Aggregation Of Silver Nanoparticles Research Articles

Oxidative Dissolution and the Aggregation of Silver Nanoparticles in Drinking and Natural Waters: The Influence of the Medium on the Process Development.

Currently, there are quite a few data on the ways silver nanoparticles get into the aquatic environment, on their subsequent dissolution in water, and on the release of toxic Ag+ ions. Differences in the experimental conditions hinder the determination of the basic regularities of this process. In this study, the stages of oxidative dissolution of AgNPs were studied, starting from the formation of silver hydrosol in deaerated solution, the reaction of silver with oxygen and with drinking and natural waters, the analysis of intermediate species of the oxidized colloidal particles, and the subsequent particle aggregation and precipitation, by optical spectroscopy, DLS, TEM, STEM, and EDX. In the presence of oxygen, silver nanoparticles undergo oxidative dissolution, which gives Ag+ ions and results in the subsequent aggregation of nanoparticles. The carbonate hydrosol loses stability when mixed with waters of various origin. This is due to the destruction of the electric double layer, which is caused by an increase in the solution's ionic strength and the neutralization of the charge of the metal core. The environmental hazard of the silver nanoparticle hydrosol would noticeably change and/or decrease when the nanoparticles get into natural waters because of their fast precipitation and because the major part of released Ag+ ions form poorly soluble salts with ions present in water.

Development of enzyme-based biosensor for residual detection of organophosphate pesticides using functionalized nanocellulose-modified silver nanoparticles

Excessive use of pesticides to satisfy the demand of a rapidly increasing population has posed numerous problems for human health and the environment. Therefore, we developed a nanocomposite comprised of rice husk-derived dialdehyde nanocellulose capped silver nanoparticles (AgNP@DANC) as an efficient immobilizing material for acetylcholinesterase (AChE) to develop a novel biosensor. This revolutionary enzyme-based biosensor was used for the rapid detection of organophosphate pesticides (OPs) using chlorpyrifos (CPF) and malathion (MLT) as representative pesticides in food stuffs. The detection of OPs is based on the inhibition of the catalytic activity of AChE in the presence of CPF and MLT coupled with the aggregation of silver nanoparticles (AgNPs) due to thiocholine that can be analyzed for rapid screening. The developed biosensor for CPF and MLT shows ultrasensitive behaviour over a linear range of 1 × 10−3 to 1 × 10-19 M and 1 × 10−3 to 1 × 10−17 M, respectively. Further, the sensitivity of the developed biosensor was also studied for real spiked samples. The developed biosensor shows great potential and sensitivity; thus, it could be a promising biosensor for the rapid and on-site detection of many OPs.

Plasmon-driven chemical transformation of a secondary amide probed by surface enhanced Raman scattering

Plasmon-driven chemical conversion is gaining burgeoning interest in the field of heterogeneous catalysis. Herein, we study the reactivity of N-methyl-4-sulfanylbenzamide (NMSB) at nanocavities of gold and silver nanoparticle aggregates under plasmonic excitation to gain understanding of the respective reaction mechanism. NMSB is a secondary amide, which is a frequent binding motive found in peptides and a common coupling product of organic molecules and biomolecules. Surface-enhanced Raman scattering (SERS) is used as a two-in-one in-situ spectroscopic tool to initiate the molecular transformation process and simultaneously monitor and analyze the reaction products. Supported by dissociative electron attachment (DEA) studies with the gas phase molecule, a hot electron-mediated conversion of NMSB to p-mercaptobenzamide and p-mercaptobenzonitrile is proposed at the plasmonic nanocavities. The reaction rate showed negligible dependence on the external temperature, ruling out the dominant role of heat in the chemical transformation at the plasmonic interface. This is reflected in the absence of a superlinear relationship between the reaction rate constant and the laser power density, and DEA and SERS studies indicate a hot-electron mediated pathway. We conclude that the overall reaction rate is limited by the availability of energetic hot electrons to the NMSB molecule.

