Enhanced oxygen sensing properties of Pt(II) complex and dye entrapped core-shell silica nanoparticles embedded in sol-gel matrix

This paper presents a highly sensitive oxygen sensor that comprises an optical fiber coated at one end with platinum(II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) and PtTFPP entrapped core-shell silica nanoparticles embedded in an n-octyltriethoxysilane (Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio I₀/I₁₀₀, where I₀ and I₁₀₀ represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results show that the oxygen sensor has a sensitivity (I₀/I₁₀₀) of 166. The response time was 1.3 s when switching from pure nitrogen to pure oxygen, and 18.6 s when switching in the reverse direction. The experimental results show that compared to oxygen sensors based on PtTFPP, PtOEP, or Ru(dpp)₃²⁺ dyes, the proposed optical fiber oxygen sensor has the highest sensitivity. In addition to the increased surface area per unit mass of the sensing surface, the dye entrapped in the core of silica nanoparticles also increases the sensitivity because a substantial number of aerial oxygen molecules penetrate the porous silica shell. The dye entrapped core-shell nanoparticles is more prone to oxygen quenching.     

Optical oxygen sensor based on fluorescence change of pyrene-1-butyric acid chemisorption film on an anodic oxidation aluminium plate

An optical oxygen-sensing material based on the fluorescence intensity changes of pyrene-1-butyric acid (PBA) chemisorption film has been developed and characterised. The fluorescence intensity of PBA film decreased with increase of oxygen concentration. The I₀/I₁₀₀ value of PBA film is estimated to be 6.14±0.15 and large Stern-Volmer constant (K_SV=0.028±0.13 Torr⁻¹) is obtained. After irradiation for 24 h with 150 W tungsten lamp, little changes of oxygen-sensing properties were observed. These results indicate that PBA film is highly oxygen-sensitive and photostability device. The response times of the PBA chemisorption film were 10.0 s for switching from argon to oxygen, and 53.0 s for switching from oxygen to argon. Moreover, the optical sensor based on the PBA chemisorption film was applied to the measurement of oxygen concentration in aqueous solution.     

Optical sensor for carbon dioxide combining colorimetric change of a pH indicator and a reference luminescent dye

A new optical CO₂ sensor based on the luminescence intensity change of the europium(III) complex tris(thenoyltrifluoroacetonato) europium(III) dihydrate ([Eu(tta)₃]) caused by the absorption change of various pH indicators—thymol blue, phenol red, or cresol red—with CO₂ was developed and its CO₂ sensing properties were investigated. For all the CO₂ sensors using pH indicators the observed luminescence intensity from [Eu(tta)₃] at 613 nm increased with increasing CO₂ concentration. The linear calibration method based on the plot of (I₁₀₀–I₀)/(I–I₀) versus the inverse of CO₂ concentration was suggested, where I₀ and I₁₀₀ were luminescence intensities at 613 nm of the CO₂ sensor film in 100% nitrogen and 100% gaseous CO₂. In all cases the plots showed good linearity and the correlation factors of the plots, r², were 0.991 for thymol blue, 0.990 for phenol red, and 0.998 for cresol red. The slopes of the plots (A/B) for thymol blue, phenol red, and cresol red were 2.2, 5.2, and 9.0%, respectively. The response times of the CO₂ sensor film were 4.0 s for thymol blue, 4.4 s for phenol red, and 8.8 s for cresol red for switching from nitrogen to CO₂, and the recovery times of films were 36 s for thymol blue, 39.2 s for phenol red, and 56.6 s for cresol red for switching from CO₂ to nitrogen. The signal changes were fully reversible and hysteresis was not observed during the measurements. The highly sensitive CO₂ sensor was developed using thymol blue as an indicator for the CO₂-sensing probe.     

