S-induced Phase Change Forming In2 O3 /In2 S3 Heterostructure for Photoelectrochemical Glucose Sensor.

In the past several decades, Photoelectrochemical (PEC) sensing still remains a great challenge to design highly-efficient semiconductor photocatalysts via a facile method. It is of much importance to design and synthesize various novel nanostructured sensing materials for further improving the response performance. Herein, we present an In2 O3 /In2 S3 heterostructure obtained by combining microwave assisted hydrothermal method with S-induced phase change, whose energy band and electronic structure could be adjusted by changing the S content. Combining theoretical calculation and spectroscopic techniques, the introduction of sulfur was proved to produce multifunctional interfaces, inducing the change of phase, oxygen vacancies and band gap, which accelerates the separation of photoexcited carriers and reduces their recombination, improving the electronic injection efficiency around the interface of In2 O3 /In2 S3 . As anticipated, an enhanced glucose response performance with a photocurrent of 0.6 mA cm-2 , a linear range of 0.1-1 mM and a detection limit as low as 14.5 µM has been achieved based on the In2 O3 /In2 S3 heterostructure, which is significant superior over its pure In2 O3 and S-doped In2 O3 counterparts. This efficient interfacial strategy may open a new route to manipulate the electrical structure, and energy band structure regulation of sensing material to improve the performance of photoelectrodes for PEC.

High-performance Vo-ZnO/ZnS benefiting nanoarchitectonics from the synergism between defect engineering and surface engineering for photoelectrochemical glucose sensors.

In this study, a ZnO/ZnS nanocluster heterojunction photoelectrode rich in surface oxygen defects (Vo-ZnO/ZnS) was prepared by applying a simple in situ anion substitution and nitrogen atmosphere annealing method. The synergism between defect and surface engineering significantly improved the photocatalysts. Given this synergism, Vo-ZnO/ZnS was endowed with a long carrier lifetime, narrow band gap, high carrier density, and high performance toward electron transfer under light conditions. Thus, Vo-ZnO/ZnS had three times the photocurrent density of ZnO under light illumination. To further evaluate its advantages in the field of photoelectric bioassay, Vo-ZnO/ZnS was applied as the photocathode of photoelectric sensor system for glucose detection. Vo-ZnO/ZnS showed excellent performance in glucose detection in various aspects, including a low detection limit, high detection sensitivity, and a wide detection range.

A Branched Rutile/Anatase Phase Structure Electrode with Enhanced Electron-Hole Separation for High-Performance Photoelectrochemical DNA Biosensor.

A photoelectrochemical (PEC) detection platform was built based on the branched rutile/anatase titanium dioxide (RA-TiO2) electrode. Theoretical calculations proved that the type-II band alignment of rutile and anatase could facilitate charge separation in the electrode. The self-generated electric field at the interface of two phases can enhance the electron transfer efficiency of the electrode. Carboxylated CdTe quantum dots (QDs) were applied as signal amplification factors. Without the target DNA presence, the CdTe QDs were riveted to the surface of the electrode by the hairpin probe DNA. The sensitization of CdTe QDs increased the photocurrent of the electrode significantly. When the target DNA was present, the structural changes of the hairpin probe DNA resulted in the failure of the sensitized structure. Benefiting from excellent electrode structure design and CdTe QDs sensitization strategy, the PEC assays could achieve highly sensitive and specific detection of target DNA in the range of 1 fM to 1 nM, with a detection limit of 0.23 fM. The electrode construction method proposed in this article can open a new avenue for the preparation of more efficient PEC sensing devices.

Effects of Maleic Anhydride-Grafted Polyethylene on the Properties of Artificial Marble Waste Powder/Linear Low-Density Polyethylene Composites with Ultra-High Filling Content.

