Visual-afterglow dual-mode immunochromatographic strip for 17β-estradiol detection in milk

Direct extraction of ten estrogens from milk samples with DVB/NVP-modified magnetic solid-phase extraction adsorbent followed by pre-column derivatization-UHPLC-MS/MS

Estrogens and their analogues can cause harm to human health through the food chain. Ten estrogens in different milk samples were directly extracted by amphiphilic divinylbenzene/N-vinyl-2-pyrrolidone (DVB/NVP)-Fe3O4@SiO2-based magnetic solid-phase extraction (MSPE) followed by pre-column derivatization and ultra-high performance liquid chromatography tandem mass-spectrometry (UHPLC-MS/MS) detection. Under the optimal conditions, the limits of detection for ten analytes were in the range of 0.05-0.38 ng mL-1 in whole liquid milk matrix and 0.04-3.00 ng g-1 in milk powder matrix. The intra-/inter-day accuracy ranged in 83.4-113.8%, with RSDs in 2.5-15.0%. A total of 15 brands of liquid milk and milk powder samples were analyzed, and only estradiol was detected in three brands of boxed liquid milk within safe range. The proposed sample pretreatment eliminated the common protein precipitation process, improved the sample throughput, and has the potential for routine testing of estrogens and their analogues in market-sale milk samples.

Facile and Ultrasensitive Food Allergen Quantification Using Microzone Paper-Based Mass Spectrometric Immunoassay

Highly sensitive and rapid measurement of food allergens is essential to avoid unanticipated food allergies and to determine whether cross-contamination occurs in the food industry. Commercial immunoassay kits offer high specificity and convenience for allergen detection but still suffer limited quantitative sensitivity, accuracy, and stability based on the optical readout. In this work, a paper-based mass spectrometric immunoassay platform was constructed to achieve facile and highly sensitive quantification of peanut allergen, which combined the advantages of good specificity and accurate quantification from mass spectrometry and simplicity from a paper-based immunoassay. In this platform, a novel quaternary ammonium-based mass tag and a paper chip with a microzone were designed and developed, contributing to a large signal enhancement. This method was able to detect Ara h1 with a linear range of 0.1-100 ng mL-1 and a detection limit of 0.08 ng mL-1 in milk matrices. It has also been successfully applied to the accurate quantification of Ara h1 in six milk-related beverages, two biscuits, and two candy bars with complicated matrices and presented a low-concentration quantitation capability. This method gives a new type of mass spectrometric immunoassay for rapid and ultrasensitive allergen regulation in the food industry and for individual allergen differentiation research.

DNA-bridged double gold nanoparticles-based immunochromatography for dual-mode detection of ochratoxin A

A novel immunochromatography strip (ICS) based on the DNA-bridged double gold nanoparticles was established and evaluated for the dual-mode detection of ochratoxin A (OTA). For this purpose, the streptavidin was coupled with the big size of gold nanoparticle (40 nm, AuNP), the OTA monoclonal antibody and biotinylated DNA-SH were simultaneously immobilized on the small size of AuNP (20 nm), and then the enhanced ICS was self-assembled and evaluated. The dual-mode detection of semi-quantification and quantification had been achieved and performed by the proposed ICS. The LOD for semi-quantification (semi-Q-LOD) was 0.06 ng/mL by the directly naked eye (eightfold enhanced than conventional ICS). By the on-site reader, the LOD for quantification (Q-LOD) was 0.03 ng/mL (threefold enhanced), with the detection range between 0.03 and 1.2 ng/mL. The specificity, reliability, and practicability had been well represented. Furthermore, the OTA-positive results of the enhanced ICS method correlated well with those obtained by the referenced HPLC-MS/MS for the market samples. This study provided a new ICS pattern of semi-quantification and quantification for OTA contamination, which could be used as a valuable reference for improving the ICS technology and enhancing the sensitivity.

Highly sensitive colorimetric aptasensor for 17β-estradiol detection in milk based on the repetitive-loop aptamer

Trace of 17β-estradiol (E2) contamination in food has been a concern for its negative impacts on human health, leading to the need for an E2-monitoring system. This work reported a new simple, sensitive, and colorimetric E2 detection based on the designed repetitive-loop aptamer and gold nanoparticles (AuNPs). The designed aptamers (L2-L5) exhibited a higher binding capability to E2 than the original truncated aptamer (L1). Although L3-L5 aptamers exhibited the highest binding capability, only L3-aptasensor demonstrated the sensitive detection of E2 in a range of 0.05-0.8 nM, with the limit of detection at 13.1 pM. The developed L3-aptasensor was 7.7-folds more sensitive for E2 detection than the L1-aptasensor. It selectively detected E2, but not the other tested chemicals with similar structures: progesterone, genistein, diethylstilbestrol, bisphenol A, and chloramphenicol. The L3-aptasensor efficiently detected E2 spiked in milk samples within the precision acceptance criterion of recovery rates (100.1%-113.0%) and the relative standard deviations (5.24%-11.06%). These results demonstrated the development of a new aptasensor based on the designed repetitive-loop aptamer that could enhance E2-detection sensitivity and be potentially used for detecting E2 in milk samples with high accuracy and reliability.

