A G-quadruplex DNAzyme-based LAMP biosensing platform for a novel colorimetric detection ofListeria monocytogenes

Colorimetric and fluorescent dual-modality assay for cell-free mitochondrial DNA copy number in saliva

Copy number of cell-free mitochondrial DNA (cf-mtDNA) has garnered significant attention as a biomarker for studying and diagnosing various diseases. However, Quantitative Real-time PCR (qPCR) and Droplet Digital PCR (ddPCR) assays for cf-mtDNA copy number detection require expensive equipment and high experiment conditions. In this study, a colorimetric and fluorescent dual-modality assay was developed for quantitative detection of cf-mtDNA copy number. With G-quadruplex (G4) sequence modified primers, the assay could quantitatively detect cf-mtDNA with spectrophotometry, RGB (Red, Green, Blue) visual method and fluorescence method, which made the application scenarios more diverse. The specificity of dual-mode method was better, and the detection limits of spectrophotometry, RGB visual method and fluorescence method were as low as 1.45 × 10-1 copies/μL, 1.65 copies/μL and 1.58 × 10-1 copies/μL, respectively. Compared with qPCR and ddPCR assays developed in previous studies, the dual-modality assay in this study had a lower detection limit. It was also independent of expensive qPCR and ddPCR equipment and the detection cost was low. Therefore, the colorimetric and fluorescent dual-modality assay represent a label-free and sensitive approach for assessing cf-mtDNA levels, offering promising implications for biomedical research and clinical diagnostics.

A CRISPR/Cas12a-based DNAzyme visualization platform for rapid discrimination of Streptococcus suis serotype 2 versus 1/2 and serotype 1 versus 14

Streptococcus suis is a major swine pathogen with serotypes 2 and 14 posing zoonotic risks. However, distinguishing serotypes 1/2 from 2 or 1 from 14 remains challenging due to high similarity in their capsule polysaccharide (CPS) loci. Here, we developed a rapid, equipment-free discriminating platform targeting a single nucleotide polymorphism (SNP) at position 483 of the cpsK gene (G in serotypes 2/14 vs. T/C in 1/2/1). The method integrates recombinase polymerase amplification (RPA) with CRISPR/Cas12a and a G-quadruplex-hemin DNAzyme visualization system. RPA enables isothermal amplification, while CRISPR/Cas12a ensures single-nucleotide specificity by cleaving target DNA. Subsequent DNAzyme catalysis converts colorimetric substrates, enabling naked-eye differentiation via distinct color changes (blue for serotypes 1/2/1 vs. colorless for 2/14). This approach achieved a sensitivity of 101-102 copies per reaction and demonstrated 100 % specificity across 29 S. suis serotypes and related strains. Compared to PCR-based or sequencing methods, our platform eliminates reliance on thermocyclers or fluorescence detectors, reducing costs and operational complexity. The entire workflow, completed within 70 min, offers a practical solution for point-of-care testing in resource-limited settings. By enabling rapid, accurate discrimination, this tool will become a complementary tool for resolving ambiguous serotypes and enhances outbreak management in swine populations and mitigates zoonotic transmission.

Colorimetric dual DNAzyme reaction triggered by loop-mediated isothermal amplification for the visual detection of Shiga toxin-producing Escherichia coli in food matrices