The need to reach carbon neutrality as soon as possible has made the use of recycled materials widespread. However, the treatment of artificial marble waste powder (AMWP) containing unsaturated polyester is a very challenging task. This task can be accomplished by converting AMWP into new plastic composites. Such conversion is a cost-effective and eco-friendly way to recycle industrial waste. However, the lack of mechanical strength in composites and the low filling content of AMWP have been major obstacles to its practical application in structural and technical buildings. In this study, a composite of AMWP/linear low-density polyethylene (LLDPE) filled with a 70 wt% AMWP content was fabricated using maleic anhydride-grafted polyethylene as a compatibilizer (MAPE). The mechanical strength of the prepared composites is excellent (tensile strength ~18.45 MPa, impact strength ~51.6 kJ/m2), making them appropriate as useful building materials. Additionally, laser particle size analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and thermogravimetric analysis were used to examine the effects of maleic anhydride-grafted polyethylene on the mechanical properties of AMWP/LLDPE composites and its mechanism of action. Overall, this study offers a practical method for the low-cost recycling of industrial waste into high-performance composites.

In situ growth of TiO2/Ti3C2 MXene Schottky heterojunction as a highly sensitive photoelectrochemical biosensor for DNA detection.

In this work, a heterojunction composed of a TiO2 nanosheet and layered Ti3C2 was synthesized by directly growing TiO2 in Ti3C2 MXene. Compared with pure TiO2, TiO2/Ti3C2 composites had increased surface area, and a light absorption range that extended from ultraviolet to visible light, which greatly extended the life of photogenerated carriers. A photoelectrochemical biosensor for DNA detection was constructed based on the TiO2/Ti3C2 heterogeneous structure, which was comprehensively studied based on photocurrent responses. In the absence of the target, the CdSe QDs were close to the surface of the electrode, resulting in enhanced sensitization and increased photocurrent. In the presence of the target, the photocurrent decreases due to the formation of rigid double strands with the probe DNA, which caused the CdSe QDs to be far away from the electrode surface. The sensor had stability and sensitivity for DNA detection in the range of 10 nM-10 fM, and the lower detection limit was 6 fM. Its outstanding characteristics also provided ideas for detecting various other target DNA for early diagnosis of various diseases.

Carbon Dot-Modified Branched TiO2 Photoelectrochemical Glucose Sensors with Visible Light Response.

The development of a photoelectrochemical (PEC) sensor for the sensitive and rapid detection of glucose is highly desirable. In PEC enzyme sensors, inhibition of the charge recombination of electrode materials is an efficient technique, and detection in visible light can prevent enzyme inactivation due to ultraviolet irradiation. In this study, a visible light-driven PEC enzyme biosensor was proposed, using CDs/branched TiO2 (B-TiO2) as the photoactive material and glucose oxidase (GOx) as the identification element. The CDs/B-TiO2 composites were produced via a facile hydrothermal method. Carbon dots (CDs) can not only act as photosensitizers but also inhibit photogenerated electron and hole recombination of B-TiO2. Under visible light, electrons in the carbon dots flowed to B-TiO2 and further to the counter electrode through the external circuit. In the presence of glucose and dissolved oxygen, H2O2 generated through the catalysis of GOx could consume electrons in B-TiO2, causing a decrease in photocurrent intensity. Ascorbic acid was added to ensure the stability of the CDs during the test. Based on the variation of the photocurrent response, the CDs/B-TiO2/GOx biosensor presented a good sensing performance of glucose in visible light, its detection range was from 0 to 9.00 mM, and the detection limit was 0.0430 mM.

Kinetics-accelerated one-step detection of MicroRNA through spatially localized reactions based on DNA tile self-assembly.

The localization of isothermal amplification systems has elicited extensive attention due to the enhanced reaction kinetics when detecting ultra-trace small-molecule nucleic acids. Therefore, the seek for an appropriate localization cargo of spatially confined reactions is urgent. Herein, we have developed a novel approach to localize the catalytic hairpin assembly (CHA) system into the DNA tile self-assembly nanostructure. Thanks to the precise programming and robust probe loading capacity, this strategy achieved a 2.3 × 105-fold higher local reaction concentration than a classical CHA system with enhanced reaction kinetics in theory. From the experimental results, this strategy could reach the reaction plateau faster and get access to a magnified effect of 1.57-6.99 times higher in the linear range of microRNA (miRNA) than the simple CHA system. Meanwhile, this strategy satisfied the demand for the one-step detection of miRNA in cell lysates at room temperature with good sensitivity and specificity. These features indicated its excellent potential for ultra-trace molecule detection in clinical diagnosis and provided new insights into the field of bioassays based on DNA tile self-assembly nanotechnology.

