Silver Surface-enhanced Raman Scattering Research Articles

Portable identification of fentanyl analogues in drugs using surface-enhanced Raman scattering

North America's opioid epidemic has created a need for drug checking technologies (DCT) that can detect potent opioids such as fentanyl and its analogues in drugs, and thus reduce the risk of accidental overdose. Here, a novel silver surface-enhanced Raman scattering (SERS) substrate is evaluated on its suitability for use as a DCT in point-of-care harm reduction applications. These substrates are assembled by electrochemically reducing silver (Ag) ions onto a silicon (Si) chip imprinted with gold (Au) microelectrodes, forming SERS-active Ag nanostructures. SERS analysis of lab-grade fentanyl analogues found that the substrates produced spectra of fentanyl, furanylfentanyl, and carfentanil that could be distinguished using principal component analysis (PCA). The limit of detection of fentanyl on the substrates was determined to be within a practical range, however estimations of fentanyl concentrations to an order of magnitude were achieved with 70% accuracy. The substrates also demonstrated the ability to detect trace fentanyl in high concentrations of heroin and caffeine, respectively. Notably, the substrates are compatible with handheld Raman spectrometers, allowing for powerful chemical detection on a compact, portable device. The performance and usability demonstrated by these SERS substrates validates their potential for use as DCTs that could be vital to the safety of people who use drugs.

Ultrasensitive and reproducible surface-enhanced Raman scattering detection via an optimized adsorption process and filter-based substrate

Wih a view to improve the surface-enhanced Raman scattering (SERS) properties, including the sensitivity and uniformity, a simple and practical pretreatment method via optimizing the adsorption process of probe molecules and the morphology of SERS-active nanostructures was studied. Excellent SERS performances were obtained using this method such as high sensitivity (5 × 10−14 M rhodamine 6G, 1 × 10−8 M melamine), remarkable uniformity (∼9% relative standard deviation (RSD)) and reproducibility (∼10% RSD). Uniform and repeatable silver nanoparticle arrays were fabricated by an optimized filter-based method, which guaranteed the reliability of SERS detection. The SERS intensity was greatly improved by adjusting the adsorption capacity of the noble metal nanostructures, which has a linear relationship with the pH value of silver solution below 10. An accurate and reliable enhancement factor (EF) of 3.28 × 108 was calculated through the quantification of the adsorbed probe molecules. It is worth noting that the lifetime of the substrates prepared by this method could be prolonged to two months, which was definitely longer than other ordinary silver SERS substrates. The pretreatment method not only provided perfect SERS properties, but also made SERS a practical analysis tool because of its good homogeneity and ultralow detection limit.

Feasibility of colloidal silver SERS for rapid bacterial screening

This study reports the feasibility of citrate-reduced colloidal silver surface-enhanced Raman scattering (SERS) for differentiating three important food borne pathogens, E. coli, Listeria, and Salmonella. FT-Raman and SERS spectra of both silver colloids and colloid-K3PO4 mixtures were collected and analyzed to evaluate the reproducibility and stability of silver colloids fabricated in a batch-production process. The results suggest that the reproducibility of the colloids over the batch process is high and that their binding effectiveness remains consistent over a 60-day storage period. Two specific SERS bands at 712 and 390 cm−1 were identified and used to develop simple 2-band ratios for differentiating E. coli-, Listeria-, and Salmonella-colloid mixtures with a 100% success. These results indicate that colloidal silver SERS technique may be a practical alternative method suitable for routine and rapid screening of E. coli, Listeria, and Salmonella bacteria.

Simple Preparation Method for Silver SERS Substrate by Reduction of AgNO3 on Copper Foil

A simple new preparation method for silver surface-enhanced Raman scattering (SERS) substrate (Ag/Cu film) was developed by reduction of aqueous Ag+ on copper foil, which is used for making print circuit board. The properties of the substrate were evaluated. The approximate limit of detection (LOD) was measured using 2,2′-bipyridine (bpy) and 1,1′-diethyl-trimethincyanine dye (TMC) as probing compounds. The LOD of bpy and TMC are 1 nanomole and 0.13 nanomole, respectively. The film-to-film reproducibility is comparable to the nitric acid etched silver foil SERS substrate. The surface morphology of the Ag/Cu film was observed by scanning electron micrography. The high SERS sensitivity of the film may be attributed to its special surface structure.

Determination of the Ion-Pair Constant between Chloride Ion and Cationic-Coated, Silver SERS Substrates Using Competitive Complexation

The interaction of chloride ion with cationic-coated silver surface-enhanced Raman scattering (SERS) substrates was monitored using a competitive complexation technique. In this approach, the nitrate concentration is kept constant and the chloride ion concentration is varied. The change in the nitrate peak area, ΔANO3, is measured as a function of chloride ion concentration, CCl. The measured response is described by the following relationship: ΔANO3 = VCCl/(K + CCl). Using the value of Κ and the value of the ion-pair constant between the cationic coatings and nitrate ion, it is possible to extract the value of the ion-pair constant for chloride ion. The selectivities of the cationic coatings for nitrate, sulfate, and chloride ions are discussed.

Surface-enhanced Raman scattering from molecules adsorbed on gallium surfaces

We report the first observation of surface-enhanced Raman scattering (SERS) for molecules adsorbed on gallium surfaces. The gallium surfaces were prepared in UHV by depositing gallium vapor on cold copper substrates. The enhanced Raman spectra could be generated by all argon ion laser wavelengths between 457.9 and 514.5 nm but the magnitude of the enhancement was at least three times greater at 457.9 nm excitation than at 514.5 nm excitation. At 514.5 nm excitation, gallium SERS is about an order of magnitude weaker than silver SERS at the same excitation wavelength.