Shiga toxin-producing Escherichia coli (STEC) is causing outbreaks worldwide and a rapid detection method is urgently needed. Loop-mediated isothermal amplification (LAMP) has attracted attention in the development of pathogen detection methods; however, current methods for the detection of LAMP amplicon suffer some drawbacks. In this study, we designed a new LAMP method by incorporating peroxidase-mimicking G-quadruplex DNAzyme for a simple colorimetric detection of the LAMP amplicon. As the new method produces LAMP amplicon containing two DNAzyme molecules per amplification unit, the method was termed colorimetric Dual DNAzyme LAMP (cDDLAMP). cDDLAMP was developed targeting 3 common STEC's virulence genes (stx1, stx2, and eae) that are associated with serious human illnesses such hemorrhagic colitis and hemolytic-uremic syndrome. Immunomagnetic enrichment was used for specific, ultrasensitive, and fast detection of STEC in food samples (leafy vegetables and milk). The sensitivity of cDDLAMP ranged from 1-100 CFU/mL in pure culture to 100-103 CFU/mL in spiked milk, and 104-109 CFU/25g of lettuce. No cross-reaction with other generic E. coli strains and non-E. coli bacteria was observed. The color signal could be observed by the naked eye or analyzed by either UV-Vis spectra or smartphone platforms. Therefore, the cDDLAMP assay is a cost-effective method for detecting STEC strains without expensive machines or extraction methods.

Colorimetric and electrochemical analysis of DNAzyme-LAMP amplicons for the detection of Escherichia coli in food matrices

Foodborne bacteria like Escherichia coli threaten global food security, necessitating affordable, on-site detection methods, especially in resource-limited settings. This study optimized loop-mediated isothermal amplification (LAMP) integrated with peroxidase-mimicking G-quadruplex DNA structures (DNAzyme), termed DNAzyme-LAMP which was designed to incorporate two different catalytic DNAzymes per amplification unit, enabling colorimetric detection of E. coli in leafy vegetables and milk samples. Additionally, we introduce a novel electrochemical method that enhances analytical sensitivity. The optimized DNAzyme-LAMP achieved a detection limit below 6.3 CFU per reaction or 0.1 aM gene copies. This system lays the groundwork for the development of on-site biosensors and can be adapted for detecting other foodborne pathogens.

New insights into the photophysical properties and interaction mechanisms of Janus green blue dye with polyanions and its applications in colorimetric visualization of loop-mediated isothermal amplification and polymerase chain reaction

In this investigation, the photophysical properties and interaction mechanisms of Janus green blue (JGB) dye with polyanions were systematically studied using spectroscopic techniques. The absorption spectral analysis revealed that JGB binds cooperatively to sodium alginate, leading to dye stacking along the polymer chain. The interaction of JGB dye with DNA was characterized by the emergence of a metachromatic peak at 564 nm, indicating the formation of dye aggregates. The analysis of absorption data reveals that JGB dye interacts with DNA at multiple binding sites, including at least one high-affinity site. The AutoDock Vina based blind docking approach was used to analyze the most probable binding location of JGB dye in DNA. By making use of the DNA-induced metachromasia, a colorimetric approach was developed for the visualization of loop-mediated isothermal amplification (LAMP) and polymerase chain reaction (PCR). The LAMP-colorimetric assay, targeting the Streptococcus pneumoniae gene, demonstrated a noticeable colour change with a detection limit of 1 pg μL-1. The practical applicability was validated by detecting S. pneumoniae in artificial urine. In addition to LAMP, we tested the JGB dye based colorimetric assay for applicability in PCR reactions. The colorimetric PCR assay using the metal-responsive transcription factor (MTF-1) gene achieved a detection limit as low as 0.1 pg μL-1. The study highlights the potential of DNA binding metachromic dye to significantly enhance colorimetric assays, offering a robust and sensitive tool for molecular diagnostics.

Recent progress on DNAzyme-based biosensors for pathogen detection

Pathogens endanger food safety, agricultural productivity, and human health. Those pathogens are spread through direct/indirect contact, airborne transmission and food/waterborne transmission, and some cause severe health consequences. As the population grows and global connections intensify, the transmission of infectious diseases expands. Traditional detection methods for pathogens still have some shortcomings, such as time-consuming procedures and high operational costs. To fulfil the demands for simple and effective detection, numerous biosensors have been developed. DNAzyme, a unique DNA structure with catalytic activity, is gradually being applied in the field of pathogen detection owing to its ease of preparation and use. In this review, we concentrated on the two main types of DNAzyme, hemin/G-quadruplex DNAzyme (HGD) and RNA-cleaving DNAzyme (RCD), explaining their research progress in pathogen detection. Furthermore, we introduced two additional novel DNAzymes, CLICK 17 DNAzyme and Supernova DNAzyme, which showed promising potential in pathogen detection. Finally, we summarize the strengths and weaknesses of these four DNAzymes and offer feasible recommendations for the development of biosensors.

