Showed Detection Limits Research Articles

Thermal analysis and FT-IR spectroscopy of synthetic clay mineral mixtures

Common clays and especially mixed-layered or interstratified clay minerals are generally mixtures of predominantly clay mineral along with minor quantity of another clay mineral, wherein the ratio of the components will determine the resulting properties of these clay materials. This study focuses on IR spectroscopy and TG/DTA analysis and their contribution to the identification of clay minerals in two-component mixtures. Identifying clay minerals in such mixtures by means of thermal analysis is often complicated by the similarity of the thermal effects of the individual clay components. Similarity in thermal behavior is mainly connected with the origin, chemical variability and crystal structure of phyllosilicates. The main problem is overlapping thermal effects of clay minerals or thermal effects related to accessory minerals (calcite, quartz, etc.) on DTA curve. A similar problem also appears in the identification of mixed clay mineral structures by infrared spectroscopy. There are also more or less overlapping absorption bands in the infrared spectra for the mixtures of clay minerals. In this paper, the prepared clay mixtures were supposed to partially simulate the natural mixed clay structures and a minimum content of detectable minerals in clay mixtures were determined according to characteristic peaks on the DTA curves and absorption bands in FT-IR spectra. The results of both methods showed that kaolinite is the most reliable detectable mineral. The detection limit for thermal analysis corresponds to 3% mass kaolinite in admixture with chlorite or montmorillonite, and 1% mass kaolinite for both of these mixtures is based on IR spectroscopy. In case of montmorillonite and chlorite, the identification by FT-IR spectroscopy shows detection limit only 30% mass in contrast to TG/DTA with the detection limit of 5% mass for montmorillonite and 5% mass or 10% mass for chlorite. The obtained results can be effectively used to solve problems in identification of clay minerals in sedimentary rocks, which is very important for subsequent applications in geotechnical, geothermal, and mining activities.

Inkjet-printed electrochemically reduced graphene oxide microelectrode as a platform for HT-2 mycotoxin immunoenzymatic biosensing

The design and application of an inkjet-printed electrochemically reduced graphene oxide microelectrode for HT-2 mycotoxin immunoenzymatic biosensing is reported. A water-based graphene oxide ink was first formulated and single-drop line working microelectrodes were inkjet-printed onto poly(ethylene 2,6-naphthalate) substrates, with dimensions of 78 μm in width and 30 nm in height after solvent evaporation. The printed graphene oxide microelectrodes were electrochemically reduced and characterized by Raman and X-ray photoelectron spectroscopies in addition to microscopies. Through optimization of the electrochemical reduction parameters, differential pulse voltammetry were performed to examine the sensing of 1-naphthol (1-N), where it was revealed that reduction times had significant effects on electrode performance. The developed microelectrodes were then used as an immunoenzymatic biosensor for the detection of HT-2 mycotoxin based on carbodiimide linking of the microelectrode surface and HT-2 toxin antigen binding fragment of antibody (anti-HT2 (10) Fab). The HT-2 toxin and anti-HT2 (10) Fab reaction was reported by anti-HT2 immune complex single-chain variable fragment of antibody fused with alkaline phosphatase (anti-IC-HT2 scFv-ALP) which is able to produce an electroactive reporter – 1-N. The biosensor showed detection limit of 1.6 ng ∙ mL−1 and a linear dynamic range of 6.3 – 100.0 ng ∙ mL−1 within a 5 min incubation with 1-naphthyl phosphate (1-NP) substrate.

Electrochemical Detection of C-Reactive Protein in Human Serum Based on Self-Assembled Monolayer-Modified Interdigitated Wave-Shaped Electrode.

