Validation of analytical method for furan determination in eight food matrices and its levels in various foods

In this study, an automated solid‐phase microextraction coupled with gas chromatography and mass spectrometry method was developed and validated for the determination of furan in eight matrices including ham, milk, apple juice, rice porridge, peanut butter, flatfish, tuna (canned) and seaweed. The calibration curves were highly linear (r² > 0.990) and the limit of detection and limit of quantification ranged from 0.01?0.02 and 0.04?0.06 ng/g, respectively. The recovery ranged from 77.81?111.47%. The validated method was used to analyse the furan levels in 120 foods. The highest levels of furan were detected in black tea (172.05 ng/g) and red ginseng extract (89.27 ng/g). Whelk (canned) contained a high furan content (21.34 ng/g) among the seafood samples.     

Separation and detection of multiple pathogens in a food matrix by magnetic SERS nanoprobes

A rapid and sensitive method was developed here for separation and detection of multiple pathogens in food matrix by magnetic surface-enhanced Raman scattering (SERS) nanoprobes. Silica-coated magnetic probes (MNPs@SiO₂) of ∼100 nm in diameter were first prepared via the reverse microemulsion method using cetyltrimethylammonium bromide as a surfactant and tetraethyl orthosilicate as the silica precursor. The as-prepared MNPs@SiO₂ were functionalized with specific pathogen antibodies to first capture threat agents directly from a food matrix followed by detection using an optical approach enabled by SERS. In this scheme, pathogens were first immuno-magnetically captured with MNPs@SiO₂, and pathogen-specific SERS probes (gold nanoparticles integrated with a Raman reporter) were functionalized with corresponding antibodies to allow the formation of a sandwich assay to complete the sensor module for the detection of multiple pathogens in selected food matrices, just changing the kinds of Raman reporters on SERS probes. Here, up to two key pathogens, Salmonella enterica serovar Typhimurium and Staphylococcus aureus, were selected as a model to illustrate the probability of this scheme for multiple pathogens detection. The lowest cell concentration detected in spinach solution was 10³ CFU/mL. A blind test conducted in peanut butter validated the limit of detection as 10³ CFU/mL with high specificity, demonstrating the potential of this approach in complex matrices.     

Covalent imprinted polymer for selective and rapid enrichment of ractopamine by a noncovalent approach

A novel molecularly imprinted polymer (MIP) for the separation and concentration of ractopamine (RAC) was prepared by a covalent imprinting approach and the template was removed successfully by hydrolysis, so that four carboxylic acid groups were left in the cavities and could specifically rebind RAC through noncovalent interaction: hydrogen bonding. The conditions for synthesis of the MIP were optimized during the polymerization process, and a molar ratio of template–functional monomer complexes to cross-linker of 1:3 was confirmed. The adsorption capacity of the MIP was 4.1-fold that of the nonimprinted polymer, and the adsorption reaction reached equilibrium after 25 min at 50 mg L^-1 concentration. The results of the competitive adsorption test showed that the MIPs had specific recognition ability for the analyte RAC. In addition, the important factors affecting the efficiency of the method which was developed using the MIPs as a solid-phase sorbent for separation and determination of RAC combined with high-performance liquid chromatography with fluorescence detection were optimized. Under the optimum experimental conditions, the linear range of the calibration curve in the method was 0.05-5 μg L^-1 (R ² = 0.98) and the limit of detection (signal-to-noise ratio of 3) was 0.01 μg L^-1. The proposed method was applied to determination of RAC in spiked feedstuffs and urine samples, with recoveries ranging from 74.17 to 114.46% and relative standard deviation (n = 3) below 4.55 in all cases.     

