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In this paper, a new, to the best of our knowledge, optical fluorescent sensor for the sensing of nitric oxide (NO) gas is developed. The optical NO sensor based on CsPbBr3 perovskite quantum dots (PQDs) is coated on the surface of filter paper. The CsPbBr3 PQD sensing material can be excited with a UV LED of a central wavelength at 380 nm, and the optical sensor has been tested in regard to monitoring different NO concentrations from 0–1000 ppm. The sensitivity of the optical NO sensor is represented in terms of the ratio IN2/I1000ppmNO, where IN2 and I1000ppmNO represent the detected fluorescence intensities in pure nitrogen and 1000 ppm NO environments, respectively. The experimental results show that the optical NO sensor has a sensitivity of 6. In addition, the response time was 26 s when switching from pure nitrogen to 1000 ppm NO and 117 s when switching from 1000 ppm NO to pure nitrogen. Finally, the optical sensor may open a new approach for the sensing of the NO concentration in the harsh reacting environmental applications.

Ratiometric optical sensor gas sensing continues to develop optical sensing techniques and materials used in various industrial and environmental applications. This research focuses on a new ratiometric optical sensor using the development of new material of FAPbI3 perovskite QDs and a simple method to detect oxygen (O2) gas. FAPbI3 perovskite QDs are used as an indicator of oxygen gas, and rhodamine 110 (Rh 110) is a reference material in a ratiometric optical sensor. All of the sensing and reference materials are embedded in an ethyl cellulose (EC) matrix and coated on the surface of the filter paper. Using a UV LED with a central wavelength of 380 nm as the excitation light source, the emission spectra results show that the emission wavelengths of the oxygen-sensitive dye (O2) FAPbI3 perovskite QDs do not overlap with the Rh 110 reference signal. Thus, oxygen concentration can be measured using a ratiometric fluorescence reference-based approach. The sensing signal will be obtained in the presence of analyte gas in the ratiometric sensitivity of R0/R100, where R0 and R100 represent the luminescence intensity detected in 100% nitrogen and 100% oxygen concentrations, respectively. The experimental results show the optical oxygen sensor's sensitivity as R0/R100 = 12.7. In addition, the response time and recovery of the oxygen gas sensor produced are 75 s and 93 s, respectively. The use of a new type of FAPbI3 perovskite QDs material has been successfully developed in the optical ratiometric sensor for oxygen gas. The sensor proposed in this study has a low cost and easy fabrication process. The effect of spurious fluctuations in the excitation source intensity can be suppressed by the ratiometric optical sensing method.

This paper presents a ratiometric optical broad range pH sensor that comprises an optical fiber coated at one end with CdSe/ZnS quantum dots (QDs) and Oxazine 170 perchlorate (O170) embedded in ethyl cellulose (EC) matrix. The feasibility of coating an optical fiber with the sensing film to fabricate a ratiometric fiber optic broad range pH sensor is investigated. Using an LED with a central wavelength 405 nm as an excitation light source, the CdSe/ZnS QDs shows that the fluorescence intensity at 575 nm decreases with increasing pH and O170 shows the fluorescence intensity at 655 nm increases with increasing pH. The ratio of fluorescence intensities at 575 and 655 nm has a linear relationship with pH value in the 1.6–13.2 range. The ratiometric sensing approach presented in this study has the advantage of suppressing spurious fluctuations in the intensity of the excitation source and optical transmission properties of the optical fiber.

In this study, a simple and cost-effective technique to fabricate a plastic optical fiber sensor for the dual sensing of hydrogen peroxide (H2O2) and dissolved oxygen (DO) was described. The optical fiber dual sensor consisted of CdSe/ZnS core–shell quantum dots (QDs), with oxygen indicators coated on the fiber end of the sensor. An ethyl cellulose (EC) matrix doped with CdSe/ZnS QDs and tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) (Ru(dpp)32+) served as the sensing materials for H2O2 and DO. The sensing materials for H2O2 and DO were excited with an light emitting diode (LED) of 405 nm, and the two emission wavelengths were separately detected. The optical fiber dual sensor was applied for the monitoring of different H2O2 and DO concentrations. The typical Stern–Volmer plot of an optical fiber dual sensor for the sensing of DO demonstrated linearity, and the attenuation of the relative phosphorescence intensity for the sensing of H2O2 concentrations also demonstrated linearity with the H2O2 concentrations in the tested range. In addition, the results indicated that the phosphorescence properties of the H2O2 sensor are independent of the presence of the DO sensor, with a unique linear response in the range of 0–132 mM. Finally, the DO sensing scheme described herein was intended to compensate for the H2O2 concentration, and the fabricated optical fiber dual sensor may be used for the sensing of H2O2 concentration and DO in the aquaculture applications.

