N-acetylcysteine induced quenching of red fluorescent oligonucleotide-stabilized silver nanoclusters and the application in pharmaceutical detection

Developing an off-on fluorescence sensor based on red copper nanoclusters wrapped by sulfhydryl and polymer double ligands for sensitive detection of N-acetyl-L-cysteine

N-acetyl-L-cysteine (NAC) as a class of thiols is commonly used in the treatment of lung diseases, detoxification and prevention of liver damage. In this paper, 4-mercaptobenzoic acid (4-MBA) coated and polyvinylpyrrolidone (PVP) attached copper nanoclusters (4-MBA@PVP-CuNCs) were successfully synthesized using a simple one-pot method with an absolute quantum yield of 10.98 %, and its synthetic conditions (like effects of single/double ligands and temperature) were studied intensively. Then Hg2+ could quench the fluorescence of the 4-MBA@PVP-CuNCs and its fluorescence was restored with the addition of NAC. Based on the above principles, an off-on switching system was established to detect NAC. That is, the 4-MBA@PVP-CuNCs-Hg probe was prepared by adding Hg2+ to switch off the fluorescence of the CuNCs by static quenching, and then NAC was added to switch on the fluorescence of the probe based on the chelation of NAC and Hg2+. Moreover, the effects of metal ion types and mercury ion doses for the probe construction were also further discussed. The method showed excellent linearity in the range of 0.05-1.25 µM and low detection limit of 16 nM. Meanwhile, good recoveries in real urine, tablets and pellets were observed, which proved the reliability of the method and provided a convenient, fast and sensitive method for NAC detection.

Aggregation-induced emission enhancement of adenosine monophosphate-capped bimetallic nanoclusters by aluminum(III) ions, and its application to the fluorometric determination of cysteine

The fluorescence of adenosine monophosphate-capped bimetallic gold and silver nanoclusters (type AuAgNC@AMP) is strongly enhanced and blue shifted in the presence of Al(III). As confirmed by transmission electron microscopy, the AuAgNC nanodots are converted to larger assembled spheres of type AuAgNC-Al(III). The fluorescence enhancement is attributed to aggregation-induced emission enhancement (AIEE). The fluorescence of the AuAgNC-Al(III) assembly (with excitation and emission maxima at 340 and 540 nm) is quenched by cysteine (Cys). The effect was applied to the fluorometric determination of Cys. The assay works in the 1.0 to 16.0 μM Cys concentration range and has a 50 nM limit of detection. The method was successfully applied to analyze Cys-spiked mineral waters and serum. The quenching mechanism is explored in depth. It is attributed to the partial replacement of AMP by Cys at the surface of the AuAgNC and alteration of the assembly structure from large spherical particles to a strip shape. Graphical abstractSchematic representation of the fluorescence enhancement of bimetallic nanoclusters capped with adenosine monophosphate by using Al(III), and its application in selective and sensitive determination of cysteine via ligand replacement and reassembly.

Structural Influence on the Post-Clustering Stability of DNA/AgNCs Fluorescence

DNA-encapsulated Silver Nanoclusters (DNA/AgNCs) based sensors have gained increasing attention in past years due to their diverse applications in bioimaging, biosensing, and enzymatic assays. Given the potential of DNA/AgNCs for practical applications, the systematic studies of the fluorescent stability over an extended period is necessary. However, the correlation between nucleic acid properties and the long-term stability of DNA/AgNCs is less known. With locking-to-unlocking sensors, in which the secondary structure of DNA template is standardized, we investigated the correlation between the DNA structure and the fluorescence stability of AgNCs. Post-synthesis of DNA/AgNCs, the fluorescence, and structures of templates were monitored over three weeks. By combining the fluorescence spectroscopy with the in-gel fluorescent assay, we found that AgNCs encapsulated by dimer-structured DNA/AgNCs templates were more stable than those of hairpin-structured DNA/AgNCs templates. While the orange fluorescence from the dimer templates increased over three weeks, the red fluorescence from the hairpin templates was diminished by >80% within two days at room temperature. Further tests revealed that hairpin-encapsulated red-emissive AgNCs is more sensitive to oxidation by atmospheric oxygen compared to dimer encapsulated orange AgNCs. Our observations may provide an important clue in encapsulating photophysically more stable AgNCs by tuning the DNA secondary structures. The proposed strategy here can be essential for pragmatic applications of DNA/AgNCs templates.

