Synergism of Holmium Orthovanadate/Phosphorus-Doped Carbon Nitride Nanocomposite: Nonenzymatic Electrochemical Detection of Hydrogen Peroxide.

Developing efficient and robust electrode materials for electrochemical sensors is critical for real-time analysis. In this paper, a hierarchical holmium vanadate/phosphorus-doped graphitic carbon nitride (HoVO4/P-CN) nanocomposite is synthesized and used as an electrode material for electrochemical detection of hydrogen peroxide (H2O2). The HoVO4/P-CN nanocomposite exhibits superior electrocatalytic activity at a peak potential of -0.412 V toward H2O2 reduction in alkaline electrolytes while compared with other reported electrocatalysts. The HoVO4/P-CN electrochemical platform operated under the optimized conditions shows excellent analytical performance for H2O2 detection with a linear concentration range of 0.009-77.4 µM, a high sensitivity of 0.72 µA µM-1 cm-2, and a low detection limit of 3.0 nΜ. Furthermore, the HoVO4/P-CN-modified electrode exhibits high selectivity, remarkable stability, good repeatability, and satisfactory reproducibility in detecting H2O2. Its superior performance can be attributed to a large specific surface area, high conductivity, more active surface sites, unique structure, and synergistic action of HoVO4 and P-CN to benefit enhanced electrochemical activity. The proposed HoVO4/P-CN electrochemical platform is effectively applied to ascertain the quantity of H2O2 in food and biological samples. This work outlines a promising and effectual strategy for the sensitive electrochemical detection of H2O2 in real-world samples.

Hydrothermal synthesis of iron titanate hexagonal nanoplates for electrochemical detection of nitrofurazone.

An electrochemical sensor is established using an iron titanate (FeTiO3) modified glassy carbon electrode (GCE) to detect nitrofurazone. Various microscopic and spectroscopic analysis was performed to reveal the properties of the prepared FeTiO3 hexagonal nanoplates. The FeTiO3/GCE presents enhanced electrochemical response to nitrofurazone at the peak reduction potential of - 0.471 V with a larger peak current than the bare GCE due to high electrical conductivity, enhanced specific surface area, and abundant active sites. The superior nitrofurazone detection performance includes the low limit of detection of 0.002 µM and the sensitivity of 0.551 µA µM-1 cm-2 in the linear concentration range of 0.01-162.2 µM. The reproducibility and selectivity studies of the FeTiO3/GCE show excellent results with a relative standard deviation of < 5%. The practicability of FeTiO3/GCE is confirmed by monitoring nitrofurazone in actual samples. This work demonstrates that perovskite-type FeTiO3 has great potential in real-world sample analysis, and provides a new way to develop high-performance electrochemical sensors.

Silver nanopopcorns decorated on flexible membrane for SERS detection of nitrofurazone.

The synthesis of three-dimensional silver nanopopcorns (Ag NPCs) onto a flexible polycarbonate membrane (PCM) for the detection of nitrofurazone (NFZ) on the fish surface by surface-enhanced Raman spectroscopy (SERS) is presented. The proposed flexible Ag-NPCs/PCM SERS substrate exhibits significant Raman signal intensity enhancement with the measured enhancement factor of 2.36 × 106. This is primarily attributed to the hotspots created on Ag NPCs, including numerous nanoscale protrusions and internal crevices distributed across the surface of Ag NPCs. The detection of NFZ by this flexible SERS substrate demonstrates a low limit of detection (LOD) of 3.7 × 10-9 M and uniform and reproducible Raman signal intensities with a relative standard deviation below 8.34%. It also exhibits excellent stability, retaining 70% of its efficacy even after 10 days of storage. Notably, the practical detection of NFZ in tap water, honey water, and fish surfaces achieves LOD values of 1.35 × 10-8 M, 5.76 × 10-7 M, and 3.61 × 10-8 M, respectively,  which highlights its effectiveness across different sample types. The developed Ag-NPCs/PCM SERS substrate presents promising potential for sensitive SERS detection of toxic substances in real-world samples.

Three-dimensional manganese cobaltate: a highly conductive electrocatalyst for paraoxon-ethyl detection.