This paper presented a new ratiometic optical sensor for sensing of urea concentrations based on CdSe/ZnS QDs and Rhodamine 110 (Rh110) doped in poly(isobutyl methacrylate) coated on the surface of glass.

A simple signal processing, low-cost technique for the fabrication of an optical oxygen sensor based on phase shift detection is described. The sensing film is based on the oxygen-sensing dye platinum tetrakis pentrafluoropheny porphine (PtTFPP) embedded in a polymer matrix. The feasibility of coating a photodiode with the oxygen-sensing film to fabricate an optical sensing device is investigated. The optical oxygen sensor is tested with regard to monitoring excitation voltage and oxygen concentration. The experiment results show that the maximum phase difference between 0% and 100% gaseous oxygen is 26°. A preparation procedure for coating photodiodes with the oxygen-sensing film that produces repetitive and reliable sensing devices is proposed. The developed optical oxygen sensor is low-cost, has simple signal processing, and lacks optical filter elements. The proposed sensor is a cost-effective alternative to traditional electrochemical-based oxygen sensors and provides a platform for other optically based sensors.

A simple, low cost technique to fabricate a ratiometric optical fiber dissolved oxygen sensor has been presented. The ratiometric optical fiber dissolved oxygen sensor comprising a plastic optical fiber coated at one end with Pd(II)/CdSe QDs or Pt(II)/CdSe QDs embedded in sol–gel matrix. Using an LED with a central wavelength of 405 nm as an excitation source, it is shown that the emission wavelengths of the oxygen-sensitive dye (PdTFPP, PdTCPP, PtTFPP and PtOEP) and the reference CdSe QDs have no spectral overlap and therefore permit the dissolved oxygen concentration to be measured using a ratiometric-based method. The sensitivity of optical fiber dissolved oxygen sensor is quantified in terms of the ratio I0/I100, where I0 and I100 represent the detected luminescence intensities in fully-deoxygenated and fully-oxygenated water, respectively. The experimental results show that the sensitivities of the ratiometric optical fiber dissolved oxygen sensors are estimated to be 21.7 for PdTFPP-doped sensor, 7.4 for PdTCPP-doped sensor, 6.5 for PtTFPP-doped sensor and 9.2 for PtOEP-doped sensor. The ratiometric sensing approach presented in this study has the advantage of suppressing the effects of spurious fluctuations in the intensity of the excitation source and optical transmission properties of the optic fiber.

This paper proposes a ratiometric optical temperature and oxygen sensor that incorporates a sol–gel matrix doped with platinum tetrakis pentafluorophenyl porphine (PtTFPP) as the oxygen-sensitive material, 7-amino-4-trifluoromethyl coumarin (AFC) as the temperature-sensing material, and rhodamine 110 (Rh110) as the temperature/oxygen-independent fluorescent dye. The feasibility of coating a color sensor with the sensing film for fabricating a ratiometric optical dual sensing device is investigated. Using an LED with a central wavelength of 405 nm as the excitation source, it is shown that the emission wavelengths of the temperature-sensitive, oxygen-sensitive, and reference dyes have no spectral overlap and therefore permit the temperature and oxygen concentration to be measured using a ratiometric-based method. The ratiometric optical dual sensor was tested with regard to monitoring various temperatures and oxygen concentrations. The results show that the luminescence properties of the temperature sensor are independent of the presence of the oxygen sensor, and have a uniquely good linear response in the 25–65 °C range. The oxygen sensing scheme presented in this work is intended for use in temperature compensation. The proposed ratiometric sensing approach suppresses the effects of spurious fluctuations in the intensity of the excitation source.

A simple, low cost technique to fabricate a ratiometric optical fiber ammonia (NH3) sensor has been presented. The ratiometric optical fiber ammonia sensor was based on the ammonia induced absorbance change of sensing material Oxazine 170 perchlorate (O170) in ethyl cellulose (EC) with the luminescence intensity of 7-amino-4-trifluoromethyl coumarin (AFC). The observed luminescence intensity from AFC at 487 nm decreased with increasing the ammonia concentration. The sensitivity of optical ammonia sensor is quantified in terms of the ratio I 0 /I 100 , where I 0 and I 100 represent the detected luminescence intensities in nitrogen and 1000 ppm ammonia concentration, respectively. The experimental result shows that the sensitivity of the ratiometric optical fiber ammonia sensor is estimated to be 1.44. The sensitive optical ammonia sensor based on fluorescence intensity changes of AFC due to the absorption change of Oxazine 170 perchlorate in EC layer with ammonia is achieved. The ratiometric sensing approach presented in this study has the advantage of suppressing spurious fluctuations in the intensity of the excitation source and optical transmission properties of the optical sensor.

