Accurate identification of acutely toxic and low-fatality mycotoxins on a large scale in a quick and cheap manner is critical for reducing population mortality. Herein, a portable photothermal immunosensing platform supported by a microelectromechanical microsystem (MEMS) without enzyme involvement was reported for point-of-care testing of mycotoxins (in the case of aflatoxin B1, AFB1) in food based on the precise satellite structure of Au nanoparticles. The synthesized Au nanoparticles with a well-defined, graded satellite structure exhibited a significantly enhanced photothermal response and were coupled by AFB1 antibodies to form signal conversion probes by physisorption for further target-promoted competitive responses in microplates. In addition, a coin-sized miniature NIR camera device was constructed for temperature acquisition during target testing based on advanced MEMS fabrication technology to address the limitation of expensive signal acquisition components of current photothermal sensors. The proposed MEMS readout-based microphotothermal test method provides excellent AFB1 response in the range of 0.5-500 ng g-1 with detection limits as low as 0.27 ng g-1. In addition, the main reasons for the efficient photothermal transduction efficiency of Au with different graded structures were analyzed by finite element simulations, providing theoretical guidance for the development of new Au-based photothermal agents. In conclusion, the proposed portable micro-photothermal test system offers great potential for point-of-care diagnostics for residents, which will continue to facilitate immediate food safety identification in resource-limited regions.

Microelectromechanical Microsystems-Supported Photothermal Immunoassay for Point-of-Care Testing of Aflatoxin B1 in Foodstuff.

Aflatoxins are a kind of fungal toxin that causes great damage to humans and animals due to its wide distribution, secretive nature, and high toxicity. For the purpose of achieving qualitative and quantitative detection of aflatoxin B1 (AFB1), a novel tri-taper-in-taper fiber-optic structure based on core mismatch of four-core fiber with a multimode fiber-based WaveFlex biosensor is developed and tested. The sensor probe's surface is coated with gold nanoparticles (AuNPs). Multi-walled carbon nanotubes and zinc oxide nanoparticles are sequentially immobilized on the sensing probe surface to enhance the sensor's sensing capabilities. Then, the AFB1 antibody is utilized to functionalize the sensor to possess specific selectivity. After the modification of nanomaterials and the corresponding bioreceptors, the final sensor structure is formed. By stimulating the localized surface plasmon resonance phenomenon of AuNPs, different concentrations of AFB1 can be detected. The sensor demonstrates high sensitivity (38.29 nm/μM) as well as low LOD (7.12 nM) within the range of 0–100 nM for detection. The sensor is also found to be stable and reproducible in repeated measurements, indicating its potential for practical application. Additionally, it exhibits satisfactory specific recognition of AFB1. These results show that AFB1 can be detected in food and agricultural products using LSPR-based optical fiber sensors, which could have significant ramifications for public health and food safety.

WaveFlex Biosensor-Using Novel Tri-Tapered-in-Tapered Four-Core Fiber With Multimode Fiber Coupling for Detection of Aflatoxin B1

Green chemistry methods for food analysis: Overview of sample preparation and determination

The global food safety issues caused by exogenous contaminants have posed increasing threat to public health. Reliable sensing approach with excellent performance for the sensitive detection of these contaminants is in great necessity and urgency in food safety control. Metal-organic frameworks (MOFs), a new class of porous crystal materials with fascinating merits of tunable compositions and structures, high porosity, and large and easy-to-functionalize surfaces, have been extensively developed to construct diverse sensors for food safety measurement. The relevant publications have increased exponentially, attracting significant research attention. Therefore, this review summarized the main types of emerging MOFs and the current state-of-the-art synthetic strategies. The MOF-based optical sensors developed over the past five years, such as the colorimetric (CM), fluorescent (FL), electrochemiluminescent (ECL), and surface-enhanced Raman spectroscopy (SERS) series, and electrochemical (EC) sensors were comprehensively discussed regarding their construction, sensing mechanisms, and real-world application for exogenous contaminants including mycotoxins, pesticide residues, and heavy metals in food. Besides highlighting the recent advances and advantages of these MOF-based sensors, their current challenges and future prospects were systematically discussed. This review aimed to provide several beneficial insights regarding the coordination chemistry and performance of MOFs and facilitate the exploration of MOF-based sensing platforms for more hazardous contaminants to guarantee food safety. 

