Tailored construction of one-dimensional TiO2/Au nanofibers: Validation of an analytical assay for detection of diphenylamine in food samples.

We report a one-dimensional titanium dioxide encapsulated with gold heterojunction nanofibers (TiO2/Au NFs) as robust electrocatalysts for electrochemical detection of diphenylamine (DPA). A TiO2/Au NFs were successfully synthesized by a coaxial electrospinning method. The formation of TiO2/Au NFs was confirmed by various analytical and spectroscopic approaches. The fabricated TiO2/Au NFs modified screen-printed carbon electrodes (SPCE) exhibit a well-enhanced detection activity towards DPA sensing as compared to other electrodes. Under the experimental conditions, the proposed electrode leading to the sensing range from 0.05 to 60 µM with a detection limit of 0.009 µM was obtained for the DPA detection. Moreover, the TiO2/Au NFs/SPCE showed good selectivity towards the electrochemical oxidation of DPA. Interestingly, the TiO2/Au NFs modified electrode was then applied to detect the effect of DPA on spiked content in the food samples.

Double-Sided, Omnidirectional γ-AlOOH Hierarchical Nanostructures: Imparting Enhanced Antireflective Properties with Self-Cleaning Capacity for Optical Devices.

Herein, we have successfully developed an integrated strategy to develop antireflective coatings with self-cleaning capabilities based on periodic double-sided photonic γ-AlOOH nanostructures to transmit maximum incident light photons. Interfacial reflections are instinctive and one of the fundamental phenomena occurring at interfaces owing to refractive index mismatch. The eradication of such undesirable light reflection is of significant consideration in many optical devices. A systematic approach was carried out to eradicate surface reflection and enhance optical transmission by tailored γ-AlOOH nanostructures. The γ-AlOOH photonic nanostructures with subwavelength features exhibited a gradient index, which almost eliminated the refractive index mismatch at the interface. Optical transmittance of 97% was achieved in the range of 350-800 nm at normal incidence compared to uncoated glass (89%). A multilayer model approach was adopted to extract the effective refractive index of the coating, which showed a graded index from the top to the bottom surface. Further, to fully comprehend the optics of these nanostructures, the omnidirectional (20-70°) antireflective property has been explored using variable-angle specular reflectance spectroscopy. The hierarchical γ-AlOOH nanostructures exhibited only ∼1.3% reflectance at the lower incident angle in the visible spectra and an average reflectance of ∼7.6% up to an incident angle of 70°. Moreover, the hierarchical nanostructures manifested contact angle (CA) >172° and roll-off angle (RA) <1° with excellent self-cleaning performance. Furthermore, the abrasion resistance of the coating is discussed in detail, which displayed a good resistance against sand erosion. Significantly, the photovoltaic performance of the coated modules exhibited a relative enhancement of ∼17% in efficiency, which is attributed to the efficient coupling of light rays. Thus, the integration of the antireflection (AR) property with self-cleaning ability can provide a cost-effective energy solution for optoelectronic devices, display devices, and thin-film optics.

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.

Unveiling the interplay between induced native defects and room temperature magnetic ordering in titanium deficient disordered-TiO2 nanoparticles.

Understanding the origin of magnetic ordering in an undoped semiconductor with native defects is an open question, which is being explored actively in research. In this investigation, the interplay between magnetic ordering and excess induced native defects in undoped anatase TiO2 nanoparticles is explained using an experimental and theoretical approach. It is demonstrated that structurally disordered TiO2 nanoparticles with a high concentration of native defects such as titanium interstitials and oxygen vacancies are synthesized using controlled atmospheric rapid cooling (i.e. quenching) process. The structural disorders in the lattice have been examined using various spectroscopic and microscopic analyses revealed the existence of Ti deficiency in both pristine and quenched TiO2 nanoparticles. A possible origin of magnetic ordering in titanium deficient anatase TiO2 system is elucidated based on first-principle calculations. It was found that the overall magnetic moment of Ti deficient TiO2 system is determined by the distance between Ti interstitials and its neighboring vacancies (i.e. either V Ti or V Os). However, quenched TiO2 nanoparticles possess excess Ti interstitials, Ti and O vacancies and therefore the net magnetic moment of the system is reduced due to anti-ferromagnetically coupled neighboring Tilattice ions.

Unidirectional Langmuir-Blodgett-Mediated Alignment of Polyaniline-Functionalized Multiwalled Carbon Nanotubes for NH3 Gas Sensor Applications.

