Graphene-like BN@SiO2 nanocomposites as efficient sorbents for solid-phase extraction of Rhodamine B and Rhodamine 6G from food samples

Rhodamine and related substances in food: Recent updates on pretreatment and analysis methods

Rhodamine, a colorant prohibited in various consumer products due to its demonstrated carcinogenic, mutagenic, and toxic properties, necessitates the development of a straightforward, efficient, sensitive, environmentally friendly, and cost-effective analytical method. This review provides an overview of recent advancements in the pretreatment and determination techniques for rhodamine across diverse sample matrices since 2017. Sample preparation methods encompass both commonly used pretreatment techniques such as filtration, centrifugation, solvent extraction, and cloud point extraction, as well as innovative approaches including solid phase extraction, dispersive liquid-liquid microextraction, hollow fiber liquid phase microextraction, magnetic solid phase extraction, and matrix solid phase dispersion. The analytical techniques encompass high performance liquid chromatography, surface-enhanced Raman scattering, and sensor-based methods. Furthermore, a comprehensive examination is conducted to offer insights for future research on rhodamine regarding the advantages, disadvantages, and advancements in various pretreatment and determination methodologies.

An update on the sample preparation and analytical methods for synthetic food colorants in food products

Colorants, especially synthetic colorants, play a crucial role in enhancing the aesthetic qualities of food owing to their cost-effectiveness and stability against environmental factors. Ensuring the safe and regulated use of colorants is essential for maintaining consumer trust in food safety. Various preparation and analytical technologies, which are continuously undergoing improvement, are currently used to quantify of synthetic colorants in food products. This paper reviews recent developments in analytical techniques for synthetic food colorants, detection and compares the operational principles, advantages, and disadvantages of each technology. Additionally, it also explores advancements in these technologies, discussing several invaluable tools of analysis, such as high-performance liquid chromatography, liquid chromatography-tandem mass spectrometry, electrochemical sensors, digital image analysis, near-infrared spectroscopy, and surface-enhanced Raman spectroscopy. This comprehensive overview aims to provide valuable insights into current progress and research in the field of food colorant analysis.

Ultrastable NAC-Capped CdZnTe Quantum Dots Encapsulated within Dendritic Mesoporous Silica As an Exceptional Tag for Anti-Interference Fluorescence Aptasensor with Signal Amplification

In this work, we explored the potential of thiol-capped CdZnTe quantum dots (QDs) as an exceptional signal tag for fluorescence aptasensing applications. Employing a one-pot hydrothermal approach, we modulated the terminal functional groups of CdZnTe QDs using l-cysteine (Lcys), 3-mercaptopropionic acid (MPA), and N-acetyl-l-cysteine (NAC) as ligands. Our comparative analysis revealed that NAC-capped CdZnTe QDs (NAC-CdZnTe QDs) exhibited superior anti-interference capabilities and storage stability across various temperatures, pH levels, and storage durations. Encouraged by these promising results, we further optimized the use of ultrastable NAC-CdZnTe QDs encapsulated in dendritic mesoporous silica nanoparticles (DMSN@QDs) as an exceptional tag for the development of an advanced anti-interference fluorescence aptasensor for aflatoxin B1 (AFB1) detection. The developed aptasensor using DMSN@QDs as signal tags achieved a remarkable signal amplification of approximately 10.2 fold compared to the NAC-CdZnTe QDs coated silica (SiO2@QDs) labeled fluorescence aptasensor. This aptasensor was able to detect AFB1 within a wide range of 1 pg mL-1 to 200 ng mL-1, achieving a limit of detection as low as 0.41 pg mL-1 (S/N = 3). Crucially, the specific binding affinity between the aptamer and the target enabled the aptasensor to be easily customized for various targets by simply replacing the aptamer sequence with the desired one. The exceptional potential of NAC-CdZnTe QDs, particularly when encapsulated in DMSNs, leads to the development of highly sensitive and selective anti-interference fluorescence aptasensors for various targets, thereby, paving the way for advancements in a diverse range of applications.

