Broad-spectrum portable magnetic relaxation switching immunosensor with gold-functionalized magnetic nanoprobes for the sensitive detection of multiple pyrethroids

Broad-spectrum detection of benzimidazoles with lateral flow immunoassay: A computational chemistry-assisted hapten design strategy and explore of molecular recognition mechanism

Benzimidazoles (BMZs) are a class of veterinary drugs with a benzimidazole ring, the abuse of which poses a serious threat to ecological balance and human health. Consequently, the development of broad-spectrum antibodies and rapid assays are crucial for detecting BMZs in food samples. Herein, we scientifically designed three hapten structures, predicted the availability of the hapten with computational chemistry, and subsequently verified the broad-spectrum with immunological experiments. A broad-spectrum monoclonal antibody (6F10) was prepared based on the predicted hapten-2. Molecular recognition studies illustrated intricate interactions between mAb 6F10 binding to BMZs attributed to halogen bonds and π-π/π-alkyl interactions, revealing key amino acid sites and demonstrating the reliability of the hapten prediction strategies. Finally, a broad-spectrum, rapid, and sensitive lateral flow immunoassay based on aggregation-induced emission microspheres with high fluorescence intensity was established. The LOD values of the proposed method for eight kinds of BMZs were 0.027, 0.032, 0.058, 0.091, 0.087, 0.246, 0.369, and 0.311 ng mL-1, respectively. In this work, a hapten prediction strategy based on a computational chemistry method effectively guided the preparation of antibodies for broad-spectrum recognition of BMZs, and the molecular recognition studies verified the interaction of mAb 6F10 with BMZs, enabling broad-spectrum and sensitive detection of BMZs in milk.

High Stability Hydrogel Magnetic Relaxation Switch Sensor Driven by pH for the Sensitive Detection of Cd2

The traditional magnetic relaxation switching (MRS) sensors have excellent sensitivity, but their stability is poor because the magnetic relaxation signal is easily affected by the external magnetic field or environmental oxidation. In this study, a highly stable hydrogel bead-based MRS (Gel-MRS) sensor was established for the accurate and sensitive detection of Cd2+ in rice. A pH-responsive hydrogel bead was applied as a core element for the target stimulus and transverse relaxation signal transduction. The stability experiments showed that the transverse relaxation time (T2) change of the Gel-MRS sensor was one-seventh that of traditional magnetic nanoparticles under an external magnetic field and less than a fifth that of Fe2+/Fe3+ conversion in air. The excellent stability was due to the fact that T2 of the Gel-MRS sensor came from the swelling system mediated by pH rather than the traditional aggregation/dispersion or Fe2+/Fe3+ conversion of magnetic nanoparticles. In addition, the target Cd2+ could exclusively trigger a pH response of the hydrogel beads, altering the T2, thus resulting in excellent relaxation properties (R2 = 56.89) and pH responsiveness of the Gel-MRS sensor. The swelling process of the hydrogel beads followed quasi-second-order dynamics. The Gel-MRS sensor demonstrated a remarkable limit of detection as low as 0.009 ng/mL for Cd2+, with a linear range of 0.01-5 ng/mL. The excellent stability and sensitivity made the Gel-MRS sensor have great application potential in food and environmental detection.

Solid-state Ru(bpy)32+ electrochemiluminescence sensor for trace detection of fenpropathrin using loofah sponge-like carbon nanofibers and CdS