Diverse methods of reducing and confirming false-positive results of loop-mediated isothermal amplification assays: A review

Loop-mediated isothermal amplification (LAMP), a rapid and sensitive isothermal nucleic acid amplification method, is a promising alternative to other molecular amplification techniques due to its superior specificity and sensitivity. However, due to primer dimerization, LAMP results in nonspecific and nontemplate amplification. And during the amplification confirmation process, there is carry-over contamination. These factors can result in false-positive results that overestimate the amount of DNA, preventing accurate detection. This review outlined several techniques for reducing false-positive LAMP results before amplification and confirming false-positive results after amplification. Before the amplification step, DNA polymerase activity can be decreased with organic additives such as dimethyl sulfoxide, betaine, and pullulan to prevent nonspecific amplification. The enzyme uracil-DNA-glycosylase (UDG) can eliminate false-positive results caused by carry-over contamination, and the hot-start effect with gold nanoparticles can reduce nonspecific amplification. When confirming false-positive results using clustered regularly interspaced short palindromic repeats, guide RNA accurately detects LAMP amplification, allowing differentiation from nonspecific amplification. By confirming amplification, the colorimetric change in the deoxyribozyme (DNAzyme) formed by the reaction of the G-quadruplex sequence of the LAMP amplicon and hemin can distinguish false-positive results. Lateral flow immunoassay can distinguish false-positive results by accurately recognizing hybridized probes to LAMP amplicons.

Recent advances in cascade isothermal amplification techniques for ultra-sensitive nucleic acid detection

Nucleic acid amplification techniques have always been one of the hot spots of research, especially in the outbreak of COVID-19. From the initial polymerase chain reaction (PCR) to the current popular isothermal amplification, each new amplification techniques provides new ideas and methods for nucleic acid detection. However, limited by thermostable DNA polymerase and expensive thermal cycler, PCR is difficult to achieve point of care testing (POCT). Although isothermal amplification techniques overcome the defects of temperature control, single isothermal amplification is also limited by false positives, nucleic acid sequence compatibility, and signal amplification capability to some extent. Fortunately, efforts to integrating different enzymes or amplification techniques that enable to achieve intercatalyst communication and cascaded biotransformations may overcome the corner of single isothermal amplification. In this review, we systematically summarized the design fundamentals, signal generation, evolution, and application of cascade amplification. More importantly, the challenges and trends of cascade amplification were discussed in depth.

Development of a Novel Phagomagnetic-Assisted Isothermal DNA Amplification System for Endpoint Electrochemical Detection of Listeria monocytogenes

The hitherto implemented Listeria monocytogenes detection techniques are cumbersome or require expensive non-portable instrumentation, hindering their transposition into on-time surveillance systems. The current work proposes a novel integrated system resorting to loop-mediated isothermal amplification (LAMP), assisted by a bacteriophage P100-magnetic platform, coupled to an endpoint electrochemical technique, towards L. monocytogenes expeditious detection. Molybdophosphate-based optimization of the bacterial phagomagnetic separation protocol allowed the determination of the optimal parameters for its execution (pH 7, 25 °C, 32 µg of magnetic particles; 60.6% of specific capture efficiency). The novel LAMP method targeting prfA was highly specific, accomplishing 100% inclusivity (for 61 L. monocytogenes strains) and 100% exclusivity (towards 42 non-target Gram-positive and Gram-negative bacteria). As a proof-of-concept, the developed scheme was successfully validated in pasteurized milk spiked with L. monocytogenes. The phagomagnetic-based approach succeeded in the selective bacterial capture and ensuing lysis, triggering Listeria DNA leakage, which was efficiently LAMP amplified. Methylene blue-based electrochemical detection of LAMP amplicons was accomplished in 20 min with remarkable analytical sensitivity (1 CFU mL^-1). Hence, the combined system presented an outstanding performance and robustness, providing a 2.5 h-swift, portable, cost-efficient detection scheme for decentralized on-field application.

