Nanostructured Titania Films Research Articles

Low‐Temperature and Water‐Based Biotemplating of Nanostructured Foam‐Like Titania Films Using ß‐Lactoglobulin

AbstractGiven the broad use of nanostructured crystalline titania films, an environmentally friendly and more sustainable synthesis route is highly desirable. Here, a water‐based, low‐temperature route is presented to synthesize nanostructured foam‐like crystalline titania films. A pearl necklace‐like nanostructure is introduced as tailored titania morphology via biotemplating with the use of the major bovine whey protein ß‐lactoglobulin (ß‐lg). It is shown that titania crystallization in a brookite‐anatase mixed phase is promoted via spray deposition at a comparatively low temperature of 120 °C. The obtained crystallites have an average grain size of (4.2 ± 0.3) nm. In situ grazing incidence small‐angle and wide‐angle X‐ray scattering (GISAXS/GIWAXS) are simultaneously performed to understand the kinetics of film formation and the templating role of ß‐lg during spray coating. In the ß‐lg:titania biohybrid composites, the crystal growth in semicrystalline titania clusters is sterically directed by the condensing ß‐lg biomatrix. Due to using spray coating, the green chemistry approach to titania‐based functional films can be scaled up on a large scale, which can potentially be used in photocatalytic processes or systems related to energy application.

In Situ Study of Order Formation in Mesoporous Titania Thin Films Templated by a Diblock Copolymer during Slot-Die Printing.

Slot-die printing, a large-scale deposition technique, is applied to fabricate mesoporous titania films. Printing is interesting, for example, for scaling up solar cells where titania films with an interconnected mesoporous network and a large surface-to-volume ratio are desired as photoanodes. A fundamental understanding of the structure evolution during printing is of high significance in tailoring these films. In this work, we provide important insights into the self-assembly of the slot-die-printed titania/polystyrene-block-poly(ethylene oxide) (PS-b-PEO) micelles into ordered hybrid structures in real time via in situ grazing-incidence small-angle X-ray scattering (GISAXS). GISAXS allows for tracking both vertical and lateral structure development of the film formation process. In the hybrid film, a face-centered cubic (FCC) structure is preferentially formed at the interfaces with air and with the substrate, while a defect-rich mixed FCC and body-centered cubic (BCC) structure forms in the bulk. After calcination, the surface and inner morphologies of the obtained nanostructured titania films are compared with the spin-coated analogues. In the printed films, the initially formed nanoscale structure of the hybrid film is preserved, and the resulting mesoporous titania film shows a superior order as compared with the spin-coated thin films which can be beneficial for future applications.

The Anatase Phase of Nanotopography Titania with Higher Roughness Has Better Biocompatibility in Osteoblast Cell Morphology and Proliferation.

Previous studies have concluded that surface-modified titanium oxide (titania, TiO2) surface properties promote osteoblast cell morphology and proliferation. To screen a suitable structured titania coating with the best biocompatibility to be used in dental implants, five titania films (two amorphous, one rutile, and two anatases) with different surfaces were successfully synthesized on polished titanium by radio frequency (RF) magnetron sputtering. We applied atomic force microscopy (AFM) and X-ray diffraction (XRD) to depict the formulations. Furthermore, MC3T3-E1, the mouse osteoblast precursor cell, was used to assess cell proliferation and observe morphologic changes at the film surface. The data indicated that the overall number of MC3T3-E1 cells on anatase films was significantly higher as compared with cells on rutile and amorphous films. Meanwhile, the actin filaments of the cells grown on the anatase phase films were well defined and fully spread. In addition, the film with higher roughness had enhanced biocompatibility than that with lower roughness. The results showed that the crystal phase and titania coated roughness had a greater influence on the biocompatibility of nanostructured titania film. The higher the roughness of the anatase phase was, the better bioactivity for the morphology and proliferation of osteoblast. This is a good surface-modified biological material and may have a good application prospect in dental implants.

