Nanozymatic degradation and simultaneous colorimetric detection of tetracycline

Colorimetric/fluorescent dual-mode biosensor based on metalloporphyrin covalently modified NH2-MIL-101(Fe) with highly efficient peroxidase-like activity for the detection of tetracycline in honey samples

Accurate detection of tetracycline residue is of great significance for ensuring product quality and protecting human health. Here, a colorimetric/fluorescent dual-mode biosensor was developed for the detection of tetracycline in honey by using metalloporphyrin [TCPP(Fe)] covalently modified NH2-MIL-101(Fe) [named NH2-MIL-101(Fe)@TCPP(Fe)]. The morphology, chemical structure and peroxidas-like activity of this hybrid nanozyme were comprehensively studied. Based on excellent catalytic activity and intrinsic fluorescence of NH2-MIL-101(Fe)@TCPP(Fe), a colorimetric/fluorescent dual-mode biosensor was developed for the detection of tetracycline. The primary mechanism for this dual mode biosensor was the inhibitory effect of tetracycline on on NH2-MIL-101(Fe)@TCPP(Fe) catalyzed chromatic reaction between H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB)/o-phenylenediamine (OPD), which was ascribed to the consumption of ·OH by tetracycline and the adsorption of tetracycline on the surface of NH2-MIL-101(Fe)@TCPP(Fe). After effective validation, this colorimetric/fluorescent dual mode method was applied to detect tetracycline residues in three actual honey samples.

Determination of tetracycline antibiotics in food using covalent organic frameworks composites-based on magnetic solid phase extraction coupled to HPLC

Tetracycline antibiotics (TCs) has been widely applied as animal and human medicine for the prevention and treatment of diseases. The unsafe residues of TCs pose serious risks to human health. Development of a rapid and sensitive method for determining TCs residues in environment and food samples is still challenging. Herein, we report the in-situ one-pot self-assembly preparation of core-shell magnetic covalent organic frameworks (Fe3O4@COFs) composites with crystalline structure for efficient magnetic solid-phase extraction (MSPE) of TCs from various samples. Fe3O4@COFs showed good enrichment performance for TCs and excellent recyclability. Under optimal MSPE conditions, the developed Fe3O4@COFs-MSPE-liquid chromatogram method possessed wide linear range (0.80-10000 µg L-1), low limits of detection (0.24-0.30 µg L-1), low adsorbent consumption (5 mg) and short extraction time (10 min). The extraction mechanism of hydrogen bonding, π-π and hydrophobic interactions was investigated by comparison experiment and adequate analysis and characterizations. This work reveals the potential of crystalline Fe3O4@COFs composites in sample pretreatment.

Recent advances in MXene nanozyme-based optical and electrochemical biosensors for food safety analysis

The importance of nanotechnology is increasing every day in different fields and, especially, the application of nanomaterials has attracted considerable attention in food safety. Among different nanomaterials, MXenes, which are two-dimensional (2D) transition metal-based layered materials made of nitrides and carbides, have revolutionized various fields as a cutting-edge scientific discovery in nanotechnology. These materials have been widely used in the structure of biosensors and sensors due to their excellent metallic conductivity, mechanical stability, optical absorbance, good redox capability, and higher heterogeneous electron transfer rate. In particular, the application of MXenes as nanozymes has highlighted their high performance to a great extent in biosensor domains. The growing interest in these nanozymes is attributed to their specific physicochemical features. The key enzymatic features of these materials include activities similar to oxidase, peroxidase, catalase, and superoxide dismutase. In this review, initially, several common synthesis methods of MXenes are presented, emphasizing their significant role as nanozymes in constructing efficient sensors. Subsequently, several common applications of MXene nanozymes in food safety analysis are delved into, including the detection of bacteria, mycotoxins, antibiotic residues, and pesticide residues, along with their applications in different electrochemical and optical biosensors. In addition, the gap, limitation, and future perspective of these novel nanozymes in food safety are highlighted.

Facile preparation of polymer dots for tetracycline and Al3+ detection and exploration of anti-counterfeiting applications via the fluorescence "ON-OFF-ON" strategy

Polymer dots (PT-PDs) were obtained through a "synthesis-modification integration" method by using polyethyleneimine (PEI) and tartaric acid (TA) as raw materials. The designed PT-PDs displayed a nanoscale structure with an average size of 1.6 nm, and bright blue fluorescence (FL) emission with a fluorescence quantum yield (QY) of 14.3%. Moreover, the PT-PDs were used as a sensing platform for the sensitive and quantitative detection of tetracyclines (TCs) and Al3+ via fluorescence quenching and recovery. The LODs for tetracycline hydrochloride (TCH), doxycycline (DOX), and Al3+ were 94.8 nM, 76.7 nM, and 177.8 nM, respectively. In addition, PT-PDs incorporated with polyacrylamide were used for the recognition of TCs and Al3+ in a portable manner on the basis of the fluorescence "ON-OFF-ON" strategy, which revealed great application in the field of anti-counterfeiting and encryption.

