An ultrasensitive dual-mode aptasensor for patulin based on the upconversion particles and G-Quadruplex-hemin DNAzyme.

Patulin (PAT) is a mycotoxin-produced secondary metabolite that can contaminate foods, causing toxic effects on animal and human health. Therefore, for the first time, we have constructed a "turn-on" dual-mode aptamer sensor for PAT using oleic acid-coated upconversion nanomaterials (OA-UCNPs) and G-Quadruplex-hemin DNAzyme (G4-DNAzyme) as fluorescent and colorimetry probes. The sensor employs aptamers binding to PAT as recognition elements for specific molecule detection. Mxene-Au can be used as a biological inducer to assist OA-UCNPs in controlling fluorescence intensity. In addition, colorimetric signal amplification was performed using the trivalent G4-DNAzyme to increase detection sensitivity and reduce false positives. Under optimal conditions, the dual-mode aptasensor has a detection limit of 5.3 pg mL-1 in fluorescence and 2.4 pg mL-1 in colorimetric methods, respectively, with the wider linear range and limit of detection (LOD) of the colorimetric assay. The combination aptasensor can detect PAT with high sensitivity and high specificity and has broad application prospects in the field of food safety detection.

Alternansucrase as a key enabling tool of biotransformation from molecular features to applications: A review.

Alternansucrase (ASR), classified in GH70, produces unique α-glucans with alternating α-1,3 and α-1,6 glycosidic linkages in the backbone chain from renewable sucrose which is easily obtained from nature with low cost. ASR has synthesized many products with valuable functionalities that hold enormous commercial interest and promising applications. The influence of biocatalysis and fermentation parameters on the yields, and properties of products are critical for the propositions made to promote the enzyme application. Investigations on ASR have been compiled in the review to provide information on the enzyme, products and parameters. This review summarizes studies on the characteristics, conversion mechanism, products, and beneficial applications of ASR and exhibits structure-based technologies to improve enzyme activity, specificity, and thermostability for industrial applications. Finally, prospects for further development are also proposed for various ASR applications in food and other fields.

Lateral flow assay for simultaneous detection of multiple mycotoxins using nanozyme to amplify signals.

Co-contamination of multiple mycotoxins produces synergistic toxic effects, leading to more serious hazards. Therefore, the simple, rapid and accurate simultaneous detection of multiple mycotoxins is crucial. Herein, a three-channel aptamer-based lateral flow assay (Apt-LFA) was established for the detection of aflatoxin M1 (AFM1), aflatoxin B1 (AFB1) and ochratoxin A (OTA). The multi-channel Apt-LFA utilized gold­iridium nanozyme to catalyze the chromogenic substrate, which effectively achieved signal amplification. Moreover, the positions and lengths of the complementary sequences were screened by changes in fluorescence intensity. After grayscale analysis, the semi-quantitative results showed that the detection limits of AFM1, AFB1 and OTA were 0.39 ng/mL, 0.36 ng/mL and 0.82 ng/mL. The recoveries of the multiplexed competitive sensors in complex matrices of real samples were 93.33%-97.01%, 95.72%-102.67%, and 106.88%-109.33%, respectively. In conclusion, the assembly principle of the three-channel Apt-LFA is simple, which can provide a new idea for the simultaneous detection of small molecule targets.

Dual pH- and ATP-Responsive Antibacterial Nanospray: On-Demand Release of Antibacterial Factors, Imaging Monitoring, and Accelerated Healing of Bacteria-Infected Wounds under NIR Activation.

The prevalence of pathogenic bacterial infections with high morbidity and mortality poses a widespread challenge to the healthcare system. Therefore, it is imperative to develop nanoformulations capable of adaptively releasing antimicrobial factors and demonstrating multimodal synergistic antimicrobial activity. Herein, an NIR-activated multifunctional synergistic antimicrobial nanospray MXene/ZIF-90@ICG was prepared by incorporating ZIF-90@ICG nanoparticles onto MXene-NH2 nanosheets. MXene/ZIF-90@ICG can on-demand release the antimicrobial factors MXenes, ICG, and Zn2+ in response to variations in pH and ATP levels within the bacterial infection microenvironment. Under NIR radiation, the combination of MXenes, Zn2+, and ICG generated a significant amount of ROS and elevated heat, thereby enhancing the antimicrobial efficacy of PDT and PTT. Meanwhile, NIR excitation could accelerate the further release of ICG and Zn2+, realizing the multimodal synergistic antibacterial effect of PDT/PTT/Zn2+. Notably, introducing MXenes improved the dispersion of the synthesized antimicrobial nanoparticles in aqueous solution, rendering MXene/ZIF-90@ICG a candidate for application as a nanospray. Importantly, MXene/ZIF-90@ICG demonstrated antimicrobial activity and accelerated wound healing in the constructed in vivo subcutaneous Staphylococcus aureus infection model with NIR activation, maintaining a favorable biosafety level. Therefore, MXene/ZIF-90@ICG holds promise as an innovative nanospray for adaptive multimodal synergistic and efficient antibacterial applications with NIR activation.

