High-Efficiency 3D DNA Walker Immobilized by a DNA Tetrahedral Nanostructure for Fast and Ultrasensitive Electrochemical Detection of MiRNA.

Herein, by directly limiting the reaction space, an ingenious three-dimensional (3D) DNA walker (IDW) with high walking efficiency is developed for rapid and sensitive detection of miRNA. Compared with the traditional DNA walker, the IDW immobilized by the DNA tetrahedral nanostructure (DTN) brings stronger kinetic and thermodynamic favorability resulting from its improved local concentration and space confinement effect, accompanied by a quite faster reaction speed and much better walking efficiency. Once traces of target miRNA-21 react with the prelocked IDW, the IDW could be largely activated and walk on the interface of the electrode to trigger the cleavage of H2 with the assistance of Mg2+, resulting in the release of amounts of methylene blue (MB) labeled on H2 from the electrode surface and the obvious decrease of the electrode signal. Impressively, the IDW reveals a conversion efficiency as high as 9.33 × 108 in 30 min with a much fast reaction speed, which is at least five times beyond that of typical DNA walkers. Therefore, the IDW could address the inherent challenges of the traditional DNA walker easily: slow walking speed and low efficiency. Notably, the IDW as a DNA nanomachine was utilized to construct a sensitive sensing platform for rapid miRNA-21 detection with a limit of detection (LOD) of 19.8 aM and realize the highly sensitive assay of biomarker miRNA-21 in the total RNA lysates of cancer cell. The strategy thus helps in the design of a versatile nucleic acid conversion and signal amplification approach for practical applications in the areas of biosensing assay, DNA nanotechnology, and clinical diagnosis.

Dual Recognition DNA Triangular Prism Nanoprobe: Toward the Relationship between K+ and pH in Lysosomes.

Lysosomal acidification is essential for its degradative function, and the flux of H+ correlated with that of K+ in lysosomes. However, there is little research on their correlation due to the lack of probes that can simultaneously image these two ions. To deeply understand the role of K+ in lysosomal acidification, here, we designed and fabricated a nanodevice using a K+-aptamer and two pH-triggered nanoswitches incorporated into a DNA triangular prism (DTP) as a dual signal response platform to simultaneously visualize K+ and pH in lysosomes by a fluorescence method. This strategy could conveniently integrate two signal recognition modules into one probe, so as to achieve the goal of sensitive detection of two kinds of signals in the same time and space, which is suitable for the detection of various signals with the correlation of concentration. By co-imaging both K+ and H+ in lysosomes, we found that the efflux of K+ was accompanied by a decrease of pH, which is of great value in understanding lysosomal acidification. Moreover, this strategy also has broad prospects as a versatile optical sensing platform for multiplexed analysis of other biomolecules in living cells.

Ultrasensitive Nucleic Acid Assay Based on AIE-Active Polymer Dots with Excellent Electrochemiluminescence Stability.

Aggregation-induced emission (AIE) active Pdots are attractive nanomaterials applied in electrochemiluminescence (ECL) fields, while the irreversible redox reaction of these Pdots is a prevailing problem, resulting in instability of ECL emission. Herein, we first designed and synthesized an AIE-active Pdot with reversible redox property, which contains a tetraphenylethene derivate and benzothiadiazole (BT) to achieve stable ECL emission. BT has a good rigid structure with excellent electrochemical behaviors, which is beneficial for avoiding the destruction of the conjugated structure as much as possible during the preparation of Pdots, thus maintaining good redox property. The tetraphenylethene derivate, as a typical AIE-active moiety, provides a channel for highly efficient luminescence in the aggregated states. The Pdots exhibited reversible and quasi-reversible electrochemical behaviors during cathodic and anodic scanning, respectively. The stable annihilation, reductive-oxidative, and oxidative-reductive ECL signals were observed. Subsequently, we constructed an ultrasensitive ECL biosensor based on the oxidative-reductive ECL mode for the detection of miRNA-21 with a detection limit of 32 aM. This work provides some inspiration for the future design of ECL materials featuring AIE-active property and stable ECL emission.

