Landing microextraction sediment phase onto surface enhanced Raman scattering to enhance sensitivity and selectivity for chromium speciation in food and environmental samples

Update on chromium speciation analysis in foods: a review of advances in analytical methods and dietary exposure assessment

Chromium occurs naturally in different oxidation states. Amongst them, hexavalent chromium is classified as both genotoxic and carcinogenic while trivalent chromium can be considered as an essential element. Therefore, speciation analysis is essential when conducting dietary exposure assessment. Several critical reviews have been published on chromium speciation analysis in foodstuffs in the last decade. However, a method that can account for species interconversion during the extraction procedure has not been reported in the reviews. In recent years, an online method using species-specific isotope dilution mass spectrometry has been developed for the simultaneous determination of trivalent and hexavalent chromium in foodstuffs. Apart from that, new methods based on offline analytical techniques, to analyse trivalent and hexavalent chromium separately, are still under development. Therefore, one of the objectives of this paper is to review these recently published analytical methods and assess whether they are fit for chromium speciation analysis in foodstuffs. Additionally, an objective is also to assess whether their limits of detection are sufficiently low for dietary exposure assessment with respect to the neoplastic effects of hexavalent chromium. Moreover, possible future research gaps are identified based on the current knowledge and existing literature.

Label-free SERS strategy for rapid detection of capsaicin for identification of waste oils

Identification of waste oils is challenging in the field of food safety due to the lack of common markers and straightforward analytical methods. Herein, we developed a novel label-free surface-enhanced Raman spectroscopy (SERS) strategy to identify waste oils using Ag nanoparticles solution (Ag NPs sol.) as a SERS substrate to significantly enhance the Raman signal of capsaicin marker molecule usually contained in the waste oils. The enhanced signal was directly detected by a portable Raman spectrometer with the limit of detection (LOD) of 2.9 μg L^-1 within 10 min. Concentration-dependent SERS investigation showed the linear relationship between the SERS signal intensity of the characteristic peaks and the concentrations of capsaicin in the range of 10-2500 μg L^-1 and the correlation coefficient was 0.9895. Our findings show the sensitivity, accessibility, and reliability of this method for the rapid identification of waste oils and furthermore for the practical applications in the field of food safety.

Deep eutectic solvent decomposition-based microextraction for chromium determination in aqueous environments by atomic absorption spectrometry with electrothermal atomization

A sensitive, rapid, and simple procedure for the determination of traces of chromium species in natural and waste waters after microextraction using a quasi-hydrophobic deep eutectic solvent based on tetrabutylammonium bromide and hexanoic acid was developed for the first time. In the developed procedure, the deep eutectic solvent played the role of a source of dispersive agent, chelating agent, and extraction solvent. During mixing the aqueous phase with the quasi-hydrophobic deep eutectic solvent, dissolution and dissociation of tetrabutylammonium bromide took place. Tetrabutylammonium bromide acted as a dispersive agent for the hexanoic acid emulsion formation and as an agent for the formation of an ion-association complex with Cr(vi) in an aqueous phase followed by its extraction in hexanoic acid. The organic phase containing Cr(vi) complexes was analyzed by atomic absorption spectrometry with electrothermal atomization. The enrichment factor value was 53, the extraction recovery was 89%, and the limit of detection calculated from a blank test, based on 3σ, was 5.0 ng L-1. The values of intra-day RSD and inter-day RSD were 3.9% and 5.0%, respectively.

Recent advancement in nano-optical strategies for detection of pathogenic bacteria and their metabolites in food safety

Pathogenic bacteria and their metabolites are the leading risk factor in food safety and are one of the major threats to human health because of the capability of triggering diseases with high morbidity and mortality. Nano-optical sensors for bacteria sensing have been greatly explored with the emergence of nanotechnology and artificial intelligence. In addition, with the rapid development of cross fusion technology, other technologies integrated nano-optical sensors show great potential in bacterial and their metabolites sensing. This review focus on nano-optical strategies for bacteria and their metabolites sensing in the field of food safety; based on surface-enhanced Raman scattering (SERS), fluorescence, and colorimetric biosensors, and their integration with the microfluidic platform, electrochemical platform, and nucleic acid amplification platform in the recent three years. Compared with the traditional techniques, nano optical-based sensors have greatly improved the sensitivity with reduced detection time and cost. However, challenges remain for the simple fabrication of biosensors and their practical application in complex matrices. Thus, bringing out improvements or novelty in the pretreatment methods will be a trend in the upcoming future.

