Gold core @ platinum shell nanozyme-mediated magnetic relaxation switching DNA sensor for the detection of Listeria monocytogenes in chicken samples

Multienzyme-Mediated Dual-Channel Magnetic Relaxation Switching Taste Biosensor (D-MRSTB) for Simultaneous Detection of Umami Compounds and Synergistic Enhancement in Food

Umami substances play a significant role in the evaluation of food quality, and their synergistic enhancement is of great importance in improving and intensifying food flavors and tastes. Current biosensors available for umami detection still confront challenges in simultaneous quantification of multiple umami substances and umami intensities. In this study, an innovative dual-channel magnetic relaxation switching taste biosensor (D-MRSTB) was developed for the quantitative detection of representative umami substances. The multienzyme signal of D-MRSTB specifically catalyzes the umami substances of interest to generate hydrogen peroxide (H2O2), which is then used to oxidate Fe2+ to Fe3+. Such a valence-state transition of paramagnetic ions was utilized as a magnetic relaxation signaling switch to influence the transverse magnetic relaxation time (T2) within the reaction milieu, thus achieving simultaneous detection of monosodium glutamate (MSG) and inosine 5'-monophosphate (IMP). The biosensor showed good linearity (R2 > 0.99) in the concentration range of 50-1000 and 10-1000 μmol/L, with limits of detection (LOD) of 0.61 and 0.09 μmol/L for MSG and IMP, respectively. Furthermore, the biosensor accurately characterized the synergistic effect of the mixed solution of IMP and MSG, where ΔT2 showed a good linear relationship with the equivalent umami concentration (EUC) of the mixed solution (R2 = 0.998). Moreover, the D-MRSTB successfully achieved the quantitative detection of umami compounds in real samples. This sensing technology provides a powerful tool for achieving the detection of synergistic enhancement among umami compounds and demonstrates its potential for application in the food industry.

Isothermal Reciprocal Catalytic DNA Circuit for Sensitive Analysis of Kanamycin

Inappropriate use of veterinary drugs can result in the presence of antibiotic residues in animal-derived foods, which is a threat to human health. A simple yet efficient antibiotic-sensing method is highly desirable. Programmable DNA amplification circuits have supplemented robust toolkits for food contaminants monitoring. However, they currently face limitations in terms of their intricate design and low signal gain. Herein, we have engineered a robust reciprocal catalytic DNA (RCD) circuit for highly efficient bioanalysis. The trigger initiates the cascade hybridization reaction (CHR) to yield plenty of repeated initiators for activating the rolling circle amplification (RCA) circuit. Then the RCA-generated numerous reconstituted triggers can reversely stimulate the CHR circuit. This results in a self-sufficient supply of numerous initiators and triggers for the successive cross-invasion of CHR and RCA amplifiers, thus leading to exponential signal amplification for the highly efficient detection of analytes. With its flexible programmability and modular features, the RCD amplifier can serve as a universal toolbox for the high-performance and accurate sensing of kanamycin in buffer and food samples including milk, honey, and fish, highlighting its enormous promise for low-abundance contaminant analysis in foodstuffs.

Multisignal Biosensors Based on Mn Paramagnetic Relaxation and Nanocatalysis for Norovirus Detection

A multisignal method for the sensitive detection of norovirus based on Mn paramagnetic relaxation and nanocatalysis was developed. This dual-modality sensing platform was based on the strong relaxation generated by cracked Au@MnO2 nanoparticles (NPs) and their intrinsic enzyme-like activity. Ascorbic acid rapidly cracked the MnO2 layer of Au@MnO2 NPs to release Mn(II), resulting in the relaxation modality being in a "switch-on" state. Under the optimal conditions, the relaxation modality exhibited a wide working range (6.02 × 103-3.01 × 107 copies/μL) and a limit of detection (LOD) of 2.29 × 103 copies/μL. Using 4,4',4″,4″'-(porphine-5,10,15,20-tetrayl) tetrakis (benzenesulfonic acid) (tpps)-β-cyclodextrin (tpps-β-CD) as a T1 relaxation signal amplification reagent, a lower LOD was obtained. The colorimetric modality exploited the "peroxidase/oxidase-like" activity of Au@MnO2 NPs, which catalyzed the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB, which exhibited a working range (6.02 × 104-6.02 × 106 copies/μL) and an LOD of 2.6 × 104 copies/μL. In addition, the rapid amplification reaction of recombinase polymerase enabled the detection of low norovirus levels in food samples and obtained a working range of 101-106 copies/mL and LOD of 101 copies/mL (relaxation modality). The accuracy of the sensor in the analysis of spiked samples was consistent with that of the real-time quantitative reverse transcription polymerase chain reaction, demonstrating the high accuracy and practical utility of the sensor.

