Gold nanorods as surface enhanced Raman spectroscopy substrates for sensitive and selective detection of ultra-low levels of dithiocarbamate pesticides

We report the use of gold nanorods as solution-based SERS substrates for the detection of ultralow-levels of three different dithiocarbamate fungicides: thiram, ferbam and ziram. Gold nanorods are attractive to use as SERS substrates due to the ability to tune the surface plasmon resonance of the nanoparticles to the laser excitation wavelength of the Raman spectrometer equipped with a 785 nm diode laser. The gold nanorods are synthesized using a seed-mediated growth method and characterized using UV-Visible spectroscopy, zeta potential, and TEM. The gold nanorods have an aspect ratio of 2.19 +/- 0.21 and have an average length of 37.81 +/- 4.83 nm. SERS spectra are acquired at different concentrations of each fungicide and calibration curves are obtained by monitoring the intensity of the band arising from the nu(C-N) stretching mode coupled to the symmetric delta(CH3) motion. The limits of detection and limits of quantitation are obtained for each fungicide. The limits of detection are 11.00 +/- 0.95 nM, 8.00 +/- 1.01 nM, and 4.20 +/- 1.22 nM for thiram, ferbam, and ziram respectively. The limits of quantitation are 34.43 +/- 0.95 nM, 25.61 +/- 1.01 nM, and 12.94 +/- 1.22 nM for thiram, ferbam, and ziram respectively. It can be seen that the three different dithiocarbamates can be detected in the low nM range based on the limits of detection that are achieved.