Loofah sponge-like carbon nanofibers (LF-Co,N/CNFs) were utilized as a carrier for Ru(bpy)32+, and then combined with CdS to create a novel solid-state electrochemiluminescence sensor capable of detecting trace amounts of fenpropathrin. LF-Co,N/CNFs, obtained through the high-temperature pyrolysis of ZIF-67 coaxial electrospinning fibers, were characterized by a loofah-like morphology and exhibited a significant specific surface area and porosity. Apart from serving as a carrier, LF-Co,N/CNFs also functioned as a luminescence accelerator, enhancing the system's luminescence efficiency by facilitating electron transmission and reducing the transmission distance. The inclusion of CdS in the luminescence reaction, in conjunction with Ru(bpy)32+, further boosted the sensor's luminescence signal. The resulting sensor demonstrated a satisfactory signal, with fenpropathrin causing significant quenching of the ECL signal. Under optimized conditions, a linear relationship between the signal quench value and fenpropathrin concentration in the range 1 × 10-12 to 1 × 10-6 M was observed, with a detection limit of 3.3 × 10-13 M (S/N = 3). This developed sensor is characterized by its simplicity, sensitivity, and successful application in detecting fenpropathrin in real samples. The study not only presents a straightforward detection platform for fenpropathrin but also introduces new avenues for the rapid determination of various food contaminants, thereby expanding the utility of carbon fibers in electrochemiluminescence sensors.

Innovative detection mechanism for deltamethrin based on a dual-emitting Fluoroprobe and its application in a smartphone-based photoelectric conversion device

Pyrethroids are widely used insecticides worldwide, while their on-site and rapid detection still faces technological challenges. Herein, an innovative detection mechanism was designed for deltamethrin, a typical kind of type II pyrethroids, based on a dual-emitting fluoroprobe consisting of NH2-SiQDs and Eu3+. Deltamethrin can rapidly hydrolyze into 3-phenoxybenzaldehyde (3-PBD) and react specifically with fluoroprobe, causing fluorescence quenching of SiQDs while maintaining the fluorescent stability of Eu3+. Building upon the above fluorescence-responsive principle, SiQDs@Eu3+ provided satisfactorily dual-emitting signals, realizing the highly-selective and sensitive detection of deltamethrin. Correlation between the surface structure of SiQDs and their absorption spectra was in-depth unraveled by TD-DFT calculation and FT-IR analysis. As for the analytical performance, the recovery and LOD of deltamethrin in lettuce, provided by SiQDs@Eu3+, were comparable or even superior over conventional chromatographic analysis. Meanwhile, an innovative smartphone-based optical device was developed, which greatly decreased errors caused by the previously reported smartphone-based fluorescence detection.

"Three-in-One": Ultrasensitive Lateral Flow Immunoassay Driven by Magnetic Enrichment and Photothermal Signal Amplification

Conventional lateral flow immunoassay (LFIA) usually suffers from poor antimatrix interference, unsatisfactory sensitivity, and lack of quantitative ability for target analyte detection in food matrices. In response to these limits, here, multifunctional nanomaterial ZnFe2O4 nanoparticles (ZFOs) were developed and integrated into LFIA for powerful magnetic separation/enrichment and colorimetric/photothermal target sensing. Under optimum conditions, the detection for clenbuterol (CL) with magnetic enrichment achieves 9-fold higher sensitivity compared to that without enrichment and 162-fold higher sensitivity compared to that based on traditional colloidal golds. Attributing the improved performances of ZFOs, CL can be detected at ultralow levels in pork and milk with 10 min of immunoreaction time. The vLODs were 0.01 μg kg-1 for two modes, and the cutoff values of CL were about 5 and 3 μg kg-1, respectively. More importantly, the enrichment ZFO-mediated LFIA (ZE-LFIA) exhibits a similar limit of detection (LOD) in both buffer solution and food matrix, demonstrating a universal resistance to the food matrix. The multitudinous performance merits of this ZE-LFIA with high sensitivity, matrix tolerance, accuracy, and specificity have ensured a broad application potential for target detection of clenbuterol and can serve as an experience for other veterinary drug residues' detection.

Cu(II)-induced magnetic resonance tuning and enhanced magnetic relaxation switching immunosensor for sensitive detection of chlorpyrifos and Salmonella

