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Monitoring environmental pollutants in drinking water supplies is vitally important for public health. Unfortunately, current technologies that are commonly adopted for waterborne pollutant analysis are expensive and time consuming. Surface-enhanced Raman spectroscopy (SERS) provides an inexpensive and fast way for water pollutant detection owing to the extraordinary optical properties of plasmonic nanoparticles. This book chapter is focused on label-free SERS, i.e., collecting Raman spectra directly from the targeted water pollutants. Following an overview of the principles, basic paradigms, and substrates of SERS, examples of label-free SERS detection of waterborne pollutants, including organic micropollutants, biotoxins, and pathogens, will be discussed in detail. In this book chapter, we will also talk about the challenges that label-free SERS sensors are facing for the sensitive, reproducible, and quantitative analysis of water pollutants.

Commercial filter membranes have been widely used in laboratory water filtration processes without any pretreatment. However, whether they will leach organics into the membrane filtrates that can potentially interfere with the subsequent water analysis has long been overlooked. In this study, we found that filtering deionized water through the five typical commercial filter membranes produced filtrates with the total organic carbon (TOC) ranging from 0.32 to 7.2 mg L–1. Scanning electron microscopy and dynamic light scattering results show that the organics are present as irregularly shaped particles with a wide size distribution. Raman spectroscopy demonstrates that the organic particles share the same vibrational and fluorescence signatures with the blue separator papers between the membranes, indicating that they originated from the separator papers. Soaking the membranes in deionized water for 24 h, washing membranes for 30 s, or using a water sample volume over 100 mL can reduce the TOC in the membrane filtrates to below 1 mg L–1. This study systematically and quantitatively evaluates the potential interferences introduced by the laboratory membrane filtration step on water analysis and guides future users to take the best practice to mitigate such interferences.

Principle of an ssDNA paired aptasensor where extra dye binding sites are created to enhance its fluorescence response.