The effect of metal ligands on the adsorption of metal coordination complexes on polystyrene nano-beads

Nanostructured metal oxides showing geometrically controlled shape are often shaped by the calcination of selected metal coordination complexes adsorbed on sacrificial polystyrene beads (PSB) in aqueous suspensions.The design of an alternative, more sustainable, method to guide the adsorption of titanium oxide precursors on sacrificial carriers into specific morphologies has been explored as part of a global strategy to produce new nano-engineered metal oxides.Among various titanium coordination complexes, ligands like β-diketones or β-ketoesters have been often investigated due to their chelating and stabilizing effect on the titanium. In particular, titanium coordination complexes like Titanium(IV)bis(ammonium lactato) dihydroxide and titanium diisopropoxide bis(acetylacetonate) have been largely applied in the fabrication of nanostructured titanium oxide films in last-generation photovoltaic devices.To date the driving force for the spontaneous adsorption of precursors on non-modified PSB had not been investigated. We propose that a major driver is the interaction between the polystyrene surface of PSB and the molecular structure of the organic ligands of the metal-complexes. The proposed mechanism is supported by proton nuclear magnetic resonance spectroscopy of the starting colloidal suspensions and by electron microscopy of the resulting nanostructured metal oxides.

Photocatalytic Activity of Nanostructured Titania Films Obtained by Electrochemical, Chemical, and Thermal Oxidation of Ti6Al4V Alloy—Comparative Analysis

Three different Ti6Al4V surface oxidation methods have been applied to obtain three types of titania materials of different nanoarchitecture. Electrochemical oxidation of titanium alloy allowed for obtaining titania nanotubes (TNT), chemical oxidation led to obtain titania nanofibers (TNF), and thermal oxidation gave titania nanowires (TNW). My earlier investigations of these nanomaterials were focused mainly on the estimation of their bioactivity and potential application in modern implantology. In this article, the comparative analysis of the photocatalytic activity of produced systems, as well as the impact of their structure and morphology on this activity, are discussed. The activity of studied nanomaterials was estimated basis of UV-induced degradation of methylene blue and also acetone, and it was determined quantitatively according to the Langmuir–Hinshelwood reaction mechanism. The obtained results were compared to the activity of Pilkington Glass ActivTM (reference sample). Among analyzed systems, titania nanofibers obtained at 140 and 120 °C, possessing anatase and anatase/amorphous structure, as well as titania nanowires obtained at 475 and 500 °C, possessing anatase and anatase/rutile structure, were better photocatalyst than the reference sample. Completely amorphous titania nanotubes, turned out to be an interesting alternative for photocatalytic materials in the form of thin films, however, their photocatalytic activity is lower than for Pilkington Glass ActivTM.

Influence of Annealing Temperature on the Optical Properties of TiO2Thin Films

Abstract The optical band gap of TiO2 films greatly determines its electro-optical and photocatalytic properties. By optimizing the annealing temperature of titania film the above said properties can be tuned. The present study investigates the influence of annealing temperature on optical properties of nanostructured titania films fabricated on quartz substrate by spray technique. The white anatasetitania nanoparticles needed for film fabrication is synthesized by precipitation method using titanium isopropoxide. Further, to have fine dispersion of TiO2 nanoparticles in spay solvent, its surface is modified using (3-Glycidyloxypropyltrimethoxysilane(GPTMS). The fabricated films are air annealed at two different temperatures 150 and 300 oC and their optical properties are studied. There is significant reduction in optical bandgap of titania film annealed at 300 oC to 1.5 eV. However, the optical band gap of the titania film annealed at 150 oC is 2.9 eV. The difference is attributed to surface defects and its presence is analyzed from PL spectra. Both the films exhibited emission attributed to oxygen vacancies. Nevertheless the emission intensity for film annealed at 300 oC is very low, which indicates the recombination rate of photogenerated electrons and holes are highly reduced. This is also confirmed from time resolved PL decay recorded for excitation 300 nm.

Electrostatic Double-Layer Interaction at the Surface of Rough Cluster-Assembled Films: The Case of Nanostructured Zirconia.

