Towards a validation of surface-enhanced Raman scattering (SERS) for use in forensic science: repeatability and reproducibility experiments

Nanoengineering Multilength-Scale Porous Hierarchy in Mesoporous Metal-Organic Framework Single Crystals

Developing a reliable method for constructing mesoporous metal-organic frameworks (MOFs) with single-crystalline forms remains a challenging task despite numerous efforts. This study presents a solvent-mediated assembly method for fabricating zeolitic imidazolate framework (ZIF) single-crystal nanoparticles with a well-defined micro-mesoporous structure using polystyrene-block-poly(ethylene oxide) diblock copolymer micelles as a soft-template. The precise control of particle sizes, ranging from 85 to 1200 nm, is achieved by regulating nucleation and crystal growth rates while maintaining consistent pore diameters in mesoporous nanoparticles and a rhombohedral dodecahedron morphology. Furthermore, this study presents a robust platform for nanoarchitecturing to prepare hierarchically porous materials (e.g., core-shell and hollow structures), including microporous ZIF@mesoporous ZIF, hollow mesoporous ZIF, and mesoporous ZIF@mesoporous ZIF. Such a multimodal pore design, ranging from microporous to microporous/mesoporous and further micro-/meso-/macroporous, provides significant evidence for the future possibility of the structural design of MOFs.

Optimization of silver nanoparticles synthesis by chemical reduction to enhance SERS quantitative performances: Early characterization using the quality by design approach

Surface-enhanced Raman scattering (SERS) is a vibrational widely used technique thanks to its multiple advantages such as its high specificity and sensitivity. The Raman signal exaltation comes from the use of metallic nanoparticles (Nps) acting as antennas by amplifying the Raman scattering. Controlling the Nps synthesis is a major point for the implementation of SERS in routine analysis and especially in quantitative applications. Effectively, nature, size and shape of these Nps considerably influence the SERS response intensity and repeatability. The Lee-Meisel protocol is the most common synthesis route used by the SERS community due to the low cost, rapidity and ease of manufacturing. However, this process leads to a significant heterogeneity in terms of particle size and shape. In this context, this study aimed to synthesize repeatable and homogeneous silver nanoparticles (AgNps) by chemical reduction. The Quality by Design strategy from quality target product profile to early characterization design was considered to optimize this reaction. The first step of this strategy aimed to highlight critical parameters by the means of an early characterization design. Based on an Ishikawa diagram, five process parameters were studied: the reaction volume as categorical variable and the temperature, the time of reaction, the trisodium citrate concentration and pH as continuous variables. A D-Optimal design of 35 conditions was performed. Three critical quality attributes were selected to maximize the SERS intensity, minimize the variation coefficient on SERS intensities and the polydispersity index of the AgNps. Considering these factors, it appeared that concentration, pH and time of reaction were identified as having a critical impact on the Nps formation and can then be considered for the further optimization step.

Label-free DNA detection using silver nanoprism decorated silicon nanoparticles: Effect of silicon nanoparticle size and doping levels

In the present work, we have fabricated silver nanoprism (AgNPrs)/silicon nanoparticle (SiNPs) hybrid arrays for highly sensitive detection of biomolecules via surface-enhanced Raman spectroscopy (SERS) technique. SiNPs having 7 to 37 nm in size and with phosphorous doping varying from 1 × 10¹⁹ to 1 × 10²⁰ cm^-3 were synthesized in nonthermal plasma synthesis. SiNPs were further immobilized on glass substrates using spin-coating, followed by deposition of AgNPrs using the drop-casting method. SERS studies showed that AgNPrs/SiNPs hybrid arrays exhibit substantial amplification of fingerprint bands of rhodamine 6G (R6G) compared to bare silicon as the reference. Raman signal intensity was found to be dependent on the size of SiNPs, with the largest nanoparticles exhibiting the highest SERS enhancement. In addition, an increase in phosphorous doping concentration was found to reduce R6G peak intensities. AgNPrs/SiNPs hybrid arrays showed excellent stability over time and high spot-to-spot reproducibility as well. Moreover, hybrid arrays enabled DNA detection through intense vibrational modes of human genomic DNA, with a lower detection limit of 1.5 pg/µL; indicating that AgNPrs/SiNPs sensors can serve as a reliable and cost-effective biosensing platform for rapid and label-free analysis of biomolecules.

