Self-assembled core-shell nanoparticles with embedded internal standards for SERS quantitative detection and identification of nicotine released from snus products

Surface enhanced Raman spectroscopy (SERS) is a unique analytical technique with excellent performance in terms of sensitivity, non-destructive detection and resolution. However, due to the randomness and poor repeatability of hot spot distribution, SERS quantitative analysis is still challenging. Meanwhile, snus is a type of tobacco product that can release nicotine and other components in the mouth without burning, and the rapid detection technique based on SERS can reliably evaluate the amount of nicotine released from snus, which is of great significance for understanding its characteristics and regulating its components. Herein, the strategy was proposed to solve the feasibility of SERS quantitative detection based on self-assembled core-shell nanoparticles with embedded internal standards (EIS) due to EIS signal can effectively correct SERS signal fluctuations caused by different aggregation states and measurement conditions, thus allowing reliable quantitative SERS analysis of targets with different surface affinity. By means of process control, after the Au nanoparticles (Au NPs) were modified with 4-Mercaptobenzonitrile (4-MBN) as internal standard molecules, Ag shell with a certain thickness was grown on the surface of the AuNP@4-MBN, and then the Au@4-MBN@Ag NPs were used to regulate and control the assembly of liquid-liquid interface. The high-density nano-arrays assembled at the liquid-liquid interface ensure high reproducibility as SERS substrates, and which could be used for SERS detection of nicotine released from snus products. In addition, time-mapping research shows that this method can also be used to dynamically monitor the release of nicotine. Moreover, such destruction-free evaluation of the release of nicotine from snus products opens up new perspectives for further research about the impact of nicotinoids-related health programs.

Turning on hotspots: supracolloidal SERS probes made brilliant by an external activation mechanism

We achieved external activation of local hot-spot sites in supracolloidal assembly structures. The concept was demonstrated by boosting surface-enhanced Raman scattering (SERS) efficiency by one order of magnitude through a heating-induced process. Our approach involves assembling gold nanoparticles with distinct dimensions, i.e. 16 and 80 nm, into well-defined planet-satellite-type arrangement structures using thermoresponsive (poly(N-isopropylacrylamide)) star polymer linkers. Insights into the assembly process were obtained by calculations within the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory framework. We observe one order of magnitude increase in SERS enhancement by a heating-induced volume-phase transition. This magnification aligns with simulations run using the finite-difference time-domain (FDTD) method. The implications of this adaptive supracolloidal concept are twofold: Firstly, our approach bypasses limitations of existing systems that are associated with the limited accessibility of electromagnetic hot-spot sites in strongly coupled, static assemblies of plasmonic nanoparticles, by providing the capability of dynamic hot-spot re-configuration. Second, these externally activated probes offer promising opportunities for the development of messenger materials and associated sensing strategies.

FTIR and Raman Spectroscopic Characterization of Cannabinoids

Tetrahydrocannabinol (THC), cannabidiol (CBD) and cannabinol (CBN) are three key phytochemical components of cannabis. All three have demonstrated phytochemical activity and are implicated in pharmacological use of cannabis. In this paper, we present the FTIR and Raman spectroscopic characterization of THC, CBD and CBN compounds obtained from certified reference materials. Spontaneous Raman, mid-Infrared (MIR) absorption spectra as well as the analogous surface-enhanced counterparts (Surface enhanced Raman spectroscopy (SERS) and surface enhanced Infrared absorption (SEIRA)) of the cannabinoids are discussed in detail here. We have also examined the laser induced photothermal changes that occur in THC and CBD under spontaneous Raman acquisition conditions as revealed in their Raman spectra. Vibrational spectroscopy provides a robust, portable and cost effective analytical approach to quality control for various medicinal and consumer cannabinoid products. The pure compound spectra of the three cannabinoids presented in this work will help end-users to establish better quantitative analysis methods based on these techniques.

