Simultaneous detection of diethylstilbestrol and estradiol residues with a single immunochromatographic assay strip

Covalent organic framework with donor-acceptor structure for rapid and sensitive photothermal sensing detection

Given the serious harm caused by dietary intake of diethylstilbestrol (DES), it is urgent to explore rapid and sensitive DES sensing methods. In this work, a photothermal DES immunochromatography sensor based on covalent organic framework (COF) was constructed. The performance of COF in the field of photothermal sensing was systematically investigated for the first time. A donor-acceptor type of COF with a photothermal conversion rate of 51.17 % was synthesized. The logarithm of the DES concentrations-temperature change value standard curve was plotted. The intensity of the photothermal sensing signal was inversely proportional to the sample concentration. The detection limit of the proposed photothermal method (0.24 μg·L-1) was 10 times higher than that of visual detection (3 μg·L-1). This work not only constructed a novel detection method for DES sensing, but also provided a feasible demonstration for the application of COF in photothermal sensing and expanded the application of their photothermal properties.

Bifunctional ligand-mediated amplification of polydiacetylene response to biorecognition of diethylstilbestrol for on-site smartphone detection

Polydiacetylene (PDA) is very suited for sensitively detecting large biomolecules, and its unique chromatic properties enable visual read-out. However, application to the selective detection of small molecules remains challenging. Here, bifunctional ligands are studied to amplify the color change of PDA for biorecognition of small molecules for the smartphone-based detection of diethylstilbestrol (DES). PDA is decorated with streptavidin (PDA-SA, blue), and biotin-modified DES (bio-DES) is prepared as a bifunctional ligand to couple with PDA-SA and DES antibody. Since multiple bio-DES can bind to a single SA, then multiple SAs on PDA lead to an increased surface coverage of the vesicle. In samples without DES, PDA-SA-bio-DES-DES antibody complexes will form, leading to a color transition (blue to red); this color transition is greatly amplified by antibody-induced aggregation of the complexes. When DES is present, aggregation is inhibited due to competition for the antibody and PDA-SA-bio-DES retains its blue color. A linear relationship (0.4-1250 ng mL^-1) is found between the colorimetric response and the logarithmic DES concentration, with adequate selectivity, accuracy (82.24-118.64%), and precision (below 8.24%). Finally, a paper-based DES PDA biosensor is developed with visual and smartphone-based detection limits of 10 ng mL^-1 and 0.85 ng mL^-1 in water, respectively.

Regenerative Flexible Upconversion-Luminescence Biosensor for Visual Detection of Diethylstilbestrol Based on Smartphone Imaging

Diethylstilbestrol (DES), an endocrine disrupting chemical, has been linked to serious health problems in humans. In this work, a regenerative flexible upconversion-fluorescence biosensor was designed for the detection of DES in foodstuffs and environmental samples. Herein, amino-functionalized upconversion nanoparticles (UCNPs) were synthesized and immobilized on the surface of a flexible polydimethylsiloxane substrate, which was further modified with complementary DNA and dabcyl-labeled DES aptamer. The fluorescence resonance energy transfer (FRET) system was established for DES detection between dabcyl and UCNPs as the acceptor and donor pairs, respectively, which resulted in the quenching of the upconversion luminescence intensity. In the presence of a target, the FRET system was destroyed and upconversion fluorescence was restored due to the stronger affinity of the aptamer toward DES. The designed biosensor was also implemented in a dual-mode signal readout based on images from a smartphone and spectra from a spectrometer. Under the optimized experimental conditions, good linear relationships were achieved based on imaging (y = 53.055x + 36.175, R² = 0.9851) and spectral data (y = 1.1582x + 1.9561, R² = 0.9897). The designed biosensor revealed great practicability with a spiked recovery rate of 77.91-97.95% for DES detection in real environment and foodstuff samples. Furthermore, the proposed biosensor was regenerated seven times with an accuracy threshold of 80% demonstrating its durability and reusability. Thus, this biosensor is expected to be applied to point-of-care and on-site detection based on the developed portable smartphone device and android application.

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.

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

The continuous intake of 17β-estradiol (E2) residue from animal-derived food may pose a threat to the health of consumers, so the rapid screen and detection of E2 is very necessary. Although visual immunochromatographic strip (ICS) has played a great role in food safety control such as the screen of many food contaminants, it cannot meet the requirements for E2 detection due to the insufficient sensitivity of traditional visual ICS and the low concentration range of estrogen in food. Here, we developed a dual-mode ICS strategy to achieve rapid and highly sensitive detection of E2. Based on the visual detection mode of a competitive ICS, the afterglow detection mode working in fluorescence resonance energy transfer mechanism was introduced by using the afterglow particles (APs) as energy donor and gold nanoparticles (AuNPs) as energy acceptor. In this method, large APs of micron size with superior afterglow were applied as the test zone-fixed fluorescence signal source, thus the contradiction between migration and afterglow characteristics was skillfully resolved. In addition, a 6 W UV lamp was used as the light source to excite APs, and a smartphone was used to capture an image of 0.5 s after the UV light was turned off to effectively remove the autofluorescence from the strips and improve the signal-to-noise ratio. The limit of detection of this afterglow mode was 0.5 ng/mL, twenty times more sensitive than that of visual mode (10 ng/mL). The strategy has been successfully applied to the detection of estradiol in milk and verified by HPLC-FLD.