Toward Automatic Label-Free Whispering Gallery Modes Biodetection with a Quantum Dot-Coated Microsphere Population

We explore a new calibration-free approach to biodetection based on whispering gallery modes (WGMs) without a reference measure and relative shifts. Thus, the requirement to keep track of the sensor position is removed, and a freely moving population of fluorophore-doped polystyrene microspheres can now fulfill this role of sensing resonator. Breaking free from fixed surface-based biosensing promotes adhesion between the microsphere sensors and the analytes since both can now be thoroughly mixed. The 70-nm-wide spectrum of green fluorescent microbeads allows us to monitor over 20 WGMs simultaneously without needing evanescent light coupling into the microspheres, hence enabling remote sensing. Since the exact radius of each microsphere is unknown a priori, it requires algorithmic analyses to obtain a reliable result for the refractive index of a solution. We first test our approach with different solutions of alcohol in water obtaining 3 × 10⁻⁴ precision on the refractive index at lower concentrations. Then, the solutions of bacterial spores in water yield clear evidence of biodetection in the statistical analysis of WGMs from 50 microspheres. To extend the fluorescence spectral range of our WGM sensors, we present preliminary results on coating microspheres with CdSe/ZnS quantum dots.     

The synthesis of titanium nitride whiskers on the surface of graphite by molten salt media

A novel method for synthesis of titanium nitride whiskers on the surface of graphite in NaF–NaCl media at 1100–1400 °C for 3 h in Ar atmosphere was investigated. The formation of TiN whiskers with the diameter of 500–600 nm and variable lengths and morphologies occurs onto graphite by a vapor–liquid–solid (VLS) mechanism. The specific surface area of graphite increases due to the growth of titanium nitride with various morphologies. The excellent oxidation resistance of surface modified graphite could be attributed to growth of TiN whiskers on the surface of graphite, which act as anti-oxidant and prevent the oxidation of graphite substrate.     

Effect of TiN concentration on microstructure and properties of Ni/W–TiN composites obtained by pulse current electrodeposition

In this study, Ni/W–TiN composites were fabricated by the pulse current electrodeposition (PCE) method. The effects of TiN concentration on the microstructure, microhardness, and wear properties of the resulting composites were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), microhardness tester, and friction wear testing. Among the four obtained composites, Ni/W–TiN composite prepared at 8 g/L showed the densest and finest surface structure. The TiN contents in obtained Ni/W–TiN composites at 8 and 16 g/L were estimated to 8.1 and 5.4 wt%, respectively. The average Ni/W grain diameter in Ni/W–TiN composite obtained at 8 g/L TiN was recorded as 84.7 nm. The protrusion and depression heights of the composite deposited at 8 g/L were 81.8 and 45.4 nm, respectively. This composite also processed an average microhardness of 897.6 HV, with only a few shallow and narrow scratches on its worn surface, demonstrating its prominent wear resistance when compared to the other three composites.     

Localized Surface Plasmon Resonance Biosensing with Large Area of Gold Nanoholes Fabricated by Nanosphere Lithography

Localized surface plasmon resonance (LSPR) has been extensively studied as potential chemical and biological sensing platform due to its high sensitivity to local refractive index change induced by molecule adsorbate. Previous experiments have demonstrated the LSPR generated by gold nanoholes and its biosensing. Here, we realize large uniform area of nanoholes on scale of cm² on glass substrate by nanosphere lithography which is essential for mass production. The morphology of the nanoholes is characterized using scanning electron microscope and atomic force microscope. The LSPR sensitivity of the nanoholes to local refractive index is measured to be 36 nm/RIU. However, the chip has demonstrated high sensitivity and specificity in biosensing: bovine serum albumin adsorption is detected with LSPR peak redshift of 27 nm, and biotin-streptavidin immunoassay renders a LSPR redshift of 11 nm. This work forms a foundation toward the cost-effective, high-throughput, reliable and robust chip-based LSPR biosensor.     