Smartphone-Based SARS-CoV-2 and Variants Detection System using Colorimetric DNAzyme Reaction Triggered by Loop-Mediated Isothermal Amplification (LAMP) with Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)

Coronavirus disease (COVID-19) has affected people for over two years. Moreover, the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants has raised concerns regarding its accurate diagnosis. Here, we report a colorimetric DNAzyme reaction triggered by loop-mediated isothermal amplification (LAMP) with clustered regularly interspaced short palindromic repeats (CRISPR), referred to as DAMPR assay for detecting SARS-CoV-2 and variants genes with attomolar sensitivity within an hour. The CRISPR-associated protein 9 (Cas9) system eliminated false-positive signals of LAMP products, improving the accuracy of DAMPR assay. Further, we fabricated a portable DAMPR assay system using a three-dimensional printing technique and developed a machine learning (ML)-based smartphone application to routinely check diagnostic results of SARS-CoV-2 and variants. Among blind tests of 136 clinical samples, the proposed system successfully diagnosed COVID-19 patients with a clinical sensitivity and specificity of 100% each. More importantly, the D614G (variant-common), T478K (delta-specific), and A67V (omicron-specific) mutations of the SARS-CoV-2 S gene were detected selectively, enabling the diagnosis of 70 SARS-CoV-2 delta or omicron variant patients. The DAMPR assay system is expected to be employed for on-site, rapid, accurate detection of SARS-CoV-2 and its variants gene and employed in the diagnosis of various infectious diseases.

G-quadruplex based biosensors for the detection of food contaminants

G-quadruplex (G4) is a very interesting DNA structure, commonly associated with cancer and its treatment. With flexible binding ability, G4 has been extended as a significant component in biosensors. On account of its simple operation, high sensitivity and low cost, G4-based biosensors have attracted considerable interest for the detection of food contaminants. In this review, research published in recent 5 years is collated from a principle perspective, that is target recognition and signal transduction. Contaminants with G4 binding capacity are illustrated, emerging G4-based biosensors including colorimetric, electrochemical and fluorescent sensors are also elaborated. The current review indicates that G4 has provided an efficient and effective solution for the rapid detection of food contaminants. A distinctive feature of G4 as recognition unit is the simple composition, but the selectivity is still unsatisfactory. As signal reporter, G4/hemin DNAzyme has not only achieved amplified signals, but also enabled visualized detection, which offers great potential for on-site measurement. With improved selectivity and visualized signal, the combination of aptamer and G4 seems to be an ideal strategy. This promising combination should be developed for the real-time monitor of multiple contaminants in food matrix.

Design of a High-Sensitivity Dimeric G-Quadruplex/Hemin DNAzyme Biosensor for Norovirus Detection

G-quadruplexes can bind with hemin to form peroxidase-like DNAzymes that are widely used in the design of biosensors. However, the catalytic activity of G-quadruplex/hemin DNAzyme is relatively low compared with natural peroxidase, which hampers its sensitivity and, thus, its application in the detection of nucleic acids. In this study, we developed a high-sensitivity biosensor targeting norovirus nucleic acids through rationally introducing a dimeric G-quadruplex structure into the DNAzyme. In this strategy, two separate molecular beacons each having a G-quadruplex-forming sequence embedded in the stem structure are brought together through hybridization with a target DNA strand, and thus forms a three-way junction architecture and allows a dimeric G-quadruplex to form, which, upon binding with hemin, has a synergistic enhancement of catalytic activities. This provides a high-sensitivity colorimetric readout by the catalyzing H2O2-mediated oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline -6-sulfonic acid) diammonium salt (ABTS). Up to 10 nM of target DNA can be detected through colorimetric observation with the naked eye using our strategy. Hence, our approach provides a non-amplifying, non-labeling, simple-operating, cost-effective colorimetric biosensing method for target nucleic acids, such as norovirus-conserved sequence detection, and highlights the further implication of higher-order multimerized G-quadruplex structures in the design of high-sensitivity biosensors.