An electrochemical capacitance immunosensor based on an interdigitated wave-shaped micro electrode array (IDWµE) for direct and label-free detection of C-reactive protein (CRP) was reported. A self-assembled monolayer (SAM) of dithiobis (succinimidyl propionate) (DTSP) was used to modify the electrode array for antibody immobilization. The SAM functionalized electrode array was characterized morphologically by atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDX). The nature of gold-sulfur interactions on SAM-treated electrode array was probed by X-ray photoelectron spectroscopy (XPS). The covalent linking of anti-CRP-antibodies onto the SAM modified electrode array was characterized morphologically through AFM, and electrochemically through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The application of phosphate-buffered saline (PBS) and human serum (HS) samples containing different concentrations of CRP in the electrode array caused changes in the electrode interfacial capacitance upon CRP binding. CRP concentrations in PBS and HS were determined quantitatively by measuring the change in capacitance (ΔC) through EIS. The electrode immobilized with anti-CRP-antibodies showed an increase in ΔC with the addition of CRP concentrations over a range of 0.01–10,000 ng mL−1. The electrode showed detection limits of 0.025 ng mL−1 and 0.23 ng mL−1 (S/N = 3) in PBS and HS, respectively. The biosensor showed a good reproducibility (relative standard deviation (RSD), 1.70%), repeatability (RSD, 1.95%), and adequate selectivity in presence of interferents towards CRP detection. The sensor also exhibited a significant storage stability of 2 weeks at 4 °C in 1× PBS.

Biosynthesized Quantum Dot for Facile and Ultrasensitive Electrochemical and Electrochemiluminescence Immunoassay.

Nanomaterials are commonly utilized for amplified immunoassay of biomarkers. However, traditional nanomaterial-based immunoassay usually requires a time-consuming and labor-intensive nanoparticle modification and conjugation process, which impedes their practical applications. Here, a new immunoassay method based on biosynthesized nanomaterials is developed with versatile functions for facile and ultrasensitive detection of cancer biomarker. In this method, the utilized biosynthesized quantum dots (BQDs) allow convenient antibody conjugation and electrode modification, and demonstrate excellent electrochemical and electrochemiluminescent responses. The differential pulse voltammetric, faradaic impedance spectroscopy, and electrochemiluminescent measurements with the BQD-modified electrode show detection limits at picomolar levels as well as good specificity toward human prostate-specific antigen detection. The inherent recognization capability as well as the inherent electrochemical and electrochemiluminescence features thus enable BQDs as good candidates for facile immunosensors with high sensitivity. Such a biosynthesized nanomaterial-based approach opens up the possibility of using innovative designs for nanoparticle-based assays, and developing reliable and practical methods for early disease diagnosis.

Multi-targeted Screening of Phytoestrogens in Food, Raw Material, and Dietary Supplements by Liquid Chromatography with Tandem Mass Spectrometry

This work was carried out to develop a high-performance liquid chromatography tandem mass spectrometry method for simultaneous determination of 11 marker compounds in phytoestrogen-rich food and dietary supplements (raw materials and formulated products) prepared from various sources: soy, red clover, chastetree, hop, and flax. The method was fully validated and showed detection limits varying from 0.2 to 1.5 μg/mL, average recoveries ranging from 95 to 105%, and relative standard deviation values lower than 4.98%. Evidently lower amounts of phytoestrogens were found in food samples than in the dietary supplements. Calculations for the actual daily dose of total phytoestrogens ranged from 0.01 to 6.61 mg among the different products. All derived total phytoestrogen amounts turned out to be below the total content stated by manufacturers (less than 63% of the claimed specifications). Moreover, two samples did not contained phytoestrogens at all. The most eye-catching batch-to-batch deviations were represented by chasteberry-based products (relative standard deviation higher than 9.8%).

