Intertwined Carbon Nanotubes and Ag Nanowires Constructed by Simple Solution Blending as Sensitive and Stable Chloramphenicol Sensors.

Chloramphenicol (CAP) is a harmful compound associated with human hematopathy and neuritis, which was widely used as a broad-spectrum antibacterial agent in agriculture and aquaculture. Therefore, it is significant to detect CAP in aquatic environments. In this work, carbon nanotubes/silver nanowires (CNTs/AgNWs) composite electrodes were fabricated as the CAP sensor. Distinguished from in situ growing or chemical bonding noble metal nanomaterials on carbon, this CNTs/AgNWs composite was formed by simple solution blending. It was demonstrated that CNTs and AgNWs both contributed to the redox reaction of CAP in dynamics, and AgNWs was beneficial in thermodynamics as well. The proposed electrochemical sensor displayed a low detection limit of up to 0.08 µM and broad linear range of 0.1-100 µM for CAP. In addition, the CNTs/AgNWs electrodes exhibited good performance characteristics of repeatability and reproducibility, and proved suitable for CAP analysis in real water samples.

A novel gradient current density output mode for effective electrochemical oxidative degradation of dye wastewater by boron-doped diamond (BDD) anode.

In order to solve the problems of high energy consumption and low current efficiency in electrochemical oxidation (EO) degradation under the traditional constant output process (COP), a gradient output process (GOP) of current density is proposed in this paper. That is, the current density is gradually reduced in a fixed degradation time, and the Reactive Blue 19 simulated dye wastewater was used as the degradation target. The general applicability of the process was further confirmed by studying the optimal gradient current density output parameters, the dye concentration, electrolyte concentration and other dye compounds with different molecular structures. The corresponding results show that the chemical oxygen demand (COD) removal (78%) and the color removal (100%) under the GOP are similar to those in the COP, and the overall energy consumption is reduced by about 50% compared with that in the traditional constant current mode. Moreover, the current efficiency in the middle and late stages of EO process has increased by 8.6 times compared with COP.

Electro-activated persulfate oxidation of malachite green by boron-doped diamond (BDD) anode: effect of degradation process parameters.

In this paper, boron-doped diamond (BDD) electro-activated persulfate was studied to decompose malachite green (MG). The degradation results indicate that the decolorization performance of MG for the BDD electro-activated persulfate (BDD-EAP) system is 3.37 times that of BDD electrochemical oxidation (BDD-EO) system, and BDD-EAP system also exhibited an enhanced total organic content (TOC) removal (2.2 times) compared with BDD-EO system. Besides, the degradation parameters such as persulfate concentration, current density, and pH were studied in detail. In a wider range of pH (2-10), the MG can be efficiently removed (>95%) in 0.02 M persulfate solution with a low current density of 1.7 mA/cm2 after 30 min. The BDD-EAP technology decomposes organic compounds without the diffusion limitation and avoids pH adjustment, which makes the EO treatment of organic wastewater more efficient and more economical.

Single-Step Formation of Ni Nanoparticle-Modified Graphene-Diamond Hybrid Electrodes for Electrochemical Glucose Detection.

The development of accurate, reliable devices for glucose detection has drawn much attention from the scientific community over the past few years. Here, we report a single-step method to fabricate Ni nanoparticle-modified graphene-diamond hybrid electrodes via a catalytic thermal treatment, by which the graphene layers are directly grown on the diamond surface using Ni thin film as a catalyst, meanwhile, Ni nanoparticles are formed in situ on the graphene surface due to dewetting behavior. The good interface between the Ni nanoparticles and the graphene guarantees efficient charge transfer during electrochemical detection. The fabricated electrodes exhibit good glucose sensing performance with a low detection limit of 2 µM and a linear detection range between 2 µM-1 mM. In addition, this sensor shows great selectivity, suggesting potential applications for sensitive and accurate monitoring of glucose in human blood.

Constructing a Hydrophilic Microsensor for High-Antifouling Neurotransmitter Dopamine Sensing.