Novel optical oxygen sensing material: metalloporphyrin dispersed in fluorinated poly(aryl ether ketone) films

A series of new fluorine-containing poly(aryl ether ketone)s (8F-PEKEK(Ar); Ar: 2-2-bis(4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane (6FBA), 2,2-bis(4-hydroxyphenyl)propane (BA), 2-(4-hydroxyphenyl)-2-(3-hydroxyphenyl)propane (3,4^′-BA) or 9,9^′-bis(4-hydroxyphenyl)fluorine (HF)) are synthesized and applied to the matrix of optical oxygen sensing using phosphorescence quenching of metalloporphyrins, platinum and palladium octaethylporphyrin, (PtOEP and PdOEP) by oxygen. The phosphorescence intensity of PtOEP and PdOEP in 8F-PEKEK(Ar) films decreased with increase of oxygen concentration. The ratio I₀/I₁₀₀ is used as a sensitivity of the sensing film, where I₀ and I₁₀₀ represent the detected phosphorescence intensities from a film exposed to 100% argon and 100% oxygen, respectively. For PtOEP in 8F-PEKEK(Ar) film, I₀/I₁₀₀ values are more than 20.0 and large Stern-Volmer constants more than 0.19%⁻¹ are obtained compared with PtOEP in polystyrene film. For PdOEP in 8F-PEKEK(Ar) film, on the other hand, the large I₀/I₁₀₀ values more than 143 are obtained. However, the Stern-Volmer plots of PdOEP in 8F-PEKEK(Ar) films exhibit considerable linearity at lower oxygen concentration range between 0% and 20%. These results indicate that PtOEP and PdOEP films are useful optical oxygen sensor at the oxygen concentration range between 0% and 100% and between 0% and 20%, respectively. The response times of PtOEP and PdOEP dispersed in 8F-PEKEK(Ar) films are 5.6 and 3.0 s on going from argon to oxygen and 110.1 and 160.0 s from oxygen to argon, respectively.     

Macroporous ordered titanium dioxide (TiO2) inverse opal as a new label-free immunosensor

Photonic crystal sensing materials have been validated that they are very sensitive to refractive index changes. Herein, three-dimensionally ordered macroporous (3DOM) (>50 nm) TiO₂ inverse opal film has been fabricated by the self-assembly technique. Based on the TiO₂ inverse opal film, the optical spectrometer was established for label-free immunosensor. The sensing performance of the 3DOM TiO₂ was investigated using human IgG/goat anti-human IgG couple, which showed that the sensitivity of 3DOM TiO₂ inverse opal film could reach to 1 μg mL⁻¹ (equivalent to 1.5 pg mm⁻²) of protein concentration detection limit. The 3DOM TiO₂ inverse opal has a large internal surface area, low fluorescence background and unique optical properties. These characteristics indicated the feasibility of 3DOM TiO₂ inverse opal in label-free immunoassay.     

Extended detection range for an optical enzymatic glucose sensor coupling with a novel data-processing method

A new data-processing method was established and applied for optical enzymatic glucose sensing, in which oxygen and glucose were simultaneously consumed. The oxygen level remaining in the detection system, which was equal to the difference between the initial and consumed oxygen concentrations, could be measured using fluorescent oxygen indicators immobilized in the sensing layer. It was deduced that the ratio of I ₀ and I was inversely proportional to glucose concentration, where I ₀ is the maximum fluorescence intensity in various glucose solutions, and I is the fluorescence intensity at various concentrations of glucose. Using the new data-processing method, the detection range of the calibration curve method was extended from 0 to 1.2 mmol L^?1, which was enlarged about 2–3 folds over that in ordinary approaches. The prepared glucose sensor could be directly applied to detect high concentrations of glucose.     

Optimising oxygen-sensitivity of optical sensor using pyrene carboxylic acid by myristic acid co-chemisorption onto anodic oxidized aluminium plate

Optical oxygen-sensitivity using pyrene carboxylic acid with long alkyl chain (1-pyrenedecanoic acid and 1-pyrenedodecanoic acid) and myristic acid co-chemisorption layer was controlled by varying the molar ratio of myristic acid to pyrene carboxylic acid. The ratio I₀/I₁₀₀, where I₀ and I₁₀₀ represent the detected fluorescence intensities from a substrate exposed to 100% argon and 100% oxygen, respectively, is used as an indicator of the sensitivity of the sensing film. At a composition ratio of 1 pyrene carboxylic acid to 10 myristic acids, the I₀/I₁₀₀ attained its maximum value and then the ratio decreased with increase in the molar ratio of myristic acid to pyrene carboxylic acid. The Stern-Volmer constant (K_SV) also attained its maximum value at a composition ratio of one pyrene carboxylic acid to ten myristic acids and then the ratio decreased with increase in the molar ratio of myristic acid to pyrene carboxylic acid. The oxygen-sensitivity of optical sensor using pyrene carboxylic acid is optimized by myristic acid co-chemisorption.     