Label-Free Saliva Test for Rapid Detection of Coronavirus Using Nanosensor-Enabled SERS

The recent COVID-19 pandemic has highlighted the inadequacies of existing diagnostic techniques and the need for rapid and accurate diagnostic systems. Although molecular tests such as RT-PCR are the gold standard, they cannot be employed as point-of-care testing systems. Hence, a rapid, noninvasive diagnostic technique such as Surface-enhanced Raman scattering (SERS) is a promising analytical technique for rapid molecular or viral diagnosis. Here, we have designed a SERS- based test to rapidly diagnose SARS-CoV-2 from saliva. Physical methods synthesized the nanostructured sensor. It significantly increased the detection specificity and sensitivity by ~ten copies/mL of viral RNA (~femtomolar concentration of nucleic acids). Our technique combines the multiplexing capability of SERS with the sensitivity of novel nanostructures to detect whole virus particles and infection-associated antibodies. We have demonstrated the feasibility of the test with saliva samples from individuals who tested positive for SARS-CoV-2 with a specificity of 95%. The SERS-based test provides a promising breakthrough in detecting potential mutations that may come up with time while also preparing the world to deal with other pandemics in the future with rapid response and very accurate results.

Investigation and Discrimination of Ballpoint Pen Inks by Analytical Techniques and Chemometrics

A population study has been performed for Pakistani ballpoint pen inks of blue, black, red, and green colors (a total of four colors) commercially used in Pakistan. Ballpoint pen inks have been investigated and discriminated by using UV/Vis spectroscopy and FTIR spectroscopy. We have calculated and compared the results in terms of discriminating power (DP). The statistical techniques of principal component analysis and cluster analysis have been applied on obtained data. By visual comparison, the best DP is obtained for green ballpoint pen inks, i.e., 0.866 by using UV/Vis spectroscopy and FTIR techniques. Black and red ballpoint pen inks showed the highest DPs by using UV/Vis spectroscopy; however, blue ballpoint pen inks got the highest DP by using FTIR spectroscopy. DP has been improved by using chemometric techniques and higher DPs are obtained as compared to visual examination.

Discrimination of Pakistani Fountain Pen Inks by Gas Chromatography-Mass Spectrometry (GC-MS)

In developing countries, the chances of fraud in written documents are comparatively high. Therefore, comparison of fountain pen inks is especially imperative in examination of forensic questioned documents. We have investigated the use of the gas chromatography-mass spectrometry technique in profiling and discrimination of fountain pen ink used in Pakistan for forensic purpose. The main purpose of this study was to discriminate different Pakistani fountain pen inks. The datum for Pakistani inks of fountain pen is not obtainable. In this research study, blue, black, and green colors fountain pen inks commercially used in Pakistan have been extracted from paper using micropunch and then investigated using the gas chromatography-mass spectrometry technique. Gas chromatography-mass spectrometry (GC-MS) was used to differentiate various brands of different colors of fountain pen inks based on their chemical composition. Molecular ion peaks for different components were obtained, and components were identified on the basis of detected ions. Results have been calculated and compared in terms of discriminating power (D.P.). The D.P. for blue, black, and green inks of fountain pen was 1.0 by using the gas chromatography-mass spectrometry technique.

Part-Per-Billion Level Chemical Sensing with a Gold-Based SERS-Active Substrate

We used surface-enhanced Raman spectroscopy (SERS) for the rapid and sensitive detection and quantification of caffeine in solution. Such a technique incorporated into a portable device is finding wide applications in trace chemical analysis in various fields, including law enforcement, medicine, environmental monitoring, and food quality control. To realize such applications, we are currently developing portable and handheld trace chemical analyzers based on SERS, which are integrated with a sensor embedded with activated gold nanoparticles in a porous glass matrix. In this study, we used this gold SERS-active substrate to measure aqueous solutions of the drug caffeine as a test chemical to benchmark sensor performance by defining sensitivity (lowest measured concentration (LMC) and estimated limit of detection (LOD)), determining concentration dependence and quantification capabilities by constructing calibration curves; by evaluating the effects of pH values of 3, 7, and 11; and by examining the reproducibility of the SERS measurements. The results demonstrate that the SERS sensor is sensitive, with caffeine detected at an LMC of 50 parts per billion (ppb) with an LOD of 0.63 ppb. The results further show that the sensor is very stable and can be used to make reproducible measurements, even under extremely acidic to basic pH conditions. Vibrational assignments of all observed SERS peaks are made and reported for the first time for caffeine on a gold substrate.