Selective colorimetric detection of trace chromium (III) based on silver nanoparticles aggregation via a domino-like reaction

A simple method for measuring and tracking Cr3+, particularly in water, are crucial for environmental protection and avoiding serious health implications. Herein, we report the synthesis of mannose functionalized silver nanoparticles (Ag@mannose NPs) for naked eye detection of Cr3+ ions. The Cr3+-induced selective stimuli on the surface of Ag@mannose NPs promote aggregation, resulting in a colour change from yellow to purple, which can be assessed by absorption spectroscopy. Zeta potential investigation revealed that the surface charge of Ag@mannose NPs was altered in the presence of Cr3+, resulting in aggregation, as validated by dynamic light scattering and transmission electron microscopy. Cyclic voltammetry study shows that the NPs surface stabilized with mannose was oxidized in the presence of Cr3+, causing a domino-like effect that resulted in NPs aggregation and colour change. The interference study demonstrated the selectivity and sensitivity of Ag@mannose NPs to Cr3+ over other metal ions. Ag@mannose NPs can detect Cr3+ in a wide pH range of 3–9. The lowest Cr3+ concentration detected by the naked eye is 0.6 μM (39 μg/L), under the World Health Organization permissible limit of chromium (50 μg/L) in drinking water. Finally, the Ag@mannose NPs sensing ability was demonstrated by detecting Cr3+ in tap and sewage water with a good recovery percentage.

Therapeutic Monitoring of Flutamide Using Aggregated Surface Enhanced Raman Spectroscopy (SERS) Substrates

It is essential to monitor the blood level of flutamide (FLT) during prostate cancer treatment since the abnormal renal elimination due to pathophysiological factors hinders attaining steady-state drug concentration. This study reports a systematic investigation of aggregation of silver nanoparticles (AgNPs) based on Hofmeister effect and eventual change in surface-enhanced Raman spectroscopy (SERS) enhancement for the determination of FLT. Among the aggregants, MgSO4 showed the maximum enhancement. The concentration of MgSO4, pH, and duration of aggregation were optimized for FLT detection. The aggregated AgNPs (a-AgNPs) SERS substrate enhanced the Raman signal of FLT by up to five-orders of magnitude under optimized conditions. The developed technique was able to determine FLT from 0.25 × 10−3 μM to 250 μM with a limit of detection (LoD) of 1 pM. The application of the SERS substrate in practical analysis has been demonstrated using FLT-spiked human serum from 0 nM to 1000 nM with a detection limit of 0.3 nM. The reported Hofmeister series of AgNPs aggregation will assist in the development of SERS substrates for other analytes.

Green assembly of silver nanoparticles on PET by using silymarin as a natural reductant

Chemical and physical synthesis of silver nanoparticles (AgNPs) has become an urgent problem due to its high application cost and secondary pollution. This study used the plant extract, silymarin, as a green reductant to prepare polyethylene terephthalate/ethylenediamine/silver nanoparticles@silymarin (PET/EDA/AgNPs@Silymarin) and explored its catalytic mechanism and effect. The results showed that the coating of AgNPs on PET demonstrates the potential of silymarin as an environmentally friendly reducing agent. The obtained AgNPs had a strong peak at 402 nm on UV–vis spectrophotometer. Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) also confirmed that AgNPs were loaded on PET and existed in various shapes with an average particle size of 20.2 nm. PET/EDA/AgNPs@Silymarin with 4-nitrophenol (4-NP) as a target pollutant also exhibited excellent catalytic properties. The catalytic productivity of PET/EDA/AgNPs@Silymarin was approximately 92.56 % after 5 cycles. Conceivably, the strategy of AgNPs synthesis by silymarin provides a new pathway for green synthesis and cost control.

Homogeneous and Label-Free Detection and Monitoring of Protein Kinase Activity Using the Impact Electrochemistry of Silver Nanoparticles.

