Efficient Photothermal Sensor Based on Coral-Like Hollow Gold Nanospheres for the Sensitive Detection of Sulfonamides.

Gold nanoparticles (AuNPs), universally regarded as colorimetric signal reporters, are widely employed in lateral flow immunoassays (LFIAs). However, it is difficult for AuNPs-LFIA to achieve a wide range and sensitive detection. Herein, novel coral-like hollow gold nanospheres (CHGNPs) are synthesized. The growth of gold nanospheres can be regulated to obtain a multibranched and hollow construction. The obtained CHGNPs possess intense broadband absorption across the visible to near-infrared region, exhibiting a high molar extinction coefficient of 14.65 × 1011 M-1 cm-1 and a photothermal conversion efficiency of 79.75%. Thus, the photothermal/colorimetric dual-readout LFIA is developed based on CHGNPs (CHGNPs-PT-LFIA and CHGNPs-CM-LFIA) to effectively improve the detection sensitivity and broaden the detection range in regard to sulfonamides (SAs). The limits of detection of the CHGNPs-PT-LFIA and CHGNPs-CM-LFIA reached 1.9 and 2.8 pg mL-1 for the quantitative detection of sulfaquinoxaline, respectively, which are 6.3-fold and 4.3-fold lower than that of the AuNPs-LFIA. Meanwhile, the CHGNPs-PT-LFIA broadened the detection range to three orders of magnitude, which ranged from 2.5 to 5000 pg mL-1 . The synthesized photothermal CHGNPs have been proven effective in improving the performance of the LFIA and provide a potential option for the construction of sensing platforms.

Polyethyleneimine-induced fluorescence enhancement strategy for AIEgen: the mechanism and application.

Aggregation-induced emission luminogens (AIEgens) are attracting extensive research attention in the biosensor fields. Herein, we report a new polyethyleneimine (PEI)-induced strategy for enhancing luminescence of TCBPE (an AIEgen) to promote its development in biosensor. The copolymer dots (TCBPE-PEI) with high quantum yield (39.7%) and outstanding stability were synthesized via a one-pot method. The fluorescence enhancement mechanism based on the PEI strategy originated from the restriction of intramolecular motions of TCBPEs and the form of donor-acceptor structures to decrease the inherent energy bandgap. Benefiting from chelating property of TCBPE-PEI by Cu2+, a fluorescence-quenching sensor for Cu2+ detection was developed based on the fluorescence quenching of the electron transfer effect. Especially, a good linear range of 10-250 nM with a low limit of detection 1.1 nM was achieved, and it was further applied in samples successfully. The current work provides a novel approach to fabricate AIEgen biosensors and shows great potential in Cu2+ detection.

Lateral flow immunoassay based on polydopamine-coated metal-organic framework for the visual detection of enrofloxacin in milk.

Herein, we report a new polydopamine (PDA)-coated metal-organic framework (MOF) as a label to improve the sensitivity of lateral flow immunoassay (LFIA). The MOF, UiO-66-NH2, was synthesized via the hydrothermal method, and it exhibited the advantageous features of ordered pore structure, strong absorbance, and high specific surface area. Subsequently, UiO-66-NH2 was coated with PDA to improve the antibody coupling effectivity and light absorption ability. The optical intensity and antibody coupling efficiency of UiO-66@PDA were superior to those of gold nanoparticles (AuNPs). Under the optimum condition, the limit of detection and cutoff value of UiO-66@PDA-LFIA in detecting enrofloxacin were 0.045 and 1.0 ng/mL, respectively, which were lower than those of AuNPs-LFIA (0.095 and 5 ng/mL). The recoveries of UiO-66@PDA-LFIA in low-fat milk and whole milk were 85.6-107.4% and 79.3-115.5%, respectively, with coefficients of variation of 2.91-9.59% and 3.91-11.8%, respectively, as further confirmed by liquid chromatography-tandem mass spectrometry. These results indicate that UiO-66@PDA can be used as a novel probe for LFIA development and applications. Graphical abstract.

Biomineralization-powered integrated immunoprobe and its application in Immunochromatographic assay.

Immunochromatographic assay (ICA) has attracted widespread attention owing to its advantages of economy, simplicity, and rapidity. However, the synthesis of immunoprobes is still limited by complicated design ideas and multistep operations from preparing nanoparticles to conjugating monoclonal antibodies (mAb) onto nanoparticles. Inspired by the biomineralization of zeolitic imidazolate framework-8 (ZIF-8), we proposed a strategy for the rapid synthesis of an integrated immunoprobe (ZIF-8@QDs-mAb), achieving a one-step integration with strong fluorescent signal output capability and specific recognition ability. In addition, different fluorescent colors of ZIF-8@QDs-mAb were generated by doping red and green quantum dots (QDs) in various ratios. With a smart detection platform, the developed ZIF-8@QDs-mAb-based multiplex ICA (ZIF-8@QDs-mAb-mICA) achieved the on-site quantitative detection of enrofloxacin, sulfamethazine, and kanamycin in milk within 15 min, with the limit of detection (LOD) of 0.052, 0.186 and 0.216 ng mL-1, which were 5.69, 2.20 and 4.40 times higher than that of gold nanoparticles-based mICA, respectively. The quantitative detection of alpha-fetoprotein and human chorionic gonadotropin was also achieved with LOD of 0.516 ng mL-1 and 0.225 mIU mL-1, respectively, which verified the universality of the strategy. This work provides a novel idea for the design of an efficient integrated immunoprobe and has broad application prospects in ICA.