Engineering Electromagnetic Hot-Spots in Nanoparticle Cluster Arrays on Reflective Substrates for Highly Sensitive Detection of (Bio)molecular Analytes

Intense electromagnetic (EM) hot-spots arising at the junctions or gaps in plasmonic nanoparticle assemblies can drive ultrahigh sensitivity in molecular detection by surface-enhanced spectroscopies. Harnessing this potential however requires access to the confined physical space at the EM hot-spots, which is a challenge for larger analytes such as biomolecules. Here, we demonstrate self-assembly derived gold nanoparticle cluster arrays (NCAs) on gold substrates exhibiting controlled interparticle (<1 nm wide) and intercluster (<10 nm wide) hot-spots as highly promising in this direction. Sensitivity of the NCAs toward detection of small (<1 nm) or large (protein-receptor interactions) analytes in surface-enhanced Raman and metal-enhanced fluorescence assays is found to be strongly impacted by the size of the cluster and the presence of reflective substrates. Experiments supported by numerical simulations attribute the higher sensitivity to higher EM field enhancements at the hot-spots, as well as greater analyte leverage over EM hot-spots. The best-performing arrays could push the sensitivity down to picomolar detection limits for sub-nanometric organic analytes as well as large protein analytes. The investigation paves the way for rational design of plasmonic biosensors and highlights the unique capabilities of a molecular self-assembly approach toward catering to this objective.

Estimation of Andrographolides and Gradation of Andrographis paniculata Leaves Using Near Infrared Spectroscopy Together With Support Vector Machine

Andrographis paniculata (Burm. F) Nees, has been widely used for upper respiratory tract and several other diseases and general immunity for a historically long time in countries like India, China, Thailand, Japan, and Malaysia. The vegetative productivity and quality with respect to pharmaceutical properties of Andrographis paniculata varies considerably across production, ecologies, and genotypes. Thus, a field deployable instrument, which can quickly assess the quality of the plant material with minimal processing, would be of great use to the medicinal plant industry by reducing waste, and quality grading and assurance. In this paper, the potential of near infrared reflectance spectroscopy (NIR) was to estimate the major group active molecules, the andrographolides in Andrographis paniculata, from dried leaf samples and leaf methanol extracts and grade the plant samples from different sources. The calibration model was developed first on the NIR spectra obtained from the methanol extracts of the samples as a proof of concept and then the raw ground samples were estimated for gradation. To grade the samples into three classes: good, medium and poor, a model based on a machine learning algorithm - support vector machine (SVM) on NIR spectra was built. The tenfold classification results of the model had an accuracy of 83% using standard normal variate (SNV) preprocessing.

Challenges and potential solutions for nanosensors intended for use with foods

Nanotechnology-adapted detection technologies could improve the safety and quality of foods, provide new methods to combat fraud and be useful tools in our arsenal against bioterrorism. Yet despite hundreds of published studies on nanosensors each year targeted to the food and agriculture space, there are few nanosensors on the market in this area and almost no nanotechnology-enabled methods employed by public health agencies for food analysis. This Review shows that the field is currently being held back by technical, regulatory, political, legal, economic, environmental health and safety, and ethical challenges. We explore these challenges in detail and provide suggestions about how they may be surmounted. Strategies that may have particular effectiveness include improving funding opportunities and publication venues for nanosensor validation, social science and patent landscape studies; prioritizing research and development of nanosensors that are specifically designed for rapid analysis in non-laboratory settings; and incorporating platform cost and adaptability into early design decisions.

