Ratiometric Fluorescent Biosensor Based on Self-Assembled Fluorescent Gold Nanoparticles and Duplex-Specific Nuclease-Assisted Signal Amplification for Sensitive Detection of Exosomal miRNA

Development of a Novel System Consisting of a Reductase-Like Nanozyme and the Reaction of Resazurin and Ammonia Borane for Sensitive Fluorometric Sensing

We report a novel system consisting of a redox reaction and a highly efficient reductase-like nanozyme, silica-palladium nanoparticles (Pd@SiO2 NPs), as a novel detection platform for fluorometric sensing. In a proof-of-concept demonstration using an oligonucleotide as the detection target, a glass fiber-based sensor is fabricated by covalently conjugating two oligo probes, which are complementary to the adjacent segments of the target oligonucleotide, on Pd@SiO2 NPs and glass fiber, respectively. In the presence of the target oligonucleotide, the two probes are drawn together by the target through sequence-specific hybridization, bringing the Pd@SiO2 NPs to the glass fiber. When the glass fiber is subsequently immersed in a mixture of resazurin and ammonia borane solution, the Pd@SiO2 NPs on the glass fiber trigger the catalytic conversion of resazurin (blue, slightly fluorescent) to resorufin (pink, highly fluorescent) with massive signal amplification, indirectly signaling the presence of the target oligonucleotide. We show that the glass fiber-based fluorometric sensor can detect a target oligonucleotide associated with the BRAF mutation linearly in the concentration range of 20 to 400 pM with a detection limit (LOD) of 15 pM and the specificity to differentiate targets with single-base difference. These results demonstrate a new frontier for the development of a sensitive, specific, and inexpensive nonenzyme-based fluorometric sensing platform as an alternative to conventional enzyme-based assays.

Empowering Exosomes with Aptamers for Precision Theranostics

As information messengers for cell-to-cell communication, exosomes, typically small membrane vesicles (30-150 nm), play an imperative role in the physiological and pathological processes of living systems. Accumulating studies have demonstrated that exosomes are potential biological candidates for theranostics, including liquid biopsy-based diagnosis and drug delivery. However, their clinical applications are hindered by several issues, especially their unspecific detection and insufficient targeting ability. How to upgrade the accuracy of exosome-based theranostics is being widely explored. Aptamers, benefitting from their admirable characteristics, are used as excellent molecular recognition elements to empower exosomes for precision theranostics. With high affinity against targets and easy site-specific modification, aptamers can be incorporated with platforms for the specific detection of exosomes, thus providing opportunities for advancing disease diagnostics. Furthermore, aptamers can be tailored and functionalized on exosomes to enable targeted therapeutics. Herein, this review emphasizes the empowering of exosomes by aptamers for precision theranostics. A brief introduction of exosomes and aptamers is provided, followed by a discussion of recent progress in aptamer-based exosome detection for disease diagnosis, and the emerging applications of aptamer-functionalized exosomes for targeted therapeutics. Finally, current challenges and opportunities in this research field are presented.

Increasing the sensitivity and accuracy of detecting exosomes as biomarkers for cancer monitoring using optical nanobiosensors

The advancement of nanoscience and material design in recent times has facilitated the creation of point-of-care devices for cancer diagnosis and biomolecule sensing. Exosomes (EXOs) facilitate the transfer of bioactive molecules between cancer cells and diverse cells in the local and distant microenvironments, thereby contributing to cancer progression and metastasis. Specifically, EXOs derived from cancer are likely to function as biomarkers for early cancer detection due to the genetic or signaling alterations they transport as payload within the cancer cells of origin. It has been verified that EXOs circulate steadily in bodily secretions and contain a variety of information that indicates the progression of the tumor. However, acquiring molecular information and interactions regarding EXOs has presented significant technical challenges due to their nanoscale nature and high heterogeneity. Colorimetry, surface plasmon resonance (SPR), fluorescence, and Raman scattering are examples of optical techniques utilized to quantify cancer exosomal biomarkers, including lipids, proteins, RNA, and DNA. Many optically active nanoparticles (NPs), predominantly carbon-based, inorganic, organic, and composite-based nanomaterials, have been employed in biosensing technology. The exceptional physical properties exhibited by nanomaterials, including carbon NPs, noble metal NPs, and magnetic NPs, have facilitated significant progress in the development of optical nanobiosensors intended for the detection of EXOs originating from tumors. Following a summary of the biogenesis, biological functions, and biomarker value of known EXOs, this article provides an update on the detection methodologies currently under investigation. In conclusion, we propose some potential enhancements to optical biosensors utilized in detecting EXO, utilizing various NP materials such as silicon NPs, graphene oxide (GO), metal NPs, and quantum dots (QDs).