Two instantaneous fluorogenic steps for detection of nanomolar amyloid beta monomer and its interaction with stoichiometric copper(II) ion

A small molecule SEA-SC2 exhibited fluorescence in response to 10–60 nM amyloid beta (Aβ)40 and Aβ42 monomers at pH 7.4, in the presence of gold nanoparticle (AuNP). Here we report the fluorogenic detection due to the response from low nanomolar level of Aβ peptide monomer. The small organic molecule or AuNP has been reported to show detection limit up to 200 nM Aβ peptide. Furthermore, fluorescence enhancement studies with different stoichiometries of Aβ:Cu(II) confirmed the initial Aβ:Cu(II) adduct at the nanomolar level. This methodology has been applied to the detection of nanomolar concentrations of Aβ monomer in artificial cerebrospinal fluid and human serum albumin.

Screening 89 Pesticides in Fishery Drugs by Ultrahigh Performance Liquid Chromatography Tandem Quadrupole-Orbitrap Mass Spectrometer.

Multiclass screening of drugs with high resolution mass spectrometry is of great interest due to its high time-efficiency and excellent accuracy. A high-scale, fast screening method for pesticides in fishery drugs was established based on ultrahigh performance liquid chromatography tandem quadrupole-Orbitrap high-resolution mass spectrometer. The target compounds - were diluted in methanol and extracted by ultrasonic treatment, and the extracts were diluted with MeOH-water (1:1, v/v) and centrifuged to remove impurities. The chromatographic separation was performed on an Accucore aQ-MS column (100 mm × 2.1 mm, 2.6 μm) with gradient elution using 0.1% formic acid in water (containing 5 mmol/L ammonium formate) and 0.1% formic acid in methanol (containing 5 mmol/L ammonium formate) in Full Scan/dd-MS2 (TopN) scan mode. A screening database, including mass spectrometric and chromatographic information, was established for identification of compounds. The screening detection limits of methods ranged between 1–500 mg/kg, the recoveries of real samples spiked with the concentration of 10 mg/kg and 100 mg/kg standard mixture ranged from 70% to 110% for more than sixty compounds, and the relative standard deviations (RSDs) were less than 20%. The application of this method showed that target pesticides were screened out in 10 samples out of 21 practical samples, in which the banned pesticide chlorpyrifos were detected in 3 out of the 10 samples.

Label-free electrochemical impedimetric immunosensor for sensitive detection of IgM rheumatoid factor in human serum

The authors report a label-free and direct detection of rheumatoid factor- Immunoglobulin M (IgM-RF) based on an impedimetric-interdigitated wave type microelectrode array (IDWμE). IDWμE was functionalized with a self-assembled monolayer (SAM) of thioctic acid for antigen immobilization. The SAM functionalized IDWμE were characterized by atomic force microscopy, Energy Dispersive X-Ray Spectroscopy, and X-ray photoelectron spectroscopy. The covalent immobilization of IgG-Fc onto the SAM modified electrode arrays was characterized morphologically via AFM and electrochemically via cyclic voltammetry and electrochemical impedance spectroscopy. Impedimetric measurements in the presence of redox probe (Potassium ferrocyanide and potassium ferricyanide) showed a significant change in both the impedance spectrum and charge transfer resistance upon IgM-RF binding. Impedance measurements were target specific and linear with an increase in IgM-RF concentrations between 1 and 200 IU mL−1 in redox probe and human serum, respectively. The sensor showed detection limits of 0.6 IU mL−1 in the presence of redox probe and 0.22 IU mL−1 in the human serum. The biosensor exhibited good reproducibility (relative standard deviation (RSD), 4.96%) and repeatability (RSD, 2.31%) with an acceptable selectivity towards IgM-RF detection. The sensor also showed a good stability for 3 weeks at 4 °C in 1X PBS. Therefore, the sensitive and stable immunosensor exhibiting IDWμE features can be integrated with a miniaturized potentiostat to develop a sensing system that detects IgM-RF for point-of-care applications.

