The discovery of graphene has ignited intensive interest in two-dimensional layered materials (2DLMs). These 2DLMs represent a new class of nearly ideal 2D material systems for exploring fundamental ...chemistry and physics at the limit of single-atom thickness, and have the potential to open up totally new technological opportunities beyond the reach of existing materials. In general, there are a wide range of 2DLMs in which the atomic layers are weakly bonded together by van der Waals interactions and can be isolated into single or few-layer nanosheets. The van der Waals interactions between neighboring atomic layers could allow much more flexible integration of distinct materials to nearly arbitrarily combine and control different properties at the atomic scale. The transition metal dichalcogenides (TMDs) (
e.g.
, MoS
2
, WSe
2
) represent a large family of layered materials, many of which exhibit tunable band gaps that can undergo a transition from an indirect band gap in bulk crystals to a direct band gap in monolayer nanosheets. These 2D-TMDs have thus emerged as an exciting class of atomically thin semiconductors for a new generation of electronic and optoelectronic devices. Recent studies have shown exciting potential of these atomically thin semiconductors, including the demonstration of atomically thin transistors, a new design of vertical transistors, as well as new types of optoelectronic devices such as tunable photovoltaic devices and light emitting devices. In parallel, there have also been considerable efforts in developing diverse synthetic approaches for the rational growth of various forms of 2D materials with precisely controlled chemical composition, physical dimension, and heterostructure interface. Here we review the recent efforts, progress, opportunities and challenges in exploring the layered TMDs as a new class of atomically thin semiconductors.
The recent progress, opportunities and challenges in exploring two-dimensional transition metal dichalcogenides as atomically thin semiconductors are reviewed, including the material synthesis and novel device concepts.
A ratiometric surface-enhanced Raman scattering (SERS) aptasensor based on internal standard (IS) methods was proposed for the ultrasensitive and reproducible quantitative detection of silver ion ...(Ag+) with Au@Ag core-shell nanoparticle (Au@Ag NP) substrate. In principle, the thiolated 5′-Rox C-containing labeled aptamer probe (Rox-aptamer) is firstly immobilized on the SERS substrate surface and then hybridizes with the complementary DNA (cDNA) to form a rigid double-stranded DNA (dsDNA), in which the Rox Raman labels is used to produce the Raman signal. Furthermore, the pyridine is employed as an IS element to provide the ratiometric determination of target. In the presence of Ag+, the Rox-aptamer is turned into the cytosine (C)-Ag+-C mediated hairpin structure, which remarkably reduces the distance between the Rox labels and the Au@Ag NP surface responsible for a measurable ‘turn-on’ signal change of Rox. This IS-based ratiometric SERS aptasensor exhibits a limit of detection of 50 pM for Ag+ with a linear detection range from 0.1 to 100 nM and the shortcoming of irreproducibility of SERS signal could be overcome. The proposed method provides a simple, robust, and rapid approach for the sensitive and reproducible quantitative detection of Ag+, and it could also be used for the detection of other metal ions which exhibits specific interactions with natural or synthetic bases.
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•An internal standard-based ratiometric SERS aptasensor was developed for ultrasensitive quantitative Ag+ detection.•The ratiometric SERS aptasensor achieves a limit of detection (LOD) to 50 pM Ag+.•This strategy may offer a new direction for development of high performance SERS aptasensors for other metal ions detection.
On the basis of the inhibition of double strand DNA (dsDNA)-templated fluorescent copper nanoparticles (CuNPs) by pyrophosphate (PPi), a novel label-free turn-on fluorescent strategy to detect ...alkaline phosphatase (ALP) under physiological conditions has been developed. This method relies on the strong interaction between PPi and Cu2+, which would hamper the effective formation of fluorescent CuNPs, leading to low fluorescence intensity. The ALP-catalyzed PPi hydrolysis would disable the complexation between Cu2+ and PPi, facilitating the formation of fluorescent CuNPs through the reduction by ascorbate in the presence of dsDNA templates. Thus, the fluorescence intensity was recovered, and the fluorescence enhancement was related to the concentration of ALP. This method is cost-effective and convenient without any labels or complicated operations. The present strategy exhibits a high sensitivity and the turn-on mode provides a high selectivity for the ALP assay. Additionally, the inhibition effect of phosphate on the ALP activity was also studied. The proposed method using a PPi substrate may hold a potential application in diagnosis of ALP-related diseases or evaluation of ALP functions in biological systems.
A stable DNA signal amplification sensor was developed on account of rolling circle amplification (RCA). This sensor includes target DNA-controlled rolling circle amplification technology and locking ...probe DNA replacement technology, which can be used to detect DNA fragments with genetic information, thus constructing a biosensor for universal detection of DNA. This study takes the homologous DNA of human immunodeficiency virus (HIV) and let-7a as examples to describe this biosensor. The padlock probe is first cyclized by T4 DNA ligase in response to the target’s reaction with it. Then, rolling cycle amplification is initiated by Phi29 DNA polymerase, resulting in the formation of a lengthy chain with several triggers. These triggers can open the locked probe LP1 with the fluorescence signal turned off, so that it can continue to react with H2 to form a stable H1-H2 double strand. This regulates the distance between B-DNA modified by the quenching group and H1 modified by fluorescent group, and the fluorescence signal is recovered.
