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Fentanyl and its analogs have been at the center of the opioid epidemic currently wreaking havoc in the United States. One major element in the opioid crisis is the growing number of clandestine fentanyl labs being reported by enforcement agencies. The development of new analytical methods for detecting and identifying fentanyl and its congeners is among the useful tools in our goal to limit the use of this dangerous family of narcotics. Herein we describe an analytical technique using surface-enhanced Raman spectroscopy (SERS) and a microfluidic device, for detecting fentanyl and two of its chemical precursors, despropionylfentanyl (4ANPP) and N-phenethyl-4-piperidinone (NPP). The vibrational spectra of this family of analytes are very similar, making them difficult to distinguish by traditional means. In addition to taking advantage of the sensitivity provided by SERS, we developed a chemometric approach utilizing a hierarchical partial least squares-discriminant analysis algorithm that allowed us to distinguish spectra that possess many similar features. [ABSTRACT FROM AUTHOR]

The observed Raman intensity measured from carbon nanotubules with well-defined diameters and wall thicknesses of∼50 and ∼4 nm, respectively, deposited on a self-affine fractal silver surface was found to be enhanced by a factor of ∼ 1.4-1.7, relative to that of freestanding nanotubules in the absence of silver. Using an analysis in which the calculated distribution of tubules-to-silver distances determined by atomic force microscopy, was convolved with the expected nanotubule-silver distance dependence of the surface enhanced Raman (SERS) enhancement, this observation was reconciled with typical SERS enhancements observed in most silver-adsorbate systems. The analysis also took into account the attenuation of the incident laser intensity, which was determined from the reduction in the resonant Raman background signal that accompanies SERS. [ABSTRACT FROM AUTHOR]

Opioid overdose deaths resulting from heroin contaminated with the potent opioid agonist fentanyl, are currently a serious public health issue. A rapid and reliable method for identifying fentanyl-laced heroin could lead to reduced opioid overdose. Herein, we describe a strategy for detecting fentanyl at low concentrations in the presence of heroin, based on the significant hydrophobicity of fentanyl compared to heroin hydrochloride, by preferentially extracting trace concentrations of fentanyl using ultrasound-assisted emulsification microextraction using octanol as the extracting phase. Surface-enhanced Raman spectroscopy (SERS), is enabled by exposing the analyte to silver nanoparticle-coated SiO2 nanoparticles, designed to be stable in mixtures of octanol and ethanol. The sample is then loaded into an SU8/glass microfluidic device that is compatible with non-aqueous solutions. The SERS-active nanoparticles are aggregated by dielectrophoresis using microelectrodes embedded in the microfluidic channels, and the nanoparticle aggregates are interrogated using Raman spectroscopy. Using this method, we were able to reliably detect fentanyl from samples with as low as 1 : 10 000 (mol/mol) fentanyl-to-heroin ratio, improving the limits of detection of fentanyl-laced heroin samples by two orders of magnitude over current techniques. The described system could also be useful in chemical detection where rapid and robust preconcentration of trace hydrophobic analytes, and rapid SERS detection in non-aqueous solvents is indicated. [ABSTRACT FROM AUTHOR]

Discovered by Richard Van Duyne in 1976, surface-enhanced Raman spectroscopy (SERS) has enjoyed a continual expansion in interest over the past 36 years benefitting from a series of discoveries, new fields, and technological capabilities, all of which have greatly contributed to the current broad interest in this topic. The focus on nanoscience and nanotechnology that began in the early 1990s naturally put a spotlight on SERS as a quintessentially nanoscale phenomenon. This article discusses some of the key field-shaping developments in SERS from a historical and a materials perspective, providing background for the articles in this issue of MRS Bulletin. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman spectroscopy (SERS), an effect discovered in the 1970s and studied systematically in the 1980s, received a significant "second wind" with the report (primarily by Nie and by Kneipp) of enhancements large enough to allow the Raman spectrum of single molecules to be obtained. It is now understood that this occurs as a result of the extremely high electromagnetic fields that can exist at appropriately configured gaps and interstices between nanoparticles and other nanostructures composed of suitable materials (such as silver). With this insight one is now in a position to fabricate structures that will dependably and repeatably produce single-molecule SERS. We describe three such strategies: using molecular linkers to self-assemble silver clusters possessing the correct geometry; fabricating nanowire rafts in which the gaps between nanowires are "hot"; and structuring the interior of nanopores so as to produce finely-architectured nanostructured arrays. [ABSTRACT FROM AUTHOR]

Ampicillin, a common antibiotic, is detected at trace concentrations in milk using surface enhanced Raman spectroscopy in a microfluidic device, using less than 20 μL of sample, in 10 minutes, with minimal off-chip preparation. The device is configured so as to favor the interaction of the analyte with colloidal silver, and the optimization of the aggregation of the silver nanoparticles so as to increase the SERS intensity and the consequential sensitivity of analyte detection. [ABSTRACT FROM AUTHOR]

The dependence of band intensities in the Raman spectrum of individual single-crystal ruthenium dioxide (RuO2) nanowires on the angle between the plane of polarization of the exciting (and collected) light and the long axis of the nanowire, is shown to be a simple, complementary technique to high resolution transmission electron microscopy (HRTEM) for determining nanowire growth direction. We show that excellent agreement exists between what is observed and what is predicted for the polarization angle dependence of the intensities of the nanowires’ Eg (525 cm-1) and the B2g (714 cm-1) Raman bands, only by assuming that the nanowires grow along the (001) crystallographic direction, as confirmed by HRTEM. [ABSTRACT FROM AUTHOR]

The article discusses the study conducted by J. F. Li and colleagues on shell-isolated nanoparticles-enhanced Raman spectroscopy (SHINERS), which relies on gold nanoparticles that are coated with thin alumina or silica. It explains that Li and colleagues tested SHINERS' versatility by applying it to food and biological systems which resulted to the detection of vibrational bands in yeast cells. It adds that Li had only invented a powder that identify and detect the molecules in the surface.

