A new integrated TLC/MU-ATR/SERS advanced approach for the identification of trace amounts of dyes in mixtures

Automated identification of pesticide mixtures via machine learning analysis of TLC-SERS spectra

Identification of components in pesticide mixtures has been a major challenge in spectral analysis. In this paper, we assembled monolayer Ag nanoparticles on Thin-layer chromatography (TLC) plates to prepare TLC-Ag substrates with mixture separation and surface-enhanced Raman scattering (SERS) detection. Spectral scans were performed along the longitudinal direction of the TLC-Ag substrate to generate SERS spectra of all target analytes on the TLC plate. Convolutional neural network classification and spectral angle similarity machine learning algorithms were used to identify pesticide information from the TLC-SERS spectra. It was shown that the proposed automated spectral analysis method successfully classified five categories, including four pesticides (thiram, triadimefon, benzimidazole, thiamethoxam) as well as a blank TLC-Ag data control. The location of each pesticide on the TLC plate was determined by the intersection of the information curves of the two algorithms with 100 % accuracy. Therefore, this method is expected to help regulators understand the residues of mixed pesticides in agricultural products and reduce the potential risk of agricultural products to human health and the environment.

Thin layer chromatography coupled with surface enhanced Raman scattering for rapid separation and on-site detection of multi-components

The separation and detection of multi-component mixtures has always been a challenging task. Traditional detection methods often suffer from complex operation, high cost, and low sensitivity. Surface enhanced Raman scattering (SERS) technique is a high sensitivity, powerful and rapid detection tool, which can realize the specific detection of single substance components, but it must solve the problem that multi-component mixtures cannot be accurately determined. Thin layer chromatography (TLC) technology, as a high-throughput separation technology, uses chromatographic plate as the stationary phase, and could select different developing phases for separation experiments. The advantages of TLC technology in short distance and rapid separation are widely used in protein, dye and biomedical fields. However, TLC technology has limitations in detection ability and difficulty in obtaining ideal signal intensity. The combination of TLC technology and SERS technology made the operation procedure simple and the sample size small, which can achieve rapid on-site separation and quantitative detection of mixtures. Due to the rapid development of TLC-SERS technology, it has been widely used in the investigation of various complex systems. This paper reviews the application of TLC-SERS technology in food science, environmental pollution and biomedicine.

Functional cotton fabric-based TLC-SERS matrix for rapid and sensitive detection of mixed dyes

A facile cotton fabric with a built-in TLC-SERS structure was fabricated to demonstrate an integrated TLC separation and SERS identification of mixed dyes. The soft and flexible SERS fabric was firstly fabricated using a simple method in which gold nanoparticles were in-situ synthesized on cotton fabrics by heating. β-CD was then grafted onto cotton fabric through crosslinking with citric acid in presence of sodium hypophosphite monohydrate via esterification reaction. The adsorption and TLC development performance of β-CD grafted fabrics were comprehensively investigated with two organic dyes, one anionic dye and one nonionic dye. Besides, the recyclable adsorption and separation performance were tested to evaluate its sustainable application prospects. It displayed less adsorption capacity loss and reusable separation performance after several cycles than the pristine cotton fabrics. Finally, two sets of mixed dyes were successfully separated on the TLC fabrics and then identified via on-site SERS according to their different migration distance. The developed TLC-SERS fabric shows the advantage of quick, easy to handle, low-cost, sensitive, and could be exploited in on-site study of synthetic dyes in art objects, textile and packaging products or forensic applications.

Recent advances and applications to cultural heritage using ATR-FTIR spectroscopy and ATR-FTIR spectroscopic imaging

Scientific investigation of cultural heritage objects plays a vital role in a responsible modern approach to conservation and archaeology. Recent advances in spectroscopy, such as the development of Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy and ATR-FTIR spectroscopic imaging, have opened up a window of opportunities for characterisation of materials in artefacts and collections from museums. This review summarises some of the recent advances and applications of these ATR-FTIR spectroscopic analytical techniques in the area of cultural heritage studies, including examples of cross-sections of oil paintings, paper, textiles, plastic objects, potteries, glasses and mineral artefacts. Two of the major advantages of ATR mode measurements are minimal or no requirements for sample preparation and its provision for high lateral spatial resolution. In addition to conventional single point detection, two-dimensional mapping and imaging is especially beneficial for chemical visualisation of multi-layered structure cultural objects. This review also explores the implications of these advantages as well as some limitations and provides a brief outlook for the possible future developments in this area.

