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Gold nanorods as SERS substrate for the ultratrace detection of cocaine in non-pretreated oral fluid samples
Abstract
This work shows the capability of surface-enhanced Raman spectroscopy (SERS) to detect ultratraces of cocaine (COC) in oral fluid (OF). It proposes a new solid substrate made of gold nanorods (Au NRs) to perform sensitive analyses of this complex matrix without any sample pretreatment. The Au NRs were synthetized optimizing the synthesis conditions, and then characterized and tested as SERS substrate. The presented results demonstrated that the SERS methodology was able to detect COC in OF with a limit of detection (LOD) as low as 10 ng/mL. This value was five orders of magnitude smaller than the one obtained with Raman spectroscopy (RS) and in the order of the cut-off value (8 ng/mL) established for confirmatory test of COC in OF. Besides, a multivariate analysis (OPLS-DA) applied on the samples analysed by SERS evidenced that it was possible to discriminate among various COC concentrations. These are quite positive results because even the 1 ng/mL COC concentration sample could be identified as different from the OF sample. In addition, the absence of sample pretreatment and the ease of the proposed method, allowed performing rapid and non-destructive analyses, making the method suitable for in situ forensic analyses.
... Apart from the aforementioned mainstream detection methods, other analytical techniques including IMS, [23,45,47,55,58] Fourier transform infrared spectroscopy (FTIR), [81,[91][92][93][94] surface-enhanced Raman spectroscopy (SERS) [31,51,56] and high-performance thin-layer chromatographic (HPTLC) [89] have been used for detection of cocaine. Among them, IMS is a detection technology that was developed in the late 1960s. ...
... SERS-based methods have also been used for analysis of cocaine, although various novel SERS substrates need to be prepared to enhance sensitivity, uniformity and reproducibility of the SERS platform. D'Elia et al. [51] proposed a new solid substrate, made of gold nanorods (AuNRs), for highly sensitive analysis of complex matrices without any sample pretreatment. Consequently, the Au NRs-SERS method effectively detected cocaine in oral fluids with a LOD as low as 10 ng/mL. ...
Cocaine abuse has attracted increased attention in the recent past since it can cause addiction and great harm to the normal human body. Due to cocaine exists in various complex matrices, the detection of it in different matrices is helpful to prevent abuse. It is thus imperative to establish efficient and accurate methods for pretreatment and detection of cocaine in different samples. The present study provides a summary of the research progress of cocaine pretreatment methods (such as different microextraction methods, QuEChERS, and solid phase extraction based on novel extraction materials) and detection approaches (such as liquid chromatography coupled with different detectors, gas chromatography and related techniques, capillary electrophoresis and sensors). A comparison of the pros and cons of different pretreatment and detection methods is presented. The findings of this study will provide a reference for selection of the most suitable cocaine pretreatment and detection techniques.
... The target molecules first diffused laterally into the side flows and salts diffused into the colloid flow, allowing nanoparticles to aggregate, resulting in a sensitive detection with strong signals. In another report, D'Elia et al. proposed a solid substrate made of gold nanorods fabricated by a seed-mediated, surfactant-assisted method for identifying ultra-traces of cocaine in saliva without any sample treatments [106]. Using Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) as a multivariate analysis method on samples analyzed by SERS, it was possible to categorize various cocaine concentrations without any sample preparation. ...
... The proposed device could identify cocaine at a concentration as low as 1.0 ng/mL. method for identifying ultra−traces of cocaine in saliva without any sample treatments [106]. Using Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS−DA) as a multivariate analysis method on samples analyzed by SERS, it was possible to categorize various cocaine concentrations without any sample preparation. ...
The rapid increase in illicit drug use and its adverse health effects and socio-economic consequences have reached alarming proportions in recent years. Surface-enhanced Raman scattering (SERS) has emerged as a highly sensitive analytical tool for the detection of low dosages of drugs in liquid and solid samples. In the present article, we review the state-of-the-art use of SERS for chemical analysis of illicit drugs in aqueous and complex biological samples, including saliva, urine, and blood. We also include a review of the types of SERS substrates used for this purpose, pointing out recent advancements in substrate fabrication towards quantitative and qualitative detection of illicit drugs. Finally, we conclude by providing our perspective on the field of SERS-based drug detection, including presently faced challenges. Overall, our review provides evidence of the strong potential of SERS to establish itself as both a laboratory and in situ analytical method for fast and sensitive drug detection and identification.
... Complex nanophotonic technologies also show potential for the tracing of illegal or adulterant drugs [73,74,85,87,89,[131][132][133][134][135]. With the developed techniques, drugs can even be traced in fingerprints [89] or in body fluids other than blood or urine such as saliva [87,90,136]. ...
... Complex nanophotonic technologies also show potential for the tracing of illegal or adulterant drugs [73,74,85,87,89,[131][132][133][134][135]. With the developed techniques, drugs can even be traced in fingerprints [89] or in body fluids other than blood or urine such as saliva [87,90,136]. D'Elia et al. recently reported about the extremely sensitive detection of cocaine in saliva via SERS, without any sample preparation [47]. ...
Innovations in Raman spectroscopic techniques provide a potential solution to current problems in pharmaceutical drug monitoring. This review aims to summarize the recent advances in the field. The developments of novel plasmonic nanoparticles continuously push the limits of Raman spectroscopic detection. In surface-enhanced Raman spectroscopy (SERS), these particles are used for the strong local enhancement of Raman signals from pharmaceutical drugs. SERS is increasingly applied for forensic trace detection and for therapeutic drug monitoring. In combination with spatially offset Raman spectroscopy, further application fields could be addressed, e.g. in situ pharmaceutical quality testing through the packaging. Raman optical activity, which enables the thorough analysis of specific chiral properties of drugs, can also be combined with SERS for signal enhancement. Besides SERS, micro- and nano-structured optical hollow fibers enable a versatile approach for Raman signal enhancement of pharmaceuticals. Within the fiber, the volume of interaction between drug molecules and laser light is increased compared with conventional methods. Advances in fiber-enhanced Raman spectroscopy point at the high potential for continuous online drug monitoring in clinical therapeutic diagnosis. Furthermore, fiber-array based non-invasive Raman spectroscopic chemical imaging of tablets might find application in the detection of substandard and counterfeit drugs. The discussed techniques are promising and might soon find widespread application for the detection and monitoring of drugs in various fields.
... Inkjet printed SERS substrates [58] 25 ng/mL Cocaine Gold nanorods [59] 10 ng/mL (oral fluid) Our method-Cocaine and Heroin Solution based 'Mix and detection' technique using BGNS-Ag3 10 pg/mL-cocaine and 100 pg/mL-heroin (water) 100 pg/mL-cocaine and 1 ng/mL-heroin (human urine) ...