Diamond-coated field-effect sensor for DNA recognition — Influence of material and morphology

The influence of nanocrystalline (< 20 nm grains) and microcrystalline (around 100 nm grains) diamond thin film morphology on the capacitance–voltage (C–V) characteristics of diamond-coated field-effect SiN sensors was characterized with respect to DNA recognition. DNA was grafted via –OH surface termination. The sensor materials and surfaces were characterized by scanning electron microscopy, Raman Spectroscopy, fluorescence microscopy, XPS, and contact angle measurements. The C–V characteristics exhibited generally an order of magnitude higher flat band voltage shifts (∆ V_F) after complementary DNA hybridization for both types of diamond-coated sensors (160 ÷ 300 mV) compared to reference SiN sensor without diamond layer (11 mV), even if incomplete DNA denaturation and ∆ V_F fluctuations (60 mV) were accounted for. While microcrystalline diamond provides the highest response, nanocrystalline diamond provides the highest sensitivity. An explanation based on interfacial charges is proposed.     

Effect of plating parameters on the properties of pulse electrodeposited Ni–TiN thin films

The influence of pulse plating parameters on the microstructure, microhardness, and properties of the Ni–TiN thin films was investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM), X–ray diffraction (XRD), scanning electron microscopy (SEM), and corrosion and wear tests. The results indicated the Ni–TiN thin films prepared via electrodeposition at 4 A/dm² current density to show an optimum microhardness and TiN content values of 984.7 HV and 8.69 wt%, respectively. The average grain sizes of Ni and TiN in the films obtained at 200 Hz were 127.8 and 48.5 nm, respectively. Numerous large pores can be noticed in the films prepared at pulse frequencies of 200 Hz and 500 Hz, whereas only a few small pits are visible on the surface of the Ni–TiN thin films deposited at 800 Hz. The films prepared at 20% duty cycle experienced the least weight loss.     

Colored amorphous silica-based powder with TiN nanocrystals precipitated by ammonolysis of Ti–Si–O ternary glass

Coloration of amorphous silica powder containing titania was investigated by nitridation in an ammonia flow. The oxide precursors were obtained by the hydrolysis of a mixture of tetraethyl orthosilicate (TEOS) and tetrabutoxy titanium (TBT). The color changed with the amount of TBT in the mixture, the hydrolysis pH and the ammonolysis temperature. The original white color of the 8 mol% TBT powder hydrolyzed under basic pH conditions changed to pale goldenrod at 700°C, then to dark olive green at 800°C, and further darkened with increasing ammonolysis temperature. A steel-blue color appeared at 900°C for the powder obtained with 3 mol% TBT, and increased in darkness at 1000°C. A similar bluish color was observed for powders obtained by acidic hydrolysis after ammonolysis above 900°C, and this was independent of the amount of titania, although the chroma decreased with increasing firing temperature for the powder with 3 mol% TBT. The ammonolysis powder products were characterized using X-ray diffraction (XRD), electron probe micro analysis (EPMA), transmission electron microscopy-electron energy-loss spectroscopy (TEM-EELS), scanning transmission electron microscopy-high-angle annular dark-field imaging (STEM-HAADF) and Ti–K edge X-ray absorption fine structure (XAFS). The color change was related to both precipitated TiN nanocrystals and residual titanium in the amorphous silica matrix. The TiN exhibited a goldish reflection and also plasmonic absorption from light blue to gray depending on the TiN crystallite size. The plasmonic absorption and resonance of nanocrystalline TiN will be useful similarly to that of gold in nanotechnology for various kinds of energy application.     

Facile synthesis of hollow F-doped SnO2 nanofibers and their efficiency in ethanol sensing

This paper reports for the first time the facile synthesis of hollow F-doped SnO₂ nanofibers by solution blow spinning (SBS) and their ethanol sensing performance. The as-prepared nanofibers were characterized using scanning electron microscopy (SEM), x-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Fourier-transform infrared spectroscopy (FTIR), and electrochemical impedance spectroscopy (EIS). The gas sensing behavior of the F-doped SnO₂ nanofibers was investigated using a homemade test chamber. The results revealed the preparation of mesoporous F-doped SnO₂ hollow fibers with a diameter ranging from 207 ± 43 to 355 ± 41 nm. The combination of nanocrystalline hollow structure and F doping led to fast high-responsive ethanol sensors at room temperature (RT) with good reproducibility and long-term stability. These results indicate that F-doped SnO₂ hollow nanofibers are good candidates for building practical low-temperature ethanol gas sensors.     