Overview of Synthetic Cannabinoids ADB-FUBINACA and AMB-FUBINACA: Clinical, Analytical, and Forensic Implications

ADB-FUBINACA and AMB-FUBINACA are two synthetic indazole-derived cannabinoid receptor agonists, up to 140- and 85-fold more potent, respectively, than trans-∆⁹-tetrahydrocannabinol (∆⁹-THC), the main psychoactive compound of cannabis. Synthesised in 2009 as a pharmaceutical drug candidate, the recreational use of ADB-FUBINACA was first reported in 2013 in Japan, with fatal cases being described in 2015. ADB-FUBINACA is one of the most apprehended and consumed synthetic cannabinoid (SC), following AMB-FUBINACA, which emerged in 2014 as a drug of abuse and has since been responsible for several intoxication and death outbreaks. Here, we critically review the physicochemical properties, detection methods, prevalence, biological effects, pharmacodynamics and pharmacokinetics of both drugs. When smoked, these SCs produce almost immediate effects (about 10 to 15 s after use) that last up to 60 min. They are rapidly and extensively metabolised, being the O-demethylated metabolite of AMB-FUBINACA, 2-(1-(4-fluorobenzyl)-1H-indazole-3-carboxamide)-3-methylbutanoic acid, the main excreted in urine, while for ADB-FUBINACA the main biomarkers are the hydroxdimethylpropyl ADB-FUBINACA, hydroxydehydrodimethylpropyl ADB-FUBINACA and hydroxylindazole ADB-FUBINACA. ADB-FUBINACA and AMB-FUBINACA display full agonism of the CB1 receptor, this being responsible for their cardiovascular and neurological effects (e.g., altered perception, agitation, anxiety, paranoia, hallucinations, loss of consciousness and memory, chest pain, hypertension, tachycardia, seizures). This review highlights the urgent requirement for additional studies on the toxicokinetic properties of AMB-FUBINACA and ADB-FUBINACA, as this is imperative to improve the methods for detecting and quantifying these drugs and to determine the best exposure markers in the various biological matrices. Furthermore, it stresses the need for clinicians and pathologists involved in the management of these intoxications to describe their findings in the scientific literature, thus assisting in the risk assessment and treatment of the harmful effects of these drugs in future medical and forensic investigations.

Enantioselective SERS sensing of pseudoephedrine in blood plasma biomatrix by hierarchical mesoporous Au films coated with a homochiral MOF

Here, we present a new family of hierarchical porous hybrid materials as an innovative tool for ultrasensitive and selective sensing of enantiomeric drugs in complex biosamples via chiral surface-enhanced Raman spectroscopy (SERS). Hierarchical porous hybrid films were prepared by the combination of mesoporous plasmonic Au films and microporous homochiral metal-organic frameworks (HMOFs). The proposed hierarchical porous substrates enable extremely low limit of detection values (10^-12 M) for pseudoephedrine in undiluted blood plasma due to dual enhancement mechanisms (physical enhancement by the mesoporous Au nanostructures and chemical enhancement by HMOF), chemical recognition by HMOF, and a discriminant function for bio-samples containing large biomolecules, such as blood components. We demonstrate the effect of each component (mesoporous Au and microporous AlaZnCl (HMOF)) on the analytical performance for sensing. The growth of AlaZnCl leads to an increase in the SERS signal (by around 17 times), while the use of mesoporous Au leads to an increase in the signal (by up to 40%). In the presence of a complex biomatrix (blood serum or plasma), the hybrid hierarchical porous substrate provides control over the transport of the molecules inside the pores and prevents blood protein infiltration, provoking competition with existing plasmonic materials at the limit of detection and enantioselectivity in the presence of a multicomponent biomatrix.

Interpol review of fibres and textiles 2016-2019

This review paper covers the forensic-relevant literature in fibres and textiles from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20Review%20Papers%202019.pdf.

Prediction of Cancer Stem Cell Fate by Surface-Enhanced Raman Scattering Functionalized Nanoprobes

Cancer stem cells (CSCs) are the fundamental building blocks of cancer dissemination, so it is desirable to develop a technique to predict the behavior of CSCs during tumor initiation and relapse. It will provide a powerful tool for pathological prognosis. Currently, there exists no method of such prediction. Here, we introduce nickel-based functionalized nanoprobe facilitated surface enhanced Raman scattering (SERS) for prediction of cancer dissemination by undertaking CSC-based surveillance. SERS profiling of CSCs of various cell lines (breast cancer, cervical cancer, and lung cancer) was compared with their cancer counterparts for the prediction of prognosis, with statistical significance of single-cell sensitivity. The single-cell sensitivity is critical as even a few CSCs are capable of initiating a tumor. Intermediate states of CSC transmutation to cancer cells and its reverse were monitored, and nanoprobe-assisted SERS profiling was undertaken. We experimentally demonstrated that the quasi-intermediate CSC states have dissimilar profiles during the transformation from cancer to CSC and vice versa enabling statistical differentiation without ambiguity. It was also observed that molecular signatures of these opposite pathways are cancer-type specific. This observation provided additional clarity to the current understanding of relatively unfamiliar quasi-intermediate states; making it possible to predict CSC dissemination for variety of cancers with ∼99% accuracy. Nano probe-based prediction of CSC fate is a powerful prediction tool for ultrasensitive prognosis of malignancy in a complex environment. Such CSC-based cancer prognosis has never been proposed before. This prediction technique has potential to provide insights for cancer diagnosis and prognosis as well as for obtaining information instrumental in designing of meaningful CSC-based cancer therapeutics.