Protein kinase activity correlates closely with that of many human diseases. However, the existing methods for quantifying protein kinase activity often suffer from limitations such as low sensitivity, harmful radioactive labels, high cost, and sophisticated detection procedures, underscoring the urgent need for sensitive and rapid detection methods. Herein, we present a simple and sensitive approach for the homogeneous detection of protein kinase activity based on nanoimpact electrochemistry to probe the degree of aggregation of silver nanoparticles (AgNPs) before and after phosphorylation. Phosphorylation, catalyzed by protein kinases, introduces two negative charges into the substrate peptide, leading to alterations in electrostatic interactions between the phosphorylated peptide and the negatively charged AgNPs, which, in turn, affects the aggregation status of AgNPs. Via direct electro-oxidation of AgNPs in nanoimpact electrochemistry experiments, protein kinase activity can be quantified by assessing the impact frequency. The present sensor demonstrates a broad detection range and a low detection limit for protein kinase A (PKA), along with remarkable selectivity. Additionally, it enables monitoring of PKA-catalyzed phosphorylation processes. In contrast to conventional electrochemical sensing methods, this approach avoids the requirement of complex labeling and washing procedures.

Label-Free Citrate-Stabilized Silver Nanoparticles-Based, Highly Sensitive, Cost-Effective, and Rapid Visual Method for the Differential Detection of Mycobacterium tuberculosis and Mycobacterium bovis.

Tuberculosis poses a global health challenge, and it demands improved diagnostics and therapies. Distinguishing between Mycobacterium tuberculosis (M. tb) and Mycobacterium bovis (M. bovis) infections holds critical "One Health" significance due to the zoonotic nature of these infections and inherent resistance of M. bovis to pyrazinamide, a key part of the directly observed treatment, short-course (DOTS) regimen. Furthermore, most of the currently used molecular detection methods fail to distinguish between the two species. To address this, our study presents an innovative molecular-biosensing strategy. We developed a label-free citrate-stabilized silver nanoparticle aggregation assay that offers sensitive, cost-effective, and swift detection. For molecular detection, genomic markers unique to M. tb and M. bovis were targeted using species-specific primers. In addition to amplifying species-specific regions, these primers also aid the detection of characteristic deletions in each of the mycobacterial species. Post polymerase chain reaction (PCR), we compared two highly sensitive visual detection methods with respect to the traditional agarose gel electrophoresis. The paramagnetic bead-based bridging flocculation assay successfully discriminates M. tb from M. bovis with a sensitivity of ∼40 bacilli. The second strategy exploits citrate-stabilized silver nanoparticles, which aggregate in the absence of amplified dsDNA on the addition of sodium chloride (NaCl). This technique enables the precise, sensitive, and differential detection of as few as ∼4 bacilli. Our study hence advances tuberculosis detection, overcoming the challenges of M. tb and M. bovis differentiation and offering a quicker alternative to time-consuming methods.

A reduction-driven directed aggregation strategy for fabricating stretchable conductive core-sheath fibers in wearable electronics

Rapid advancement of wearable electronics is profoundly reshaping our daily lives. At the heart of these innovations, stretchable conductive fibers (SCFs) assume pivotal roles in the high-sensitivity strain sensing and the high-conductivity flexible electrical conduction. Here, the stretchable conductive core-sheath fibers (SCCFs) are developed by a reduction-driven directed aggregation strategy. A conductive sheath layer of the silver nanoparticles aggregation and an elastic core layer of polymer matrix constitute an SCCF with the effective interface bonding. An SCCF with the high initial conductivity of over 1.77 × 105 S m−1 is fabricated with the features of reliability and good washability through the systematic optimization. On one hand, leveraging the microcrack effect, the strain sensing with the high resistance sensitivity under subtle strain is achieved by using a straight SCCF. On the other hand, the SCCF with a three-dimensional helical structure is designed to act as the flexible electrical conduction with the low resistance sensitivity under great strain. Notably, these SCCFs not only exhibit exceptional sensitivity for monitoring human movements, but also demonstrate efficient electrical energy conduction capabilities. This work proposes a prospective strategy to fabricate the versatile SCFs with great reliability, stability, and durability for wearable electronics.