Electrochemiluminescence Energy Resonance Transfer System between RuSi Nanoparticles and Hollow Au Nanocages for Nucleic Acid Detection.

This paper describes an electrochemiluminescence resonance energy transfer (ECL-RET) system using Ru(bpy)32+-doped silica nanoparticles (RuSi NPs) as the ECL donor and hollow Au nanocages as the ECL acceptor. Tetrahedron DNA (TD) was used to construct the biosensing interface and control the distance (4.8 nm) between the ECL donor-acceptor pairs. The surface plasmon resonance (SPR) nanostructures, Au nanocages were assembled via the hairpin based sandwich assay. Due to the well overlap between the plasmon absorption spectrum of Au nanocages (628 nm) and the ECL emission spectrum of RuSi NPs (620 nm), high efficient energy transfer could occur. Subsequent cyclic DNA amplification further increased the binding amount of Au nanocages. Since the ECL inhibition is closely related with the binding amount of Au nanocages, a general "signal-off" ECL bioassay could thus be tailored with high sensitivity. At the optimized conditions, this ECL-RET system performed well with great stability and repeatability for nucleic acid detection in the range from 1.0 fM to 10 pM. This work manifested the great promise of hollow Au nanocages for an ECL-RET biosensor that to the best of our knowledge has not been reported. We believe that it could inspire more interest in the design and development of numerous other SPR nanostructures for advanced ECL-RET biosensors.

Multi-segmented CdS-Au nanorods for electrochemiluminescence bioanalysis.

In this study, we have developed a programmable electrochemiluminescence (ECL) system based on multi-segmented CdS-Au nanorod arrays with a sequential and highly tunable structure. The nanorod arrays were synthesized by an electrodeposition method using anodic aluminum oxide (AAO) as the template in which the Au and CdS segments were alternately electrodeposited. Compared to pure CdS nanorod arrays, multi-segmented CdS-Au nanorod arrays have showed a better ECL performance, which can be attributed to two factors: the favorable electron transfer and the surface plasma resonance (SPR) effect of the Au segment. On the one hand, we demonstrated that the Au segment can increase the charge transfer rate of CdS, which is beneficial for the ECL process because the generation of the radical state needs to accept electrons and then generate the radical state. On the other hand, the SPR of Au plasmon-induced local electromagnetic field enhancement can increase the radiative decay rate of CdS which makes the ECL process more efficient and lead to a higher ECL intensity. And also, an ECL sensor with multi-segmented CdS-Au nanorod arrays was constructed to detect prostate protein antigen (PSA). This study provides some basis for designing high-performance ECL emission materials and the construction of biosensors.

A simple method to fabricate a chitosan-gold nanoparticles film and its application in glucose biosensor.

A novel film of chitosan-gold nanoparticles is fabricated by a direct and facile electrochemical deposition method and its application in glucose biosensor is investigated. HAuCl(4) solution is mixed with chitosan and electrochemically reduced to gold nanoparticles, which can be stabilized by chitosan and electrodeposited onto glassy carbon electrode surfaces along with the electrodeposition of chitosan. Then a model enzyme, glucose oxidase (GOD) is immobilized onto the resulting film to construct a glucose biosensor through self-assembly. The resulting modified electrode surfaces are characterized with both AFM and cyclic voltammetry. Effects of chitosan and HAuCl(4) concentration in the mixture together with the deposition time and the applied voltage on the amperometric response of the biosensor are also investigated. The linear range of the glucose biosensor is from 5.0 x 10(-5) approximately 1.30 x 10(-3) M with a Michaelis-Menten constant of 3.5 mM and a detection limit of about 13 microM.

Analytical aspects of fet-based biosensors.

