A CuO nanothorns/Cu foam (NTs-CuO/Cu foam) was synthesized using a low-cost and facile method. The morphology and composition of the NTs-CuO/Cu foam were characterized using SEM, TEM and XRD. Copper foam as the current collector played a key role in the formation of the NTs-CuO/Cu foam. The CuO nanothorns were freely grown on copper foam, and can make contact with the underneath conductive copper foam directly. The NTs-CuO/Cu foam was used as an electrocatalyst for the detection of glucose in an electrochemical sensor. The CuO nanothorns/Cu foam electrode shows an extremely high sensitivity of 5.9843 mA mM−1 cm−2 and a low detection limit of 0.275 μM based on a signal to noise ratio of 3. Due to its excellently high sensitivity, stability and anti-interference ability, the NTs-CuO/Cu foam will be a promising material for constructing practical non-enzymatic glucose sensors.

•The pod-like Cu2O nanowire arrays grown on the 3D copper foam is synthesized.•The Cu2O PLNWs/Cu foam as electrocatalysts for the detection of glucose and H2O2.•Cu2O PLNWs/Cu foam exhibits extremely high sensitivities, low detection limits.The pod-like Cu2O nanowire arrays (denoted as Cu2O PLNWs/Cu foam) grown on the three-dimensional copper foam is synthesized by a low-cost and convenient method. The morphology and composition of the Cu2O PLNWs/Cu foam are characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction, respectively. The high conductivity of Cu foam as current collector can facilitate the charge and mass transfer, and the Cu foam with opened framework provides large amounts of anchoring sites for the deposition of Cu2O NWs during the synthesis of the Cu2O PLNWs/Cu foam. Accordingly, The Cu2O PLNWs/Cu foam is used as electrocatalysts for the detection of glucose and H2O2. The Cu2O PLNWs/Cu foam electrode shows extremely high sensitivity of 6.6807 mA mM−1 cm−2 and a low detection limit of 0.67 μM for the electrocatalytic oxidation for glucose. The nonenzymatic sensor also demonstrates good response toward hydrogen peroxide with high sensitivity of 1.4773 mA mM−1 cm−2 and the detection limit of 1.05 μM. Due to the excellently high sensitivity, stability and anti-interference ability, the Cu2O PLNWs/Cu foam will be the potential candidate for constructing practical non-enzymatic glucose and hydrogen peroxide sensors.The pod-like Cu2O nanowire arrays supported on copper foam is prepared by a low-cost and facile method and works as highly sensitive and efficient nonenzymatic glucose and H2O2 biosensor.

AuNPs possess peroxidase-like activity that could catalyze 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2, leading to color change of the solution. Herein we propose a simple and sensitive colorimetric aptasensor for the quantitative analysis of ricin by using AuNPs. It is shown that the peroxidase-like activity of AuNPs can be improved by surface activation with target-specific aptamers. However, with target molecules, the aptamer is desorbed from the AuNPs' surface, resulting in a decrease of the catalytic abilities of AuNPs. The color change of the solution was relevant to the target concentration, and this can be judged by the naked eye and monitored by UV-vis spectrometry. The linear range for the current analytical system was from 0.05 nM to 10 nM. The corresponding limit of detection (LOD) was 0.05 nM. Some other proteins such as thrombin (Th), glucose oxidase (GOx), and bovine albumin (BSA) all had a negligible effect on the determination of ricin. What is more, several practical samples spiked with ricin were analyzed using the proposed method with excellent recoveries. This colorimetric aptasensor is superior to the other conventional methods owing to its simplicity, low cost, and high sensitivity.

