Size-dependent surface enhanced Raman scattering activity of plasmonic AuNS@AgNCs for rapid and sensitive detection of Butyl benzyl phthalate

Surface-enhanced Raman scattering based on noble metal nanoassemblies for detecting harmful substances in food

Residues of harmful substances in food can severely damage human health. The content of these substances in food is generally low, making detection difficult. Surface-enhanced Raman scattering (SERS), based on noble metal nanomaterials, mainly gold (Au) and silver (Ag), has exhibited excellent capabilities for trace detection of various substances. Noble metal nanoassemblies, in particular, have extraordinary flexibility and tunable optical properties, which cannot be offered by single nanoparticles (NPs). These nanoassemblies, with their various morphologies synthesized using NPs through artificially induced self-assembly or template-driven preparation, can significantly enhance the local electric field and create "hot spots" due to the gaps between adjacent NPs. Consequently, the SERS properties of NPs become more prominent, leading to improved performance in the trace detection of various substances and detection limits that are considerably lower than the current relevant standards. Noble metal nanoassemblies show promising potential in ensuring food safety. This review discusses the synthesis methods and SERS properties of noble metal nanoassemblies and then concentrates on their application in detecting biotoxins, drug residues, illegal additives, and heavy metals. The study provides valuable references for further research into the application of nanoassemblies in food safety detection.

Ultra-small water-soluble fluorescent copper nanoclusters for p-nitrophenol detection

Due to the widespread application of p-nitrophenol (p-NP) across various industries, particularly in the pharmaceutical and chemical sectors, it has emerged as a significant environmental contaminant in both soil and water ecosystems. The development of swift and sensitive detection platforms for p-NP is therefore demanding. Herein, a fluorescence sensor based on ultra-small copper nanoclusters with exterior glutathione ligands determined by electrospray ionization mass spectrometry (ESI-MS) as [Cu14(SG)12]+ (denoted as Cu-SG NCs) has been prepared in high efficiency, and shown high selectivity for p-NP detection. The Cu-SG NCs, synthesized via a facile one-pot chemical reduction technique, exhibit emission maxima at 620 nm. Notably, the introduction of p-NP into the nanocluster system causes a significant quenching of the Cu-SG NCs fluorescence. The quenching phenomenon arises predominantly as a result of the inner filter effect (IFE), which stems from the substantial overlap between the UV-Vis absorption spectrum of p-NP and the excitation wavelength of Cu-SG NCs. The developed fluorescence sensor platform demonstrates a wide determination range for p-NP, ranging from 0.04 to 2000 µM, with a detection limit of 30 nM. Additionally, the sensor efficacy was successfully validated in the analysis of actual water samples. The ease of synthesis, excellent optical properties, and low toxicity of Cu-SG NCs represent significant advantages over the reported noble metal nanomaterials and is highly promising for future practical applications.

A review on solution- and vapor-responsive sensors for the detection of phthalates

Phthalic acid esters, largely referred to as phthalates, are today acknowledged as important pollutants used in the manufacture of polyvinyl chloride (PVC)-based plastics, whose use extends to almost every aspect of modern life. The risk of exposure to phthalates is particularly relevant as high concentrations are regularly found in drinking water, food-contact materials and medical devices, motivating an immense body of research devoted to methods for their detection in liquid samples. Conversely, phthalate vapors have only recently been acknowledged as potentially important atmospheric pollutants and as early fire indicators; additionally, deposition of these vapors can pose significant problems to the proper functioning of spacecraft and diverse on-board devices, leading to major space agencies recognizing the need of developing vapor-responsive phthalate sensors. In this manuscript we present a literature survey on solution- and vapor-responsive sensors and analytical assays for the detection of phthalates, providing a detailed analysis of a vast array of analytical data to offer a clear idea on the analytical performance (limits of detection and quantification, linear range) and advantages provided by each class of sensor covered in this review (electrochemical, optical and vapor-responsive) in the context of their potential real-life applications; the manuscript also gives detailed fundamental information on the various physicochemical responses exploited by these sensors and assays that could potentially be harnessed by new researchers entering the field.