Recent Developments in the Field of Explosive Trace Detection

Explosive trace detection (ETD) technologies play a vital role in maintaining national security. ETD remains an active research area with many analytical techniques in operational use. This review details the latest advances in animal olfactory, ion mobility spectrometry (IMS), and Raman and colorimetric detection methods. Developments in optical, biological, electrochemical, mass, and thermal sensors are also covered in addition to the use of nanomaterials technology. Commercially available systems are presented as examples of current detection capabilities and as benchmarks for improvement. Attention is also drawn to recent collaborative projects involving government, academia, and industry to highlight the emergence of multimodal screening approaches and applications. The objective of the review is to provide a comprehensive overview of ETD by highlighting challenges in ETD and providing an understanding of the principles, advantages, and limitations of each technology and relating this to current systems.

Surface Enhanced Raman Spectroscopy for Quantitative Analysis: Results of a Large-Scale European Multi-Instrument Interlaboratory Study

Surface-enhanced Raman scattering (SERS) is a powerful and sensitive technique for the detection of fingerprint signals of molecules and for the investigation of a series of surface chemical reactions. Many studies introduced quantitative applications of SERS in various fields, and several SERS methods have been implemented for each specific application, ranging in performance characteristics, analytes used, instruments, and analytical matrices. In general, very few methods have been validated according to international guidelines. As a consequence, the application of SERS in highly regulated environments is still considered risky, and the perception of a poorly reproducible and insufficiently robust analytical technique has persistently retarded its routine implementation. Collaborative trials are a type of interlaboratory study (ILS) frequently performed to ascertain the quality of a single analytical method. The idea of an ILS of quantification with SERS arose within the framework of Working Group 1 (WG1) of the EU COST Action BM1401 Raman4Clinics in an effort to overcome the problematic perception of quantitative SERS methods. Here, we report the first interlaboratory SERS study ever conducted, involving 15 laboratories and 44 researchers. In this study, we tried to define a methodology to assess the reproducibility and trueness of a quantitative SERS method and to compare different methods. In our opinion, this is a first important step toward a “standardization” process of SERS protocols, not proposed by a single laboratory but by a larger community.

Graphene oxide/gold nanorod plasmonic paper – a simple and cost-effective SERS substrate for anticancer drug analysis

A simple and cost-effective plasmonic paper as a SERS substrate based on a combination of graphene oxide (GO) and gold nanorods (AuNRs).

Rapid detection of synthetic cannabinoids in herbal highs using surface-enhanced Raman scattering produced by gold nanoparticle co-aggregation in a wet system

Synthetic cannabinoids (SCs) are a major category of new psychoactive substances that are frequently distributed after addition to plants. To date, various SCs with small differences in their chemical structures have prevailed in the illegal drug market. Thus, the development of a method for rapid detection with high discrimination capability is critically important for the forensic field. Vibrational spectroscopy is a possible analytical technique for this purpose because it can sensitively reflect differences among chemical structures. In this study, we applied surface-enhanced Raman scattering (SERS) with gold nanoparticle co-aggregation in a wet system to plant samples containing SCs. The experimental protocol used was simple and involved only mixing of the sample with several other solutions. It was possible to detect SERS spectra from various stock solutions of SCs by this method. The method was then applied to street samples containing SCs. Some of the plant samples containing SCs did not produce significant SERS signals even though stock solutions of the same SCs did produce SERS spectra. We investigated the reason for this discrepancy and speculated that the solubility in aqueous solutions was a factor determining whether a significant SERS signal could be detected or not. According to this hypothesis, minimal sample pre-treatment methods were applied. This allowed for the detection of SERS spectra from the examined plant samples. The developed approach is a powerful method for screening analysis of SCs in plant fragments.