Screening method for the analysis of Rhodamine B in chili powder

Rhodamine B is a synthetic dye known to enhance the visual appearance of chili powder. Due to its toxicity and carcinogenicity, chromatographic methods have been developed to monitor its presence in adulterated chili powder, but their assays are laborious, time consuming and expensive for screening purposes. The present studies propose an alternative for screening Rhodamine B in chili powder samples. The method combines thin layer chromatography (TLC) to solid surface room-temperature fluorescence spectroscopy. The scrape-dissolution procedure common to the instrumental analysis of TLC procedures was replaced with a fiber optic probe coupled to a commercial spectrofluorometer. The determination of Rhodamine B on the chromatographic plate is based on its retardation factor and maximum excitation and emission wavelengths. The limit of detection (1.9 ng.mL-1) and the limit of quantitation (5.2 ng.mL-1) are well below the usual contamination of Rhodamine B in adulterated foods.

Surface-enhanced Raman scattering using flower-like Ag/ZnO as active substrates for the label-free and sensitive detection of rhodamine 6G and melamine

The reliable and accurate detection of unauthorized additives in food is significant to prevent health risks. In recent years, surface-enhanced Raman spectroscopy (SERS) with fast, simple, and sensitive capabilities has been widely used for food safety analysis. In order to detect illegally added dye molecule rhodamine 6G and small molecule melamine in food, we have proposed a fast, convenient, and label-free SERS detection technology using flower-like Ag/ZnO as the SERS substrate. The structure and morphology of the flower-like Ag/ZnO were characterized by scanning electron microscopy, energy dispersive spectrometery, transmission electron microscopy, and X-ray diffraction analysis. We investigated the SERS effect and sensitivity of flower-like Ag/ZnO toward rhodamine 6G and melamine. The synergistic effect of flower-like Ag/ZnO provides high SERS activity for the detection of rhodamine 6G and melamine at the lowest detection concentrations of 0.5 ng mL-1 and 1.0 ng mL-1, respectively. Therefore, flower-like Ag/ZnO with good sensitivity and uniformity has potential for improving the detection of illegal food additives.

Metal-organic framework functionalized with deep eutectic solvent for solid-phase extraction of Rhodamine 6G in water and cosmetic products

An NH2 -MIL-53(Al)-DES(ChCl-Urea) nanocomposite was synthesized for extraction and determination of Rhodamine (Rh) 6G from environmental and cosmetic samples. The deep eutectic solvent (DES) was prepared by mixing choline chloride and urea in a mole ratio of 1:2. NH2 -MIL-53(Al)-DES(ChCl-Urea) nanocomposite was synthesized using the impregnation method at a ratio of 60:40 (w/w). The optimum conditions were determined after NH2 -MIL-53(Al)-DES(ChCl-Urea) characterization was performed. The optimum conditions were determined as pH 8, adsorbent amount of 15 mg, total adsorption-desorption time of 6 min, and enrichment factor of 20. The recovery values of the solid-phase extraction method for water and cosmetic samples under optimum conditions were between 95% and 106%. NH2 -MIL-53(Al)-DES(ChCl-Urea) nanocomposite was an economically advantageous adsorbent because of its reusability of 15 times. All analyses were performed using the ultraviolet-visible spectrophotometer. The linear range, limit of detection, and limit of quantification of the method were 100-1000, 9.80, and 32.68 μg/L, respectively. The obtained results showed that the synthesized nanocomposite is a suitable adsorbent for the determination of Rh 6G in water and cosmetic samples. The real sample applications were verified with the high-performance liquid chromatography system.

Nanoscale Materials Applying for the Detection of Mycotoxins in Foods

Trace amounts of mycotoxins in food matrices have caused a very serious problem of food safety and have attracted widespread attention. Developing accurate, sensitive, rapid mycotoxin detection and control strategies adapted to the complex matrices of food is crucial for in safeguarding public health. With the continuous development of nanotechnology and materials science, various nanoscale materials have been developed for the purification of complex food matrices or for providing response signals to achieve the accurate and rapid detection of various mycotoxins in food products. This article reviews and summarizes recent research (from 2018 to 2023) on new strategies and methods for the accurate or rapid detection of mold toxins in food samples using nanoscale materials. It places particular emphasis on outlining the characteristics of various nanoscale or nanostructural materials and their roles in the process of detecting mycotoxins. The aim of this paper is to promote the in-depth research and application of various nanoscale or structured materials and to provide guidance and reference for the development of strategies for the detection and control of mycotoxin contamination in complex matrices of food.