Shape- and Size-Dependent Refractive Index Sensing and SERS Performance of Gold Nanoplates

Plasmonic sensors are promising for ultrasensitive chemical and biological analysis. Gold nanoplates (Au NPLs) show unique geometrical structures with high ratios of surface to bulk atoms, which display fascinating plasmonic properties but require optimization. This study presented a systematic investigation of the influence of different parameters (shape, aspect ratio, and resonance mode) on localized surface plasmon resonance properties, refractive index (RI, n) sensitivities, and surface-enhanced Raman scattering (SERS) enhancement ability of different types of Au NPLs through finite-difference time-domain (FDTD) simulations. As a proof of concept, triangular, circular, and hexagonal Au NPLs with varying aspect ratios were fabricated via a three-step seed-mediated growth method by the experiment. Both FDTD-simulated and measured experimental results confirm that the RI sensitivities increase with the aspect ratio. Furthermore, choosing a lower order resonance mode of Au NPLs benefits higher RI sensitivities. The SERS enhancement abilities of Au NPLs also predicted to be highly dependent on the shape and aspect ratio. The triangular Au NPLs showed the highest SERS enhancement ability, while it drastically decreased for circular Au NPLs after the rounding process. The SERS enhancement ability gradually became more intense as the hexagonal Au NPLs overgrown on circular Au NPLs with increasing volumes of HAuCl₄ solution. The results are expected to help develop effective biosensors.

A Multilayer Interlaced Ag Nanosheet Film Prepared by an Electrodeposition Method on a PPy@PEDOT:PSS Film: A Strategy to Prepare Sensitive Surface-Enhanced Raman Scattering Substrates

A highly sensitive multilayer interlaced silver (Ag) nanosheet (MISN) film was prepared on a PPy@PEDOT:PSS film via an electrodeposition method for surface-enhanced Raman scattering (SERS) applications. After the PPy@PEDOT:PSS film was pretreated with ascorbic acid solution, many sparse Ag nanoparticles (NPs) could be directly reduced on the surface of the PPy@PEDOT:PSS film in AgNO₃ solution. Then, the MISN film was directionally grown along the surface of sparse Ag NPs by using an electrochemical galvanostatic method to form a Ag/PPy@PEDOT:PSS film for a SERS substrate. The results indicated that with the increase in electrodeposition time, the density of Ag nanosheets was also increased for boosting the SERS effect. Accordingly, owing to the directional growth of Ag NPs, the increase in the length-width ratio of single Ag nanosheets would further promote the SERS signal of the substrate. Moreover, the maximum enhancement factor of the SERS substrate could reach to 12,478, and the minimum limit of detection of melamine solution was down to 5.42 ng/mL. The SERS sensitivity of the Ag nanosheet film reached 100.65. This method of preparing the SERS substrate provides a novel and robust strategy for the low-cost and high-sensitivity detection in biomedicine, drugs, and food.

Iodide Functionalized Paper-Based SERS Sensors for Improved Detection of Narcotics

An inkjet-printed paper-based Surface-enhanced Raman scattering (SERS) sensor is a robust and versatile device that provides trace sensing capabilities for the detection and analysis of narcotics and drugs. Such sensors generally work well for analytes with good binding affinity towards the Au or Ag plasmonic nanoparticles (NPs) resident in the sensors. In this report, we show that iodide functionalization of the printed sensors helps to remove adsorbed contaminants from AuNP surfaces enabling superior performance with improved detection of narcotics such as fentanyl, heroin and cocaine by SERS. SERS signals are easily doubled with the iodide-functionalized sensors which also showed orders of magnitude improvement in detection limit. In this report, we show that a short (90 s) iodide treatment of the sensors significantly improved the detection of heroin. We propose that iodide functionalization be integrated into field detection kits through the solvent that wets paper-based sensor prior to swabbing for narcotics. Alternatively, we have also demonstrated that iodide functionalized sensors can be stored in ambient for up to 1 week and retain the improved performance towards heroin detection. This report will help to significantly improve the performance of paper-based sensors for field detection of narcotic drugs.

Multiplexed SERS Detection of Microcystins with Aptamer-Driven Core-Satellite Assemblies

We describe surface-enhanced Raman spectroscopy (SERS) aptasensors that can indirectly detect MC-LR and MC-RR, individually or simultaneously, in natural water and in algal culture. The sensor is constructed from nanoparticles composed of successive layers of Au core-SERS label-silver shell-gold shell (Au@label@Ag@Au NPs), functionalized on the outer Au surface by MC-LR and/or MC-RR aptamers. These NPs are immobilized on asymmetric Au nanoflowers (AuNFs) dispersed on planar silicon substrates through DNA hybridization of the aptamers and capture DNA sequences with which the AuNFs are functionalized, thereby forming core-satellite nanostructures on the substrates. This construction led to greater electromagnetic (EM) field enhancement of the Raman label-modified region, as supported by finite-difference time-domain (FDTD) simulations of the core-satellite assembly. In the presence of MC-LR and/or MC-RR, the aptamer-functionalized NPs dissociate from the AuNFs because of the stronger affinity of the aptamers with the MCs, which decreases the SERS signal, thus allowing indirect detection of the MCs. The improved SERS sensitivity significantly decreased the limit of detection (LOD) for separate MC-LR detection (0.8 pM) and for multiplex detection (1.5 pM for MC-LR and 1.3 pM for MC-RR), compared with other recently reported SERS-based methods for MC-LR detection. The aptasensors show excellent selectivity to MC-LR/MC-RR and excellent recoveries (96-105%). The use of these SERS aptasensors to monitor MC-LR production over 1 week in a culture medium of M. aeruginosa cells demonstrates the applicability of the sensors in a realistic environment.

