Critical review of challenges and opportunities for portable nucleic acid testing in water sources

Microbial water quality is a key indicator for safety and potability of any water sources. Monitoring biological water quality can limit the spread of waterborne diseases and deadly pathogens in drinking water, provide crucial information on the status of environmental matrices, assist in the identification of pollution sources and aid the conservation of wildlife and biodiversity. It plays an important role in epidemiology studies, enabling rapid identification of pathogens within a population via wastewater analysis. Nucleic acid testing represents one of the most attractive solutions for monitoring of microbial water quality. However, nucleic acid testing currently relies on laboratory-based equipment, limiting the potential for in-field testing applications and rapid assessment of water quality at the source. Although some portable biosensors for nucleic acid testing were reported, these still depend on manual steps or laboratory assets; moreover, very few devices were designed for water matrices, thus more efforts are needed to fulfil this gap. This critical review provides an insight into inspiring technologies and approaches that can pave the way forward for portable nucleic acid testing to be used in water diagnostics. Whilst several studies have already implemented DNA/RNA purification and detection in portable devices, low concentration of the analyte in water sources represents certainly the biggest challenge, requiring very low limit of detection. This article focuses on three core areas of development: i) analyte concentration, ii) nucleic acid purification, and iii) detection through loop-mediated isothermal amplification (LAMP). We believe that the integration of these three features into a single portable device can successfully enable affordable, rapid, and sensitive detection and deliver the vision of an accurate and robust in-field microbial monitoring in water sources.