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

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

Using Graphene-Based Plasmonic Nanocomposites to Quench Energy from Quantum Dots for Signal-On Photoelectrochemical Aptasensing

On the basis of the absorption and emission spectra overlap, an enhanced resonance energy transfer caused by excition-plasmon resonance between reduced graphene oxide (RGO)-Au nanoparticles (AuNPs) and CdTe quantum dots (QDs) was obtained. With the synergy of AuNPs and RGO as a planelike energy acceptor, it resulted in the enhancement of energy transfer between excited CdTe QDs and RGO-AuNPs nanocomposites. Upon the novel sandwichlike structure formed via DNA hybridization, the exciton produced in CdTe QDs was annihilated. A damped photocurrent was obtained, which was acted as the background signal for the development of a universal photoelectrochemical (PEC) platform. With the use of carcinoembryonic antigen (CEA) as a model which bonded to its specific aptamer and destroyed the sandwichlike structure, the energy transfer efficiency was lowered, leading to PEC response augment. Thus a signal-on PEC aptasensor was constructed. Under 470 nm irradiation at −0.05 V, the PEC aptasensor for CEA determination exhibited a linear range from 0.001 to 2.0 ng mL^–1 with a detection limit of 0.47 pg mL^–1 at a signal-to-noise ratio of 3 and was satisfactory for clinical sample detection. Since different aptamers can specifically bind to different target molecules, the designed strategy has an expansive application for the construction of versatile PEC platforms

Dual Signal Amplification Using Gold Nanoparticles-Enhanced Zinc Selenide Nanoflakes and P19 Protein for Ultrasensitive Photoelectrochemical Biosensing of MicroRNA in Cell

Using Au nanoparticles (NPs)-decorated, water-soluble, ZnSe-COOH nanoflakes (NFs), an ultrasensitive photoelectrochemical (PEC) biosensing strategy based on the dual signal amplification was proposed. As a result of the localized surface plasmon resonance (SPR) of Au NPs, the ultraviolet–visible absorption spectrum of Au NPs overlapped with emission spectrum of ZnSe-COOH NFs, which generated efficient resonant energy transfer (RET) between ZnSe-COOH NFs and Au NPs. The RET improved photoelectric conversion efficiency of ZnSe-COOH NFs and significantly amplified PEC signal. Taking advantage of the specificity and high affinity of p19 protein for 21–23 bp double-stranded RNA, p19 protein was introduced. P19 protein could generate remarkable steric hindrance, which blocked interfacial electron transfer and impeded the access of the ascorbic acid to electrode surface for scavenging holes. This led to the dramatic decrease of photocurrent intensity and the amplification of PEC signal change versus concentration change of target. Using microRNA (miRNA)-122a as a model analyte, an ultrasensitive signal-off PEC biosensor for miRNA detection was developed under 405 nm irradiation at −0.30 V. Owing to RET and remarkable steric hindrance of p19 protein as dual signal amplification, the proposed strategy exhibited a wide linear range from 350 fM to 5 nM, with a low detection limit of 153 fM. It has been successfully applied to analyze the level of miRNA-122a in HeLa cell, which would have promising prospects for early diagnosis of tumor

Fe-Porphyrin-Based Covalent Organic Framework As a Novel Peroxidase Mimic for a One-Pot Glucose Colorimetric Assay

Covalent organic frameworks (COFs) have recently emerged as very fascinating porous polymers due to their attractive design synthesis and various applications. However, the catalytic application of COF materials as enzymatic mimics remains largely unexplored. In this work, the Fe-porphyrin-based covalent organic framework (Fe-COF) has been successfully synthesized through a facile postsynthetic strategy for the first time. In the presence of hydrogen peroxide (H₂O₂), the Fe-COF can catalyze a chromogenic substrate (3,3′,5,5′-tetramethylbenzidine (TMB)) to produce color, and this just goes to show that it has an inner peroxidase-like activity. Moreover, the kinetic studies indicate that the Fe-COF nanomaterial has a higher affinity toward both the substrate H₂O₂ and TMB than the natural enzyme, horseradish peroxidase (HRP). Under the optimized conditions, the Fe-COF nanomaterial was applied in a colorimetric sensor for the sensitive detection of H₂O₂. The detection range was from 7 to 500 μM, and the detection limit was 1.1 μM. Furthermore, the combination of the Fe-COF with glucose oxidase (GOx) can be implemented to measure glucose by a one-pot method, and the obtained detection range was from 5 to 350 μM; the detection limit was 1.0 μM. It was proved that the sensor can be successfully used to detect the concentration of glucose in human serum samples. As a peroxidase mimic, the Fe-COF exhibits the advantages of easy preparation, good stability, and ultrahigh catalytic efficiency. We believed that the proposed method in this work would facilitate the applications of COF-based composites as enzymatic mimics in biomedical fields

A Few-Layer SnS₂/Reduced Graphene Oxide Sandwich Hybrid for Efficient Sodium Storage

Rechargeable sodium-ion batteries have lately received considerable attention as an alternative to lithium-ion batteries because sodium resources are essentially inexhaustible and ubiquitous around the world. Despite recent reports on cathode materials for sodium-ion batteries have shown electrochemical activities close to their lithium-ion counterparts, the major scientific challenge for sodium-ion batteries is to exploit efficient anode materials. Herein, we demonstrate that a hybrid material composed of few-layer SnS₂ nanosheets sandwiched between reduced graphene oxide (RGO) nanosheets exhibits a high specific capacity of 843 mAh g^–1 (calculated based on the mass of SnS₂ only) at a current density of 0.1 A g^–1 and a 98% capacity retention after 100 cycles when evaluated between 0.01 and 2.5 V. Employing <i>ex situ</i> high-resolution transmission electron microscopy and selected area electron diffraction techniques, we illustrate the high specific capacity of our anode through a 3-fold mechanism of intercalation of sodium ions along the <i>ab</i>-plane of SnS₂ nanosheets and the subsequent formation of Na₂S₂ and Na₁₅Sn₄ through conversion and alloy reactions. The existence of RGO nanosheets in the hybrid material functions as a flexible backbone and high-speed electronic pathways, guaranteeing that an appropriate resilient space buffers the anisotropic dilation of SnS₂ nanosheets along the <i>ab</i>-plane and <i>c</i>-axis for stable cycling performance

Aggregation of Individual Sensing Units for Signal Accumulation: Conversion of Liquid-Phase Colorimetric Assay into Enhanced Surface-Tethered Electrochemical Analysis

A novel concept is proposed for converting liquid-phase colorimetric assay into enhanced surface-tethered electrochemical analysis, which is based on the analyte-induced formation of a network architecture of metal nanoparticles (MNs). In a proof-of-concept trial, thymine-functionalized silver nanoparticle (Ag-T) is designed as the sensing unit for Hg²⁺ determination. Through a specific T-Hg²⁺-T coordination, the validation system based on functionalized sensing units not only can perform well in a colorimetric Hg²⁺ assay, but also can be developed into a more sensitive and stable electrochemical Hg²⁺ sensor. In electrochemical analysis, the simple principle of analyte-induced aggregation of MNs can be used as a dual signal amplification strategy for significantly improving the detection sensitivity. More importantly, those numerous and diverse colorimetric assays that rely on the target-induced aggregation of MNs can be augmented to satisfy the ambitious demands of sensitive analysis by converting them into electrochemical assays via this approach