Surface-enhanced Raman imaging through sprayed probes for the application in chemical visualization of methamphetamine within fingerprints.

For fingerprint-involved forensic investigations, cyanoacrylates and inorganic nanophosphors are mostly used for fingerprint visualization. However, methods to simultaneously report fingerprint images and the corresponding specific chemical information have yet to be realized. In this work, chemical visualization of the analytes in fingerprints is achieved through surface-enhanced Raman spectroscopy (SERS) measurements with the aid of spray-dispersed gold nanorods (AuNRs). The optimal coverage of AuNRs was studied by theoretical simulations and experimental operations. A rapid sampling of fingerprints with the chemical of interest was developed by tuning the spray parameters. In particular, the SERS imaging of methamphetamine in fingerprint latent was attempted by addressing the SERS spectral features of methamphetamine. This chemical visualization method reflects both the graphical and chemical characteristics of fingerprints in a single batch measurement, in which methamphetamine can be detected and mapped at the concentration of 10-5 M. The data processing approach was also modified by employing relevant logical judgments. The improved SERS images with sharpened patterns of fingerprints were obtained by involving the scored multi-peak judgments.

Fabrication of an Optoplasmonic Raft with Improved SERS Performance Detecting Methamphetamine through Bubble Enrichment.

In this work, a novel raft-like structure that combines noble metal nanoparticles (NPs) with an interconnected layer of hemispherical dielectric shell was fabricated and characterized. It was discovered that this hybrid material can enhance the optoplasmonic interaction between plasmonic and dielectric components, thereby improving the sensing performance in surface-enhanced Raman spectroscopy (SERS). Varied geometric parameters of the fabricated optoplasmonic raft, including the inner diameter and thickness of the dielectric shell, were attempted and analyzed through numerical simulation and experimental SERS measurements. With particular size, thickness, and incident orientation, the silica shell focuses the incident optical flow into the deposited silver NPs, undergoing similar near-field focusing behavior in comparison with other optoplasmonic entities. This optoplasmonic raft floating on the water surface is able to harvest the target molecules effectively through bubble enrichment, which rapidly captures and concentrates analytes from the aqueous phase. With a limited sampling time, the sensing performance of the developed optoplasmonic raft is improved by applying the optimized parameters involved in bubble enrichment. The substrates and corresponding enrichment method were implemented in the detection of methamphetamine (METH), achieving a limit of detection (LOD) down to 0.035 nM. As for practical onsite detection, the developed substrate and bubbling strategy were applied in an assembled set, employing a portable Raman spectrometer and an air pump. This set is able to detect METH dissolved in regular commercial beer, which is quite competent in the investigation of drug abuse.