Vertically aligned multi-walled carbon nanotubes based flexible immunosensor for extreme low level detection of multidrug resistant leukemia cells

We report an advanced flexible immunosensor for extreme low level detection of multidrug resistant myeloid leukemia cells. The detection mechanism is analyzed in terms of novel nanoscale interactions of target molecules with vertically aligned multi-walled carbon nanotubes (VA-MWNT). The immunosensor is fabricated by transferring VA-MWNTs on a polyethylene terephthalate substrate by hot press technique without losing CNTs’ pristine character. Sensing is performed using doxorubicin treated leukemia K562 cells in varying concentrations from 1.5 × 102 cells mL–1 to 1.5 × 107 cells mL–1 and sensor showed detection limit of 10 cells mL–1. The calibration plot of peak current versus logarithmic concentration of DOX/leukemia K562 cells exhibited good linearity with a regression coefficient of ˜0.98. Sensing mechanism is explained in terms of charge transfer induced Fermi level shift of sub μeV order, causing band bending at the interface of CNT-molecular species; and it is reflected in lowering detection limit of the fabricated sensor. Theoretical analysis is done to correlate Fermi energy shift with sensitivity of the device on cancer cell immobilization. Additionally, the developed immunosensor shows good stability, reproducibility and fast detection vis-à-vis the devices reported so far. The notable advantages of proposed flexible sensor are its durability, chemical and moisture resistance, making it a potentially competitive device for point-of-care diagnostics.

Synthesis, characterization, and supramolecular architectures of two distinct classes of probes for the visualization of endogenously generated hypochlorite ions in response to cellular activity

Two distinct classes of compounds, (E)-2-(((3-amino-4-nitrophenyl) imino) methyl)-5-(diethylamino) phenol (SB) and 5-(diethylamino)-2-(5-nitro-1H-benzo[d]imidazol-2-yl) phenol (IM) were synthesized. SB, a bright red colored compound was crystallized in acetonitrile as a triclinic crystal system while IM, yellow colored compound crystallized as a monoclinic crystal system in dimethylformamide by vapor diffusion of diethylether. These compounds were characterized using spectroscopic techniques (IR, UV–visible, 1H, and 13C NMR), and X-ray crystallography. SB and IM displayed classical and non-classical H-bonding involving C-H…O and π…π interactions. These compounds detected hypochlorite ions in aqueous DMSO (1: 9, v/v, HEPES buffer, pH 7.4), and detection was visible via color changes by naked eye. We also performed UV–visible and fluorescence titrations, showing detection limits of 8.82 × 10−7 M for SB and 2.44 × 10−7 M for IM. The fluorometric responses from SB and IM were also studied against different ROS and anions. DFT calculations were performed to strengthen the proposed sensing mechanisms of both SB and IM. Hypochlorite, which is endogenously generated by myeloperoxidase in endosomes, was specifically visualized using SB and IM in lipopolysaccharide-treated RAW264.7 cells. These probes were also used to image the generation of hypochlorite by RAW264.7 cells during phagocytosis of non-fluorescent polystyrene beads.

Qualitative screening and quantitative determination of 569 pesticide residues in honeysuckle using ultrahigh-performance liquid chromatography coupled to quadrupole-Orbitrap high resolution mass spectrometry

A method for both qualitative screening and quantitative determination of 569 pesticides in honeysuckle was developed based on ultrahigh-performance liquid chromatography (UHPLC) coupled to quadrupole-Orbitrap high resolution mass spectrometry and an in-house executable compound database involving the theoretical masses of precursor and fragment ions and retention times. Different workflows were evaluated, validated and compared including Full MS-SIM, Full MS/ddMS2, Full MS/AIF and Full MS/DIA. For qualitative analysis, Full MS/DIA showed relatively low screening detection limits (SDLs) for most pesticides, but its MS2 identification seemed to be not reliable enough. Full MS/ddMS2 showed good repeatability of fragment ion recognition and less false positives. For quantitative analysis, the results of four workflows were comparable in terms of linearity and trueness, while Full MS-SIM and Full MS/ddMS2 gave better precision than the other two workflows for most pesticides at the spiking level of 0.01 mg/kg. Therefore, UHPLC-Full MS/ddMS2 was considered as the optimal workflow for both qualitative and quantitative analysis of honeysuckle samples. Pesticides were present in 75 of the 82 investigated samples, with concentrations ranging from 10.0 to 4116.9 μg/kg in some of the most severely contaminated samples.

