Synthesis Of Surface Enhanced Raman Scattering Substrate And Its Application For Determination Of Trace Explosives

In recent years, with frequent terrorist activities, the demand for explosive detection is increasing. For example, a rapid and simple detection method is particular importan for the airport or the train station. Surface enhanced Raman scattering (SERS) is considered to be one of the most powerful analytical methods in explosive detection in public area, due to its high sensitivity and capability of material qualitative analysis. At the same time, Raman instruments are also portable without sacrificing analytical performance.In this work, based on the wipe sampling method, we have prepared a new type of SERS substrate for the detection of trace explosives. Firstly, we fabricated many SERS substrates by using various methods to modify different textiles. We found that, by the using of Q-tip, a material that is widely used in daily life, a three-dimensional flexible SERS substrate could be fabricated. We discussed the influence on SERS performance of different factors for the SERS swab. These factors included the brand of the cotton swabs, and the growing protocol for the silver nanomaterials. Eventually, the optimized preparation condition for the swab substrate is self-assembly of Ag NPs for once and followed by in situ growing with 50 mM NaBH4 in the presence of AgNO3.Then, the limit of detection (LOD) and the reproducibility of the swab have been explored by applying a Raman probe (NBA). The characteristic SERS peak for NBA at-593 cm-1 can still be clearly identified even when the concentration is only 0.1 ppt (there is only 0.78 fg of analyte). We believe this is the lowest LOD in literature for this kind of swab analysis to the best of our knowledge. At the same time, a SERRS mapping signal falls into a Gaussian distribution with ～30% of RSD. It shows that the reproducibility is good. We also tested explosive 2,4-DNT. The LOD of 2,4-DNT is 250 ppb. Since the contaminated surface is ～4 cm2, the calculated surface density of 2,4-DNT is only ～1.2 ng/cm2. It is 2 orders of magnitude lower than what was achieved by the use of fiber optic coupled absorption/reflection infrared spectroscopy on metal surface. In the end, we demonstrate that it can be applied for the direct swab detection of 2,4-DNT. It is clear that even after 27th touch, the characteristic bands of 2,4-DNT are still clearly visible. The swab substrate can go with the portable Raman spectrometer, so the swab substrate can be widely used in the field of environmental safety.