Development of Surface-Enhanced Raman Spectroscopy on Monitoring of Microcystins in the Fresh Water

Abstract

Microcystin-LR (MC-LR) one of the most important cyanotoxins is carcinogenic and may cause damage of human liver The World Health Organization (WHO) sets the recommended drinking water standard to 1 μg/L of MC-LR and the detection methods commonly used include high-performance liquid chromatograph tandem mass spectrometry (HPLC/MS-MS) and enzyme-linked immunosorbent assay (ELISA) However the instrument itself and the consumables for sample pretreatments are expensive for HPLC/MS-MS and the activity of enzyme for ELISA is unstable In addition the time for detection for both methods are relatively long in the time scale of hours to days Therefore a novel and rapid detection technique Raman spectroscopy is a possible alternative method for MC-LR monitoring in fresh water In this study Surface-Enhanced Raman Scattering (SERS) substrates nano-porous gold film prepared by physical vapor deposition at high temperature was employed to enlarge the Raman signal One μL of MC-LR standard dissolved in methanol was dripped on the metal coating substrate Then during the drying process MC-LR was concentrated when coffee ring was formed on the periphery of the droplets Under this condition the strongest MC-LR Raman signal would be present on the coffee ring After confirming the characteristic peaks and area of measurement the parameters of Raman spectroscopy such as exposure time slit and spectral range were optimized in this study The MC-LR standards was used to determine that the characteristic Raman peaks measured with 632 8 nm and 532 nm lasers According to the established calibration curves of concentration of MC-LR and intensity of the characteristic peaks the detection concentrations were determined to be ranged from 1 to 500 mg/L with high coefficient of determination R^2>0 9 To measure environmental samples water samples were purified with solid phase extraction (SPE) and purged with nitrogen blowing As the fluorescence present in natural under Raman scattering overlapped with the Raman spectrum of MC-LR to be able to apply the method for environmental analysis more studies are needed to be conduct for reducing the matrix effect on analysis

Date of Award	2020
Original language	English
Supervisor	Tsair-Fuh Lin (Supervisor)