Real-time sensing of dopamine is essential for understanding its physiological function and clarifying the pathophysiological mechanism of diseases caused by impaired dopamine systems. However, severe fouling from nonspecific protein adsorption, for a long time, limited conventional neural recording electrodes concerning recording stability. This study reported a high-antifouling nanocrystalline boron-doped diamond microsensor grown on a carbon fiber substrate. The antifouling properties of this diamond sensor were strongly related to the grain size (i.e., nanocrystalline and microcrystalline) and surface terminations (i.e., oxygen and hydrogen terminals). Experimental observations and molecular dynamics calculations demonstrated that the oxygen-terminated nanocrystalline boron-doped diamond microsensor exhibited enhanced antifouling characteristics against protein adsorption, which was attributed to the formation of a strong hydration layer as a physical and energetic barrier that prevents protein adsorption on the surface. This finally allowed for in vivo monitoring of dopamine in rat brains upon potassium chloride stimulation, thus presenting a potential solution for the design of next-generation antifouling neural recording sensors. Experimental observations and molecular dynamics calculations demonstrated that the oxygen-terminated nanocrystalline boron-doped diamond (O-NCBDD) microsensor exhibited ultrahydrophilic properties with a contact angle of 4.9°, which was prone to forming a strong hydration layer as a physical and energetic barrier to withstand the adsorption of proteins. The proposed O-NCBDD microsensor exhibited a high detection sensitivity of 5.14 µA µM-1 cm-2 and a low detection limit of 25.7 nM. This finally allowed for in vivo monitoring of dopamine with an average concentration of 1.3 µM in rat brains upon 2 µL of potassium chloride stimulation, thus presenting a potential solution for the design of next-generation antifouling neural recording sensors.

Nanocrystalline diamond matrix deposited on copper substrate by radical species restricted diffusion.

Nanocrystalline diamond matrix (or patterned nanocrystalline diamond) have been grown by hot filament chemical vapor deposition (HFCVD) on copper substrates, which were masked by a copper template filled with through-holes. The influence of the mixing ratio for CH4/H2 source gases, total gas pressure and the aspect ratio (the ratio of hole depth to its diameter) on the morphology, grain size and quality of diamond films were investigated. Continuous diamond films were obtained under 2.0 kpa. When increasing the aspect ratio from 0.67 to 2.0, a gradual reduction of diamond grain size from micrometer to nanometers scale was observed. The formation of nanocrystalline diamond (NCD) matrix can be attributed to the restricted diffusion of radical species and the diamond nucleation kinetics on copper substrates. By through-holes of templates on copper substrates to restrict the diffusion and transport of radical species, NCD matrix was successfully deposited on copper substrates.

Co-generation of hydroxyl and sulfate radicals via homogeneous and heterogeneous bi-catalysis with the EO-PS-EF tri-coupling system for efficient removal of refractory organic pollutants.

Advanced oxidation processes are commonly considered one of the most effective techniques to degrade refractory organic pollutants, but the limitation of a single process usually makes it insufficient to achieve the desired treatment. This work introduces, for the first time, a highly-efficient coupled advanced oxidation process, namely Electro-Oxidation-Persulfate-Electro-Fenton (EO-PS-EF). Leveraging the EO-PS-EF tri-coupling system, diverse contaminants can be highly efficiently removed with the help of reactive hydroxyl and sulfate radicals generated via homogeneous and heterogeneous bi-catalysis, as certified by radical quenching and electron spin resonance. Concerning degradation of tetracycline (TC), the EO-PS-EF system witnessed a fast pseudo-first-order reaction kinetic constant of 2.54 × 10-3 s-1, ten times that of a single EO system and three-to-four times that of a binary system (EO-PS or EO-EF). In addition, critical parameters (e.g., electrolyte, pH and temperature) are systematically investigated. Surprisingly, after 100 repetitive trials TC removal can still reach 100% within 30 min and no apparent morphological changes to electrode materials were observed, demonstrating its long-term stability. Finally, its universality was demonstrated with effective degradation of diverse refractory contaminants (i.e., antibiotics, dyes and pesticides).

Nanoscale Modification of Titanium Implants Improves Behaviors of Bone Mesenchymal Stem Cells and Osteogenesis In Vivo.

