Target-Recycling-Amplified Colorimetric Detection of Pollen Allergen Using Non-Cross-Linking Aggregation of DNA-Modified Gold Nanoparticles

DNA-Assisted CRISPR-Cas12a Enhanced Fluorescent Assay for Protein Detection in Complicated Matrices

Proteins are important biological macromolecules that perform a wide variety of functions in the cell and human body, and can serve as important biomarkers for early diagnosis and prognosis of human diseases as well as monitoring the effectiveness of disease treatment. Hence, sensitive and accurate detection of proteins in human biospecimens is imperative. However, at present, there is no ideal method available for the detection of proteins in clinical samples, many of which are present at ultralow (less than 1 pM) concentrations and in complicated matrices. Herein, we report an ultrasensitive and selective DNA-assisted CRISPR-Cas12a enhanced fluorescent assay (DACEA) for protein detection with detection limits reaching as low as attomolar concentrations. The high assay sensitivity was accomplished through the combined DNA barcode amplification (by using dual-functionalized AuNPs) and CRISPR analysis, while the high selectivity and high resistance to the matrix effects of our method were accomplished via the formation of protein-antibody sandwich structure and the specific recognition of Cas12a (under the guidance of crRNA) toward the designed target ssDNA. Given its ability to accurately and sensitively detect trace amounts of proteins in complicated matrices, the DACEA protein assay platform pioneered in this work has a potential application in routine protein biomarker testing.

Screening, identification, and application of aptamers against allergens in food matrices

Food allergies have become one of the most pressing issues in food safety and public health globally along with their incidence increasing in recent years. The reliable recognition of allergens from different sources, especially food-hidden allergens, is essential for preventing and controlling food allergies. Recently, aptamers, as emerging recognition elements, have gained considerable attention in food allergy, especially in the detection of food allergens. This review systematically summarizes the latest progress in screening, identification, and application of aptamers against food allergens over the past five years. We first introduce a brief overview of food allergy and aptamers, followed by a detailed focus on the aptamers' research against different food allergens broadly based on the major categories of the Big-8 allergens: highlighting the newly screened aptamers and their applied systematic evolution of ligands by exponential enrichment (SELEX) strategies, and emphasizing their practical applications including aptasensors, allergy inhibitors, or affinity adsorptions. Finally, the remaining challenges and future exploitations faced by aptamers in food allergens are comprehensively discussed and depicted. This review holds the promise of inspiring a broader range of researchers to gain an in-depth understanding of food allergy assisted by aptamer recognition and to facilitate improved biochemical analyses and successful application.

Sensing Interfaces Engineering for Organic Thin Film Transistors-Based Biosensors: Opportunities and Challenges

Organic thin film transistors (OTFTs) enable rapid and label-free high-sensitivity detection of target analytes due to their low cost, large-area processing, biocompatibility, and inherent signal amplification. At the same time, the freedom of synthesis, tailorability, and functionalization of organic semiconductor materials and their ability to be combined with flexible substrates make them one of the ideal platforms for biosensing. However, OTFTs-based biosensors still face significant challenges, such as unexpected surface adsorption, disordered conformation, inhomogeneous graft density, and flexibility of probe molecules that biological sensing probes would face during immobilization. In this review, efficient immobilization strategies based on OTFTs biological sensing probes developed in the last 5 years are highlighted. First, the biosensors are classified according to their sensing interface. Second, a comprehensive discussion of the types of biological sensing probes is presented. Third, three commonly used methods for immobilizing biological sensing probes and their challenges are briefly described. Finally, the applications of OTFTs-based biosensors for liquid phase detection are summarized. This review provides a comprehensive and timely review of optimization in sensing interface engineering so that efficient immobilization of biological sensing probes with sensing interfaces will contribute to the development of high-performance OTFTs-based biosensors.

