile phone camera to record the measurement, producing a detection limit of 5 μM. However, copper remains the main interferent of concern. Water-soluble CdTe QDs show little sensitivity to As(3+) even with a GSH surface, but they remain sensitive to Cu(2+), allowing a copper baseline to be established from the CdTe measurement. Despite anticipating that spectrally non overlapping fluorescence would be required from the two types of QDs to achieve this, a method is demonstrated using RGB channels from a mobile phone and processing the raw data for CdTe QDs, with an emission wavelength of 600 nm, and CdSe/ZnS QDs, with emission maximum of 630 nm. It is shown that As(3+) measurement remains feasible at the WHO guideline value of 10 μg L(-1) up to a copper concentration of around 0.3 μM Cu(2+), which corresponds to the highest recorded level in a selection of large rivers world-wide.This is the author accepted manuscript. The final version is available via RSC at http://pubs.rsc.org/en/Content/ArticleLanding/2015/AN/c4an02368d#!divAbstract

New Field Test for Lead (Pb2+) in Soil

Field tests for the detection of lead in soil are not frequently accepted, since the tests are rather cumbersome or not reliable for screening determinations. Recently, we developed the LEADQuick field test kit for the detection of lead in water with 3 µg/L sensitivity. This test is further modified to detect lead in soil with a sensitivity 0.03 µg. We developed an extraction protocol using nitric acid and potassium nitrate for the extraction of lead from soil. Most of the organic and inorganic compounds of lead are readily extracted as Pb2+ using the developed extraction procedure and are detected using the LEADQuick field test kit. The solubility of the lead salts in the soil is adequate for a quick extraction procedure without any heating. The experimental details, results of the soil testing and interferences are presented. This will demonstrate the potential application of our extraction procedure along with LEADQuick field test kit for soil lead monitoring