Recently a high demand for fast, cheap and easy to use selective and sensitive methods for trace detection of explosives developed. Beside other techniques like sensitive mass detections SERS (Surface-enhanced Raman spectroscopy) is a very powerful tool to enhance signals in the order of 104 - 1010 for Raman-active analytic molecules. SERS based on the interaction between surface plasmon of metal nanoparticles (10 – 300 nm) like gold, silver, aluminum and gold/palladium alloy with traces of contaminants like explosives. Here we present our results for different explosives on different available and self-made SERS-substrates with varying parameters, like laser excitation (266 nm, 532 nm, 633 nm, 785 nm and 1064 nm), laser power, spot size and local energetic efficiency to acquire the best practice for an easy, effective and safe treatment of explosive traces.
Tougher security requirements and an increasing number of terror attacks have led to rapid advances in the field of explosive detection in the past few years. Detection systems have to be tested and validated with realistic samples and amounts as early as possible during the development. However, at present, well defined and homogeneous test materials which are a crucial requirement for development and validation of trace detection systems are not available.
Existing preparation methods of reference samples, such as drop-and-dry (drop casting) methods, present a range of variability and reproducibility issues, including inhomogeneous sample coverage and material waste. Especially for the preparation of samples for optical stand-off technologies the drop-on-demand and inkjet printing technology could be a promising method of producing standardized chemically contaminated test materials with high accuracy, precision, scalability, and flexibility to allow for the inexpensive, high-throughput production.
Test samples with contaminations ranging from nanogrammes to microgrammes have been prepared and analysed over several weeks of storage. The influence of plot parameters on the morphology and durability of printed samples of various common explosives have been investigated on different substrates.
HPLC measurements were made to quantitatively evaluate the durability of printed samples. The morphology of the test samples was additionally characterized by optical microscopy and confocal Raman-microscopy. Besides the occurrence of polymorphic phase changes, described in literature for low concentrated drop-on-demand samples of RDX, we observed changes in sample distribution by recrystallization of some explosives in the printed samples.
This paper focuses on the optimization of methods for the preparation of test samples and on the analysis especially concerning the effect of polymorphic phase changes caused by inkjet printing of samples.