Synthesis and application of quantum dots in detection of environmental contaminants in food: A comprehensive review

Advanced chemically modified electrodes and platforms in food analysis and monitoring

Electrochemical sensors and electroanalytical techniques become emerging as effective and low-cost tools for rapid assessment of special parameters of the food quality. Chemically modified electrodes are developed to change properties and behaviour, particularly sensitivity and selectivity, of conventional electroanalytical sensors. Within this comprehensive review, novel trends in chemical modifiers material structure, electrodes construction and flow analysis platforms are described and evaluated. Numerous recent application examples for the detection of food specific analytes are presented in a form of table to stimulate further development in both, the basic research and commercial field.

CdTe@ZnS quantum dots for rapid detection of organophosphorus pesticide in agricultural products

Organophosphorus pesticides (OPPs) constitute the most widely employed class of pesticides. However, the prevalent use of OPPs, while advantageous, raises concerns due to their toxicity, posing serious threats to food safety. Chemical sensors utilizing quantum dots (QDs) demonstrate promising applications in rapidly detecting OPPs residues, thereby facilitating efficient inspection of agricultural products. In this study, we employ an aqueous synthesis approach to prepare low toxic CdTe@ZnS QDs with stable fluorescence properties. To mitigate the risk of imprecise measurements stemming from the inherent susceptibility of fluorescence to quenching, we have adopted the principle of fluorescence resonance energy transfer (FRET) for the construction of the turn-on quantum dot sensor. With a detection limit for chlorpyrifos as low as 10 ppb (10 μg/L), the QDs sensor exhibits notable resistance to interference from various pesticides. Application of this system to detect organophosphorothioate pesticides in apples produced results consistent with those obtained from high-performance liquid chromatography (HPLC) detection, affirming the promising application prospects of this sensing system for the rapid detection of OPPs residues.

A highly efficient and selective rapid detection method applied to the detection of amide herbicides in fish serum

Misuse of amide herbicides in the fisheries environment can pose unpredictable harm to aquatic products and ultimately human health. Thus, the development of a real-time, rapid on-site detection method is crucial. This study proposes for the first time, a paper-based visual detection method for amide herbicides in fish serum, by coating the molecularly imprinted polymer layer onto quantum dots, prepared fluorescent sensing materials (QDs@MIPs) for the detection of amide herbicides in aquatic products. These materials specifically cause fluorescence quenching in the presence of amide herbicides resulting in a color change. For practical application, this research designed a rapid test strip based on QDs@MIPs, meanwhile, incorporate a smartphone or a fluorescence spectrophotometer for qualitative and quantitative measurements, the limit of detection ranges of 0.061-0.500 μM. The method can be used for on-site evaluation of aquatic products, providing new technology for monitoring the safety of aquatic products.

Elevating nanomaterial optical sensor arrays through the integration of advanced machine learning techniques for enhancing visual inspection of food quality and safety

Food quality and safety problems caused by inefficient control in the food chain have significant implications for human health, social stability, and economic progress and optical sensor arrays (OSAs) can effectively address these challenges. This review aims to summarize the recent applications of nanomaterials-based OSA for food quality and safety visual monitoring, including colourimetric sensor array (CSA) and fluorescent sensor array (FSA). First, the fundamental properties of various advanced nanomaterials, mainly including metal nanoparticles (MNPs) and nanoclusters (MNCs), quantum dots (QDs), upconversion nanoparticles (UCNPs), and others, were described. Besides, the diverse machine learning (ML) and deep learning (DL) methods of high-dimensional data obtained from the responses between different sensing elements and analytes were presented. Moreover, the recent and representative applications in pesticide residues, heavy metal ions, bacterial contamination, antioxidants, flavor matters, and food freshness detection were comprehensively summarized. Finally, the challenges and future perspectives for nanomaterials-based OSAs are discussed. It is believed that with the advancements in artificial intelligence (AI) techniques and integrated technology, nanomaterials-based OSAs are expected to be an intelligent, effective, and rapid tool for food quality assessment and safety control.

Quantum dots as advanced nanomaterials for food quality and safety applications: A comprehensive review and future perspectives

The importance of food quality and safety lies in ensuring the best product quality to meet consumer demands and public health. Advanced technologies play a crucial role in minimizing the risk of foodborne illnesses, contamination, drug residue, and other potential hazards in food. Significant materials and technological advancements have been made throughout the food supply chain. Among them, quantum dots (QDs), as a class of advanced nanomaterials with unique physicochemical properties, are progressively demonstrating their value in the field of food quality and safety. This review aims to explore cutting-edge research on the different applications of QDs in food quality and safety, including encapsulation of bioactive compounds, detection of food analytes, food preservation and packaging, and intelligent food freshness indicators. Moreover, the modification strategies and potential toxicities of diverse QDs are outlined, which can affect performance and hinder applications in the food industry. The findings suggested that QDs are mainly used in analyte detection and active/intelligent food packaging. Various food analytes can be detected using QD-based sensors, including heavy metal ions, pesticides, antibiotics, microorganisms, additives, and functional components. Moreover, QD incorporation aided in improving the antibacterial and antioxidant activities of film/coatings, resulting in extended shelf life for packaged food. Finally, the perspectives and critical challenges for the productivity, toxicity, and practical application of QDs are also summarized. By consolidating these essential aspects into this review, the way for developing high-performance QD-based nanomaterials is presented for researchers and food technologists to better capitalize upon this technology in food applications.