Split aptamer regulated CRISPR/Cas12a biosensor for 17β-estradiol through a gap-enhanced Raman tags based lateral flow strategy

It is significant to exploit the full potential of CRISPR/Cas based biosensor for non-nucleic-acid targets. Here, we developed a split aptamer regulated CRISPR/Cas12a and gap-enhanced Raman tags based lateral flow biosensor for small-molecule target, 17β-estradiol. In this assay, one split aptamer of 17β-estradiol was designed to complement with crRNA of Cas12a so that the trans-cleavage ability of CRISPR/Cas12a can be regulated by the competitive binding of 17β-estradiol and split aptamers. Through integration of the signal amplification ability of CRISPR/Cas12a and the ultra-sensitive gap-enhanced Raman tags based lateral flow assay, a visible-SERS dual mode determination of 17β-estradiol can be established. 17β-estradiol can be visibly recognized as low as 10 pM and accurately quantified with a detection limit of 180 fM by SERS signals, which is at least 10³-fold lower than that of the previous immunoassay lateral flow strategies. Our assay provides a novel perspective to develop split aptamer regulated CRISPR/Cas12a coupling with SERS lateral flow strips for ultrasensitive and easy-to-use non-nucleic-acid targets detection.

Vanadium Disulfide Nanosheet Boosts Optical Signal Brightness as a Superior Enzyme Label to Improve the Sensitivity of Lateral Flow Immunoassay

The color-enzyme lateral flow immunoassay (LFIA) has attracted widespread attention to expand the detection range and improve sensitivity via amplifying the color signal after catalyzing the substrate. As a kind of layered transition-metal dichalcogenide (TMD), the vanadium disulfide nanosheet (VS₂NS) possesses superior peroxidase-like catalytic activity. Here, a VS₂NS was applied as an enzyme label in the LFIA to detect 17β-estradiol (E2). Compared to natural horseradish peroxidase, the VS₂NS expresses a more prominent enzyme catalytic performance, stability, and adsorption ability. Under optimal conditions, the calculated limit of detection (cLOD) of the VS₂NS-based LFIA is 0.065 ng mL^-1 for E2, which is sixfold lower than that of the optimized colloidal nanoparticle-based LFIA (cLOD = 0.406 ng mL^-1). Besides, the detection linear range of the VS₂NS-based LFIA can be widened by 1.5 times after the catalytic reaction. Moreover, the VS₂NS-based LFIA exhibits excellent practicability in real sample detection. Simultaneously, this study helps open up the application of the VS₂NS in the trace analysis of LFIAs, which can broaden TMDs' scope of application and better show their properties of color enzymes.

A Polydopamine-Coated Gold Nanoparticles Quenching Quantum Dots-Based Dual-Readout Lateral Flow Immunoassay for Sensitive Detection of Carbendazim in Agriproducts

In this study, a fluorometric and colorimetric dual-readout lateral flow immunoassay (LFIA) using antibody functionalized polydopamine-coated gold nanoparticles (Au@PDAs) as a probe was developed for the detection of carbendazim (CBD). Colloidal gold nanoparticles (AuNPs) were coated with polydopamines (PDA) by the oxidation of dopamine to synthesize Au@PDA nanoparticles. The Au@PDA nanoparticles mediated ZnCdSe/ZnS quantum dots (QDs) fluorescence quenching and recovery, resulting in a reverse fluorescence enhancement detection format of CBD. The CBD detection was obtained by the competition between the CBD and the immobilized antigen for Au@PDAs labelled antibody binding, resulting in a significant fluorescence increase and colorimetry decrease corresponded to the concentration of CBD. Dual readout modes were incorporated into the LFIA using the colorimetry signal under natural light and the fluorescence signal under UV light. The cut-off value in the mode of the colorimetric signal and fluorometric signal for CBD detection was 0.5 μg/mL and 0.0156 μg/mL, respectively. The sensitivity of LFIA of the fluorescence mode was 32 times higher than that of the colorimetry mode. There was negligible cross reactivity obtained by using LFIA for the determination of thiabendazole, benomyl, thiophanate-methyl, and thiophanate-ethyl. Consistent and satisfactory results have been achieved by comparing the results of Au@PDAs-QDs-LFIA and liquid chromatography-tandem mass spectrometry (LC-MS/MS) testing spiked cucumber and strawberry samples, indicating good reliability of the Au@PDAs-QDs-LFIA.

Universal fluorescence nanoprobes to enhance the sensitivity of immunochromatographic assay for detection of 17β-estradiol in milk

The pollution caused by estrogens in the environment and food has received increasing attention. It is still challenging for on-site immunochromatographic assay (ICA) detection of estrogens. The performance of the prepared probes plays a decisive role in the sensitivity and stability of the ICA system. The published probes usually directly couple the detection antibody to the label, ignoring the influence of the label on the activity of the antibody. In this study, 17β-estradiol (E₂) was used as a model analyte for the ICA system. Two universal probes were constructed based on quantum dot nanobeads (QBs), recombinant protein A (SPA, from Staphylococcus aureus), and rabbit anti-mouse immunoglobulin G antibody (anti-IgG). The probes were prepared by coupling QBs with SPA, releasing anti-E₂ monoclonal antibody (mAb), and maintaining its activity. The prepared universal probes can orient recognize the Fc region of mAb and fully expose its Fab region, improving the detection sensitivity of the ICA system. The free anti-E₂ mAb and the universal probe (QBs@SPA or QBs@SPA@anti-IgG) were used as the detection antibodies and signal donors, respectively. The results show that the proposed ICA based on QBs@SPA and QBs@SPA@anti-IgG probes could detect E₂ with IC₅₀ of 8.83 and 0.93 ng/mL, respectively, within 15 min under optimal conditions. The recovery results of ICA based on QBs@SPA and QBs@SPA@anti-IgG probes showed good agreement with the findings of the high-performance liquid chromatography (HPLC) analysis for spiked samples. The developed ICA system based on universal probes was superior in terms of sensitivity, rapidity, and applicability, and held great promise for its implementation in detecting environmental and food small-molecule pollutants.