Colorimetric detection of African swine fever (ASF)-associated microRNA based on rolling circle amplification and salt-induced gold nanoparticle aggregation

African swine fever (ASF) is a severe viral disease with a high mortality rate in domestic and wild pigs, for which no effective vaccine and antiviral drugs are available. The great infectivity of the ASF virus highlights the need for sensitive, simple, and on-site detection assays of ASF. We herein developed a colorimetric sensing strategy for the detection of an ASF-associated miRNA, based on isothermal rolling circle amplification (RCA) and salt-induced gold nanoparticle aggregation. Ssc-miR-451 was selected as the target ASF biomarker due to its high expression in ASF virus-infected pigs. With a red-purple-blue color shifting, this biosensing platform offers convenient detection of ssc-miR-451 with a UV-Vis spectrometer or the naked eye. The proposed assay exhibits a dose-response relationship between the optical absorbance ratio (A525/A640) and the amounts of ssc-miR-451, with a detection limit calculated as 3.56 fmol (equivalent to 11.86 pM in 300 μL reaction mixture). This assay's coefficient of variation (CV%) was determined to be less than 5.95%, revealing its reproducibility is satisfactory. In addition, the newly developed method was successfully applied in the detection of spiked ssc-miR-451 in pig serum samples. In light of its simplicity, convenience (colorimetric), sensitivity, and energy efficiency (isothermal amplification), this biosensing strategy presents great potential to be applied in the local swine industry and pig farming for screening of viral diseases affecting pigs.

Outdoor airborne allergens: Characterization, behavior and monitoring in Europe

Aeroallergens or inhalant allergens, are proteins dispersed through the air and have the potential to induce allergic conditions such as rhinitis, conjunctivitis, and asthma. Outdoor aeroallergens are found predominantly in pollen grains and fungal spores, which are allergen carriers. Aeroallergens from pollen and fungi have seasonal emission patterns that correlate with plant pollination and fungal sporulation and are strongly associated with atmospheric weather conditions. They are released when allergen carriers come in contact with the respiratory system, e.g. the nasal mucosa. In addition, due to the rupture of allergen carriers, airborne allergen molecules may be released directly into the air in the form of micronic and submicronic particles (cytoplasmic debris, cell wall fragments, droplets etc.) or adhered onto other airborne particulate matter. Therefore, aeroallergen detection strategies must consider, in addition to the allergen carriers, the allergen molecules themselves. This review article aims to present the current knowledge on inhalant allergens in the outdoor environment, their structure, localization, and factors affecting their production, transformation, release or degradation. In addition, methods for collecting and quantifying aeroallergens are listed and thoroughly discussed. Finally, the knowledge gaps, challenges and implications associated with aeroallergen analysis are described.

Recent Advances in Design and Application of Nanomaterials-Based Colorimetric Biosensors for Agri-food Safety Analysis

A colorimetric sensor detects an analyte by utilizing the optical properties of the sensor unit, such as absorption or reflection, to generate a structural color that serves as the output signal to detect an analyte. Detecting the refractive index of an analyte by recording the color change of the sensor structure on its surface has several advantages, including simple operation, low cost, suitability for onsite analysis, and real-time detection. Colorimetric sensors have drawn much attention owing to their rapidity, simplicity, high sensitivity and selectivity. This Review discusses the use of colorimetric sensors in the food industry, including their applications for detecting food contaminants. The Review also provides insight into the scope of future research in this area.

Nanotechnology in Food and Plant Science: Challenges and Future Prospects

Globally, food safety and security are receiving a lot of attention to ensure a steady supply of nutrient-rich and safe food. Nanotechnology is used in a wide range of technical processes, including the development of new materials and the enhancement of food safety and security. Nanomaterials are used to improve the protective effects of food and help detect microbial contamination, hazardous chemicals, and pesticides. Nanosensors are used to detect pathogens and allergens in food. Food processing is enhanced further by nanocapsulation, which allows for the delivery of bioactive compounds, increases food bioavailability, and extends food shelf life. Various forms of nanomaterials have been developed to improve food safety and enhance agricultural productivity, including nanometals, nanorods, nanofilms, nanotubes, nanofibers, nanolayers, and nanosheets. Such materials are used for developing nanofertilizers, nanopesticides, and nanomaterials to induce plant growth, genome modification, and transgene expression in plants. Nanomaterials have antimicrobial properties, promote plants' innate immunity, and act as delivery agents for active ingredients. Nanocomposites offer good acid-resistance capabilities, effective recyclability, significant thermostability, and enhanced storage stability. Nanomaterials have been extensively used for the targeted delivery and release of genes and proteins into plant cells. In this review article, we discuss the role of nanotechnology in food safety and security. Furthermore, we include a partial literature survey on the use of nanotechnology in food packaging, food safety, food preservation using smart nanocarriers, the detection of food-borne pathogens and allergens using nanosensors, and crop growth and yield improvement; however, extensive research on nanotechnology is warranted.