SERS Sensors Based on Aptamer-Gated Mesoporous Silica Nanoparticles for Quantitative Detection of Staphylococcus aureus with Signal Molecular Release

This work describes a simple and novel biosensor for the quantitative determination of Staphylococcus aureus (S. aureus) based on target-induced release of signal molecules from aptamer-gated aminated mesoporous silica nanoparticles (MSNs) coupled with surface-enhanced Raman scattering (SERS) technology. MSNs were synthesized and then modified with amino groups by (3-aminopropyl) triethoxysilane to make them positively charged. Next, signal molecules (4-aminothiophenol, 4-ATP) were loaded into the pores of MSNs. Then, negatively charged aptamers of S. aureus were assembled on the surface of MSNs through electrostatic interactions. Upon the addition of S. aureus, the assembled aptamers were specifically bound to the bacteria. Consequently, the "gates" were opened, resulting in the release of 4-ATP from the pores of MSNs. The released molecules were measured by a Raman spectrometer, and the intensity of 4-ATP at 1071 cm^-1 was linearly related to the S. aureus concentration. A silver nanoflower silica core-shell structure (Ag NFs@SiO₂) was prepared and it served as a SERS substrate. Under optimized experimental conditions, a good linear relationship (y = 2107.93 + 1536.30x, R² = 0.9956) in the range from 4.7 × 10 to 4.7 × 10⁸ cfu/mL was observed with a limit of detection of 17 cfu/mL. The method was successfully applied for the analysis of S. aureus in fish samples and the recovery rate was 91.3-109%.

Rapid detection of mercury in food via rhodamine 6G signal using surface-enhanced Raman scattering coupled multivariate calibration

Considering food safety and limitations of biorecognition elements, this study focused on the development of a novel method for predicting mercury (Hg²⁺) in fish and water samples using surface-enhanced Raman scattering (SERS) coupled wavenumber selection chemometric method. Herein, core-shell Au@Ag nanoparticles (Au@Ag NPs) were synthesized as SERS substrate, and rhodamine 6G (R6G) was used as signaling probe for Hg²⁺. In the presence of Hg²⁺, citrate ion of Au@Ag NPs induced complexation and become amalgam causes desorption of R6G occurred, resulted in decreased SERS signal intensity. Compared to surface Plasmon resonance method, SERS coupled genetic algorithm-partial least squares realized good correlation coefficient (0.9745 and 0.9773) in their prediction over the concentration ranges 1.0 × 10² to 1.0 × 10^-3 µg/g. The recovery (88.45 - 94.73%) and precision (coefficient of variations, 3.28 - 5.76%) exhibiting satisfactory results suggested that the proposed method could be employed to predict Hg²⁺ in fish and water samples towards quality and safety monitoring.

Recent development of antibiotic detection in food and environment: the combination of sensors and nanomaterials

In recent years, the abuse of antibiotics has led to the pollution of soil and water environment, not only poultry husbandry and food manufacturing will be influenced to different degree, but also the human body will produce antibody. The detection of antibiotic content in production and life is imperative. In this review, we provide comprehensive information about chemical sensors and biosensors for antibiotic detection. We classify the currently reported antibiotic detection technologies into chromatography, mass spectrometry, capillary electrophoresis, optical detection, and electrochemistry, introduce some representative examples for each technology, and conclude the advantages and limitations. In particular, the optical and electrochemical methods based on nanomaterials are discussed and evaluated in detail. In addition, the latest research in the detection of antibiotics by photosensitive materials is discussed. Finally, we summarize the pros and cons of various antibiotic detection methods and present a discussion and outlook on the expansion of cross-scientific areas. The synthesis and application of optoelectronic nanomaterials and aptamer screening are discussed and prospected, and the future trends and potential impact of biosensors in antibiotic detection are outlined.Graphical abstract.