Ni-Pt nanozyme-mediated relaxation and colorimetric sensor for dual-modality detection of norovirus

An NiPt nanozyme-mediated relaxation and colorimetric sensor is developed for dual-modality detection of norovirus (NoV). The relaxation modality is based on the "catalase-like" activity of the NiPt nanozyme, which adjusts the hydrogen peroxide (H2O2) mediated Fe (II)/Fe(III) conversion, thereby changing the relaxation signal. Poly-γ-glutamic acid (MW ≈ 1w) can enhance the relaxivity of Fe(III) (r1 = 7.11 mM-1 s-1; r2 = 8.94 mM-1 s-1). The colorimetric modality exploits the "peroxidase-like" activity of the NiPt nanozyme, which can catalyze the oxidation of colorless 3, 3', 5, 5'-tetramethylbenzidine (TMB) to blue oxTMB in H2O2. Under optimal conditions, the relaxation modality exhibits a wide working range (1.0 × 101-1.0 × 104 fM) and a limit of detection (LOD) of 4.7 fM (equivalent to 2820 copies/μL). The spiked recoveries range from 99.593 to 106.442 %, and the relative standard deviation (RSD) is less than 5.124 %. The colorimetric modality exhibited the same working range with a lower LOD of 2.9 fM (equivalent to 1740 copies/μL) and an RSD of less than 2.611 %. Additionally, the recombinase polymerase amplification reaction enabled the detection of low NoV levels in food samples with a working range of 102-106 copies/mL and LOD of 102 copies/mL. The accuracy of the sensor in the analysis of spiked samples is consistent with the gold standard method (real-time quantitative reverse transcription-polymerase chain reaction), demonstrating the high accuracy and practical utility of the sensor.

Fluorescence Resonance Energy Transfer (FRET)-Based Sensor for Detection of Foodborne Pathogenic Bacteria: A Review

Sensitive and rapid determination of foodborne pathogenic bacteria is of practical importance for the control and prevention of foodborne illnesses. Nowadays, with the prosperous development of fluorescence assays, fluorescence resonance energy transfer (FRET)-derived diagnostic strategies are extensively employed in quantitative analysis of different pathogenic bacteria in food-related matrices, which displays a rapid, simple, stable, reliable, cost-effective, selective, sensitive, and real-time way. Considering the extensive efforts that have been made in this field so far, we here discuss the up-to-date developments of FRET-based diagnostic approaches for the determination of key foodborne pathogens like Staphylococcus aureus, Escherichia coli, Vibrio parahaemolyticus, Salmonella spp., Campylobacter spp., and Bacillus cereus in complex food-related matrices. Moreover, the principle of this technology, the choosing standards of acceptor-donor pairs, and the fluorescence properties are also profiled. Finally, the current prospects and challenges in this field are also put forward.

Recent Advances in Nanozyme-Mediated Strategies for Pathogen Detection and Control

Pathogen detection and control have long presented formidable challenges in the domains of medicine and public health. This review paper underscores the potential of nanozymes as emerging bio-mimetic enzymes that hold promise in effectively tackling these challenges. The key features and advantages of nanozymes are introduced, encompassing their comparable catalytic activity to natural enzymes, enhanced stability and reliability, cost effectiveness, and straightforward preparation methods. Subsequently, the paper delves into the detailed utilization of nanozymes for pathogen detection. This includes their application as biosensors, facilitating rapid and sensitive identification of diverse pathogens, including bacteria, viruses, and plasmodium. Furthermore, the paper explores strategies employing nanozymes for pathogen control, such as the regulation of reactive oxygen species (ROS), HOBr/Cl regulation, and clearance of extracellular DNA to impede pathogen growth and transmission. The review underscores the vast potential of nanozymes in pathogen detection and control through numerous specific examples and case studies. The authors highlight the efficiency, rapidity, and specificity of pathogen detection achieved with nanozymes, employing various strategies. They also demonstrate the feasibility of nanozymes in hindering pathogen growth and transmission. These innovative approaches employing nanozymes are projected to provide novel options for early disease diagnoses, treatment, and prevention. Through a comprehensive discourse on the characteristics and advantages of nanozymes, as well as diverse application approaches, this paper serves as a crucial reference and guide for further research and development in nanozyme technology. The expectation is that such advancements will significantly contribute to enhancing disease control measures and improving public health outcomes.

