A simple and sensitive sensor for lactose based on cascade reactions in Au nanoclusters and enzymes co-encapsulated metal-organic frameworks

Imidazole Compounds: Synthesis, Characterization and Application in Optical Analysis

Imidazole is a five-membered heterocyclic ring containing three carbon atoms, two nitrogen atoms, and two double bonds. Among two nitrogen atoms, one of which carries with a hydrogen atom is a pyrrole-type nitrogen atom, another is a pyridine type nitrogen atom. Hence, the imidazole ring belongs to the π electron-rich aromatic ring and can accept strong suction to the electronic group. Moreover, the nitrogen atom of the imidazole ring is coordinated with metal ions to form metal-organic frameworks. In recent years, because of imidazole compounds' unique optical properties, their applications have attracted more and more attention in optical analysis. Thus, this review has summarized the synthesis, characterization, and application with emphasis on the research progress of imidazole compounds in optical analysis, including fluorescence probe, colorimetric probe, electrochemiluminescence sensor, fiber optical sensor, surface plasmon resonance, etc. This paper will suggest the direction for the development of imidazole-containing sensors with high sensitivity and selectivity.

A novel fluorescence sensor based on Al3+-mediated aggregation of gold nanoclusters for determination of citric acid in beverages

This paper revealed a new strategy for citric acid (CA) detection using aggregation-induced emission (AIE)-based fluorescent gold nanoclusters (AuNCs). AuNCs was synthesized using glutathione (GSH) as the template and reducing agent and used as the fluorescent probe to detect CA under aluminum ion (Al3+) mediation. The fluorescence intensity of AuNCs increased about 4 times with the addition of Al3+, but the enhanced fluorescence was quenched after the addition of CA. Based on this fluorescence phenomenon, an "on-off" fluorescence strategy was designed for the sensitive determination of CA and a linear detection range for CA was achieved within 0-80.0 μM. In addition, the developed probe exhibited high selectivity and accuracy for determination of CA. The mechanism of fluorescence enhancement and quenching of AuNCs was explored in detail. The established probe was used successfully for CA detection in beverages. The spiked recoveries from 97.50% to 103.67% were gratifying, which indicated the probe had potential prospects for detecting CA in food.

Recent advances and synergistic effect of bioactive zeolite imidazolate frameworks (ZIFs) for biosensing applications

The rapid developments in the field of zeolitic imidazolate frameworks (ZIFs) in recent years have created unparalleled opportunities for the development of unique bioactive ZIFs for a range of biosensor applications. Integrating bioactive molecules such as DNA, aptamers, and antibodies into ZIFs to create bioactive ZIF composites has attracted great interest. Bioactive ZIF composites have been developed that combine the multiple functions of bioactive molecules with the superior chemical and physical properties of ZIFs. This review thoroughly summarizes the ZIFs as well as the novel strategies for incorporating bioactive molecules into ZIFs. They are used in many different applications, especially in biosensors. Finally, biosensor applications of bioactive ZIFs were investigated in optical (fluorescence and colorimetric) and electrochemical (amperometric, conductometric, and impedance) fields. The surface of ZIFs makes it easier to immobilize bioactive molecules like DNA, enzymes, or antibodies, which in turn enables the construction of cutting-edge, futuristic biosensors.

ZIF-8 encapsulated-enzymes integrated nanozyme cascade biocatalysis platform for the colorimetric sensing of glucose and lactose in milk

Cascade biocatalytic reactions have a wide range of applications, especially in the filed of food analysis. Herein, a multi-enzyme composite (ZGGPC) was prepared by in-situ synthesis of Zeolite imidazole framework-8 (ZIF-8) on Prussian blue (PB) modified carbon cloth (CC). The composite encapsulated both glucose oxidase and β-galactosidase simultaneously during the synthesis process. CC and ZIF-8 showed high loading capacity for PB and natural enzymes, respectively. And ZIF-8 also displayed excellent tolerance in protecting enzyme activity under extreme conditions. Based on the cascade biocatalysis, ZGGPC was used to detect glucose and lactose by colorimetric method with detection limits of 1.2 μM and 1.7 mM, respectively. Benefiting from the merits of low cost, easy preparation, and good stability, the sensing system was used to successfully determine glucose and lactose in different milk samples. The present cascade biocatalysis system is hopeful to develop simple and efficient sensing platforms for food analysis.