Magnetic relaxation switching (MRS) biosensors have been recognized as useful analytical tools for a range of targets; however, traditional MRS biosensors are limited by the "prozone effect", resulting in a narrow linear range and low sensitivity. Herein, we proposed a paramagnetic Cu2+-induced magnetic resonance tuning (MRET) strategy, based on which Cu2+ ions and magnetic nanoparticles (MNPs) were adopted to construct a Cu-MNP-mediated MRS (Cu-M-MRS) immunosensor with Cu2+ ions acting as a quencher and MNPs as an enhancer. An Fe3O4@polydopamine-secondary antibody conjugate was prepared and used to correlate the amount of Cu2+ ions to the target concentration through an immunoassay. Based on the immunoreaction, the Cu-M-MRS immunosensor enabled the sensitive detection of chlorpyrifos (0.05 ng/mL, a 77-fold enhancement in sensitivity compared with the traditional MRS immunosensor) and Salmonella (50 CFU/mL). The proposed MRET strategy effectively improved the sensitivity and accuracy of the MRS immunosensor, offering a promising and versatile platform for food safety detection.

Preparation of immunomagnetic composite nanostructures with bifunctional four-arm PEG derivatives as linkers for the ultrafast enrichment of zearalenone and its metabolites

It is challenging to prepare sample pretreatment materials with simple use, strong selectivity and satisfactory enrichment performance. In this study, the antibody (3D4) that can specifically recognize zearalenone (ZEN) and its metabolites was immobilized on the surface of gold-coated magnetic Fe3O4 nanoparticles (GMN) by streptavidin (SA)-biotin interaction using GMN as the substrate and our designed four-arm PEG derivative (HS-4ARMPEG10K-(CM)3) as the linker. The immunomagnetic nanoparticles (GMN-4ARMPEG10K-SA-3D4) prepared by this strategy can achieve rapid enrichment (only 5 min) of analytes directly in the matrix, and higher enrichment capacity compared with the previous immunomagnetic particles. The sensitive and accurate analysis of ZEN and its metabolites can be achieved coupled with HPLC-MS/MS. The LODs and LOQs were 0.02-0.05 μg/kg and 0.05-0.10 μg/kg, respectively. The recoveries were 84.13%-112.67%, and the RSDs were 1.09%-9.39%. The method can provide a powerful tool for highly sensitive and rapid monitoring of mycotoxins in complex matrices due to its' strong selectivity and resistance to matrix interference.

Carboxymethyl chitosan-modified UiO-66 for the rapid detection of fenpropathrin in grains

Fenpropathrin residues in grain are potentially harmful to humans. Therefore, a fluorimetric lateral flow immunoassay using a zirconium-based organic skeleton (UiO-66) as a signal marker was developed for detecting fenpropathrin. Herein, carboxymethyl chitosan (CMCS) was used to modify UiO-66 and improve its water solubility to facilitate stable binding with sodium fluorescein (NaFL). This resulted in formation of a new fluorescent probe that is more suitable for lateral flow immunoassay (LFIA). The materials were characterized via electron microscopy, Fourier-transform infrared spectroscopy, and powder X-ray diffraction. CMCS and NaFL were successfully bound to UiO-66. Under optimized conditions, the constructed NaFL/UiO-66@CMCS-LFIA exhibited a good linear relationship within the range of 0.98-62.5 μg/L, with a detection limit of 3.91 μg/L. This probe was fourfold more sensitive than traditional colloidal gold nanoparticle-based LFIA. Finally, NaFL/UiO-66@CMCS-LFIA was successfully applied to detect fenpropathrin in wheat and maize samples. The detection limit was 1.56 μg/kg and recoveries ranged from 96.58 % to 118.56 %. This study provides a sensitive, stable, and convenient method for the rapid detection of pesticide residues.

Lanthanide-Assisted Nanozyme Performs Optical and Magnetic Resonance Dual-Modality Logical Signal for In Vitro Diagnosis