TiO2/ZnO double-layer broadband antireflective and down-shifting coatings for solar applications

Making full use of sunlight in solar cells requires reducing the reflection of light and minimizing spectral mismatch. Here, a TiO₂/ZnO double-layer coating with both wider band antireflection and down-shifting performance was prepared. TiO₂ sols and ZnO nanoparticles were synthesized via the sol-gel method and then successively coated on the surface of the Si substrate by dip-coating. Computational simulations were used to obtain the optimal refractive index and thickness of the coatings. In the experiments, the thicknesses of the TiO₂ and ZnO coatings were adjusted by changing the lifting speed, and the refractive index of the TiO₂ and ZnO coatings were adjusted by adding the porosity inducing agent and varying the concentration of the solution. The TiO₂/ZnO coating reduces the reflectivity of the silicon substrate by 24.97% in the 400–1100 nm band, and the ZnO nanoparticles can convert light at approximately 345 nm–527 nm, reducing the spectral mismatch of the solar cell. The photocurrent of solar cells coated with TiO₂/ZnO coatings was markedly improved, with an increase of 29% in the average photocurrent at 300–800 nm. Herein, TiO₂/ZnO coatings have the potential to benefit the development of multifunctional coatings that are important for improving the efficiency of solar cells.     

Negative permittivity in titanium nitride-alumina composite for functionalized structural ceramics

The study on novel physical properties of structural ceramics or ceramic composites could make them more conducive to be function- and structure-integrated materials. Herein, titanium nitride-alumina (TiN–Al₂O₃) duplex ceramics were prepared and the dielectric spectra of the ceramics were studied from 10 MHz to 1 GHz. Negative permittivity appeared when TiN content exceeded 40 wt% due to the induced plasmonic state of massive delocalized electrons in connected TiN grain networks. Meanwhile, alternating current conduction behaviors of the duplex ceramics were discussed with percolation theory. Furthermore, the analysis of reactance by equivalent circuit models indicated that negative permittivity ceramics exhibited inductive character. This work realized negative dielectric behaviors in TiN–Al₂O₃ duplex ceramics and would promote the study of electromagnetic functionalization in wave shielding or attenuation for structural ceramics.     

B deficiency in TiB2 and B solid solution in TiN in TiN–TiB2 composites prepared by spark plasma sintering

Dense TiN–TiB₂ composites were prepared by spark plasma sintering at 2573 K using TiN and TiB₂ powders. With increasing TiN content from 60 to 90 vol%, the c-axis length of TiB₂ in the TiN–TiB₂ composites decreased from the stoichiometric value (0.3230 nm) to 0.3227 nm because of B deficiency in TiB₂, whereas the a-axis length of TiB₂ was unchanged from the stoichiometric value of 0.3031 nm. The lattice parameter of TiN increased from the stoichiometric value (0.4243 nm) to 0.4250 nm with increasing TiB₂ content from 0 to 60 vol% because of B solid solution in TiN.     

Anisotropy and densification of polymer ultrathin films as seen by multi-angle ellipsometry and X-ray reflectometry

The chain conformations of cyclo-olefin polymer (COP) and polystyrene (PS) in less than 200-nm thick films on silicon wafers were investigated on the basis of the refractive index measured by multi-angle spectroscopic ellipsometry (MASE), and density measured by X-ray reflectometry (XRR). For both COP and PS, the density measured by XRR increases by decreasing the film thickness to below 50 nm. Densification may be caused by close packing of unentangled polymer chains in ultrathin films spincast from dilute solutions with polymer concentrations less than the overlap concentration (C*). For COP films, the refractive indices at incident angles of 45° and 70° measured by MASE agree well with those calculated by the Lorentz–Lorenz equation, indicating that densification of COP ultrathin films enhances their refractive indices. For PS films thinner than 50 nm, although the refractive index at an incident angle of 45° agrees with a calculation based on the Lorentz–Lorenz equation, one at 70° significantly deviates downward. A comparison of them with the results of quantum chemical calculation (QCC) suggested a plane-arrangement of benzene rings in PS ultrathin films, which was likely brought about by stacking of benzene rings and attractive interaction between π-electrons in the benzene rings and the substrate surface.     