Fabrication of Au Nanorods by the Oblique Angle Deposition Process for Trace Detection of Methamphetamine with Surface-Enhanced Raman Scattering

Oblique angle deposition (OAD) is a simple, low cost, effective, and maskless nanofabrication process. It can offer a reliable method for the mass fabrication of uniform metal nanorods which can be used as the surface-enhanced Raman scattering (SERS) substrate with an excellent enhancing performance. Up to now, Ag nanorods SERS substrates have been extensively studied. However, Ag is chemically active and easy to oxidize under atmospheric conditions. Comparatively, Au is chemically stable and has better biocompatibility than Ag. In this paper, we in detail, studied the electromechanical (EM) field distribution simulation, fabrication, and application of Au nanorods (AuNRs) on trace detection of methamphetamine. According to the finite-difference time-domain (FDTD) calculation results, the maximum EM intensity can be obtained with the length of AuNRs to be 800 nm and the tilting angle of AuNRs to be 71° respectively. The aligned Au nanorod array substrate was fabricated by the OAD process. The two key process parameters, deposition angle, and deposition rate were optimized by experiments, which were 86° and 2 Å/s, respectively. Using 1,2-bis (4-pyridyl) ethylene (BPE) as the probe molecule, the limit of detection (LOD) was characterized to be 10⁻¹¹ M. The AuNRs were also used to detect methamphetamine. The LOD can be down to M (i.e., 14.92 pg/ml), which meet the requirements of the on-site rapid detection of the methamphetamine in human urine (500 ng/ml).

Rapid detection of hypnotics using surface-enhanced Raman scattering based on gold nanoparticle co-aggregation in a wet system

Sensitive detection of drugs using a method with high qualification capability is important for forensic drug analysis. Vibrational spectroscopy is a powerful screening technique because it can provide detailed structural information of the compounds included in samples with simple experimental protocols. Among various spectroscopic techniques, surface enhanced Raman scattering (SERS) spectroscopy has attracted enormous attention owing to its ultra-high sensitivity. In this study, we developed a method for rapid detection of hypnotics using SERS with gold nanoparticle co-aggregation in a wet system. The developed method required a simple analytical protocol. This enabled rapid analysis with high stability and repeatability. We analyzed various hypnotics (19 types including benzodiazepines and nonbenzodiazepines) to investigate the structure-spectrum relationship. As a proof of concept for application to real crime samples, simulated spiked beverages containing one hypnotic (etizolam, flunitrazepam, zolpidem, or zopiclone) were analyzed. Diluting the beverage samples decreased the matrix effect and allowed for detection of these hypnotics. Except for flunitrazepam, strong signals were observed for all hypnotics, and the estimated lower limit of detection was 50 ppm in apple drink. The developed approach is a rapid method for screening analysis of hypnotics with low sample requirements.

Forensic Discrimination Potential of Blue, Black, Green, and Red Colored Fountain Pen Inks Commercially Used in Pakistan, by UV/Visible Spectroscopy, Thin Layer Chromatography, and Fourier Transform Infrared Spectroscopy

Examination and comparison of fountain pen inks are very important in forensic questioned documents examination in developing countries where the chances of fraud are greater in cases of cheques, marriage papers, entry of birth and death, etc. In this study, fountain pen inks of blue, black, green, and red colours that are commercially used in Pakistan have been discriminated by UV-Vis spectroscopy, TLC, and FTIR spectroscopy. We have calculated and compared the results in terms of discriminating power. UV/Visible Spectroscopy of fountain pen inks of different brands showed different composition despite their similar colours. TLC was effectively used to differentiate between the colored components of inks. FTIR results showed that each brand could be distinguished by studying the pattern of their absorption spectra that appeared due to the presence of different functional groups. On the basis of combined results of UV-VIS, TLC, and FTIR, the DP was found from 0.73-0.8 for blue, 0.80-1.0 for black, 0.5-1.0 for green, and 1.0 for red colored fountain pen inks. Overall, this study demonstrated the elevated worth of analysis of fountain pen inks commercially used in Pakistan as the study for fountain pen inks, while not very common, remains an interesting target study.