A rapid, in-field, and reliable method for the detection of illegal drugs of abuse in biological fluids without any sample pretreatment would potentially be helpful for law enforcement, drug control officials, and public healthcare. In this study, we presented a cost-effective and highly reproducible solution-based surface-enhanced Raman scattering (SERS) platform utilizing a portable Raman instrument for fast sensitive SERS detection of illegal drugs, such as cocaine, and heroin in human urine without any sample preprocessing. The SERS platform was constructed for the first time by combining the superior SERS enhancement properties of bimetallic silver-coated gold nanostars (BGNS-Ag) and the advantages of suitable alkaline metal salts such as NaI for SERS signal amplification. The effects of the silver thickness of BGNS-Ag and alkaline salts on the SERS performance were investigated in detail; we observed that the maximum SERS enhancement was obtained for BGNS-Ag with the maximum silver thickness (54 ± 5 nm) in presence of NaI salt. Our SERS platform shows ultra-high sensitivity of cocaine and heroin with a limit of detection (LOD) as low as 10 pg/mL for cocaine and 100 pg/mL for heroin, which was 100 times lower than that of the traditional silver nanoparticle-based illegal drug detection. As a demonstration, the platform was further applied to detect cocaine and heroin spiked in human urine without any sample preprocessing achieving a LOD of 100 pg/mL for cocaine and 1 ng/mL for heroin. Overall, our SERS detection platform shows potential for rapid, onsite, ultra-low-cost portable applications for trace detection of illegal drugs and biomarkers.
... Raman spectroscopy is a valuable technique to study chemical and intramolecular bonds by producing and examining inelastic scattering generated from molecules, thus providing a vibrational fingerprint, unique for each molecule, becoming a powerful tool to identify chemical species, supplying both qualitative and quantitative molecular information from any sample. Unfortunately, this is a very weak process, but it has been found that when the molecules are located near a rough metal surface or metal nanoparticles (NP), a Raman scattering boost occurs, greatly enhancing the signal intensity [8], thus opening the way to a new emerging research field: the surface-enhanced Raman scattering (SERS) spectroscopy, that has proved to be a powerful technique for non-invasive, rapid and reliable sensing of chemicals and biomolecules [9][10][11]. The Raman enhancement in SERS spectroscopy occurs when an incident electromagnetic field interacts with surface plasmon resonance at a metal surface (SERS effect) [12]. ...
In SERS analysis, the specificity of molecular fingerprints is combined with potential single-molecule sensitivity so that is an attractive tool to detect molecules in trace amounts. Although several substrates have been widely used from early on, there are still some problems such as the difficulties to bind some molecules to the substrate. With the development of nanotechnology, an increasing interest has been focused on plasmonic metal nanoparticles hybridized with (2D) nanomaterials due to their unique properties. More frequently, the excellent properties of the hybrids compounds have been used to improve the drawbacks of the SERS platforms in order to create a system with outstanding properties. In this review, the physics and working principles of SERS will be provided along with the properties of differently shaped metal nanoparticles. After that, an overview on how the hybrid compounds can be engineered to obtain the SERS platform with unique properties will be given.
... In fact, the investigation of many drugs of abuse has been explored with SERS including amphetamines, MDMA, and amphetamine-like substances (Bell et al., 2000;Sägmüller et al., 2001;Faulds et al., 2002); barbiturates (Farquharson and Lee, 2000); mephedrone (Mabbott et al., 2013); and other types of drugs including cocaine, morphine, hydrocodone, fentanyl, codeine, diazepam, and fentanyl analogs Rana et al., 2011;Leonard et al., 2017;Haddad et al., 2018;Shende et al., 2019b;Wang et al., 2019, Smith et al., 2021Wang H. et al., 2021;Wang L. et al., 2021;Wilson et al., 2021;Zhang et al., 2021). The use of SERS has also enabled the analysis of these drug analytes in toxicological specimens such as urine, saliva, and blood Andreou et al., 2013;D'Elia et al., 2018;Shende et al., 2019a;Sivashanmugan et al., 2019;Han et al., 2021). ...
Reliable identification of fentanyl and fentanyl analogs present in seized drug samples is imperative to the safety of first responders and laboratory personnel and informs the future analysis process and handling procedures. The electrochemical-surface enhanced Raman spectroscopy (EC-SERS) method developed in this work allows the in-situ preparation of the SERS substrate providing a rapid, efficient, and accurate approach to detect fentanyl, even at low percent by weight concentrations common in seized drugs. Optimization of the electrochemical potentials suitable for the SERS substrate preparation and adsorption of the analyte was achieved using multi-pulse amperometric detection. This method demonstrated large enhancement of the SERS response. This method was applied to six fentanyl analogs with substitutions to the amide group, representing small changes in the fentanyl core structure. Identification of these analogs through differences in the EC-SERS spectra was evident. Interference studies incorporating analytes frequently encountered with fentanyl including heroin, cocaine, methamphetamine, naltrexone, and naloxone were assessed and found to offer limited to no interference. The limits of detection of the fentanyl compounds were in the low to mid nanograms per milliliter range, with the most sensitive compound detected at 10 ng/ml. Application of the method to simulated drug mixtures was performed to determine fit-for-purpose. In all mixtures with fentanyl as the minor contributor, fentanyl was correctly identified, including mixture samples comprised of 5 and 1% fentanyl. This approach represents the first in-situ EC-SERS analysis of fentanyl and its analogs and provides accurate and efficient screening for fentanyl in seized drug samples.
... The transversal one is situated at approximately 520 nm and the longitudinal one, characteristic to GNRs, is related to their aspect ratio (length/width ratio). Although GNRs are intensely investigated for a wide range of sensing applications [9][10][11][12], their utility as colloidal SERS substrates is somewhat limited, as Raman signal amplification is conditioned by a perpendicular orientation of the laser to the long axis of the rod [13]. Consequently, in colloidal dispersion, due to the random orientation of the rods, the overall signal enhancement efficiency is far from ideal. ...
Extensive effort and research are currently channeled towards the implementation of SERS (Surface Enhanced Raman Spectroscopy) as a standard analytical tool as it has undisputedly demonstrated a great potential for trace detection of various analytes. Novel and improved substrates are continuously reported in this regard. It is generally believed that plasmonic nanostructures with plasmon resonances close to the excitation wavelength (on-resonance) generate stronger SERS enhancements, but this finding is still under debate. In the current paper, we compared off-resonance gold nanobones (GNBs) with on-resonance GNBs and gold nanorods (GNRs) in both colloidal dispersion and as close-packed films self-assembled at liquid-liquid interface. Rhodamine 6G (R6G) was used as a Raman reporter in order to evaluate SERS performances. A 17-, 18-, and 55-fold increase in the Raman signal was observed for nanostructures (off-resonance GNBs, on-resonance GNBs, and on-resonance GNRs, respectively) assembled at liquid-liquid interface compared to the same nanostructures in colloidal dispersion. SERS performances of off-resonance GNBs were superior to on-resonance nanostructures in both cases. Furthermore, when off-resonance GNBs were assembled at the liquid interface, a relative standard deviation of 4.56% of the recorded signal intensity and a limit of detection (LOD) of 5 × 10−9 M could be obtained for R6G, rendering this substrate suitable for analytical applications.
... For circumventing these issues, seedless synthesis techniques were developed, by generating the seeds in situ [17][18][19][20].In biomedicine, AuNRs are utilized as delivery agents for drugs or genes [21][22][23] in photothermal cancer medicine [24][25][26][27] or cell and biomolecule imaging [28][29][30]. They are also employed in optical sensors [31] based on surface-enhanced Raman spectroscopy (SERS) [32][33][34][35] and surface plasmon resonance (SPR) [36,37]. ...
Surface plasmon resonance (SPR) is a label-free, real-time bio-sensing technique with high potential in the diagnostic area, especially when a signal amplification strategy is used to improve the detection limit. We report here a simple method for enhancing the detection limit of bovine serum albumin (BSA), by attaching gold nanorods (AuNRs).