In situ assembly of silver nanoparticles throughout electrospun oriented alginate nanofibers for hazardous rust trace detection on bronze

A convenient and reliable surface-enhanced Raman scattering (SERS) substrate has been developed for the surface corrosion analysis of bronze artifacts. The substrate consists of oriented alginate nanofiber membranes containing silver nanoparticles (Ag NPs), which were obtained through electrostatic spinning, ion exchange, and in-situ reduction. By controlling the reduction time, Ag/alginate nanofiber membranes with different contents, sizes, and distributions were obtained. The Ag/alginate nanofiber#20 membranes, obtained with a reduction time of 20 min, reached a detection limit of 10−12 M for R6G with an enhancement factor of 6.64 × 107. In the trace detection of bronze patina, the intensity of the characteristic peaks of harmful patina located at 513, 846, 911, and 974 cm−1 were increased by more than 500 %. This was due to the uniform loading of a large number of Ag NPs on the surface of the nanofiber membrane obtained by reduction for 20 min, and the formation of a large number of hot spots between the oriented nanofibers. This significantly improved the SERS performance of the flexible substrate layer under the joint action with the Ag NPs. These results indicate that the flexible substrate layer can greatly enhance the Raman characteristic peaks of alkali copper chloride and be effectively used for trace analysis of the surface composition of bronze artifacts.

Flexible silver ring SERS substrate array fabrication by vortex evaporation method and its application for high sensitive detection of sulfonamides residues in water

Flexible surface-enhanced Raman scattering (SERS) substrates have driven much attention in Raman detection of environmental pollutants due to their unique advantage of sensitivity, low-cost and fast sampling. However, it is still a high challenge for fabricating flexible SERS substrate with high reproducibility and sensitivity. In this study, we developed a novel silver nanoparticle assembly method based on vortex evaporation method to batch assemble multiple silver ring (SR) SERS substrate array on a parafilm. The flexible SR SERS substrates were uniformly covered with active silver nano-islands, which significantly improved the Raman signal intensity of the targets by 126 folds and showed 5 times Raman enhancement compared with the common SERS substrate by direct evaporation method, and also represented the unique bending response properties of flexible substrate. The Raman detection for sulfonamide residues in water with SR SERS substrate represented high sensitivity, which limits of detection for Sulfapyridine and Sulfacloropyridazine were 9.46 and 9.3 × 10−8 mol/L, respectively. The quantitative relationships were obtained in wide linear range of 4 orders with good accuracy and stability. The flexible SR SERS substrate array can be large-scale prepared with good repeatability, stability, and low-cost, which has promising applications for trace contaminants detection in water environment.

Hydrogel SERS chip with strong localized surface plasmon resonance for sensitive and rapid detection of T-2 toxin

T-2 toxin is one of the naturally dangerous food contaminants, which is harmful to people and animals. Because of its strong toxicity and wide distribution, it is vital to develop a rapid and effective method for the detection of T-2 toxin. Herein, an excellent hydrogel surface-enhanced Raman scattering (SERS) chip is constructed for developing a novel SERS sensor to detect T-2 toxin using a portable Raman spectrometer. The SERS chip is prepared by in-situ Ca2+-mediated assembly of silver nanoparticles (AgNPs) in PVA solution, followed by a physical crosslinking possess. The assembled AgNPs produces a strong localized surface plasmon resonance (LSPR) at around 532 nm, which enables the high activity of SERS chip under the irradiation of 532 nm laser. Additionally, the unique structure of hydrogel makes the obtained chip show excellent reliability and anti-interference ability in detection. As a result, the developed SERS sensor shows many obvious advantageous including free of complex sample pretreatment (only a simple extraction), fast response (5 min), low limit of detection (0.41 ppb), wide detection range (1–10000 ppb), good recoveries (90.26–101.81 %) and relative standard deviations (2.8–6.7 %). Therefore, this SERS sensor provides a promising choice for rapid scanning and sensitive detection of trace T-2 toxin in complex matrices.