3D aluminum/silver hierarchical nanostructure with large areas of dense hot spots for surface‐enhanced raman scattering

Plasmonic nanomaterials possessing large‐volume, high‐density hot spots with high field enhancement are highly desirable for ultrasensitive surface‐enhanced Raman scattering (SERS) sensing. However, many as‐prepared plasmonic nanomaterials are limited in available dense hot spots and in sample size, which greatly hinder their wide applications in SERS devices. Here, we develop a two‐step physical deposition protocol and successfully fabricate 3D hierarchical nanostructures with highly dense hot spots across a large scale (6 × 6 cm²). The nanopatterned aluminum film was first prepared by thermal evaporation process, which can provide 3D quasi‐periodic cloud‐like nanostructure arrays suitable for noble metal deposition; then a large number of silver nanoparticles with controllable shape and size were decorated onto the alumina layer surfaces by laser molecular beam epitaxy, which can realize large‐area accessible dense hot spots. The optimized 3D‐structured SERS substrate exhibits high‐quality detection performance with excellent reproducibility (13.1 and 17.1%), whose LOD of rhodamine 6G molecules was 10^?9 M. Furthermore, the as‐prepared 3D aluminum/silver SERS substrate was applied in detection of melamine with the concentration down to 10^?7 M and direct detection of melamine in infant formula solution with the concentration as low 10 mg/L. Such method to realize large‐area hierarchical nanostructures can greatly simplify the fabrication procedure for 3D SERS platforms, and should be of technological significance in mass production of SERS‐based sensors.     

Enzyme Free Electrochemiluminescence Sensor of Histamine Based on Graphite-carbon Nitride Nanosheets

The determination of histamine as one of the most important seafood poisoning compounds is essential nowadays. This paper reports a simple novel ECL sensor with g−C₃N₄ nanosheets (NSs) as an effective signal probe for the measurement of histamine without using any enzymatic reactions or complicated modifications. The ECL response of the sensor was linearly proportional to the concentration of histamine ranging from 1.0×10⁻⁷ to 7.5×10⁻⁴ mol/L, with a detection limit of 4.30×10⁻⁸ mol/L (R²=0.98401). The relative standard deviation (RSD) in repeatability and reproducibility tests were calculated to be 4.7 % and 3.6 % respectively. The presented sensor was successfully applied to the determination of histamine in canned tuna fish samples where it gave recoveries that ranged from 99.72 % to 101.96 % indicating that the method presented here is sensitive with high precision and is expected to have significant potential applications in clinical and the freshness quality of seafood.     

Electrochemical sensor for parabens based on molecular imprinting polymers with dual-templates

A selective, sensitive, rapid and reliable method based on molecularly imprinted polymers (MIPs) with dual templates to determine total content of parabens in cosmetics was developed. With methylparaben (MP) and propylparaben (PP) as dual-templates, methacrylic acid (MAA) as a functional monomer and tripropylene glycol diacrylate (TPGDA) as a cross-linker, MIPs film on a glassy carbon electrode was constructed as paraben sensor. At oxidation potential of 0.94 V (vs. SCE), the peak currents on the MIPs sensor were proportional to the concentration of parabens with square wave voltammetry. As the ratio of MP to PP in the MIPs was 1:1.25, the regression equations for four parabens were almost the same. The linear range was 20-100 μM for MP and EP, 5-100 μM for PP, and 5-80 μM for BP, with detection limit of 0.4 μM for MP and EP, 0.2 μM for the others. The total content of parabens could be calculated according to the average of these four regress equations. At least 10 times of structural analogs, such as p-hydroxybenzoic acid, p-aminobenzoic acid and phenol would not interfere with the determination of parabens. Nonanalogous coexistences such as vitamin C had no response on the sensor at all. Rapid response of the MIPs sensor was obtained within 1 min. MIPs sensor had been used to determine total content of parabens in cosmetic samples with recoveries between 98.7% and 101.8%. It reveals that the MIPs sensor with multi-templates has a potential to determine the total content of a group of homologous compounds.     