AuNRs were obtained by a seedless synthesis technique and characterized using scanning electron microscopy (SEM), UV-VIS spectroscopy, FT-IR spectroscopy and dynamic light scattering (DLS). Finite element method (FEM) simulations were employed to explore the enhancement of the SPR signal by adding AuNRs on the SPR sensor's metallic layer. SPR spectroscopy was used to analyze the changes in the refractive index brought by the immobilization of unconjugated BSA and BSA modified with AuNRs.
The results confirmed that the AuNRs conjugated with the protein increase the SPR signal ~ 10 times, leading to a limit of detection of 1.081 × 10⁻⁸ M (0.713 μg/mL).
... Cocaine detection at trace levels as low as 10ng/ml was reported using gold nanorods synthesized using seed-mediated, surfactant assisted method (D'Elia et al. 2018). Silver doped sol-gel SERS substrates were used to detect 5-fluorouracil, chemotherapeutic drug spiked in saliva at physiological . ...
Human saliva can be treated as a pool of biological markers able to reflect on the state of personal health. Recent years have witnessed an increase in the use of optical devices for the analysis of body fluids. Several groups have carried out studies investigating the potential of saliva as a non-invasive and reliable clinical specimen for use in medical diagnostics. This brief review aims to highlight the optical technologies, mainly surface plasmon resonance (SPR), Raman, and Fourier transform infrared (FTIR) spectroscopy, which are being used for the probing of saliva for diverse biomedical applications. Advances in bio photonics offer the promise of unambiguous, objective and fast detection of abnormal health conditions and viral infections (such as COVID-19) from the analysis of saliva.
... As mentioned above, the size and shape of metal nanoparticles affect the intensity of SERS through surface plasmon resonance, so the development of nanosubstrates of different sizes and shapes is of great significance for high sensitivity detection. D'Elia et al. fabricated gold nanorods for ultra-trace detection of cocaine in unprepared oral fluid samples, and the results confirmed the increased sensitivity and high stability and reproducibility of the detection with gold nanorods [30]. Wang et al. developed a novel solvothermal method to synthesize Ag nanocubes with controllable size. ...
Food safety and quality have gained much attention and the capability to evaluate food quality and safety in a sensitive, rapid, and reliable manner is of great importance in the food industry. Surface-enhanced Raman scattering (SERS) with the advantages of excellent sensitivity, high selectivity, non-destructive nature, and significant enhancement to identify the target has demonstrated a great potential for quick detection of the food sample. The enhancement of Raman signals for SERS is not only related to the interactions between substrates and samples but also the functionalization of substrates to gain SERS active substrates. In the present review, this paper summarized the progress of SERS quantitative analysis and application in food safety detection. The future trends and perspectives were also given.
... SERS technique has the capability to detect even small amount of COC in biological media. For example, D'Elia et al. [138] reported COC detection up to 32 nM using Au nanorods (AuNRs) as SERS substrate which is several orders of magnitude smaller in amount compared to Raman spectroscopy-based detection. Besides AuNRs, Au film also assisted in SERS-based detection of cocaine. ...
Illicit drug-related incidents such as traffic accidents and sexual assaults are gaining epidemic proportions worldwide. Besides, there is the rampant use of drugs at some critical workplaces, which can result in serious safety breaches. As a result, point-of-care diagnostic and monitoring devices are becoming increasingly important for clinical diagnostics, onsite investigation of crime, workplace testing of personnel, and roadside drug detection to prevent driving under the influence. This review focuses on the recent state of rapid and real-time diagnostics of the most common illicit drugs such as cocaine (COC), tetrahydrocannabinol (THC), methamphetamine, amphetamine, fentanyl, opioids (morphine, codeine), heroin, and benzodiazepine (alprazolam, chlordiazepoxide, diazepam, oxazepam, and clonazepam), using colorimetric, fluorescence, Raman spectroscopy, electrochemical, and lateral flow assay (LFA). It also discusses the possible evolution of some of these techniques for the rapid detection of drugs at ultra-low levels, thereby giving an insight into the future of sensor technology.
... Surface enhanced Raman spectroscopy (SERS) [1] is a reliable, facile, rapid, non-destructive, and label-free analytical technique with a detection limit down to a single molecule. Because of these advantages, SERS is widely applied in different areas, including chemical and biological sensing [2][3][4], environmental monitoring [5,6], pharmaceutical analysis [7], catalysis [8], diagnosis [9], and so on. One area of particular interest is detection of drug molecules. ...
... The realization that "hot spots" are the key to achieving strong SERS enhancements motivates the shape-controlled synthesis of nanostructured substrates for SERS (Bai & Liu, 2012;Xia, Xiong, Lim, & Skrabalak, 2008;Xiao & Qi, 2011). Various plasmonic nanomaterials and nanostructures have been fabricated and used as SERS substrates, including nanorods (D 'Elia, Retama, Ortega-Ojeda, Ruiz, & Montalvo, 2018;Yang, You, Gao, Zhang, & Yin, 2018;Fu, Sun, Pu, & Wei, 2019), nanostars (Ma, Xu, Xia, & Wang, 2018;Talemi, Mousavi, & Afruzi, 2017), dendritic nanostructures (Agrawal, Kulkarni, & Rao, 2008;Thilawala, Kim, & Lee, 2019;Zhou et al., 2015), amongst others (Carlini et al., 2017;Qi et al., 2016;Qiu et al., 2019;Wu et al., 2011;Xie et al., 2019). However, for most of these SERS substrates, reproducibility and stability remain serious performance limitations. ...
Representing tremendous enhancement effect for the Raman signal of trace chemicals, branched gold nanoparticles (Au NPs) are particularly attractive as surface-enhanced Raman spectroscopy (SERS) substrates, though precise morphology control during synthesis might remain challenging. Herein, snowflake-like gold nanoparticles served as SERS substrates were successfully prepared by reducing chloroauric acid (HAuCl4) with ascorbic acid in aqueous solutions of tetradecylpiperidinium (C14PDB) surfactant. At a C14PDB/HAuCl4 molar concentration ratio of 4.2/1 and a reaction time of 6 h, the Au NPs resembled hexagonal snowflakes were produced. The snowflake-like Au NPs substrates performed great SERS activity and afforded limits of detection around 3 × 10⁻⁹ mol L⁻¹ in aqueous rhodamine 6G (R6G) solutions and 1 × 10⁻⁸ mol L⁻¹ for organophosphorus pesticides in solution. And applying these SERS substrates for practical detection on five fruit or vegetable peels, the detection limit of parathion-methyl, triazophos and phosmet on apple peels was 0.026 ng cm⁻², 0.031 ng cm⁻² and 0.032 ng cm⁻², respectively. SERS results suggest that snowflake-like Au NPs used as SERS substrates hold great promise for the detection of organophosphorus pesticides at trace concentrations.
The use of non-destructive forensic methods for cocaine identification is of outstanding importance, given the amount of samples seized. Techniques such as ATR-FTIR, Raman, and NIR spectroscopy have become alternatives to circumvent this problem, as they allow fast, cheap analysis, and enable the reanalysis of samples. When combined with chemometrics, these spectroscopic methods can be used to determine and quantify cocaine samples, meaning that the limitations of existing techniques can be overcome. This review article covers spectroscopic techniques for identifying cocaine in different forms and matrices, such as food and textiles, which are materials used for smuggling. The chemometric identification of cocaine in oral fluid and water is also discussed. In addition, vibrational spectroscopy techniques using portable equipment are described. This work seeks to evaluate the main chemometric applications of spectroscopic data and to find new perspectives on the identification of cocaine using chemometrics.