Herein, a sensitive and selective colorimetric biosensor for the detection of ricin was demonstrated with a 40-mer ricin-binding aptamer (RBA) as recognition element and unmodified gold nanoparticles (AuNPs) as probe. The sensitivity of the assay was greatly improved after optimizing several key parameters such as the amount of aptamer adsorbed on AuNPs, the concentration of NaCl, and the reaction time after adding NaCl. The linear range for the current analytical system was from 0.31 nM to 11.55 nM. The corresponding limit of detection (LOD) was 0.31 nM. Some different proteins such as thrombin (Th), horseradish peroxidase (HRP), lysozyme (Lys), glucose oxidase (GOx), and bovine albumin (BSA) showed no or just a little interference in the determination of ricin. This colorimetric aptasensor is superior to the other conventional methods owing to its simplicity, low cost, high sensitivity and detection with the naked eye, which can be used in real samples.

This study demonstrates a cocaine sensing method employing graphene oxide (GO), gold nanoparticles and a structure switching aptamer, which can fold into a three-way junction in the presence of cocaine. On the observation of gold nanoparticles (Au NPs) induced graphene oxide fluorescence quenching, a structure switching aptamer of cocaine was introduced as the linker between the two parts. Firstly, two fragments of a cocaine aptamer were immobilized covalently onto GO and Au NPs, respectively. Then when the three-way junction formed, the Au NPs were drawn near to the GO surface and induced a fluorescence intensity decrease. The limit of detection was 0.1 μM for cocaine in purified water, and well defined results were also obtained in biological fluids and the specificity experiment, which expands the feasibility of the as-prepared sensor for practical applications.

A sensitive hydrogen peroxide (H2O2) sensor was fabricated based on a Prussian blue @ gold nanocomposite (PB@Au). Au nanoparticles (Au NPs) were first electrodeposited on a glassy carbon electrode (GCE) to increase the conductivity and to catalyze the chemical deposition of PB. Electrochemical measurements showed that the PB@Au modified electrode exhibited good electrocatalytic behavior for the detection of H2O2 with a wide linear range from 2 μM to 8.56 mM (R2 = 0.9980), a low detection limit down to 0.1 μM (S/N = 3), and a high sensitivity of 39.72 μA mM−1. The sensor also displayed a good anti-interference ability, an acceptable reproducibility, an excellent long-term stability and good repeatability. The desirable recoveries achieved in disinfected fetal bovine serum verified that the developed sensor could have a potential use in the detection of H2O2 in real samples. Moreover, the operating simplicity and low expense of the fabrication made the as-prepared electrode attractive.

Water safety is one of the most pervasive problems afflicting people throughout the world. Microcystin, a hepatotoxin produced by cyanobacteria, poses a growing and serious threat of water safety. According to World Health Organization (WHO), the limit of content of microcystin-LR (MC-LR) in drinking water is as low as 1 μg/L; it is thus necessary to explore a sensitive method for the trace detection of microcystins (MCs). Based on the observation of gold nanoparticles (Au NPs) induced graphene oxide (GO) fluorescence quenching, a reliable biosensor was developed here for microcystins detection. MCs could be attached on Au NPs through the interaction with single strand-DNA (ss-DNA) modified on Au NPs, which formed Au–DNA–MCs complexes. These MCs in the complexes could be immunologically recognized by the antibodies adsorbed on GO sheets, as a result, Au NPs were close enough to quench the photoluminescence of GO by the fluorescence resonance energy transfer (FRET). The fluorescence intensity decreased with the increase of MCs as more Au NPs linked onto GO surface. The limit of detection was 0.5 and 0.3 μg/L for microcystin-LR and microcystin-RR (MC-RR), respectively, which satisfies the strictest standard of WHO. Well defined results were also obtained in natural lake water and the specificity experiment. The antibody used here could recognize Adda group, the conservative part of MCs, which allowed the biosensor to detect both single toxin and the total content of MCs existing in the water sample.Highlights► Based on the observation of gold nanoparticles (Au NPs) induced graphene oxide (GO) fluorescence quenching, a reliable MCs biosensor was developed here for microcystins detection. ► Limit of detection was 0.5 and 0.3 μg/L for MC-LR and MC-RR, respectively, which satisfies the strictest standard of WHO. ► Well defined results were also obtained in natural lake water and the specificity experiment.