Molecularly imprinted polymer nanocarriers for recognition and sustained release of diclofenac

In this study, a series of imprinted poly(methacrylic acid‐co‐ethylene glycol dimethacrylate) nanocarriers for diclofenac and corresponding nonimprinted polymer nanocarriers have been synthesized in 4 different types of solvents by precipitation polymerization. The products were characterized by Fourier transform infrared, scanning electron microscopy, dynamic light scattering, and Brunauer‐Emmett‐Teller measurement. Results showed that uniformly sized molecularly imprinted polymer (MIP) nanospheres with relatively good porosity could only be obtained in acetonitrile. The effects of solvents on the recognition and release properties of polymer particles were also carefully investigated. The binding experiments indicated that MIPs prepared in acetonitrile displayed much higher binding capacity than other MIPs with a maximum binding capacity of 65.18 mg g⁻¹. The Scatchard analysis showed that synthetic MIPs have special recognition sites for diclofenac, while nonimprinted polymers have not. The Sips model could provide a best fit to the equilibrium data of nanocarriers over whole concentrations. The experimental data of an adsorption kinetic study were well fitted to the pseudo–second‐order kinetic model, indicating the chemisorption mechanism between diclofenac and MIPs in the process of adsorption. The drug release of diclofenac from MIPs could well be described by the Ritger‐Peppas model, suggesting a non‐Fickian diffusion mechanism. In addition, we successfully used MIPs to extract diclofenac at low levels from fetal bovine serum.     

Provision of proficiency testing for histamine mass fraction in canned tuna to improve the capability of chemical laboratories in the Philippines

Accreditation and Quality Assurance - In this work, two reference materials (RMs) for mass fraction of histamine in canned tuna were developed to address the need of local testing laboratories for...     

Thin-layer chromatographic screening methods for histamine in tuna fish

Twelve solvent systems were tested for their ability to separate histamine and histidine on a variety of thin-layer coatings. The best solvent-adsorbent systems were: chloroform-methanol-ammonia (2:2:1), methanol-ammonia (20:1), acetone-ammonia (95:5), and double development with (a) n-butanol-acetone-water (2:2:1) and (b) chloroform-methanol-ammonia (12:7:1), all on silica-gel layers. Ninhydrin was used as the visualization reagent. These four systems were then evaluated for their potential use as rapid screening procedures in the detection of possibly deleterious levels of histamine in tuna fish. Successful separation of histamine from the other ninhydrin-positive components of methanolic tuna fish extracts was achieved with all four systems. A sample from a lot of tuna implicated in human illness was found to have a histamine level considerably higher than tuna purchased from a local retail outlet or an extract spiked to a histamine level considered to be a threshold value for toxicity symptoms. The methanol-ammonia (20:1) and chloroform-methanol-ammonia (2:2:1) systems, used with silica-gel plates, are the most promising for rapid preliminary screening of tuna fish extracts for histamine.     

Novel fabrication of silver-coated glass capillaries for ready SERS-based detection of dissolved chemical species

A novel method to deposit a highly surface-enhanced Raman scattering (SERS) active silver film onto the inside surface of a glass capillary is developed. Firstly, Ag sol was synthesized by the reaction of AgNO₃ with poly-(ethylenimine) (PEI), and then toluene and benzenethiol (BT) were added into the sol. The mixture was flowed through the glass capillary to obtain the SERS-active Ag film-coated glass capillary. The SERS activity of the Ag-coated capillary was dependent on the amount of PEI and BT used. In addition, BT could be easily desorbed from the Ag surface by treating it with a borohydride solution, maintaining the initial SERS activity. The SERS enhancement factor at 632.8-nm excitation was estimated to be on the order of 10⁶. The detection limits of adenine and dipicolinic acid were then as low as 1.0 × 10⁻⁸ and 1.0 × 10⁻⁷ M, respectively, based on an S/N ratio of 3. This clearly suggests that the Ag-coated capillary is an invaluable device for the analysis of effluent chemicals by SERS.     

