Ultrabright orange-yellow aggregation-induced emission nanoparticles for highly sensitive immunochromatographic quantification of ochratoxin A in corn

Fully Inter-restricted Assembly of Aggregation-Induced Emission Luminogens and Polymers Enables Ultra-bright Nanoparticles for Sensitive Point-of-Care Diagnosis

Fluorescent lateral flow immunoassay (LFIA) is recognized as a leading quantitative point-of-care (POC) platform for precise clinical diagnostics. However, conventional fluorescent nanoprobes are hampered by low quantum yield (QY), which constrain the sensitivity of fluorescent LFIA. Herein, we employed a butterfly aggregation-induced emission luminogen (AIEgen) and developed the fully inter-restricted assembly with a polyphenyl polymer poly(maleicanhydride-styrene) (PMPS) to create highly fluorescent homogeneous nanoparticles (ho-AIENPs) with QY over 91%. Compared to conventional fluorescent nanoparticles with a core-shell heterostructure (he-AIENPs), ho-AIENPs demonstrate a homogeneous structure with AIEgens uniformly dispersed in the PMPS matrix nanoparticles. The robust and broad intermolecular interaction (e.g., π-π interactions) between PMPS and AIEgens effectively restricts the molecular motion of AIEgens, producing a 30% increase in the QY of ho-AIENPs than he-AIENPs. Ho-AIENPs exhibit a 5-fold and 80-fold improved sensitivity compared to traditional he-AIENP-based fluorescent LFIAs and AuNP-based colorimetric LFIAs. Owing to the excellent optical properties of ho-AIENPs, we developed ho-AIENP-based multiplex LFIAs, which can simultaneously detect lung cancer biomarkers with exceptionally high sensitivity. In contrast to the conventional core-shell assembly and physical encapsulation strategies, the fully inter-restricted assembly strategy is promising, versatile, and efficient in enhancing the polymer matrix-derived fluorescent particles and sensitizing the immunoassays.

Engineering an Ionic Aggregation-Induced Luminescence-Labeled Fluorescence Lateral Flow Immunoassay for C-Reactive Protein in Human Plasma

The surge of lateral flow immunoassays (LFAs) stimulates researchers to explore the novel vibrant aggregation-induced emission luminogen (AIEgen)-doped nanoparticles to improve the accuracy and reliability of LFAs. However, the loading amount of AIEgens currently used for the LFA in microspheres is limited due to their symmetrical large conjugated skeleton structure, which significantly reduces the fluorescence brightness of the signal reporter in the LFA. Herein, an ionic AIEgens with a donor-acceptor type was developed as the signal reporter of the LFA for C-reactive protein (CRP). Ionic AIEgens are unable to enter the hydrophobic cavity of polystyrene nanoparticles (PS) because of their low hydrophobic nature. By altering ionic AIEgens with extended alkyl chains, it is possible to increase their hydrophobicity, thereby potentially increasing the loading capacity within PS. Notably, the fluorescent nanoparticles (denoted as AIETPANPs) formed by embedding (E)-4-(4-(diphenylamino)styryl)-1-octadecylpyridin-1-ium iodide (TPA) in PS showed orange-red fluorescence emission and have high fluorescence quantum yield. Anti-CRP antibody (mAb1) could be effectively conjugated to the surface of AIETPANPs by an amino-carboxyl reaction, resulting in AIETPANPs-mAb1. The AIETPANPs-mAb1 exhibited a fluorescence emission at 613 nm, a point detectable by the naked eye with minimal background interference. The entire analysis was accomplished in just 10 min, achieving a limit of detection of 4.06 ng/mL for CRP. The AIETPANPs-mAb1-based LFA demonstrates excellent stability and specificity and fully meets the requirements for clinical diagnosis.

Bifunctional bovine serum albumin modification driven sensitivity-enhanced lateral flow immunoassay for small molecule hazards monitoring in food

Traditional lateral flow immunoassays (TLFIAs) are valued for their simplicity, speed, and user-friendliness. However, the specificity of conventional test strips often necessitates large quantities of antigen-protein conjugates for target detection, which can be resource-intensive. Here, we present a strategy aimed at enhancing the universality of test strips while reducing the consumption of antigen-protein conjugates, without compromising sensitivity. By coating streptavidin on the test line and employing bifunctional antigen-protein conjugates (competitor to target and immunoprobe linker), the test strip was thus served as a universal module. We developed three universal lateral flow immunoassays (ULFIAs) for the detection of aflatoxin B1 (AFB1), carbendazim (CBZ), and enrofloxacin (ENR). Compared to traditional methods based on the same aggregation-induced emission fluorescent microspheres, the proposed ULFIAs demonstrated a significant increase in sensitivity, with enhancements of 11.0-fold for AFB1, 10.9-fold for CBZ, and 4.1-fold for ENR. Additionally, this approach substantially reduced the consumption of antigen-protein conjugates by 19.1-fold, 40.9-fold, and 23.8-fold, respectively, thereby promoting greener detection methods. This bifunctional antigen conjugate strategy offers a promising pathway for the sensitive detection of small molecule hazards.

