A signal-on, colorimetric determination of deoxyribonuclease I activity utilizing the photoinduced synthesis of gold nanoparticles

Enzyme activity termination by titanium carbide nanosheet and its application for the detection of deoxyribonuclease I

Deoxyribonuclease I (DNase I) is a typical nuclease that plays key roles in many physiological processes and the development of a novel biosensing strategy for DNase I detection is of fundamental significance. In this study, a fluorescence biosensing nanoplatform based on a two-dimensional (2D) titanium carbide (Ti₃C₂) nanosheet for sensitive and specific detection of DNase I was reported. Fluorophore-labeled single-stranded DNA (ssDNA) can be spontaneously and selectively adsorbed on Ti₃C₂ nanosheet through the hydrogen bond and metal chelate interaction between phosphate groups of ssDNA and titanium of Ti₃C₂ nanosheet, resulting in effective quenching of the fluorescence emitted by fluorophore. Notably, it was found the enzyme activity of DNase I will be terminated by the Ti₃C₂ nanosheet. Therefore, the fluorophore-labeled ssDNA was firstly digested by DNase I and the "post-mixing" strategy of Ti₃C₂ nanosheet was chosen to evaluate the enzyme activity of DNase I, which provided the possibility of improving the accuracy of the biosensing method. Experimental results demonstrated that this method can be utilized for quantitative analysis of DNase I activity and exhibited a low detection limit of 0.16 U/ml. Additionally, the evaluation of DNase I activity in human serum samples and the screening of inhibitors with this developed biosensing strategy were successfully realized, implying that it has high potential as a promising nanoplatform for nuclease analysis in bioanalytical and biomedical fields.

Pyrophosphate-Enhanced Oxidase Activity of Cerium Oxide Nanoparticles for Colorimetric Detection of Nucleic Acids

In recent years, cerium oxide (CeO₂) nanoparticles (NPs) have drawn significant attention owing to their intrinsic enzyme mimetic properties, which make them powerful tools for biomolecular detection. In this work, we evaluated the effect of pyrophosphate (PPi) on the oxidase activity of CeO₂ NPs. The presence of PPi was found to enhance the oxidase activity of CeO₂ NPs, with enhanced colorimetric signals. This particular effect was then used for the colorimetric detection of target nucleic acids. Overall, the PPi-enhanced colorimetric signals of CeO₂ NPs oxidase activity were suppressed by the presence of the target nucleic acids. Compared with previous studies using CeO₂ NPs only, our proposed system significantly improved the signal change (ca. 200%), leading to more sensitive and reproducible colorimetric analysis of target nucleic acids. As a proof-of-concept study, the proposed system was successfully applied to the highly selective and sensitive detection of polymerase chain reaction products derived from Klebsiella pneumoniae. Our findings will benefit the rapid detection of nucleic acid biomarkers (e.g., pathogenic bacterial DNA or RNA) in point-of-care settings.

Fluorescence nucleobase analogue-based strategy with high signal-to-noise ratio for ultrasensitive detection of food poisoning bacteria

We developed a simple and ultrasensitive strategy for the identification of foodborne pathogens utilizing a fluorescent nucleobase analogue [2-aminopurine (2-AP)]-containing split G-quadruplex that binds blocker DNA. Compared to a previous strategy that did not use blocker DNA, this strategy showed a significant increase in the signal-to-noise ratio-by approximately 300%-owing to the displacement of the blocker DNA by the target DNA that induces the formation of an active G-quadruplex structure, thereby leading to a substantial increase in the 2-AP fluorescence signal. The proposed strategy was rationally combined with polymerase chain reaction, which resulted in the successful determination of genomic DNA (within the range of 10-106 copies) derived from the food poisoning bacterium Escherichia coli, with a limit of detection of 5.2 copies and high selectivity. In addition, the practical applicability of this method was demonstrated by analyzing E. coli-spiked lettuce samples.

Protecting the Normal Physiological Functions of Articular and Periarticular Structures by Aurum Nanoparticle-Based Formulations: an Up-to-Date Insight

Taking the articular and periarticular structures as a litmus test for gold-based nanoformulations, the potential of gold nanoparticles in protecting the normal physiological functions of these structures particularly in geriatric patients is one of the research areas of current interest. Aside from its use to make the traditional and fashionable ornaments for human usage, the gold metal is also known for its rich therapeutic activity. This is especially true when the gold is converted from its bulk form into nanosized form before its administering into the human body. Since it is the age of nanocomponents in medical and pharmaceutical research areas, this review is therefore mainly focused on nanoparticulate systems consisting of aurum. Accumulating research reports nevertheless show concrete evidence indicating the potential of gold-based nanoformulations to manage joint syndromes such as osteoarthritis and rheumatoid arthritis. This review embarks from preparation techniques and characterization methods to therapeutical application potentials of gold-based nanoformulations.