Novel luminescent Ir(III) dyes for developing highly sensitive oxygen sensing films

New sensing films have been developed for the detection of molecular oxygen. These films are based on luminescent Ir(III) dyes incorporated either into polystyrene (with and without plasticizer) or metal oxide, nanostructured material. The preparation and characterization of each film have been investigated in detail. Due to their high sensitivity for low oxygen concentration, the parameters pO₂(S=1/2) and ΔI_1% have been also evaluated in order to establish the most sensitive membrane for controlling concentrations between 0 and 10% and low oxygen concentrations (lower than 1%), respectively. The results show that the use of nanostructured material increased the sensitivity of the film; the most sensitive membrane for controlling O₂ between 0 and 10% is based on N1001 immobilized in AP200/19 (k_sv = 2848 ± 101 bar⁻¹ and pO₂(S=1/2)=0.0006), and the complex N969 incorporated into AP200/19 seems to be the most suitable for applications in oxygen trace sensing (ΔI_1% = 93.13 ± 0.13%).     

An optical sensor for mercury ion based on the fluorescence quenching of tetra(p-dimethylaminophenyl)porphyrin

An optical sensor for mercury ion (Hg²⁺), based on quenching the fluorescence of the sensing reagent porphyrin immobilized in plasticized poly(vinyl chloride) (PVC) membrane, has been developed. The responses to mercury ion were compared for the sensors modified with three porphyrin compounds including 5,10,15,20-tetraphenylporphyrin (TPP), tetra(p-dimethylaminophenyl)porphyrin (TDMAPP) and tetra(N-phenylpyrazole) porphyrin (TPPP). Among them, TDMAPP showed the most remarkable response to Hg²⁺. The drastic decrease of the TDMAPP fluorescence intensity was attributed to the formation of a complex between TDMAPP and Hg²⁺, which has been utilized as the fabrication basis of a Hg²⁺-sensitive fluorescence sensor. The analytical performance characteristics of the TDMAPP modified sensor was investigated. The response mechanism, especially involving the response difference of three porphyrin compounds, was discussed in detail. The sensor can be applied to the quantification of Hg²⁺ with a linear range covering from 4.0 × 10⁻⁸ mol L⁻¹ to 4.0 × 10⁻⁶ mol L⁻¹. The limit of detection was 8.0 × 10⁻⁹ mol L⁻¹. The sensor exhibited excellent reproducibility, reversibility and selectivity. Also, the TDMAPP-based sensor was successfully used for the determination of Hg²⁺ in environmental water samples.     

Fiber-optic fluorescence sensor for dissolved oxygen detection based on fluorinated xerogel immobilized with ruthenium (II) complex

A fiber-optic sensor based on fluorescence quenching was designed for dissolved oxygen (DO) detection. The fluorinated xerogel-based sensing film of the present sensor was prepared from 3, 3, 3-trifluoropropyltrimethoxysilane (TFP–TriMOS). Oxygen-sensitive fluorophores of tris (2, 2′- bipyridine) ruthenium (II) (Ru(bpy)₃²⁺) were immobilized in the sensing film and the emission fluorescence was quenched by dissolved oxygen. In the sensor fabrication, a two-fiber probe was employed to obtain the best fluorescence collection efficiency and the sensing film was attached to the probe end. Scanning electron microscope (SEM), UV–Vis absorption spectroscopy (UV–Vis) and fourier transform infrared spectroscopy (FTIR) measurements have been used to characterize the sensing film. The sensor sensitivity is quantified by I _deoxy/I _oxy, where I _deoxy and I _oxy represented the detected fluorescence intensities in fully deoxygenated and fully oxygenated environments, respectively. Compared with tetramethoxysilane (TMOS) and methyltriethoxysilane (MTMS)-derived sensing films, TFP–TriMOS-based sensor exhibited excellent performances in dissolved oxygen detection with short response time of 4 s, low limit of detection (LOD) of 0.04 ppm (R.S.D. = 2.5%), linear Stern–Volmer calibration plot from 0 to 40 ppm and long-term stability during the past 10 months. The reasons for the preferable performances of TFP–TriMOS-based sensing film were discussed.     