High-flux smartphone-integrated lateral flow assay based on chrysanthemum-like Au@polydopamine for sensitive detection of enrofloxacin in milk.

Lateral flow assays (LFAs) are widely used in screening analysis. However, the detection flux and sensitivity of LFAs are unsatisfactory because of the 'one-to-one' read mode and the ordinary performance conventional probe. In this work, a high-flux smartphone-integrated LFA (sLFA) based on chrysanthemum-like Au@polydopamine (AuNC@PDA) for the detection of enrofloxacin (ENR) in milk was established. The smartphone-integrated device was developed and applied in the LFA, giving rise to a reading maximum of 64 samples with only two photos in less than 2 min compared to a 'one-to-one' read mode of a conventional LFA in more than 14 min with a 36.4% deviation. For ENR detection, the limits of detection of sLFA based on AuNC@PDA (33.78 pg mL-1) had 5.0-fold and 6.4-fold reduction compared with those based on AuNP (169.99 pg mL-1, conventional probe) and vvAuNP (216.47 pg mL-1, commercial probe), respectively. This study provides an effective technical means for screening ENR in large quantities of milk samples.

Triple strategy-enhanced immunochromatographic assay based on APCB and AIEFM for the ultrasensitive detection of AFM1.

Aflatoxin M1 (AFM1) is highly toxic, widely distributed, and difficult to monitor, posing a serious threat to human health. Therefore, a highly sensitive, rapid, convenient, and low-cost detection method must be urgently established. In this study, a triple strategy-enhanced immunochromatographic assay (ICA) was developed to satisfy these detection requirements. First, a turn-on signal output mode of the fluorescence quenching ICA substituted the turn-off mode of the traditional ICA for sensitive response to trace AFM1, with the limit of detection (LOD) reduced by approximately 4.9-fold. Then, a novel Au and polydopamine (PDA) cogrowth chrysanthemum-like blackbody was prepared as the quenching probe to reduce the background signal. This probe combined the excellent properties of Au nanoparticles with PDA. Thus, its fluorescence quenching constant was higher than that of single Au and PDA nanoparticles by 25.8- and 4.9-fold, respectively. Furthermore, an aggregation-induced emission fluorescence microsphere with a 5.7-fold higher relative quantum yield than a commercial fluorescence microsphere was selected as the signal output carrier to improve the signal-to-noise ratio. The integration of the above triple strategies established a 53.4-fold sensitivity-enhanced fluorescence quenching ICA (LOD = 0.9 pg/mL) for detecting AFM1 in milk, providing a strong technical guarantee for the safety monitoring of milk products.

Sensitive lateral flow immunoassay strips based on Fe3+-chelated polydopamine nanospheres for the detection of kanamycin.

As kanamycin (KAN) residue in animal products is harmful to consumers, a rapid and sensitive method for KAN detection needs to be established. KAN monoclonal antibody (KAN-mAb, 1D11) with the half maximal inhibitory concentration of 1.16 ng/mL was prepared in this study. A one-pot method was used to synthesize Fe3+-chelated polydopamine nanospheres (Fe@PDANs) with excellent characteristics of strong light absorption. The novel label of Fe@PDANs and KAN-mAb was used to develop a lateral flow immunoassay (LFIA) for the sensitive detection of KAN. The limit of detection of the Fe@PDANs-based LFIA (Fe@PDANs-LFIA) for KAN was 0.0191 ng/mL, which was 2.75 times lower than PDANs-based LFIA. Furthermore, the Fe@PDANs-LFIA was successfully applied to detect KAN in pork, milk, and honey samples, with recoveries ranging from 93.75% to 113.80% (coefficient of variation < 10%). Therefore, Fe@PDANs have potential for the detection of analytes in LFIA.

Synthesis of PDA-Mediated Magnetic Bimetallic Nanozyme and Its Application in Immunochromatographic Assay.

Immunochromatographic assay (ICA) is widely applied in various fields. However, severe matrix interference and weak signal output present major challenges in achieving accurate and ultrasensitive detection in ICA. Here, a polydopamine (PDA)-mediated magnetic bimetallic nanozyme (Fe3O4@PDA@Pd/Pt) with peroxidase-like activity was synthesized and used as a probe in ICA. The magnetic property of Fe3O4@PDA@Pd/Pt enabled effective magnetic enrichment of targets, thereby reducing the matrix interference in the sample. PDA coating on the magnetic bimetallic nanozyme was employed as a mediator and a stabilizer. It improved the catalytic ability and stability of the magnetic bimetallic nanozyme by providing more coordination sites for Pd/Pt growth and functional groups (-NH and -OH). In addition, the Pd/Pt bimetallic synergistic effect could further enhance the catalytic ability of the nanozyme. A method was developed by integrating Fe3O4, PDA, and Pd/Pt into Fe3O4@PDA@Pd/Pt as a probe in ICA. With the proposed method, human chorionic gonadotropin and Escherichia coli O157:H7 were successfully detected to be as low as 0.0094 mIU/mL in human blood serum and 9 × 101 CFU/mL in the milk sample, respectively. This method may be readily adapted for accurate and ultrasensitive detection of other biomolecules in various fields.