Influence of Ni Catalyst Layer and TiN Diffusion Barrier on Carbon Nanotube Growth Rate

Dense, vertically aligned multiwall carbon nanotubes were synthesized on TiN electrode layers for infrared sensing applications. Microwave plasma-enhanced chemical vapor deposition and Ni catalyst were used for the nanotubes synthesis. The resultant nanotubes were characterized by SEM, AFM, and TEM. Since the length of the nanotubes influences sensor characteristics, we study in details the effects of changing Ni and TiN thickness on the physical properties of the nanotubes. In this paper, we report the observation of a threshold Ni thickness of about 4 nm, when the average CNT growth rate switches from an increasing to a decreasing function of increasing Ni thickness, for a process temperature of 700°C. This behavior is likely related to a transition in the growth mode from a predominantly “base growth” to that of a “tip growth.” For Ni layer greater than 9 nm the growth rate, as well as the CNT diameter, variations become insignificant. We have also observed that a TiN barrier layer appears to favor the growth of thinner CNTs compared to a SiO₂ layer.     

A supersensitive wearable sensor constructed with PDMS porous foam and multi-integrated conductive pathways structure

In recent years, wearable multifunctional strain sensors have attracted attention for their promising applications in wearable electronics and portable devices. To achieve a high-performance wearable strain sensor with a wide sensing range and high gauge factor (GF), wisely choosing appropriate conductive materials and a rational structural design is essential. Herein, we develop a supersensitive sensor that contains one-dimensional conductive material CNT and two-dimensional material MXene built on a PDMS porous foam that is made based on a sugar template. The one-dimensional carbon nanotube (CNT) functionalizes as a conductive scale layer through solvent swelling and evaporation on the surface of the PDMS skeleton. The two-dimensional MXene is applied on top of the CNT layer to form final conductive pathways. The PDMS/CNT@MXene (PCM) sensor has a wide sensing range (150%), high sensitivity (GF = 26438), rapid response speed (response/recovery time of 60/71 ms), and exceptional durability (>1000 cycles) owing to its unique porous structure with scale layers and graded fracture of conductive pathways. Moreover, the PCM sensor is capable of monitoring subtle and significant human activities and is used for wireless sensing and medical diagnostics, even for solvent identification. The superior performance of the PCM sensor provides vast application potential in human movement, health monitoring, and warning devices.     

Ultrasensitive NO2 gas sensing performance of two dimensional ZnO nanomaterials: Nanosheets and nanoplates

Highly sensitive NO₂ gas sensors with low detection limit are vital for practical application in air pollution monitoring. Here, the NO₂ gas sensing performance of porous ZnO nanosheets and nanoplates were investigated, with different shape and thickness. It was found that ultra-thin ZnO nanoplates had a higher sensitivity than coral-like ZnO nanosheets. The results were attributed to the high specific surface and very small thickness of the ultrathin nanoplates. The nanoplates have indeed a thickness of 15 nm compared to that of the nanosheets which is 100 nm, and a BET surface area of 75 m²/g, while that of the nanosheets is 6 m²/g. The chemosensor based on ultra-thin ZnO nanoplates shows a response (calculated as the ratio between the resistance of the sensor in the presence of the gas and in its absence) of 76 to 0.5 ppm of NO₂ at 200 °C, with a theoretical detection limit of 3 parts per trillion and a selectivity higher than 760 towards acetone, ethanol, isopropyl alcohol, triethylamine, SO₂ and CO. The specific surface and the small thickness of the ultra-thin nanoplates contribute to its highly improved sensing performance, making it ideal for NO₂ gas sensing.     