Fluorometric method for the determination of hydrogen peroxide and glucose with Fe3O4 as catalyst

In this paper, we utilized the instinct peroxidase-like property of Fe₃O₄ magnetic nanoparticles (MNPs) to establish a new fluorometric method for determination of hydrogen peroxide and glucose. In the presence of Fe₃O₄ MNPs as peroxidase mimetic catalyst, H₂O₂ was decomposed into radical that could quench the fluorescence of CdTe QDs more efficiently and rapidly. Then the oxidization of glucose by glucose oxidase was coupled with the fluorescence quenching of CdTe QDs by H₂O₂ producer with Fe₃O₄ MNPs catalyst, which can be used to detect glucose. Under the optimal reaction conditions, a linear correlation was established between fluorescence intensity ratio I₀/I and concentration of H₂O₂ from 1.8 × 10⁻⁷ to 9 × 10⁻⁴ mol/L with a detection limit of 1.8 × 10⁻⁸ mol/L. And a linear correlation was established between fluorescence intensity ratio I₀/I and concentration of glucose from 1.6 × 10⁻⁶ to 1.6 × 10⁻⁴ mol/L with a detection limit of 1.0 × 10⁻⁶ mol/L. The proposed method was applied to the determination of glucose in human serum samples with satisfactory results.     

Glucose concentration determination based on silica sol-gel encapsulated glucose oxidase optical biosensor arrays

Optical biosensor arrays for rapidly determining the glucose concentrations in a large number of beverage and blood samples were developed by immobilizing glucose oxidase (GOD) on oxygen sensor layer. Glucose oxidase was first encapsulated in silica based gels through sol-gel approach and then immobilized on 96-well microarrays integrated with oxygen sensing film at the bottom. The oxygen sensing film was made of an organically modified silica film (ORMOSIL) doped with tris(4,7-diphenyl-1,10-phenanthroline) ruthenium dichloride (Ru(dpp)₃Cl₂). The oxidation reaction of glucose by glucose oxidase could be monitored through fluorescence intensity enhancement due to the oxygen consumption in the reaction. The luminescence changing rate evaluated by the dynamic transient method (DTM) was correlated with the glucose concentration with the wide linear range from 0.1 to 5.0 mM (Y = 13.28X − 0.128, R = 0.9968) and low detection limit (0.06 mM). The effects of pH and coexisting ions were systemically studied. The results showed that the optical biosensor arrays worked under a wide range of pH value, and normal interfering species such as Na⁺, K⁺, Cl⁻, PO₄³⁻, and ascorbic acid did not cause apparent interference on the measurement. The activity of glucose oxidase was mostly retained even after 2-month storage, indicating their long-term stability.     

A novel gaseous pinacolyl alcohol sensor utilizing cataluminescence on alumina nanowires prepared by supercritical fluid drying

A cataluminescence (CTL) sensor using Al₂O₃ nanowires as the sensing material was developed for the determination of trace pinacolyl alcohol in air samples based on the catalytic chemiluminescence (CL) of pinacolyl alcohol on Al₂O₃ nanowires. Eight catalysts were examined and the CL intensity on Al₂O₃ nanowires prepared by supercritical fluid drying was the strongest. This novel CL sensor showed high sensitivity and selectivity to gaseous pinacolyl alcohol at optimal temperature of 340 °C. Quantitative analysis was performed at a wavelength of 460 nm. The linear range of CTL intensity versus concentration of gaseous pinacolyl alcohol was 0.09 × 10⁻⁶ to 2.56 × 10⁻⁶ g mL⁻¹ (r = 0.9983, n = 6) with a detection limit (3σ) of 0.0053 × 10⁻⁶ g mL⁻¹. None or only very low levels of interference were observed while the foreign substances such as water vapor, ethanol, ammonia, chloroform, benzene, nitrogen dioxide, methylbenzene, hydrochloric acid, methanol and butanol were passing through the sensor. The response time of the sensor is less than 100 s, and the sensor had a long lifetime more than 60 h. The sensor would be potentially applied to analysis of the nerve agents such as Soman.     

