Detection of Polynitro Compounds at Low Concentrations by SERS Using Ni@Au Nanotubes

Abstract

The identification of high-energy compounds in trace concentrations not only in the laboratory, but also in field conditions is of particular interest. The process should be clear, easy, and well-recognizable. We formed SERS-active substrates by using elongated nickel nanotubes synthesized by electrochemical deposition in the pores of ion-track membranes and coated them with gold for further application in the detection of low concentrations of analytes. The substrates were characterized using various techniques to determine the morphology of the nanotubes and modifying gold layer. The possibility of obtaining two types of gold-layer morphology was shown: in the form of a smooth film up to 20–50 nm thick and a coating with nanoneedles up to 250 nm long. The electric fields around the nanotubes were simulated at a laser wavelength of 532 nm to demonstrate the influence of the gold-layer morphology on the field distribution. The “needle” morphology was chosen to form the most effective SERS-active substrates for detection of low concentrations of aromatic polynitro compounds. The spectral peaks were identified by comparing the model and experimental Raman spectra at concentrations down to 10−5 M. Within this limit, all peaks (“fingerprints” of the substance) were clearly distinguishable.

Keywords

• template synthesis
• magnetic nanotubes
• Ni@Au nanocomposite
• surface-enhanced Raman scattering (SERS)
• track-etched membranes
• local E-field modelling