Orthogonal
sensing of nitroguanidine neonicotinoid insecticides is explored by combining
both surface enhanced Raman Spectroscopy (SERS) and nanoelectrochemical analysis.
Silver nanostructured surfaces were
fabricated for qualitative SERS-based detection of clothianidin and imidacloprid,
to provide characteristic molecular spectra of the molecules, Density
functional theory (DFT) studies were undertaken to assign the Raman active
vibrational modes for clothianidin and imidacloprid. The Raman spectrum of clothianidin is assigned
for the first time. Discrete arrays of on-chip
fully integrated gold nanowire electrodes were developed to provide
quantitative detection of the insecticides.
Square-wave voltammetry permits highly sensitive and rapid determination
of the neonicotinoids. Two electrochemical reduction peaks for clothianidin and
imidacloprid were identified, and detection limits of 0.22 ng/mL and 2.15 ng/mL
were subsequently achieved, respectively. These detection limits are
significantly lower than previously reported electrochemical techniques and are
comparable with significantly more complex and expensive chromatographic
methods. By employing both techniques in combination, SERS characterisation
provides the unique molecular fingerprint of each pesticide, while the nanoelectrochemical
measurement provides a quantitative determination to ultra-low limits of
detection. This combined spectro-electrochemical
approach has the potential to significantly reduce false positives, that arise
in remote monitoring, greatly increasing the robustness and credibility of these
measurements.
The multivariate detection limit for Mycoplasma pneumoniae as determined by nanorod array-surface enhanced Raman spectroscopy and comparison with limit of detection by qPCR