Here, we investigated the influence of the nanoscale surface morphology on the electrostatic double layer at corrugated surfaces in aqueous electrolytes. For this purpose, we have produced cluster-assembled nanostructured zirconium dioxide (ns-ZrO x, x ≈ 2) films with controlled morphological properties by supersonic cluster beam deposition (SCBD) and measured the double-layer interaction by atomic force microscopy with colloidal probes. SCBD allowed tuning the characteristic widths of the corrugated interface (root-mean-square roughness, correlation length) across a wide range of values, matching the width of the electrostatic double layer (Debye length) and the typical size of nanocolloids (proteins, enzymes, and catalytic nanoparticles). To accurately characterize the surface charge density in the high-roughness regime, we have developed a two-exponential model of the electrostatic force that explicitly includes roughness and better accounts for the roughness-induced amplification of the interaction. We were then able to observe a marked reduction of the isoelectric point of ns-ZrO x surfaces of increasing roughness. This result is in good agreement with our previous observations on cluster-assembled nanostructured titania films and demonstrates that the phenomenon is not limited to a specific material, but more generally depends on peculiar nanoscale morphological effects, related to the competition of the characteristic lengths of the system.

Deformation of Mesoporous Titania Nanostructures in Contact with D2 O Vapor.

For many applications, mesoporous titania nanostructures are exposed to water or need to be backfilled via infiltration with an aqueous solution, which can cause deformations of the nanostructure by capillary forces. In this work, the degree of deformation caused by water infiltration in two types of mesoporous, nanostructured titania films exposed to water vapor is compared. The different types of nanostructured titania films are prepared via a polymer template assisted sol-gel synthesis in conjunction with a polymer-template removal at high-temperatures under ambient conditions versus nitrogen atmosphere. Information about surface and inner morphology is extracted by scanning electron microscopy and grazing incidence small-angle neutron scattering (GISANS) measurements, respectively. Furthermore, complementary information on thin film composition and porosity are probed via X-ray reflectivity. The backfilling induced deformation of near surface structures and structures inside the mesoporous titania films is determined by GISANS before and after D2 O infiltration. The respective atmosphere used for template removal influences the details of the titania nanostructure and strongly impacts the degree of water induced deformation. Drying of the films shows reversibility of the deformation.

Photoelectrochemical Reduction of Carbon Dioxide at Copper(I) Oxide Modified with Ultra-Thin Polymer Layers

There has been growing recent interest in the development of electrochemical and photoelectrochemical approaches toward effective fixation (reduction) of carbon dioxide. Having in mind a fact that the linear O=C=O molecule is very stable, the CO2 electroreduction requires large overpotentials. In other words, utilization of renewable energy to convert carbon dioxide and water into fuels would require selective CO2-reduction catalysts or efficient and robust semiconductors. There is a need to design unique nano-architectures consisting of the CO2 photocatalyst/semiconductor stabilized with the outer protective layer. Our study utilizes copper(I) oxide either stabilized with nanostructured titania or ultra-thin films of certain, conducting or redox, polymers (e.g. polyaniline, polypyrrole, PEDOT, poly(4-vinylpyridine)). While in a case of the mixed oxide semiconductor, we have explored formation the p-n heterojunction favoring increase of density of the electron population within the conduction band following deposition of TiO2 over the electrodeposited large crystals of Cu2O, in the latter case we tailor light absorption properties and affect the system’s stability. Upon illumination (from the copper(I) oxide side), charge transport to the reaction sites should be enhanced and the overall electric conductivity (at the catalytic interface) increases. Having in mind both hydrophilic and hydrophobic properties of Nafion over-coating, the outer-most ultra-thin film of Nafion, having properties of both robust (protective) layer and wetting (favoring proton mobility) medium, has been applied. Moreover, the outer-most over-layer of Nafion is expected to facilitate attraction of CO2 (dissolved in the sodium sulfate electrolyte) at the photoelectrochemically active mixed-metal-oxides interfaceSpecial attention has been paid to synthesis, characterization and optimization of the hybrid photocathode, namely the Nafion-protected mixed-oxides (Cu2O-TiO2) and polymer modified copper(I) oxide systems (deposited on fluorine-doped tin oxide covered glass, FTO) toward photoelectrochemical reduction of carbon dioxide.

