Microplastics and nanoplastics are emerging pollutants, widespread both in marine and in freshwater environments. Cyanobacteria are also ubiquitous in water and play a vital role in natural ecosystems, using photosynthesis to produce oxygen. Using photography, fluorescence microscopy and cryogenic and scanning electron microscopy (cryo-SEM, SEM) we investigated the physicochemical response of one of the most predominant seawater cyanobacteria (Synechococcus elongatus, PCC 7002) and freshwater cyanobacteria (S. elongatus Nageli PCC 7942) when exposed to 10 μm diameter polystyrene (microPS) and 100 nm diameter polystyrene (nanoPS) particles. Marine and freshwater cyanobacteria formed aggregates with the nanoPS, bound together by extracellular polymeric substances (EPS), and these aggregates sedimented. The aggregates were larger, and the sedimentation was more rapid for the marine system. Aggregate morphologies were qualitatively different for the microPS samples, with the bacteria linking up a small number of particles, all held together by EPS. There was no sedimentation in these samples. The cyanobacteria remained alive after exposure to the particles. The particle size-and salt concentration-dependent response of cyanobacteria to these anthropogenic stressors is an important factor to consider for a proper understanding of the fate of the particles as well as the bacteria.
Surface-enhanced Raman scattering (SERS) is a powerful tool for detection of analytes at low concentrations. Because the electric field generated by surface plasmons decays exponentially with distance, the analyte must be in close proximity to the substrate to generate a measurable Raman signal. This often requires customization of the substrate for a specific subset of molecules. We have produced hybrid carbon−gold nanoparticles for the detection of a broad spectrum of molecules using SERS. Carboxyl-terminated carbon black (CB) nanoparticles were coated with the cationic polyelectrolyte poly(L-lysine) (PLL) and exposed to a tetrachloroauric acid solution. Gold−carbon black (Au-PLLCB) particles were formed by the reduction of gold chloride ions that concentrated on the surfaces of the PLL-coated CB templates. The Au-PLLCB particles produced strong SERS signals for 4-nitrobenzenethiol (4-NBT) in ethanol and for Congo red, crystal violet, and nitrate and sulfate ions in water. The underlying morphology of the carbon black template and the presence of PLL promoted the formation of highly curved gold structures on the surface, yielding hot spots for Raman enhancement. The underlying carbon acted as an absorbent for organic molecules, allowing analytes with poor affinity for the gold surface to concentrate in regions close enough to the particle surfaces to enable detection by SERS. The morphology and chemical nature of the underlying template make the Au-PLLCB particles applicable for SERS-based detection of a wide range of analytes in solution. KEYWORDS: surface-enhanced Raman spectroscopy (SERS), gold−carbon black nanoparticles, SERS-based sensor, analyte detection, nanosensor
Inelastic scattering from molecules because of vibrational modes produces unique Raman shifts, allowing these analytes to be detected with high specificity. Because Raman scattering is weak, surface-enhanced Raman scattering (SERS) has been used as a label-free technique for the detection of a variety of analytes at low concentrations. Using simple solution-based colloidal processing techniques, we have fabricated gold-coated carbon-black nanoparticles that show enhanced Raman activity. By varying the fabrication conditions, we create particles of different surface morphologies, allowing control over the peak wavelength for localized surface plasmon resonance (LSPR). By matching the LSPR wavelength to the incident laser wavelength, we get the highest signal from two model analytes, 4-nitrobenzenethiol (4-NBT) and Congo Red (CR). Our straightforward room-temperature-solution-based approach for making tunable SERS-active particles expands the range of incident radiation wavelengths that can be used for the detection of analytes using Raman scattering.
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