A Recent Advancement in Food Quality Assessment: Using MOF-Based Sensors: Challenges and Future Aspects

Monitoring food safety is crucial and significantly impacts the ecosystem and human health. To adequately address food safety problems, a collaborative effort needed from government, industry, and consumers. Modern sensing technologies with outstanding performance are needed to meet the growing demands for quick and accurate food safety monitoring. Recently, emerging sensors for regulating food safety have been extensively explored. Along with the development in sensing technology, the metal-organic frameworks (MOF)-based sensors gained more attention due to their excellent sensing, catalytic, and adsorption properties. This review summarizes the current advancements and applications of MOFs-based sensors, including colorimetric, electrochemical, luminescent, surface-enhanced Raman scattering, and electrochemiluminescent sensors. and also focused on the applications of MOF-based sensors for the monitoring of toxins such as heavy metals, pesticide residues, mycotoxins, pathogens, and illegal food additives from food samples. Future trends, as well as current developments in MOF-based materials.

Nanohybrids of atomically precise metal nanoclusters

Atomically precise metal nanoclusters (NCs) with molecule-like structures are emerging nanomaterials with fascinating chemical and physical properties. Photoluminescence (PL), catalysis, sensing, etc., are some of the most intriguing and promising properties of NCs, making the metal NCs potentially beneficial in different applications. However, long-term instability under ambient conditions is often considered the primary barrier to translational research in the relevant application fields. Creating nanohybrids between such atomically precise NCs and other stable nanomaterials (0, 1, 2, or 3D) can help expand their applicability. Many such recently reported nanohybrids have gained promising attention as a new class of materials in the application field, exhibiting better stability and exciting properties of interest. This perspective highlights such nanohybrids and briefly explains their exciting properties. These hybrids are categorized based on the interactions between the NCs and other materials, such as metal-ligand covalent interactions, hydrogen-bonding, host-guest, hydrophobic, and electrostatic interactions during the formation of nanohybrids. This perspective will also capture some of the new possibilities with such nanohybrids.

Integration of chemo- and bio-catalysis to intensify bioprocesses

Nature has evolved highly efficient and complex systems to perform cascade reactions by the elegant combination of desired enzymes, offering a strategy for achieving efficient bioprocess intensification. Chemoenzymatic cascade reactions (CECRs) merge the complementary strengths of chemo-catalysis and bio-catalysis, such as the wide reactivity of chemo-catalysts and the exquisite selective properties of biocatalysts, representing an important step toward emulating nature to construct artificial systems for achieving bioprocess intensification. However, the incompatibilities between the two catalytic disciplines make CECRs highly challenging. In recent years, great advances have been made to develop strategies for constructing CECRs. In this regard, this chapter introduces the general concepts and representative strategies, including temporal compartmentalization, spatial compartmentalization and chemo-bio nanoreactors. Particularly, we focus on what platform methods and technologies can be used, and how to implement these strategies. The future challenges and strategies in this burgeoning research area are also discussed.

Metal-organic frameworks for food contaminant adsorption and detection

Metal-organic framework materials (MOFs) have been widely used in food contamination adsorption and detection due to their large specific surface area, specific pore structure and flexible post-modification. MOFs with specific pore size can be targeted for selective adsorption of some contaminants and can be used as pretreatment and pre-concentration steps to purify samples and enrich target analytes for food contamination detection to improve the detection efficiency. In addition, MOFs, as a new functional material, play an important role in developing new rapid detection methods that are simple, portable, inexpensive and with high sensitivity and accuracy. The aim of this paper is to summarize the latest and insightful research results on MOFs for the adsorption and detection of food contaminants. By summarizing Zn-based, Cu-based and Zr-based MOFs with low cost, easily available raw materials and convenient synthesis conditions, we describe their principles and discuss their applications in chemical and biological contaminant adsorption and sensing detection in terms of stability, adsorption capacity and sensitivity. Finally, we present the limitations and challenges of MOFs in food detection, hoping to provide some ideas for future development.

