Molecular detection using aptamer-modified gold nanoparticles with an immobilized DNA brush for the prevention of non-specific aggregation

Design and application of microfluidics in aptamer SELEX and Aptasensors

Aptamers are excellent recognition molecules obtained from systematic evolution of ligands by exponential enrichment (SELEX) that have been extensively researched for constructing aptasensors. However, in the process from SELEX to the construction of aptasensors, there are many disadvantages, such as tedious and repetitive operations, interference from external factors, and low efficiency, which seriously limits their application scope and development. Introducing the microfluidic technology can realize the integration and intelligence of SELEX and aptasensing, improve the efficiency of SELEX, and enhance the detection performance and convenience of aptasensing. Hence, in this review, the characteristics of various chips based on different driving forces are described firstly. And then summarizing the design of microfluidic devices based on different SELEX methods and showing the strategies of microfluidic aptasensors based on different detection modes. Finally, discussing the difficulties and challenges encountered when microfluidic is integrated with the SELEX and the aptasensors.

Using gold-based nanomaterials for fighting pathogenic bacteria: from detection to therapy

Owing to the unique quantum size effect and surface effect, gold-based nanomaterials (GNMs) are promising for pathogen detection and broad-spectrum antimicrobial activity. This review summarizes recent research on GNMs as sensors for detecting pathogens and as tools for their elimination. Firstly, the need for pathogen detection is briefly introduced with an overview of the physicochemical properties of gold nanomaterials. And then strategies for the application of GNMs in pathogen detection are discussed. Colorimetric, fluorescence, surface-enhanced Raman scattering (SERS) techniques, dark-field microscopy detection and electrochemical methods can enable efficient, sensitive, and specific pathogen detection. The third section describes the antimicrobial applications of GNMs. They can be used for antimicrobial agent delivery and photothermal conversion and can act synergistically with photosensitizers to achieve the precise killing of pathogens. In addition, GNMs are promising for integrated pathogen detection and treatment; for example, combinations of colorimetric or SERS detection with photothermal sterilization have been demonstrated. Finally, future outlooks for the applications of GNMs in pathogen detection and treatment are summarized.

Detection of estradiol with a digital immunoassay using an anti-immunocomplex antibody and single-molecule observation of gold nanoparticles

Gold nanoparticles (AuNPs) have been widely applied to molecular sensors due to their optical properties. We previously reported a molecular detection by observing the scattered light of AuNPs at a single nanoparticle level using dark field microscopy (DFM). Recently, a molecular detection method using digital immunoassay has been reported, taking advantage of the characteristics of DFM. However, the digital immunoassays reported so far have been performed by a conventional sandwich immunoassay, which is difficult to apply to the detection of small molecules. In this study, with the aim of small molecule detection, we developed a digital immunoassay method using an anti-immunocomplex antibody that specifically recognizes immunocomplexes of small molecules with antibodies. The number of AuNPs modified with anti-immunocomplex antibody bound to immunocomplex of estradiol and anti-estradiol antibody was counted at a single nanoparticle level using DFM. We demonstrated for the first time that estradiol molecule can be detected by digital immunoassay using DFM and an anti-immunocomplex antibody with a detection sensitivity of 1 pg/mL.

Anti HER-2 aptamer functionalized gold nanoparticles of dasatinib for targeted chemo-radiotherapy in breast cancer cells