Nanomaterial interfaces designed with different biorecognition elements for biosensing of key foodborne pathogens

Foodborne diseases caused by pathogen bacteria are a serious problem toward the safety of human life in a worldwide. Conventional methods for pathogen bacteria detection have several handicaps, including trained personnel requirement, low sensitivity, laborious enrichment steps, low selectivity, and long-term experiments. There is a need for precise and rapid identification and detection of foodborne pathogens. Biosensors are a remarkable alternative for the detection of foodborne bacteria compared to conventional methods. In recent years, there are different strategies for the designing of specific and sensitive biosensors. Researchers activated to develop enhanced biosensors with different transducer and recognition elements. Thus, the aim of this study was to provide a topical and detailed review on aptamer, nanofiber, and metal organic framework-based biosensors for the detection of food pathogens. First, the conventional methods, type of biosensors, common transducer, and recognition element were systematically explained. Then, novel signal amplification materials and nanomaterials were introduced. Last, current shortcomings were emphasized, and future alternatives were discussed.

Ultrasensitive detection of Staphylococcus aureus using a non-fluorescent cDNA-grafted dark BBQ®-650 chromophore integrated hydrophilic upconversion nanoparticles/aptamer system

A highly structured fluorometric bioassay has been proposed for screening Staphylococcus aureus (S. aureus). The study exploits (i) the spectral attributes of the hexagonal NaYF₄:Yb,Er upconversion nanoparticle (UCNP)-coated 3-aminopropyl)triethoxysilane; (ii) the intrinsic non-fluorescent quenching features of the highly stable dark blackberry (BBQ®-650) receptor; (iii) the aptamer (Apt-) biorecognition and binding affinity, and (iv) the complementary DNA hybridizer-linkage efficacy. The principle relied on the excited state energy transfer between the donor Apt-labeled NH₂-UCNPs at the 3' end, and cDNA-grafted BBQ®-650 at the 5' end, as the effective receptors. The donor moieties in proximity (< 10.0 nm) trigger hybridization with the cDNA-grafted dark BBQ®-650, as the receptors of energy from the ²F_5/2 level of Yb³⁺ ions to initiate the Förster resonance energy transfer pathway. This was confirmed by the decline in the excited-state lifetimes from 223.52 μs (τ₁) to 179.26 μs (τ₂). The existence of the target S. aureus in the bioassay attracts the Apt- resulting in the detachment of the acceptor, and disintegration of the complex configuration via conformation reversal. The re-activated fluorescence monitored at λex/em = 980/652 nm, as a function of the logarithmic concentration of S. aureus (42 to 4.2 × 10⁸ CFU mL^-1), yielded an ultra-low detection response of 2.0 CFU mL^-1. The bioassay screening of S. aureus in real samples revealed satisfactory recoveries (92.44-107.82%) and validation results (p > 0.05). Hence, the comprehensive Apt-labeled NH₂-UCNPs-cDNA-grafted dark BBQ®-650 bioassay offered fast and precise S. aureus screening in food and environmental settings.

Magnetic relaxation switch sensor based on aptamer-modified poly-L-lysine-ferroferric oxide magnetic nanoparticles and graphene oxide for the determination of insecticides in vegetables

A simple and effective graphene oxide-magnetic relaxation switch (GO-MRS) sensor that combines graphene oxide (GO) and aptamer-modified poly-L-lysine(PLL)-Fe₃O₄ nanoparticles (Fe₃O₄@PLL-Apt NPs) was designed for the detection of acetamiprid (ACE). In this sensor, Fe₃O₄@PLL-Apt NPs acted as a relaxation signal probe and GO facilitated the generation of relaxation signal changes (dispersion/aggregation shift), while the aptamer is a molecular component that recognizes ACE. This GO-assisted magnetic signal probe improves the stability of magnetic nanoparticles in solution and enhances their sensitivity to small molecules while avoiding cross-reactions. Under optimal conditions, the sensor exhibits a wide working range (10-80 nM) and low detection limit (8.43 nM). The spiked recoveries ranged from 96.54 to 103.17%, with a relative standard deviation (RSD) of less than 2.3%. In addition, the performance of the GO-MRS sensor matched that of the standard method (liquid chromatography-mass spectrometry (LC-MS)), indicating that the GO-MRS sensor is suitable for the detection of ACE in vegetables.