Molecularly imprinted 3D SERS sensor with inorganic frameworks for specific and recyclable SERS sensing application

Poor selectivity and reusability of Au/Ag nanostructures are the main challenges for surface-enhanced Raman spectroscopy (SERS) in real sample detection. Herein, a novel specific and reusable three-dimensional (3D) SERS sensor with dual functions of selective trapping and photocatalytic degradation was designed. Firstly, Au-Ag bimetallic nanoparticles decorated silicon nanowires array (SiNWs-AuAg) were prepared as 3D SERS substrate. Then, silicon-based inorganic-framework molecularly imprinted TiO₂ (TiO₂@SiMIP) was synthesized and immobilized on SiNWs-AuAg by using rhodamine 6G (R6G) as template molecule. Owing to the excellent SERS performance of SiNWs-AuAg and the specific affinity of TiO₂@SiMIP to template molecule, the prepared SERS sensor enables sensitive and selective detection of R6G in food samples with a limit of detection (LOD) of 0.27 nM. In addition, due to the photocatalysis of TiO₂ and the stability of silicon-based inorganic framework, the residual templates in TiO₂@SiMIP can be completely removed by UV irradiation, and the imprinted cavity of regenerated sensors still maintained good selectivity after regeneration by UV irradiation.

Adsorption and Removal of Antibiotic Pollutants using CuO-Co3 O4 Co-modified Porous Boron Nitride Fibers in Aqueous Solution

The presence of antibiotic contaminants in aqueous environment already poses significant risks to ecological sustainability, biodiversity and human public health and safety. Therefore, it is urgent to develop practical water pollution control technologies and new materials. Here, we prepared CuO-Co₃ O₄ co-modified porous boron nitride fibers (P-BNFs) for the adsorption and removal of tetracycline antibiotics (TCs) in aqueous environment. The prepared adsorbents were characterized by XRD, FTIR, XPS, SEM, TEM and BET, and the adsorption behavior was explored by batch experiments. The results show that the removal percentage for doxycycline (DC) reaches 98.68 %, which was much higher than that of P-BNFs, and the modification results of P-BNFs with CuO or Co₃ O₄ alone. After five regeneration cycles, the removal rate of DC by CuO-Co₃ O₄ /P-BNFs was still as high as 89.33 %. This is promising and indicates that the prepared CuO-Co₃ O₄ /P-BNFs adsorbent has good renewable recycling performance and practical application prospects.

Arrays of Ag-nanoparticles decorated TiO2 nanotubes as reusable three-dimensional surface-enhanced Raman scattering substrates for molecule detection

Three-dimensional surface-enhanced Raman scattering (SERS) substrates usually provide more hot spots in the excitation light beam and higher sensitivity when compared with the two-dimensional counterpart. Here a simple approach is presented for the fabrication of arrays of Ag-nanoparticles decorated TiO2 nanotubes. Arrays of ZnO nanorods were fabricated in advance by a hydrothermal method. Then TiO2 nanotube arrays were achieved by immersing the arrays of ZnO nanorods in an aqueous solution of (NH4)2TiF6 for 1.5 h. Vertically aligned TiO2 nanotube arrays were modified with dense Ag nanoparticles by Ag mirror reaction. High density of Ag nanoparticles decorated on the fabricated TiO2 nanotubes provide plenty of hotspots for Raman enhancement. In addition, the fabricated array of Ag nanoparticles modified TiO2 nanotubes can serve as a reusable SERS substrate because of the photocatalytic activity of the TiO2 nanotubes. The SERS substrate adsorbed with analyte molecules can realize self-cleaning in deionized water after UV irradiation for 2.5 h. The sensitivity of the fabricated SERS substrate was investigated by the detection of organic dye molecules. The detectable concentration limits of rhodamine 6G (R6G), malachite green (MG) and methylene blue (MB) were found to be 10−12 M, 10−9 M and 10−8 M, respectively. The enhancement factor (EF) of the three-dimensional SERS substrate was estimated to be as high as ∼1.4×108. Therefore, the prepared Ag nanoparticles modified TiO2 nanotube arrays have promising potentials to be applied to rapid and trace SERS detection of organic chemicals.