Triggerable H2O2-Cleavable Switch of Paper-Based Biochips Endows Precision of Chemometer/Ratiometric Electrochemical Quantification of Analyte in High-Efficiency Point-of-Care Testing.

In this work, a triggerable H2O2-cleavable fluid switch mediated paper-based biochip, being amenable to multiplexing and quantitative analysis with the dual-response output of visual screening and ratiometric electrochemistry, was developed for sensitive detection of target on-site. By properly implanting hydrophobic Ag-H2O2 responsive material in specific zone to form a programmable fluid switch, the biochip could achieve different modes of blocking/connecting switching automatically. In order to improve the test performance, a ratiometric electrochemical signal readout was designed, which was enhanced by a secondary in situ growth method fabricating trepang-shaped Au modified paper working electrode. In virtue of hybridization chain reaction, classic competitive recognition interactions of aptamer and target, and ratiometric internally calibrated mechanisms, ultrasensitive detection of the target was realized. To acquire a more quantitative and straightforward naked eye visual screening, the hydrophobic Ag switch was triggered by stimulating instructions from H2O2, thus reconnecting the electrochemical and ratiometric units automatically and resulting in a "signal on" visual fluidic flow on the chemometer characterized by the accurate distance of color development as a detection motif. With MCF-7 and K562 cells as models, wider linear detection ranges from 150 to 1.0 × 107 and 220 to 7.0 × 106 cells mL-1 for MCF-7 and K562 cells, respectively, were achieved. Meanwhile, thanks to the paper fluid chemometer, an acceptable screening detection limit of 103 cells mL-1 was obtained in the quantitative colorimetric assays. The proposed paper-based biochips opened up new horizons for designing of integratable, easy-to-use, and precise point-of-care testing devices.

Ultra-high-performance liquid chromatography coupled to quadrupole orbitrap high-resolution mass spectrometry for multi-residue screening of pesticides, (veterinary) drugs and mycotoxins in edible insects

A generic extraction and UHPLC-Q-Orbitrap™-HRMS method was developed for four insect species (mealworm, grasshopper, house cricket and black soldier fly) analyzing a large spectrum of organic chemical contaminants, including pesticides (n = 25), (veterinary) drugs (n = 29), and mycotoxins (n = 23). To prove the method as ‘fit-for-purpose’, a successful validation was performed, both qualitatively, by determining the screening detection limit (SDL), selectivity and specificity, as well as semi-quantitatively, by assessing the within-day precision (relative standard deviation (RSD)) and recovery. For both the mealworm, grasshopper, house cricket and black soldier fly, 64, 61, 59 and 62 compounds were detected at the respective SDL levels (1–100 μg kg−1), predominantly below existing maximum residue limits for other edible matrices. Mean recoveries ranged between 70% and 120% and RSD-values were in line with European regulations (CD 2002/657/EC; SANCO). Finally, the potential of the screening methodology was demonstrated on real insect samples, revealing minor to no contamination.

Synthesis and spectral analysis of fluorescent probes for Ce4+ and OCl- ions based on fluorescein Schiff base with amino or hydrazine structure: Application in actual water samples and biological imaging.