Metal-organic framework (MOF)-based sensors for exogenous contaminants in food: Mechanisms, advances, and prospects

New advanced materials' potential as sorbents during the sample preparation process has recently been highlighted by developments in contemporary analytical chemistry applications. The tunable compositions of advanced materials in combination with the variety of possible surface modifications, provide excellent potential for developing sample preparation techniques for different analytes. Advanced materials have been shown to give higher pre-concentration factors, which improves analytical sensitivity and selectivity to target specific analytes in a variety of matrices. The size of pores, surface area, the stability in thermal and chemical, physical and chemical properties of the sorbent material are crucial for their efficiency as extraction phase. Recent developments in the design and use of advanced materials as an extraction phase in sample preparation will be highlighted in this review, which influences their performance as an extraction phase for analytical sample preparation. We cover a broad range of materials including metal/metal oxide nanomaterials, magnetic nanoparticles, quantum dots, ionic liquids, carbon-based nanomaterials, layered double hydroxides, covalent-organic frameworks, metal–orgaّnic frameworks, polyoxometalates, MXenes, nanofibers, aptamers, conductive polymers, molecularly imprinted materials, restricted access materials, immunosorbent and natural materials. Future applications and challenges associated with the development of new sorbents for analytical applications will be also highlighted. 

Advanced materials in sorbent-based analytical sample preparation

Advances in metal-organic framework-plasmonic metal composites based SERS platforms: Engineering strategies in chemical sensing, practical applications and future perspectives in food safety

Advances of the functionalized covalent organic frameworks for sample preparation in food field

Sulfonic acid-functionalized covalent organic frameworks as the coating for stir bar sorptive extraction of fluoroquinolones in milk samples

In this work, the Cu-based metal−organic frameworks composite, labelled as [email protected] @antibody, was prepared by simple reaction at room temperature to construct a competitive immunocolorimetric Aflatoxin B1(AFB1) sensor. In this assay, the HKUST-1 composite was given a triple function: glucose oxidase(GOx) stabilizer, peroxidase mimic and carrier material of AFB1 antibody. Under coordination modulation of benzoic acid, glucose oxidase encapsulated HKUST-1 presented octahedron with uniform size (average size: 10.3 µm), which was conducive to the immune reaction and magnetic separation. By immune combination and magnetic separation, [email protected] @antibody was redispersed and used as reactor of the cascade to amplify the detection signal. With the help of the external HKUST-1, GOx can catalyze glucose to produce hydrogen peroxide to oxidize 3,3′,5,5′-tetramethylbenzidine (TMB), which turns the solution blue. The target AFB1 can compete with AFB1-BSA-modified Fe3O4 nanoparticles for [email protected] @antibody, which can result to the decreasing of the color signal. The method showed ultra high sensitivity for AFB1 with a detection limit of 0.004 ng mL−1, and high stability owing to the protection effect of HKUST-1 on the GOx and antibody. In addition, such competitive immunoassays can be extended to the detection of other biotoxin targets. 

A novel immunocolorimetric probe for aflatoxin B1 based on multifunctional metal−organic frameworks

A Cellular Automaton-Finite Element (CAFE) model and a secondary dendrite arm spacing (SDAS) model are established to study the evolutionary behavior of the macrostructure and the secondary dendrites on a 295 × 2270 mm2 slab cross-section of experimental steel, respectively. The relationship between the element content, SDAS, equiaxed crystal ratio (ECR) and macrosegregation in continuously cast experimental slabs was studied comprehensively. It is found that with the increase in carbon content, the ECR increases at first and then decreases, and the ECR reaches the maximum value when the carbon content is 0.3%. With the increase in carbon content, the SDAS and average grain size of the equiaxed crystal zone increase, whereas the Si and Al content evidently affects the SDAS and average grain size of the equiaxed crystal zone to a greater extent than the Mn content. In addition, the SDAS can be reduced by reducing the content of C and Si within the acceptable range of alloy composition.

/pdf/effects-of-alloying-elements-on-solidification-structures-1xha3zbb.pdf

Effects of Alloying Elements on Solidification Structures and Macrosegregation in Slabs

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