Surface‐enhanced Raman spectroscopy (SERS) is a rapidly emerging technology that offers a fast, extremely sensitive, and quantitative approach to trace chemical detection. Such a technique incorporated into a portable device is attractive to law enforcement and emergency room personnel for rapid accurate on‐site screening of illicit and abused drugs. Toward this we are developing an analyzer in a hand‐held unit, based on SERS that is integrated with a capillary sensor embedded with activated gold nanoparticles in a porous glass matrix. In this preliminary study we have used this gold sol‐gel capillary to measure aqueous solutions of 14 high‐priority drugs to define sensitivity (lowest measured concentration (LMC) and estimated limit of detection (LOD)), determine concentration dependence and quantification capabilities by constructing calibration curves, examine effects of pH at 3, 7 and 11 on SERS measurements, and perform multicomponent analysis of fentanyl laced drug mixtures and spectral identification on our portable and handheld units. Of particular significance fentanyl was detected with an LMC of 1 ng/mL and estimated LOD at 0.11 ng/mL, while other representative drugs such as cocaine and phenylcyclidine produced LMCs and LODs at 5.0 and 0.77 ng/mL, and 10.0 and 0.62 ng/mL respectively. These sub ng/mL detection limits are comparable or lower than previously reported and confirm that this gold sol‐gel has the potential to meet the sensitivity requirements for saliva analysis. Most importantly, these sensors can be manufactured easily and cheaply, and when integrated with our portable Raman units produce high‐quality spectra and accurate identification within 1.2 sec.
In this study, a natural extract from the plant Radix hedysari (ER) was proven to be useful for the green synthesis of silver nanoparticles (AgNPs) and ER-AgNPs in particular. Considering the complexity of plant extracts, high-pressure liquid chromatography (HPLC) was effective at confirming the components of ER, surprisingly, formononetin was found to comprise more than 85% of the total contents. Since formononetin was confirmed to be the primary component of ER, this compound was also used as the basis to synthesize AgNPs designated FMT-AgNPs that was highly pure and of high quality. The FMT-AgNPs functionalized by formononetin were optimized for further study. A simple, fast and sensitive colorimetric method detect formothion was achieved using FMT-AgNPs. A wide linear range from 0.1 μM to 10 μM was established with a low limit of detection (LOD) of 14.6 nM. Since formononetin performed multiple roles during the synthesis, it was confirmed that the mechanism of detection was based on aldol condensation, intermolecular hydrogen bonds and electrostatic attraction between formononetin and formothion. Finally, the green synthesized FMT-AgNPs were further applied in typical fruit and vegetable samples, indicating that FMT-AgNPs were potentially highly useful.
Optical biosensors are low-cost, sensitive and portable devices that are poised to revolutionize the medical industry. Healthcare monitoring has already been transformed by such devices, with notable recent applications including heart rate monitoring in smartwatches and COVID-19 lateral flow diagnostic test kits. The commercial success and impact of existing optical sensors has galvanized research in expanding its application in numerous disciplines. Drug detection and monitoring seeks to benefit from the fast-approaching wave of optical biosensors, with diverse applications ranging from illicit drug testing, clinical trials, monitoring in advanced drug delivery systems and personalized drug dosing. The latter has the potential to significantly improve patients’ lives by minimizing toxicity and maximizing efficacy. To achieve this, the patient’s serum drug levels must be frequently measured. Yet, the current method of obtaining such information, namely therapeutic drug monitoring (TDM), is not routinely practiced as it is invasive, expensive, time-consuming and skilled labor-intensive. Certainly, optical sensors possess the capabilities to challenge this convention. This review explores the current state of optical biosensors in personalized dosing with special emphasis on TDM and provides an appraisal on recent strategies. The strengths and challenges of optical biosensors are critically evaluated, before concluding with perspectives on the future direction of these sensors.
Metal nanoparticles (NP) that exhibit localized surface plasmon resonance play an important role in metal‐enhanced fluorescence (MEF) and surface‐enhanced Raman scattering (SERS). Among the optical biosensors, MEF and SERS stand out to be the most sensitive techniques to detect a wide range of analytes from ions, biomolecules to macromolecules and microorganisms. Particularly, anisotropic metal NPs with strongly enhanced electric field at their sharp corners/edges under a wide range of excitation wavelengths are highly suitable for developing the ultrasensitive plasmon‐enhanced biosensors. In this review, we first highlight the reliable methods for the synthesis of anisotropic gold NPs and silver NPs in high yield, as well as their alloys and composites with good control of size and shape. It is followed by the discussion of different sensing mechanisms and recent advances in the MEF and SERS biosensor designs. This includes the review of surface functionalization, bioconjugation and (directed/self) assembly methods as well as the selection/screening of specific biorecognition elements such as aptamers or antibodies for the highly selective bio‐detection. The right combinations of metal nanoparticles, biorecognition element and assay design will lead to the successful development of MEF and SERS biosensors targeting different analytes both in‐vitro and in‐vivo. Finally, the prospects and challenges of metal‐enhanced biosensors for future nanomedicine in achieving ultrasensitive and fast medical diagnostics, high‐throughput drug discovery as well as effective and reliable theranostic treatment are discussed.
The abuse of illicit drugs usually associated with dramatic crimes may cause significant problems for the whole society. Wastewater-based epidemiology (WBE) has been demonstrated to be a novel and cost-effective way to evaluate the abuse of illicit drugs at the community level, and has been used as a routine method for monitoring and played a significant role for combating the crimes in some countries, e.g. China. The method can also provide temporal and spatial variation of drugs of abuse. The detection methods mainly remain on the conventional liquid chromatography coupled with mass spectrometry, which is extremely sensitive and selective, however needs advanced facility and well-trained personals, thus limit it in the lab. As an alternative, sensors have emerged to be a powerful analytical tool for a wide spectrum of analytes, in particular aptamer sensors (aptasensors) have attracted increasing attention and could act as an efficient tool in this field due to the excellent characteristics of selectivity, sensitivity, low cost, miniaturization, easy-to-use, and automation. In this review, we will briefly introduce the context, specific assessment process and applications of WBE and the recent progress of illicit drug aptasensors, in particular focusing on optical and electrochemical sensors. We then highlight several recent aptasensors for illicit drugs in new technology integration and discuss the feasibility of these aptasensor for WBE. We will summarize the challenges and propose our insights and opportunity on aptasensor for WBE to evaluate community-wide drug use trends and public health.
Quantitative analysis of surface-enhanced Raman scattering (SERS) spectra has been a critical step in trace level analysis. In this study, a novel variable selection method called interval combination iterative optimization approach coupled with SIMPLS (ICIOA-SIMPLS) was proposed for simultaneously predicting the volume ratios of various pesticides by quantitative analysis of the SERS spectra of the compounds. Four strategies, including interval selection, model population analysis (MPA), weighted bootstrap sampling (WBS) and soft shrinkage were combined in the current designed ICIOA-SIMPLS approach. Firstly, the SERS spectra were split into a series of equal-width spectral intervals. Secondly, WBS, as a random sampling method was applied based on the initial weights of spectral intervals to generate random combinations of spectral intervals, namely sub-datasets. On this basis, multivariate calibration sub-models were developed by applying SIMPLS followed by MPA to statistically analyze the outputs of sub-models and update the weights of spectral intervals. Finally, using an iterative optimization procedure the optimal spectral interval combination with the lowest root mean squares error of cross-validation (RMSECV) was searched in a soft shrinkage manner. For the sake of investigating the performance of ICIOA-SIMPLS, four methods including SIMPLS, VCPA-SIMPLS, VISSA-SIMPLS and ICIOA-SIMPLS were tested on two groups of SERS spectra for comparison. The findings revealed that the best prediction performance was obtained with ICIOA-SIMPLS. Hence, this proposed method offers a robust and effective variable selection strategy for quantitative analysis of spectroscopic datasets.