The surficial micro/nanotopography and physiochemical properties of titanium implants are essential for osteogenesis. However, these surface characters' influence on stem cell behaviors and osteogenesis is still not fully understood. In this study, titanium implants with different surface roughness, nanostructure, and wettability were fabricated by further nanoscale modification of sandblasted and acid-etched titanium (SLA: sandblasted and acid-etched) by H2O2 treatment (hSLAs: H2O2 treated SLA). The rat bone mesenchymal stem cells (rBMSCs: rat bone mesenchymal stem cells) are cultured on SLA and hSLA surfaces, and the cell behaviors of attachment, spreading, proliferation, and osteogenic differentiation are further analyzed. Measurements of surface characteristics show hSLA surface is equipped with nanoscale pores on microcavities and appeared to be hydrophilic. In vitro cell studies demonstrated that the hSLA titanium significantly enhances cell response to attachment, spreading, and proliferation. The hSLAs with proper degree of H2O2 etching (h1SLA: treating SLA with H2O2 for 1 hour) harvest the best improvement of differentiation of rBMSCs. Finally, the osteogenesis in beagle dogs was tested, and the h1SLA implants perform much better bone formation than SLA implants. These results indicate that the nanoscale modification of SLA titanium surface endowing nanostructures, roughness, and wettability could significantly improve the behaviors of bone mesenchymal stem cells and osteogenesis on the scaffold surface. These nanoscale modified SLA titanium scaffolds, fabricated in our study with enhanced cell affinity and osteogenesis, had great potential for implant dentistry.

Surface Modification Using Polydopamine-Coated Liquid Metal Nanocapsules for Improving Performance of Graphene Paper-Based Thermal Interface Materials.

Given the thermal management problem aroused by increasing power densities of electronic components in the system, graphene-based papers have raised considerable interest for applications as thermal interface materials (TIMs) to solve interfacial heat transfer issues. Significant research efforts have focused on enhancing the through-plane thermal conductivity of graphene paper; however, for practical thermal management applications, reducing the thermal contact resistance between graphene paper and the mating surface is also a challenge to be addressed. Here, a strategy aimed at reducing the thermal contact resistance between graphene paper and the mating surface to realize enhanced heat dissipation was demonstrated. For this, graphene paper was decorated with polydopamine EGaIn nanocapsules using a facile dip-coating process. In practical TIM application, there was a decrease in the thermal contact resistance between the TIMs and mating surface after decoration (from 46 to 15 K mm2 W-1), which enabled the decorated paper to realize a 26% enhancement of cooling efficiency compared with the case without decoration. This demonstrated that this method is a promising route to enhance the heat dissipation capacity of graphene-based TIMs for practical electronic cooling applications.

A Double-Deck Structure of Reduced Graphene Oxide Modified Porous Ti3C2Tx Electrode towards Ultrasensitive and Simultaneous Detection of Dopamine and Uric Acid.

Considering the vital physiological functions of dopamine (DA) and uric acid (UA) and their coexistence in the biological matrix, the development of biosensing techniques for their simultaneous and sensitive detection is highly desirable for diagnostic and analytical applications. Therefore, Ti3C2Tx/rGO heterostructure with a double-deck layer was fabricated through electrochemical reduction. The rGO was modified on a porous Ti3C2Tx electrode as the biosensor for the detection of DA and UA simultaneously. Debye length was regulated by the alteration of rGO mass on the surface of the Ti3C2Tx electrode. Debye length decreased with respect to the rGO electrode modified with further rGO mass, indicating that fewer DA molecules were capable of surpassing the equilibrium double layer and reaching the surface of rGO to achieve the voltammetric response of DA. Thus, the proposed Ti3C2Tx/rGO sensor presented an excellent performance in detecting DA and UA with a wide linear range of 0.1-100 µM and 1-1000 µM and a low detection limit of 9.5 nM and 0.3 µM, respectively. Additionally, the proposed Ti3C2Tx/rGO electrode displayed good repeatability, selectivity, and proved to be available for real sample analysis.

Ultrahigh-Aspect-Ratio Boron Nitride Nanosheets Leading to Superhigh In-Plane Thermal Conductivity of Foldable Heat Spreader.