Multifold improvement in allergen detection capability of dipstick-type immunosensors via macromolecular crowding

Dipstick-type lateral flow immunosensors are used widely for on-site detection of food allergens. The weakness of the immunosensors of this type, however, is their low sensitivity. Contrary to current methods, that focus on improving detection capability through the introduction of novel labels or multistep protocols, this work exploits macromolecular crowding to modify and regulate the microenvironment of the immunoassay, thus promoting the interactions that are responsible for allergen recognition and signal generation. The effect of 14 macromolecular crowding agents was explored using, as a model, commercially available and widely applied dipstick immunosensors, which are already optimized in terms of reagents and conditions for peanut allergen detection. An about 10-fold improvement in detection capability was achieved by using polyvinylpyrrolidone, Mr 29,000, as a macromolecular crowder without compromising simplicity and practicality. The proposed approach is complementary to other methods of improving the sensitivity by using novel labels. Because biomacromolecular interactions have a fundamental role in all types of biosensors, we foresee that the proposed strategy will also find applications in other biosensors and analytical devices.

Gold Nanoparticles-Based Colorimetric Assays for Environmental Monitoring and Food Safety Evaluation

Recent years have witnessed an exponential increase in the research on gold nanoparticles (AuNPs)-based colorimetric sensors to revolutionize point-of-use sensing devices. Hence, this review is compiled focused on current progress in the design and performance parameters of AuNPs-based sensors. The review begins with the characteristics of AuNPs, followed by a brief explanation of synthesis and functionalization methods. Then, the mechanisms of AuNPs-based sensors are comprehensively explained in two broad categories based on the surface plasmon resonance (SPR) characteristics of AuNPs and their peroxidase-like catalytic properties (nanozyme). SPR-based colorimetric sensors further categorize into aggregation, anti-aggregation, etching, growth-mediated, and accumulation-based methods depending on their sensing mechanisms. On the other hand, peroxidase activity-based colorimetric sensors are divided into two methods based on the expression or inhibition of peroxidase-like activity. Next, the analytes in environmental and food samples are classified as inorganic, organic, and biological pollutants, and recent progress in detection of these analytes are reviewed in detail. Finally, conclusions are provided, and future directions are highlighted. Improving the sensitivity, reproducibility, multiplexing capabilities, and cost-effectiveness for colorimetric detection of various analytes in environment and food matrices will have significant impact on fast testing of hazardous substances, hence reducing the pollution load in environment as well as rendering food contamination to ensure food safety.

Universal and Flexible Signal Transduction Module Based on Overload Triggering Probe Escape for Sensitive Detection of Tau Protein

Aptamer-based methods have attracted increasing interest due to flexible engineering, but their generality is limited by the heterogeneity of signal transduction mechanisms. Given the fact that nonlinear and large molecules are more likely to make the nanosurface overloaded, we investigated a novel signal transduction process to extend the application of aptasensors. In this work, an aptamer complementary element (ACE) is designed with a primer region to serve as the signal probe, which can fully hybridize with an aptamer and be separated by magnetic beads (MBs). Upon target binding, the formed aptamer/target complex is much larger than the linear aptamer/ACE-primer dimer, causing overload of MBs on account of steric hindrance. An extra aptamer/ACE-primer can escape from the surface to the supernatant, which can be amplified by a catalytic hairpin assembly (CHA) circle. The size-dependent signal transduction and the modular design endow the method with high generality and flexibility for protein analysis. The proposed aptasensor was successfully applied to the detection of tau proteins ranging from 0.5 to 1000 ng mL^-1 with a limit of detection (LOD) as low as 0.254 ng mL^-1. The recovery tests in both human serum and cerebra spinal fluid confirmed the high accuracy and stability. Furthermore, a successful distinction was made between AD patients and healthy controls by the method, suggesting the possible applicability for practical analysis of tau proteins.