Expanding the Toolbox for Label-Free Enzyme Assays: A Dinuclear Platinum(II) Complex/DNA Ensemble with Switchable Near-IR Emission

Switchable luminescent bioprobes whose emission can be turned on as a function of specific enzymatic activity are emerging as important tools in chemical biology. We report a promising platform for the development of label-free and continuous enzymatic assays in high-throughput mode based on the reversible solvent-induced self-assembly of a neutral dinuclear Pt(II) complex. To demonstrate the utility of this strategy, the switchable luminescence of a dinuclear Pt(II) complex was utilized in developing an experimentally simple, fast (10 min), low cost, and label-free turn-on luminescence assay for the endonuclease enzyme DNAse I. The complex displays a near-IR (NIR) aggregation-induced emission at 785 nm in aqueous solution that is completely quenched upon binding to G-quadruplex DNA from the human c-myc oncogene. Luminescence is restored upon DNA degradation elicited by exposure to DNAse I. Correlation between near-IR luminescence intensity and DNAse I concentration in human serum samples allows for fast and label-free detection of DNAse I down to 0.002 U/mL. The Pt(II) complex/DNA assembly is also effective for identification of DNAse I inhibitors, and assays can be performed in multiwell plates compatible with high-throughput screening. The combination of sensitivity, speed, convenience, and cost render this method superior to all other reported luminescence-based DNAse I assays. The versatile response of the Pt(II) complex to DNA structures promises broad potential applications in developing real-time and label-free assays for other nucleases as well as enzymes that regulate DNA topology.

Cationic porphyrins with large side arm substituents as resonance light scattering ratiometric probes for specific recognition of nucleic acid G-quadruplexes

Specific G-quadruplex-probing is crucial for both biological sciences and biosensing applications. Most reported probes are focused on fluorescent or colorimetric recognition of G-quadruplexes. Herein, for the first time, we reported a new specific G-quadruplex-probing technique-resonance light scattering (RLS)-based ratiometric recognition. To achieve the RLS probing of G-quadruplexes in the important physiological pH range of 7.4-6.0, four water soluble cationic porphyrin derivatives, including an unreported octa-cationic porphyrin, with large side arm substituents were synthesized and developed as RLS probes. These RLS probes were demonstrated to work well for ratiometric recognition of G-quadruplexes with high specificity against single- and double-stranded DNAs, including long double-stranded ones. The working mechanism was speculated to be based on the RLS signal changes caused by porphyrin protonation that was promoted by the end-stacking of porphyrins on G-quadruplexes. This work adds an important member in G-quadruplex probe family, thus providing a useful tool for studies on G-quadruplex-related events concerning G-quadruplex formation, destruction and changes in size, shape and aggregation. As a proof-of-concept example of applications, the RLS probes were demonstrated to work well for label-free and sequence-specific sensing of microRNA. This work also provides a simple and useful way for the preparation of cationic porphyrins with high charges.

The use of a 2-aminopurine-containing split G-quadruplex for sequence-specific DNA detection

A simple, sequence-specific DNA detection method, utilizing a fluorescent 2-aminopurine (2-AP) nucleobase analogue-containing split G-quadruplex as the key detection component, is described. In the sensor, the 2-AP-containing G-quadruplex is split into two segments and linked to a target-specific overhang sequence. The separate G-quadruplex sequences form an active G-quadruplex structure only in the presence of a complementary target DNA, which leads to a significant increase in the intensity of fluorescence from the 2-AP fluorophore. This simple, one-step, homogenous assay was successfully employed to detect target DNA with a high selectivity. In addition, the practical applicability of the detection method was demonstrated by its use in analyzing target DNAs in human serum. To the best of our knowledge, this is the first time that an investigation was carried out in which a fluorescent nucleobase analogue was incorporated into a split G-quadruplex structure and this structure was utilized as the foundation for a specific DNA sensor.

Gold nanoprobe-based non-crosslinking hybridization for molecular diagnostics: an update

INTRODUCTION

An update on the uses and applications of the non-cross-linking (NCL) hybridization assay based on the spectral modulation of gold nanoparticles (AuNPs) are presented, emphasizing DNA and RNA detection. Areas covered: Nanotechnology is strongly impacting the way we address diagnostics and therapeutics. In fact, nanoscale devices and particles have been used in a variety of platforms for improved biosensing and, more interestingly, for molecular diagnostics. AuNPs have been used in a great diversity of DNA and RNA detection strategies that are based on their nanoscale properties. Their unique optical properties have put them at the forefront of colorimetric sensing platforms. Among these, those relying on the NCL mechanism using DNA-modified AuNPs have shown remarkable versatility and simplicity for molecular detection of human pathogens, identification of single base alterations at the basis of human disease, gene expression, among others. Application of the NCL assay to molecular diagnostics will be discussed considering the challenges for validation and clinically relevant targets. Expert commentary: Integration of the NCL approach using AuNPs into chip biosensing platforms, projecting miniaturization and portability, will be addressed in terms of the future, i.e. clinical validation and translation to market.