Monodisperse gold nanorods with different sizes were synthesized and adsorbed on chemically modified glass substrates. Influence of surfactant molar concentration on nanorod adsorption was studied and the optimum range was determined. During substrate coverages we monitored the growth of longitudinal localized surface plasmon resonances at short times due to density increase of isolated nanorods and, at longer times, their subsequent decrease and a concurrent growth of coupling resonances owing to nanoparticle surface mobility and aggregation. Temporal evolution of amplitudes of resonance peaks in extinction spectra and nanorod counting statistics in electron micrographs were used to model both coverage and aggregation processes, as exponential-like functions of time. Their characteristic times and saturation values were analyzed and related to kinetic parameters, nanorod dimensions and extinction coefficients. This work can be used as a predictive tool to prepare plasmonic substrates with desired optical resonances.
Background:
Δ9-Tetrahydrocannabinol (THC) is already considered one of the most addictive substances since an increasing number of consumers/abusers of THC and THC based products are observed worldwide. In this work, the capabilities of a novel miniaturized and portable MicroNIR spectrometer were investigated in order to propose a practical and intelligible test allowing the rapid and easy screening of Δ9-Tetrahydrocannabinol (THC) oral fluids without any pretreatment.
Methods:
Specimens from volunteers were collected in order to consider any sources of variability in the spectral response and spiked with increasing amount of THC in order to realize predictive models to be used in real cases. Partial Least Square-Discriminant Analysis (PLS-DA) and Partial Least Square regression (PLSr) for the simultaneously detection and quantification of THC, were applied to baseline corrected spectra pre-treated by first derivative transform.
Results:
Results demonstrated that MicroNIR/Chemometric platform is statistically able to identify THC abuse in simulated oral fluid samples containing THC from 10 to 100 ng/ml, with a precision and a sensitivity of about 1.51% and 0.1% respectively.
Conclusions:
The coupling MicroNIR/Chemometrics permits to simplify THC abuse monitoring for roadside drug testing or workplace surveillance and provides the rapid interpretation of results, as once the model is assessed, it can be used to process real samples in a "click-on" device.
The residue of fishery drugs in aquatic food products has not diminished and has caused worldwide attention. This study aimed to develop a surface-enhanced Raman spectroscopy (SERS) method coupled with gold nanorods (AuNRs) substrates to rapidly detect methylene blue (MB) and malachite green (MG) in fish tissues. Three different aspect ratios (AR) of AuNRs were synthesized by a seed-mediated growth method based on adjusting the amount of 0.1 M of sliver nitrate solution. The 3.5 AR of AuNRs was selected as the optimal substrate because it showed the highest enhancement effect on the probe molecule. MB and MG standard solutions were detected at levels as low as 0.5 and 0.1 ng/mL, respectively. After processing the four fish tissues through a simplified sample preparation method, we compared matrix interference for SERS detection. For the four fish species, the lowest detectable concentration of MB was 5 ng/g for snakehead fish, and 1 ng/g for yellow catfish, black carp, and tilapia fillets. The lowest detectable concentration of MG was 1 ng/g for snakehead fish, 0.5 ng/g for yellow catfish and black carp, and 0.3 ng/g for tilapia fillets. This study shows that SERS coupled with AuNRs could be used for the analysis of trace amounts of contaminants in intricate food matrices as an active, fast and sensitive approach.
Nowadays, chronic kidney disease (CKD) becomes a principal barrier in clinical diagnosis and treatment. For clinical patients, chronic kidney disease will potentially lead to multiple lesion that increase the risk of mortality. The most significant challenge in CKD is detecting uremic toxins, including small water-soluble solutes (uric acid, urea and creatinine) and protein-bound solutes (p-cresol and indoxyl sulfate). Surface-enhanced Raman scattering (SERS) platform is rapid and sensitive nanotechnology for bio-detection. Thus, the floating-typed SERS substrate is prepared by embedded silver nanoparticles (AgNPs) on the poly (diallyldimethyl-ammonium) chloride (PDDA) modified graphene oxide (GO) nanosheets for the biomolecules and uremic toxins detection. The optimal interparticle distances of AgNPs are modulated to generate the strong “hot spots” for enhancing Raman signals. The characterizations of AgNPs/GO-PDDA nanosheets are evaluated by transmission electron microscopy, zeta potential, FTIR, X-ray photoelectron spectroscopy, and Raman spectroscopy. The results show that the floating SERS-active substrate provides quantitatively linear measurement (i.e., 3.8 × 10⁻² ˜10⁻⁵ M of urea) and ultrasensitive SERS detection (i.e., detection limit of adenine: lower than 10⁻¹⁰ M) of biomolecules, which offers great potential for practical clinical applications in rapid and label-free detection of clinical uremic toxins.
In the field of forensic toxicology, the use of non-destructive and easy-to-use analytical techniques deserves remarkable attention, especially in those situations involving public health and security. In addition, the miniaturization and portability of one-touch devices for the detection of specific threats is required more and more.
In this study, a novel on-site MicroNIR/Chemometric platform was developed to perform a real-time prediction of cocaine and its metabolites in non pre-treated oral fluid.
Simulated oral fluids were prepared in water in order to calibrate the instrumental response and the matrix effect was consequently evaluated by processing spiked oral fluids collected from volunteers. The procedure was optimized using a proper experimental design taking into account the equilibrium between cocaine and benzoylecgonine in the range 10–100 ng-ml and validated by comparing results with the reference official method (GC-MS).
The developed method was statistically able to discriminate oral fluid samples containing cocaine from 10 to 100 ng/ml and demonstrated to be not affected by the variability of the matrix as all the blank samples of different volunteers (smokers and non smokers, assuming caffeine, sugars, chewing-gum or alcohol) as well as spiked oral fluids were correctly predicted by the model. In addition, results from six real samples confirmed the feasibility of the miniaturized platform to provide a correct identification of cocaine abuse and to propose the MicroNIR as innovative personal screening system to prevent accidents and in cases involving workplace surveillance.
A novel entirely automated MicroNIR/Chemometric platform was developed for the “Lab-on-Click” detection of illicit drugs in non-pretreated oral fluids and a novel tool for the first level test is proposed. Calibration of the method was achieved by collecting oral fluids specimens from volunteers and chemometric analysis was considered for the development of models of prediction for cocaine, amphetamine and Δ9-Tetrahydrocannabinol. In addition, a comprehensive model was optimized for the simultaneously prediction of positive/negative samples and the specific illicit drug used by abusers in single “click”. The detection ability of the method was checked for true positive and false positive outcomes and results were validated by GC-MS reference official method. The MicroNIR/Chemometric platform provided the simultaneously prediction of the three most frequently addictive drugs with the sensitivity and accuracy of the confirmatory analyses, offering the advantages of rapidity and simplicity and demonstrating to be a promising tool supporting public health surveillance.
