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Principado de Asturias, Spain [FC-GRUPIN-IDI/2021/000081]; Ministry of Science and Innovation, Spain [PID2019-109698GB-I00, PID2020-117282RB-I00]; Fundacion Española para la Ciencia y la Tecnología [MCIU-20-FCT-PRECIPITA]; Banco Santander; University of Oviedo [PAPI-19-PF22]

The microbiological quality of drinking water is a concern to consumers, water suppliers, regulators, and public health authorities alike. Monitoring the microbiological quality of drinking water largely relies on the examination of indicator bacteria such as coliforms like Escherichia coli . E. coli is widely used as an indicator of fecal pollution when monitoring the microbial quality of drinking water, because it is abundant in all mammal feces and, therefore, is found in sewage and in natural waters contaminated with fecal matter, from human origin, wild animals, or derived from agricultural activity. This paper describes the development of a novel handheld fluorimeter for the rapid detection of E. coli in drinking water based on a specific cellular biomarker. The measurement system is based on a photomultiplier tube that captures the fluorescence signal produced by the cellular biomarker when it is excited by an ultraviolet LED. The cellular biomarker is also developed and it consists of a chimeric protein with a Green fluorescent protein (GFP) in the N-terminal domain and a specific amino acid sequence in the C-terminal domain (Colicin S4) that targets specifically the structure of the microorganism to be detected. The instrument is simple to use, lightweight, and can be powered by either an ac/dc power adapter or a rechargeable battery, making it an excellent choice for the rapid detection of E. coli in drinking water in field studies and laboratory measurements.

Photoinduced fluorescence enhancement of colloidal quantum dots (QDs) is a hot topic addressed in many studies due to its great influence on the bioanalytical performance of such nanoparticles. However, understanding of this process is not a simple task, and it cannot be explained by a general mechanism as it greatly depends on the QDs' nature, solubilization strategies, surrounding environment, etc. In this vein, we have critically compared the behavior of CdSe QDs (widely used in bioanalytical applications) with different surface modifications (ligand exchange and polymer coating), in different controlled experimental conditions, in the presence-absence of the ZnS layer and in different media when exposed for long times to intense UV irradiation. Thus six different types of colloidal QDs were finally studied. This research was carried out from a novel perspective, based on the analysis of the dynamic behavior of the photoactivation process (of great interest for further applications of QDs as labels in biomedical applications). The results showed a different behavior of the studied colloidal QDs after UV irradiation in terms of their photoluminescence characteristics, potential toxicity due to metal release to the environment, nanoparticle stability and surface coating degradation.