In the present study, gold nanoparticles functionalized with anti HER-2 aptamer were designed for effective targeted delivery of dasatinib (DSB) to breast cancer cells. Anti HER-2 aptamer attached to porous or plain gold nanoparticles were compared for dasatinib delivery. Activated drug with succinic anhydride and L-cysteine linker was used for conjugation of DSB to gold nanoparticles. The loading efficiency of the activated drug on plain and porous gold nanoparticles was 52 and 68 %, respectively, which was significantly more than the loading of free DSB in gold nanoparticles (1-2.5 %). The anti HER-2 aptamer was conjugated to porous gold nanoparticles loaded with the activated drug. Various characterization techniques such as FESEM, TEM, AFM, zeta potential and ICP-MS were used to confirm the binding of the drug to gold nanoparticles. 1HNMR and FTIR spectroscopic analyses were employed to examine the structural characteristics of the conjugated drug. These analytical techniques confirmed the successful incorporation of succinyl and thiol groups onto the drug molecule. The amount of aptamer binding to different types of gold nanoparticles was obtained from the intensity of the light emitted from the bands observed in electrophoresis gel and due to the presence of porosity in porous gold nanoparticles, the amount of aptamer conjugation on porous gold nanoparticles increased compared to plain ones. Cell cytotoxicity and cellular uptake were evaluated by MTT assay and TEM in BT-474 and MCF-7 cells. Aptamer-functionalized porous gold nanoparticles containing activated dasatinib showed higher cytotoxicity and cellular uptake than modified DSB-loaded nanoparticles and un-activated DSB. The combination of radiation therapy with the modified dasatinib attached to porous gold nanoparticles and aptamer demonstrated a notable reduction in the IC50 values for both the BT-474 and MCF-7 cell lines. Specifically, the IC50 value for the BT-474 cells decreased from 6.95 μM (for unmodified dasatinib) to 2.57 μM, while for the MCF-7 cells, it decreased from 13.97 μM to 8.57 μM. These findings indicate a significant improvement in the efficacy of the modified dasatinib compared to its unmodified counterpart when used in conjunction with radiation therapy.

Effect of DNA density immobilized on gold nanoparticles on nucleic acid detection

Gold nanoparticles (AuNPs) have been utilized as colorimetric biosensors, where target molecule-induced AuNP aggregation can be recognized by a colour change from red to blue. Particularly, single-stranded DNA (ssDNA)-immobilized AuNPs (ssDNA-AuNPs) have been applied to genetic diagnosis due to their rapid and sequence-specific aggregation properties. However, the effect of the density of immobilized ssDNA have not been investigated yet. In this study, we developed a method to control the amount of immobilized ssDNA by use of ethylene glycol, which is expected to control the ice crystal spacing in a freezing-thawing ssDNA-AuNP synthesis method. We also investigated the effect of the DNA density on the sensitivity of the target ssDNA detection, and found that the detection sensitivity was improved at lower DNA densities. To discuss the reason for the improved detection sensitivity, we modified the ssDNA-AuNPs with alkane thiol for better dispersion stability against salt. The results suggest that the DNA density, rather than the dispersion stability, has a significant impact on detection sensitivity.

Recent Advances in Biomolecular Detection Based on Aptamers and Nanoparticles

The fast, accurate detection of biomolecules, ranging from nucleic acids and small molecules to proteins and cellular secretions, plays an essential role in various biomedical applications. These include disease diagnostics and prognostics, environmental monitoring, public health, and food safety. Aptamer recognition (DNA or RNA) has gained extensive attention for biomolecular detection due to its high selectivity, affinity, reproducibility, and robustness. Concurrently, biosensing with nanoparticles has been widely used for its high carrier capacity, stability and feasibility of incorporating optical and catalytic activity, and enhanced diffusivity. Biosensors based on aptamers and nanoparticles utilize the combination of their advantages and have become a promising technology for detecting of a wide variety of biomolecules with high sensitivity, reliability, specificity, and detection speed. Via various sensing mechanisms, target biomolecules have been quantified in terms of optical (e.g., colorimetric and fluorometric), magnetic, and electrical signals. In this review, we summarize the recent advances in and compare different aptamer-nanoparticle-based biosensors by nanoparticle types and detection mechanisms. We also share our views on the highlights and challenges of the different nanoparticle-aptamer-based biosensors.