Graphical abstract Highlights • Short range order in amorphous MnO x can be probed using Raman. • Under applied potential MnO x changes to resemble α-MnO 2. • For stable films, catalytic activity increases over time. Abstract Manganese oxides are promising water oxidation catalysts that have attracted great interest in the fuel cell industry. Previous studies have investigated differences in electrode activity based on the phases of MnO 2 involved determining structures and composition ex-situ. Here we compare two preparations of MnO 2 films, with differing catalytic activities as prepared, and observe morphological changes as a function of increasingly oxidizing potentials using in-operando Raman spectroscopy. We find that the Raman spectra of the films, both as-deposited and in solution, can be modelled as a binary mixture of amorphous manganese oxide and pure-phase cryptomelane that develop greater cryptomelane (α-MnO 2) character as the oxidizing potential increases in 1M KOH. Analyzing the Raman spectra using classical least squares fitting, we determine that both films converge on a cryptomelane score of approximately 0.25; concurrently their catalytic activities improve. These results suggest that significant variations in electrocatalytic activity arise from short range ordering in the catalyst that is not easily determined using ex-situ structure determination. [ABSTRACT FROM AUTHOR]

Single-molecule surface-enhanced Raman spectroscopy (SERS) offers new opportunities for exploring the complex chemical and biological processes that cannot be easily probed using ensemble techniques. However, the ability to place the single molecule of interest reliably within a hot spot, to enable its analysis at the single-molecule level, remains challenging. Here we describe a novel strategy for locating and securing a single target analyte in a SERS hot spot at a plasmonic nanojunction. The "smart" hot spot was generated by employing a thiol-functionalized cucurbit[6]uril (CB[6]) as a molecular spacer linking a silver nanoparticle to a metal substrate. This approach also permits one to study molecules chemically reluctant to enter the hot spot, by conjugating them to a moiety, such as spermine, that has a high affinity for CB[6]. The hot spot can accommodate at most a few, and often only a single, analyte molecule. Bianalyte experiments revealed that one can reproducibly treat the SERS substrate such that 96% of the hot spots contain a single analyte molecule. Furthermore, by utilizing a series of molecules each consisting of spermine bound to perylene bisimide, a bright SERS molecule, with polymethylene linkers of varying lengths, the SERS intensity as a function of distance from the center of the hot spot could be measured. The SERS enhancement was found to decrease as 1 over the square of the distance from the center of the hot spot, and the single-molecule SERS cross sections were found to increase with AgNP diameter. [ABSTRACT FROM AUTHOR]

The article provides information on a study that investigates hot spots in silver nanowire bundles for surface-enhanced Raman spectroscopy. It demonstrated a simple strategy for obtaining hot spots of the form "metal/molecule/metal", which automatically and eventually positions many analyte molecules in the junction between neighboring tips of silver nanowires that were fabricated in porous aluminum oxide (PAO) then exposed by the controlled dissolution of the alumina matrix. The article informs that silver nanowires were grown in highly ordered PAO template by AC electrodeposition.

The aggregation kinetics of silvernanoparticles in sessile dropletswere investigated both experimentally and through numerical simulationsas a function of temperature gradient and evaporation rate, in orderto determine the hydrodynamic and aggregation parameters that leadto optimal surface-enhanced Raman spectroscopic (SERS) detection.Thermal gradients promote effective stirring within the droplet. Theaggregation reaction ceases when the solvent evaporates forming acircular stain consisting of a high concentration of silver nanoparticleaggregates, which can be interrogated by SERS leading to analyte detectionand identification. We introduce the aggregation parameter, Γa τevap/τa, whichis the ratio of the evaporation to the aggregation time scales. Fora well-stirred droplet, the optimal condition for SERS detection wasfound to be Γa,opt= kcNPτevap≈ 0.3, which is a product of the dimerizationrate constant (k), the concentration of nanoparticles(cNP), and the droplet evaporation time(τevap). Near maximal signal (over 50% of maximumvalue) is observed over a wide range of aggregation parameters 0.05< Γa< 1.25, which also defines the time windowduring which trace analytes can be easily measured. The results ofthe simulation were in very good agreement with experimentally acquiredSERS spectra using gas-phase 1,4-benzenedithiol as a model analyte. [ABSTRACT FROM AUTHOR]

The article presents a chemically driven surface enhanced Raman spectroscopy-active system to meet the challenge which includes the construction of dimerlike nanoaggregates, nanowire bundles, and aligned rafts, or highly ordered periodic 2-dimensional nanostructures. It is emphasized that through a short linker molecule as a model analyte in conjunction with a novel microsphere patterning technique, nanoparticle hot spots can be found through routine optical microscopy.

The article examines the study regarding surface-enhanced Raman spectroscopy for DNA detection by nanoparticle assembly. The approach is likely to be suitable for the detection of RNA and DNA. Probe-tethered silver nanoparticles were assembled on a silver film through the agency of the complementary target DNA strand. The Raman spectra of molecules serving as Raman labels residing in the hot spot are strongly enhanced.

The article reports on a study concerning the utility of the surface-enhanced Raman spectroscopy (SERS) method for DNA Detection. In this study, researchers analysed how a single-stranded DNA (ssDNA) identification method takes advantage of surface-bound acids (PNAs) and an interplay of electrostatic interactions which produces SERS signals upon ssDNA/PNA hybridization.