Cyanide SERS as a platform for detection of volatile organic compounds and hazardous transition metal ions

It is demonstrated herein that cyanide adsorbed on nanostructured Au is a very useful system for the detection of not only volatile organic compounds (VOCs) but also transition metal ions by means of surface-enhanced Raman scattering (SERS). This technique exploits the susceptibility of the CN stretching frequency of cyanide on Au to the variation of the surface potential of the Au nanostructures that occurs in response to the adsorption of VOCs onto these surfaces. It also exploits the susceptibility to the binding of transition metal cations to the pendant nitrogen atom, which reduces the anti-bonding character of the nitrogen lone pair of electrons. The CN stretching band was illustrated to undergo a blue-shift by up to 20 cm−1 in response to a typical biogenic VOC farnesol, whereas the band was red-shifted by 10 cm−1 in response to the typical biogenic VOC (+)-α-pinene. This method is considered to be highly sensitive given that the peak shift of 2 cm−1 could be reproducibly measured even at a partial pressure of 1 Pa, corresponding to 76 ppm of farnesol. The CN stretching band was also demonstrated to undergo a blue-shift by up to 60–64 cm−1 in the presence of trivalent cations such as Fe3+ and Cr3+, whereas the band was blue-shifted by 26–35 cm−1 in the presence of divalent metal ions such as Mn2+ and Fe2+. The present SERS method is regarded as very promising because transition metal ions were detectable at concentration levels as low as 1 fM.