This review highlights recent advanced researches on the assembly of various metallic nanostructures by oligonucleotide and plasmid DNA. The obtained DNA–nanoconjugates show many unique and attractive properties, while this review focuses on their properties related to SERS detection. The applications of DNA-based assemblies in SERS detections were fully commented upon, for the detection of DNA, proteins, small molecules, and metallic ions. Finally, a concluding section is given, which covers the challenges and scope for DNA assembled nanostructures as well as for the DNA assemblies-related SERS detections.

Ni(OH)2 nanoplates were successfully synthesized and in situ assembled on reduced graphene oxide (RGO) nanosheets by a simple one-pot method. This RGO-Ni(OH)2 nanocomposite was characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). TEM images showed that the composite was round and that leaf-shaped nanoplates with a diameter of about 150 nm assembled on the RGO nanosheets. EDX, XRD, Raman and XPS characterization proved that the constituent parts of the composite were Ni(OH)2 and RGO. Moreover, the amount of Ni(OH)2 assembled on the RGO could be adjusted simply by changing the volume of NiCl2 added to the reactant mixture. For the strong catalytic ability of the high-valent oxydroxide species (NiOOH) formed in alkaline media, the RGO-Ni(OH)2 nanocomposite was used as the matrix for the non-enzymatic detection of glucose. A low detection limit of 0.6 μM with a wide linear range from 2 μM to 3.1 mM (R = 0.9987) could be obtained. The operating simplicity and low expense of fabrication make this Ni(OH)2-based electrode attractive in sensor construction.

Au nanocages (AuNCs) were synthesized by a simple one-pot method without the use of any solid templates or Au seeds. The structure of the as-prepared AuNCs was characterized by SEM, TEM, EDS and XRD. For their good electrochemical properties and large surface-to-volume ratio, the AuNCs were utilized to modify glassy carbon electrode (GCE) directly for nonenzymatic detection of H2O2. Electrochemical experiments showed that the AuNCs displayed high electrocatalytic activity towards the reduction of H2O2 and obtained a wide linear range from 0.5 μM to 5.8885 mM (R = 0.9993) with a detection limit down to 0.1 μM (S/N = 3). The sensitivity of the H2O2 sensor was as high as 273.83 μA mM−1 cm−2. The sensor also exhibits good anti-interference ability to electroactive molecules, including uric acid, ascorbic acid, glucose, ethanol, and glycine. Moreover, the operating simplicity and low expense of fabrication made this electrode more attractive.Highlights► Au nanocages (AuNCs) were synthesized by a simple one-pot method. ► The structure of the as-prepared AuNCs was characterized by SEM, TEM, EDS and XRD. ► The AuNCs displayed high electrocatalytic activity towards the reduction of H2O2. ► The sensor has a wide linear range with a detection limit down to 0.1 μM (S/N = 3). ► The sensitivity of the H2O2 sensor was as high as 273.83 μA mM−1 cm−2.

A novel electrochemical sensor based on the silver decorated carbon nanotube is reported here for the accurate and rapid determination of hydrogen peroxide. The hybrid nanostructure was synthesized separately and characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The high focus on the silver-based hydrogen peroxide sensor spurred us to investigate the determination of the electrocatalytic activity towards hydrogen peroxide. The as-prepared electrochemical senor exhibited well-defined response to the reduction of hydrogen peroxide. The detection limit of hydrogen peroxide was found to be 1.6 μM, which was lower than the certain enzyme-based biosensor.Research highlights► CNT-Ag nanocomposites were synthesized by noncovalent method. ► The structure of the hybrid nanostructure was characterized by SEM, EDX, and XPS. ► A H2O2 sensor based on the silver decorated carbon nanotube is reported. ► The sensor exhibited well-defined response to the reduction of hydrogen peroxide. ► The detection limit of hydrogen peroxide was found to be 1.6 μM.