DEOXYRIBOZYMES IN DETECTION OF PATHOGENIC BACTERIA

Aim. The purpose of the review was to analyze the use of DNAzyme biosensors for the detection of pathogens. In the recent years, deoxyribozymes (DNAzymes) have a significant impact as biosensors in diverse fields, from detection of metal ions in the environment to theranostic applications and detection of microorganisms. Although routinely used sophisticated instrumental methods are available to detect pathogenic bacterial contamination, they involve time-consuming, complicated sample pre-treatment and expensive instruments. As an alternative, pathogen-specific DNAzymes have demonstrated a series of advantages: a non-destructive rapid analysis technique with in situ and real-time detection of bacteria with high sensitivity and selectivity. A wide range of pathogen-specific DNAzymes has been developed using colorimetric and fluorescence-based detections for pathogenic bacterial contamination in various samples. The current review summarizes the in vitro selection of pathogen-specific DNAzymes, various strategies utilized in the sensor designs, and their potential use in theranostic applications.

DNAzyme-Based Biosensors: Immobilization Strategies, Applications, and Future Prospective

Since their discovery almost three decades ago, DNAzymes have been used extensively in biosensing. Depending on the type of DNAzyme being used, these functional oligonucleotides can act as molecular recognition elements within biosensors, offering high specificity to their target analyte, or as reporters capable of transducing a detectable signal. Several parameters need to be considered when designing a DNAzyme-based biosensor. In particular, given that many of these biosensors immobilize DNAzymes onto a sensing surface, selecting an appropriate immobilization strategy is vital. Suboptimal immobilization can result in both DNAzyme detachment and poor accessibility toward the target, leading to low sensing accuracy and sensitivity. Various approaches have been employed for DNAzyme immobilization within biosensors, ranging from amine and thiol-based covalent attachment to non-covalent strategies involving biotin-streptavidin interactions, DNA hybridization, electrostatic interactions, and physical entrapment. While the properties of each strategy inform its applicability within a proposed sensor, the selection of an appropriate strategy is largely dependent on the desired application. This is especially true given the diverse use of DNAzyme-based biosensors for the detection of pathogens, metal ions, and clinical biomarkers. In an effort to make the development of such sensors easier to navigate, this paper provides a comprehensive review of existing immobilization strategies, with a focus on their respective advantages, drawbacks, and optimal conditions for use. Next, common applications of existing DNAzyme-based biosensors are discussed. Last, emerging and future trends in the development of DNAzyme-based biosensors are discussed, and gaps in existing research worthy of exploration are identified.

Integrating multiple hybridization chain reactions on gold nanoparticle and alkaline phosphatase-mediated in situ growth of gold nanobipyramids: An ultrasensitive and high color resolution colorimetric method to detect the mecA gene of Staphylococcus aureus

Colorimetry has been considered as a potential instrument-free platform for point-of-care genomic detection. However, it is limited by the poor sensitivity and low color resolution. Herein, we report a high-resolution colorimetric biosensor based on multiple hybridization chain reactions (HCRs) on gold nanoparticle (AuNP) and alkaline phosphatase (ALP)-mediated in situ growth of gold nanobipyramids (AuNBPs) for ultrasensitive detection of the Staphylococcus aureus (S. aureus) mecA gene. In our design, target DNA is hybridized with capture hairpin DNA on magnetic beads and then amplified by multiple HCRs on AuNP. Since biotin-labeled hairpin-structured nucleic acids are utilized to conduct HCRs, together with the large specific surface area of AuNP, the biotin- and streptavidin- based reaction results in a large amount of ALP on AuNP. With the aid of NADPH, ALP-mediated in situ growth of AuNBPs is observed, and a series of rainbow-like colors are associated with different target DNA concentrations. Through the multiple-amplification strategy produced by AuNP, HCRs, and enzymatic reactions, the target DNA as low as 2.71 pM can be detected with high specificity. Moreover, this method has been successfully applied to detect the mecA gene extracted from S. aureus. Therefore, the proposed method holds great potential in clinical diagnosis.