Herein, we report the formation of well-aligned ultrathin films of polyaniline-functionalized multiwalled carbon nanotubes (PANI@MWCNTs) with a high orientational order over a macroscopic area by Langmuir-Blodgett (LB) technique and its enhanced ammonia gas sensing properties. During the interfacial assembly process, the PANI@MWCNTs gradually align to form small ordered blocks at the air-water interface, which further organize as a well-defined oriented monolayer. The orientation and alignment of PANI@MWCNTs in Langmuir films at the air-water interface were systematically studied as a function of interface temperature using transmission electron microscopic analysis. Surface functionalization of MWCNTs with polyaniline was found to overcome the 3D aggregation of CNTs leading to an oriented assembly of PANI@MWCNTs. The formation and stability of the compact monolayer/multilayer structures of PANI@MWCNTs-based LB films have been extensively studied using a π-A isotherm analysis and thermodynamic approach. For the first time, such highly oriented LB films of PANI-functionalized MWCNTs have been employed for ammonia gas sensing applications at room temperature. The sensor was found to exhibit outstanding sensitivity toward NH3 at room temperature compared to random networks, which is attributed to the directed electron transport through the aligned PANI@MWCNTs. The ultrathin LB film allows fast analyte diffusion due to the adequate molecular accommodation in the oriented assembly of the active sensing layer. The large-scale alignment of PANI@MWCNTs demonstrated in this investigation would enable the fabrication of high-density MEMS (micro-electromechanical system)-based nanoscale sensor arrays for high-performance NH3 gas sensor applications.

Evolution of Temperature-Driven Interfacial Wettability and Surface Energy Properties on Hierarchically Structured Porous Superhydrophobic Pseudoboehmite Thin Films.

Interaction of water on heterogeneous nonwetting interfaces has fascinated researchers' attention for wider applications. Herein, we report the evolution of hierarchical micro-/nanostructures on superhydrophobic pseudoboehmite surfaces created from amorphous Al2O3 films and unraveled their temperature-driven wettability and surface energy properties. The influence of hot water immersion temperature on the dissolution-reprecipitation mechanism and the surface geometry of the Al2O3 film have been extensively analyzed, which helped in attaining the optimal Cassie-Baxter state. The evolution of pseudoboehmite films has been structurally characterized using grazing incidence X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy. Interfacial surface energy components on the structured superhydrophobic surface exhibited a very low surface energy of ∼4.6 mN/m at room temperature and ultrahigh water contact angle >175°. The interaction between water droplets on the nonwetting surface was comprehended and correlated to the temperature-dependent surface energy properties. The surface energy and wettability of the structured pseudoboehmite superhydrophobic surface exhibited an inverse behavior as a function of temperature. Interestingly, the superhydrophobic surface exhibited "Leidenfrost effect" below the boiling point of water (67 °C), which is further correlated with the intermolecular forces, interfacial water molecules and surface-terminated groups. These high-temperature wetting transition studies could be potentially valuable for solid-liquid systems working at nonambient temperatures, and also this approach can pave new pathways for better understanding of the solid/liquid interfacial interactions on nanoengineered superhydrophobic surfaces.

Porous, n-p type ultra-long, ZnO@Bi2O3 heterojunction nanorods - based NO2 gas sensor: new insights towards charge transport characteristics.

Herein, porous 1D n-p type ultra-long ZnO@Bi2O3 heterojunction nanorods have been synthesized by a solvothermal method and their complex charge transport characteristics pertaining to NO2 gas sensing properties have been investigated. The porous structure of the ZnO@Bi2O3 heterojunction nanorods assisted in achieving superior sensing properties compared to pristine ZnO nanorods. Temperature-dependent in situ electrical studies of the porous heterojunction nanorods explored the unique electron transport properties under different environments, which revealed the accumulation/depletion of electrons and charge carrier recombination leading to band bending at the metal oxide heterojunctions. The formation of electron depletion layers at n-ZnO/p-Bi2O3 interfaces is believed to increase the adsorption of oxidizing gas, resulting in a fast response time (10-12 s) and 10 times higher sensitivity than that of the ZnO nanorod-based sensor towards 500 ppb NO2. To study the structure-property correlation of the ultra-long ZnO@Bi2O3 heterojunction nanorods-based sensor, a crystallographic model supported by transmission electron microscopy analysis was adopted to understand the NO2 gas adsorption properties on the surface. The crystallographic model helps to visualize the dangling bonds and the ratio of metal to oxygen ions present at the exposed crystal planes. The results suggest that porous, ultralong n-p type ZnO@Bi2O3 heterojunction nanorods could be a promising candidate for a high performance NO2 sensor for real time applications.

Boosting the performance of NO2 gas sensors based on n-n type mesoporous ZnO@In2O3 heterojunction nanowires: in situ conducting probe atomic force microscopic elucidation of room temperature local electron transport.