Boosting the Photocatalytic Ability of TiO2 Nanosheet Arrays for MicroRNA-155 Photoelectrochemical Biosensing by Titanium Carbide MXene Quantum Dots.

The electrodes of two-dimensional (2D) titanium dioxide (TiO2) nanosheet arrays were successfully fabricated for microRNA-155 detection. The (001) highly active crystal face was exposed to catalyze signaling molecules ascorbic acid (AA). Zero-dimensional (0D) titanium carbide quantum dots (Ti3C2Tx QDs) were modified to the electrode as co-catalysts and reduced the recombination rate of the charge carriers. Spectroscopic methods were used to determine the band structure of TiO2 and Ti3C2Tx QDs, showing that a type Ⅱ heterojunction was built between TiO2 and Ti3C2Tx QDs. Benefiting the advantages of materials, the sensing platform achieved excellent detection performance with a wide liner range, from 0.1 pM to 10 nM, and a low limit of detection of 25 fM (S/N = 3).

Engineering exposed vertical nano-TiO2 (001) facets/BiOI nanosheet heterojunction film for constructing a satisfactory PEC glucose oxidase biosensor.

In the field of photoelectrochemical (PEC) enzyme biosensors, constructing efficient photoelectrodes, in which the recombination of photogenerated carriers is an important factor affecting the performance, is of great significance. Herein, to enhance the separation efficiency of photogenerated carriers, titanium dioxide (TiO2) nanosheet (NS)/bismuth oxyiodide (BiOI) NS/glucose oxidase (GOx) composites were prepared via hydrothermal and solvothermal methods. Single-crystal anatase TiO2 NSs with a high percentage of (001) facets lead to better photocarrier separation due to heterojunctions between facets. After coupling with BiOI NSs, the photoelectrochemical performance of the electrode was greatly improved. The photogenerated electrons from TiO2 and BiOI gathered at TiO2 (101) and were exported through the fluorine-doped tin oxide (FTO) substrate to generate electrical signals. Photogenerated holes were transferred to TiO2 (001) and BiOI to participate in the enzymatic reaction, showing the outstanding separation of electrons and holes. The prepared TiO2 NS/BiOI NS/GOx glucose biosensor achieved satisfactory results, with sensitivity of 14.25 µA mM-1 cm-2, a linear measurement range of 0-1 mM, and a limit of detection (3S/N) of 0.01 mM in phosphate buffered saline (PBS) at a pH of 7.4. The mechanism for the efficient separation of photogenerated carriers based on the facet heterojunctions introduced in this paper also provides new insights into other optoelectronic biosensors.

Enhanced Photocatalytic Hydrolysis Performance of Chiral Molecule Loaded Titanium Disulfide Nanosheets.

The photoelectrochemical (PEC) water decomposition is a promising method to produce hydrogen from water. To improve the water decomposition efficiency of the PEC process, it is necessary to inhibit the generation of H2 O2 byproducts and reduce the overpotential required by cheap catalysts and a high current density. Studies have shown that coating the electrode with chiral molecules or chiral films can increase the hydrogen production and reduce the generation of H2 O2 byproducts. This is interpreted as the result of a chiral induced spin selectivity (CISS) effect, which induces a spin correlation between the electrons that are transferred to the anode. Here, we report the adsorption of chiral molecules onto titanium disulfide nanosheets. Firstly, titanium disulfide nanosheets were synthesized via thermal injection and then dispersed through ultrasonic crushing. This strategy combines the CISS with the plasma effect caused by the narrow bandgap of two-dimensional sulfur compounds to promote the PEC water decomposition with a high current density.

