Preparation of Silicon–Carbon-Based Dots@Dopamine and Its Application in Intracellular Ag⁺ Detection and Cell Imaging

A novel nanocomposite, silicon–carbon-based dots@dopamine (Si-CDs@DA) was prepared using (3-aminopropyl) triethoxysilane, glycerol, and dopamine as raw materials via a rapid microwave-assisted irradiation. This type of Si-CDs@DA exhibited ultrabright fluorescence emission (quantum yield of 12.4%) and could response to Ag⁺ selectively and sensitively. Moreover, the obtained Si-CDs@DA can be further applied in sensing intracellular Ag⁺ and cell imaging, because of its photostability, salt stability, and low cytotoxicity. This study provides a simple and efficient approach for preparing novel Ag⁺ fluorescent probes, which could expand the application of carbon nanomaterials in designing related biosensors

Near-Infrared Light Excited and Localized Surface Plasmon Resonance-Enhanced Photoelectrochemical Biosensing Platform for Cell Analysis

Under near-infrared (NIR) light of 810 nm wavelength for irradiation, a very simple and highly sensitive photoelectrochemical (PEC) biosensing platform has been established using the localized surface plasmon resonance effect of Au nanoparticles (NPs) as signal amplification for the nondestructive analysis of living cells. The water-dispersible Ag₂S quantum dots (QDs) synthesized by a one pot method were employed as photoelectrochemically active species, and they exhibited excellent PEC properties irradiated with NIR light which was chosen due to the obvious absorption and fluorescent emission in the NIR light region. After the incorporation of Au NPs on the Ag₂S QDs modified ITO electrode, the photoelectric conversion efficiency was greatly increased, at ∼2.5 times that of the pure Ag₂S QDs modified electrode. Additionally, 4-mercaptophenylboronic acid (MPBA) molecules, as recognition elements, self-assembled on the electrode surface through Au–S bonds. On the basis of the chemical reaction between sialic acid on the cytomembranes and boric acid of MPBA, the very simple PEC biosensing platform was used for the quantitative determination of MCF-7 cells and dynamic evaluation of cell surface glycan expression under the external stimulus of sialidase. Under NIR light of 810 nm and a potential of 0.15 V, this proposed strategy exhibited a wide linear range from 1 × 10² to 1 × 10⁷ cells/mL, with an experimental detection limit of 100 cells/mL. Importantly, this work provided a promising application for NIR Ag₂S QDs coupled with Au NPs in the development of a novel PEC biosensing platform for the nondestructive analysis of biological samples

Versatile Biosensing Platform for DNA Detection Based on a DNAzyme and Restriction-Endonuclease-Assisted Recycling

On the basis of a DNAzyme and a restriction-endonuclease-assisted target recycling strategy using Pd–Au alloy nanocrystals to immobilize probe DNA on an electrode and catalyze the reduction of H₂O₂ which amplified signal and promoted the detection sensitivity, a versatile biosensing platform for DNA detection was proposed. Using p53 and oral cancer genes as models, hemin/G-quadruplex simultaneously acted as a reduced nicotinamide adenine dinucleotide (NADH) oxidase and a horseradish peroxidase (HRP)-mimicking DNAzyme, and a versatile DNA biosensor was designed for the first time based on the good electrocatalytic activity of Pd–Au alloy nanocrystals. Hemin/G-quadruplex catalyzed the reduction of H₂O₂, which was generated from NADH in the presence of O₂, to produce an electrochemical signal when thionine functioned as the electron mediator. Moreover, the nicking endonuclease N.BstNB I caused the target DNA to cycle for multiple rounds and further amplified the electrochemical response. This versatile DNA biosensor exhibited linear ranges for the detection of p53 and oral cancer genes from 0.1 fmol L^–1 to 0.1 nmol L^–1 and 0.1 fmol L^–1 to 1 nmol L^–1, respectively. The detection limits, established as 3σ, were estimated to be 0.03 and 0.06 fmol L^–1 for the p53 and oral cancer genes, respectively. The as-prepared biosensor could discriminate mismatched sequences, indicating a satisfactory selectivity and validating the feasibility of the proposed strategy. More importantly, simply by changing the helper DNA, this versatile DNA biosensor could detect different target DNA species, which could create a new avenue for the potential diagnosis of cancer

Photoelectrochemical Bioanalysis Platform for Cells Monitoring Based on Dual Signal Amplification Using in Situ Generation of Electron Acceptor Coupled with Heterojunction

