Herein, a reliable surface-enhanced Raman scattering (SERS)-active substrate has been prepared by synthesizing gold nanoparticles (AuNPs)-decorated MoS2 nanocomposite. The AuNPs grew in situ on the surface of MoS2 nanosheet to form efficient SERS hot spots by a spontaneous redox reaction with tetrachloroauric acid (HAuCl4) without any reducing agent. The morphologies of MoS2 and AuNPs-decorated MoS2 nanosheet were characterized by TEM, HRTEM, and AFM. The formation of hot spots greatly depended on the ratio of MoS2 and HAuCl4. When the concentration of HAuCl4 was 2.4 mM, the as-prepared AuNPs@MoS2-3 nanocomposite exhibited a high-quality SERS activity toward probe molecule due to the generated hot spots. The spot-to-spot SERS signals showed that the relative standard deviation (RSD) in the intensity of the main Raman vibration modes (1362, 1511, and 1652 cm(-1)) of Rhodamine 6G were about 20%, which displayed good uniformity and reproducibility. The AuNPs@MoS2-based substrate was reliable, sensitive, and reproducible, which showed great potential to be an excellent SERS substrate for biological and chemical detection.
A conjugated‐polymer‐based “mix‐and‐detect” optical sensor for mercury ions is fabricated by using a water‐soluble poly[3‐(3′‐N,N,N‐triethylamino‐1′‐propyloxy)‐4‐methyl‐2,5‐thiophene hydrochloride] (PMNT) and a label‐free, mercury‐specific oligonucleotide (MSO) probe. PMNT binds to the Hg2+‐free MSO and the Hg2+–MSO complex in different ways, and exhibits distinguishable and specific optical responses to the target‐induced conformation change.
An electrochemical sensor has been developed for simultaneous detection of dopamine (DA), uric acid (UA) and ascorbic acid (AA) based on a gold nanoparticle-decorated MoS 2 nanocomposite (AuNPs@MoS 2 ) modified electrode. The AuNPs@MoS 2 nanocomposite has been synthesized by electrodeposition of AuNPs on the MoS 2 nanosheets, which possesses better properties than pure AuNPs and MoS 2 . The AuNPs@MoS 2 film modified electrode showed excellent electrocatalytic activity toward the oxidation of AA, DA and UA with three well-resolved oxidation peaks. The peak separation of AA-DA, DA-UA and AA-UA is 151 mV, 137 mV and 288 mV, respectively, which permits the modified electrode to individually or simultaneously analyze AA, DA and UA by differential pulse voltammetry (DPV). Under optimum conditions, the AuNPs@MoS 2 modified electrode exhibits linear response toward AA, DA and UA in the range of 50-100 000 mM, 0.05-30 mM and 50-40 000 mM, respectively. Moreover, the MoS 2 -based modified electrode was successfully employed to determine DA in human serum samples with satisfactory results.
Herein, we report a convenient approach to developing quantum dots (QDs)-based nanosensors for DNA and micro-RNA (miRNA) detection. The DNA-QDs conjugate was prepared by a ligand-exchange method. Thiol-labeled ssDNA is directly attached to the QD surface, leading to highly water-dispersible nanoconjugates. The DNA-QDs conjugate has the advantages of the excellent optical properties of QDs and well-controlled recognition properties of DNA and can be used as a nanoprobe to construct a nanosensor for nucleic acid detection. With the addition of a target nucleic acid sequence, the fluorescence intensity of QDs was quenched by an organic quencher (BHQ2) via Förster resonance energy transfer. This nanosensor can detect as low as 1 fM DNA and 10 fM miRNA. Moreover, the QDs-based nanosensor exhibited excellent selectivity. It not only can effectively distinguish single-base-mismatched and random nucleic sequences but also can recognize pre-miRNA and mature miRNA. Therefore, the nanosensor has high application potential for disease diagnosis and biological analysis.
Novel MnO 2 petal nanosheet and nanorod/graphene composites are successfully fabricated by a facile one-step hydrothermal method through changing the content of the Mn source. The formation mechanism of different morphologies of MnO 2 /graphene composites have been studied. The structure of the MnO 2 /graphene is "sandwich"-like, with MnO 2 petal nanosheets and nanorods homogeneously anchored on each side of the graphene. Furthermore, the MnO 2 /graphene composites with different shapes can be used for supercapacitor electrode materials. The experimental results show that the MnO 2 petal nanosheet/graphene composite has better capacitance performance than that of the MnO 2 nanorod/graphene composite. The MnO 2 petal nanosheet/graphene composite shows excellent specific capacitance as high as 516.8 F g À1 at a scan rate of 1 mV s À1 in 1 M Na 2 SO 4 electrolyte and good longterm cycle stability, indicating its potential application to act as a promising electrode material for highperformance supercapacitors. This study provides a facile and in situ method to prepare metal oxide/ graphene composite materials and a novel scaffold to construct other metal oxides with graphene for energy storage.
The performance for biomolecular detection is closely associated with the interfacial structure of a biosensor, which profoundly affects both thermodynamics and kinetics of the assembly, binding and signal transduction of biomolecules. Herein, it is reported on a one-step and template-free on-electrode synthesis method for making shape-controlled gold nanostructures on indium tin oxide substrates, which provide an electrochemical sensing platform for ultrasensitive detection of nucleic acids. Thus-prepared hierarchical flower-like gold nanostructures (HFGNs) possess large surface area that can readily accommodate the assembly of DNA probes for subsequent hybridization detection. It is found that the sensitivity for electrochemical DNA sensing is critically dependent on the morphology of HFGNs. By using this new strategy, a highly sensitive electrochemical biosensor is developed for label-free detection of microRNA-21 (miRNA-21), a biomarker for lung cancers. Importantly, it is demonstrated that this biosensor can be employed to measure the miRNA-21 expression level from human lung cancer cell (A549) lysates and worked well in 100% serum, suggesting its potential for applications in clinical diagnosis and a wide range of bioanalysis.
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