title: A step towards mobile arsenic measurement for surface waters.
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 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.
authors.affiliation: Institute of Biotechnology, Department of Chemical Engineering and Biotechnology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QT, UK. lisa.hall@biotech.cam.ac.uk.
authors.forename: C A
authors.initials: CA
authors.lastname: de Villiers
authors.forename: M C
authors.initials: MC
authors.lastname: Lapsley
authors.forename: E A H
authors.initials: EA
authors.lastname: Hall
mesh_terms: D001151:Arsenic / Q000032:analysis* / Q000737:chemistry; D015374:Biosensing Techniques / Q000379:methods*; D002138:Calibration; D005978:Glutathione / Q000737:chemistry; D008024:Ligands; D057230:Limit of Detection; D010455:Peptides / Q000737:chemistry; D045663:Quantum Dots / Q000737:chemistry; D012995:Solubility; D013050:Spectrometry, Fluorescence; D014867:Water / Q000737:chemistry*
chemical_list: D008024:Ligands; D010455:Peptides; D014867:Water; D005978:Glutathione; D001151:Arsenic