RNA-cleaving DNAzymes as a diagnostic and therapeutic agent against antimicrobial resistant bacteria

The development of nucleic-acid-based antimicrobials such as RNA-cleaving DNAzyme (RCD), a short catalytically active nucleic acid, is a promising alternative to the current antibiotics. The current rapid spread of antimicrobial resistance (AMR) in bacteria renders some antibiotics useless against bacterial infection, thus creating the need for alternative antimicrobials such as DNAzymes. This review summarizes recent advances in the use of RCD as a diagnostic and therapeutic agent against AMR. Firstly, the recent diagnostic application of RCD for the detection of bacterial cells and the associated resistant gene(s) is discussed. The next section summarises the therapeutic application of RCD in AMR bacterial infections which includes direct targeting of the resistant genes and indirect targeting of AMR-associated genes. Finally, this review extends the discussion to challenges of utilizing RCD in real-life applications, and the potential of combining both diagnostic and therapeutic applications of RCD into a single agent as a theranostic agent.

Development of an in-situ signal amplified electrochemical assay for detection of Listeria monocytogenes with label-free strategy

Listeria monocytogenes is an important foodborne pathogen, which imposes great burdens on public health. The current methods for detecting L. monocytogene are limited in several ways such as time consuming and lab equipment dependent. In this study, we developed a new electrochemical assay to improve the efficacy. This assay allows us to generate numerous G-quadruplex sequences while loop-mediated isothermal amplification happens. Then, these G-quadruplex sequences form DNAzyme to produce a color change and an electrochemical signal by oxidizing tetramethylbenzidine. This assay could be finished in 2 h, which significantly reduced the detection time. Also, we confirmed the limit of detection of this assay at 6.8 CFU/mL according to 3σ criterion. Our assay shows good sensitivity to detect bacteria range from 52.5 to 5.25 × 10⁴ CFU/mL. This assay's reliability was also confirmed by detecting artificially contaminated pork samples. Thus, we propose this electrochemical assay for rapid and sensitive detection of L. monocytogenes in food.

Solid-Phase PCR-Amplified DNAzyme Activity for Real-Time FO-SPR Detection of the MCR-2 Gene

The polymerase chain reaction (PCR) has been the gold standard molecular analysis technique for decades and has seen quite some evolution in terms of reaction components, methodology, and readout mechanisms. Nucleic acid enzymes (NAzymes) have been used to further exploit the applications of PCR, but so far the work was limited to the colorimetric G-quadruplex or fluorescent substrate cleaving NAzymes. In this study, a solid-phase, fiber optic surface plasmon resonance (FO-SPR) technique is presented as an alternative readout for PCR utilizing NAzymes. First, the surface cleavage activity of DNAzyme-extended amplicons (DNAzyme-amps) is established, followed by optimization of the PCR conditions, which are required for compatibility with the FO-SPR system. Next, by integrating the complement of a 10-23 DNAzyme into the primer pair, PCR-amplified DNAzyme-amps were generated, tested, and validated on qPCR for the detection of the antimicrobial resistance gene MCR-2. Once validated, this primer concept was developed as a one-step assay, driven by PCR-amplified DNAzymes, for FO-SPR-based sensitive and specific detection. Using gold nanoparticle labeled RNA-DNA hybrid strands as substrate for the DNAzyme, PCR-amplified DNAzyme-amps generated in the presence of MCR-2 gene were monitored in real-time, which resulted in an experimental limit of detection of 4 × 10⁵ copy numbers or 6.6 fM. In addition, the DNAzyme-based FO-PCR assay was able to discriminate between the MCR-1 and MCR-2 genes, to further prove the specificity of this assay. Henceforth, this DNAzyme-based fiber optic PCR assay provides a universally applicable, real-time system for the detection of virtually any target NA, in a specific and sensitive manner.