Two Schiff base fluorescein probes (FDA, FDH) based on fluorescein-aldehyde and nitroaniline derivatives were synthesized. The effects of amino and hydrazine substituents in fluorescein backbones were examined via fluorescence and absorbance spectra. In the presence of Ce4+, the fluorescence of FDA was quenched due to the ligand to metal charge transfer (LMCT). Hypochloric acid can react with the CN bond, and blocking the photo induced electron transfer (PET) of FDH leads to enhancement of the fluorescence. FDA showed detection limits for Ce4+ and OCl- as low as 63 nM in concentration range of 0-4 μM. FDH showed detection limits for OCl- as low as 0.8 μM in concentration rang 0-100 μM. Polyvinylidene fluoride (PVDF) membrane containing the probes was prepared for the real-time qualitative detection of Ce4+ and OCl- in real water samples. The probes were successfully applied to biological imaging in vascular smooth muscle cells (VSMCs) and are expected to find applications in biosensing.

Determination of pesticides and Pharmaceuticals from Fish Cultivation Water by parallel solid-phase extraction (SPE) and liquid chromatography–quadrupole time-of-flight mass spectrometry (LC-QTOF-MS)

A screening method for multiple classes of pesticides and pharmaceuticals from fish cultivation water was established using liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (LC-QTOF-MS). Parallel solid-phase extraction (SPE) with different adsorbents was selected for extracting and purifying analytes with different properties. This method allowed for efficient and economical screening of a virtually unlimited number of compounds without reference standards. In order to evaluate the feasibility of this method, 25 pesticides and pharmaceuticals with different properties were selected. The screening detection limit of this method was 0.015 µg L−1, which was lower than the maximum residue limits. This value showed that the method was suitable for screening organic contaminants in fish cultivation water. In a simulation experiment, the organic contaminants with high intensity (atrazine and carbendazim) were identified by retention time, accurate mass, isotopic pattern, and the main fragment ions. Moreover, the information about the organic contaminants and MS2 spectra was added into a database. Since the QTOF-MS data were traceable, they were saved and could be reexamined for compounds that previously were unexpected. This method provides insight into the screening and identification of organic contaminants in water samples, as well as risk assessment and fishery accident identification.

Rapid screening and identification of 52 pesticide residues in flavored tea by improved QuEChERS combined with liquid chromatography-quadrupole-time-of-flight mass spectrometry

An improved method to screen 52 pesticide residues in flavored tea using QuEChERS coupled with liquid chromatography-quadrupole-time-of-flight mass spectrometry (LC-Q-TOF-MS) has been investigated. The flavored tea was extracted with acetonitrile and purified using by primary secondary amine (PSA), graphitized carbon black (GCB) and C18 sorbent. The resultant residues were then analyzed using LC-Q-TOF-MS. The recoveries of all the pesticides in flavored tea at the four spiked levels of 10, 20, 50 and 100 μg/kg were 70%-120% and the relative standard deviations (RSDs, n=3) were less than 20%. The calibration curves of the 52 pesticide residues had good linear relationships, and the correlation coefficients were more than 0. 99. The screening detection limits (SDLs) and the limits of quantitation (LOQs) for the 52 pesticides were in the range of 0.001-0.01 mg/kg and 0.002-0.02 mg/kg, respectively, which were lower than maximum residue limits standard permitted by the European Union (EU). This method is simple, rapid, reliable, and can meet the requirements for the simultaneous determination of 52 pesticide residues in flavored tea.

Point-of-care assay to detect foodborne pathogenic bacteria using a low-cost disposable medical infusion extension line as readout and MnO2 nanoflowers

The extended application of low cost disposable infusion extension lines, used primarily in the medical field, is limited. In this study, a facile signal readout method was developed for point-of-care (POC) detection of foodborne pathogenic bacteria using disposable medical infusion extension lines. Herein, organic-inorganic hybrid nanoflowers loaded with sufficient MnO2 have been easily prepared. The MnO2 nanoflowers with pathogenic bacteria recognition function decomposed hydrogen peroxide (H2O2) into oxygen (O2), an amplified gas signal, which was measured by a disposable medical infusion extension line. The generation of O2 from H2O2 by the catalytic dissociation of MnO2 nanoflowers increased the pressure in a confined space. Dye was then pushed along the channel of the disposable medical infusion extension line, connected to a sealed glass vial via a needle. The distance moved by the dye, which was detectable by the naked eye, was proportional to the concentration of foodborne pathogenic bacteria. Experimental results showed detection limits as low as 101 CFU/mL for Salmonella sp. and Escherichia coli O157:H7. The biosensor method based on a low-cost disposable medical infusion extension line gas signal readout was a powerful tool for POC testing of foodborne pathogenic bacteria under resource-limited settings.