The synthesis of manganese cobaltate (MnCo2O4) with the hybrid three-dimensional architecture has been developed as an electrocatalyst for the electrochemical sensing of paraoxon-ethyl (PEL). The detailed physicochemical and structural characterization of MnCo2O4 is meticulously examined. The MnCo2O4-modified screen-printed carbon electrode (SPCE) exhibits good electrocatalytic activity for the reduction of PEL compared with the bare SPCE due to numerous unique properties. By profiting from these advantages, the proposed MnCo2O4/SPCE shows superior sensing performance toward the determination of PEL, including low cathodic peak potential (- 0.64 V), wide detection range (0.015-435 µM), low limit of detection (0.002 µM), high detection sensitivity (2.30 µA µM-1 cm-2), excellent selectivity, and good reproducibility. Notably, the electrochemical performance of the MnCo2O4-based electrocatalyst is superior to those previously reported in the literatures. The practical application of the MnCo2O4/SPCE is effectively assessed in the analysis of food and water samples with satisfied recoveries of 96.00-99.35%. The superior performance of the proposed MnCo2O4 electrocatalyst holds considerable potential for future development of electrochemical sensing platforms.

Electrochemical Behavior of Three-Dimensional Cobalt Manganate with Flowerlike Structures for Effective Roxarsone Sensing.

Rational design and construction of the finest electrocatalytic materials are important for improving the performance of electrochemical sensors. Spinel bioxides based on cobalt manganate (CoMn2O4) are of particular importance for electrochemical sensors due to their excellent catalytic performance. In this study, three-dimensional CoMn2O4 with the petal-free, flowerlike structure is synthesized by facile hydrothermal and calcination methods for the electrochemical sensing of roxarsone (RXS). The effect of calcination temperature on the characteristics of CoMn2O4 was thoroughly studied by in-depth electron microscopic, spectroscopic, and analytical methods. Compared to previous reports, CoMn2O4-modified screen-printed carbon electrodes display superior performance for the RXS detection, including a wide linear range (0.01-0.84 µM; 0.84-1130 µM), a low limit of detection (0.002 µM), and a high sensitivity (33.13 µA µM-1 cm-2). The remarkable electrocatalytic performance can be attributed to its excellent physical properties, such as good conductivity, hybrid architectures, high specific surface area, and rapid electron transportation. More significantly, the proposed electrochemical sensor presents excellent selectivity, good stability, and high reproducibility. Besides, the detection of RXS in river water samples using the CoMn2O4-based electrochemical sensor shows satisfactory recovery values in the range of 98.00-99.80%. This work opens a new strategy to design an electrocatalyst with the hybrid architecture for high-performance electrochemical sensing.

Zinc Manganate: Synthesis, Characterization, and Electrochemical Application toward Flufenamic Acid Detection.

The construction of novel electrocatalysts for efficient and economic electrochemical sensors is continuously a significant conceptual barrier for the point-of-care technology. Binary metal oxides with heterostructures have gained plenty of attention due to their promising physicochemical properties. Herein, we develop a rapid and sensitive electrochemical probe for the detection of flufenamic acid (FFA) by using a zinc manganate (ZnMnO)-modified electrode. The formation of ZnMnO was confirmed by various analytical techniques, such as X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and field-emission scanning electron microscopy with energy dispersive X-ray spectroscopy and elemental mapping. The ZnMnO-based electrocatalyst, which was used for the electrochemical detection of FFA, shows better performance than the previously reported electrode materials. The ZnMnO assay shows a linear quantitative range from 0.05 to 116 µM with a limit of detection of 0.003 µM and sensitivity of 0.385 µA µM-1 cm-2. Its good electrochemical performance can be ascribed to the large surface area, rapid charge mass transfer, copious active sites, and high carrier mobility. The electrochemical study displays that the fabricated ZnMnO-based sensor has the potential to be applied in the clinical analysis. This work constructs an advanced functional electrode material with a microscale architecture for the point-of-care technology.

Heterostructured bismuth oxide/hexagonal-boron nitride nanocomposite: A disposable electrochemical sensor for detection of flutamide.

