Quantitative detection of aflatoxin B1 using quantum dots-based immunoassay in a recyclable gravity-driven microfluidic chip

Recent advances in nucleic acid signal amplification-based aptasensors for sensing mycotoxins

Mycotoxin contamination in food products may cause serious health hazards and economic losses. The effective control and accurate detection of mycotoxins have become a global concern. Even though a variety of methods have been developed for mycotoxin detection, most conventional methods suffer from complicated operation procedures, low sensitivity, high cost, and long assay time. Therefore, the development of simple and sensitive methods for mycotoxin assay is highly needed. The introduction of nucleic acid signal amplification technology (NASAT) into aptasensors significantly improves the sensitivity and facilitates the detection of mycotoxins. Herein, we give a comprehensive review of the recent advances in NASAT-based aptasensors for assaying mycotoxins and summarize the principles, features, and applications of NASAT-based aptasensors. Moreover, we highlight the challenges and prospects in the field, including the simultaneous detection of multiple mycotoxins and the development of portable devices for field detection.

A review of SERS coupled microfluidic platforms: From configurations to applications

Microfluidic systems have attracted considerable attention due to their low reagent consumption, short analysis time, and ease of integration in comparison to conventional methods, but still suffer from shortcomings in sensitivity and selectivity. Surface enhanced Raman scattering (SERS) offers several advantages in the detection of compounds, including label-free detection at the single-molecule level, and the narrow Raman peak width for multiplexing. Combining microfluidics with SERS is a viable way to improve their detection sensitivity. Researchers have recently developed several SERS coupled microfluidic platforms with substantial potential for biomolecular detection, cellular and bacterial analysis, and hazardous substance detection. We review the current development of SERS coupled microfluidic platforms, illustrate their detection principles and construction, and summarize the latest applications in biology, environmental protection and food safety. In addition, we innovatively summarize the current status of SERS coupled multi-mode microfluidic platforms with other detection technologies. Finally, we discuss the challenges and countermeasures during the development of SERS coupled microfluidic platforms, as well as predict the future development trend of SERS coupled microfluidic platforms.

Microfluidics in environmental analysis: advancements, challenges, and future prospects for rapid and efficient monitoring

Microfluidic devices have emerged as advantageous tools for detecting environmental contaminants due to their portability, ease of use, cost-effectiveness, and rapid response capabilities. These devices have wide-ranging applications in environmental monitoring of air, water, and soil matrices, and have also been applied to agricultural monitoring. Although several previous reviews have explored microfluidic devices' utility, this paper presents an up-to-date account of the latest advancements in this field for environmental monitoring, looking back at the past five years. In this review, we discuss devices for prominent contaminants such as heavy metals, pesticides, nutrients, microorganisms, per- and polyfluoroalkyl substances (PFAS), etc. We cover numerous detection methods (electrochemical, colorimetric, fluorescent, etc.) and critically assess the current state of microfluidic devices for environmental monitoring, highlighting both their successes and limitations. Moreover, we propose potential strategies to mitigate these limitations and offer valuable insights into future research and development directions.

Multiple Isothermal Amplification Coupled with CRISPR-Cas14a for the Naked-eye and Colorimetric Detection of Aflatoxin B1

Aflatoxin B1 (AFB1) is highly toxic and challenging to remove, posing significant risks to both human health and economic development. Therefore, there is an urgent need to develop rapid, simple, and sensitive detection technologies. In this study, we introduce a naked-eye and colorimetric method based on multiple isothermal amplifications coupled with CRISPR-Cas14a and investigate its biosensing properties. This technique utilizes composite nanoprobes (MAPs) comprising magnetic nanoparticles and gold nanoparticles. AFB1 is efficiently identified through an aptamer competition process facilitated by magnetic nanoparticles , which triggers multiple isothermal amplification. This converts trace amounts of the toxin into a large quantity of DNA signal. Upon specific activation of the CRISPR-Cas14a complex, the MAPs are cleaved, resulting in significant changes in both color and colorimetric signal. The method demonstrates acceptable sensitivity, with a detection limit of 31.90 pg mL-1 and a wide detection range from 0.05 to 10 ng mL-1. Furthermore, the assay exhibits satisfactory specificity and high accuracy when it is applied to practical samples. Our approach offers a universal sensing platform with potential applications in food safety, environmental monitoring, and clinical diagnostics.