Multiplex Sensing of Complex Mixtures by Machine Vision Analysis of TLC-SERS Images

Thin layer chromatography in tandem with surface-enhanced Raman scattering (TLC-SERS) has demonstrated tremendous potentials as a new analytical chemistry tool to detect a wide range of substances from real-world samples. However, it still faces significant challenges of multiplex sensing from complex mixtures due to the imperfect separation by TLC and the resulting interference of SERS detection. In this article, we propose a multiplex sensing method of complex mixtures by machine vision analysis of the scanning image of the TLC-SERS results. Briefly, various pure substances in solution and the complex mixture solution are separated by TLC followed by one-dimensional SERS scanning of the entire TLC plate, which generates TLC-SERS images of all target substances along the chromatography path. After that, a machine vision method is employed to extract the template images from the TLC-SERS images of pure substance solutions. Finally, we apply a feature point matching strategy based on the Winner-take-all principle, which matches the template image of each pure substance with the mixture image to confirm the existence and derive the position of each target substance in the TLC plate, respectively. Our experimental results based on the mixture solution of five different substances show that the proposed machine vision analysis is highly selective, sensitive and does not require artificial analysis of the SERS spectra. Therefore, we envision that the proposed machine vision analysis of the TLC-SERS imaging is an objective, accurate, and efficient method for multiplex sensing of trace level of target substances from complex mixtures.

Dual Functions of a Au@AgNP-Incorporated Nanocomposite Desalination Membrane with an Enhanced Antifouling Property and Fouling Detection Via Surface-Enhanced Raman Spectroscopy

Membrane fouling has remained a major challenge limiting the wide application of membrane technology because it reduces the efficiency and shortens the lifespan of the membrane, thus increasing the operation cost. Herein we report a novel dual-function nanocomposite membrane incorporating silver-coated gold nanoparticles (Au@AgNPs) into a sulfosuccinic acid (SSA) cross-linked poly(vinyl alcohol) (PVA) membrane for a pervaporation desalination. Compared with the control PVA membrane and PVA/SSA membrane, the Au@AgNPs/PVA/SSA membrane demonstrated a higher water flux and better salt rejection as well as an enhanced antifouling property. More importantly, Au@AgNPs provided an additional function enabling a foulant detection on the membrane surface via surface-enhanced Raman spectroscopy (SERS) as Au@AgNPs could amplify the Raman signals as an SERS substrate. Distinct SERS spectra given by a fouled membrane helped to distinguish different protein foulants from their characteristic fingerprint peaks. Their fouling tendency on the membrane was also revealed by comparing the SERS intensities of mixed foulants on the membrane surface. The Au@AgNPs/PVA/SSA nanocomposite membrane presented here demonstrated the possibility of a multifunction membrane to achieve both antifouling and fouling detection, which could potentially be used in water treatment.

The Identification of Cotton Fibers Dyed with Reactive Dyes for Forensic Purposes

Some of the most common microtraces that are currently collected at crime scenes are fragments of single fibers. The perpetrator leaves them at a crime scene or takes them away, for example, on their clothing or body. In turn, the microscopic dimensions of such traces mean that the perpetrator does not notice them and therefore usually does not take action to remove them. Cotton and polyester fibers dyed by reactive and dispersion dyes, respectively, are very popular within clothing products, and they are hidden among microtraces at the scene of a crime. In our recently published review paper, we summarized the possibilities for the identification of disperse dyes of polyester fibers for forensic purposes. In this review, we are concerned with cotton fibers dyed with reactive dyes. Cotton fibers are natural ones that cannot easily be distinguished on the basis of morphological features. Consequently, their color and consequently the dye composition are often their only characteristics. The presented methods for the identification of reactive dyes could be very interesting not only for forensic laboratories, but also for scientists working in food, cosmetics or pharmaceutical/medical sciences.