By using in situ generation of electron acceptor coupled with heterojunction as dual signal amplification, a simple photoelectrochemical (PEC) bioanalysis platform was designed. The synergic effect between the photoelectrochemical (PEC) activities of carbon nitride (C₃N₄) nanosheets and PbS quantum dots (QDs) achieved almost nine-fold photocurrent intensity increment compared with the C₃N₄ alone. After the G-quadruplex/hemin/Pt nanoparticles (NPs) with catalase-like activity toward H₂O₂ were introduced, oxygen was in situ generated and acted as electron donor by improving charge separation efficiency and further enhancing photocurrent response. The dually amplified signal made enough sensitivity for monitoring H₂O₂ released from live cells. The photocathode was prepared by the stepwise assembly of C₃N₄ nanosheets and PbS QDs on indium tin oxide (ITO) electrode, which was characterized by scanning electron microscope. A signal-on protocol was achieved for H₂O₂ detection in vitro due to the relevance of photocurrent on the concentration of H₂O₂. Under the optimized condition, the fabricated PEC bioanalysis platform exhibited a linear range of 10–7000 μM with a detection limit of 1.05 μM at S/N of 3. Besides, the bioanalysis platform displayed good selectivity against other reductive biological species. By using HepG2 cells as a model, a dual signal amplifying PEC bioanalysis platform for monitoring cells was developed. The bioanalysis platform was successfully applied to the detection of H₂O₂ release from live cells, which provided a novel method for cells monitoring and would have prospect in clinical assay

Stable and Reusable Electrochemical Biosensor for Poly(ADP-ribose) Polymerase and Its Inhibitor Based on Enzyme-Initiated Auto-PARylation

A stable and reusable electrochemical biosensor for the label-free detection of poly­(ADP-ribose) polymerase (PARP) is designed in this work. C-kit-1, a thiol-modified G-quadruplex oligonucleotide, is first self-assembled on a gold electrode surface. The G-quadruplex structure of c-kit-1 can specifically tether and activate PARP, resulting in the generation of negatively charged poly­(ADP-ribose) polymer (PAR). On the basis of electrostatic attraction, PAR facilitates the surface accumulation of positively charged electrochemical signal molecules. Through the characterization of electrochemical signal molecules, the label-free quantification of PARP is simply implemented. On the basis of the proposed method, selective quantification of PARP can be achieved over the linear range from 0.01 to 1 U with a calculated detection limit of 0.003U. Further studies also demonstrate the applicability of the proposed method to biosamples revealing the broad potential in practical applications. Furthermore, inhibitor of PARP has also been detected with this biosensor. Meanwhile, benefited from self-assembly on solid surface, this biosensor possesses two important features, i.e., reusability and stability, which are desirable in related biosensors

Graphene Quantums Dots Combined with Endonuclease Cleavage and Bidentate Chelation for Highly Sensitive Electrochemiluminescent DNA Biosensing

A novel strategy for highly sensitive electrochemiluminescence (ECL) detection of DNA was proposed based on site-specific cleavage of <i>Bam</i>HI endonuclease combined with the excellent ECL activity of graphene quantum dots (GQDs) and bidentate chelation of the dithiocarbamate DNA (DTC-DNA) probe assembly. The difference between photoluminescence and ECL spectral peaks suggested that a negligible defect existed on the GQDs surface for generation of an ECL signal. The formed DTC-DNA was directly attached to the gold surface by bidentate anchoring (S–Au–S bonds), which conferred a strong affinity between the ligands and the gold surface, increasing the robustness of DNA immobilization on the gold surface. <i>Bam</i>HI endonuclease site-specifically recognized and cleaved the duplex symmetrical sequence, which made the double-stranded DNA fragments and GQDs break off from the electrode surface, inducing a decrease of the ECL signal. Using hepatitis C virus-1b genotype complementary DNA (HCV-1b cDNA) as a model, a novel signal-off ECL DNA biosensor was developed based on variation of the ECL intensity before and after digestion of the DNA hybrid. Electrochemical impedance spectroscopy confirmed the successful fabrication of the ECL DNA biosensor. This ECL biosensor for HCV-1b cDNA determination exhibited a linear range from 5 fM to 100 pM with a detection limit of 0.45 fM at a signal-to-noise ratio of 3 and showed satisfactory selectivity and good stability, which validated the feasibility of the designed strategy. The proposed strategy may be conveniently combined with other specific biological recognition events for expansion of the biosensing application, especially in clinical diagnoses

Tin Nanoparticles Impregnated in Nitrogen-Doped Graphene for Lithium-Ion Battery Anodes

Tin possesses a high theoretical specific capacity as anode materials for Li-ion batteries, and considerable efforts have been contributed to mitigating the capacity fading along with its huge volume expansion during lithium insertion and extraction processes, mainly through nanostructured material design. Herein, we present Sn nanoparticles encapsulated in nitrogen-doped graphene sheets through heat-treatment of the SnO₂ nanocrystals/nitrogen-doped graphene hybrid. The specific architecture of the as-prepared Sn@N-RGO involves three advantages, including a continuous graphene conducting network, coating Sn surface through Sn–N and Sn–O bonding generated between Sn nanoparticles and graphene, and porous and flexible structure for accommodating the large volume changes of Sn nanoparticles. As an anode material for lithium-ion batteries, the hybrid exhibits a reversible capacity of 481 mA h g^–1 after 100 cycles under 0.1 A g^–1 and a charge capacity as high as 307 mA h g^–1 under 2 A g^–1