The principal objective of this work was to demonstrate the capability of Raman spectroscopy to detect small amounts of cocaine in nasal fluid, and to identify the main drug and the most widely used cutting agents. Initially, standard samples were analysed and sampling conditions were studied by comparing different swabs used for the sample collection. Once the most appropriate swab was selected, which permitted a relatively simple detection of the standard cocaine hydrochloride, qualitative analyses of real samples were carried out. Three street cocaine samples were analysed, and the presence of cutting substances was highlighted by the appearance of different bands not corresponding to the ones of the standard cocaine. To identify the substances present in each sample, the spectra of the street cocaine samples were collected and compared with a digital library created on purpose with the spectra of the most common cutting agents. In this case, correlation coefficients permitted to recognize the most important substances presumably present in the samples, and gave an estimation of the purity of the cocaine. However, when nasal fluid was present, its strong signal could overlap or interfere with the smaller signal of the cutting substances, hindering their identification.
Increases in illicit drug use and the number of emergency-room visits attributable to drug misuse or abuse highlight the need for an efficient, reliable method to detect drugs in patients in order to provide rapid and appropriate care. A surface-enhanced Raman spectroscopy (SERS)-based method was successfully developed to rapidly measure cocaine in saliva at clinical concentrations, as low as 25 ng/mL. Pretreatment steps comprising chemical separation, physical separation, and solid-phase extraction were investigated to recover the analyte drug from the saliva matrix. Samples were analyzed using Fourier-transform (FT) and dispersive Raman systems, and statistical analysis of the results shows that the method is both reliable and accurate, and could be used to quantify unknown samples. The procedure requires minimal space and equipment and can be completed in less than 16 minutes. Finally, due to the inclusion of a buffer solution and the use of multiple robust pretreatment steps, with minimal further development this method could also be applied to other drugs of interest.
This feature article highlights work from the authors' laboratories on the synthesis, assembly, reactivity, and optical applications of metallic nanoparticles of nonspherical shape, especially nanorods. The synthesis is a seed-mediated growth procedure, in which metal salts are reduced initially with a strong reducing agent, in water, to produce ∼4 nm seed particles. Subsequent reduction of more metal salt with a weak reducing agent, in the presence of structure-directing additives, leads to the controlled formation of nanorods of specified aspect ratio and can also yield other shapes of nanoparticles (stars, tetrapods, blocks, cubes, etc.). Variations in reaction conditions and crystallographic analysis of gold nanorods have led to insight into the growth mechanism of these materials. Assembly of nanorods can be driven by simple evaporation from solution or by rational design with molecular-scale connectors. Short nanorods appear to be more chemically reactive than long nanorods. Finally, optical applications in sensing and imaging, which take advantage of the visible light absorption and scattering properties of the nanorods, are discussed.
Small gold nanorods (GNRs) with longitudinal plasmon absorption in the near-infrared window (700–900 nm) are of great interest for in vivo optical applications (e.g., photothermal therapy) and for their high-payload-to-carrier ratio for drug delivery. Common synthetic strategies for GNR production afford spherical and cubical nanoparticles in addition to the desired GNRs. Thus, several methods have been proposed for the selective separation of GNRs from the reaction by-products. For example, centrifugation has been used to separate the high aspect ratio (AR) GNRs (AR > 4). However, it is difficult to separate small sized GNRs with low AR (AR ≤ 4) that are particularly promising for biomedical applications. Here, we describe a simple and fast procedure for the separation of small GNRs with AR of 4, and length of 28 nm from reaction by-products.
The shape separation is achieved through centrifugation according to the following steps:•Isolation of all gold products of the reaction from the excess of cetyltrimethylammonium bromide through a first cycle of centrifugation.•Optimization of the speed and the time of centrifugation for the separation of GNRs from the reaction by-products.•Shape separation of GNRs through a second cycle of centrifugation.
The effectiveness of this procedure is documented.
The number of drug-related emergency room visits in the United States doubled from 2004 to 2009 to 4.6 million. Consequently there is a critical need to rapidly identify the offending drug(s), so that the appropriate medical care can be administered. In an effort to meet this need we have been investigating the ability of surface-enhanced Raman spectroscopy (SERS) to detect and identify numerous drugs in saliva at ng/mL concentrations within 10 minutes. Identification is provided by matching measured spectra to a SERS library comprised of over 150 different drugs, each of which possess a unique spectrum. Trace detection is provided by fused gold colloids trapped within a porous glass matrix that generate SERS. Speed is provided by a syringe-driven sample system that uses a solid-phase extraction capillary combined with a SERS-active capillary in series. Spectral collection is provided by a portable Raman analyzer. Here we describe successful measurement of representative illicit, prescribed, and over-the-counter drugs by SERS, and 50 ng/mL cocaine in saliva as part of a focused study.
Rapid analysis of drugs in emergency room overdose patients is critical to selecting appropriate medical care. Saliva analysis has long been considered an attractive alternative to blood plasma analysis for this application. However, current clinical laboratory analysis methods involve extensive sample extraction followed by gas chromatography and mass spectrometry, and typically require as much as one hour to perform. In an effort to overcome this limitation we have been investigating metal-doped sol-gels to both separate drugs and their metabolites from saliva and generate surface-enhanced Raman spectra. We have incorporated the sol-gel in a disposable lab-on-a-chip format, and generally no more than a drop of sample is required. The detailed molecular vibrational information allows chemical identification, while the increase in Raman scattering by six orders of magnitude or more allows detection of microg/mL concentrations. Measurements of cocaine, its metabolite benzoylecgonine, and several barbiturates are presented.
The characteristics of the OPLS method have been investigated for the purpose of discriminant analysis (OPLS-DA). We demonstrate how class-orthogonal variation can be exploited to augment classification performance in cases where the individual classes exhibit divergence in within-class variation, in analogy with soft independent modelling of class analogy (SIMCA) classification. The prediction results will be largely equivalent to traditional supervised classification using PLS-DA if no such variation is present in the classes. A discriminatory strategy is thus outlined, combining the strengths of PLS-DA and SIMCA classification within the framework of the OPLS-DA method. Furthermore, resampling methods have been employed to generate distributions of predicted classification results and subsequently assess classification belief. This enables utilisation of the class-orthogonal variation in a proper statistical context. The proposed decision rule is compared to common decision rules and is shown to produce comparable or less class-biased classification results. Copyright © 2007 John Wiley & Sons, Ltd.
Detection and identification of blood, semen and saliva stains, the most common body fluids encountered at a crime scene, are very important aspects of forensic science today. This study targets the development of a nondestructive, confirmatory method for body fluid identification based on Raman spectroscopy coupled with advanced statistical analysis. Dry traces of blood, semen and saliva obtained from multiple donors were probed using a confocal Raman microscope with a 785-nm excitation wavelength under controlled laboratory conditions. Results demonstrated the capability of Raman spectroscopy to identify an unknown substance to be semen, blood or saliva with high confidence.
Driven by the search for new materials with interesting and unique properties and also by the fundamental question of how atomic and molecular physical behaviour develops with increasing size, the field of nanoparticle research has grown immensely in the last two decades. Partially for these reasons, colloidal solutions of metallic (especially silver and gold) nanoparticles have long fascinated scientists because of their very intense colours. The intense red colour of colloidal gold nanoparticles is due to their surface plasmon absorption. This article describes the physical origin of the surface plasmon absorption in gold nanoparticles with emphasis on the Mie and also the Maxwell-Garnett theory and reviews the effects of particle size and shape on the resonance condition. A better understanding of the relationship between the optical absorption spectrum (in particular, the plasmon resonance) and such particle properties as its dimensions or surrounding environment can prove fruitful for the use of the plasmon absorption as an analytical tool. The plasmon resonance has also had a great impact on the Raman spectrum of surface-adsorbed molecules and a large enhancement of the fluorescence quantum yield of gold nanorods is observed. Furthermore, following the changes in the plasmon absorption induced by excitation (heating) with ultrashort laser pulses allows one to monitor the electron dynamics (electron-electron and electron-phonon interactions) in real time, which is important in understanding such fundamental questions regarding the thermal and electrical conductivity of these nanoparticles. Very intense heating with laser pulses leads to structural changes of the nanoparticles (nuclear rearrangements in the form of melting and fragmentation).