Microcystin-LR (MC-LR) is one of the hepatotoxins produced by cyanobacteria in the eutrophicated fresh water. In this work, the minor groove binding mode of MC-LR to plasmid DNA was explored by using UV and fluorescence spectra, and the binding characteristics of MC-LR for plasmid DNA were calculated via the fluorescence quenching of ethidium bromide (EB) and mole ratio method. Furthermore, atomic force microscopy (AFM) was used to observe DNA morphology change in the presence of MC-LR. With the increasing concentration of MC-LR, circle DNA strands twined gradually to rod condensates. The possible reason for the condensation might be the masking of the electrostatic repulsion between DNA double strands by MC-LR. The present study might provide useful information for the pathopoiesis mechanism of MC-LR. More, because the condensation of DNA could affect the progresses of gene expression and protein transcription, it may implicate another trend to explore the nosogenesis of MC-LR.

A superhydrophobic substrate that combines the superhydrophobic condensation effect and high enhancement ability of silver nanoparticle coated zinc oxide nanorods array (Ag@ZnO) is explored for surface enhanced Raman scattering (SERS). The effects of water contact angle and droplet volume on the final SERS signal intensity are also investigated for the first time. Our results indicate the superhydrophobic substrate could exhibit 3-fold signal enhancement more than the ordinary hydrophilic Ag@ZnO substrate due to the superhydrophobic condensation effect. This signal amplification effect is affected by the water contact angle and water droplet volume on the substrate, i.e., (1) the higher the contact angle is, the higher the SERS signal is; (2) the SERS intensity fluctuates as the droplet volume increases, and proper volume, not the largest one, should be chosen to achieve a stronger signal. Most importantly, this superhydrophobic substrate with high signal reproducibility is successfully applied to detect small molecules such as adenine and melamine, with the detection limits of 1 order of magnitude less than those on the hydrophilic Ag@ZnO substrate. It is expected this superhydrophobic SERS substrate can be widely used in the trace analysis in the future.

Gold nanoparticle decorated lysozyme microtubes, with the diameters of 1–2 μm and lengths on the order of millimeters, were spontaneously formed via a simple aging process of the lysozyme–gold nanoparticle aqueous solution under ambient conditions for 1 week. These novel microtubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX), as well as Fourier-transform infrared (FTIR) spectroscopy. It was confirmed that the microtubes were made up of the protein lysozyme. In addition, formation of the microtubes was accompanied by a decrease in lysozyme concentration in the sample solution, which also indicated that these microtubes originated from lysozyme. The formation of microtubes was attributed to the formation of hydrogen bonding networks between the lysozyme molecules. Partially unfolded lysozyme molecules on gold nanoparticles probably seed the formation of the lysozyme microtubes. These novel protein microtubes not only provide some useful insights for protein study but may also have the potential to be used in the biomedical field.

Dopamine (2-(3,4-dihydroxyphenyl)ethylamine) is known as a natural chemical neurotransmitter and is also a cytotoxic and genotoxic molecule for cell apoptosis. In this work, the interaction of DNA with dopamine was investigated. Though the electrostatic interaction of DNA and dopamine was weak in aqueous solution, dopamine condensed circular pBR322 DNA into toroids on the mica surface cooperatively with ethanol. The formed DNA toroids came from the shrinking of DNA that was driven by ethanol-enhanced DNA−dopamine electrostatic interaction. The size of the DNA toroids could be modulated by varying the concentration of dopamine. This study offers useful information about the DNA condensation induced by monovalent cations and the sample preparation for AFM measurement and application. On the other hand, this work provides the potential strategies to prepare morphology and size controllable DNA condensates, which have valuable applications in gene transfection and nanotechnology.