Solid‐phase microextraction based on an agarose‐chitosan‐multiwalled carbon nanotube composite film combined with HPLC–UV for the determination of nonsteroidal anti‐inflammatory drugs in aqueous samples

We describe the preparation, characterization, and application of a composite film adsorbent based on blended agarose‐chitosan‐multiwalled carbon nanotubes for the preconcentration of selected nonsteroidal anti‐inflammatory drugs in aqueous samples before determination by high performance liquid chromatography with ultraviolet detection. The composite film showed a high surface area (4.0258 m²/g) and strong hydrogen bonding between the multiwalled carbon nanotubes and agarose/chitosan matrix, which prevent adsorbent deactivation and ensure long‐term stability. Several parameters, such as sample pH, addition of salt, extraction time, desorption solvent, and concentration of multiwalled carbon nanotubes in the composite film were optimized using a one‐factor‐at‐time approach. The optimum extraction conditions obtained were as follows: isopropanol as conditioning solvent, 10 mL of sample solution at pH 2, extraction time of 30 min, stirring speed of 600 rpm, 100 μL of isopropanol as desorption solvent, desorption time of 5 min under ultrasonication, and 0.4% w/v of composite film. Under the optimized conditions, the calibration curve showed good linearity in the range of 1–500 ng/mL (r² = 0.997–0.999), and good limits of detection (0.89–8.05 ng/mL) were obtained with good relative standard deviations of < 4.59% (n = 3) for the determination of naproxen, diclofenac sodium salt, and mefenamic acid drugs.     

Enhanced Raman spectroscopy coupled to chemometrics for identification and quantification of acetylcholinesterase inhibitors

In this work, we present a new complete method using Surface Enhanced Raman Spectroscopy (SERS) and chemometrics for the qualitative and quantitative detection of pesticides by measuring the acetylcholinesterase (ACHE) activity. The Raman SERS is not only used for measuring the ACHE activity, but also for the direct detection of pesticides individually and for their identification. Gold nanoparticles (AuNPs) were used as dynamic SERS substrates for sensitive monitoring of ACHE activity in the presence of very low levels of organophosphate and carbamate pesticides, chemical warfare agents that are known to be ACHE inhibitors. The lowest detectable level for paraoxon was determined at 4.0 × 10⁻¹⁴ M and 1.9 × 10⁻⁹ M for carbaryl. The use of the enzyme allowed limits of detection for both pesticides that were much lower than the limits obtained by direct SERS analysis of the pesticides. The system shows a linear relationship between the intensity band at 639 cm⁻¹ and pesticide concentration. These results suggest that this biosensor could be used in the future for the non-selective detection of all ACHE inhibitors at very low concentrations with possible identification of the inhibitor.     

Determination of putrescine and cadaverine in seafood (finfish and shellfish) by liquid chromatography using pyrene excimer fluorescence

A liquid chromatography (LC) method is described for the easy determination of the biogenic diamines putrescine (PUT) and cadaverine (CAD) in canned tuna, frozen tuna loin, fresh mahimahi fillet, frozen raw shrimp, cooked lump crabmeat, and fresh and cold-smoked salmon. The method is also a useful screen for histamine (HTA). The method involves homogenization of fish tissue, extraction of biogenic amines into borate-trichloroacetic acid solution, centrifugation, and derivatization of supernatant with 1-pyrenebutanoic acid succinimidyl ester. The derivatized diamine species allow for the intramolecular excimer fluorescence of the pyrene moiety at a higher emission wavelength than is possible for the endogenous tissue monoamines, thus providing visual specificity of detection. All seafood species were fortified with 0.5, 1.0, 5.0, 10.0, and 15.0 microg/g (ppm) of PUT and CAD. Determination was based on standard graphs for PUT and CAD using peak areas with standard solutions equivalent to 0.375, 1.0, 5.0, 10.0, and 20.0 ppm in tissue. A set of five matrix controls (unfortified seafood tissue) were also analyzed; endogenous PUT was found in all samples except the canned tuna, and CAD found only in the shrimp, crab, and cold-smoked salmon. The background amines were thus subtracted prior to determining spike recovery. The intra-assay average recoveries ranged from 71 to 94% across species and spike levels.     