Emission-based optical carbon dioxide sensing with HPTS in green chemistry reagents: room-temperature ionic liquids

We describe the characterization of a new optical CO₂ sensor based on the change in the fluorescence signal intensity of 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) in green chemistry reagents—room-temperature ionic liquids (RTILs). As far as we are aware, this is the first time RTILs, 1-methyl-3-butylimidazolium tetrafluoroborate (RTIL-I) and 1-methyl-3-butylimidazolium bromide (RTIL-II), have been used as matrix materials with HPTS in an optical CO₂ sensor. It should be noted that the solubility of CO₂ in water-miscible ionic liquids is approximately 10 to 20 times that in conventional solvents, polymer matrices, or water. The response of the sensor to gaseous and dissolved CO₂ has been evaluated. The luminescence intensity of HPTS at 519 and 521 nm decreased with the increasing concentrations of CO₂ by 90 and 75% in RTIL-I and RTIL-II, respectively. The response times of the sensing reagents were in the range 1–2 min for switching from nitrogen to CO₂, and 7–10 min for switching from CO₂ to nitrogen. The signal changes were fully reversible and no significant hysteresis was observed during the measurements. The stability of HPTS in RTILs was excellent and when stored in the ambient air of the laboratory there was no significant drift in signal intensity after 7 months. Our stability tests are still in progress.      

A highly selective pyrene based fluorescent sensor toward Hg detection

A new pyrene-containing fluorescent sensor has been synthesized from 2,3,3-trimethylindolenine. Spectroscopic and photophysical properties of sensor are presented. The large change in fluorescence intensity (I/I₀ = 0.13) at 381 nm and affinity to Hg²⁺ over other cations such as K⁺, Na⁺, Ca²⁺, Mg²⁺, Pb²⁺, and Cu²⁺ make this compound a useful chemosensor for Hg²⁺ detection in hydrophilic media. The sensor (6.0 × 10⁻⁶ M) displays significant fluorescence quenching upon addition of Hg²⁺ in pH 7.4 HEPES buffer without excimer formation. Job’s plot analysis shows the binding stoichiometry to be 2:1 (host/guest).     

A fluorescence ratiometric sensor for hypochlorite based on a novel dual-fluorophore response approach

A fluorescence ratiometric sensor for OCl⁻ has been developed based on a novel dual fluorophore response approach. The sensor molecule contains a coumarin fluorophore and a rhodamine fluorophore, and the two fluorophores are directly linked to an OCl⁻ recognition group. The structure of the sensor was characterized by ESI-MS, NMR, and X-ray crystallographic analysis. Upon treatment with OCl⁻, both fluorophores in the sensor responded simultaneously at two separate optical windows, with large enhancement of the fluorescence ratio (I₅₇₈/I₅₀₁) from 0.01 to 39.55. The fluorescence ratios for the sensor showed a good linearity with the concentration of OCl⁻ in the range of 0.2–40 μM and the detection limits is 0.024 μM (S N⁻¹ = 3). Investigation of reaction products indicated that the sensor reaction with OCl⁻ produced two new fluorescent molecules, which were responsible for the fluorescence changes in two optical windows. In addition, the sensor showed high selectivity to OCl⁻ over other reactive oxygen species, reactive nitrogen species, cations, and anions. The sensor has also been successfully applied to detection of OCl⁻ in natural water samples with satisfactory recovery.     

Novel low humidity sensor made of TiO(2) nanowires/poly(2-acrylamido-2-methylpropane sulfonate) composite material film combined with quartz crystal microbalance

A novel ceramic nanowires of TiO₂ and poly(2-acrylamido-2-methylpropane sulfonate) (TiO₂ NWs/PAMPS) composite material films coated on quartz crystal microbalance (QCM) was prepared as a low humidity sensor. The 50 wt.% of TiO₂ NWs/PAMPS composite material films showed excellent sensitivity (2.63 −ΔHz/Δppm_v) at 31.5 ppm_v), linearity (R² = 0.9959) and acceptable response time (64 s at 34.6 ppm_v). The low humidity sensing mechanism was discussed in terms of surface texture and nanostructured morphology of the composite materials. Moreover, the adsorption dynamic analysis, molecular mechanics calculation (association constant), was used to elucidate the effect of adding 50 wt.% TiO₂ NWs into PAMPS in the increased sensitivity of low humidity sensing.     