Aquatic contamination from the accumulation of pharmaceuticals has induced severe toxicological impact to the ecological environment, especially from non-steroidal anti-inflammatory drugs (NSAIDs). Real-time monitoring of flutamide, which is a class of NSAIDs, is very significant in environmental protection. In this work, we have synthesized the hexagonal-h boron nitride decorated on bismuth oxide (Bi2O3/h-BN) based nanocomposite for the effective electrochemical detection of flutamide (FTM). The structural and morphological information of the heterostructured Bi2O3/h-BN nanocomposite was analyzed by using a sequence of characterization methods. Voltammetric techniques were used to evaluate the analytical performance of the Bi2O3/h-BN modified screen-printed carbon electrode (SPCE) for the FTM detection. The Bi2O3/h-BN modified SPCE displays a synergetic catalytic effect for the reduction of FTM due to large surface area, numerous active sites, fast charge transfer and abundant defects. The proposed electrochemical sensing platform demonstrates high selectivity, low detection limit (9.0 nM), good linear ranges (0.04-87 µM) and short response time for the detection of FTM. The feasibility of the electrochemical sensor has been proved by the successful application to determine FTM in environmental samples.

Strontium tungstate-modified disposable strip for electrochemical detection of sulfadiazine in environmental samples.

Rapid-monitoring of drugs has attracted tremendous consideration owing to robust global demand for cost-effective and high effectiveness. Binary metal oxides with various morphology have been reported as electrodes for electrochemical sensor to fulfilling the clinical and enviromental requirements. In this study, strontium tungstate (SrWO4) nanoflakes have been successfully prepared via the facile sonochemical method for the first time. The characteristics of as-prepared SrWO4 are systematically measured by various analytical and spectroscopic methods. The SrWO4 nanoflakes are utilized to modify the electrochemical electrode for the sulfadiazine (SDZ) determination. The SrWO4 modified electrode possesses excellent electrocatalytic activity and high recognition capability for the electrochemical detection of SDZ. Impressively, the as-fabricated SrWO4 modified electrode attainted lowest oxidation peak at +0.93 V (vs Ag/AgCl2) with the limit of detection of 0.009 µM, the sensitivity of 0.123 µA µM-1 cm2 and linear detection range of 0.05-235 µM. The enhanced performance of proposed SrWO4-based sensors could be attributed to the catalytic effect, large surface area, good electrical conductivity and physicochemical nature. Notably, the electrocatalytic performances of the SDZ sensors are good as compared to the previous literature, indicating the significance of the newly designed SrWO4 modified electrode. The real-sample diagnosis by the SDZ detection in environmental sample demonstrates the proposed SrWO4-based sensors with good recovery range.

A photochemical approach to anchor Au NPs on MXene as a prominent SERS substrate for ultrasensitive detection of chlorpromazine.

As a novel two-dimensional (2D) material, metal carbide (MXene) has been identified as a hotspot research topic in the field of surface-enhanced Raman spectroscopy (SERS). Herein, we report the increment of SERS activity of titanium carbide (TiC) by incorporation of gold nanoparticles (Au NPs) by a facile photoreduction process for the detection of antipsychotic drug. TiC anchored with Au NPs produce a remarkable SERS enhancement by the synergistic action of chemical and electromagnetic mechanisms. The hotspots are formed in the nanometer-scale gaps between Au NPs on the TiC surface for the effective interaction with probe molecules. The proposed TiC/Au-NPs SERS substrate was employed for the detection of chlorpromazine (CPZ) with the wide linear range of 10-1-10-10 M and the ultra-low limit of detection of 3.92 × 10-11 M. Besides, the SERS effect of the optimized TiC/Au-NPs for the 532 nm excitation exhibits the enhancement factor in the order of 109 with the relative standard deviation of < 13% for the uniformity and < 8.80% for the reproducibility. To ensure the practical feasibility of the proposed TiC/Au-NPs SERS substrate, the spike and recovery method was used for the detection of CPZ in human biological fluids like urine and saliva. This work can open up a new approach to improve the SERS activity of MXene-based SERS substrate for practical applications, especially the determination of antipsychotic drugs in environmental pollution management.