Examination of performance of glassy carbon paste electrode modified with gold nanoparticle and xanthine oxidase for xanthine and hypoxanthine detection

A composite electrode was prepared by modifying glassy carbon microparticles with gold nanoparticles (Au-nps) and xanthine oxidase enzyme (XOD) for xanthine (X) and hypoxanthine (Hx) detection. After the optimization of the system for X, the biosensor was characterized for X and Hx. A linearity was obtained in the concentration range between 5.00 × 10⁻⁷ and 1.00 × 10⁻⁵ M for X with equation of y = 0.24x + 0.712 and 5.00 × 10⁻⁶ to 1.50 × 10⁻⁴ M for Hx, with equation of y = 0.014x + 0.575, respectively. Obtained results were compared to X and/or Hx biosensors including/not including Au-np in the structure. The developed system was also applied for detection of Hx in canned tuna fish sample and very promising results were obtained.     

Surface-Enhanced Raman Spectroscopy (SERS) for characterization SARS-CoV-2

We used SERS with silver nanoparticles (AgNPs) as the active substrate to develop a, simple, quick, and accurate method for the detection and characterization SARS-CoV-2 without the need for RNA isolation and purification. Inactivated SARS-CoV-2 was used. The SERS signals were more than 10⁵ times enhanced than the normal Raman (NR) spectra. The SERS spectra of SARS-CoV-2 fingerprint revealed pronounced intensity signals of nucleic acids; aromatic amino acid side chains: 1007 cm^?1 (Phe marker), 1095 cm^?1 (CN and PO₂^? markers), 1580 cm^?1 (Tyr, Trp markers). Vibrations of the protein main chain: 1144 cm^?1 (CN and NH₂ markers), 1221 cm^?1 (CN and NH markers), 1270 cm^?1 (NH₂ marker), 1453 cm^?1 (CHCH₂ marker). All of these biomolecules could be adsorbed on the AgNPs surface's dense hot patches. The intensity of the SERS band varied with the concentration of SARS-CoV-2, with a virus detection limit of less than 10³ vp/mL and RSDs of 20 %.     

茶叶浸出液中农药残留表面拉曼光谱检测与初步定量分析

选取甲基对硫磷和水胺硫磷为研究对象,改良了传统的QuEChERS前处理工艺,以自制纳米金溶胶为增强基底,利用表面增强拉曼光谱(SERS)技术,对茶叶浸出液中的农药残留进行检测。通过比对两种有机磷农药的拉曼特征峰进行定性分析。同时,选取570,1034,1107和1202 cm^-1等拉曼位移附近的特征峰光谱数据,利用微分等数学手段,结合偏最小二乘法(PLSR)建立回归方程,预测样品中农药残留含量。所得预测数值与气相色谱-质谱联用(GC-MS)法检测值对比,验证本方法的可行性与可信度。结果表明:基于SERS技术对上述两种有机磷农药的检出限可达0.05 mg/L;通过数学模型分析建立回归方程,其线性相关系数范围为0.9077~0.9824,预测均方根误差(RMSEP)范围为0.77%~2.68%;利用回归方程得到的预测值与GC-MS检测结果基本接近,相对误差范围-5.16%~9.03%,回收率为81.4%~115.1%,说明可以用SERS技术对茶叶浸出液中的有机磷农药残留进行定性和初步定量分析。     

In situ laser-induced photochemical silver substrate synthesis and sequential SERS detection in a flow cell

A new, simple, and effective approach for multianalyte sequential surface-enhanced Raman scattering (SERS) detection in a flow cell is reported. The silver substrate was prepared in situ by laser-induced photochemical synthesis. By focusing the laser on the 320 μm inner diameter glass capillary at 0.5 ml/min continuous flow of 1 mM silver nitrate and 10 mM sodium citrate mixture, a SERS active silver spot on the inner wall of the glass capillary was prepared in a few seconds. The test analytes, dacarbazine, 4-(2-pyridylazo)resorcinol (PAR) complex with Cu(II), and amoxicillin, were sequentially injected into the flow cell. Each analyte was adsorbed to the silver surface, enabling the recording of high intensity SERS spectra even at 2 s integration times, followed by desorption from the silver surface and being washed away from the capillary. Before and after each analyte passed the detection window, citrate background spectra were recorded, and thus, no “memory effects” perturbed the SERS detection. A good reproducibility of the SERS spectra obtained under flow conditions was observed. The laser-induced photochemically synthesized silver substrate enables high Raman enhancement, is characterized by fast preparation with a high success rate, and represents a valuable alternative for silver colloids as SERS substrate in flow approaches.     