Application of microfluidic technology based on surface-enhanced Raman scattering in cancer biomarker detection: A review

With the continuous discovery and research of predictive cancer-related biomarkers, liquid biopsy shows great potential in cancer diagnosis. Surface-enhanced Raman scattering (SERS) and microfluidic technology have received much attention among the various cancer biomarker detection methods. The former has ultrahigh detection sensitivity and can provide a unique fingerprint. In contrast, the latter has the characteristics of miniaturization and integration, which can realize accurate control of the detection samples and high-throughput detection through design. Both have the potential for point-of-care testing (POCT), and their combination (lab-on-a-chip SERS (LoC-SERS)) shows good compatibility. In this paper, the basic situation of circulating proteins, circulating tumor cells, exosomes, circulating tumor DNA (ctDNA), and microRNA (miRNA) in the diagnosis of various cancers is reviewed, and the detection research of these biomarkers by the LoC-SERS platform in recent years is described in detail. At the same time, the challenges and future development of the platform are discussed at the end of the review. Summarizing the current technology is expected to provide a reference for scholars engaged in related work and interested in this field.

Microfluidic Biosensor Integrated with Signal Transduction and Enhancement Mechanism for Ultrasensitive Noncompetitive Assay of Multiple Mycotoxins

To achieve high-throughput ultrasensitive detection of mycotoxins in food, a functional DNA-guided transition-state CRISPR/Cas12a microfluidic biosensor (named FTMB) was successfully constructed. The signal transduction CRISPR/Cas12a strategy in FTMB has utilized DNA sequences with a specific recognition function and activators to form trigger switches. Meanwhile, the transition-state CRISPR/Cas12a system was constructed by adjusting the composition ratio of crRNA and activator to achieve a high response for low concentrations of target mycotoxins. On the other hand, the signal enhancement of FTMB has efficiently integrated the signal output of quantum dots (QDs) with the fluorescence enhancement effect of photonic crystals (PCs). The construction of universal QDs for the CRISPR/Cas12a system and PC films matching the photonic bandgap produced a significant signal enhancement by a factor of 45.6. Overall, FTMB exhibited a wide analytic range (10^-5-10¹ ng·mL^-1), low detection of limit (fg·mL^-1), short detection period (∼40 min), high specificity, good precision (coefficients of variation <5%), and satisfactory practical sample analysis capacity (the consistency with HPLC at 88.76%-109.99%). It would provide a new and reliable solution for the rapid detection of multiple small molecules in the fields of clinical diagnosis and food safety.

Inner filter effect-based near-infrared fluorescent probe for detection of metronidazole on a smartphone-integrated analytical platform

Antibiotic residues pose a serious threat to ecosystems and food safety. Developing convenient, visual, and on-site detection methods is therefore in high demand and has a practical purpose. In this work, a near-infrared (NIR) fluorescent probe with an analysis platform based on a smartphone has been constructed for quantitative and on-site detection of metronidazole (MNZ). CdTe quantum dots with NIR emission at 710 nm (QD710) were prepared by using a simple hydrothermal method and showed good properties. A spectral overlap between absorption of MNZ and excitation of QD710 resulted in an effective inner filter effect (IFE) between QD710 and MNZ. Because of the IFE, the fluorescence of QD710 decreased gradually with increasing concentrations of MNZ. Based on the fluorescence response, quantitative detection and visualization of MNZ was achieved. NIR fluorescence analysis and the special IFE between probe and target can improve sensitivity and selectivity for MNZ. Additionally, these were also utilized for quantitative detection of MNZ in real food samples and the results were reliable and satisfactory. Meanwhile, a portable visual analysis platform in a smartphone was constructed for on-site analysis of MNZ, which can be used as an alternative method for detection of MNZ residues in situations with limited instrumental conditions. Therefore, this work provides a convenient, visual, and real-time analysis method for detection of MNZ and the analysis platform shows great potential for commercialization.