Sequence and Structure Dual-Dependent Interaction between Small Molecules and DNA for the Detection of Residual Silver Ions in As-Prepared Silver Nanomaterials

Investigations on interaction between small molecules and DNA are the basis of designing advanced bioanalytical systems. We herein propose a novel interaction between heterocyclic aromatic compounds (HACs) and single-stranded DNA (ssDNA). Taking methylene blue (MB) as a typical HAC, it is found that MB can interact with cytosine (C)-rich ssDNA in an enthalpy-driven process. The interaction between MB and C-rich ssDNA is sequence and structure dual-dependent: at least three consecutive C and single-stranded structure are necessary, affecting the fluorescence response of metal nanoparticles. With the exception of the single-stranded structure, double-stranded, i-motif, and C–Ag–C mismatch structures will remarkably impede the interaction with MB. UV–vis absorption, fluorescent, and electrochemical curves demonstrate that the conjugated system, electron transition, and electron transfer of MB are remarkably affected by MB-C-rich ssDNA interaction. In particular, the absorption peak of MB at 664 nm decreases, and a new peak at 538 nm emerges. Therefore, the interaction can be characterized by a colorimetric and ratiometric signal. Relying on the inhibition of C–Ag–C mismatch and the enhanced analytical performances of the ratiometic signal, the MB-C-rich ssDNA interaction is further employed to quantify silver ions (Ag⁺) selectively and sensitively. In addition, since silver nanomaterials cannot introduce C–Ag–C mismatch, the fabricated biosensor is able to sense residual Ag⁺ in silver nanoparticles and silver nanowires, which is of great value in the precise and economical preparation of silver nanomaterials

Fluorescence Regulation of Copper Nanoclusters via DNA Template Manipulation toward Design of a High Signal-to-Noise Ratio Biosensor

Because of bioaccumulation of food chain and disability of biodegradation, concentration of toxic mercury ions (Hg²⁺) in the environment dramatically varies from picomolar to micromolar, indicating the importance of well-performed Hg²⁺ analytical methods. Herein, reticular DNA is constructed by introducing thymine (T)–Hg²⁺–T nodes in poly­(T) DNA, and copper nanoclusters (CuNCs) with aggregate morphology are prepared using this reticular DNA as a template. Intriguingly, the prepared CuNCs exhibit enhanced fluorescence. Meanwhile, the reticular DNA reveals evident resistance to enzyme digestion, further clarifying the fluorescence enhancement of CuNCs. Relying on the dual function of DNA manipulation, a high signal-to-noise ratio biosensor is designed. This analytical approach can quantify Hg²⁺ in a very wide range (50 pM to 500 μM) with an ultralow detection limit (16 pM). Besides, depending on the specific interaction between Hg²⁺ and reduced l-glutathione (GSH), this biosensor is able to evaluate the inhibition of GSH toward Hg²⁺. In addition, pollution of Hg²⁺ in three lakes is tested using this method, and the obtained results are in accord with those from inductively coupled plasma mass spectrometry. In general, this work provides an alternative way to regulate the properties of DNA-templated nanomaterials and indicates the applicability of this way by fabricating an advanced biosensor

Fluorescence Regulation of Poly(thymine)-Templated Copper Nanoparticles via an Enzyme-Triggered Reaction toward Sensitive and Selective Detection of Alkaline Phosphatase

The activity of alkaline phosphatase (ALP) is a crucial index of blood routine examinations, since the concentration of ALP is highly associated with various human diseases. To address the demands of clinical tests, efforts should be made to develop more approaches that can sense ALP in real samples. Recently, we find that fluorescence of poly­(30T)-templated copper nanoparticles (CuNPs) can be directly and effectively quenched by pyrophosphate ion (PPi), providing new perspective in designing sensitive biosensors based on DNA-templated CuNPs. In addition, it has been confirmed that phosphate ion (Pi), product of PPi hydrolysis, does not affect the intense fluorescence of CuNPs. Since ALP can specifically hydrolyze PPi into Pi, fluorescence of CuNPs is thus regulated by an ALP-triggered reaction, and a novel ALP biosensor is successfully developed. As a result, ALP is sensitively and selectively quantified with a wide linear range of 6.0 × 10^–2 U/L to 6.0 × 10² U/L and a low detection limit of 3.5 × 10^–2 U/L. Besides, two typical inhibitors of ALP are evaluated by this analytical method, and different inhibitory effects are indicated. More importantly, by challenging this biosensor with real human serums, the obtained results get a fine match with the data from clinical tests, and the serum sample from a patient with liver disease is clearly distinguished, suggesting promising applications of this biosensor in clinical diagnosis