Carbon Nanomaterials Application as a Counter Electrode for Dye-Sensitized Solar Cells

AbstractThe paper presents the results of the structure investigation of a counter electrode in dye-sensitized solar cells using the carbon nanomaterials. Solar cells were fabricated on the glass with transparent conductive oxide TCO (10Ω/sq). Nanocrystalline titania based photoanode was prepared by spreading TiO2paste onto TCO glass and subsequently annealed at 450°C for at least 30 min to convert anatase phase and make an interparticle network. After then the nanostructured titania films was immersed into an ethanolic solution of the ruthenium-based dye. As a counter electrodes of dye-sensitized solar cells composite films of carbon nanomaterials and polystyrene sulfonate doped poly (3,4-ethylenedioxythiophene) PEDOT-PSS (Sigma-Aldrich) were deposited onto TCO substrates. Because carbon nanoelements and titanium oxide consist of nano-metric structural units to determine the properties of the cells and their parameters several surface sensitive techniques and methods, i.e. Raman spectroscopy, Scanning Electron Microscopy (SEM), High-Resolution Transmission Electron Microscopy (HRTEM), and electric properties of conductive layers were used.

Cost-efficient platinum-free DSCs using colloidal graphite counter electrodes combined with D35 organic dye and cobalt (II/III) redox couple

Aqueous dispersions of colloidal graphite (CG) were deposited by spin coating on fluorine doped tin oxide (FTO) substrates and the resulting electrodes were characterized by a variety of experimental microscopic and spectroscopic techniques. The performed analysis has shown that the optical and electronic properties of the CG electrodes depend on the colloidal graphite’s concentration and the number of the deposited layers. Tafel plots confirmed that the constructed CG electrodes show excellent electrocatalytic activity towards the Co(bpy)33+ reduction. Robust dye-sensitized solar cells (DSCs) based on nanostructured titania film electrodes sensitized with D35 organic dye have been prepared employing the Co(bpy)3(PF6)2/Co(bpy)3(PF6)3 −based redox electrolyte. Colloidal graphite films, showing sub-micron plate-like morphology with excessive edge graphitic planes exposed, are excellent counter electrodes (CE) in DSCs, surpassing in efficiency the commonly used very expensive platinum (Pt) analogues and considerably reducing the cell fabrication costs. Electrochemical impedance spectroscopy (EIS) confirmed that the higher performance of the CG electrodes is due to lower electron transfer resistance at the corresponding electrolyte/counter electrode interface, in agreement with cyclic voltammetry (CV) experiments showing high stability and faster charge-transfer rate for carbon electrodes than that obtained for Pt. Using the CV data, the Fermi energy of the TiO2 photoelectrode under open circuit (OC) conditions was determined and the corresponding energy diagram in the DSC device was constructed. Additional EIS analysis on complete DSCs in the dark and under illumination certifies that the cobalt (II/III) couple works as a very effective electronic shuttle, enabling fast charge transfer at the CG counter electrode and also efficiently reducing the oxidized dye on the surface of the sensitized photoelectrode.

Preparation of nanostructured titania thin films by sol–gel technology

This study is concerned with the preparation of hydrolytically active heteroligand complex [Ti(OC4H9)3.61(O2C5H7)0.39] from titanium butoxide and acetylacetone and with the gel formation kinetics in a solution of this complex upon hydrolysis and polycondensation. Single-layer and double-layer thin films of a solution of this precursor were coated on polished silicon substrates using the dip-coating method. The crystallization of nanostructured titania films during the heat treatment of these xerogel coatings was studied using various protocols; the anatase–rutile phase transition temperature was found to depend on the film thickness. The effects of the precursor solution viscosity on the film thickness and crystallite size were determined.

Preparation and Photocatalytic Activity of Potassium- Incorporated Titanium Oxide Nanostructures Produced by the Wet Corrosion Process Using Various Titanium Alloys.

Nanostructured potassium-incorporated Ti-based oxides have attracted much attention because the incorporated potassium can influence their structural and physico-chemical properties. With the aim of tuning the structural and physical properties, we have demonstrated the wet corrosion process (WCP) as a simple method for nanostructure fabrication using various Ti-based materials, namely Ti–6Al–4V alloy (TAV), Ti–Ni (TN) alloy and pure Ti, which have 90%, 50% and 100% initial Ti content, respectively. We have systematically investigated the relationship between the Ti content in the initial metal and the precise condition of WCP to control the structural and physical properties of the resulting nanostructures. The WCP treatment involved various concentrations of KOH solutions. The precise conditions for producing K-incorporated nanostructured titanium oxide films (nTOFs) were strongly dependent on the Ti content of the initial metal. Ti and TAV yielded one-dimensional nanowires of K-incorporated nTOFs after treatment with 10 mol/L-KOH solution, whereas TN required a higher concentration (20 mol/L-KOH solution) to produce comparable nanostructures. The obtained nanostructures revealed a blue-shift in UV absorption spectra due to the quantum confinement effects. A significant enhancement of the photocatalytic activity was observed via the chromomeric change and the intermediate formation of methylene blue molecules under UV irradiation. This study demonstrates the WCP as a simple, versatile and scalable method for the production of nanostructured K-incorporated nTOFs to be used as high-performance photocatalysts for environmental and energy applications.