A sandwich-type electrochemical immunosensor using trimetallic nanozyme as signal amplification for NT-proBNP sensitive detection.

Heart failure (HF) is a major public health problem trigged by a heart circulation disorder. Early detection and diagnosis are conducive to the prevention and treatment of HF. N-terminal B-type natriuretic peptide precursor (NT-proBNP) is considered to be a sensitive diagnostic biomarker of HF. In this study, we constructed a NT-proBNP sandwich electrochemical immunosensor by using electroplated gold nanoparticles (Au NPs) as the substrate and utilizing rough-surfaced trimetallic Au@PdPt nanozymes (Au@PdPt RTNs) as current signal amplification. The Au NPs as substrate material modified glassy carbon electrode (GCE) have excellent conductivity and biocompatibility, which not only accelerate electron transfer rate, but also improve the loading capacity of primary antibody (Ab1). Moreover, the Au@PdPt RTNs were synthesized by a one-pot method and used as the labels to bound with secondary antibodies (Ab2) via the Pt-N. The large specific surface area and excellent catalytic properties for H2O2 of Au@PdPt RTNs can effectively enhance the stability and sensitivity of the immunosensor. With the favorable cooperation of Au NPs and Au@PdPt RTNs, the constructed immunosensor exhibited a wide concentration range from 0.1 pg mL-1 to 100 ng mL-1 and a low detection limit of 0.046 pg mL-1. Furthermore, the accuracy of the analysis of NT-proBNP in diluted human serum samples was satisfactory. The results revealed the electrochemical immunosensor has a prospective application in clinical detection.

Photoelectrochemical Enzyme Biosensor Based on TiO2 Nanorod/TiO2 Quantum Dot/Polydopamine/Glucose Oxidase Composites with Strong Visible-Light Response.

Although photoelectrochemical (PEC) enzyme biosensors based on visible-light detection would have a high practical value, their development has been limited by the weak visible-light response of available photoactive substrates. Here, to enhance the visible-light response of a photoelectric substrate, a TiO2 nanorods (NRs)/TiO2 quantum dots (QDs)/polydopamine (PDA)/glucose oxidase nanocomposite was prepared via hydrothermal synthesis, followed by photopolymerization. TiO2 QDs with strong light absorption and excellent photocatalytic activity were introduced between the TiO2 NRs and the PDA. An efficient electron transport interface that formed as a result of the combination of the TiO2 NRs, TiO2 QDs, and the PDA could not only transfer electrons quickly and orderly, but also substantially improve the response of the TiO2 NRs under visible light. Through a series glucose detection, a sensor based on the nanocomposite was found to exhibit superior sensing performance under visible light with a sensitivity of 4.63 µA mM-1 cm-2, a linear response over the concentration 0.1-4 mM, and a detection limit of 8.16 µM. This work proposes a biosensor that can detect under visible light, thereby expanding the application range of PEC enzyme biosensors.

Gold and Platinum Nanoparticle-Functionalized TiO2 Nanotubes for Photoelectrochemical Glucose Sensing.

Developing stable photoelectrochemistry (PEC) glucose biosensors with high sensitivity and a low detection limit is highly desirable in the biosensor field. Herein, a highly sensitive and stable enzymatic glucose PEC biosensor is rationally designed and fabricated using a TiO2NTs/Au/Pt/GOx electrode. First, we prepared one-dimensional TiO2 nanotube arrays which could realize the orthogonalization of the light-incident direction and the carrier diffusion direction via anodization. Subsequently, we used the method of photoassisted deposition for anchoring Pt nanoparticles on TiO2NTs after electrodepositing Au nanoparticles. Among them, Au nanoparticles promote light absorption via the surface plasmon resonance effect and the separation of photogenerated carriers through forming a Schottky junction. Moreover, the Pt nanoparticles on the electrode surface can react with hydrogen peroxide (H2O2) generated from glucose (Glu) oxidation by glucose oxidase (GOx), accelerating the electron-transfer process during glucose oxidation and greatly improving the sensitivity of the glucose biosensor. As a result, TiO2NTs/Au/Pt/GOx exhibited excellent PEC performance, achieving a high sensitivity of 81.93 µA mM-1 cm-2 and a low detection limit (1.39 µM), far exceeding the performance of TiO2NTs/M/GOx (M = Au, Pt). Therefore, the introduction of Pt nanoparticles as active substances to promote enzymatic reactions is important for designing high-performance enzyme biosensors.