A review of recent progress in the application of Raman spectroscopy and SERS detection of microplastics and derivatives

The global environmental concern surrounding microplastic (MP) pollution has raised alarms due to its potential health risks to animals, plants, and humans. Because of the complex structure and composition of microplastics (MPs), the detection methods are limited, resulting in restricted detection accuracy. Surface enhancement of Raman spectroscopy (SERS), a spectral technique, offers several advantages, such as high resolution and low detection limit. It has the potential to be extensively employed for sensitive detection and high-resolution imaging of microplastics. We have summarized the research conducted in recent years on the detection of microplastics using Raman and SERS. Here, we have reviewed qualitative and quantitative analyses of microplastics and their derivatives, as well as the latest progress, challenges, and potential applications.

Simultaneous and rapid detection of polychlorinated phenols in water samples by surface-enhanced Raman spectroscopy combined with principal component analysis

In this work, a simple, high-throughput, and sensitive analytical method based on surface-enhanced Raman spectroscopy (SERS) and principal component analysis (PCA) was fabricated for simultaneous and rapid determination of three polychlorinated phenols (PCPs) including 2,4-dichlorophenol (2,4-DCP), 2,4,5-trichlorophenol (2,4,5-TCP), and 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP). The aggregated Ag nanoparticles (AgNPs) induced by inorganic salt ions were used as sensitive SERS substrate, and the electromagnetic field distribution of AgNPs with different distances was simulated by finite difference time domain (FDTD) to verify the theory feasibility. The high throughput and rapid detection can be achieved by commercial 96-pore plate. Under the optimum conditions, the linear relationship between the Raman intensity and the concentrations of PCPs was established with satisfied correlation coefficient. The limits of detection (LOD) for 2,4-DCP, 2,4,5-TCP, and 2,3,4,6-TeCP are 0.27 mg L-1, 0.09 mg L-1, and 0.10 mg L-1 by rules of 3σ, respectively. The simultaneous quantitative analysis can be achieved thanks to the independent Raman characteristic peaks of three PCPs. Afterwards, the PCA method was used to eliminate the limitations of overlapping of characteristic Raman peaks in structural analogues of 2,4-DCP, 2,4,5-TCP, and 2,3,4,6-TeCP. The recovery experiments including single PCPs and mixed PCP samples show satisfied recoveries ranging from 85.0 to 113.9% and 80.4 to 114.0% with RSDs in range of 0.4-9.5% and 1.1-10.7%, respectively. The proposed method shows great potentials in rapid, high-throughput, and sensitive monitoring of the contaminants in water and pesticide samples with similar structure. Here, we introduced aggregated Ag nanoparticles (AgNPs) induced by inorganic salt ion for simultaneous, rapid, and sensitive determination of polychlorinated phenols (PCPs) including 2,4-dichlorophenol (2,4-DCP), 2,4,5-trichlorophenol (2,4,5-TCP), and 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP) by surface-enhanced Raman spectroscopy (SERS) combined with principal component analysis (PCA). The AgNPs induced by inorganic salt ions were used as sensitive SERS substrate, and the electromagnetic field distribution of AgNPs with different distances was simulated by finite difference time domain (FDTD) to verify the theory feasibility. The PCA method was used to eliminate the limitations of overlapping of characteristic Raman peaks in structural analogues of 2,4-DCP, 2,4,5-TCP, and 2,3,4,6-TeCP. The proposed method shows great potentials in rapid, high-throughput, and sensitive monitoring of the contaminants in water and pesticide samples with similar structure.

