engleski

Seawater Anions, Salinity And Organic Content Simultaneously Assessed By Surface Enhanced Raman Scattering

Environmental seawater of Dubrovnik-Neretva County (Croatia) has been investigated for the first time using vibrational spectroscopy techniques in order to assess the possibility to monitor the salinity, anions concentration and possible contaminants resulted from intensive agriculture, aquaculture, navigation transport and mining in the Neretva basin river. Complex economic activity in the area leads to very different properties of land and water like salinity, temperature, heavy metals content of pesticides and herbicides, oil derivatives and PAH-s, etc. These pollutant materials could potentially harm local population and tourists. Raman spectroscopy was unable to evidence such species, therefore, we employed surface enhanced Raman scattering (SERS) using highly reproducible noble metal nanoparticles and different water samples both from aquaculture and wild environment. SERS signal of the seawater provided complex and rich information within a simultaneous manner concerning the inorganic phosphates, nitrates, nitrites, ammonia, carbonates, sulphates content as well as organic species and micro-organisms. The preliminary results revealed accurate, narrow, very well resolved SERS bands, for different seawater samples, using three different prepared Ag colloidal nanoparticles and without any chemical preparation of the raw seawater (samples collected from four distinct regions of the Croatian coast). The signal has been obtained within 3 seconds integration time using a compact, mini-Raman spectrometer. Seawater anions monitoring could be achieved by recording and calibrating the SERS intensity and half-width of the SERS fingerprint bands of individual components. Calibrations curves were used to track the SERS signal intensity as a function of concentration in domain compatible with the aquaculture conditions. The presence of the chloride in the SERS system is proved by the ubiquitously observed huge band at 242 cm-1, that has been assigned to the Ag-Cl bond. Its intensity is sensitive to the halide concentration, as previously shown by Liang et al. for a large range of halide concentrations and aggregation status of nanoparticles. Monitoring the three parameters of this SERS band, position, intensity and half-width, respectively, would provide the water salinity range concentration for fast tracking, simultaneously with the anions tracking. Moreover, in situ prepared Ag nanoparticles could provide fast and efficient SERS sensing approach, suitable for long run marine monitoring programs.

SERS; seawater

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