Thin-layer chromatography combined with surface-enhanced Raman scattering for rapid detection of benzidine and 4-aminobiphenyl in migration from food contact materials based on gold nanoparticle doped metal-organic framework

In this work, a rapid and sensitive thin-layer chromatography combined with surface-enhanced Raman spectroscopy method was established for rapid detection of benzidine and 4-aminobiphenyl in migration from food contact materials based on Au nanoparticle doped metal-organic framework. Benzidine and 4-aminobiphenyl were firstly separated by thin-layer chromatography to solve the limitation of their overlapping Raman peaks. Then the target molecules were monitored by adding AuNPs/MIL-101(Cr) on the sample spots. Under the optimum conditions, the concentration of benzidine and 4-aminobiphenyl can be quantitatively measured in the range of 2.0-20.0 and1.0-15.0 μg/L, respectively with good linear relationship, and the limits of detection were 0.21 and 0.23 μg/L, respectively. Furthermore, the developed method was applied to analyze benzidine and 4-aminobiphenyl in migration of different food contact materials. The recoveries of benzidine and 4-aminobiphenyl for migration of food contact materials, including paper cups, polypropylene food containers, and polyethylene glycol terephthalate bottles, were 80.6-116.0 and 80.7-118% with relative standard deviations of 1.1-9.1 and 3.1-9.9%, respectively. Surface-enhanced Raman scattering detection was performed conveniently in the on-plate mode without additional elution process. The method shows great potential in rapid monitoring of hazardous substances with overlapping characteristic Raman peaks in food contact materials.

Manipulating chemistry through nanoparticle morphology

We demonstrate that the protonation chemistry of molecules adsorbed at nanometer distances from the surface of anisotropic gold nanoparticles can be manipulated through the effect of surface morphology on the local proton density of an organic coating. Direct evidence of this remarkable effect was obtained by monitoring surface-enhanced Raman scattering (SERS) from mercaptobenzoic acid and 4-aminobenzenethiol molecules adsorbed on gold nanostars. By smoothing the initially sharp nanostar tips through a mild thermal treatment, changes were induced on protonation of the molecules, which can be observed through changes in the measured SERS spectra. These results shed light on the local chemical environment near anisotropic colloidal nanoparticles and open an alternative avenue to actively control chemistry through surface morphology.

Recent trends in the application of Fourier Transform Infrared (FT-IR) spectroscopy in Heritage Science: from micro- to non-invasive FT-IR

The relevance of FT-IR spectroscopy in heritage science has experienced a constant grow in the last two decades owing to analytical peculiarities that make it an extremely useful tool to answer the questions posed by the study and conservation of art-historical and archaeological materials. High versatility, sensitivity and molecular specificity are, in fact, all requirements that FT-IR spectroscopy fulfils allowing for the investigation of the chemical properties of heritage materials spanning from the micro- to the macro-scale and offering a variety of approaches to minimize sample manipulation and maximize extracted information. Molecular identification and localisation at high lateral resolution of organic and inorganic components in micro-samples was, over recently, the mostly exploited use of FT-IR in heritage science; however, benefiting from technological progress and advances in optical materials and components achieved in the last decade, it now stands out also for non-invasive surface analysis of artworks by fully portable instrumentation.

Predictions on the SERS enhancement factor of gold nanosphere aggregate samples

A boundary element method simulation is used to accurately predict the SERS EFs of gold nanoparticle aggregates via their experimental extinction spectra.

Thin-layer chromatography/metal underlayer-ATR FTIR methodology for the study of synthetic dyes extracted from degraded wool fibres

The integration of an enhanced FTIR method with a multi-step micro-extraction protocol and the use of AgI@Au supports are proposed to analyse dyes in aged fibres.