The potential for water pollution outbreaks requires the development of rapid, yet simple detection methods for water quality monitoring. Plasmonic nanostructures such as gold (AuNPs) and silver (AgNPs) nanoparticles are compelling candidates for the development of highly sensitive biosensors due to their unique localized surface plasmon resonances (LSPRs). The LSPR of AuNPs and AgNPs lies in the visible and infrared light range and is sensitive to the composition, size, shape, surrounding medium, and aggregation state of these NPs. This plasmonic behavior provides the basis for fabrication of colorimetric sensors for environmental analyses. Furthermore, the LSPR also enhances the electromagnetic field near the NP surface, which provides the basis for surface-enhanced Raman spectroscopy (SERS) based detection.Organic or inorganic pollutants and pathogens can be detected and differentiated based upon the fingerprint spectra that arise when they enter SERS-active hot spots. In this tutorial review, we summarize progress made towards environmental analysis based on LSPR-based colorimetric and SERS detection. The problems and challenges that have hindered the development of LSPR-based nanosensors for real-world environmental pollutant monitoring are extensively discussed.The localized surface plasmon resonance (LSPR) of gold (AuNP) and silver nanoparticles (AgNP) enables rapid identification and detection of environmental pollutants. Using a LSPR-based colorimetric assay it is possible to detect contaminants either visually or via spectroscopic approaches. For even greater sensitivity, LSPR enabled surface-enhanced Raman spectroscopy (SERS) makes single molecule or single pathogen detection achievable.

There is interest in the controlled aggregation of gold nanorods (GNRs) for the production of extended nanoassemblies. Prior studies have relied upon chemical modification of the GNR surface to achieve a desired final aggregate structure. Herein we illustrate that control of electrolyte composition can facilitate end-to-end assembly of cetyltrimethylammonium-bromide-coated (CTAB) GNRs. By adjusting either the sulfate anion concentration or the exposure time it is possible to connect GNRs in chain-like assemblies. In contrast, end-to-end assembly was not observed in control experiments using monovalent chloride salts. We attribute the end-to-end assembly to the localized association of sulfate with exposed quaternary ammonium head groups of CTAB at the nanorod tip. To quantify the assembly kinetics, visible-near-infrared extinction spectra were collected over a predetermined time period, and the colloidal behavior of the GNR suspensions was interpreted using plasmon band analysis. Transmission electron microscopy and atomic force microscopy results support the conclusions reached via plasmon band analysis, and the colloidal behavior is consistent with Derjaguin-Landau-Verwey-Overbeek theory.

No abstract