Eighty drugs of abuse and metabolites were successfully measured by surface-enhanced Raman spectroscopy (SERS) using gold- and silver-doped sol-gels immobilized in glass capillaries. A method was developed that provided consistent detection of 50 ppb cocaine in saliva in a focused study. This general method was successfully applied to the detection of a number of additional drugs in saliva, such as amphetamine, diazepam, and methadone.
The ability of surface-enhanced Raman spectroscopy (SERS) to measure 5-fluorouracil (5-FU) in saliva is presented. The approach is based on the capacity of Raman spectroscopy to provide a unique spectral signature for virtually every chemical, and the ability of SERS to provide microg/mL sensitivity. A simple sampling method, that employed 1-mm glass capillaries filled with silver-doped sol-gels, was developed to isolate 5-FU from potential interfering chemical components of saliva and simultaneously provide SERSactivity. The method involved treating a 1 mL saliva sample with 1 mL of acetic acid, drawing 10 microL of sample into a SERS-active capillary by syringe, and then measuring the SER spectrum. Quality SER spectra were obtained for samples containing as little as 2 microg of 5-FU in 1 mL saliva. The entire process, the acid pretreatment, extraction and spectral measurement, took less than 5 minutes. The SERS of 5-fluorouridine and 5-fluoro-2'-deoxyuridine, two major metabolites of 5-FU, were also measured and shown to have unique spectral peaks. These measurements suggest that disposable SERS-active capillaries could be used to measure 5-FU and metabolite concentrations in chemotherapy patient saliva, thereby providing metabolic data that would allow regulating dosage. Tentative vibrational mode assignments for 5-FU and its metabolites are also given.
Noble metal particles have long fascinated scientists because of their intense color, which led to their application in stained glass windows as early as the Middle Ages. The recent resurrection of colloidal and cluster chemistry has brought about the strive for new materials that allow a bottoms-up approach of building improved and new devices with nanoparticles or artificial atoms. In this review, we discuss some of the properties of individual and some assembled metallic nanoparticles with a focus on their interaction with cw and pulsed laser light of different energies. The potential application of the plasmon resonance as sensors is discussed.
In this work we investigated the antibacterial properties of differently shaped silver nanoparticles against the gram-negative
bacterium Escherichia coli, both in liquid systems and on agar plates. Energy-filtering transmission electron microscopy images revealed considerable
changes in the cell membranes upon treatment, resulting in cell death. Truncated triangular silver nanoplates with a {111}
lattice plane as the basal plane displayed the strongest biocidal action, compared with spherical and rod-shaped nanoparticles
and with Ag+ (in the form of AgNO3). It is proposed that nanoscale size and the presence of a {111} plane combine to promote this biocidal property. To our
knowledge, this is the first comparative study on the bactericidal properties of silver nanoparticles of different shapes,
and our results demonstrate that silver nanoparticles undergo a shape-dependent interaction with the gram-negative organism
E. coli.
This chapter is aimed at complete newcomers looking for a broad map that will guide him/her toward more advanced studies and applications of surface-enhanced Raman spectroscopy (SERS). The SERS effect is about amplifying Raman signals (almost exclusively coming from molecules) by several orders of magnitude. The amplification of the signals in SERS comes (mainly) through the electromagnetic interaction of light with metals, which produces large amplifications of the laser field through excitations generally known as plasmon resonances. To profit from these, the molecules must typically be adsorbed on the metal surface, or at least be very close to it. The denomination SERS summarizes particularly well these three cornerstones of the effect. It discusses SERS effect in its historical context, and highlights its present status and future challenges. It also provides a brief overview of the content of the book, A Quick Overview of Surface-Enhanced Raman Spectroscopy, which provides a bird's eye view about the general principles and applications of SERS. It helps those who might be curious or interested in how the technique actually works in practice at a basic level. Furthermore, it suggests a reading plan that can cater to a wide variety of potential readers with different needs.
The present work aims to review all the papers published so far, focused on the determination of drugs of abuse in oral fluid. This fluid provides a simpler, faster and more controllable sampling in comparison with the other biological fluids such as blood or urine. Actually, the main goal of the researchers is to lower the limit of detection (LOD) to detect quantities of drugs smaller than the cut-off limits established by law for drug controls. Advances in Raman, Infrared (IR) and Nuclear Magnetic Resonance (NMR) spectroscopy applications are here discussed. Surface Enhanced Raman Spectroscopy (SERS) has been shown as the most sensitive technique for the detection of illicit drugs in oral fluid. The use of IR spectroscopy for determining drugs of abuse in oral fluid is growing although the LODs obtained until now do not yet satisfy the necessities in the forensic field. Finally, NMR spectroscopy has been seldom used to determine drugs in oral fluid. Another future trend seems to be related with the use of portable instrumentation, which would permit to perform in-situ analysis. This last application seems to be particularly promising to perform roadside drug tests and to identify overdose drugs in patients in emergency conditions.
This chapter discusses the fundamentals of the surface-enhanced Raman scattering (SERS) effect. SERS consists in using the large local field enhancements that can exist at metallic surfaces (under the right conditions, typically by profiting from localized surface plasmon resonances) to boost the Raman scattering signal of molecules at (or close to) the surface. A similar approach can be used to boost the fluorescence signal, and it is called surface-enhanced fluorescence. That technique is also discussed in this chapter in the context of SERS. It addresses the issues such as how much the signal can be boosted, i.e. to know what the enhancement factor is, and what its physical origins are, by defining rigorously the SERS enhancement factors, and then by discussing their origin, with a strong emphasis on the electromagnetic (EM) mechanisms. It only focuses on the methodology and the physics of the phenomena, not on the actual solution of the EM problem for a particular geometry. It therefore always assumes that it has a solution of the EM problems it may encounter. Furthermore, the theoretical results of this chapter are illustrated with concrete examples.
The field of nanoparticle research has drawn much attention in the past decade as a result of the search for new materials. Size confinement results in new electronic and optical properties, possibly suitable for many electronic and optoelectronic applications. A characteristic feature of noble metal nanoparticles is the strong color of their colloidal solutions, which is caused by the surface plasmon absorption. This article describes our studies of the properties of the surface plasmon absorption in metal nanoparticles that range in size between 10 and 100 nm. The effects of size, shape, and composition on the plasmon absorption maximum and its bandwidth are discussed. Furthermore, the optical response of the surface plasmon absorption due to excitation with femtosecond laser pulses allowed us to follow the electron dynamics (electron−electron and electron−phonon scattering) in these metal nanoparticles. It is found that the electron−phonon relaxation processes in nanoparticles, which are smaller than the electron mean free path, are independent of their size or shape. Intense laser heating of the electrons in these particles is also found to cause a shape transformation (photoisomerization of the rods into spheres or fragmentation), which depends on the laser pulse energy and pulse width.