Effectively designed molecularly imprinted polymers for selective isolation of the antidiabetic drug metformin and its transformation product guanylurea from aqueous media

In the present study, two novel molecularly imprinted polymers (MIPs) with remarkable recognition properties for metformin and its transformation product, guanylurea, have been prepared for their selective, enrichment, isolation and removal from aqueous media. The prepared adsorbents were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and swelling experiments. The performance of the prepared MIPs was evaluated by various parameters including the influence of pH, contact time, temperature and initial compound concentration. The effects on the adsorption behavior of the removal process parameters were studied and the equilibrium data were fitted by the Langmuir and Freundlich models. Due to the imprinting effect, adsorption performance of MIPs was always superior to its corresponding NIP (non-imprinted polymer), with maximum adsorption capacity ∼80 mg g⁻¹ for both MIPs. Stability and reusability of the MIPs up to the 5th cycle meant that they could be applied repeatedly without losing substantial removal ability. In the next step, the prepared MIP nanoparticles were evaluated as sorbents in a dispersive solid phase extraction (D-SPE) configuration for selective enrichment and determination of metformin and guanylurea in different aqueous matrices. Under the working extraction conditions, the D-SPE method showed good linearity in the range of 50–1000 ng L⁻¹, repeatability of the extractions (RSD 2.1–5.1%, n = 3), and low limits of detection (1.5–3.4 ng L⁻¹). The expanded uncertainty of the data obtained was estimated following a bottom-up approach. The proposed method combined the advantages of MIPs and D-SPE, and it could become an alternative tool for analyzing the residues of METF and its transformation product GUA in complex water matrices, such as wastewaters.     

Physicochemical parameter influences and their optimization on the biosynthesis of MnO2 nanoparticles using Vernonia amygdalina leaf extract

The manganese dioxide nanoparticles (MnO₂ NPs) were synthesized using Vernonia amygdalina leaf extract which was used as a reducing, capping, and stabilizing agents due to the presence of bioactive phytochemical compounds. Twenty five runs were designed to investigate the effect of V. amygdalina leaf extract ratio (A), initial potassium permanganate (KMnO₄) concentration (B), pH (C), and reaction time (D) on the biosynthesized MnO₂ NPs using 4-factor, 4-level D-Optimal Response Surface Quadratic Design Model approach. The relationship between physicochemical variables and absorption responses were established using transform second degree polynomial quadratic model. The effects of each absorption responses were analyzed by ANOVA principle using quadratic equations. A very low p-values (<0.0001), non-significant Lack of Fit F-values, and reasonable regression coefficient values (coefficient R² = 0.9790, adjusted R² = 0.9496, and predicted R² = 0.8452) suggested that there is an effective correlation between experimental results and predicted values. Numerical and graphical optimized results demonstrated that the optimized conditions for the predicted absorbance at 320 nm (1.095) were suggested at 43.72%, 1.81 mM, 6.02, and 103.42 min for V. amygdalina leaf extract ratio, initial KMnO₄ concentration, pH, and reaction time, respectively. Under these optimal conditions, the average absorbance from four experimental run was recorded to be 0.9678. This result was very closest to the predicted values. The average size elucidated by X-ray diffraction (XRD) analysis was found in the range between 20 nm and 22 nm. The stretching/or and vibrational, surface topography, thermal, and surface roughness as well as its porosity distributions were investigated by UV–Vis spectroscopy, Fourier transforms infrared (FTIR), scanning electron microscopy (SEM), differential scanning calorimeter (DSC), and Gwyddion software analysis.