Multisystem Inflammatory Syndrome in Neonates Associated with COVID-19 in Neonatal ICU of a Tertiary Care Hospital.

OBJECTIVE: Neonatal multisystem inflammatory syndrome (MIS-N) is a unique disease of neonates described in several case reports from all over the world with a myriad of presentations and the emergence of new cases. STUDY DESIGN: Retrospective case series. Place and Duration of the Study: Department of Paediatrics, Fazaia Medical College, Pakistan Air Force Hospital, Islamabad, Pakistan, from December 2021 to November 2022. METHODOLOGY: The study was conducted on neonates who were managed as MIS-N in the neonatal ICU. Data were collected and analysed on SPSS version 24. RESULTS: Patients in this study ranged from newborns to 13 days of age with a mean age of 3.27 ± 4.29 days and average gestational age of 35.18 ± 3.67 weeks. Among these neonates, 7 (63.6%) had bleeding diathesis, 11 (100%) had seizures, 8 (72.2%) presented with haemodynamic instability and shock, and 7 (63.3%) had signs of heart failure. All neonates (100%) had markedly raised SARS-CoV2 IgG antibodies, CRP, ferritin, D-dimers, interleukin 6, procalcitonin, 10 (90.9%) had hypoalbuminemia, and 7 (63.3%) had deranged coagulation profile. Cardiac involvement was seen in all neonates (100%) with raised proBNP and myocardial dysfunction on echocardiography. Pulmonary hypertension was present in 6 (54.4%) neonates. High mortality was observed at 6 (54.5%) among which 4 (66.6%) were premature neonates. CONCLUSION: MIS-N is a new disease entity which is still under research. There is a high propensity for cardiovascular system involvement and higher mortality among preterm neonates. KEY WORDS: Neonatal multisystem inflammatory syndrome (MIS-N), Multisystem inflammatory syndrome in children (MIS-C), SARS-CoV2 infection, SARS-CoV2 spike protein, SARS-CoV2 IgG antibodies.

Upconversion fluorescence nanosensor based on enzymatic inhibited and copper-triggered o-phenylenediamine oxidation for the detection of dimethoate pesticides.

Pesticide residues in agricultural products pose a significant threat to human health. Herein, a sensitive fluorescence method employing upconversion nanoparticles was developed for detecting organophosphorus pesticides (OPs) based on the principle of enzyme inhibition and copper-triggered o-phenylenediamine (OPD) oxidation. Copper ions (Cu2+) oxidized the colorless OPD to a yellow 2,3-diaminophenazine (oxOPD). The yellow solution oxOPD quenched the fluorescence of upconversion nanoparticles due to the fluorescence resonance energy transfer. The high affinity of Cu2+ for thiocholine reduced the level of oxOPD, resulting in almost no fluorescence quenching. The addition of dimethoate led to the inhibition of acetylcholinesterase activity and thus prevented the formation of thiocholine. Subsequently, Cu2+ oxidized OPD to form oxOPD, which attenuated the fluorescence signal of the system. The detection system has a good linear range of 0.01 ng/mL to 50 ng/mL with a detection limit of 0.008 ng/mL, providing promising applications for rapid detection of dimethoate.

Aptamer-modified paper-based analytical devices for the detection of food hazards: Emerging applications and future perspective.

Food analysis plays a critical role in assessing human health risks and monitoring food quality and safety. Currently, there is a pressing need for a reliable, portable, and quick recognition element for point-of-care testing (POCT) to better serve the demands of on-site food analysis. Aptamer-modified paper-based analytical devices (Apt-PADs) have excellent characteristics of high portability, high sensitivity, high specificity, and on-site detection, which have been widely used and concerned in the field of food safety. The article reviews the basic components and working principles of Apt-PADs, and introduces their representative applications detecting food hazards. Finally, the advantages, challenges, and future directions of Apt-PADs-based sensing performance are discussed, to provide new directions and insights for researchers to select appropriate Apt-PADs according to specific applications.

Covalent modification of γ-cyclodextrin with geraniol: An antibacterial agent with good thermal stability, solubility and biocompatibility.