Green reduction and uniform assembly of silver nanoparticles on polydopamine functionalized sulfur-doped graphitic carbon nitride nanosheets for highly sensitive H2O2 detection via nonenzymatic approach

In this study, we demonstrate a new strategy to fabricate an enzyme-free hydrogen peroxide (H2O2) sensor electrode based on silver nanoparticles (AgNPs) decorated polydopamine/sulfur-doped graphitic carbon nanocomposite (denoted as AgNPs@PDA/S-g-C3N4). The S-g-C3N4 nanosheets are derived from the pyrolysis of trithiocyanouric acid, followed by thermal exfoliation. A mussel-inspired PDA nanolayer enhances the solubility and high dispersion of S-g-C3N4 nanosheets and AgNPs in aqueous phase synthesis. The amine and catecholic functional groups of PDA are the major nucleation sites for Ag+ ions adsorption and ascorbic acid was further used as a green reducing agent for the growth of AgNPs. PDA adhesion layer can effectively connect the AgNPs and S-g-C3N4 nanosheets via electrostatic interaction to increase the stability and biocompatibility of the ternary composite structure. Various spectroscopy and microscopy techniques confirmed the formation of AgNPs@PDA/S-g-C3N4 nanocomposite. Our AgNPs@PDA/S-g-C3N4 nanocomposite fabricated disposable sensor exhibited outstanding sensing ability to H2O2 reduction at −0.65 V (vs. Ag/AgCl), which is confirmed through an amperometric detection method. The sensor exhibits rapid response (2 s) to H2O2 sensing with high sensitivity (1020 μA mM−1 cm−2), wide detection range (0.002–23 mM) and low limit of detection of 0.086 μM. The practicality of the H2O2 sensor was evaluated with commercial milk and mouthwash samples, which retained satisfactory recoveries. Thus, our results indicate that the PDA functionalization not only enhances the S-g-C3N4 solubility but also increases the interfacial charge transport in AgNPs@PDA/S-g-C3N4 nanocomposite material which develops a potential sensing method for nonenzymatic H2O2 sensor. Due to the effective surface modification strategies, such as PDA nanocoating and AgNPs deposition, the exfoliated S-g-C3N4 nanosheets gained excellent electrochemical properties, facilitating potential candidates in electrochemical applications.

Study on Low-Temperature Conductive Silver Pastes Containing Bi-Based Glass for MgTiO3 Electronic Power Devices.

Low-temperature lead-free silver pastes deserve thorough investigation for sustainable development and application of MgTiO3 ceramics in electronic devices. In this study, a series of Bi2O3-B2O3-ZnO-SiO2-Al2O3-CaO glasses with suitable softening temperatures were prepared via melt quenching using a type of micrometer silver powder formed by silver nanoparticle aggregates. The composite pastes containing silver powder, Bi2O3 glass powder and an organic vehicle were then screen-printed. The effects of glass powder concentration and sintering temperature on the microstructure of the surface interface were also investigated. The results showed that the silver paste for microwave dielectric ceramic filters (MgTiO3) possessed good electrical conductivity (2.28 mΩ/□) and high adhesion (43.46 N/mm2) after medium temperature (670 °C) sintering. Thus, this glass powder has great application potential in non-toxic lead-free silver pastes for metallization of MgTiO3 substrates.

A Protease-Responsive Polymer/Peptide Conjugate and Reversible Assembly of Silver Clusters for the Detection of Porphyromonas gingivalis Enzymatic Activity.