The rapid development of integrated circuits and electronic devices creates a strong demand for highly thermally conductive yet electrically insulating composites to efficiently solve "hot spot" problems during device operation. On the basis of these considerations, hexagonal boron nitride nanosheets (BNNS) have been regarded as promising fillers to fabricate polymer matrix composites. However, so far an efficient approach to prepare ultrahigh-aspect-ratio BNNS with large lateral size while maintaining an atomically thin nature is still lacking, seriously restricting further improvement of the thermal conductivity for BNNS/polymer composites. Here, a rapid and high-yield method based on a microfluidization technique is developed to obtain exfoliated BNNS with a record high aspect ratio of ≈1500 and a low degree of defects. A foldable and electrically insulating film made of such a BNNS and poly(vinyl alcohol) (PVA) matrix through filtration exhibits an in-plane thermal conductivity of 67.6 W m-1 K-1 at a BNNS loading of 83 wt %, leading to a record high value of thermal conductivity enhancement (≈35 500). The composite film then acts as a heat spreader for heat dissipation of high-power LED modules and shows superior cooling efficiency compared to commercial flexible copper clad laminate. Our findings provide a practical route to produce electrically insulating polymer composites with high thermal conductivity for thermal management applications in modern electronic devices.

Multiscale Structural Modulation of Anisotropic Graphene Framework for Polymer Composites Achieving Highly Efficient Thermal Energy Management.

Graphene is usually embedded into polymer matrices for the development of thermally conductive composites, preferably forming an interconnected and anisotropic framework. Currently, the directional self-assembly of exfoliated graphene sheets is demonstrated to be the most effective way to synthesize anisotropic graphene frameworks. However, achieving a thermal conductivity enhancement (TCE) over 1500% with per 1 vol% graphene content in polymer matrices remains challenging, due to the high junction thermal resistance between the adjacent graphene sheets within the self-assembled graphene framework. Here, a multiscale structural modulation strategy for obtaining highly ordered structure of graphene framework and simultaneously reducing the junction thermal resistance is demonstrated. The resultant anisotropic framework contributes to the polymer composites with a record-high thermal conductivity of 56.8-62.4 W m-1 K-1 at the graphene loading of ≈13.3 vol%, giving an ultrahigh TCE per 1 vol% graphene over 2400%. Furthermore, thermal energy management applications of the composites as phase change materials for solar-thermal energy conversion and as thermal interface materials for electronic device cooling are demonstrated. The finding provides valuable guidance for designing high-performance thermally conductive composites and raises their possibility for practical use in thermal energy storage and thermal management of electronics.

Nitric oxide sensors using nanospiral ZnO thin film deposited by GLAD for application to exhaled human breath.

ZnO is a promising gas sensing material for its excellent gas sensing response characteristics and long-term stability. Moreover, the improvement in the sensitivity and response speed of ZnO gas sensors can be achieved by the nanostructure fabrication. This paper proposes a facile method to deposit ZnO nanospirals using glancing angle deposition (GLAD) for application in nitric oxide (NO) sensors. ZnO nanospirals with porous characteristics have larger relative surface area and more active surfaces, compared with dense ZnO thin film. A sensor using nanospiral ZnO film shows a response factor of 16.9 to 100 ppb NO at 150 °C in 40% RH, which is 3 times larger than that of the sensor using dense ZnO film. Such a ZnO nanospiral sensor system can detect NO as low as 10 ppb which is below the NO concentration (>30 ppb) in exhaled breath of patients with asthma. The effects of working temperature and humidity on the sensor performance were investigated systematically in this work. Moreover, the sensor response showed a good selectivity to NO and high stability as the time increased up to 24 days. NO gas sensing mechanism was discussed in detail and nanospiral ZnO film sensors are promisingly applicable for exhaled human breath application compared with some other NO sensors.

Fabrication of boron-doped diamond films electrode for efficient electrocatalytic degradation of cresols.