Evaluation of poly(ethylene terephthalate) photostabilisation using FTIR spectrometry of evolved carbon dioxide

Carbon dioxide evolution from poly(ethylene terephthalate) (PET) films during ultraviolet (UV) exposure has been monitored using FTIR interrogation of the atmosphere surrounding the test pieces. Measurement periods as little as 4 h could easily discriminate between CO₂ emission rates when tests were conducted to investigate the effect of using different reaction atmospheres or of including UV absorber in the PET samples. Samples containing UV absorbers either homogeneously distributed through the film or in thin surface layers (∼0.7 μm thick) were also tested. Relatively small reductions in CO₂ emission rates were observed with samples containing UV absorbers but the rates were not very sensitive to the distribution and concentration of the absorbers. A thin surface layer containing only 2% stabiliser (equivalent to 0.23% stabiliser when averaged over the whole film thickness) provided oxidation reduction similar to that observed when 1% stabiliser was distributed evenly throughout the sample. Tests were conducted in wet oxygen, dry oxygen and dry nitrogen. For as-received bi-axially drawn PET film containing no absorber, the CO₂ emission rate under UV illumination in wet oxygen was much higher than in dry oxygen or dry nitrogen. For as-received PET the difference between the rates observed in dry oxygen and dry nitrogen was small. For PET films that had been pre-exposed to UV (for 9 days) prior to insertion into the in situ CO₂ measurement cell the rate of CO₂ generation in oxygen was significantly larger than that in nitrogen. In both nitrogen and oxygen the presence of UV absorbers significantly decreased the rate of CO₂ generation.     

Porous α-Fe2O3 hollow microspheres and their application for acetone sensor

Porous α-Fe₂O₃ hollow microspheres were synthesized through a simple and efficient carbon sphere template method. The samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and N₂ adsorption-desorption. Structural characterization indicated that as-prepared α-Fe₂O₃ hollow microspheres had porous structure with around 200 nm in diameter and thin shell about 10 nm thick. The average pore size and Brunauer-Emmett-Teller specific surface area of α-Fe₂O₃ hollow microspheres were 6.5 nm and 111.6 m²/g, respectively. The gas sensing behavior investigation showed that as-synthesized α-Fe₂O₃ hollow microspheres exhibited very good gas sensing property to acetone vapor.     

Stabilization of sensing performance for mixed-potential-type zirconia-based hydrocarbon sensor

The recently reported sensing characteristics of the mixed-potential-type yttria-stabilized zirconia (YSZ)-based hydrocarbon (HC) sensor attached with ZnCr₂O₄-sensing electrode (SE) were found to be changed after the 10-day operation at 550 °C under the wet condition (5 vol.% water vapor). To improve the stability of the present sensor, the several modifications of the SE material by adding YSZ powder were examined. As a result, the sensor using the laminated (ZnCr₂O₄/YSZ)-SE gave the stable electromotive force (emf) response against 100 ppm C₃H₆ at 550 °C for about one month examined. Based on the scanning electron microscopy (SEM) observation and the AC complex-impedance measurements, it was concluded that the stable behavior of the sensor using the laminated (ZnCr₂O₄/YSZ)-SE was provided by the stabilization of the interface between ZnCr₂O₄ grains and YSZ particles. The fabricated sensor exhibited the linear dependence of sensitivity on the logarithm of either C₃H₆ concentration (in the range of 20-800 ppm) or mixtures of various hydrocarbons (HCs) (in the range of 90-2600 ppmC). In addition, the emf response was not altered by the change of O₂ (2-20 vol.%), H₂O (0-10.8 vol.%) and CO₂ (0-20 vol.%) concentrations, and no interference of other gases (CO, NO, NO₂, H₂, and CH₄) was observed.