Field-effect transistor (FET)-based biosensors (BioFETs) have undergone great progress especially in the last decade, since they were first realized in 1980. Recently, BioFETs have become one of the most important branches of biosensors. This paper briefly reviewed the operating principles of BioFETs and summarized the improvement and application of BioFETs, finally, the future prospects of BioFETs were discussed with 126 references.

Electrochemically deposited chitosan hydrogel for horseradish peroxidase immobilization through gold nanoparticles self-assembly.

A new strategy for immobilization of horseradish peroxidase (HRP) has been presented by self-assembling gold nanoparticles on chitosan hydrogel modified Au electrode. From a mildly acidic chitosan solution, a chitosan film is electrochemically deposited on Au electrode surface via a negative voltage bias. This process is accompanied by the hydrogen evolution reaction, and the released hydrogen gas made the deposited chitosan film with porous structure, which facilitates the assembly of gold nanoparticles and HRP. The resulting substrates were characterized by atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). The immobilized HRP displayed an excellent catalytic property to the reduction of H2O2 in the presence of methylene blue mediator. The resulting biosensor (HRP-modified electrode) showed a wide dynamic range of 8.0 microM-15 mM H2O2, and the linear ranges were 8.0 microM-0.12 mM and 0.50-12 mM, with a detection limit of 2.4 microM estimated at a signal-to-noise ratio of 3. Moreover, the biosensor remained about 85% of its original sensitivity after four weeks' storage.

A sensitive biosensor for lactate based on layer-by-layer assembling MnO2 nanoparticles and lactate oxidase on ion-sensitive field-effect transistors.

A sensitive enzyme-based FET biosensor for lactate has been obtained by introducing MnO2 nanoparticles at the gate surface via a layer-by-layer assembling method.

Electrochemically deposited nanocomposite of chitosan and carbon nanotubes for biosensor application.

A simple and controllable electrodeposition method for the formation of a chitosan-carbon nanotube nanocomposite film on an electrode surface was proposed and further used for the construction of an electrochemical biosensor.

A novel glucose ENFET based on the special reactivity of MnO2 nanoparticles.

Generally a glucose-sensitive enzyme field-effect transistor (ENFET) is based on local pH change in biomembranes resulted from the formation of gluconic acid. Here we proposed a glucose ENFET based on a new principle. The glucose ENFET was fabricated by coimmobilizing glucose oxidase (GOD) and MnO(2) nanoparticles on the gate of an ion-sensitive field-effect transistor (ISFET). The proposed glucose biosensor shows a significant local pH increase in the sensitive membrane with the increase of glucose concentration. The driving force of the pH change in our sensor is essentially different from all the other glucose ENFETs, including those prepared by bulk MnO(2). The special reaction ability of MnO(2) nanoparticles with hydrogen peroxide might be the main cause of the pH change. In addition, the influence of buffer concentration, pH and ionic strength on the glucose ENFET is investigated in detail. It is found that the ionic strength has little effect on the performance of the ENFET. Under optimal conditions, the proposed ENFET exhibits a linear response with glucose in the range of 0.025-1.90 mM, an extended dynamic upper limit of 3.5 mM glucose, and considerable good reproducibility and stability.

A glucose biosensor based on chitosan-glucose oxidase-gold nanoparticles biocomposite formed by one-step electrodeposition.

An amperometric biosensor for the quantitative measurement of glucose is reported. The biosensor is based on a biocomposite that is homogeneous and easily prepared. This biocomposite is made of chitosan hydrogel, glucose oxidase, and gold nanoparticles by a direct and facile electrochemical deposition method under enzyme-friendly conditions. The resulting biocomposite provided a shelter for the enzyme to retain its bioactivity at considerably extreme conditions, and the decorated gold nanoparticles in the biocomposite offer excellent affinity to enzyme. The biosensor exhibited a rapid response (within 7s) and a linear calibration range from 5.0 microM to 2.4 mM with a detection limit of 2.7 microM for the detection of glucose. The combination of gold nanoparticles affinity and the promising feature of the biocomposite with the onestep nonmanual technique favor the sensitive determination of glucose with improved analytical capabilities.