In this paper, a hollow Au/Pd core/shell nanostructure with a raspberry surface was developed for methanol, ethanol, and formic acid oxidation in alkaline media. The results showed that it possessed better electrocatalyst performance than hollow Au nanospheres or Pd nanoparticles. The nanostructure was fabricated via a two-step method. Hollow Au nanospheres were first synthesized by a galvanic replacement reaction, and then they were coated with a layer of Pd grains. Several characterizations such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) were used to investigate the prepared nanostructures. The intensive studies of fuel cells encouraged us to examine the electrocatalytic properties of the prepared nanostructures, and that alkaline media could supply a more active environment than acidic electrolyte in previous reports inspired us to operate the experiments in alkaline media. According to the results, this hollow Au/Pd core/shell nanostructure with a raspberry surface possesses excellent electrocatalytic properties and can be further used in direct alcohol/formic acid fuel cells (DAFCs or DFAFCs), sensors, and catalysts.

In this article, highly rough and stable surface enhanced Raman scattering (SERS)-active substrates had been fabricated by a facile layer-by-layer technique. Unique λ-DNA networks and CTAB capped silver nanoparticles (AgNP) were alternatively self-assembled on the charged mica surface until a desirable number of bilayers were reached. The as-prepared hybrid architectures were characterized by UV–vis spectroscopy, tapping mode atomic force microscopy (AFM) and confocal Raman microscopy, respectively. Linear increases of the maximum absorbance of DNA band with the number of bilayers present a common LBL assembly feature. The red-shift of surface plasmon of silver nanoparticles within the hybrid films was mainly due to the aggregation effect. With the increase of number of bilayers, the surface coverage of nanoparticles on the substrate became larger, as well as the rising of total amount of nanoparticles and the surface roughness of hybrid films. These rough metallic hybrid architectures could be utilized as SERS-active substrates. A significant enhanced Raman scattering effect of the adsorbed analytes, e.g., methylene blue (MB), on these hybrid films was easily exploited by the confocal Raman microscopy. The enhancement factor depended on the surface coverage of nanoparticles and number of bilayers of λ-DNA/AgNP.Schematic representation of the formation process of λ-DNA networks mediated monolayered/multilayered AgNP membranes through the LBL assembly approach and their application in SERS.

A circular bacterial artificial chromosome of 148.9 kbp on human chromosome 3 has been extended and fixed on bare mica substrates using a developed fluid capillary flow method in evaporating liquid drops. Extended circular DNA molecules were imaged with an atomic force microscope (AFM) under ambient conditions. The measured total lengths of the whole DNA molecules were in agreement with sequencing analysis data with an error range of ±3.6%. This work is important groundwork for probing single nucleotide polymorphisms in the human genome, mapping genomic DNA, manipulating biomolecular nanotechnology, and studying the interaction of DNA–protein complexes investigated by AFM.

Ni(OH)2 nanoplates were successfully synthesized and in situ assembled on reduced graphene oxide (RGO) nanosheets by a simple one-pot method. This RGO-Ni(OH)2 nanocomposite was characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). TEM images showed that the composite was round and that leaf-shaped nanoplates with a diameter of about 150 nm assembled on the RGO nanosheets. EDX, XRD, Raman and XPS characterization proved that the constituent parts of the composite were Ni(OH)2 and RGO. Moreover, the amount of Ni(OH)2 assembled on the RGO could be adjusted simply by changing the volume of NiCl2 added to the reactant mixture. For the strong catalytic ability of the high-valent oxydroxide species (NiOOH) formed in alkaline media, the RGO-Ni(OH)2 nanocomposite was used as the matrix for the non-enzymatic detection of glucose. A low detection limit of 0.6 μM with a wide linear range from 2 μM to 3.1 mM (R = 0.9987) could be obtained. The operating simplicity and low expense of fabrication make this Ni(OH)2-based electrode attractive in sensor construction.

This review highlights recent advanced researches on the assembly of various metallic nanostructures by oligonucleotide and plasmid DNA. The obtained DNA–nanoconjugates show many unique and attractive properties, while this review focuses on their properties related to SERS detection. The applications of DNA-based assemblies in SERS detections were fully commented upon, for the detection of DNA, proteins, small molecules, and metallic ions. Finally, a concluding section is given, which covers the challenges and scope for DNA assembled nanostructures as well as for the DNA assemblies-related SERS detections.