In this work, novel silver sulphide quantum dots (Ag2S QD) are electrochemically quantified for the first time. The method is based on the electrochemical reduction of Ag+ to Ag0 at −0.3 V on screen-printed carbon electrodes (SPCEs), followed by anodic stripping voltammetric oxidation that gives a peak of currents at +0.06 V which represents the analytical signal. The optimized methodology allows the quantification of water-stabilized Ag2S QD in the range of approximately 2 × 109–2 × 1012 QD·mL−1 with a good reproducibility (RSD: 5%). Moreover, as proof-of-concept of relevant biosensing application, Ag2S QD are evaluated as tags for Escherichia coli (E. coli) bacteria determination. Bacteria tagged with QD are separated by centrifugation from the sample solution and placed on the SPCE surface for quantitative analysis. The effect of two different Ag2S QD surface coating/stabilizing agents on both the voltammetric response and the bacteria sensing is also evaluated. 3-mercaptopropionic acid (3-MPA) is studied as model of short length coating ligand with no affinity for the bacteria, while boronic acid (BA) is evaluated as longer length ligand with chemical affinity for the polysaccharides present in the peptidoglycan layer on the bacteria cells surface. The biosensing system allows to detect bacteria in the range 10−1-103 bacteria·mL−1 with a limit of detection as low as 1 bacteria·mL−1. This methodology is a promising proof-of-concept alternative to traditional laboratory-based tests, with good sensitivity and short time and low cost of analysis.
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This work has been supported by the FC-GRUPIN-ID/2018/000166 project from the Asturias Regional Government and the CTQ2017–86994-Rand CTQ2016–79412-P projects from the MINECO (Spain). O. Amor-Gutiérrez thanks the University of Oviedo for the award of a grant “Ayudas para la realización de tesis doctorales” (PAPI-18-PF-13). A. Iglesias-Mayor thanks the MECD (Spain) for the award of a FPU Grant (FPU2014/04686). P. Llano-Suárez thanks the University of Oviedo for the award of a grant "Ayudas para la realización de tesis doctorales" (PAPI-18-PF-08). A. de la Escosura-Muñiz acknowledges the MICINN (Spain) for the “Ramón y Cajal” Research Fellow (RyC-2016-20299) and the University of Oviedo for the “Ayudas Proyectos Emergentes 2019” project (PAPI-19-EMERG-17). F. Parra laboratory was funded by the Municipality of Ribera de Arriba/La Ribera (Asturias, Spain). Authors would like to acknowledge the technical support provided by Servicios Científico-Técnicos de la Universidad de Oviedo (Alaa Adawy at the laboratory of HR-TEM).
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This article is part of the Topical Collection on IX NyNA 2019. International Congress on Analytical Nanoscience and Nanotechnology
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Amor-Gutiérrez, O., Iglesias-Mayor, A., Llano-Suárez, P. et al. Electrochemical quantification of Ag2S quantum dots: evaluation of different surface coating ligands for bacteria determination. Microchim Acta 187, 169 (2020). https://doi.org/10.1007/s00604-020-4140-z
- Silver sulphide
- Quantum dots
- Electrochemical determination
- Anodic stripping voltammetry
- Bacteria quantification
- E. coli