We report the reversible aggregation of silver nanoparticle (AgNP) assemblies using the combination of a cationic arginine-based peptide and sulfur-capped polyethylene glycol (PEG). The formation and dissociation of the aggregates were studied by optical methods and electron microscopy. The dissociation of silver clusters depends on the peptide sequence and PEG size. A molecular weight of 1 kDa for PEG was optimal for the dissociation. The most important feature of this dissociation method is that it can operate in complex biofluids such as plasma, saliva, bile, urine, cell media, or even seawater without a significant decrease in performance. Moreover, the peptide-particle assemblies are highly stable and do not degrade (or express of loss of signal upon dissociation) when dried and resolubilized, frozen and thawed, or left in daylight for a month. Importantly, the dissociation capacity of PEG can be reduced via the conjugation of a peptide-cleavable substrate. The dissociation capacity is restored in the presence of an enzyme. Based on these findings, we designed a PEG-peptide hybrid molecule specific to the Porphyromonas gingivalis protease RgpB. Our motivation was that this bacterium is a key pathogen in periodontitis, and RgpB activity has been correlated with chronic diseases including Alzheimer's disease. The RgpB limit of detection was 100 pM RgpB in vitro. This system was used to measure RgpB in gingival crevicular fluid (GCF) samples with a detection rate of 40% with 0% false negatives versus PCR for P. gingivalis (n = 37). The combination of PEG-peptide and nanoparticles dissociation method allows the development of convenient protease sensing that can operate independently of the media composition.

EV71 virus induced silver nanoparticles self-assembly in polymer composites with an application as virus biosensor

We conducted a set of experiments to show that EV71 virus could induce a self-assembly process of silver nanoparticles in polyacrylamide. Silver nanoparticles were self-assembled aggregated to form EV71 specific binding site in the presence of EV71 template. The EV71 composites was applied as an EV71 biosensor to detect EV71 down to 0.0001 PFU/mL and 0.001 PFU/mL in PBS and serum respectively. Partial response to Coxsackie but Zika virus was observed. This was a direct method for EV71 detection in serum alternative to a widely used indirect antibody detection. The virus concentration that triggered silver nanoparticles aggregation was extremely low. This suggests more concern should be put on application of nanoparticles in humans where virus at small quantity could trigger nanoparticle aggregation.

Single versus Double Coffee-Ring Effect Patterns in Thin-Layer Chromatography Coupled with Surface-Enhanced Raman Spectroscopic Analysis of Anti-Diabetic Drugs Adulterated in Herbal Products.

In thin-layer chromatography coupled with surface-enhanced Raman spectroscopy (TLC-SERS), the coffee ring effect (CRE) describes the formation of a ring-shape spot (blank in the middle and darker on the edge) caused by the aggregation of silver nanoparticles (Ag NPs), alone (single CRE) or with the analytes (double CRE). In this work, the SCRE and DCRE were investigated in two anti-diabetic drugs, hydrophobic glibenclamide (GLB) and more hydrophilic metformin (MET). The SCRE occurred in GLB analysis, as opposed to the DCRE that occurred in MET. It was proven that for optimization of the TLC-SERS analytical procedure, it is necessary to distinguish the CRE patterns of analytes. Additionally, MET and GLB were analyzed with the developed TLC-SERS method and confirmed by another validated method using high-performance liquid chromatography. Four herbal products collected on the market were found to be adulterated with GLB or/and MET; among those, one product was adulterated with both MET and GLB, and two products were adulterated with GLB at a higher concentration than the usual GLB prescription dose. The TLC-SERS method provided a useful tool for the simultaneous detection of adulterated anti-diabetic herbal products, and the comparison of the SCRE and DCRE provided more evidence to predict CRE patterns in TLC-SERS.