Plasmonic enzyme immunoassay via nanobody-driven controllable aggregation of gold nanoparticles for detection of ochratoxin A in pepper

Ochratoxin A (OTA) in food poses a serious challenge to public health. Herein, using the nanobody-driven controllable aggregation of gold nanoparticles (AuNPs) in a glucose oxidase-tyramine-horseradish peroxidase (GOx-TYR-HRP) system, we propose a direct competitive plasmonic enzyme immunoassay (dc-PEIA) for OTA detection. The OTA-GOx conjugate catalyzes glucose to produce hydrogen peroxide (H2O2), and then HRP catalyzes H2O2 to generate hydroxyl radical which induces the crosslink of TYR. Crosslinked TYR leads to aggregation of AuNPs through strong electrostatic interactions, which is tunable based on the competition of OTA-GOx and free OTA for binding the immobilized nanobody. The optimized dc-PEIA achieves an instrumental limit of detection (LOD) of 0.275 ng/mL and a visual LOD of 1.56 ng/mL. It exhibits good selectivity for OTA and accuracy in the analysis of pepper samples, with the confirmation of high-performance liquid chromatography. Overall, the dc-PEIA is demonstrated as a useful tool for detecting OTA in food.

Aggregation-induced emission nanoparticles facilitating multicolor lateral flow immunoassay for rapid and simultaneous detection of aflatoxin B1 and zearalenone

Herein we developed a multicolor lateral flow immunoassay (LFIA) test strip for rapid and simultaneous quantitative detection of aflatoxin B1 (AFB1) and zearalenone (ZEN). Three differently colored aggregation-induced emission nanoparticles (AIENPs) were designed as LFIA signal tags, with red and green AIENPs for targeting AFB1 and ZEN at the test line, and yellow AIENPs for indicating the validity of the test strip at the control (C) line. After surface functionalization with antibodies, the developed AIENP-based multicolor LFIA allows simultaneous and accurate quantification of AFB1 and ZEN using an independent C-line assisted ratiometric signal output strategy. The detection limits of AFB1 and ZEN were 6.12 and 26 pg/mL, respectively. The potential of this method for real-world applications was well demonstrated in corn and wheat. Overall, this multicolor LFIA shows great potential for field screening of multiple mycotoxins and can be extended to rapid and simultaneous monitoring of other small molecule targets.

A nanoparticle-assisted signal-enhancement technique for lateral flow immunoassays

Lateral flow immunoassay (LFIA), an affordable and rapid paper-based detection technology, is employed extensively in clinical diagnosis, environmental monitoring, and food safety analysis. The COVID-19 pandemic underscored the validity and adoption of LFIA in performing large-scale clinical and public health testing. The unprecedented demand for prompt diagnostic responses and advances in nanotechnology have fueled the rise of next-generation LFIA technologies. The utilization of nanoparticles to amplify signals represents an innovative approach aimed at augmenting LFIA sensitivity. This review probes the nanoparticle-assisted amplification strategies in LFIA applications to secure low detection limits and expedited response rates. Emphasis is placed on comprehending the correlation between the physicochemical properties of nanoparticles and LFIA performance. Lastly, we shed light on the challenges and opportunities in this prolific field.

A simple and reliable interenzyme distance regulation strategy based on a DNA quadrangular prism scaffold for ultrasensitive ochratoxin A detection

Developing sensitive and accurate Ochratoxin A (OTA) detection methods is essential for food safety. Herein, a simple and reliable strategy for regulating interenzyme distance based on a rigid DNA quadrangular prism as a scaffold was proposed to establish a new electrochemical biosensor for ultrasensitive detection of OTA. The interenzyme distances were precisely adjusted by changing the sequences of the hybridized portions of hairpins SH1 and SH2 to the DNA quadrangular prism, avoiding the complexity and instability of the previous DNA scaffold-based enzyme spacing adjustment strategies. The electrochemical biosensor constructed at the optimal interenzyme distance (10.4 nm) achieved sensitive detection of OTA in a dynamic concentration range from 10 fg/mL to 250 ng/mL with a detection limit of 3.1 fg/mL. In addition, the biosensor was applied to quantify OTA in real samples, exhibiting great application potential in food safety.

Aptamer-modified paper-based analytical devices for the detection of food hazards: Emerging applications and future perspective

Food analysis plays a critical role in assessing human health risks and monitoring food quality and safety. Currently, there is a pressing need for a reliable, portable, and quick recognition element for point-of-care testing (POCT) to better serve the demands of on-site food analysis. Aptamer-modified paper-based analytical devices (Apt-PADs) have excellent characteristics of high portability, high sensitivity, high specificity, and on-site detection, which have been widely used and concerned in the field of food safety. The article reviews the basic components and working principles of Apt-PADs, and introduces their representative applications detecting food hazards. Finally, the advantages, challenges, and future directions of Apt-PADs-based sensing performance are discussed, to provide new directions and insights for researchers to select appropriate Apt-PADs according to specific applications.

Magnetically actuated microfluidic chip combined with a G-quadruplex DNAzyme-based fluorescent/colorimetric sensor for the dual-mode detection of ochratoxin A in wheat

In this work, a portable fluorescent/colorimetric sensor based on G-quadruplex DNAzyme was constructed to achieve rapid and dual-mode detection of ochratoxin A (OTA) in wheat. OTA aptamers coupled with magnetic beads (MBs) can self-assemble with two segments of DNA and hemin to form a G-quadruplex DNAzyme structure that can catalyze the oxidation of Amplex Red (ADHP) with H2O2, making the solution red and producing strong fluorescence in solution. However, in the presence of OTA, the structure of the G-quadruplex DNAzyme was damaged, resulting in reduced catalytic activity. According to the principle of detection, a magnet-controlled chip integrating the reaction, washing, and detection was designed in this study. Shuttling the MB-DNAzyme probes onto a magnetically controlled chip considerably reduced the background signal and improved the detection efficiency and sensitivity. In addition, a portable fluorescence and colorimetric detection platform was built for on-site OTA detection.