A User-Centric 3D-Printed Modular Peristaltic Pump for Microfluidic Perfusion Applications

Microfluidic organ-on-a-chip (OoC) technology has enabled studies on dynamic physiological conditions as well as being deployed in drug testing applications. A microfluidic pump is an essential component to perform perfusion cell culture in OoC devices. However, it is challenging to have a single pump that can fulfil both the customization function needed to mimic a myriad of physiological flow rates and profiles found in vivo and multiplexing requirements (i.e., low cost, small footprint) for drug testing operations. The advent of 3D printing technology and open-source programmable electronic controllers presents an opportunity to democratize the fabrication of mini-peristaltic pumps suitable for microfluidic applications at a fraction of the cost of commercial microfluidic pumps. However, existing 3D-printed peristaltic pumps have mainly focused on demonstrating the feasibility of using 3D printing to fabricate the structural components of the pump and neglected user experience and customization capability. Here, we present a user-centric programmable 3D-printed mini-peristaltic pump with a compact design and low manufacturing cost (~USD 175) suitable for perfusion OoC culture applications. The pump consists of a user-friendly, wired electronic module that controls the operation of a peristaltic pump module. The peristaltic pump module comprises an air-sealed stepper motor connected to a 3D-printed peristaltic assembly, which can withstand the high-humidity environment of a cell culture incubator. We demonstrated that this pump allows users to either program the electronic module or use different-sized tubing to deliver a wide range of flow rates and flow profiles. The pump also has multiplexing capability as it can accommodate multiple tubing. The performance and user-friendliness of this low-cost, compact pump can be easily deployed for various OoC applications.

MnO2 nanosheets-triggered oxVB1 fluorescence immunoassay for detection zearalenone

In this study, an alkaline phosphatase (ALP)-mediated fluorescence immunoassay for detecting zearalenone (ZEN) was established based on the oxVB₁ fluorescence signal modulated by MnO₂ nanosheets (MnO₂ NS). As the ALP-antibody content increased, more 2-phosphoascorbic acid (AAP) was hydrolyzed to ascorbic acid (AA) which destroyed the MnO₂ NS rapidly. In the lack of MnO₂ NS, VB₁ cannot be oxidized to oxVB₁ for emitting fluorescence. On the contrary, the fluorescence of oxVB₁ recovered slowly with the decrease of the ALP-antibody concentration. In the optimization condition, the detection limit of this method was 15.5 pg mL^-1. Moreover, the recovery of ZEN in real samples ranged from 94.24 % to 108.26 %, which indicated the remarkable accuracy and reliability of this approach. Meanwhile, the proposal of this fluorescence immunoassay provided a new possibility for detecting other targets by replacing antibodies and antigens.

A microfluidic immunosensor based on magnetic separation for rapid detection of okadaic acid in marine shellfish

Okadaic acid (OA) is a marine biotoxin that accumulates in seafood and can cause diarrheic shellfish poisoning if consumed. Accordingly, many countries have established regulatory limits for the content of OA in shellfish. At present, methods used for the detection of marine toxins are time-consuming and labor-intensive. In order to realize rapid, simple, and accurate detection of OA, we developed a novel microfluidic immunosensor based on magnetic beads modified with a highly specific and sensitive monoclonal antibody (mAb) against OA that is used in conjunction with smartphone imaging to realize the rapid detection of OA in shellfish. The method achieves on-site detection results within 1 h with an IC₅₀ value of 3.30 ng/mL for OA and a limit of detection (LOD) of 0.49 ng/mL. In addition, the analysis of real samples showed that the recoveries for spiked shellfish samples ranged from 84.91% to 95.18%, and the results were confirmed by indirect competitive enzyme-linked immunosorbent assay (icELISA), indicating that the method has good accuracy and precision. Furthermore, the results are reported in a specially designed smartphone app. The microfluidic immunosensor has the advantages of simple operation, rapid detection, and high sensitivity, providing a reliable technical solution for detecting OA residues in shellfish.

Target-responsive aptamer-cross-linked hydrogel sensors for the visual quantitative detection of aflatoxin B1 using exonuclease I-Triggered target cyclic amplification

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An AFB₁-responsive aptamer-cross-linked hydrogel sensor was successfully constructed.

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Dual signal amplification strategy with Encapsulation of enzymesand exonuclease I.