A method is used for preparing gold NRs with aspect ratios ranging from 1.5 to 10 for which the surface plasmon absorption maxima are between 600 and 1300 nm. This method has been adapted from a previously published seed-mediated growth method (Jana et al. Adv. Mater. 2001, 13, 1389). The disadvantages and limitations of the earlier method (i.e., formation of noncylindrical NRs, φ-shaped particles, and formation of a large fraction of spherical particles) have been overcome by use of a hexadecyltrimethylammonium bromide (CTAB)-capped seed instead of a citrate-capped one. In a single-component surfactant system, the silver content of the growth solution was used to grow NRs to a desired length. This results in reproducible formation of NRs with aspect ratios ranging from 1.5 to 4.5. To grow longer NRs with aspect ratios ranging from 4.6 to 10, a binary surfactant mixture composed of benzyldimethylhexadecylammoniumchloride (BDAC) and CTAB was used. NRs are grown in this mixture either by aging or by addition of a growth solution suitable to shorter NRs. Effects of the silver ion and the cosurfactant along with the growth mechanism of NRs are discussed.
The well-known Martens factorization for PLS1 produces a single y-related score, with all subsequent scores being y-unrelated. The X-explanatory value of these y-orthogonal scores can be summarized by a simple expression, which is analogous to the ‘P’ loading weights in the orthogonalized NIPALS algorithm. This can be used to rearrange the factorization into entirely y-related and y-unrelated parts. Systematic y-unrelated variation can thus be removed from the X data through a single post hoc calculation following conventional PLS, without any recourse to the orthogonal projections to latent structures (OPLS) algorithm. The work presented is consistent with the development by Ergon (PLS post-processing by similarity transformation (PLS + ST): a simple alternative to OPLS. J. Chemom. 2005; 19: 1–4), which shows that conventional PLS and OPLS are equivalent within a similarity transform. Copyright © 2009 John Wiley & Sons, Ltd.
In this work, we show that the projections of the predictors on the normalized regression vectors represent a target rotation with the responses (concentration vectors) as targets. By means of this operation the predictive ability of a latent-variable (LV) regression model and the importance of each predictor for all the responses is obtained. The two features can be portrayed simultaneously and quantitatively in an LV regression BIPLOT display. This graph shows how modelled interferents influence prediction, information as important as the detection of and correction for unmodelled interferents when using a regression model for prediction.For samples characterized by whole digital profiles rather than a collection of peaks, graphs showing the covariances between the responses and the original or the reproduced predictor space appear to provide the most useful information for interpreting an LV regression model.
The potential use of Raman spectroscopy for nondestructive, confirmatory identification of body fluids at the crime scene has been reported recently (Virkler and Lednev, Forensic Sci.,Int., 2008, 181, e1-e5). However, those experiments were performed using only one sample of each body fluid and did not investigate the potential for spectral variations among different donors of the same fluid. This paper reports on the role of heterogeneity within a single human saliva sample as well as among samples from multiple donors. Near-infrared (NIR) Raman spectroscopy was used to measure spectra of pure dried human saliva samples from multiple donors in a controlled laboratory environment. Principal component analysis of spectra obtained from multiple spots on dry samples showed that dry saliva is heterogeneous and its Raman spectra could be presented as a linear combination of a fluorescent background and three spectral components. The major chemical components known to be present in saliva were used to tentatively identify the principal spectral components. The issue of potential spectral variations that could arise between different donors of saliva was also addressed. The relative contribution of each of the three components varies with donor, so no single spectrum could effectively represent an experimental Raman spectrum of dry saliva in a quantitative way. The combination of these three spectral components could be considered to be a spectroscopic signature for saliva. This proof of concept approach shows the potential for Raman spectroscopy to identify an unknown substance to be saliva during forensic analysis.
A photoinduced method for converting large quantities of silver nanospheres into triangular nanoprisms is reported. The photo-process
has been characterized by time-dependent ultraviolet-visible spectroscopy and transmission electron microscopy, allowing for
the observation of several key intermediates in and characteristics of the conversion process. This light-driven process results
in a colloid with distinctive optical properties that directly relate to the nanoprism shape of the particles. Theoretical
calculations coupled with experimental observations allow for the assignment of the nanoprism plasmon bands and for the first
identification of two distinct quadrupole plasmon resonances for a nanoparticle. Unlike the spherical particles they are derived
from that Rayleigh light-scatter in the blue, these nanoprisms exhibit scattering in the red, which could be useful in developing
multicolor diagnostic labels on the basis not only of nanoparticle composition and size but also of shape.
In the past decade, colloidal solutions have been assumed to be very efficient templates for controlling particle size and shape. A large number of groups have used reverse micelles to control the size of spherical nanoparticles. This makes it possible to determine the various parameters involved in such processes, and demonstrates that nanoparticles can be considered to be efficient nanoreactors. However, some discrepancies arise. There are few reports concerning the control of particle shape, and it is still rather difficult to determine the key parameters, such as the adsorption of salts and other molecules, and the synthesis procedure. Here, we discuss these controls of the size and shape of inorganic nanomaterials.
In this paper we overview our recent studies of anisotropic noble metal (e.g. gold and silver) nanoparticles, in which a combination of theory and experiment has been used to elucidate the extinction spectra of the particles, as well as information related to their surface enhanced Raman spectroscopy. We used wet-chemical methods to generate several structurally well-defined nanostructures other than solid spheres, including silver nanodisks and triangular nanoprisms, and gold nanoshells and multipods. When solid spheres are transformed into one of these shapes, the surface plasmon resonances in these particles are strongly affected, typically red-shifting and even splitting into distinctive dipole and quadrupole plasmon modes. In parallel, we have developed computational electrodynamics methods based on the discrete dipole approximation (DDA) method to determine the origins of these intriguing optical features. This has resulted in considerable insight concerning the variation of plasmon wavelength with nanoparticle size, shape and dielectric environment, as well as the use of these particles for optical sensing applications.
This tutorial review presents an introduction to the field of noble metal nanoparticles and their current applications. The origin of the surface plasmon resonance and synthesis procedures are described. A number of applications are presented that take advantage of the electromagnetic field enhancement of the radiative properties of noble metal nanoparticles resulting from the surface plasmon oscillations.
Gold nanorods were synthesized by the colloidal seed-mediated, surfactant-assisted approach [Gou et al., Chem. Mater. 2005, 17, 3668-3672] using CTAB (hexadecylcetyltrimethylammonium bromide) obtained from ten different suppliers. The yield of gold nanorods depended strongly on the CTAB used: with the same recipe, three of the CTABs did not yield nanorods and produced only spherical gold particles, whereas the other CTABs yielded nanorods with nearly 100% yield. These results suggest that an impurity in the CTAB is very important for nanorod formation.
One-dimensional nanostructures: synthesis, characterization, and applications
- Xia
Y. Xia, P. Yang, Y. Sun, Y. Wu, B. Mayers, B. Gates, Y. Yin, F. Kim, Y. Yan, Onedimensional nanostructures: synthesis, characterization, and applications, Adv.
Mater. 15 (2003) 353-389, http://dx.doi.org/10.1002/adma.200390087.
Substance Abuse and Mental Health Services Administration
Substance Abuse and Mental Health Services Administration, Fed. Regist. 80 (94)
(2015) 28063. Available at: https://www.gpo.gov/fdsys/pkg/FR-2015-05-15/pdf/
2015-11523.pdf (Accessed April 2017).