Optical Immunosensor for the Detection of Listeria monocytogenes in Food Matrixes

In this paper, simple imine-based organic fluorophore 4-amino-3-(anthracene-9 yl methyleneamino) phenyl (phenyl) methanone (APM) has been synthesized via a greener approach and the same was used to construct a fluorescent immunoassay for the detection of Listeria monocytogenes (LM). A monoclonal antibody of LM was tagged with APM via the conjugation of the amine group in APM and the acid group of anti-LM through EDC/NHS coupling. The designed immunoassay was optimized for the specific detection of LM in the presence of other interfering pathogens based on the aggregation-induced emission mechanism and the formation of aggregates and their morphology was confirmed with the help of scanning electron microscopy. Density functional theory studies were done to further support the sensing mechanism-based changes in the energy level distribution. All photophysical parameters were measured by using fluorescence spectroscopy techniques. Specific and competitive recognition of LM was done in the presence of other relevant pathogens. The immunoassay shows a linear appreciable range from 1.6 × 10⁶-2.7024 × 10⁸ cfu/mL using the standard plate count method. The LOD has been calculated from the linear equation and the value is found as 3.2 cfu/mL, and this is the lowest LOD value reported for the detection of LM so far. The practical applications of the immunoassay were demonstrated in various food samples, and their accuracy obtained was highly comparable with the standard existing ELISA method.

Hierarchical Flower-like WO3 Nanospheres Decorated with Bimetallic Au and Pd for Highly Sensitive and Selective Detection of 3-Hydroxy-2-butanone Biomarker

Listeria monocytogenes, which is abundant in environment, can lead to many kinds of serious illnesses and even death. Nowadays, indirectly detecting the metabolite biomarker of L. monocytogenes, 3-hydroxy-2-butanone, has been verified to be an effective way to evaluate the contamination of L. monocytogenes. However, this detection approach is still limited by sensitivity, selectivity, and ppb-level detection limit. Herein, low-cost and highly sensitive and selective 3-hydroxy-2-butanone sensors have been proposed based on the bimetallic AuPd decorated hierarchical flower-like WO₃ nanospheres. Notably, the 1.0 wt % AuPd-WO₃ based sensors displayed the highest sensitivity (R_a/R_g = 84 @ 1 ppm) at 250 °C. In addition, the sensors showed outstanding selectivity, rapid response/recovery (8/4 s @ 10 ppm), and low detection limit (100 ppb). Furthermore, the evaluation of L. monocytogenes with high sensitivity and specificity has been achieved using 1.0 wt % AuPd-WO₃ based sensors. Such a marvelous sensing performance benefits from the synergistic effect of bimetallic AuPd nanoparticles, which lead to thicker electron depletion layer and increased adsorbed oxygen species. Meanwhile, the unique hierarchical nanostructure of the flower-like WO₃ nanospheres benefits the gas-sensing performance. The AuPd-WO₃ nanosphere-based sensors exhibit a particular and highly selective method to detect 3-hydroxy-2-butanone, foreseeing a feasible route for the rapid and nondestructive evaluation of foodborne pathogens.

Electrochemical Biosensors as a Novel Platform in the Identification of Listeriosis Infection

Listeria monocytogenes (L.M.) is a gram-positive bacillus with wide distribution in the environment. This bacterium contaminates water sources and food products and can be transmitted to the human population. The infection caused by L.M. is called listeriosis and is common in pregnant women, immune-deficient patients, and older adults. Based on the released statistics, listeriosis has a high rate of hospitalization and mortality; thus, rapid and timely detection of food contamination and listeriosis cases is necessary. During the last few decades, biosensors have been used for the detection and monitoring of varied bacteria species. These devices are detection platforms with great sensitivity and low detection limits. Among different types of biosensors, electrochemical biosensors have a high capability to circumvent several drawbacks associated with the application of conventional laboratory techniques. In this review article, different electrochemical biosensor types used for the detection of listeriosis were discussed in terms of actuators, bioreceptors, specific working electrodes, and signal amplification. We hope that this review will facilitate researchers to access a complete and comprehensive template for pathogen detection based on the different formats of electrochemical biosensors.

Ultrasensitive hairpin mediated upconversion fluorescence biosensor for Staphylococcus aureus detection in foods and waters exploiting g-C3N4-assisted catalysis

A novel g-C₃N₄ nanosheets (g-C₃N₄ NSs)-assisted upconversion fluorescent aptasensor was proposed for Staphylococcus aureus (S. aureus) detection by adopting hybridization chain reaction (HCR) as a sensitizer. Two hairpin (H1 and H2) structured DNA probes were engineered predicated on the partial complementary sequence (cDNA) of S. aureus aptamer and modified on the exterior of the upconversion nanoparticles (UCNPs), respectively. The presence of S. aureus initiated the HCR system and activated H1 and H2 probes to form a double-helix away from the g-C₃N₄ NSs vicinity. This led to the decrease in peroxidase-like activity (PA) of the g-C₃N₄ NSs and corresponding fluorescence recovery proportional to the concentration of S. aureus (10-10⁶ cfu mL^-1). The method was applied to real food samples with acceptable recoveries (91.1-101.6%) and further validated by traditional plate counting method (p > 0.05).