TiO2 nanostructures with different crystal phases for sensitive acetone gas sensors.

Gas sensors have become increasingly significant because of the rapid development in electronic devices that are applied in detecting noxious gases. Adjusting the crystal phase structure of sensing materials can optimize the band gap and oxygen-adsorptive capacity, which influences the gas sensing characteristics. Therefore, titanium dioxide (TiO2) materials with different crystal phase structures including rutile TiO2 nanorods (R-TiO2 NRs), anatase TiO2 nanoparticles (A-TiO2 NRs) and brookite TiO2 nanorods (B-TiO2 NRs) were synthesized successfully via one-step hydrothermal process, respectively. The gas sensing characteristics were also investigated systematically. The sensors based on R-TiO2 NRs displayed the higher response value (12.3) to 100 ppm acetone vapor at 320 °C compared to A-TiO2 NRs (4.1) and B-TiO2 NRs (2.3). Furthermore, gas sensors based on R-TiO2 NRs exhibited excellent repeatability under six cycles and good selectivity to acetone. The outstanding sensing properties of gas sensors based on R-TiO2 NRs can be ascribed to relatively narrow band gap and more oxygen vacancies of rutile phase, which showed a probable way for design gas sensors based on metal oxide semiconductors with remarkable gas sensing performances by the crystal phase adjustment engineering in the future.

Enhancing Hydrogen Evolution by Optimizing the Hydrogen Adsorption on Titanium Monoxide Nanodot-Decorated Cobalt Sulfide Nanosheets.

Modulating the local electronic state of metal compounds through interfacial interaction has become a key method for manufacturing high-performance hydrogen evolution reaction (HER) electrocatalysts. The electron-rich active sites can promote the adsorption of hydrogen, which accelerates the Volmer step and thereby enhances the electrocatalytic performance of HER. Here, we found that the strong interfacial interaction between TiO nanodots (TiO/Co-S) and Co-S nanosheets could advantageously improve the performance toward HER of electrocatalyst. Meanwhile, XPS results showed that modulating the local electronic structure of the TiO nanodots produces electron-rich regions on Co. As a result, the overpotential of the TiO/Co-S nanocomposite at 10 mA cm-2 was 107 mV, and the Tafel slope was 83.3 mV dec-1 . This study focused on the effect of the solid-solid interface on the local electronic structure of the catalytic metal active sites and successfully improved the catalytic activity of transition metal materials in HER catalysis.

Donor-Acceptor Compensated ZnO Semiconductor for Photoelectrochemical Biosensors.

Hindering the recombination of a photogenerated carrier is a crucial method to enhance the photoelectrochemical performance of ZnO due to its high exciton binding energy. Herein, the intramolecular donor-acceptor compensated semiconductor ZnO (I-D/A ZnO), introducing C dopants and oxygen vacancies, was prepared with the assistance of ascorbic acid (AA). According to the DFT calculations, the asymmetry DOS could lead to the longer carrier lifetime and the smaller electron transfer resistance. Then, the photoelectrochemical biosensor toward glucose was regarded as a model to discuss the application of ZnO in biosensors. As a result, the biosensor based on I-D/A ZnO showed good performance with high sensitivity, low limit of detection, and fine anti-interference, meaning that I-D/A ZnO is a promising semiconductor for photoelectrochemical biosensors.

Highly Accurate and Fast Electrochemical Detection of Scrub Typhus DNA via a Nanoflower NiFe-Based Biosensor.