A competitive dual-mode for tetracycline antibiotics sensing based on colorimetry and surface-enhanced Raman scattering

Tetracycline antibiotics (TCs) are extensively used as broad-spectrum antimicrobials. However, their excessive use and misuse have led to serious accumulation in foods and environments, posing a significant threat to human health. To solve such public issue, we have designed a novel dual-mode detection method, integrating colorimetric sensing with surface-enhanced Raman scattering (SERS) technology, for sensitive and rapid evaluation on TCs. In this method, an Ag@NH2-MIL-101(Al)-Ag nanoprobe that leverages the synergistic effect between silver nanoparticles (AgNPs) and NH2-MIL-101(Al), resulting in remarkable peroxidase-like activity and enhanced SERS performance, was proposed. Moreover, for the instant colorimetric sensing, a competitive oxidative-reaction between TCs and 3,3',5,5'-tetramethylbenzidine (TMB) was developed based on the peroxidase-like activity of nanoprobe. Our innovative colorimetric-SERS dual-mode approach demonstrated high sensitivity accompanied by robust selectivity with limits of detection (LODs) for TCs of 10-3 ppm in colorimetric mode and 10-5 ppm in SERS mode. Furthermore, TCs can be reliably detected in honey samples with recoveries ranging from 87.69% to 120.49%. This dual-mode sensing strategy effectively combining the ease of colorimetric detection with high sensitivity of SERS provides significant values for rapid, direct, and multiplexed evaluation on various hazards in environment and food chains.

Integration of ratiometric, ultrafast, sensitive detection as well as rapid and efficient removal of tetracycline based on a novel Zn (II) functionalized magnetic covalent organic framework

BACKGROUND

Based on the low volatility and refractory nature of Tetracycline (TC), excessive use leads to its continuous accumulation in water environments, posing serious risks to the ecological environment and human health. Although a very limited number of nanomaterials capable of simultaneously detecting and removing TC have been fabricated, they generally exist issues associated with a single detection signal ("on" or "off") or low adsorption rates with low adsorption capacities. As a result, it is crucial to develop a reliable technique to achieve ratiometric detection as well as rapid and efficient removal of TC.

RESULTS

Herein, a novel Zn (II) Functionalized magnetic covalent organic framework (Fe3O4@COF@Zn) was created. As the role of a fluorescent probe, it had excellent characteristics of ratiometric (F529/F436), ultrafast response (1 min), and ultra-low detection limit (16 nM). As the role of an adsorbent, it demonstrated a high capacity of adsorption (414.94 mg/g) in the pH-neutral range, fast kinetics (10 min), desirable regeneration capability, and convenient magnetic separation. By theoretical and experimental analysis, the detection and adsorption mechanism for TC was systematically revealed. Moreover, as an attempt, Fe3O4@COF@Zn showed it potential for crop remediation by adsorbing TC-contaminated water.

SIGNIFICANCE

This work demonstrates the exceptional performance of Zn-functionalized fluorescent COF for ratiometric, ultrafast, sensitive detection as well as rapid and efficient removal of TC, thereby illustrating its significant potential for the rapid monitoring and treatment of TC contamination.

Self-assembled Fe3O4-COOH @ hydrogen-bonded organic framework composites for magnetic solid-phase extraction of tetracycline in food samples coupled with HPLC determination

Magnetic solid-phase extraction (MSPE) technology for tetracycline (TCC) was developed by employing the novel and pre-designed Fe3O4-COOH@hydrogen-bonded organic frameworks (HOFs) adsorbents in complex food samples. The HOF shell was grown onto the Fe3O4-COOH core by in-situ self-assembled method. The excellent MSPE performances with less solvent, less adsorbent and time consumption were derived from the hydrogen bonding, π-π and hydrophobic interactions between HOF shell and TCC. Combined with HPLC analysis, Fe3O4@ HOFs adsorbent reduced matrix effects and the established MSPE-HPLC method for TCC gave the linearity of 0.001-6 μg mL-1 with the limit of detection 0.0003 μg mL-1. The recoveries in pure milk, canned yellow peach and carrot were 82.4-103.7 %. The method provided a simple, efficient and dependable alternative to monitor trace TCC antibiotics in food or environmental samples.

Integrated Eu3+ loaded covalent organic framework with smartphone for ratiometric fluorescence detection of tetracycline

Developing rapid tetracycline sensing system is of great significance to monitor the illegal addition to drugs and pollution to food and ecosystem. By loading covalent organic frameworks (COFs) with Eu3+, a new hybridized material (COF@Eu3+) was prepared for tetracycline determination. Based on the Schiff base reaction, the COFs were by synthesized through solvent evaporation in 30 min at room temperature. Thereafter, Eu3+ was modified into COFs to develop the COF@Eu3+ sensing platform by adsorption and coordination. In presence of tetracycline, tetracycline can displace water molecules and coordinate with Eu3+ through the antenna effect. As a result, the red fluorescence of Eu3+ was enhanced by tetracycline with green fluorescence of COF as a reference. The developed ratiometric fluorescence sensor exhibits a linear range of 0.1-20 μM for detecting tetracycline with a detection limit of 30 nM. Integrated with a smartphone, the rapid tetracycline detection can be realized in situ, which is potential for high-throughput screening of tetracycline contaminated samples. Furthermore, the COF@Eu3+ fluorescence sensor has been successfully applied to the detection of tetracycline in traditional Chinese medicine compound preparation with satisfied recoveries. Therefore, a smartphone-assisted device was successfully developed based on Eu3+-functionalized COF, which is an attractive candidate for further applications of fluorescence sensing and visual detection.