Unraveling the electrochemical properties of lanthanum cobaltite decorated halloysite nanotube nanocomposite: An advanced electrocatalyst for determination of flutamide in environmental samples.

Prostate cancer is one of the primary causes of death around the world. As an important drug, flutamide has been used in the clinical diagnosis of prostate cancer. However, the over dosage and improper discharge of flutamide could affect the living organism. Thus, it necessary to develop the sensor for detection of flutamide with highly sensitivity. In this paper, we report the synthesis of lanthanum cobaltite decorated halloysite nanotube (LCO/HNT) nanocomposite prepared by a facile method and evaluated for selective reduction of flutamide. The as-prepared LCO/HNT nanocomposite shows the best catalytic performance towards detection of flutamide, when compared to other bare and modified electrodes. The good electrochemical performance of the LCO/HNT nanocomposite modified electrode is ascribed to abundant active sites, large specific surface area and their synergetic effects. Furthermore, the LCO/HNT modified electrode exhibits low detection limit (0.002 µM), wide working range (0.009-145 µM) and excellent selectivity with remarkable stability. Meaningfully, the developed electrochemical sensor was applied in real environmental samples with an acceptable recovery range.

Lanthanum cobaltite supported on graphene nanosheets for non-enzymatic electrochemical determination of catechol.

An electrochemical sensor is described for the determination of catechol (CT) based on the nanocomposite of lanthanum cobaltite supported on graphene nanosheets (LaCo/GNS). The nanocomposite was systematically examined by various analytical and spectroscopic methods. The LaCo/GNS-modified electrode exhibites good electrochemical activity towards CT determination compared to other modified and unmodified electrodes. The electrochemical signal was acquired at a redox potential of 0.21 (Epa) and 0.17 (Epc) Volt (vs. Ag/AgCl). The proposed electrode exhibits low detection limit (1.0 nM), wide working range (0.009-132 µM), and good sensitivity (5.68 µA µM-1 cm-2). The electrochemical nanoprobe has good selectivity over potentially interfering compounds. The electrochemical sensor was applied to the analysis of environmental samples with acceptable recovery. Graphical abstractSchematic representation of electrochemical determination of catechol in the environmental sample analysis using lanthanum cobaltite supported on graphene nanosheets.

Photochemical decoration of gold nanoparticles on MoS2 nanoflowers grafted onto the flexible carbon cloth as a recyclable SERS sensor for the detection of antibiotic residues on curved surfaces.

Surface-enhanced Raman spectroscopy (SERS)-based flexible substrate has recently been demonstrated to be effective in detecting molecules on curved surfaces, however a suitable method for fabricating the flexible SERS substrate still remains a hurdle. In this paper, we fabricated a flexible SERS substrate by anchoring the plasmonic gold nanoparticles (Au-NPs) onto the hydrothermally grown flower-like molybdenum disulfide (MoS2) grafted onto carbon cloth (CC) via a facile photoreduction route. Benefitting from the abundant hotspots generation of the Au-NPs and photo-induced charge-transfer ability of MoS2, the constructed Au-NPs/MoS2/CC substrate exhibit a superior SERS sensing ability, excellent SERS enhancement factor, high flexibility and mechanical stability towards the nitrofurantoin (NFT) with an ultra-low detection limit of 10-11 M. As a trial for practical applications, the flexible substrate was used to detect NFT (10-4 M) in the curved surfaces of meat samples via swab technique. The ability of the flexible Au-NPs/MoS2/CC substrate to sustain the robust Raman signals of NFT even after recycling up to 4 cycles validated its reusability. The proposed flexible SERS substrate with reusable capability indicates its great potential in practical applications for the detection of target molecules on the curved surfaces.

Synergistic SERS enhancement of NiCo-LDHs microurchins and silver nanoparticles for ultra-sensitive and reusable detection of thiabendazole.

