Selective detection of TNT withmodified SERS-surfaces : Investigation of TNT adsorption and detection using goldand silver nano structured surfaces modified by cysteineand cysteamine

Abstract: In the search for trace amounts of explosives in various environmental samples, the analytical procedure is in need of improvements. If it is for national security or for environmental purposes the detection of trace amounts of for example 2,4,6- trinitrotoluene (TNT) is a costly and time consuming procedure. The use of Raman spectrometry for trace amounts detection is one of the research areas that are in the advancement and mainly because of the discovery of Surface-Enhanced Raman spectroscopy (SERS). Raman spectrometry detects the inelastically scattered light from molecules giving a fingerprint spectrum that can be interpreted and species can be detected. The inelastically scattering of light only occurs in a small amount of the molecules making the signal low and sensitive for interferences. SERS enhances the signal from the molecules making it possible to detect very low concentrations. The surfaces used in SERS need to be selective for the wanted species to be useful for the analysis of environmental samples that often contains a wide variety of compounds. This project’s aim was to investigate the possibility of modifying gold- and silvercoated SERS surfaces (provided by DTU Nanotech) to get a selective detection of trace amounts of TNT in water and air samples. The results from the modification indicated some problems with the surfaces. The modification molecules were cysteine or cysteamine. The hypothesis was that both of them should bind to the surface by sulphur bond. But for cysteine this was not the case. The results indicated a binding of the carboxyl group making the use of the modification for the selective detection of TNT impossible. The modification by cysteamine was more successful but the detection of TNT in water samples was hard to get clear results from. The detection of TNT in air samples was carried out by a method never tested before using a so-called Linkam cell in conjunction with a TNT treated GC-column which together create a controlled environment. The results from this experiment were very positive where a clear SERS-signal from TNT could be detected.