Recent advances in ratiometric electrochemical sensors for food analysis

Ratiometric electrochemical sensors are renowned for their dual-signal processing capabilities, enabling automatic correction of background noise and interferences through built-in calibration, thus providing more accurate and reproducible measurements. This characteristic makes them highly promising for food analysis. This review comprehensively summarizes and discusses the latest advancements in ratiometric electrochemical sensors and their applications in food analysis, emphasizing their design strategies, detection capabilities, and practical uses. Initially, we explore the construction and design strategies of these sensors. We then review the detection of various food-related analytes, including nutrients, additives, metal ions, pharmaceutical and pesticide residues, biotoxins, and pathogens. The review also briefly explores the challenges faced by ratiometric electrochemical sensors in food testing and potential future directions for development. It aims to provide researchers with a clear introduction and serve as a reference for the design and application of new, efficient ratiometric electrochemical sensors in food analysis.

A handy way for forming N-doped TiO2/carbon from pectin and d,l-serine hydrazide hydrochloride

N-doped TiO2/carbon composites (N-TiPC) have shown excellent photodegradation performances to the organic contaminants but are limited by the multistage preparation (i.e., preparation of porous carbon, preparation of N-doped TiO2, and loading of N-doped TiO2 on porous carbon). Here, we develop a handy way by combining the Pickering emulsion-gel template route and chelation reaction of polysaccharides. The N-TiPC is obtained by calcinating pectin/Dl-serine hydrazide hydrochloride (SHH)-Ti4+ chelate and is further described by modern characterization techniques. The results show that the N atom is successfully doped into the TiO2 lattice, and the bandgap value of N-TiPC is reduced to 2.3 eV. Moreover, the particle size of N-TiPC remains about 10 nm. The configurations of the composites are simulated using DFT calculation. The photocatalytic experiments show that N-TiPC has a high removal efficiency for methylene blue (MB) and oxytetracycline hydrochloride (OTC-HCL). The removal ratios of MB (20 mg/L, 50 mL) and OTC-HCL (30 mg/L, 50 mL) are 99.41 % and 78.29 %, respectively. The cyclic experiments show that the photocatalyst has good stability. Overall, this study provides a handy way to form N-TiPC with enhanced photodegradation performances. It can also be promoted to other macromolecules such as cellulose and its derivatives, sodium alginate, chitosan, lignin, etc.

Deep learning assisted logic gates for real-time identification of natural tetracycline antibiotics

The overuse and misuse of tetracycline (TCs) antibiotics, including tetracycline (TTC), oxytetracycline (OTC), doxycycline (DC), and chlortetracycline (CTC), pose a serious threat to human health. However, current rapid sensing platforms for tetracyclines can only quantify the total amount of TCs mixture, lacking real-time identification of individual components. To address this challenge, we integrated a deep learning strategy with fluorescence and colorimetry-based multi-mode logic gates in our self-designed smartphone-integrated toolbox for the real-time identification of natural TCs. Our ratiometric fluorescent probe (CD-Au NCs@ZIF-8) encapsulated carbon dots and Au NCs in ZIF-8 to prevent false negative or positive results. Additionally, our independently developed WeChat app enabled linear quantification of the four natural TCs using the fluorescence channels. The colorimetric channels were also utilized as outputs of logic gates to achieve real-time identification of the four individual natural tetracyclines. We anticipate this strategy could provide a new perspective for effective control of antibiotics.

A paper-based ratiometric fluorescence sensor based on carbon dots modified with Eu3+ for the selective detection of tetracycline in seafood aquaculture water

Paper-based ratiometric fluorescence sensors are normally prepared using two or more types of fluorescent materials on a paper chip for simple, low-cost and fast detection. However, the choice of multi-step and one-step modifications on the paper chip affects the analytical performance. Herein, a novel paper-based dual-emission ratiometric fluorescence sensor was designed for the selective detection of tetracycline (TC). Carbon dots (CDs) modified with Eu3+ were combined with a sealed paper-based microfluidic chip by two methods: one-step grafting of CDs-Eu3+ on paper and step-by-step grafting of CDs and Eu3+ on paper. The analytical performance was studied and optimized respectively. The red fluorescence of Eu3+ at 450 nm is enhanced and the blue fluorescence of CDs at 617 nm is quenched by energy transfer in the presence of TC. Under optimal conditions, TC is selectively determined in the linear range from 0.1 μM to 100 μM with a detection limit of 0.03 μM by the step-by-step grafting method. In addition, the sealed paper chip could effectively prevent pollution and volatilization from the reagent. This technique has been used to analyze TC in seafood aquaculture water with satisfactory results.