A "signal off-on" fluorescence bioassay based on 2D-MoS2-tetrahedral DNA bioconjugate for rapid virus detection

In this work we present the preparation of a 2D molybdenum disulphide nanosheets (2D-MoS2) and tetrahedral DNA nanostructures (TDNs) bioconjugate, and its application to the development of a bioassay for rapid and easy virus detection. The bioconjugate has been prepared by using TDNs carrying the capture probe labelled with 6-carboxyfluoresceine (6-FAM). As case of study to assess the utility of the assay developed, we have chosen the SARS-CoV-2 virus. Hence, as probe we have used a DNA sequence complementary to a region of the SARS-CoV-2 ORF1ab gene (TDN-ORF-FAM). This 6-FAM labelled capture probe is located on the top vertex of the tetrahedral DNA nanostructure, the three left vertices of TDNs have a thiol group. These TDNs are bounded to 2D-MoS2 surface through the three thiol groups, allowing the capture probe to be oriented to favour the biorecognition reaction with the analyte. This biorecognition resulting platform has finally been challenged to the detection of the SARS-CoV-2 ORF1ab gene sequence as the target model by measuring fluorescence before and after the hybridization event with a detection limit of 19.7fM. Furthermore, due to high sensitivity of the proposed methodology, it has been applied to directly detect the virus in nasopharyngeal samples of infected patients without the need of any amplification step. The developed bioassay has a wide range of applicability since it can be applied to the detection of any pathogen by changing the probe corresponding to the target sequence. Thus, a novel, hands-on strategy for rapid pathogen detection has proposed and has a high potential application value in the early diagnosis of infections causes by virus or bacteria.

Signal Amplification by Spatial Concentration for Immunoassay on Cellulose Media

Immunoassay is one of the most common bioanalytical techniques from lab-based to point-of-care settings. Over time, various approaches have been developed to amplify signals for greater sensitivity. However, the need for effective, versatile, and simple signal amplification methods persists yet. This paper presents a novel signal amplification method for immunoassay that utilizes spatial concentration of a cellulose-based plate possessing sensor transducers, specifically gold nanoparticles. By modifying the dimensions of the plate, the density of nanoparticles increased, resulting in intensified color signals. The coating material, polydopamine, which is utilized to protect the gold nanoparticles. Chemical changes in nanocomposites are characterized using scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The application of this method to colorimetric quantification demonstrated great consistency across various concentrations of nanoparticles, with better reliability at lower concentration ranges. A model immunoassay is designed to evaluate the analytical performance. As a result, this method successfully corrected a false-negative result with a lowered Kd of 0.509 pmol per zone. This method shows strong signal enhancement capability that can correct false-negative signals in the immunoassays, with potential benefits including versatility, simplicity, low cost, and the ability to operate multiple plates simultaneously.