Large-scale individual thyroid monitoring following nuclear accidents by means of non-spectrometric devices

In order to properly respond to an emergency caused by an accident in a nuclear power plant with a spread of radionuclides in the atmosphere, we propose a field procedure to perform a large-scale individual thyroid monitoring of internal contamination due to inhalation of 131I, by means of non-spectrometric equipment, in particular dose rate meters. Specific attention is paid to the individual monitoring of children, because of the very high radiosensitivity of the child’s thyroid to the carcinogenic effects of ionising radiation. The device performance was evaluated by measuring mock iodine sources provided in the Child and Adult Thyroid Monitoring After Reactor Accident (CAThyMARA) intercomparison and, just for a scintillator dose rate meter, by means of 60 s acquisitions of healthy volunteers’ thyroids. All the devices showed a remarkable accuracy in quantification of equivalent 131I activity in the thyroids of persons of all ages. The selected scintillator dose rate meter showed detection limit values resulting in a maximum committed equivalent dose to thyroid HT, assuming an acute 131I inhalation occurred five days before the measurement, equal to 10 mSv (related to five-year-old children). Considering the level of HT values associated with the calculated detection limit activities, the proposed procedure has a significant sensitivity to be used for fast internally thyroid monitoring in nuclear or radiological emergencies, allowing daily monitoring a large amount of individuals.

Determination of phenolic acid profiles by HPLC-MS in vegetables commonly consumed in China.

This study aimed to establish a precise HPLC-MS approach to determine the concentrations and distribution of major phenolic acids in six categories of vegetables that are commonly consumed in China. We detected 17 phenolic acids within 15 min under optimized conditions. The method showed detection limits varying from 0.008 mg/L to 0.042 mg/L, average recoveries ranging from 71.0% to 110.7%, and a RSD of ≤9.98%. The average concentrations of total phenolic acids followed the order of flower > root > leafy > stem > bean > fruit vegetables. The phenolic acids were more abundant in the leafy, root, and stem vegetables than in the other vegetable samples. Furthermore, the levels of isoferulic acid, p-coumaric acid, and ferulic acid were greater than those of other phenolic acids in the vegetables. Free soluble phenolic acids were the dominant species in all vegetables (P < 0.001), except in the stem vegetables (P < 0.027).

Chemical-staining based lateral flow immunoassay: A nanomaterials-free and ultra-simple tool for a small molecule detection

The nanomaterials based lateral flow immunoassays (LFIAs) have been widely used for on-site detection of small molecules contaminants. Nevertheless, their practical applications are often constrained by the complicated materials synthesis and surface modification process of nanomaterials. Herein, inspired by chemical-staining, a crystal violet (CV) staining based LFIAs was innovatively developed for the first time to analyze small molecules contaminant with significantly simplified behaviour and surpassing repeatability. This nanomaterials-free technique overcomes the intrinsic limitations of nanomaterials, owing to the superior protein dye property of CV. To demonstrate the feasibility of the unique strategy, furazolidone (FZD) was used as a model analyte, results showed detection limits of as low as 7 and 1.53 ng mL−1 by visual observation and quantitative analysis, respectively. Finally, to validate its applicability in actual conditions, the platform is well applied in three kinds of food samples (shrimp, fish and pork). Furthermore, as the detection principle is based on the molecular recognition between antigen and antibody, our method may find general applications by staining other antibodies against other target analytes.