Application of zeolites and zeolitic imidazolate frameworks in the biosensor development

Biosensors are advanced devices for analysis of composition of blood, urine, environmental samples, and many other media. Their current development is tightly linked with nanomaterials, such as zeolites and zeolitic imidazolate framework (ZIFs). The present review describes electrochemical (amperometric, conductometric, ISFET) and optical (fluorescent and colorimetric) biosensors that incorporate zeolites and ZIFs in their biorecognition elements. The biosensors are based on immobilized enzymes (such as glucose oxidase, urease, and acetylcholinesterase), antibodies, DNA, and aptamers. The review present reasons for application of these nanomaterials, and discusses advantages of zeolite- and ZIF-containing biosensors over other biosensors. In most cases, the biosensors have improved sensitivity, better limit of detection, wider linear range, and other improved characteristics. It is demonstrated that immobilization of biomolecules such as enzymes or antibodies on the surface of zeolites and ZIFs enables creation of unique advanced biosensors that have a potential for further development and practical applications.

Polydopamine-Functionalized Copper Peroxide/ZIF-8 Nanoparticle-Based Fluorescence-Linked Immunosorbent Assay for the Sensitive Determination of Carcinoembryonic Antigen by Self-Supplied H2O2 Generation

Copper peroxide/zeolitic imidazolate framework/polydopamine nanoparticles (CP/ZIF-8/PDA)-based fluorescence-linked immunosorbent assay (FLISA) was designed for the sensitive and high-throughput determination of carcinoembryonic antigen (CEA) by self-supplied H₂O₂ generation. Specifically, the CEA aptamer was modified on the surface of CP/ZIF-8/PDA to form an immunoprobe. The structures of CP and ZIF-8 could be broken under acidic conditions, and produced the Cu²⁺ and H₂O₂ due to the dissociation the CP. A subsequent Fenton-type reaction of Cu²⁺ and H₂O₂ generated hydroxyl radical (·OH). o-phenylenediamine (OPD) was oxidized by the ·OH to form 2, 3-diaminophenazine (DPA) with a significant fluorescence signal. CP/ZIF-8/PDA could be used as an efficient Fenton-type reactant to generate a large amount of ·OH to promote OPD oxidation. The sensitive detection of CEA could be realized. Under optimal conditions, the FLISA platform displayed a linear detection range from 0.01 to 20 ng mL^-1 with a detection limit of 7.6 pg mL^-1 for CEA. This strategy has great application potential for sensitive and high-throughput determination for other biomarkers in the field of biomedicine.

Highly dispersive AuNCs/ChOx@ZIF-8/PEI nanocomplexes for fluorescent detection of cholesterol in human serum

Gold nanoclusters (AuNCs) are widely used in the fluorescence detection of biomolecules in human serum due to their good fluorescence properties, low toxicity, and better biocompatibility. However, the weak fluorescence intensity of AuNCs limits the fluorescence detection of molecules within a wide concentration range. It is reported that coating AuNCs in ZIF-8 with adjustable pore size can effectively improve the fluorescence intensity of AuNCs and broaden the detection range. And the AuNCs wrapped in the gaps of ZIF-8 can prevent the fluorescence quenching caused by the aggregation of AuNCs. However, ZIF-8 has high crystallinity, poor dispersion, and easy deposition, which reduces the fluorescence stability of the detection system and affects the detection. Based on the above research, the highly hydrophilic polymer PEI was modified to the surface of ZIF-8, and a kind of nanocomposite material AuNCs/ChOx@ZIF-8/PEI was obtained by co-encapsulating AuNCs prepared with glutathione as a ligand and cholesterol oxidase (ChOx) into ZIF-8 modified with PEI. The composite material emits strong red light at 650 nm under the excitation of 395-nm light, and the system can sensitively detect cholesterol (Chol) in human serum. Compared with other materials, the PEI-modified composite has better solubility and stability, so the detection effect of Chol is better. Encapsulation of ChOx in the ZIF-8 shell can protect the enzyme and increase the local concentration of ChOx, thereby speeding up the reaction rate. Compared with free AuNCs/ChOx, the quenching rate of AuNCs/ChOx@ZIF-8/PEI system is doubled. Secondly, the addition of Fe²⁺ to the detection process results in higher quenching rate and detection sensitivity. The system can detect Chol in the concentration range 0.1-2.4 μM, with a detection limit of 0.073 μM. The determination is a fast and sensitive strategy. In addition, the practicability of this assay in the detection of Chol in human serum has been verified. Due to its selectivity and sensitivity, it has potential application value in clinical diagnosis.