Geraniol (Ger) is an essential oil molecule with excellent biological activity. High hydrophobicity and volatility limit its practical application. Cyclodextrins (CDs) are water-soluble cyclic oligosaccharides with hydrophobic cavities. Physical encapsulation of CDs to improve the solubility and stability of essential oil molecules is not satisfactory. Therefore, this study synthesized the γ-CD derivative (γ-CD-Ger) by grafting Ger onto γ-CD using a bromide-mediated method. Compared to the inclusion complexes (γ-CD/Ger) formed by both, the derivatives exhibit better solubility and thermal stability. The derivative has better antibacterial activity when the ratio of γ-CD to Ger was 1:2. In addition, the derivatives did not exhibit cytotoxic and hemolytic properties. These results indicate that this research provides a water-soluble antibacterial agent with a wide range of promising applications and offers new ideas for the application of alcohol hydrophobic molecules in aqueous systems.

Fluorescent DNA-Silver nanoclusters in food safety detection: From synthesis to application.

In recent years, the conventional preparation of silver nanoclusters (AgNCs) has attracted much attention due to their ultra-small size, tunable fluorescence, easy-to-engineer, as well as biocompatible material. Moreover, its great affinity towards cytosine bases on single-stranded DNA has led to the construction of biosensors, especially aptamers, for a broad variety of applications in food safety and environmental protection. In past years, numerous researchers paid attention to the construction of AgNCs aptasensor. Therefore, this review will be an effort to summarize the synthetic strategy along with the influences of factors on synthesis, categorize the sensing mechanism of aptamer-functionalized AgNCs biosensors, as well as their specific applications in food safety detection including heavy metal, toxin, and foodborne pathogenic bacteria. Furthermore, a brief conclusion and outlook regarding the prospects and challenges of their applications in food safety were drawn in line with the developments in DNA-AgNCs.

Corrigendum: Probiotics: mechanism of action, health benefits and their application in food industries.

[This corrects the article DOI: 10.3389/fmicb.2023.1216674.].

High-affinity truncated aptamers for detection of Cronobacter spp with magnetic separation-assisted DNAzyme-driven 3D DNA walker.

After optimizing the original aptamer sequence by truncation strategy, a magnetic separation-assisted DNAzyme-driven 3D DNA walker fluorescent aptasensor was developed for detecting the food-borne pathogen Cronobacter species. Iron oxide magnetic nanoparticles (MNPs) modified with a hybrid of truncated aptamer probe and DNAzyme strand (AP-E1) denoted as MNPs@AP-E1, were employed as capture probes. Simultaneously, a DNAzyme-driven 3D-DNA walker was utilized as the signal amplification element. The substrate strand (Sub) was conjugated with the gold nanoparticles (AuNPs), resulting in the formation of AuNPs@Sub, which served as a 3D walking track. In the presence of the target bacteria and Mg2+, E1-DNAzyme was activated and moved along AuNPs@Sub, continuously releasing the signal probe. Under optimized conditions, a strong linear correlation was observed for Cronobacter sakazakii (C. sakazakii) in the concentration range 101 to 106 CFU mL-1, with a low detection limit of 2 CFU mL-1. The fluorescence signal responses for different Cronobacter species exhibited insignificant differences, with a relative standard deviation of 3.6%. Moreover, the aptasensor was successfully applied to determine  C. sakazakii in real samples with recoveries of 92.86%-108.33%. Therefore, the novel method could be a good candidate for ultra-sensitive and selective detection of Cronobacter species without complex manipulation.

Probiotics: mechanism of action, health benefits and their application in food industries.

Probiotics, like lactic acid bacteria, are non-pathogenic microbes that exert health benefits to the host when administered in adequate quantity. Currently, research is being conducted on the molecular events and applications of probiotics. The suggested mechanisms by which probiotics exert their action include; competitive exclusion of pathogens for adhesion sites, improvement of the intestinal mucosal barrier, gut immunomodulation, and neurotransmitter synthesis. This review emphasizes the recent advances in the health benefits of probiotics and the emerging applications of probiotics in the food industry. Due to their capability to modulate gut microbiota and attenuate the immune system, probiotics could be used as an adjuvant in hypertension, hypercholesterolemia, cancer, and gastrointestinal diseases. Considering the functional properties, probiotics are being used in the dairy, beverage, and baking industries. After developing the latest techniques by researchers, probiotics can now survive within harsh processing conditions and withstand GI stresses quite effectively. Thus, the potential of probiotics can efficiently be utilized on a commercial scale in food processing industries.