Herein, n-n type one dimensional ZnO@In2O3 heterojunction nanowires have been developed and their local electron transport properties during trace-level NO2 gas sensing process have been probed at room-temperature using conducting probe atomic microscopy. Solvothermally synthesized 1D ZnO@In2O3 heterojunction nanowires have been characterized by various spectroscopic and microscopic techniques, which revealed the mesoporous structure indicating their enhanced sensing properties. The dangling bonds and fraction of metal ions to oxygen ions existing on the exposed crystal facets of the heterojunction nanowires have been visualized by employing crystallographic simulations with TEM analysis, which aided in forecasting the nature of surface adsorption of NO2 gas species. In situ electrical characteristics and Scanning Spreading Resistance Microscopic (SSRM) imaging of single ZnO@In2O3 heterojunction nanowires revealed the local charge transport properties in n-n type ZnO@In2O3 heterojunction nanowires. Moreover, the ZnO@In2O3 heterojunction nanowires based sensor exhibited excellent sensitivity (S = 274%), a fast response (4-6 s) and high selectivity towards trace-level concentration (500 ppb) of NO2 gas under ambient conditions with low power consumption. Spatially resolved surface potential (SP) variations in ZnO@In2O3 heterojunction nanowires have been visualized using in situ Scanning Kelvin Probe Force Microscopy (SKPM) under NO2 gas environment at room temperature, which was further correlated with its energy band structure. The work functions of the material evaluated by SKPM reveal considerable changes in the energy band structure owing to the local electron transport between ZnO and In2O3 at the heterojunctions upon exposure to NO2 gas indicating the charge carrier recombination. A plausible mechanism has been proposed based on the experimental evidences. The results suggest that new insights into complex sensing mechanisms deduced from the present investigation on n-n type MOS based heterojunction nanowires under ambient conditions can pave the way for the novel design and development of affordable and superior real-time gas sensors.

Development of low-cost hybrid multi-walled carbon nanotube-based ammonia gas-sensing strips with an integrated sensor read-out system for clinical breath analyzer applications.

This work demonstrates the development of Ag@polyaniline/multi-walled carbon nanotube nanocomposite-based sensor strips and a suitable integrated electronic read-out system for the measurement of trace-level concentrations of ammonia (NH3). The sensor is optimized under various operating conditions and the resulting sensor exhibited an enhanced response (32% for 2 ppm) with excellent selectivity. Stable performance was observed towards NH3 in the presence of high concentrations of CO2 (>40 000 ppm), simulated and real breath samples. A suitable electronic sensor read-out system has also been designed and developed based on multi-scale resistance-to-voltage conversion architecture, processed by a 32-bit microcontroller which is operatable over a wide range of sensor resistance (1 kΩ to 200 MΩ). As a proof of concept, integration of gas-sensing strips with the electronic read-out system was tested with various levels of NH3 (<2 ppm as normal, >2 ppm as critical and 2 ppm as threshold), which is important for clinical breath analyzer applications. The developed prototype device can be readily incorporated into a portable, low-cost and non-invasive point-of-care breath NH3 detection unit for portable pre-diagnostic breath analyzer applications.

Highly Sensitive, Temperature-Independent Oxygen Gas Sensor Based on Anatase TiO2 Nanoparticle Grafted, 2D Mixed Valent VO x Nanoflakelets.

Herein, we report a facile approach for the synthesis of TiO2 nanoparticles tethered on 2D mixed valent vanadium oxide (VO x/TiO2) nanoflakelets using a thermal decomposition assisted hydrothermal method and investigation of its temperature-independent performance enhancement in oxygen-sensing properties. The material was structurally characterized using XRD, TEM, Raman, DSC, and XPS analysis. The presence of mixed valent states, such as V2O5 and VO2 in VO x, and the metastable properties of VO2 have been found to play crucial roles in the temperature-independent electrical conductivity of VO x/TiO2 nanoflakelets. Though pristine VO x exhibited characteristic semiconductor-to-metal transition of monoclinic VO2, pure VO x nanoflakelets exhibited poor sensitivity toward sensing oxygen. VO x/TiO2 nanoflakelets showed a very low temperature coefficient of resistance above 150 °C with improved sensitivity (35 times higher than VO x for 100 ppm) toward oxygen gas. VO x/TiO2 nanoflakelets exhibited much higher response, faster adsorption and desorption toward oxygen as compared to pristine VO x beyond 100 °C, which endowed the sensor with excellent temperature-independent sensor properties within 150-500 °C. The faster adsorption and desorption after 100 °C led to shorter response time (3-5 s) and recovery time (7-9 s). The results suggest that 2D VO x/TiO2 can be a promising candidate for temperature-independent oxygen sensor applications.

Technologies for Clinical Diagnosis Using Expired Human Breath Analysis.

This review elucidates the technologies in the field of exhaled breath analysis. Exhaled breath gas analysis offers an inexpensive, noninvasive and rapid method for detecting a large number of compounds under various conditions for health and disease states. There are various techniques to analyze some exhaled breath gases, including spectrometry, gas chromatography and spectroscopy. This review places emphasis on some of the critical biomarkers present in exhaled human breath, and its related effects. Additionally, various medical monitoring techniques used for breath analysis have been discussed. It also includes the current scenario of breath analysis with nanotechnology-oriented techniques.