Recent Advancements in Aptamer-Based Surface Plasmon Resonance Biosensing Strategies

Surface plasmon resonance (SPR) can track molecular interactions in real time, and is a powerful as well as widely used biological and chemical sensing technique. Among the different SPR-based sensing applications, aptamer-based SPR biosensors have attracted significant attention because of their simplicity, feasibility, and low cost for target detection. Continuous developments in SPR aptasensing research have led to the emergence of abundant technical and design concepts. To understand the recent advances in SPR for biosensing, this paper reviews SPR-based research from the last seven years based on different sensing-type strategies and sub-directions. The characteristics of various SPR-based applications are introduced. We hope that this review will guide the development of SPR aptamer sensors for healthcare.

Plasmon switching of gold nanoparticles through thermo-responsive terminal breathing of surface-grafted DNA in hydrated ionic liquids

Self-assembly performed in ionic liquids (ILs) as a unique solvent promises distinct functions and applications in sensors, therapeutics, and optoelectronic devices due to the rich interactions between nanoparticle building blocks and ILs. However, the general consideration that common nanoparticles are readily destabilized by counterions in an IL has largely prevented researchers from investigating controlled nanoparticle assembly in IL-based systems. This study explores the assembling behaviour of double-stranded (ds) DNA-functionalized gold nanoparticles (dsDNA-AuNPs) in hydrated ionic liquids. The DNA base pair stacking assembly of dsDNA-AuNPs occurs at a low IL concentration (<5%). However, a moderate ionic liquid concentration (5-40%) can de-hybridize dsDNA and leaves single-stranded (ss) DNA stabilizing the AuNPs. In concentrated ionic liquids (>40%), interestingly, the higher ionic strength leads to the assembly of DNA-AuNPs. The triphasic assembly trend is also generally observed regardless of the type of IL. By down-regulation of DNA's melting temperature with the IL, the assembly of DNA-AuNPs affords robust response to a lower temperature range, promising applications in plasmonic devices and range-tunable temperature sensors.

Transcription-Based Amplified Colorimetric Thrombin Sensor Using Non-Crosslinking Aggregation of DNA-Modified Gold Nanoparticles

Gold nanoparticles (AuNPs) have been employed as colorimetric biosensors due to the color difference between their dispersed (red) and aggregated (blue) states. Although signal amplification reactions triggered by structural changes of the ligands on AuNPs have been widely used to improve measurement sensitivity, the use of ligands is limited. In this study, we designed a AuNP-based signal-amplifying sandwich biosensor, which does not require a conformational change in the ligands. Thrombin was used as a model target, which is recognized by two different probes. In the presence of the target, an extension reaction occurs as a result of hybridization of the two probes. Then RNA synthesis is started by RNA polymerase activation due to RNA promoter duplex formation. The amplified RNA drives aggregation or dispersion of the AuNPs, and a difference of the color if the AuNP solution is observed. As this detection system does not require a conformational change in the ligand, it can be generically applied to a wide range ligands.

Terminal Sequence-Specific Interparticle Attraction between DNA Duplex-Carrying Polystyrene Microparticles in Aqueous Salt Solution Assessed by Optical Tweezers

The dispersion behavior of DNA duplex-carrying colloidal particles in aqueous high-salt solutions shows extraordinary selectivity against the duplex terminal sequence. We investigated the interparticle force between DNA duplex-carrying polystyrene (dsDNA-PS) microparticles in aqueous salt solutions and examined their behavior in relation to the duplex terminal sequences. Force-distance (F-D) curves for a pair of dsDNA-PS particles were recorded with a dual-beam optical tweezers system with the two optically trapped particles closely approaching each other. Interestingly, only 3-5% of the oligo-DNA strands on the dsDNA-PS particles formed a duplex with complementary DNAs, and the F-D curves showed a distinct specificity to the duplex terminal sequences in the interparticle force at a high-NaCl concentration; a clear attraction peak was observed in F-D curves only when the duplex terminal was a complementary base pair. The attractive strength reached 2.6 ± 0.5 pN at 500 mM NaCl and 4.3 ± 1.0 pN at 750 mM NaCl. By sharp contrast, no significant attraction occurred for the particles with mismatched duplex terminals even at 750 mM NaCl. Similar duplex terminal-specificity in the interparticle force was also confirmed for dsDNA-PS particles in divalent MgCl₂ solutions. Considering that the duplex terminal sequences on the dsDNA-PS particles showed only a negligible difference in their surface charges under identical salt conditions, we concluded that the interparticle attraction observed only for the dsDNA-PS particles with complementary duplex terminals is attributable to the salt-facilitated stacking interaction between the paired terminal nucleobases (i.e., blunt-end stacking) on the dsDNA-PS surfaces. Our results thus demonstrate the occurrence of a duplex terminal-specific interparticle force between dsDNA-PS particles under high-salt conditions.