Concatenated dynamic DNA network modulated SERS aptasensor based on gold-magnetic nanochains and Au@Ag nanoparticles for enzyme-free amplification analysis of tetracycline.

Tetracycline (TC) poses a great threat to food and environmental safety due to its misuse in animal husbandry and aquaculture. Therefore, an efficient analytical method is needed for the detection of TC to prevent possible hazards. Herein, a cascade amplification SERS aptasensor for sensitive determination of TC was constructed based on aptamer, enzyme-free DNA circuits, and SERS technology. The capture probe and signal probe were obtained by binding DNA hairpins H1 and H2 to the prepared Fe3O4@hollow-TiO2/Au nanochains (Fe3O4@h-TiO2/Au NCs) and Au@4-MBA@Ag nanoparticles, respectively. The dual amplification of EDC-CHA circuits significantly facilitated the sensitivity of the aptasensor. Additionally, the introduction of Fe3O4 simplified the operation of the sensing platform due to its superb magnetic capability. Under optimal conditions, the developed aptasensor exhibited a distinct linear response to TC with a low limit of detection of 15.91 pg mL-1. Furthermore, the proposed cascaded amplification sensing strategy exhibited excellent specificity and storage stability, and its practicability and reliability were verified by TC detection of real samples. This study provides a promising idea for the development of specific and sensitive signal amplification analysis platforms in the field of food safety.

Preparation and characterization of curcumin/chitosan conjugate as an efficient photodynamic antibacterial agent.

Curcumin (Cur) is a natural pigment with excellent biological activity. The poor stability and insolubility of Cur in water severely limit its application. Therefore, to overcome these dilemmas which are big hindrances in their application, a novel derivative (COCS-Cur) was prepared by the esterification reaction of carboxylated chitosan (COCS) and Cur. The structure and properties of conjugate were determined through a series of characterizations. The derivatives had excellent solubility as well as stability. In addition, antioxidant and photodynamic antibacterial experiments proved that COCS-Cur had the excellent free radical scavenging ability and photodynamic antibacterial activity. The derivatives presented a better antibacterial effect on Staphylococcus aureus (S. aureus) than Escherichia coli (E. coli). Noteworthy, the COCS-Cur derivatives showed no obvious toxicity which makes them a stronger contender and potential antimicrobial agent or functional nutrient for application in the food industry.

Study of binding mechanism of aptamer to kanamycin and the development of fluorescent aptasensor in milk detection.

Aptasensors being versatile sensing platforms presented higher sensitivity toward target detection. However, lacking theoretical basis of recognition between most targets and their corresponding aptamers has impeded their applications. Herein, we conducted a study to explore the binding mechanism of aptamer to kanamycin (Kana) and developed rapid fluorescent aptasensing methods. Based on the fluorescence polarization results, base mutations were performed at different sites of the aptamer. The key binding nucleotides of Kana was identified as T7, T8, C13 and A15 by using isothermal titration calorimetry (ITC). The Kmut3 (2.18 µM) with lower dissociation constants (Kd), one-third of the native aptamer (6.91 µM), was also obtained. In addition, the lower K+ concentration and temperature were found to be conducive to Kana binding. Circular dichroism (CD) results revealed that the binding of Kana can trigger the change of base stacking force and helix force. On the aforementioned basis, a fluorescent sensor was designed with the native aptamer and Kmut3 as recognition elements. The comparison results proved that the Kmut3 presented a 3 times lower limit of detection of 59 nM compared to the native aptamer (148 nM). Notably, this developed aptasensor can be finished in 45 min and was convenient to operate.

Cascade DNA Circuits Mediated CRISPR-Cas12a Fluorescent Aptasensor based on Multifunctional Fe3 O4 @hollow-TiO2 @MoS2 Nanochains for Tetracycline Determination.

Herein, for the first time, the CRISPR-Cas12a system is combined with aptamer, cascaded dynamic DNA network circuits, and Fe3 O4 @hollow-TiO2 @MoS2 nanochains (Fe3 O4 @h-TiO2 @MoS2 NCs) to construct an efficient sensing platform for tetracycline (TC) analysis. In this strategy, specific recognition of the target is transduced and amplified into H1-H2 duplexes containing the specific sequence of Cas12a-crRNA through an aptamer recognition module and the dual amplification dynamic DNA network. Subsequently, the obtained activated Cas12a protein non-specifically cleaves the adjacent reporter gene ssDNA-FAM to dissociate the FAM molecule from the quencher Fe3 O4 @h-TiO2 @MoS2 NCs, resulting in the recovery of the fluorescence signal and further signal amplification. Particularly, the synthesized multifunctional Fe3 O4 @h-TiO2 @MoS2 NCs composites also exhibit superb magnetic separability and photocatalytic degradation ability. Under optimal conditions, the aptasensor displays a distinct linear relationship with the logarithm of TC concentration, and the limit of detection is as low as 0.384 pg mL-1 . Furthermore, the results of spiked recovery confirm the viability of the proposed aptasensor for TC quantification in real samples. This study extends the application of the CRISPR-Cas12a system in the field of analytical sensing and contributes new insights into the exploration of reliable tools for monitoring and treating hazards in food and environment.