Contribution of Raman and Surface Enhanced Raman Spectroscopy (SERS) to the analysis of vehicle headlights: Dye(s) characterization

Although ubiquitous on accident scenes, the polymers from headlight optics are often neglected in hit-and-run cases, and their evidential value restrained to direct comparison once a corresponding vehicle is found. Multilayered automotive paint fragments are preferred for their access to corresponding databases (PDQ, EUCAP) to infer models and brands of cars. The potential of polymers headlights for providing forensic intelligence has never been exploited, principally due to the lack of diversity, of appropriate databases, and of case examples. The motives are very simple however. Headlight polymers suffer from a lack of differentiation, and about 90% of them are composed of polymethylmethacrylate (PMMA). The discriminating powers using techniques in sequence typically range from 30 to 60%. In this paper, we take advantage of the extreme sensitivity of Surface Enhanced Raman Spectroscopy (SERS) to analyze the dye composition of the polymer headlights. The measurements by standard Raman spectroscopy at 488, 633, and 785nm permits us to identify the polymer type with relative ease. 51 out of 53 samples are composed of PMMA, the two remaining being either Polycarbonate or Polybutylene terephthalate. Additionally, using SERS with silver colloids at 488 and 633nm, provides enhanced spectra of the dyes used in the composition with an extreme sensitivity and specificity. With SERS we are able to differentiate the majority of the headlights with a remarkable 90-100% discriminating power. Solvent Orange 60, Solvent Red 52 and Solvent Red 111 were successfully identified as dyes used in the manufacture of the headlights. These results demonstrate that a combined Raman-SERS approach has the potential to replace an otherwise lengthy sequence of many different analytical techniques. With one single instrument, we offer the possibility to combine an analysis of the polymer type, and of the dye components with high discriminating capabilities. These results open up new opportunities for exploiting headlight plastics in road accidents investigations. It has the potential to help in source attribution, and/or database building in a forensic intelligence perspective.

Competitive Binding Investigations and Quantitation in Surface-Enhanced Raman Spectra of Binary Dye Mixtures

This research presents a study in surface-enhanced Raman quantitation of dyes present in mixtures of alizarin and purpurin using standard calibration curves and Langmuir isotherm calibration models. Investigations of the nature of competitive adsorption onto silver nanoparticles by centrifugation indicates that both dyes in the mixture interact with the nanoparticles simultaneously, but only the stronger adsorbing one is seen to dominate the spectral characteristics. Calibration can be carried out by careful selection of peaks characteristic to each dye in the mixture. Comparisons of peak height and peak area calibrations reveal that peak heights, when selected by the maximum value and accounting for peak shifts, prove the better model for quantitation. It is also shown that the microwave nanoparticle synthesis method produces stable nanoparticles with a shelf-life of at least one year that give very little variation within and between uses.

Facile fabrication of silver nanoparticle-coated silica-C18 core–shell microspheres and their applications in SERS detection

We present a one-step method to prepare silver nanoparticle (Ag NP) shell coated functional microspheres as a surface-enhanced Raman scattering (SERS) substrate.

Surface enhanced Raman spectroscopy (SERS) as a method for the toxicological analysis of synthetic cannabinoids

Synthetic cannabinoids (K2, spice) present problems in forensic investigations because standard presumptive methods, such as immunoassays, are insufficiently specific for the wide range of potential target compounds. This issue can lead to problems with low sensitivity and yield false negative results. A potential solution to this problem is surface enhanced Raman spectroscopy (SERS). In this study we demonstrate the analysis of a set of structurally similar synthetic cannabinoids using SERS. The procedure involves mixing the analyte with gold nanoparticles prepared in a solution containing alkali or alkaline earth salt solutions. The salts produce aggregation of the nanoparticles with a resultant spectral enhancement due to the formation of spectral hotspots with enhanced field effects within the aggregate. Among the salts tested, 0.0167M MgCl₂ produced the lowest limit of detection and best overall sensitivity. The method produces clearly distinguishable spectra for each synthetic cannabinoid with detection limits as low as 18ng/mL. Spiked urine samples were also analyzed following a cleanup procedure involving support liquid extraction. When using a portable Raman system, a higher concentration of MgCl₂ was needed to produce similar a LOD. The results demonstrate that this procedure has great potential as a method for presumptive screening of synthetic cannabinoids.