Visual monitoring of biocatalytic processes using small molecular fluorescent probes: strategies-mechanisms-applications

Real-time monitoring of biocatalytic-based processes is significantly improved and simplified when they can be visualized. Visual monitoring can be achieved by integrating a fluorescent unit with the biocatalyst. Herein, we outline the design strategies of fluorescent probes for monitoring biocatalysis: (1) probes for monitoring biocatalytic transfer: γ-glutamine is linked to the fluorophore as both a recognition group and for intramolecular charge transfer (ICT) inhibition; the probe is initially in an off state and is activated via the transfer of the γ-glutamine group and the release of the free amino group, which results in restoration of the "Donor-π-Acceptor" (D-π-A) system and fluorescence recovery. (2) Probes for monitoring biocatalytic oxidation: a propylamine is connected to the fluorophore as a recognition group, which cages the hydroxyl group, leading to the inhibition of ICT; propylamine is oxidized and subsequently β-elimination occurs, resulting in exposure of the hydroxyl group and fluorescence recovery. (3) Probes for monitoring biocatalytic reduction: a nitro group attached to a fluorophore as a fluorescence quenching group, this is converted to an amino group by catalytic reduction, resulting in fluorescence recovery. (4) Probes for monitoring biocatalytic hydrolysis: β-D-galactopyranoside or phosphate acts as a recognition group attached to hydroxyl groups of the fluorophore; the subsequent biocatalytic hydrolysis reaction releases the hydroxyl group resulting in fluorescence recovery. Following these 4 mechanisms, fluorophores including cyanine, coumarin, rhodamine, and Nile-red, have been used to develop systems for monitoring biocatalytic reactions. We anticipate that these strategies will result in systems able to rapidly diagnose and facilitate the treatment of serious diseases.

Quantum Dot-Based Immunoassays: Unraveling Sensitivity Discrepancies and Charting Future Frontiers

The 2023 Nobel Prize in Chemistry honors the groundbreaking contributions of Alexei Ekimov, Louis Brus, and Moungi Bawendi to the field of quantum dots (QDs). In this spirit, we developed a direct competitive QD fluorescence immunoassay (dc-QD-FLISA) to detect aristolochic acid type I (AAI), a potent carcinogen found in herbal remedies. Unexpectedly, the dc-QD-FLISA exhibited lower sensitivity than that of an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA), contrary to our initial expectations. This discrepancy in the sensitivity prompted a comprehensive analysis of the entire experimental process. We propose that steric hindrance between QDs and antigen-binding sites on antibodies may significantly diminish the binding efficiency, reducing sensitivity within the dc-QD-FLISA method. Furthermore, issues such as buffer conditions, antibody handling, and separation methods are also contributing factors. We recommend site-directed QD modification and stringent consideration of the experimental conditions. This study not only provides insights into QD-based immunoassays but also highlights the need for future advancements in immunoassay technology in terms of augmenting sensitivity and specificity, potentially revolutionizing disease diagnosis, biomarker discovery, and biomedical research.

Photoluminescence from Two-Phase Nanocomposites Embedded in Polymers

A set of polymer-embedded, two-colored nanocomposites were prepared where the co-existing emission peaks (~578 nm and ~650 nm) had different ratios at their emission thresholds. The nanocomposite samples were simultaneously excited by a 405 nm laser, and the growth of photoluminescence intensities was studied as a function of excitation intensity. The two peaks showed different growth evolution mechanisms. The factors impacting this difference could be (1) energy transfer between the two sized nanoparticles; (2) relaxation mechanism of smaller nanoparticles; and (3) material properties of the polymer.

Boric Acid-Functionalized Carbon Dots as a High-Performance Antibacterial Agent against Escherichia coli

Bacterial infections and antibiotic abuse are a global threat to human health. In recent years, there has been a boom in research on antimicrobial agents with low toxicity and efficient nanomaterials. Boric acid-functionalized carbon dots (B-CDs) with negative surface charge were synthesized by the hydrothermal method. Covalent bonds were formed between the boric acid groups and the cis-diol groups of the polysaccharide in the bacterial cell wall, and numerous B-CDs were trapped on the bacterial surface. In the experiments of antibacterial activity, B-CDs presented strong bactericidal activity against Escherichia coli (E. coli) with a minimum bactericidal concentration of 12.5 μg/mL. The antibacterial mechanism suggested that B-CDs entered the cell interior by diffusion and posed significant damage to the double helix structure of E. coli DNA. Furthermore, B-CDs exhibited low toxicity. The results demonstrated that the novel antimicrobial B-CDs not only fought against E. coli infection and antibiotic misuse but also provided new ideas for safe and effective antimicrobial agents of carbon nanomaterials.