Controllable synthesis of flower-like AuNFs@ZIF-67 core-shell nanocomposites for ultrasensitive SERS detection of histamine in fish.

Histamine is a significant biomarker to assess the freshness of fish products. In this study, a novel MOF-based SERS sensor for histamine determination was synthesized by wrapping PVP-capped Au nanoflowers with a ZIF-67 shell (Au NFs@ZIF-67). The highly branched Au NFs core exhibited a strong electromagnetic field enhancement effect and provided an ultra-sensitive SERS fingerprint spectrum, while ZIF-67 shell was the contributor to enrich the target and stabilize the substrate. The morphology of the core-shell structures can be easily controlled by the concentrations of the capping agent PVP and MOF precursor Co ion. Consequently, 4-MBA pre-grafted on the optimized SERS substrate can act as the Raman internal standard (IS) to eliminate signal fluctuations through standardizing all spectra against its peak at 1074 cm-1. Moreover, as the specific receptor for histamine molecules, 4-MBA helped reach the low detection sensitivity, where the SERS intensity ratio, I1172/I1074 presented a good linear relationship towards the histamine concentrations (10-3-10-7 M) with the LOD of 0.87 × 10-7 M (R2 = 0.9930). Furthermore, the application in monitoring fish spoilage process demonstrated the feasibility and reliability of the developed sensor. This work provided a facile strategy to construct MOF-based SERS substrate as a potential platform for the shelf-life prediction of fish products.

Advances in riboswitch-based biosensor as food samples detection tool.

Food safety has always been a hot issue of social concern, and biosensing has been widely used in the field of food safety detection. Compared with traditional aptamer-based biosensors, aptamer-based riboswitch biosensing represents higher precision and programmability. A riboswitch is an elegant example of controlling gene expression, where the target is coupled to the aptamer domain, resulting in a conformational change in the downstream expression domain and determining the signal output. Riboswitch-based biosensing can be extensively applied to the portable real-time detection of food samples. The numerous key features of riboswitch-based biosensing emphasize their sustainability, renewable, and testing, which promises to transform engineering applications in the field of food safety. This review covers recent developments in riboswitch-based biosensors. The brief history, definition, and modular design (regulatory mode, reporter, and expression platform) of riboswitch-based biosensors are explained for better insight into the design and construction. We summarize recent advances in various riboswitch-based biosensors involving theophylline, malachite green, tetracycline, neomycin, fluoride, thrombin, naringenin, ciprofloxacin, and paromomycin, aiming to provide general guidance for the design of riboswitch-based biosensors. Finally, the challenges and prospects are also summarized as a way forward stratagem and signs of progress.

Split aptamer acquisition mechanisms and current application in antibiotics detection: a short review.

Antibiotic contamination is becoming a prominent global issue. Therefore, sensitive, specific and simple technology is desirable the demand for antibiotics detection. Biosensors based on split aptamer has gradually attracted extensive attention for antibiotic detection due to its higher sensitivity, lower cost, false positive/negative avoidance and flexibility in sensor design. Although many of the reported split aptamers are antibiotics aptamers, the acquisition and mechanism of splitting is still unknow. In this review, six reported split aptamers in antibiotics are outlined, including Enrofloxacin, Kanamycin, Tetracycline, Tobramycin, Neomycin, Streptomycin, which have contributed to promote interest, awareness and thoughts into this emerging research field. The study introduced the pros and cons of split aptamers, summarized the assembly principle of split aptamer and discussed the intermolecular binding of antibiotic-aptamer complexes. In addition, the recent application of split aptamers in antibiotic detection are introduced. Split aptamers have a promising future in the design and development of biosensors for antibiotic detection in food and other field. The development of the antibiotic split aptamer meets many challenges including mechanism discovery, stability improvement and new biosensor development. It is believed that split aptamer could be a powerful molecular probe and plays an important role in aptamer biosensor.