Glutathione modified Ag nanoparticles as efficient detector for pyrimethanil

This work reports on glutathione modified Ag nanoparticles (GSH-Ag NPs) as a chemosensor for detecting pyrimethanil in an aqueous medium. The GSH-Ag NPs were expediently obtained by reducing AgNO₃ with NaBH₄ and modified with glutathione based on the Ag-S bond. The rapid discrimination for pyrimethanil from other pesticides exhibited the high selectivity of GSH-Ag NPs, then the selectivity was proved by ¹H NMR, FT-IR and computational simulation. Based on the good properties of localized surface plasmon resonance, the selective recognition was transformed to visible optical signal in colorimetric test. Additionally the quantitative detection was achieved with good sensitivity and could be applied to analyze practical samples. The experimental results have shown a good linear relationship with pyrimethanil concentration ranging from 10 μM to 1 mM and a low detection limit of 3.87 μM.

Quantitative measurement of carbon isotopic composition in CO2 gas reservoir by Micro-Laser Raman spectroscopy

The use of Micro-Laser Raman spectroscopy technology for quantitatively determining gas carbon isotope composition is presented. In this study, ¹²CO₂ and ¹³CO₂ were mixed with N₂ at various molar fraction ratios to obtain Raman quantification factors (F_12CO2 and F_13CO2), which provide a theoretical basis for calculating the δ¹³C value. And the corresponding values were 0.523 (0<C_12CO2/C_N2<2) and 1.11998 (0<C_13CO2/C_N2<1.5) respectively. It has shown that the representative Raman peak area can be used for the determination of δ¹³C values within the relative errors range of 0.076% to 1.154% in ¹³CO₂/¹²CO₂ binary mixtures when F_12CO2/F_13CO2 is 0.466972625. In addition, measurement of δ¹³C values by Micro-Laser Raman analysis were carried out on natural CO₂ gas from Shengli Oil-field at room temperature under different pressures. The δ¹³C values obtained by Micro-Laser Raman spectroscopy technology and Isotope Ratio Mass Spectrometry (IRMS) technology are in good agreement with each other, and the relative errors range of δ¹³C values is 1.232%-6.964%. This research provides a fundamental analysis tool for determining gas carbon isotope composition (δ¹³C values) quantitatively by using Micro-Laser Raman spectroscopy. Experiment of results demonstrates that this method has the potential for obtaining δ¹³C values in natural CO₂ gas reservoirs.

Evaluation of cigarette flavoring quality via surface-enhanced Raman spectroscopy

Herein, surface-enhanced Raman spectroscopy (SERS) combined with principal component analysis (PCA) has been successfully applied in the evaluation of cigarette flavoring quality using monolayer films of Au nanoparticles as substrates.

Various Silver Nanostructures on Sapphire Using Plasmon Self-Assembly and Dewetting of Thin Films

Silver (Ag) nanostructures demonstrate outstanding optical, electrical, magnetic, and catalytic properties and are utilized in photonic, energy, sensors, and biomedical devices. The target application and the performance can be inherently tuned by control of configuration, shape, and size of Ag nanostructures. In this work, we demonstrate the systematical fabrication of various configurations of Ag nanostructures on sapphire (0001) by controlling the Ag deposition thickness at different annealing environments in a plasma ion coater. In particular, the evolution of Ag particles (between 2 and 20 nm), irregular nanoclusters (between 30 and 60 nm), and nanocluster networks (between 80 and 200 nm) are found be depended on the thickness of Ag thin film. The results were systematically analyzed and explained based on the solid-state dewetting, surface diffusion, Volmer-Weber growth model, coalescence, and surface energy minimization mechanism. The growth behavior of Ag nanostructures is remarkably differentiated at higher annealing temperature (750 °C) due to the sublimation and temperature-dependent characteristic of dewetting process. In addition, Raman and reflectance spectra analyses reveal that optical properties of Ag nanostructures depend on their morphology.