DNA metallization: principles, methods, structures, and applications

This review summarizes the research activities on DNA metallization since the concept was first proposed in 1998, covering the principles, methods, structures, and applications.

Constructing a Robust Fluorescent DNA-Stabilized Silver Nanocluster Probe Module by Attaching a Duplex Moiety

Fluorescent DNA-templated silver nanoclusters (DNA-Ag NCs) have served as excellent luminescent probes and operation units in various applications. However, the fluorescence property of DNA-Ag NCs is very sensitive to elongation or modification of the DNA template, limiting the breadth of applications. In this work, we propose a strategy for constructing a robust fluorescent DNA-Ag NCs probe module by attaching a duplex moiety to the nanocluster-bearing sequence. The fluorescence intensity of the DNA-Ag NCs can be enhanced 90-fold upon hybridization of the elongated moiety. Adenine in the linker sequence has a further enhancing effect on the fluorescence intensity, whereas thymine has a quenching effect. The transformation from a non-fluorescent species to fluorescent nanoclusters is responsible for the fluorescence enhancement with duplex formation of the elongated moiety. We hope that this design will aid future diversification of experimental designs to facilitate more applications that are currently limited by the aforementioned problems.

MicroRNA Biomarkers in Neurodegenerative Diseases and Emerging Nano-Sensors Technology

MicroRNAs (miRNAs) are essential small RNA molecules (20–24 nt) that negatively regulate the expression of target genes at the post-transcriptional level. Due to their roles in a variety of biological processes, the aberrant expression profiles of miRNAs have been identified as biomarkers for many diseases, such as cancer, diabetes, cardiovascular disease and neurodegenerative diseases. In order to precisely, rapidly and economically monitor the expression of miRNAs, many cutting-edge nanotechnologies have been developed. One of the nanotechnologies, based on DNA encapsulated silver nanoclusters (DNA/AgNCs), has increasingly been adopted to create nanoscale bio-sensing systems due to its attractive optical properties, such as brightness, tuneable emission wavelengths and photostability. Using the DNA/AgNCs sensor methods, the presence of miRNAs can be detected simply by monitoring the fluorescence alteration of DNA/AgNCs sensors. We introduce these DNA/ AgNCs sensor methods and discuss their possible applications for detecting miRNA biomarkers in neurodegenerative diseases.

Branched polyethylenimine-functionalized carbon dots as sensitive and selective fluorescent probes for N-acetylcysteine via an off–on mechanism

A novel fluorescence (FL) analytical method to determine N-acetylcysteine (NAC) was established by using a branched polyethyleneimine-functionalized carbon dot fluorescent system involving FL quenching by Cu²⁺ and subsequent FL recovery upon addition of NAC.

Recent advances in the field of bionanotechnology: an insight into optoelectric bacteriorhodopsin, quantum dots, and noble metal nanoclusters

Molecular sensors and molecular electronics are a major component of a recent research area known as bionanotechnology, which merges biology with nanotechnology. This new class of biosensors and bioelectronics has been a subject of intense research over the past decade and has found application in a wide variety of fields. The unique characteristics of these biomolecular transduction systems has been utilized in applications ranging from solar cells and single-electron transistors (SETs) to fluorescent sensors capable of sensitive and selective detection of a wide variety of targets, both organic and inorganic. This review will discuss three major systems in the area of molecular sensors and electronics and their application in unique technological innovations. Firstly, the synthesis of optoelectric bacteriorhodopsin (bR) and its application in the field of molecular sensors and electronics will be discussed. Next, this article will discuss recent advances in the synthesis and application of semiconductor quantum dots (QDs). Finally, this article will conclude with a review of the new and exciting field of noble metal nanoclusters and their application in the creation of a new class of fluorescent sensors.

A DNA–Ag cluster as a sensor for BODIPY isomers and HepG-2 cells

Near-infrared fluorescent DNA–AgNCs with a parallel homoduplex conformation can recognize one isomer of BODIPY based on the difference in energy transfer between the DNA–AgNCs and compounds conjugated system. A simple way to detect the change in hypoxia-inducible factor in cancer cells was also suggested.