Recent advances in gold nanoparticle-based colorimetric aptasensors for chemical and biological analyses

Aptasensors are amazing among many currently formed procedures due to their excellent particularity, selectivity and responsiveness. These biosensors get more popular in combination with gold nanoparticles (AuNPs) to detect chemical and biological molecules. The response of AuNPs by changing color provides a simple explanation of outcomes. The authors review the recent developments in AuNP-based colorimetric aptasensors designed to sense different chemical and biological molecules. They summarize the procedure of AuNP-based detection and the ordinary instances of currently formed AuNP-based colorimetric procedures. Furthermore, their uses for detecting different analytes based on analyte types are given and the present challenges, overview, and positive views for forming new aptasensors are also regarded.

Shape dependent sensing potential of gold nanoparticles in etching based multicolorimetric plasmonic-ELISA

In the present study, a systematic investigation has been carried out for the first time to assess the potential of three different shapes of gold nanoparticles (AuNPs), viz. nanorods (AuNRs), nanotriangles (AuNTs), and nanospheres (AuNSs), to develop a horseradish peroxidase (HRP) enzyme-mediated etching-based plasmonic ELISA (p-ELISA) strategy. The etching of the AuNPs in ELISA is achieved by 3'-3-5'-5-tetramethylbenzidine (TMB²⁺), which is produced by the biocatalytic conversion of chromogenic TMB via HRP. All three types of AuNPs were interacted with varying concentrations of TMB²⁺ (7-131 μM) (product of HRP enzyme reaction) and characterized for visible color change and by UV-Vis spectroscopy and transmission electron microscopy (TEM). From the comparative analysis of all three shapes of AuNPs, AuNRs exhibited vivid visible color change and absorbance intensity change compared to spherical and triangle-shaped nanoparticles. The TEM analysis of the etched nanoparticles revealed the gradual etching pattern of AuNRs compared to AuNTs which resulted in multicolor generation as opposed to AuNTs where the etching was relatively very fast and thus shows a faster shape transformation and poor color discrimination. Further, the potential of the AuNR etching-based optimized strategy was successfully demonstrated to develop an indirect competitive p-ELISA for human IgG detection. The developed p-ELISA showed an ultra-low visual limit of detection of 1 fg mL^-1 (∼6.54 aM) without the aid of any sophisticated instruments. In the future, the developed competitive p-ELISA strategy can be easily employed to develop cost-effective, portable, and point-of-care assays for the detection of various disease biomarkers with ultra-high sensitivity.

Recent advances in research on biointerfaces: From cell surfaces to artificial interfaces

Biointerfaces are regions where biomolecules, cells, and organic materials are exposed to environmental media or come in contact with other biomaterials, cells, and inorganic/organic materials. In this review article, six research topics on biointerfaces are described to show examples of state-of-art research approaches. First, biointerface design of nanoparticles for molecular detection is described. Functionalized gold nanoparticles can be used for sensitive detection of various target molecules, including chemical compounds and biomolecules, such as DNA, proteins, cells, and viruses. Second, the interaction between bacterial cell surfaces and material surfaces, including the introduction of advances in analytical methods and theoretical calculations, are explained as well as their applications to bioprocesses. Third, bioconjugation technologies for localizing functional proteins at biointerfaces are introduced, in particular, by focusing the potential of enzymes as a catalytic tool for designing different types of bioconjugates that function at biointerfaces. Forth topics is focusing on lipid-protein interaction in cell membranes as natural biointerfaces. Examples of membrane lipid engineering are introduced, and it is mentioned how their compositional profiles affect membrane protein functions. Fifth topic is the physical method for molecular delivery across the biointerface being developed currently, such as highly efficient nanoinjection, electroporation, and nanoneedle devices, in which the key is how to perforate the cell membrane. Final topic is the chemical design of lipid- or polymer-based RNA delivery carriers and their behavior on the cell interface, which are currently attracting attention as RNA vaccine technologies targeting COVID-19. Finally, future directions of biointerface studies are presented.

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.