A SERS aptasensor based on AuNPs functionalized PDMS film for selective and sensitive detection of Staphylococcus aureus

In this study, a sensitive biosensor was developed based on aptamer functionalized polydimethylsiloxane (PDMS) film for the detection of Staphylococcus aureus (S. aureus) using surface-enhanced Raman scattering (SERS) technology. Initially, the surface of PDMS film was chemically modified by piranha solution and 3-Aminopropyltriethoxysilane (APTES), and then AuNPs-PDMS film was prepared by coating gold nanoparticles (AuNPs) through electrostatic interaction. Next, the aptamers were immobilized on the AuNPs-PDMS membrane via gold-sulfur bond to form the capture substrate. Meanwhile, gold-silver core-shell nanoflowers (Au@Ag NFs) modified with mercaptobenzoic acid (4-MBA) and aptamers were applied as a signal probe. In the presence of the target, the signal molecular probe and the capturing substrate specifically combined with the target and resulted in a sandwich structure "capture substrate-target-signal molecular probe". Under the optimized experimental condition, the signal of 4-MBA at 1085 cm^-1 was linearly related to the S. aureus concentration in the range of 4.3 × 10 cfu mL^-1-4.3 × 10⁷ cfu mL^-1 (y = 326.91x-117.62, R² = 0.9932) with a detection limit of 13 cfu mL^-1. The method was successfully applied to spiked actual samples and a 92.5-110% recovery rate was achieved.

Signal optimized rough silver nanoparticle for rapid SERS sensing of pesticide residues in tea

Trace detection of toxic chemicals in foodstuffs is of great concern in recent years. Surface-enhanced Raman scattering (SERS) has drawn significant attention in the monitoring of food safety due to its high sensitivity. This study synthesized signal optimized flower-like silver nanoparticle-(AgNP) with EF at 25 °C of 1.39 × 10⁶ to extend the SERS application for pesticide sensing in foodstuffs. The synthesized AgNP was deployed as SERS based sensing platform to detect methomyl, acetamiprid-(AC) and 2,4-dichlorophenoxyacetic acid-(2,4-D) residue levels in green tea via solid-phase extraction. A linear correlation was twigged between the SERS signal and the concentration for methomyl, AC and 2,4-D with regression coefficient of 0.9974, 0.9956 and 0.9982 and limit of detection of 5.58 × 10^-4, 1.88 × 10^-4 and 4.72 × 10^-3 µg/mL, respectively; the RSD value < 5% was recorded for accuracy and precision analysis suggesting that proposed method could be deployed for the monitoring of methomyl, AC and 2,4-D residue levels in green tea.

SERS-based rapid detection of 2,4-dichlorophenoxyacetic acid in food matrices using molecularly imprinted magnetic polymers

In order to remove the limitations of natural antibodies or enzymes, a nano-magnetic biomimetic platform based on a surface-enhanced Raman scattering (SERS) sensor has been developed for highly sensitive capture and detection of 2,4-dichlorophenoxyacetic acid (2,4-D) in food and water samples. Magnetic-based molecular imprinted polymer nanoparticles (Mag@MIP NPs) were constructed to capture the target 2,4-D molecule via biomimetic recognition, and gold nanoparticles (Au NPs) served as SERS-based probes, which are bound to the Mag@MIP NPs by electrostatic adsorption. The as-prepared SERS-MIP sensor for sensing of 2,4-D achieved a good linear relationship with a low detection limit (LOD) of 0.00147 ng/mL within 2 h and exhibited high sensitivity. The sensor was successfully applied to detect 2,4-D in milk and tap water and achieved good recoveries ranging from 93.5 to 102.2%. Moreover, the designed sensor system exhibited satisfactory results (p > 0.05) compared to HPLC by validation analysis. Hence, the findings demonstrated that the proposed method has significant potential for practical application in food safety and environmental protection. Graphical abstract .