DNA Terminal-Specific Dispersion Behavior of Polystyrene Latex Microparticles Densely Covered with Oligo-DNA Strands Under High-Salt Conditions

We prepared microspheres densely covered with oligo-DNA strands by immobilizing amino-terminated oligo-DNA strands on the surface of carboxylate polystyrene latex (PS) particles via the amide bond formation. The obtained microspheres (ssDNA-PS) stably dispersed in neutral pH buffer containing high concentrations of NaCl. For the ssDNA-PS ≥1 μm diameter, only 3 - 5% of surface-immobilized oligo-DNA could form a duplex with the complementary strands. Nevertheless, the resulting ssDNA-PS showed a distinct duplex terminal dependency in their dispersion behavior under neutral pH and high NaCl conditions; the microspheres with fully-matched duplexes on the surface spontaneously aggregated in a non-crosslinking manner. By contrast, the microspheres with terminal-mismatched duplexes remained dispersed under the identical conditions. These results suggest that the micrometer-scale particles covered with oligo-DNA strands also have high susceptibility to a duplex terminal sequence in their dispersion property, similar to previously reported DNA-functionalized nanoparticles. This property could potentially be used in various applications including analytical purposes.

Using Simple-Structured Split Aptamer for Gold Nanoparticle-based Colorimetric Detection of Estradiol

Demand for the detection of estradiol, which is a naturally occurring hormone, has been increasing. Gold nanoparticle-based colorimetric aptasensors have been developed for estradiol detection; however, the long sequence of aptamers due to the formation of the secondary structure likely affects the sensitivity of the aptasensors. Herein, a sensitive colorimetric biosensor is developed for label-free detection of estradiol by using an estradiol-specific split aptamer. The results demonstrate that a superior response is observed when a split aptamer with a high free energy of the secondary structure (ΔG > -3 kcal/mol) is used, in comparison to that observed using a split aptamer with a low free energy of the secondary structure (ΔG < -3 kcal/mol) at 27°C. After selecting the appropriate split aptamer, the standard calibration curve obtained for estradiol has a detection limit of 6.7 nM, with a linear range of 6.7 nM - 66.7 μM in the logarithmic scale. Furthermore, this assay is sensitive, easy-to-operate, inexpensive, and non-time-consuming (provides results within 50 min), thereby showing potential for clinical applications (detection of other small molecular targets).

Interfacing DNA with Gold Nanoparticles for Heavy Metal Detection

The contamination of heavy metals (e.g., Hg, Pb, Cd and As) poses great risks to the environment and human health. Rapid and simple detection of heavy metals of considerable toxicity in low concentration levels is an important task in biological and environmental analysis. Among the many convenient detection methods for heavy metals, DNA-inspired gold nanoparticles (DNA-AuNPs) have become a well-established approach, in which assembly/disassembly of AuNPs is used for colorimetric signaling of the recognition event between DNA and target heavy metals at the AuNP interface. This review focuses on the recent efforts of employing DNA to manipulate the interfacial properties of AuNPs, as well as the major advances in the colorimetric detection of heavy metals. Beginning with the introduction of the fundamental aspects of DNA and AuNPs, three main strategies of constructing DNA-AuNPs with DNA binding-responsive interface are discussed, namely, crosslinking, electrostatic interaction and base pair stacking. Then, recent achievements in colorimetric biosensing of heavy metals based on manipulation of the interface of DNA-AuNPs are surveyed and compared. Finally, perspectives on challenges and opportunities for future research in this field are provided.

Enhancement of the Peroxidase-Like Activity of Iodine-Capped Gold Nanoparticles for the Colorimetric Detection of Biothiols

A colorimetric assay was developed for the detection of biothiols, based on the peroxidase-like activity of iodine-capped gold nanoparticles (AuNPs). These AuNPs show a synergetic effect in the form of peroxidase-mimicking activity at the interface of AuNPs, while free AuNPs and iodine alone have weak catalytic properties. Thus, iodine-capped AuNPs possess good intrinsic enzymatic activity and trigger the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), leading to a change in color from colorless to yellow. When added to solution, biothiols, such as cysteine, strongly bind to the interface of AuNPs via gold-thiol bonds, inhibiting the catalytic activity of AuNPs, resulting in a decrease in oxidized TMB. Using this strategy, cysteine could be linearly determined, at a wide range of concentrations (0.5 to 20 μM), with a detection limit of 0.5 μM using UV-Vis spectroscopy. This method was applied for the detection of cysteine in diluted human urine.