Synthesis of water-soluble, ultrabright Cu nanoclusters with core-shell structure via facile reduction approach for determination of 4-nitrophenol

In this work, we reported a facile reduction approach for fabrication of water-soluble and ultrabright Cu nanoclusters with core-shell structure. A certain amount of reducing agent as NaBH₄was introduced into the polyethyleneimine-stabilized Cu nanoclusters (CuNCs@PEI) system, which exhibited 4-fold fluorescence enhancement along with a blue shift of the emission peak. The variations of morphology, valence states and functional groups demonstrated that a Cu shell was formed surround CuNCs (defined as CuNCs-Cu@PEI), attributable to metal complex (PEI-Cu⁺and PEI-Cu²⁺) reduction. The effect of core-shell morphology on luminous and electron relaxation mechanism of CuNCs-Cu@PEI was investigated via temperature-dependent steady and time-resolved fluorescence measurements. The CuNCs-Cu@PEI with a high fluorescence quantum yields of 22.59% were able to homogeneously disperse in aqueous phase, indicating their potential applications in biological labeling, sensing and invivoimaging. Finally, the CuNCs-Cu@PEI was employed as a fluorescence probe to determine 4-nitrophenol, of which the detection limit was much lower than initial CuNCs@PEI.

Surface-Enhanced Raman Sensing of Semi-Volatile Organic Compounds by Plasmonic Nanostructures

Facile detection of indoor semi-volatile organic compounds (SVOCs) is a critical issue to raise an increasing concern to current researchers, since their emissions have impacted the health of humans, who spend much of their time indoors after the recent incessant COVID-19 pandemic outbreaks. Plasmonic nanomaterial platforms can utilize an electromagnetic field to induce significant Raman signal enhancements of vibrational spectra of pollutant molecules from localized hotspots. Surface-enhanced Raman scattering (SERS) sensing based on functional plasmonic nanostructures has currently emerged as a powerful analytical technique, which is widely adopted for the ultra-sensitive detection of SVOC molecules, including phthalates and polycyclic aromatic hydrocarbons (PAHs) from household chemicals in indoor environments. This concise topical review gives updated recent developments and trends in optical sensors of surface plasmon resonance (SPR) and SERS for effective sensing of SVOCs by functionalization of noble metal nanostructures. Specific features of plasmonic nanomaterials utilized in sensors are evaluated comparatively, including their various sizes and shapes. Novel aptasensors-assisted SERS technology and its potential application are also introduced for selective sensing. The current challenges and perspectives on SERS-based optical sensors using plasmonic nanomaterial platforms and aptasensors are discussed for applying indoor SVOC detection.

Quantitative SERS sensor based on self-assembled Au@Ag heterogeneous nanocuboids monolayer with high enhancement factor for practical quantitative detection

Accurate and rapid quantitative detection of pesticide and pollutant levels in the actual sample can aid in protecting food security, environmental security, and human health. A high Raman enhancement factor and good repeatability of the surface-enhanced Raman spectroscopy (SERS) substrates are favorable to quantitative analysis. Herein, a quantitative SERS sensor based on constructed self-assembled plasmonic Au@Ag heterogeneous nanocuboids (Au@Ag NCs) monolayer was developed. The sensor was used to quantitatively detect the trace pesticides extracted from pear surfaces and pollutants in fishpond water. Densely packed Au@Ag NCs fabricated into large-scale monolayer films were chemically functionalized using 4-methyl-thiobenzoic acid (4-MBA) at the organic/aqueous interface, in which plentiful nanogaps contribute to increase hotspots. Their sharp corners and edges make the sensor have high SERS performance through providing abundant "hot spots." The obtained optically SERS-based sensor with uniform liquid-state interfacial nanoparticle arrays appeared to have nice SERS performance and uniformity using crystal violet (CV) as a probe molecule. In particular, the proposed SERS sensor was applied for quantitative detection of thiabendazole (TBZ) extracted from pear surfaces and malachite green (MG) in fishpond water down to levels of 0.0105 nM and 0.87 nM for SERS assay respectively. As a result, our proposed SERS quantitative detection strategy is quite preferred to on-site analysis and supervision of contaminant in food samples.