Urea-linked covalent organic framework functionalized polytetrafluoroethylene film for selective and rapid thin film microextraction of rhodamine B

Incorporation of highly selective and stable adsorbent with facile extraction technology is desired in practical analysis. Here we show the rational preparation of a urea-linked covalent organic framework functionalized polytetrafluoroethylene film (COF-117-PTFE) with ordered porous structure, rich functional groups, and large surface area-to-volume ratio as the effective adsorbent for convenient, selective and rapid thin film microextraction (TFME) of rhodamine B (RB). The COF-117-PTFE based TFME coupled with high performance liquid chromatography-fluorescence detector (HPLC-FLD) successfully realized the determination of RB with the limit of detection of 0.007 μg L^-1, the linear range of 0.1 - 100 μg L^-1. The relative standard deviation (RSD) of intraday (n = 5) and interday (n = 5) for the determination of 10 μg L^-1 RB were 2.3% and 6.8%, respectively. The absolute recoveries were 80.3%, 71.2% and 67.9% in river water, chili powder and Sichuan pepper powder, respectively. The recoveries for RB spiking in complicated real samples (dry chili, chili powder, dry Sichuan pepper, Sichuan pepper powder and river water) ranged from 90.4% to 107.5%. The developed COF-117-PTFE based TFME-HPLC-FLD method is promising in practical application. This work reveals the high potential of functionalized COF film as the adsorbent for effective extraction of trace contaminants in complicated samples.

Surface-Enhanced Raman Spectroscopy Substrates for Food Safety and Quality Analysis

Surface-enhanced Raman spectroscopy (SERS) has been identified as a fundamental surface-sensitive technique that boosts Raman scattering by adsorbing target molecules on specific surfaces. The application of SERS highly relies on the development of smart SERS substrates, and thus the fabrication of SERS substrates has been constantly improved. Herein, we investigate the impacts of different substrates on SERS technology including plasmonic metal nanoparticles, semiconductors, and hybrid systems in quantitative food safety and quality analysis. We first discuss the fundamentals, substrate designs, and applications of SERS. We then provide a critical review of the recent progress of SERS in its usage for screening and detecting chemical and biological contaminants including fungicides, herbicides, insecticides, hazardous colorants, and biohazards in food samples to assess the analytical capabilities of this technology. Finally, we investigate the future trends and provide practical techniques that could be used to fulfill the requirements for rapid analysis of food at a low cost.

Cu-Doped Boron Nitride Nanosheets for Solid-Phase Extraction and Determination of Rhodamine B in Foods Matrix

Cu-doped boron nitride nanosheets (Cu-BNNS) were first reported as promising adsorbents for the solid-phase extraction and determination of rhodamine B (RhB) dye in a food matrix. Different characterizations, including XRD, FTIR, XPS, SEM, and TEM, were performed to confirm the formation of the adsorbent. Then, the adsorption performance of Cu-BNNS was investigated by adsorption kinetics, isotherms, and thermodynamics. Multiple extraction parameters were optimized by single-factor experiments. Under optimized conditions, the recoveries in the food matrix were in the range of 89.8–95.4%, with the spiked levels of 100 ng/mL and 500 ng/mL, respectively. This novel system was expected to have great potential to detect RhB in a wide variety of real samples.