The iron nanozyme-based colorimetric method, which is widely applied for biosubstrate detection in in vitro diagnosis (IVD), faces some limitations. The optimal catalytic conditions of iron nanozymes necessitate a strong acidic environment, high temperature, and other restrictive factors; additionally, the colorimetric results are highly influenced by optical interferences. To address these challenges, iron nanozymes doped with various transition elements were efficiently prepared in this study, and notably, the manganese-modified one displayed a high catalytic activity owing to its electron transfer property. Furthermore, the introduction of lanthanide ions into the catalytic reactions, specifically the neodymium ion, significantly boosted the generation efficiency of hydroxyl radicals; importantly, this enhancement extended to a wide range of pH levels and temperatures, amplifying the detection signal. Moreover, the nanozyme's superparamagnetic characteristic was also employed to perform a logical optical and magnetic resonance dual-modality detection for substrates, effectively eliminating background optical interference and ensuring a reliable verification of the signal's authenticity. Based on this magnetic signal, the integration of natural glucose oxidase with the nanozyme resulted in a notable 61.5% increase in detection sensitivity, surpassing the capabilities of the traditional colorimetric approach. Consequently, the incorporation of lanthanide ions into the magnetic nanozyme enables the effective identification of physiological biomarkers through the dual-modality signal. This not only guarantees enhanced sensitivity but also demonstrates significant potential for future applications.

Well plate-based LF-NMR/colorimetric dual-mode homogeneous immunosensor for Vibrio parahaemolyticus detection

A 96-well plate-based low-field nuclear magnetic resonance (LF-NMR)/colorimetric dual-mode homogeneous immunosensor was developed for the detection of pathogen bacteria, using Vibrio parahaemolyticus (VP) as a detection template. The signal unit MNS@Ab2 is graphene oxide (GO) simultaneously loaded with VP antibody and Fe3O4 nanoparticles. A 96-well plate coated with VP antibody captures the target VP, which then binds the signal unit to form the immunocomplex. After acidolysed, Fe3O4 nanoparticles are transformed into Fe3+ and Fe2+, so the non-homogeneous system is transformed into a homogeneous one. The addition of KMnO4 can not only convert Fe2+ into Fe3+ but also provide Mn2+, improving the detection sensitivity. And, colorimetric analysis can be achieved by the quantitative reduction of KMnO4. Under the optimal experimental conditions, the limit of detection was 60 CFU/mL with good selectivity, stability, precision, accuracy, and consistency, providing a simple and reliable detection platform for pathogenic bacteria in food.

Highly specific colorimetric detection based on aggregation of l-cysteine functionalized gold nanoparticles for cypermethrin in water samples

A fast, simple, and selective colorimetric assay for quantifying cypermethrin in water samples is proposed using l-cysteine functionalized gold nanoparticles (AuNPs@Cyst). Cypermethrin is hydrolyzed by potassium hydroxide to obtain hydrolyzed cypermethrin in the form of 3-phenoxybenzaldehyde by-product (HCy). The detection strategy is based on the aggregation of AuNPs@Cyst caused by hydrogen-bonding recognition between the aldehyde group of HCy and the amine group of l-cysteine on the surface of AuNPs@Cyst. As a result, in the presence of HCy under optimal pH 7, AuNPs@Cyst aggregates within 7 min, exhibiting a distinct color change from red to blue-gray, which can be evaluated with the naked eye and UV-visible spectrophotometry. From FE-TEM image, the stable and spherical AuNPs@Cyst had an average size of 13.8 ± 1.6 nm, and from zeta potential analysis, the charge of AuNPs@Cyst was -25.04 ± 1.66 mV. The surface plasmon resonance band of dispersed AuNPs@Cyst was red shifted from 525 nm to 634 nm when AuNPs@Cyst was aggregated. The absorbance ratio (A634/A525) was linearly related to cypermethrin concentrations from 0.5 to 13.0 mg L-1. The limit of detection was 0.2 mg L-1 and precision, expressed as relative standard deviations (RSDs), ranged from 1.9 to 7.3%. In the presence of interfering pesticides (carbaryl, ethion, profenofos and abamectin), only cypermethrin produced a significantly different response, confirming the selectivity of AuNPs@Cyst. Finally, AuNPs@Cyst was applied to determine cypermethrin in water samples, achieving very satisfied recoveries (>98.6%) and RSDs lower than 6.1%.