Titania nanotubes from weak organic acid electrolyte: fabrication, characterization and oxide film properties.

In this study, TiO2 nanotubes were fabricated using anodic oxidation in fluoride containing weak organic acid for different durations (0.5h, 1h, 2h and 3h). Scanning electron microscope (SEM) micrographs reveal that the morphology of titanium oxide varies with anodization time. Raman spectroscopy and X-ray diffraction (XRD) results indicate that the as-formed oxide nanotubes were amorphous in nature, yet transform into crystalline phases (anatase and rutile) upon annealing at 600°C. Wettability measurements show that both as-formed and annealed nanotubes exhibited hydrophilic behavior. The electrochemical behavior was ascertained by DC polarization and AC electrochemical impedance spectroscopy (EIS) measurements in 0.9% NaCl solution. The results suggest that the annealed nanotubes showed higher impedance (10(5)-10(6)Ωcm(2)) and lower passive current density (10(-7)Acm(-2)) than the as-formed nanotubes. In addition, we investigated the influence of post heat treatment on the semiconducting properties of the oxides by capacitance measurements. In vitro bioactivity test in simulated body fluid (SBF) showed that precipitation of Ca/P is easier in crystallized nanotubes than the amorphous structure. Our study uses a simple strategy to prepare nano-structured titania films and hints the feasibility of tailoring the oxide properties by thermal treatment, producing surfaces with better bioactivity.

Effects of silver concentrations on microstructure and properties of nanostructured titania films

To prevent bacterial proliferation on biomedical titanium implants, significant efforts have been focused on modifying its surface composition and structure. In this study, nanostructured titania (TiO2) films with different concentrations of silver were prepared by magnetron sputtering and subsequently annealed at 600°C in air. The effects of silver concentrations on microstructure, antibacterial property, corrosion resistance and hardness were studied. The results indicate that silver contribute to the growth of the TiO2 grains and is uniformly dispersed on the surface of annealed samples. The annealed films with a thickness of about 2.5μm are uniform and mainly composed of rutile phase and pure titanium. Silver mainly exists in the metallic state in the TiO2 films. The Ag-doped TiO2 films can effectively kill Staphylococcus aureus within 24h and the antibacterial ability increases with the silver content. The dynamic potential polarization results show that silver incorporation into TiO2 films slightly lower the corrosion potential, but significantly decrease the current density, and the current density decreases as the silver addition increases. Moreover, the hardness of the Ag-doped TiO2 films is also greatly improved.

Enhancing photovoltaic performances of dye-sensitized solar cells by multi-layered nanostructured titanium oxide photoelectrode

In the present study, a multi-layered nanostructured titanium oxide film has been fabricated as the photoelectrode for dye-sensitized solar cells (DSSCs). The multi-layered TiO2 electrode has the advantages of easy fabrication, being compatible with current deposition process and readily modifiable by adjusting the process parameters. The application of TiO2–MWCNTs (multiwalled carbon nanotube) as a nanocomposite overlayer reduces the inhomogeneity of dispersing carbon nanotubes (CNTs) throughout the whole photoanode, which largely simplifies the fabrication process and improves the performance of the as-prepared photoanodes. By using a multi-layered photoelectrode comprising a structure of TiO2–MWCNT/Degussa P25-TiO2/compact TiO2/TCO glass, a 27% enhancement in conversion efficiency is realized in DSSC as compared with pristine P25-TiO2 photoanode of identical thickness. The enhancement in efficiency brought by incorporation of MWCNTs, as revealed by electrochemical impedance spectroscopy (EIS), could be attributed to the excellent charge transport properties of CNTs, which led to efficient charge transfer within nanoporous TiO2 networks. A compact TiO2 blocking layer suppresses effectively the dark current, thus enhancing both JSC and VOC prominently.

