Fabrication of SERS swab for direct detection of trace explosives in fingerprints.

Swab sampling is of great importance in surface contamination analysis. A cotton swab (cotton Q-tip) was successfully transformed into surface-enhanced Raman scattering (SERS) substrate (SERS Q-tip) through a bottom-up strategy, where Ag NPs were first self-assembled onto the Q-tip followed by in situ growing. The capability for direct swab detection of Raman probe Nile Blue A (NBA) and a primary explosive marker 2,4-dinitrotoluene (2,4-DNT) using the SERS Q-tip was explored. It was found that at optimum conditions, a femotogram of NBA on glass surface could be swab-detected. The lowest detectable amount for 2,4-DNT is only ∼1.2 ng/cm(2) (total amount of 5 ng) on glass surface, 2 orders of magnitude more sensitive than similar surface analysis achieved with infrared technique, and comparable even with that obtained by ion mobility spectrometry-mass spectrometry. Finally, 2,4-DNT left on fingerprints was also analyzed. It was found that SERS signal of 2,4-DNT from 27th fingerprint after touching 2,4-DNT powder can still be clearly identified by swabbing with the SERS Q-tip. We believe this is the first direct SERS swabbing test of explosives on fingerprint on glass. Considering its relative long shelf life (>30 d), the SERS Q-tip may find great potential in future homeland security applications when combined with portable Raman spectrometers.

A silver nanoparticle embedded hydrogel as a substrate for surface contamination analysis by surface-enhanced Raman scattering.

A surface enhanced Raman scattering (SERS) substrate, capable of extracting small amounts of organic species from surfaces of different types of materials with variable roughness, has been fabricated. The substrate consists of Ag NPs encapsulated in poly(vinyl alcohol) (PVA) hydrogels, commonly known as PVA "slime". Unlike traditional SERS substrates, such as colloidal suspensions, the resulting PVA slime SERS substrate presents good viscoelasticity, allowing it to conform to the surface of various materials of arbitrary roughness. Surfaces of different materials, including sandpapers, cotton, metal, and wood, previously contaminated with nile blue A (NBA) were analyzed with the PVA slime SERS substrate. Limits of detection (LOD) as low as 100 ppb (0.79 ng in a total amount on an area of ∼3 cm(2)) were achieved for all surfaces tested. Pesticides and Sudan red III on the glass surface have also been detected, with a LOD of 1.6 ng per ∼3 cm(2).