Owing to the lack of specific diagnostic methods, Scrub typhus can sometimes be difficult to diagnose in the Asia-Pacific region. Therefore, an efficient and rapid detection method urgently needs to be developed. Based on competitive single-stranded DNA over modified glassy carbon electrode (GCE), an electrochemical biosensor was established to detect the disease. The nano-flower NiFe layered double hydroxide (NiFe-LDH) modified GCE has a large specific surface area, which supported a large amount of gold nanoparticles, so that a wide linear detection range from 25 fM to 0.5 µM was obtained. The beacon DNA (B-DNA) with the same sequence as the Scrub typhus DNA (T-DNA), but labeled with methylene blue, was used to construct a competitive relationship. When T-DNA and B-DNA were present on the sensor simultaneously, they would hybridize with probe DNA in a strong competition, and the corresponding electrochemical response signal would be generated via testing. It contributed to reducing tedious experimental procedures and excessive response time, and achieved fast electrochemical detection of DNA. The strategy provides a worthy avenue and possesses promising applications in disease diagnosis.

A novel electrochemical biosensor for ultrasensitive Hg2+ detection via a triple signal amplification strategy.

We developed a novel electrochemical biosensor for ultrasensitive Hg2+ detection via a triple signal amplification strategy of a DNA dual cycle, organic-inorganic hybrid nanoflowers (Cu3(PO4)2 HNFs) and gold nanoparticle (AuNP) probe. The DNA dual cycle was triggered by exonuclease III (Exo III) in the presence of Hg2+, and Cu3(PO4)2 HNFs were synthesized as an AuNP probe carrier. The electrochemical biosensor displayed high stability, high sensitivity and excellent specificity, which was improved by up to seven orders of magnitude compared to the World Health Organization (WHO) allowed Hg2+ levels in drinking water. This signal amplification strategy could be easily modified and extended to detect other hazardous heavy metals and nucleic acids.

Enhancing the performance of photoelectrochemical glucose sensor via the electron cloud bridge of Au in SrTiO3/PDA electrodes.

Developing photoelectrochemical biosensors via efficient photogenerated-charge separation remains a challenging task in biomolecular detection. In this study, we utilised a simple approach for constructing an efficient photoactive organic-inorganic heterojunction interface composed of SrTiO3 with high photocatalytic activity and polydopamine (PDA) with high biocompatibility and electrical conductivity. Gold nanoparticles with dense electron cloud properties were introduced as a bridge between SrTiO3 and PDA (SrTiO3/Au/PDA). The Au bridge allowed the PDA to uniformly and tightly attach on the surface of SrTiO3 electrodes and also provided a separate transmission channel for electrons from PDA to SrTiO3. The rapidly transmitted electrons were captured by a signal-acquisition system, thereby improving the photocurrent signal output. The 3D hollowed out SrTiO3/Au/PDA biosensor manufactured herein was used for glucose detection. The biosensor achieved ultrahigh sensitivities reaching 23.7 µA mM-1 cm-2, an extended linear range (1-20 mM), and a low detection limit (0.012 mM). The excellent results of glucose analysis in serum samples further confirmed the feasibility of the biosensor in clinical applications. In summary, the proposed strategy allowed for the use of an electronic cloud bridge in the construction of glucose biosensors with satisfactory performances, which is promising for the future fabrication of high-performance biosensors.

Glucose photoelectrochemical enzyme sensor based on competitive reaction of ascorbic acid.

A new method based on the competitive reaction of ascorbic acid (AA) was used to improving the performance of photoelectrochemical glucose enzyme sensor. In this method, amplifying the photoelectric signal of H2O2 by the competitive reaction of AA is the key step. The detection can be well operated at 0 V under optimal AA concentration of 10 mM. In the method, AA was regarded as not only the electron donor to capture the hole in the conduction band of ZnO, but also the remover of H2O2 produced by the oxidation of glucose. Both these factors led to the formation of a pair of competitive reactions that enhanced the response towards glucose detection. Compared to the detection without AA, the stability of the response current, detection ranges of 1-19 mM, detection limit of 80 µM and sensitivity of 2.88 µA mM-1·cm-2 were optimized prominently.