Application of ZnS/S/S-RGO three-component nanocomposites in dispersive solid-phase microextraction coupled with ion mobility spectrometry for ultra-trace determination of multiclass pesticides

A fast, effective, and sensitive dispersive solid-phase microextraction method coupled with ion mobility spectrometry for the simultaneous determination of bendiocarb, butachlor, and diazinon was developed using zinc sulfide/sulfur/sulfur-doped reduced graphene oxide (ZnS/S/S-RGO) nanocomposites. ZnS/S/S-RGO three-component nanocomposites were synthesized through a single-step solvothermal procedure, and their properties were characterized by FT-IR, XRD, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and energy-dispersive x-ray spectroscopy (EDX). The influence of different parameters was optimized on the efficiency of the extraction including the type and the volume of desorption solvent, pH, type and the volume of buffer, the amount of absorbent, sorption and  desorption times. Under the optimal conditions, linear ranges were achieved 0.8-110, 1.0-110, and 0.5-100 ng mL^-1 with detection limits of 0.32±0.01, 0.40±0.02, and 0.27±0.02 ng mL^-1 for bendiocarb, butachlor, and diazinon, respectively. The method was employed for the ultra-trace determination of the three pesticides in water, rice, and soil samples with acceptable recovery values within the range 96.6±4.8-104.4±6.4%.

Facile preparation of core-shell magnetic organic covalent framework via self-polymerization of two-in-one strategy as a magnetic solid-phase extraction adsorbent for determination of Rhodamine B in food samples

The monomer of two-in-one molecular design strategy (i.e., A₂B₂ type monomer) 1,6-bis(4-formylphenyl)-3,8-bis((4-aminophenyl) ethynyl)) pyrene (BFBAEPy) was self-polymerized and coated on the modified Fe₃O₄ surface to synthesize a magnetic covalent organic framework (Fe₃O₄@COF) nanocomposite with a core-shell structure. Before high-performance liquid chromatography with ultraviolet detection (HPLC-UV) determination, Fe₃O₄@COF was used as a magnetic solid-phase extraction (MSPE) adsorbent to enrich Rhodamine B (RhB) illegally added to Chili powder and Chinese prickly ash. It had a large specific surface area and suitable pore size, which promoted the efficient adsorption of RhB dye and eliminated the interference of the matrix. Several key parameters affecting the extraction recovery rate were investigated, including adsorption capacity, adsorption time, pH, ionic strength, elution solvent, elution volume and elution time. Under the best optimized conditions, within the linear detection range of 0.05-5 µg/mL for RhB with the limit of detection (LOD) was 0.0038 µg/mL, excellent linearity (correlation coefficient R²=0.9997), and good repeatability (relative standard deviations RSD%< 3.8%), satisfactory extraction recovery rate (91.7%-97.5%). Therefore, the application of the established method to the detection of RhB in food samples has bright prospects.

A novel analytical strategy for the determination of perfluoroalkyl acids in various food matrices using a home-made functionalized fluorine interaction SPME in combination with LC-MS/MS

In this study, a fluorine-fluorine interaction approach through fluoridating boron nitride nanosheets (BNNs) for sensing perfluoroalkyl acids (PFAAs) in multiple food matrices was developed. Through a facile hydrothermal fluorination modification, the BNNs were transferred into homogeneous fluorinated boron nitride nanoparticles (F-BNNs) with robust networks and specific surface area. After morphological modification, the particles displayed strong adsorption and sensing capabilities on PFAAs in both solid and liquid food matrix. Under the evaluation of mass spectrometry, F-BNNs based microextraction approach exhibited low method detection limits (MDLs) in the ranges of 0.9-3.9 pg mL^-1 and 3.6-15.8 pg g^-1 for milk and meat matrices, respectively, with satisfactory repeatability (RSD% <13.5%) and recoveries (77.7-110.5%). This work not only depicted a facile approach for preparing F-BNNs based SPME fiber, but also provided a routine analysis protocol for monitoring PFAAs in food systems.

Development and perspectives of rapid detection technology in food and environment

Food safety become a hot issue currently with globalization of food trade and food supply chains. Chemical pollution, microbial contamination and adulteration in food have attracted more attention worldwide. Contamination with antibiotics, estrogens and heavy metals in water environment and soil environment have also turn into an enormous threat to food safety. Traditional small-scale, long-term detection technologies have been unable to meet the current needs. In the monitoring process, rapid, convenient, accurate analysis and detection technologies have become the future development trend. We critically synthesizing the current knowledge of various rapid detection technology, and briefly touched upon the problem which still exist in research process. The review showed that the application of novel materials promotes the development of rapid detection technology, high-throughput and portability would be popular study directions in the future. Of course, the ultimate aim of the research is how to industrialization these technologies and apply to the market.

