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Issue 8, 2015
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A step towards mobile arsenic measurement for surface waters

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Abstract

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 As3+ 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 As3+ even with a GSH surface, but they remain sensitive to Cu2+, 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 As3+ measurement remains feasible at the WHO guideline value of 10 μg L−1 up to a copper concentration of around 0.3 μM Cu2+, which corresponds to the highest recorded level in a selection of large rivers world-wide.

Graphical abstract: A step towards mobile arsenic measurement for surface waters

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Article information


Submitted
23 Dec 2014
Accepted
18 Feb 2015
First published
25 Feb 2015

Analyst, 2015,140, 2644-2655
Article type
Paper
Author version available

A step towards mobile arsenic measurement for surface waters

C. A. de Villiers, M. C. Lapsley and E. A. H. Hall, Analyst, 2015, 140, 2644
DOI: 10.1039/C4AN02368D

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