Exosomes as Powerful Biomarkers in Cancer: Recent Advances in Isolation and Detection Techniques

Exosomes, small extracellular vesicles derived from cells, are known to carry important bioactive molecules such as proteins, nucleic acids, and lipids. These bioactive components play crucial roles in cell signaling, immune response, and tumor metastasis, making exosomes potential diagnostic biomarkers for various diseases. However, current methods for detecting tumor exosomes face scientific challenges including low sensitivity, poor specificity, complicated procedures, and high costs. It is essential to surmount these obstacles to enhance the precision and dependability of diagnostics that rely on exosomes. Merging DNA signal amplification techniques with the signal boosting capabilities of nanomaterials presents an encouraging strategy to overcome these constraints and improve exosome detection. This article highlights the use of DNA signal amplification technology and nanomaterials' signal enhancement effect to improve the detection of exosomes. This review seeks to offer valuable perspectives for the enhancement of amplification methods applied in practical cancer diagnosis and prognosis by providing an overview of how these novel technologies are utilized in exosome-based diagnostic procedures.

Identification and detection of microRNA kidney disease biomarkers in liquid biopsies

PURPOSE OF REVIEW

MicroRNAs (miRNAs) are emerging rapidly as a novel class of biomarkers of major organ disorders, including kidney diseases. However, current PCR-based detection methods are not amenable to development for high-throughput, cost-effective miRNA biomarker quantification.

RECENT FINDINGS

MiRNA biomarkers show significant promise for diagnosis and prognosis of kidney diseases, including diabetic kidney disease, acute kidney injury, IgA nephropathy and delayed graft function following kidney transplantation. A variety of novel methods to detect miRNAs in liquid biopsies including urine, plasma and serum are being developed. As miRNAs are functional transcripts that regulate the expression of many protein coding genes, differences in miRNA profiles in disease also offer clues to underlying disease mechanisms.

SUMMARY

Recent findings highlight the potential of miRNAs as biomarkers to detect and predict progression of kidney diseases. Developing in parallel, novel methods for miRNA detection will facilitate the integration of these biomarkers into rapid routine clinical testing and existing care pathways. Validated kidney disease biomarkers also hold promise to identify novel therapeutic tools and targets.

VIDEO ABSTRACT

http://links.lww.com/CONH/A43.

Ratio fluorescence test strip visualized by amino-functionalized metal-organic framework for rapid sensing of glyphosate

As glyphosate is a broad-spectrum herbicide extensively used in agriculture worldwide, rapid glyphosate detection is essential for food safety and human health. Herein, a ratio fluorescence test strip was prepared and coupled with an amino-functionalized bismuth-based metal-organic framework (NH₂-Bi-MOF) that bonded with copper ion for rapid visualization and determination of glyphosate. NH₂-Bi-MOF had excellent fluorescence performance, and the copper ion, a Lewis acid, was selected as the quencher. The strong chelation of glyphosate with copper ion and its quick interaction with NH₂-Bi-MOF would turn on the fluorescence signal, thus enabling the quantitative sensing of glyphosate, with a linear range of 0.10-200 µmol L^-1, and recoveries between 94.8% and 113.5%. The system was then expanded to a ratio fluorescence test strip, in which the fluorescent ring sticker was set as a binding-in self-calibration to reduce errors from the angle and light dependency. The method realized the visual semi-quantitation referring to a standard card, as well as the ratio quantitation using the gray value output with LOD of 0.82 µmol L^-1. And the as-developed test strip was accessible, portable, and reliable, thus offering a platform for the rapid on-site detection of glyphosate and other residual pesticides.

Fluorescent nano- and microparticles for sensing cellular microenvironment: past, present and future applications

The tumor microenvironment (TME) demonstrates distinct hallmarks, including acidosis, hypoxia, reactive oxygen species (ROS) generation, and altered ion fluxes, which are crucial targets for early cancer biomarker detection, tumor diagnosis, and therapeutic strategies. Various imaging and sensing techniques have been developed and employed in both research and clinical settings to visualize and monitor cellular and TME dynamics. Among these, ratiometric fluorescence-based sensors have emerged as powerful analytical tools, providing precise and sensitive insights into TME and enabling real-time detection and tracking of dynamic changes. In this comprehensive review, we discuss the latest advancements in ratiometric fluorescent probes designed for the optical mapping of pH, oxygen, ROS, ions, and biomarkers within the TME. We elucidate their structural designs and sensing mechanisms as well as their applications in in vitro and in vivo detection. Furthermore, we explore integrated sensing platforms that reveal the spatiotemporal behavior of complex tumor cultures, highlighting the potential of high-resolution imaging techniques combined with computational methods. This review aims to provide a solid foundation for understanding the current state of the art and the future potential of fluorescent nano- and microparticles in the field of cellular microenvironment sensing.