The choice of anode materials has a significant influence on the electrocatalytic degradation of organics. Accordingly, the electrocatalytic activity of several active anodes (Ti/Ru-Ir, Ti/Ir-Ta, Ti/Pt) and non-active anodes (Ti/PbO2, Ti/SnO2, Si/BDD (boron-doped diamond)) was compared by electrocatalytic degradation of m-cresol. The results indicated Si/BDD electrode had the strongest mineralization ability and the lowest energy consumption. And the order of the activity of m-cresol degradation was as follows: Si/BDD > Ti/SnO2>Ti/PbO2>Ti/Pt > Ti/Ir-Ta > Ti/Ru-Ir. Also their intermediate products were compared. The effects of experimental parameters on electrocatalytic degradation of m-cresol with Si/BDD electrode showed m-cresol conversion was affected slightly by the electrode spacing and electrolyte concentration, but affected greatly by the temperature and current density. And smaller electrode spacing and current density, higher electrolyte concentration and temperature were beneficial to reduce energy consumption. Their degradation processes were all accord with the pseudo-first-order reaction kinetics completely. In addition, the results of electrocatalytic degradation of m, o, p-cresol indicated there was almost no significant difference on conversion rate between cresols isomers with the current density of 30 mA cm-2. However, the influence of group position was shown when the current density was reduced to 10 mA cm-2 and cresols conversion followed the sequence of m-cresol ≈ o-cresol > p-cresol.

A high performance surface acoustic wave visible light sensor using novel materials: Bi2S3 nanobelts.

Low dimensional Bi2S3 materials are excellent for use in photodetectors with excellent stability and fast response time. In this work, we developed a visible light sensor with good performance based on surface acoustic wave (SAW) devices using Bi2S3 nanobelts as the sensing materials. The SAW delay-line sensor was fabricated on ST-cut quartz with a designed wavelength of 15.8 microns using conventional photolithography techniques. The measured center frequency was 200.02 MHz. The Bi2S3 nanobelts prepared by a facile hydrothermal process were deposited onto SAW sensors by spin-coating. Under irradiation of 625 nm visible light with a power intensity of 170 µW cm-2, the sensor showed a fast and large response with a frequency upshift of 7 kHz within 1 s. The upshift of the frequency of the SAW device is mainly attributed to the mass loading effect caused by the desorption of oxygen from the Bi2S3 nanobelts under visible light radiation.

Persulfate enhanced electrochemical oxidation of highly toxic cyanide-containing organic wastewater using boron-doped diamond anode.

Cyanide-containing organic wastewater is discharged in large quantities by coking, electroplating and pharmaceutical industries, which seriously endangers environmental safety and human health. In this paper, Electrochemical Oxidation-Persulfate (EO-PS) Advanced Oxidation Process (AOP) was firstly used to treat high concentration cyanide-containing organic wastewater obtained from a chemical enterprise. The potential application of this process in the treatment of high concentration cyanide-containing organic wastewater was explored for the first time, and the effects of current density, initial pH, temperature and initial concentration on chemical oxygen demand (COD), total organic carbon (TOC) and total cyanide (CN-) removal in wastewater were systematically investigated. The results shown that the EO-PS process had an excellent removal effect on organics and cyanide in high concentration cyanide-containing organic wastewater which contained 11,290 mg L-1 COD, 4456 mg L-1 TOC and 1280.15 mg L-1 CN-. The COD, TOC and CN- removal at optimized operating parameters for 24 h were 95.8%, 87.8% and 98.4%, respectively. The corresponding electrical energy per order was only 41.6 kWh m-3 order-1. In addition, the pollutants removal can be accelerated under conditions of high current density, acidic solution, appropriate temperature and low pollutant concentration, among which low current density, low pH, appropriate temperature and low pollutant concentration can effectively diminish energy consumption. Cyanide, COD and TOC degradation in all reaction conditions followed the pseudo-first-order kinetic model.

Modulated light-activated electrochemistry at silicon functionalized with metal-organic frameworks towards addressable DNA chips.