Two-dimensional layered semiconductor materials as a distinctive class of materials are comprehensively explored for widespread applications due to narrow bandgap, controllable morphology, and tunable metal cation composition. Herein, we constructed a sensing platform of surface enhanced Raman spectroscopy (SERS) by combination of nickel­cobalt layered double hydroxide (NiCo-LDH) microurchins and plasmonic silver nanoparticles (Ag NPs) for fungicide detection of thiabendazole (TBZ). The NiCo-LDHs/Ag-NPs microcomposites consist of NiCo-LDHs microurchins having a large number of nanoneedles deposited with photoreduced Ag NPs. The SERS platform with NiCo-LDHs/Ag-NPs shows an excellent SERS performance for TBZ detection, including an ultra-low detection limit of 1.49 × 10-11 M, a sublime enhancement factor of 1.71 × 109, high uniformity, good reproducibility, and long-term storage stability. The ultrahigh SERS activity of NiCo-LDH/Ag-NPs can be attributed to strong electromagnetic enhancement in the nanoscale gaps between Ag NPs, massive charge transfer through large-area NiCo-LDH/Ag-NPs interfaces, and the synergistic action of electromagnetic and charge transfer mechanisms. Besides, the unique morphology of NiCo-LDHs/Ag-NPs microcomposite provides a broad surface area for adsorption of TBZ molecules for further Raman signal enhancement. The practicability of the proposed SERS platform is confirmed by detecting TBZ in the real samples of apple juice and river water. The exceptional self-cleaning capability of the NiCo-LDHs/Ag-NPs microcomposite with an retention rate of 81.97 % even after the fifth degradation cycle underscores its impressive sustainable reusability and cost-effectiveness. The findings in this work lay the foundation for the development of high-performance SERS platforms to ensure food safety and environmental protection.

Radially realigning nematic liquid crystal for efficient tuning of microring resonators.

The efficient tuning of microring resonator with the radially realigning nematic liquid crystal (NLC) cladding is presented. By applying the voltage on the in-plane annular electrodes, the produced electric field realigns the homeotropically-aligned NLC in the radial direction. Under the voltage sufficient for 90° NLC reorientation, the guided mode senses the consistent cladding index distribution along the microring waveguide with the maximal index change equal to the optical anisotropy of NLC. The resultant tuning of the resonant wavelength has a blue shift of 23.1nm for the TM mode and a red shift of 10.1nm for the TE mode. The tuning rates for the TM and TE modes are -1.95nm/V and 0.90nm/V. The proposed microring resonator owns the excellent features of wide tuning ranges and high tuning rates for the TM and TE modes.

Structural growth of zinc oxide nanograins on carbon cloth as flexible electrochemical platform for hydroxychloroquine detection.

Pharmaceutical pollution that imposes a health threat worldwide is making accurate and rapid detection crucial to prevent adverse effects. Herein, binder-free zinc oxide nanograins on carbon cloth (ZnO NGs@CC) have been synthesized hydrothermally and employed to fabricate a flexible electrochemical sensor for the quantification of hydroxychloroquine (HCQ) that is typical pharmaceutical pollution. The characteristics of ZnO NGs@CC were investigated by various in-depth electron microscopic, spectroscopic and electroanalytical approaches. Compared with the pristine CC platform, the ZnO NGs@CC platform exhibits superior electrochemical performance in detecting HCQ with a large oxidation current at a low over-potential of +0.92 V with respect to the Ag/AgCl (Sat. KCl) reference electrode. With the support of desirable characteristics, the fabricated ZnO NGs@CC-based electrochemical sensor for HCQ detection displays good performances in terms of wide sensing range (0.5-116 µM), low detection limit (0.09 µM), high sensitivity (0.279 µA µM-1 cm-2), and strong selectivity. By the resulting 3D hierarchical nanoarchitecture, ZnO NGs@CC has progressive structural advantages that led to its excellent electrochemical performance in sensing applications. Furthermore, the electrochemical sensor is employed to detect HCQ in biological and environmental samples and also achieves good recovery rates. Thus, the designed ZnO NGs@CC demonstrates admirable electrochemical activity toward HCQ real-time monitoring and would be an excellent electrochemical platform for HCQ sensing.

Integrated-optic polarization rotator with obliquely deposited columnar thin film.