Highly sensitive colorimetric detection and effective adsorption of phosphate based on MOF-808(Zr/Ce)

MOF-808(Zr/Ce) has been successfully used for the sensitive and rapid detection of phosphate and phosphate removal by effective adsorption.

A self-healing carboxymethyl chitosan/oxidized carboxymethyl cellulose hydrogel with fluorescent bioprobes for glucose detection

Self-healing hydrogel as a soft material with high durability and life-time has been successfully applied in various fields, including electronic skins, wearable electronic devices, and soft sensors. However, it is still a challenge to design a hydrogel with rapid self-healing, biodegradable and biosensing properties. Here, a self-healing carboxymethyl chitosan (CMCS)/oxidized carboxymethyl cellulose (OCMC) hydrogel with fluorescent bioprobes was developed for glucose detection. In this biosensing system, gold nanoclusters (AuNCs) and glucose oxidase (GOx) were encapsulated into the CMCS/OCMC hydrogel matrix as the fluorescent bioprobes. The CMCS/OCMC hydrogel with fluorescent bioprobes exhibited high sensitivity for glucose sensing with a linearly detection range of 100 μM to 5 mM and a detection limit of 0.029 mM, which covered the level of glucose in clinical detection. Furthermore, this hydrogel exhibited good biocompatibility. Finally, In vitro blood fluorescence tests and in vivo fluorescence investigation of the AuNCs-CMCS/OCMC hydrogel in diabetic mice indicated that this biocompatible and self-healing hydrogel based on fluorescent sensing system had potential application in implantable biosensing area for glucose monitoring.

Metal-organic frameworks for food applications: A review

Metal-organic frameworks (MOFs) are high surface-to-volume ratio crystalline hybrid porous coordination materials composed of metal ions as nodes and organic linkers. The goal of this paper was to provide an updated and comprehensive state-of-the-art review of MOFs for different food applications such as active food contact materials, antimicrobial nanocarriers, controlled release nanosystems for active compounds, nanofillers for food packaging materials, food nanoreactors, food substance nanosensors, stabilizers and immobilizers for active compounds and enzymes, and extractors of food contaminants. Extraction and sensing of several food contaminants have been the main food applications of MOFs. The other applications listed above require further investigation, as they are at an early stage. However, interesting results are being reported for these other fields. Finally, an important limitation of MOFs has been the use of non-renewable feedstocks for their synthesis, but this has recently been solved through the manufacture and use of γ-cyclodextrin-based MOFs.

Stabilization of β-Galactosidase on Modified Gold Nanoparticles: A Preliminary Biochemical Study to Obtain Lactose-Free Dairy Products for Lactose-Intolerant Individuals

The unique chemical, optical, and electrical characteristics of nanoparticles make their utilization highly successful in every field of biological sciences as compared to their bulk counterpart. These properties arise as a result of their miniature size, which provides them an excellent surface area-to-volume ratio, inner structure, and shape, and hence increases their surface characteristics. Therefore, this study was undertaken to engineer gold nanoparticles (AuNPs) for improving their catalytic activity and stability in biotechnological processes. The characterization of AuNPs was performed by XRD, UV spectra, and TEM. The synthesized AuNPs were surface-modified by polyvinyl alcohol (PVA) for binding the enzyme in excellent yield. The developed immobilized enzyme system (PVA-AuNPs-β-galactosidase) displayed pH optima at pH 7.0 and temperature optima at 40 °C. Moreover, the stability of PVA-AuNPs-β-galactosidase was significantly enhanced at wider pH and temperature ranges and at higher galactose concentrations, in contrast to the free enzyme. β-galactosidase bound to PVA-modified AuNPs exhibited greater operational activity, even after its sixth reuse. The developed nanosystem may prove useful in producing lactose-free dairy products for lactose-intolerant patients.