The Use of a Combination of a Sugar and Surfactant to Stabilize Au Nanoparticle Dispersion against Aggregation during Freeze-Drying

Drying a suspension of nanoparticles typically results in the irreversible aggregation of nanoparticles; however, solutions that contain unstable ingredients are often converted into dried powders to prolong their shelf lives. In this study, the use of a combination of a surface-active agent and sugar was investigated with regard to avoiding the aggregation of nanoparticles during drying. Suspensions of Au nanoparticles (∼60 nm diameter, AuNPs) were freeze-dried in the presence of different combinations of various sugars with a surfactant. Sucrose monopalmitate (SEC16) was mainly used as the surfactant, based on a comparison of antiaggregation effects conferred by various surfactants. The freeze-dried AuNP suspension was then reconstituted, and the avoidance of AuNP aggregation was then examined. The results demonstrated that the use of a combination of a small amount of SEC16 and sugar resulted in a greater redispersibility of AuNPs after freeze-drying than when the individual components were used. Repetition tests of freeze-drying and reconstitution were conducted. The sucrose/SEC16 mixture was freeze-dried on an electroless-plated Au film and then analyzed by infrared spectroscopy. Strong interactions between SEC16 and the Au surface were detected, and these interactions appear to play a crucial role in the antiaggregation of AuNPs during freeze-drying.

Characterizing the non-crosslinked aggregation of DNA-modified gold nanoparticles: effects of DNA length and terminal base pair

We previously reported that fully complementary DNA duplexes formed on gold nanoparticle (GNP) surfaces aggregate at high salt concentrations. We previously reported that DNA-functionalized gold nanoparticles (GNPs) aggregate by hybridization with fully complementary DNA at high salt concentrations. Although this behavior has been applied to some precise naked-eye colorimetric analyses of DNA-related molecules, the aggregation mechanism is still unclear and comprehensive studies are needed. In this paper, we reveal the key factors that influence GNP aggregation. The effects of temperature, electrolyte concentration, probe length, and particle size, which control the stabilities of double-stranded DNAs and GNPs, were investigated. Larger GNPs aggregated more easily, and GNP aggregates were easily formed with ∼15-mer-long probes, while longer probes prevented aggregation, perhaps by preventing the formation of rigid double-stranded DNA layers, compared to shorter probes. Furthermore, GNPs with purine bases at their 5' ends aggregated more easily than those with these bases at their 3' ends. This phenomenon is different from that based on the melting-temperature trend calculated using the nearest-neighbor method.

Gold nanomaterials as key suppliers in biological and chemical sensing, catalysis, and medicine

BACKGROUND

Gold nanoparticles (AuNPs) with unique physicochemical properties have received a great deal of interest in the field of biological, chemical and biomedical implementations. Despite the widespread use of AuNPs in chemical and biological sensing, catalysis, imaging and diagnosis, and more recently in therapy, no comprehensive summary has been provided to explain how AuNPs could aid in developing improved sensing and catalysts systems as well as medical settings.

SCOPE OF REVIEW

The chemistry of Au-based nanosystems was followed by reviewing different applications of Au nanomaterials in biological and chemical sensing, catalysis, imaging and diagnosis by a number of approaches, and finally synergistic combination therapy of different cancers. Afterwards, the clinical impacts of AuNPs, future application of AuNPs, and opportunities and challenges of AuNPs application were also discussed.

MAJOR CONCLUSIONS

AuNPs show exclusive colloidal stability and are considered as ideal candidates for colorimetric detection, catalysis, imaging, and photothermal transducers, because their physicochemical properties can be tuned by adjusting their structural dimensions achieved by the different manufacturing methods.

GENERAL SIGNIFICANCE

This review provides some details about using AuNPs in sensing and catalysis applications as well as promising theranostic nanoplatforms for cancer imaging and diagnosis, and sensitive, non-invasive, and synergistic methods for cancer treatment in an almost comprehensive manner.