Magnetically Assisted Immobilization-Free Detection of microRNAs Based on the Signal Amplification of Duplex-Specific Nuclease

The double specific nuclease (DSN)-based methods for microRNAs (miRNAs) detection usually require the immobilization of DNA probes on a solid surface. However, such strategies have the drawbacks of low hybridization and cleavage efficiency caused by steric hindrance effect and high salt concentration on the solid surface. Herein, we proposed an immobilization-free method for miRNA detection on the basic of DSN-assisted signal amplification. The biotin- and fluorophore-labeled probes were captured by streptavidin-modified magnetic beads through streptavidin-biotin interactions, thus producing a poor fluorescence signal. Once the DNA probes were hybridized with target miRNA in solution to form DNA-miRNA duplexes, DNA stands in the duplexes would be selectively digested by DSN. The released target miRNA could initiate the next hybridization/cleavage recycling in the homogeneous solution, finally resulting in the release of numerous fluorophore-labeled fragments. The released fluorophores remained in solution and emitted strong fluorescence after treatment by the streptavidin-modified magnetic beads. The immobilization-free method achieved the assays of miRNA-21 with a detection limit down to 0.01 pM. It was employed to evaluate the expression levels of miRNA-21 in different cancer cells with satisfactory results.

A Ratiometric Fluorescence Amplification Using Copper Nanoclusters with o-Phenylenediamine Sensor for Determination of Mercury (II) in Natural Water

A simple and rapid method for determining mercury (II) has been developed using L-cysteine-capped copper nanocluster (CuNCs) with o-phenylenediamine (OPD) as the sensor. The characteristic fluorescence peak of the synthesized CuNCs was observed at 460 nm. The fluorescence properties of CuNCs were strongly influenced by the addition of mercury (II). Upon addition, CuNCs were oxidized to form Cu²⁺. Then, the OPD were rapidly oxidized by Cu²⁺ to form o-phenylenediamine oxide (oxOPD), as evidenced by the strong fluorescence peak at 547 nm, resulting in a decrease in the fluorescence intensity at 460 nm and an increase in the fluorescence intensity at 547 nm. Under optimal conditions, a calibration curve between the fluorescence ratio (I547/I460) and mercury (II) concentration was constructed with a linearity of 0-1000 µg L^-1. The limit of detection (LOD) and limit of quantification (LOQ) were found at 18.0 µg L^-1 and 62.0 µg L^-1, respectively. The recovery percentage was in the range of 96.8-106.4%. The developed method was also compared with the standard ICP-OES method. The results were found to be not significantly different at a 95% confidence level (t_stat = 0.365 < t_crit = 2.262). This demonstrated that the developed method could be applied for detecting mercury (II) in natural water samples.

Gold Nanoparticles as a Biosensor for Cancer Biomarker Determination

Molecular biology applications based on gold nanotechnology have revolutionary impacts, especially in diagnosing and treating molecular and cellular levels. The combination of plasmonic resonance, biochemistry, and optoelectronic engineering has increased the detection of molecules and the possibility of atoms. These advantages have brought medical research to the cellular level for application potential. Many research groups are working towards this. The superior analytical properties of gold nanoparticles can not only be used as an effective drug screening instrument for gene sequencing in new drug development but also as an essential tool for detecting physiological functions, such as blood glucose, antigen-antibody analysis, etc. The review introduces the principles of biomedical sensing systems, the principles of nanomaterial analysis applied to biomedicine at home and abroad, and the chemical surface modification of various gold nanoparticles.