Synthesis and characterization of γ-MnO2/chitosan/Fe3O4 cross-linked with EDTA and the study of its efficiency for the elimination of zinc(II) and lead(II) from wastewater

In this research, a novel γ-MnO₂/chitosan/Fe₃O₄ nanocomposite was synthesized and modified by ethylenediaminetetraacetic acid (EDTA) for the separation and simultaneous elimination of Zn(II) and Pb(II) ions from aqueous solutions in a batch system. The magnetic nanocomposite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and elemental analysis (EDAX). The results demonstrated that the magnetic nanocomposite was successfully synthesized and cross-linked. The predominant influential experimental parameters including pH, contact time, initial concentration, and temperature were analyzed in relation to the adsorption capacity. The experimental data were well converged with the double exponential kinetic model. Also, the results were well matched with the Langmuir isotherm, where the maximum adsorption values were 310.4 and 136 mg g^-1 for Pb(II) and Zn(II), respectively. On the other hand, in the binary-component system, the Langmuir-Freundlich model dominated the experimental data. The thermodynamic results (ΔG° < 0, ΔH° > 0, and ΔS° > 0) within the temperature range of 25-40 °C showed that the nature of adsorption by the nanocomposite for both ions was spontaneous and endothermic and was favored at higher temperatures. The simultaneous removal of two ions, the excellent magnetic separation, and the high efficiency in reuse (five effective recovery cycles) indicated the high capability of the EDTA-modified γ-MnO₂/chitosan/Fe₃O₄ nanocomposite in the treatment of industrial effluents from Pb(II) and Zn(II).

Boron nitride-based materials for water purification: Progress and outlook

Analogous to the carbon family, boron nitride (BN)-based materials have gained considerable attention in recent times for applications in various fields. Owing to their extraordinary characteristics, i.e., high surface area, low density, superior thermal stability, mechanical strength, and conductivity, excellent corrosion, and oxidation resistance, the BN nanomaterials have been explored in water remediation. This article critically evaluates the latest development in applications of BN-based materials in water purification with focus on adsorption, synthesis of novel membranes and photocatalytic degradation of pollutants. The adsorption of various noxious pollutants, i.e., dyes, organic compounds, antibiotics, and heavy metals from aqueous medium BN-based materials are described in detail by illustrating the adsorption mechanism and regeneration potential. The major hurdles and opportunities related to the synthesis and water purification applications of BN-based materials are underscored. Finally, a roadmap is suggested for future research to assure the effective applications of BN-based materials in water purification. This review is beneficial in understanding the current status of these unique materials in water purification and accelerating the research focusing their future water remediation applications.

Hierarchical porous boron nitride with boron vacancies for improved adsorption performance to antibiotics

Designing atomically defective adsorbents with high specific surface area has emerged as a promising approach to improve sorption properties. Herein, hierarchical porous boron nitride nanosheets with boron vacancies (Bv-BNNSs) were in-situ synthesized via a one-step ZnCl₂-assisted strategy. Being benefitted from the dual-functional template of zinc salt, highly-active boron vacancies and abundant hierarchical pores were simultaneously generated in the Bv-BNNSs framework. By employing the boron vacancies engineering strategy, the morphological and electronic structures were controllably tuned. Meanwhile, the specific surface area was improved to as high as 1104 m²/g. Owning to the abundance of accessible surface active-sites, the sorption capacity to antibiotic tetracycline (TC) on Bv-BNNSs was boosted by 38% compared to the pristine boron nitride nanosheets (BNNSs). Detailed fitting results showed that TC sorption on Bv-BNNSs obeyed the pseudo-second order kinetic equation and the Freundlich isotherm model. The pi - pi interaction with a multi-layered stacking form was proposed as the dominated sorption mechanism. Furthermore, DFT calculations verified that the interaction energy between Bv-BNNSs and TC was enhanced. The high activity, excellent selectivity, and remarkable durability of the Bv-BNNSs nanomaterial suggest the great potential in practical wastewater treatment.