Chemically Fueled Plasmon Switching of Gold Nanorods by Single-Base Pairing of Surface-Grafted DNA

The interactions between metal ions and biomolecules are crucial to various bioprocesses. Development of plasmon switching nanodevices that exploit these molecular interactions is of fundamental and technological interest. Here, we show plasmon switching based on rapid aggregation/dispersion of double-stranded DNA-modified gold nanorods (dsDNA-AuNRs) that exhibit colloidal behaviors depending on pairing/unpairing of the terminal bases. The dsDNA-AuNRs bearing a thymine-thymine (T-T) mismatch at the penultimate position undergo spontaneous non-cross-linking aggregation in the presence of Hg²⁺ due to T-Hg-T base pairing. Inversely, the subsequent addition of cysteine (Cys) gives rise to the removal of Hg²⁺ from the T-Hg-T base pair to reproduce the T-T mismatch, resulting in stable dispersion of the dsDNA-AuNRs. The chemical-responsive plasmon switch allows for the rapid and repeatable cycles at room temperature. The validity of the present method is further exemplified by developing another plasmon switch fueled by Ag⁺ and Cys by installing the Ag⁺-binding DNA sequence in the dsDNA-AuNR.

Highly Sensitive in Vitro Diagnostic System of Pandemic Influenza A (H1N1) Virus Infection with Specific MicroRNA as a Biomarker

Several microRNAs (miRNAs) have been reported to be closely related to influenza A virus infection, replication, and immune response. Therefore, the development of the infectious-disease detection system using miRNAs as biomarkers is actively underway. Herein, we identified two miRNAs (miR-181c-5p and miR-1254) as biomarkers for detection of pandemic influenza A H1N1 virus infection and proposed the catalytic hairpin assembly-based in vitro diagnostic (CIVD) system for a highly sensitive diagnosis; this system is composed of two sets of cascade hairpin probes enabling to detect miR-181c-5p and miR-1254. We demonstrated that CIVD kits could not only detect subnanomolar levels of target miRNAs but also distinguish even single-base mismatches. Moreover, this CIVD kit has shown excellent detection performance in real intracellular RNA samples and confirmed results similar to those of conventional methods (microarray and quantitative real-time polymerase chain reaction).

Gold Nanoparticle-Based Colorimetric Strategies for Chemical and Biological Sensing Applications

Gold nanoparticles are popularly used in biological and chemical sensors and their applications owing to their fascinating chemical, optical, and catalytic properties. Particularly, the use of gold nanoparticles is widespread in colorimetric assays because of their simple, cost-effective fabrication, and ease of use. More importantly, the gold nanoparticle sensor response is a visual change in color, which allows easy interpretation of results. Therefore, many studies of gold nanoparticle-based colorimetric methods have been reported, and some review articles published over the past years. Most reviews focus exclusively on a single gold nanoparticle-based colorimetric technique for one analyte of interest. In this review, we focus on the current developments in different colorimetric assay designs for the sensing of various chemical and biological samples. We summarize and classify the sensing strategies and mechanism analyses of gold nanoparticle-based detection. Additionally, typical examples of recently developed gold nanoparticle-based colorimetric methods and their applications in the detection of various analytes are presented and discussed comprehensively.

Regioselective DNA Modification and Directed Self-Assembly of Triangular Gold Nanoplates

As a class of emerging nanoparticles, gold nanotriangles (AuNTs) are characterized by unique structural anisotropy and plasmonic properties. The organization of AuNTs into well-defined architecture potentially promises collective properties that are difficult to produce by individual AuNTs. To date, however, the orientation-controlled self-assembly of AuNTs has been achieved with limited success. Here, we describe an effective and straightforward approach to induce directed self-assembly of AuNTs. By taking advantage of the uneven chemical reactivity of AuNT surfaces, we implement regioselective modification of the edges and the top/bottom surfaces with two different double-stranded DNA (dsDNA) sequences. By means of terminal single base pairing/unpairing, controlled assembly of the dsDNA-modified AuNTs evolves in a face-to-face or edge-to-edge manner based on blunt-end stacking interaction on an intentional region of the AuNTs, along with entropic repulsion by unpaired terminal nucleobases on the other region. This approach could be useful for achieving directed self-assembly of other anisotropic nanoparticles.