Quantitative Phase Composition of TiO2-Coated Nanoporous Au Monoliths by X-ray Absorption Spectroscopy and Correlations to Catalytic Behavior

Porous titania/metal composite materials have many potential applications in the fields of green catalysis, energy harvesting, and storage in which both the overall morphology of the nanoporous host material and the crystallographic phase of the titania (TiO2) guest determine the material’s performance. New insights into the structure–function relationships of these materials were obtained by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy that, for example, provides quantitative crystallographic phase composition from ultrathin, nanostructured titania films, including sensitivity to amorphous components. Here, we demonstrate that crystallographic phase, morphology, and catalytic activity of TiO2-functionalized nanoporous gold (np-Au) can be controlled by a simple annealing procedure (T < 1300 K). The material was prepared by atomic layer deposition of ∼2 nm thick TiO2 on millimeter-sized samples of np-Au (40–50 nm mean ligament size) and catalytically investigated with respect to aerobic CO oxidation. The annealing-induced changes in catalytic activity are correlated with concurrent morphology and phase changes as provided by cross-sectional scanning electron microscopy, transmission electron microscopy, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy.

Optical and structural characterization of TiO2 films doped with silver nanoparticles obtained by sol–gel method

Nanostructured titanium oxide films with incorporated Ag nanoparticles were deposited by sol–gel spin coating method. The films were annealed at 300°C, 400°C, 500°C and 600°C in oxygen and nitrogen ambient. X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and UV–VIS spectroscopy had been applied for studying the influence of the thermal treatments and the gas ambient on the structural and optical properties of TiO2 and TiO2:Ag films. The XRD analysis revealed the presence of metallic Ag phase without traces of silver oxides and these results were confirmed by FTIR spectra. It has been revealed that the annealing temperatures and the ambient, where the annealing is carried out is crucial for TiO2 crystallization, when there is Ag incorporation and especially for appearance of anatase and rutile phase. The nitrogen and oxygen ambient influences quite different the crystallization of TiO2:Ag films. Transmission and absorption spectra have been analyzed. Optical band gap values were evaluated for pure titania and Ag incorporated TiO2 films.

Solvent-controlled preparation and photocatalytic properties of nanostructured TiO2 thin films with different morphologies

A low-temperature growth method of nanostructured TiO2 thin films with different morphologies was reported. Rod-like, grass-like and nanosheet structured films have been successfully fabricated just by adjusting the ratio of different solvents. The effects of the solvent on the morphologies of the TiO2 nanostructures were investigated. The formation mechanism of different morphologies was proposed based on the experiment results. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). The photocatalytic activity of as-prepared samples for the degradation of methylene blue (MB) in water was evaluated under UV illumination. Results showed that the solvents exhibited important effect on the morphologies and photocatalytic activity of as-prepared nanostructured titania films.

Stable Protein Device Platform Based on Pyridine Dicarboxylic Acid-Bound Cubic-Nanostructured Mesoporous Titania Films

Here we shortly report a protein device platform that is extremely stable in a buffer condition similar to human bodies. The protein device platform was fabricated by covalently attaching cytochrome c (cyt c) protein molecules to organic coupler molecules (pyridine dicarboxylic acid, PDA) that were already covalently bound to an electron-transporting substrate. A cubic nanostructured mesoporous titania film was chosen as an electron-transporting substrate because of its large-sized cubic holes (∼7 nm) and highly crystalline cubic titania walls (∼0.4 nm lattice). Binding of PDA molecules to the mesoporous titania surface was achieved by esterification reaction between carboxylic acid groups (PDA) and hydroxyl groups (titania) in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) mediator, whereas the immobilization of cyt c to the PDA coupler was carried out by the EDC-mediated amidation reaction between carboxylic acid groups (PDA) and amine groups (cyt c). Results showed that the 2,4-position isomer among several PDAs exhibited the highest oxidation and reduction peak currents. The cyt c-immobilized PDA-bound titania substrates showed stable and durable electrochemical performances upon continuous current-voltage cycling for 240 times (the final current change was less than 3%) and could detect superoxide that is a core indicator for various diseases including cancers.