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This method has great potential for AFB₁ detection in peanut oil.

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The accuracy and consistency repeatability of this method are close to those of UPLC-HRMS.

For the on-site detection of aflatoxin B₁ (AFB₁), a DNA hydrogel was prepared as a biosensor substrate, while an AFB₁ aptamer was used as the recognition element. An AFB₁-responsive aptamer-cross-linked hydrogel sensor was constructed using an enzyme-linked signal amplification strategy; AFB₁ binds competitively to the aptamer, causing the hydrogel to undergo cleavage and release horseradish peroxidase (HRP). The addition of exonuclease I (ExoI) to the hydrogel causes the release of AFB₁ from the aptamer, promoting additional hydrogel cleavage to release more HRP, ultimately catalysing the reaction between 3,3′,5,5′-tetramethylbenzidine and H₂O₂. The hydrogel sensor exhibited an outstanding sensitivity (limit of detection, 4.93 nM; dynamic range, 0–500 nM), and its selectivity towards seven other mycotoxins was confirmed. The feasibility and reliability were verified by measuring the AFB₁ levels in peanut oil (recoveries, 89.59–95.66 %; relative standard deviation, <7%); the obtained results were comparable to those obtained by UPLC-HRMS.

Quantum-Dot-Bead-Based Fluorescence-Linked Immunosorbent Assay for Sensitive Detection of Cry2A Toxin in Cereals Using Nanobodies

In this study, a quantum-dot-bead (QB)-based fluorescence-linked immunosorbent assay (FLISA) using nanobodies was established for sensitive determination of the Cry2A toxin in cereal. QBs were used as the fluorescent probe and conjugated with a Cry2A polyclonal antibody. An anti-Cry2A nanobody P2 was expressed and used as the capture antibody. The results revealed that the low detection limit of the developed QB-FLISA was 0.41 ng/mL, which had a 19-times higher sensitivity than the traditional colorimetric ELISA. The proposed assay exhibited a high specificity for the Cry2A toxin, and it had no evident cross-reactions with other Cry toxins. The recoveries of Cry2A from the spiked cereal sample ranged from 86.6–117.3%, with a coefficient of variation lower than 9%. Moreover, sample analysis results of the QB-FLISA and commercial ELISA kit correlated well with each other. These results indicated that the developed QB-FLISA provides a potential approach for the sensitive determination of the Cry2A toxin in cereals.

Magnetic Relaxation Switching Immunoassay Based on Hydrogen Peroxide-Mediated Assembly of Ag@Au-Fe3 O4 Nanoprobe for Detection of Aflatoxin B1

Magnetic relaxation switching (MRS) sensors have shown great potential in food safety monitoring due to their high signal-to-noise ratio and simplicity, but they often suffer from insufficient sensitivity and stability due to the lack of excellent magnetic nanoprobes. Herein, dumbbell-like Au-Fe₃ O₄ nanoparticles are designed as magnetic nanoprobes for developing an aflatoxin B1-MRS immunosensor. The Fe₃ O₄ portion in the Au-Fe₃ O₄ nanoparticles functions as the magnetic probe to provide transverse relaxation signals, while the Au segments serve as a bridge to grow Ag shell and assemble the Au-Fe₃ O₄ nanoparticles, thus modulating transverse relaxation time of surrounding water molecular. The formation of Ag@Au-Fe₃ O₄ is triggered by hydrogen peroxide. After degraded by horseradish peroxidase, hydrogen peroxide reduces Ag⁺ to Ag nanoparticles which assemble dispersed Au-Fe₃ O₄ to aggregated Ag@Au-Fe₃ O₄ , thus dramatically improving the sensitivity of traditional MRS sensor. Combined with competitive immunoreaction, this Ag@Au-Fe₃ O₄ -MRS immunosensor can detect aflatoxin B1 with a high sensitivity (3.81 pg mL^-1 ), which improved about 21 folds and 9 folds than those of enzyme-linked immunosorbent assay and high-performance liquid chromatography (HPLC), respectively. The good consistency with HPLC in real samples detection indicates the good accuracy of this immunosensor. This Ag@Au-Fe₃ O₄ -MRS immunosensor offers an attractive tool for detection of harmful substances.