Smartphone-assisted biosensor based on broom-like bacteria-specific magnetic enrichment platform for colorimetric detection of Listeria monocytogenes

Pathogenic bacteria contamination poses a major threat to human health. The detection of low-abundance bacteria in complex samples has always been a knotty problem, and high-sensitivity bacterial detection remains challenging. In this work, a novel magnetic platform with high enrichment efficiency for L. monocytogenes was developed. The magnetic platform was designed by branched polyglutamic acid-mediated indirect coupling of cefepime on magnetic nanoparticles (Cefe-PGA-MNPs), and the specific enrichment of low-abundance L. monocytogenes in real samples was achieved by an external magnet, with a capture efficiency over 90%. A controllable and highly active platinum-palladium nanozyme was synthesized and further introduced in the magnetic nanoplatform for the construction of enzymatic colorimetric biosensor. The total detection time for L. monocytogenes was within 100 min. The colorimetric signals generated by labelled nanozyme were corresponding to different concentrations of L. monocytogenes, with a limit of detection (LOD) of 3.1 × 101 CFU/mL, and high reliability and accuracy (with a recovery rate ranging from 96.5% to 116.4%) in the test of real samples. The concept of the developed method is applicable to various fields of biosensing that rely on magnetic separation platforms.

Construction of a Highly Selective Enrichment, Ionization, and Detection Platform Based on a Broad-Spectrum Antibody

Ambient mass spectrometry (AMS) allows direct analysis of various raw food samples with minimal or no sample pretreatment, but the trace analytes in complex food samples still have problems with limitations. In this work, we developed a platform based on coated stainless steel sheet spray mass spectrometry for fast, in situ, high-throughput, and high selectivity multiresidue analysis of fluoroquinolone drugs (FQs). The sensitivity of the platform was enhanced via coupling broad-spectrum antibodies against FQs to graphene oxide coated blade spray (CBS)-MS through a streptavidin-biotin (SA-biotin) interaction. The prepared platform had sufficient loading capacity for SA (1.37 mg/piece) and the antibody (84.8 μg/piece), which is greater than that of physical mixing and the EDC/NHS covalent coupling strategy. With simplified sample pretreatment, this platform demonstrated comparable sensitivity to high performance liquid chromatography-mass spectrometry (HPLC-MS/MS) (0.08-0.16 ng/mL in phosphate-buffered saline and 0.21-0.32 ng/mL in diluted milk). Meanwhile, compared with HPLC-MS/MS, the method is rapid (enrichment: 10 min, detection: <1 min) and acceptable recoveries (81.94-102.08%) can be obtained. The presence of analytes can be monitored by MS/MS spectra, and multiple analytes can be measured simultaneously in a single assay. This study is expected to provide a powerful and portable tool for rapid laboratory analysis and reliable screening in the field.

A facile and sensitive magnetic relaxation sensing strategy based on the conversion of Fe3+ ions to Prussian blue precipitates for the detection of alkaline phosphatase and ascorbic acid oxidase

Herein, a novel magnetic relaxation sensing strategy based on the change in Fe³⁺ content has been proposed by utilizing the conversion of Fe³⁺ ions to Prussian blue (PB) precipitates. Compared with the common detection approach based on the valence state change of Fe³⁺ ions, our strategy can cause a larger change in the relaxation time of water protons and higher detection sensitivity since PB precipitate can induce a larger change in the Fe³⁺ ion concentration and has a weaker effect on the relaxation process of water protons relative to Fe²⁺ ions. Then, we employ alkaline phosphatase (ALP) as a model target to verify the feasibility and detection performance of the as-proposed strategy. Actually, ascorbic acid (AA) generated from the ALP-catalyzed L-ascorbyl-2-phosphate hydrolysis reaction can reduce potassium ferricyanide into potassium ferrocyanide, and potassium ferrocyanide reacts with Fe³⁺ to form PB precipitates, leading to a higher relaxation time. Under optimum conditions, the method for ALP detection has a wide linear range from 5 to 230 mU/mL, and the detection limit is 0.28 mU/mL, sufficiently demonstrating the feasibility and satisfactory analysis performance of this strategy, which opens up a new path for the construction of magnetic relaxation sensors. Furthermore, this strategy has also been successfully applied to ascorbic acid oxidase detection, suggesting its expansibility in magnetic relaxation detection.