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A separation platform has been developed mediated by a combination of magnetic beads and the CRISPR/Cas12a system to achieve ultrasensitive and rapid detection of miRNA-21 at a low level. In this ...system, with the assistance of an auxiliary probe, the target miRNA-21 can be specifically combined with three-stranded probes to initiate the SDR reaction. Abundant aptamer A3 was added to the solution that can activate the CRISPR/Cas12a system and initiate the trans-cleavage reaction to recover the fluorescence signal. Using magnetic beads to mediate the separation considerably greatly improves the signal conversion efficiency and detection sensitivity. At the 492 nm excitation wavelength, and 502–650 nm scan range, through analyzing the fluorescence peak intensity at 520 nm, the biosensor’s determination range and limit of detection is 8 fM-250 nM and 2.42 fM, respectively, and the RSD is 19.03–37.80. Compared with other biosensors, the biosensor developed exhibited superior performance and the signal recovered excellently in 1% human serum and the LOD is 12.12 fM. This method provides a novel highly sensitive scheme for detecting miRNA .
Graphical Abstract
This paper reports a label-free electrochemical immunosensor for the determination of aflatoxin B1 (AFB1), which is based on a gold electrode modified by a biocompatible film of carbon ...nanotubes/poly(diallyldimethylammoniumchloride)/Pd–Au nanoparticles (CNTs/PDDA/Pd–Au). The nanocomposite was characterized by transmission electron microscopy and the electrochemical behavior of modified electrodes was investigated by cyclic voltammetry. The CNTs/PDDA/Pd–Au nanocomposites film showed good electron transfer ability, which ensured high sensitivity to detect AFB1 in a range from 0.05 to 25 ng mL−1 with a detection limit of 0.03 ng mL−1 obtained at 3σ (where σ is the standard deviation of the blank solution, n = 10). The proposed immunosensor provides a simple tool for AFB1 detection. This strategy can be extended to any other antigen detection by using the corresponding antibodies.
A novel highly-sensitive liquid crystal (LC) biosensing approach based on target-triggering DNA dendrimers was developed for the detection of p53 mutation gene segment at the LC–aqueous interface. In ...this study, the mutant-type p53 gene segment was the target to trigger the formation of DNA dendrimers from hairpin DNA probes by hybridization chain reaction, and the latter as a ‘signal enhancement element’ further induced the LC reorientation from tilted to homeotropic alignment, resulting in a corresponding optical changes of LC biosensors from birefringent to honeycombed textures or dark framework. The distinct optical reorientational appearances can serve as a characteristic signal to distinguish target concentrations ranging from 0.08nM to 8nM. Moreover, these optical phenomena suggest that the LC reorientation is related to the electric-dipole coupling between the adsorbed DNA and LC molecules, the conformational constraints of DNA and the internal electric field induction upon hybridization. This label-free LC biosensing strategy can open up a new platform for the sensitive detection of specific DNA sequences and enrich the application scope of an LC biosensing technique.
•Target-triggering DNA dendrimer was constructed by hybridization chain reaction.•The DNA dendrimer enhanced the LC reorientation at the LC–aqueous interface.•Direct sensing mechanism between DNA and LC molecules was discussed.•The sensor showed high sensitivity and selectivity for detecting p53 mutation gene.
Phosphorylation of DNA by polynucleotide kinase (PNK) takes an important role in DNA damage repair, replication and recombination. The evaluation of PNK activity has received an increasing attention ...due to the significance of PNK. Here, we present a label-free fluorescent method for PNK activity assay using double strand DNA (dsDNA) -templated copper nanoparticles (CuNPs) as a fluorescent indicator. Upon the PNK reaction, the dsDNA template is phosphorylated and then digested by λ exonuclease immediately, prohibiting the formation of fluorescent CuNPs due to the lack of dsDNA template. This homogeneous PNK activity assay does not require any other additional modifications of DNA substrate or complex design, making the proposed strategy simple, cost-effective and high throughput. The proposed strategy is sensitive, selective and exhibits a good assay performance in complex biological samples. The strategy presented here opens a new avenue for PNK assay and nucleic acid phosphorylation related research.
► A simple PNK activity assay using dsDNA-templated CuNPs as a fluorescent indicator was presented. ► Any other additional modifications of DNA substrate or complex design were not required for this method. ► PNK activity was sensitively and selectively detected. ► In complex biological samples, this method exhibited a good assay performance.
We developed a novel electrochemical strategy for ultrasensitive DNA detection using a dual amplification strategy based on the circular strand-displacement polymerase reaction (CSDPR) and the ...hybridization chain reaction (HCR). In this assay, hybridization of hairpin-shaped capture DNA to target DNA resulted in a conformational change of the capture DNA with a concomitant exposure of its stem. The primer was then hybridized with the exposed stem and triggered a polymerization reaction, allowing a cyclic reaction comprising release of target DNA, hybridization of target with remaining capture DNA, polymerization initiated by the primer. Furthermore, the free part of the primer propagated a chain reaction of hybridization events between two DNA hairpin probes with biotin labels, enabling an electrochemical reading using the streptavidin-alkaline phosphatase. The proposed biosensor showed to have very high sensitivity and selectivity with a dynamic response range through 10fM to 1nM, and the detect limit was as low as 8fM. The proposed strategy could have the potential for molecular diagnostics in complex biological systems.
•An electrochemical biosensor for DNA detection was developed.•Dual signal amplification was achieved by combining CSDPR and HCR.•DNA was detected sensitively and selectively.•The biosensor worked well in complex biological samples.