A new integrated-optic polarization rotator with anisotropic cladding formed by oblique angle deposition is presented. Optical anisotropy with tilt principal axes in the obliquely deposited columnar thin film induces hybrid polarization modes in the waveguide and thus produces polarization rotation. The dependence of device characteristics on columnar film parameters, such as column angle, film thickness, extraordinary index, and optical anisotropy, is investigated by 3D full-vectorial finite difference beam propagation method. The polarization rotator with Ta2O5 columnar thin film has polarization conversion efficiency as high as 99% and extinction ratio of 25dB.

High-quality LiNbO3 microdisk resonators by undercut etching and surface tension reshaping.

We report ultra-smooth LiNbO(3) microdisk resonators fabricated by selective ion implantation, chemical etching, and thermal treatment. The undercut microdisk structure is produced by chemically etching the buried lattice damage layer formed by selective ion implantation. By thermal treatment, surface tension smoothes and reshapes microdisk surface topography. The resonant characteristics of microdisk resonators are simulated by finite element method and are well consistent with the experimental results. The 20µm-diameter microdisk resonator has the FSR of 16.43nm and the Q factor of 2.60 × 10(4). The produced LiNbO(3) microdisk resonators can be utilized in new microdisk applications with electro-optic and nonlinear-optic effects.

Wide tuning of SiN microring resonators by auto-realigning nematic liquid crystal.

We present wide electrical tuning of microring resonators with auto-realigned nematic liquid crystal (NLC) cladding. By applying electric field, homeotropically-aligned negative Δε NLC with non-rubbed alignment layers is auto-realigned along the microring waveguide due to the protruding of the ridge structure. The consistent cladding index distribution along the microring waveguide produces effective tuning of the resonant wavelength. It achieves a large tuning range of 13nm for TM mode and 2.1nm for TE mode. The NLC reorientation characteristics are investigated by minimizing Oseen-Frank energy. The proposed microring resonator owns the features of large tuning range and bi-polarization wavelength tuning.

Retraction: Synergistic action of star-shaped Au/Ag nanoparticles decorated on AgFeO2 for ultrasensitive SERS detection of a chemical warfare agent on real samples.

Retraction of 'Synergistic action of star-shaped Au/Ag nanoparticles decorated on AgFeO2 for ultrasensitive SERS detection of a chemical warfare agent on real samples' by Nazar Riswana Barveen et al., Anal. Methods, 2020, 12, 1342-1352, DOI: 10.1039/C9AY02347J.

Enhanced photoluminescence and shortened lifetime of DCJTB by photoinduced metal deposition on a ferroelectric lithography substrate.

The photodeposition of metallic nanostructures onto ferroelectric surfaces could enable new applications based on the assembly of molecules and patterning local surface reactivity by enhancing surface field intensity. DCJTB (4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran) is an excellent fluorescent dye and dopant material with a high quantum efficiency used for OLED displays on the market. However, how to raise the photoluminescence (PL) and reduce the lifetime of DCJTB in a substrate remain extraordinary challenges for its application. Here, we demonstrate a tunable ferroelectric lithography plasmon-enhanced substrate to generate photo-reduced silver nanoparticles (AgNPs) and achieve enhanced PL with a shortened lifetime depending on the substrate's annealing time. The enhanced PL with shortened lifetimes can attribute to the localized electromagnetic (EM) wave produced by the nanotextured AgNPs layers' surface and gap plasmon resonances. The simulation is based on the three-dimensional finite element method to explain the mechanism of experimental results. Since the absorption increases, the remarkable enhanced PL of DCJTB can attain in the fabricated periodically proton exchanged (PPE) lithium niobate (LiNbO3) substrate. Furthermore, the proposed fabrication method demonstrates to help tune the surface EM wave distribution in the substrate, which can simultaneously achieve the significantly shortened lifetime and high PL intensity of DCJTB in the substrate. Compared with the un-annealed substrate, the PL intensity of DCJTB in the assembly metallic nanostructures is enhanced 13.70 times, and the PL's lifetime is reduced by 12.50%, respectively. Thus, the fabricated substrate can be a promising candidate, verifying chemically patterned ferroelectrics' satisfaction as a PL-active substrate.