Adsorption behaviour on silver nanocolloids at various concentrations of a bioactive therapeutic derivative of methylhydrazine: Experimental, DFT and molecular docking investigations

A detailed theoretical and experimental study was implemented on a novel bioactive molecule 2-(3-bromobenzoyl)-N-methylhydrazine-1-carboxamide (BMC). Density Functional Theory (DFT), Time Dependent (TD)-DFT and Surface Enhanced Raman Scattering (SERS) studies were reported for the adsorption of BMC on silver hydrosols. SERS at various concentrations are discussed and there are orientation changes for BMC with concentration and BMC assumes a tilted orientation with the metal. The adsorption energy of BMC is −64.41 kcal/mol when adsorbed with Ag6, pointing to a chemisorption process. TD-DFT predicts a Ultraviolet (UV)-vis absorption of 595.11 when BMC adsorbed on Ag6, while that of BMC is 276.12 nm and the redshift, lowered intensity in UV spectra, caused by the aggregation of colloidal silver nano particles, was used to establish the adsorption of BMC on Ag6. Molecular docking is performed on BMC and BMC-Ag6 to find their ability to bind to target proteins, IP0I (human butyrylcholinesterase) and 4PQE (human acetylcholinesterase) and drug likeness properties are also assessed. The binding scores are high for BMC-Ag6 and hence the Ag6 will perform as a drug delivery vehicle.

Investigating the effect of 532 nm and 1064 nm wavelengths and different liquid media on the qualities of silver nanoparticles yielded through laser ablation

The ablation environment's effect upon the very nature of silver nanoparticles produced by a pulsed Nd: YAG laser ablation procedure in a liquid medium was probed experimentally. Accordingly, at first, generation of silver nanoparticles was done in water with no stabilizers or surfactants in two wavelengths of 532 and 1064 nm. The effect of laser wavelength on the SPR properties was then thoroughly investigated by UV–Vis absorption spectroscopy. Also, size distribution was probed through Dynamic Light Scattering (DLS), Transmission Electron Microscope (TEM) and field emission scanning electron microscopy (FE-SEM) of silver nanoparticles. The optimum wavelength for synthesizing silver nanoparticles was obtained at the wavelength of 532 and the effect of this wavelength was investigated in different liquid media. Eventually, pulses of an Nd: YAG laser of 532 nm wavelength were applied for irradiating the silver target in different environments in water, acetone, cetyltrimethylammonium chloride (CTAC), sodium dodecyl sulfate (SDS) and polyvinyl pyrrolidone (PVP). Characterization of the obtained nanoparticles was done by UV–Vis, Atomic absorption spectroscopy (AAS) and DLS. The obtained results showed that the maximum ablation rate occurred in acetone, and the smallest nanoparticles were produced in PVP. The present research study then developed a technique for controlling the size distribution, production efficiency as well as aggregation of silver nanoparticles by modifying the liquid medium's nature.

Mirror-Stamping: A new TLC-SERS method for color authentication

Adulteration of natural colorants with artificial ones compromises the authenticity, quality, and safety of food products. It is significant for food companies to check the raw colorant ingredients to avoid potential adulteration. Combining thin-layer chromatography (TLC) and surface-enhanced Raman spectroscopy (SERS) is a promising colorant separation and detection approach. Herein, we developed a novel and simple TLC-SERS approach based on silver mirror-stamping, which was achieved by pressing a layer of aggregated silver nanoparticles on top of the target analytes on the developed TLC chip. The performance of the stamping method was evaluated on the separation and signal enhancement of an adulterated saffron model matrix (saffron and red 40) as compared to the other two methods (mirror-first and mirror-last methods). The results demonstrated that the mirror-stamping method achieved optimal separation performance with strong SERS signals. This can be attributed to the reduced sample disruption and dilution. Therefore, the mirror-stamping approach demonstrates great potential for use in TLC-SERS analysis to rapidly and accurately determine natural colorant authenticity and quality.