Gold Nanozymes: Smart Hybrids with Outstanding Applications

Nanozymes are nanostructured artificial enzymes that have attracted great attention among researchers because of their ability to mimic relevant biological reactions carried out by their natural counterparts, but with the capability to overcome natural enzymes’ drawbacks such as low thermostability or narrow substrate scope. The promising enzyme-like properties of these systems make nanozymes excellent candidates for innovative solutions in different scientific fields such as analytical chemistry, catalysis or medicine. Thus, nanozymes with different type of activities are of special interest owing to their versatility since they can reproduce several biological reactions according to the substrates and the environmental conditions. In this context, gold-based nanozymes are a representative example of multifunctional structures that can perform a great number of enzyme-like activities. In addition, the combination of gold-based materials with structures of organic and inorganic chemical nature yields even more powerful hybrid nanozymes, which enhance their activity by providing improved features. This review will carry out a deep insight into gold-based nanozymes, revisiting not only the different type of biological enzymatic reactions that can be achieved with these kinds of systems, but also structural features of some of the most relevant hybrid gold-based nanozymes described in the literature. This literature review will also provide a representative picture of the potential of these structures to solve future technological challenges.

Prospects for the next generation of artificial enzymes for ensuring the quality of chilled meat: Opportunities and challenges

As living standards rise, the demand for high-quality chilled meat among consumers also grows. Researchers and enterprises have been interested in ensuring the quality of chilled meat in all links of the downstream industry. Nanozyme has shown the potential to address the aforementioned requirements. Reasons and approaches for the application of nanozymes in the freshness assessment or shelf life extension of chilled meat were discussed. The challenges for applying these nanozymes to ensure the quality of chilled meat were also summarized. Finally, this review examined the safety, regulatory status, and consumer attitudes toward nanozymes. This review revealed that the freshness assessment of chilled meat is closely related to mimicking the enzyme activities of nanozymes, whereas the shelf life changes of chilled meat are mostly dependent on the photothermal activities and pseudophotodynamic activities of nanozymes. In contrast, studies regarding the shelf life of chilled meat are more challenging to develop, as excessive heat or reactive oxygen species impair its quality. Notably, meat contains a complex matrix composition that may interact with the nanozyme, reducing its effectiveness. Nanopollution and mass manufacturing are additional obstacles that must be overcome. Therefore, it is vital to choose suitable approaches to ensure meat quality. Furthermore, the safety of nanozymes in meat applications still needs careful consideration owing to their widespread usage.

Magnetic Relaxation Switch Sensor Based on Magnetophoresis and "T-Hg(II)-T" Signal Amplification

In this study, we designed a magnetic relaxation switch (MRS) sensor combined with magnetophoresis technology (MS-MRS), which helps solve the problems of traditional MRS sensors. The sensor is based on a new combined magnet and is composed of small magnetic blocks and iron sheets that can rapidly separate magnetic nanoparticles of different sizes within 5 min. The MS-MRS sensor consists of aptamer-functionalized magnetic nanoparticles (diameter: 200 nm) (MNP₂₀₀-Apt), complementary DNA-functionalized magnetic nanoparticles (diameter: 20 nm) (MNP₂₀-cDNA), and a combined magnet ("M2" magnet). The MNP₂₀₀-Apt probe could be separated by an "M2" magnet but the MNP₂₀-cDNA probe could not. To further improve the sensitivity of the sensor, we successfully constructed an MS-MRS-Hg sensor based on the "T-Hg(II)-T" specific recognition that aggregated MNP₂₀-cDNA probes to amplify the relaxation signal. The detection working range of the MS-MRS sensor is 0.5-100 ng/mL and that of the MS-MRS-Hg sensor is 0.05-100 ng/mL. Their limit of detection (LOD) values are 0.15 and 0.01 ng/mL, respectively. The relative recoveries of the MS-MRS and MS-MRS-Hg sensors are 95.2-119.5% and 93.1-113.1%, respectively. These results indicate that the proposed sensors have a high accuracy level.