A signal cascade amplification strategy based on RT-PCR triggering of a G-quadruplex DNAzyme for a novel electrochemical detection of viable Cronobacter sakazakii

Cronobacter sakazakii is an important opportunistic food-borne pathogen, and it can cause severe diseases with main symptoms including neonatal meningitis, necrotizing enterocolitis, and sepsis. For the achievement of practical and convenient detection of viable C. sakazakii, a simple and robust strategy based on the cascade signal amplification of RT-PCR triggered G-quadruplex DNAzyme catalyzed reaction was firstly used to develop an effective and sensitive DNAzyme electrochemical assay. Without viable C. sakazakii in the samples there are no RT-PCR and DNAzyme products, which can cause a weak electrochemical response. Once viable C. sakazakii exists in the samples, an obvious enhancement of the electrochemical response can be achieved after the target signal is amplified by RT-PCR and the resulting DNAzyme, which catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 with the assistance of the cofactor hemin. Our novel assay can be performed in a range of 2.4 × 107 CFU mL-1 to 3.84 × 104 CFU mL-1 (R2 = 0.9863), with a detection limit of 5.01 × 102 CFU mL-1. Through the assay of 15 real samples, electrochemical detection assay provided the same results as conventional detection methods. Therefore, detection of viable C. sakazakii based on G-quadruplex DNAzyme electrochemical assay with RT-PCR demonstrates the significant advantages of high sensitivity, low cost and simple manipulation over existing approaches and offers an opportunity for potential application in pathogen detection.

Advances in Using Nanotechnology Structuring Approaches for Improving Food Packaging

Recent advances in food packaging materials largely rely on nanotechnology structuring. Owing to several unique properties of nanostructures that are lacking in their bulk forms, the incorporation of nanostructures into packaging materials has greatly improved the performance and enriched the functionalities of these materials. This review focuses on the functions and applications of widely studied nanostructures for developing novel food packaging materials. Nanostructures that offer antimicrobial activity, enhance mechanical and barrier properties, and monitor food product freshness are discussed and compared. Furthermore, the safety and potential toxicity of nanostructures in food products are evaluated by summarizing the migration activity of nanostructures to different food systems and discussing the metabolism of nanostructures at the cellular level and in animal models.

Amplified visual detection of microRNA-378 through a T4 DNA ligase-mediated circular template specific to target and target-triggering rolling circle amplification

MicroRNA-378 (miRNA-378) is widely regarded as a novel noninvasive serum biomarker for early detection of gastric cancer.

Visual diagnostic of Helicobacter pylori based on a cascade amplification of PCR and G-quadruplex DNAzyme as a color label

Helicobacter pylori is a spiral-shaped, Gram-negative, microaerophilic and fastidious bacterium. It is the main cause of chronic gastritis as well as gastric and duodenal ulcers. The diagnosis of H. pylori infection is significant for the selection of therapy and for the follow up of eradication success. A simple and robust strategy based on the cascade of PCR and DNAzyme catalyzed reaction was utilized to detect H. pylori. The design of the primer pair would enable PCR to synthesize aptamer of DNAzyme at the 3' end of PCR products. G-quadruplex DNAzyme as a color label can exhibit peroxidase-like activity to amplify the specific signal and demonstrate a colorimetric signal to indicate the diagnostic result. This assay can detect genomic DNA of H. pylori specifically with as low as 100 pg/reaction by the naked eye. This is a powerful demonstration of G-quadruplex DNAzyme to be used for PCR-based assay with significant advantages of high sensitivity, low cost and simple manipulation over existing approaches and offers the potential opportunity for clinical application.