Modulated light-activated electrochemistry (MLAE) at semiconductor/liquid interfaces derived from light-addressable potentiometric sensor (LAPS) and light-activated electrochemistry (LAE) for addressable photoelectrochemical sensing has been proposed as a new sensor platform. In this system, a bias voltage is applied to create a depletion layer at the silicon/electrolyte interface. Meanwhile, intensity-modulated light illuminates the movable electrode to generate electron/hole pairs and causes a detectable local AC photocurrent. The AC measurement showed a higher signal-to-noise ratio (SNR) of photocurrents compared to the traditional DC response, while a steeper photocurrent-voltage (I-V) curve than that of LAPS with an insulating layer was obtained. Furthermore, to stabilize and functionalize the silicon substrate, metal-organic framework (MOF) nanoparticles were grown in-situ on the silicon electrode. The successful modification was validated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The AC photocurrent increased as a result of the adsorption of negatively charged DNA, which contributed to the enhancement of the cathodic reduction process at the semiconductor electrodes, indicating a different response mechanism of MLAE from LAPS. The results obtained demonstrate the potential of MOF functionalized MLAE as a robust platform for light-addressable DNA chips with high sensitivity and specificity.

Metal-Level Thermally Conductive yet Soft Graphene Thermal Interface Materials.

Along with the technology evolution for dense integration of high-power, high-frequency devices in electronics, the accompanying interfacial heat transfer problem leads to urgent demands for advanced thermal interface materials (TIMs) with both high through-plane thermal conductivity and good compressibility. Most metals have satisfactory thermal conductivity but relatively high compressive modulus, and soft silicones are typically thermal insulators (0.3 W m-1 K-1). Currently, it is a great challenge to develop a soft material with the thermal conductivity up to metal level for TIM application. This study solves this problem by constructing a graphene-based microstructure composed of mainly vertical graphene and a thin cap of horizontal graphene layers on both the top and bottom sides through a mechanical machining process to manipulate the stacked architecture of conventional graphene paper. The resultant graphene monolith has an ultrahigh through-plane thermal conductivity of 143 W m-1 K-1, exceeding that of many metals, and a low compressive modulus of 0.87 MPa, comparable to that of silicones. In the actual TIM performance measurement, the system cooling efficiency with our graphene monolith as TIM is 3 times as high as that of the state-of-the-art commercial TIM, demonstrating the superior ability to solve the interfacial heat transfer issues in electronic systems.

A Paper-Like Inorganic Thermal Interface Material Composed of Hierarchically Structured Graphene/Silicon Carbide Nanorods.

With the increasing integration of devices in electronics fabrication, there are growing demands for thermal interface materials (TIMs) with high through-plane thermal conductivity for efficiently solving thermal management issues. Graphene-based papers consisting of a layer-by-layer stacked architecture have been commercially used as lateral heat spreaders; however, they lack in-depth studies on their TIM applications due to the low through-plane thermal conductivity (<6 W m-1 K-1). In this study, a graphene hybrid paper (GHP) was fabricated by the intercalation of silicon source and the in situ growth of SiC nanorods between graphene sheets based on the carbothermal reduction reaction. Due to the formation of covalent C-Si bonding at the graphene-SiC interface, the GHP possesses a superior through-plane thermal conductivity of 10.9 W m-1 K-1 and can be up to 17.6 W m-1 K-1 under packaging conditions at 75 psi. Compared with the current graphene-based papers, our GHP has the highest through-plane thermal conductivity value. In the TIM performance test, the cooling efficiency of the GHP achieves significant improvement compared to that of state-of-the-art thermal pads. Our GHP with characteristic structure is of great promise as an inorganic TIM for the highly efficient removal of heat from electronic devices.

Highly Sensitive and Selective Potassium Ion Detection Based on Graphene Hall Effect Biosensors.

Potassium (K⁺) ion is an important biological substance in the human body and plays a critical role in the maintenance of transmembrane potential and hormone secretion. Several detection techniques, including fluorescent, electrochemical, and electrical methods, have been extensively investigated to selectively recognize K⁺ ions. In this work, a highly sensitive and selective biosensor based on single-layer graphene has been developed for K⁺ ion detection under Van der Pauw measurement configuration. With pre-immobilization of guanine-rich DNA on the graphene surface, the graphene devices exhibit a very low limit of detection (≈1 nM) with a dynamic range of 1 nM-10 µM and excellent K⁺ ion specificity against other alkali cations, such as Na⁺ ions. The origin of K⁺ ion selectivity can be attributed to the fact that the formation of guanine-quadruplexes from guanine-rich DNA has a strong affinity for capturing K⁺ ions. The graphene-based biosensors with improved sensing performance for K⁺ ion recognition can be applied to health monitoring and early disease diagnosis.