Selective surface-enhanced Raman scattering detection of Tabun, VX and Cyclosarin nerve agents using 4-pyridine amide oxime functionalized gold nanopillars.

We have earlier demonstrated sensitive detection of low the volatile nerve agents Tabun, Cyclosarin and VX by using handheld Raman instrumentation in conjunction with surface-enhanced Raman scattering (SERS) attained with gold and silver coated Si nanopillar substrates. In the present proof-of-concept study, the gold substrates chemically are functionalized to realize selectivity towards organophosphorus compounds (OPs) with high sensitivity. A potential capturer and reporter molecule, chemical nerve agent antidote, 4-pyridine amide oxime, is evaluated due to its high Raman cross section, high chemical affinity towards gold, and binding specificity to the target substances Tabun, VX and Cyclosarin via the oxime group. Upon selective and covalent binding, the SERS probe undergoes structural changes which are reflected in the spectral SERS responses, making it suitable for indirect monitoring of nerve agents in aqueous solution. With the probe attached to the hotspots of Au-coated Si nanopillars, the SERS signals distinctly discriminate between specific and non-specific analyte binding of Tabun, Cyclosarin and VX down to sub ppm levels. SERS spectrum of 4-PAO is measured after microliter drop coating of aqueous sample solution onto the functionalized substrates and subsequent water evaporation from surfaces. This binding assay is complemented by letting functionalized substrates being immersed into sample solutions 1 h before measuring. Binding specific SERS response decreases in following order: Tabun > VX > Cyclosarin. Overall, the concept looks promising, as expected the candidate probe 4-PAO introduces selectivity to the nanopillar gold substrates without loss of sensitivity.