Enhanced NO2 gas sensor device based on supramolecularly assembled polyaniline/silver oxide/graphene oxide composites

Herein, we report a successful synthesis of supramolecularly assembled polyaniline/silver oxide/graphene oxide composite (PANI/Ag₂O/GO) for enhanced NO₂ gas sensing application. The PANI/Ag₂O/GO composite was synthesized by facile stirring followed by an ultrasonication process. The prepared material was characterized by different techniques such as x-ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and Raman-scattering spectroscopy. The detailed analysis revealed that the average crystallite sizes of PANI/Ag₂O and PANI/Ag₂O/GO composites were found to be 37.37 nm and 41.55 nm, respectively. FESEM and TEM analysis showed coral-like rough-surfaced and extensively agglomerated morphology for PANI and ultrathin flexible sheet-like morphology for GO. Ag₂O nanoparticles with diameters 20–30 nm were well incorporated in the GO sheets and PANI matrix in the case of PANI/Ag₂O/GO composites. The synthesized materials were used to make resistive sensor devices that had a high response to NO₂ gas. The fabricated sensors were examined at various temperatures to obtain the optimal sensing temperature. The fabricated NO₂ gas sensor device based on PANI/Ag₂O/GO composite exhibited a highest sensitivity of 5.85 for 25 ppm at an optimized temperature (100 °C) as compared to the pure PANI (2.5) and PANI/Ag₂O composite (3.25). Further, the fabricated sensor device based on PANI/Ag₂O/GO composite was also examined at different NO₂ gas concentrations.     

Kinetics and mechanism of electrolytic corrosion of titanium-based ceramics in 3% NaCl solution

The kinetics of electrolytic oxidation (in 3% NaCl solution at 20 °C) of TiN–AlN, TiB₂–AlN, TiB₂–TiN and TiC_0.5N_0.5 binary ceramics, manufactured by HIP method, were studied using a potential-dynamic method of polarization curves. For determination of oxidation mechanism, the chemical analysis concerning titanium ions state in the solution as well as an XRD, SEM and AES analyses of oxidized surface layers were used. In all the cases the oxidation of ceramics above proved to be the multistage process, the peculiarities of different stages were discussed on the base of experimental data obtained by the methods pointed out. It was shown that these ceramics are exceptionally corrosion-resistant. The rate of oxidation only slightly increases in the row: TiN–AlN → TiB₂–AlN → TiB₂–TiN → TiC_0.5N_0.5.     

Synthesis of highly refractive and transparent poly(arylene sulfide sulfone) based on 4,6-dichloropyrimidine and 3,6-dichloropyridazine

A highly refractive and transparent poly(arylene sulfide sulfone) (PASS) containing pyrimidine (or pyridazine) unit has been developed. The polymer was prepared by a polycondensation reaction of 4,4′-dimercaptodiphenyl sulfone (DMDPS) and 4,6-dichloropyrimidine (DCPM) (or 3,6-dichloropyridazine (DCPD)). They showed good thermal stabilities such as a relatively high glass transition temperature of 193–202 °C and a 5% weight loss temperature (T_5%) of 370–372 °C. The optical transmittance of the polymer at 450 nm is higher than 81%. The heterocycles unit and plural –S– linkages provides the polymer with a high refractive index of 1.737–1.743 at 633 nm and a low birefringence of 0.003–0.004.     

Microstructure and corrosion properties of Ni-TiN nanocoatings prepared by jet pulse electrodeposition

Ni–TiN nanocoatings were successfully prefabricated by jet pulse electrodeposition. The effect of jet rate on cross-sectional composition, microstructure, microhardness, and corrosion properties of nanocoatings was examined by X-ray photoelectron spectroscopy, high-resolution transmission electron microscope, atomic force microscopy, microhardness tester and electrochemical workstation. Results illustrated that Ni–TiN nanocoatings deposited at jet rate of 3 m/s exhibited high concentration of Ni and Ti with average concentrations of Ni and Ti of 54.5 at% and 19.8 at%, respectively. Average diameters of Ni grains and TiN nanoparticles in Ni–TiN nanocoatings prepared at 3 m/s were 47.8 nm and 30.5 nm, respectively. Nanocoatings deposited at 1 m/s, 3 m/s and 5 m/s showed surface root-mean-square roughness value of 95.431, 30.091 and 58.454 nm, respectively, and presented maximum microhardness of 789.5, 876.2, and 849.9 HV, respectively. Ni–TiN nanocoating obtained at 3 m/s demonstrated minimum I_corr and E_corr values of 1.02 × 10⁻³ mA/cm² and − 0.551 V, respectively, signifying to offer the best corrosion resistance.