A new optical carbon dioxide sensor based on the colormetric change of pH indicator α-naphtholphthalein with the internal reference fluorescent CIS/ZnS quantum dots (QDs) was developed. The luminescence intensity of CIS/ZnS QDs increased with increasing carbon dioxide concentration. The sensing films consisting of α-naphtholphthalein in polyIBM and CIS/ZnS QDs in polystyrene layer. The sensitivity of optical carbon dioxide sensor is quantified in terms of the ration I 100 /I 0 , where I 100 and I 0 represent the detected luminescence intensities in pure carbon dioxide and pure nitrogen environments, respectively. The experimental result reveals that the new optical carbon dioxide sensor has sensitivity of I 100 /I 0 =13.4.

A new simple, low-cost technique for the fabrication of a portable optical sensor for the dual sensing of temperature and oxygen is described. The sensing film is based on the oxygen sensing dye platinum tetrakis pentrafluoropheny porphine (PtTFPP) and 7-amino-4-trifluoromethyl coumarin (AFC) embedded in tetraethylorthosilane (TEOS)/n-octyltriethoxysilane (Octyl-triEOS) composite xerogels. The feasibility of coating a color sensor with the sensing film to fabricate a portable optical dual sensing device is investigated. The temperature and oxygen indicators can both be excited with an LED at a wavelength 405 nm. The portable optical dual sensor has been tested with regard to monitoring different temperatures and oxygen concentrations, the oxygen response of which is quantified in terms of the ratio I N 2 / I O 2 , where I N 2 and I O 2 represent the detected phosphorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results reveal that the portable optical oxygen sensor has a response of I N 2 / I 100 O 2 = 1.75 . In addition, our results show that the luminescence properties of the temperature sensor are independent of the presence of the oxygen sensor, and have a uniquely good linear response in the 25–65 °C range. Finally, the oxygen sensing scheme presented in this work is intended for use in temperature compensation, and the portable optical dual sensor is a cost-effective alternative to traditional electrochemical-based temperature and oxygen sensors and provides a platform for other optically based sensors.

A simple, low-cost technique for fabrication of highly sensitive fiber-optic oxygen sensor is described. An organically modified silicate (ORMOSIL) as a matrix for the fabrication of oxygen sensing film was produced. The technique is based on coating the end of a plastic optical fiber with ormosil composite xerogel film sequestered with luminophore palladium (II) meso-tetra(4-carboxyphenyl)porphyrin (PdTCPP) prepared by a sol–gel process. The composite xerogel studied is tetraethylorthosilane (TEOS)/n-octyltriethoxysilane (Octyl-triEOS). Result shows that, expect for PdTCPP-doped TEOS/Octyl-triEOS composite xerogel show the high sensitivity and linear Stern–Volmer relationship which indicate the homogenous environment of the luminophore. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio I N2 / I O2 , where I N2 and I O2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental result reveals that the PdTCPP-doped TEOS/Octyl-triEOS oxygen sensor has sensitivity of 153.

A simple, low cost technique to fabricate a plastic optical fiber sensor for dual sensing of temperature and oxygen has been described. The optical fiber dual sensor consists of temperature and oxygen indicators that were coated on the fiber end. A fluorinated xerogels doped with platinum tetrakis pentrafluoropheny porphine (PtTFPP) and 5(6)-carboxyfluorescein (CF) serves as the oxygen and temperature sensing material. The temperature and oxygen indicators can both be excited with an LED of 405 nm, and the two emission wavelengths can be detected separately. The optical fiber dual sensor has been tested with regard to monitoring different temperatures and oxygen concentrations. The typical Stern–Volmer plot of an optical fiber dual sensor for oxygen sensing shows linearity, and the attenuation of the relative luminescence intensity for temperature sensing also has a linear relationship with temperature in the tested range. In addition, our results show that the luminescence properties of the temperature sensor are independent of the presence of the oxygen sensor, and have a uniquely good linear response in the 25–66 °C range. Finally, the oxygen sensing scheme presented in this work is intended for use in temperature compensation, and optical fiber dual sensor can be used for the contactless-sensing of temperature and oxygen in biological, medical and environmental applications.

This paper presents a new optical fiber carbon dioxide (CO2) sensor based on the emission wavelength shift of CuInS2/ZnS quantum dots (CIS/ZnS QDs) due to changes in the absorption of a pH indicator (α-naphtholphthalein) with a changing CO2 concentration. Using an LED with a central wavelength of 375 nm as the excitation source, it is shown that using the red emission of CIS/ZnS QDs allows for the detection of CO2 concentration over the range of 0-100%, and the associated wavelength shift was found to be 630 pm/%CO2. Moreover, the observed luminescence intensity from CIS/ZnS QDs at 578 nm increases as the CO2 concentration increases. The observed luminescence intensity change by CO2 is expressed as I100/I0, which I0 is used to represent the sensitivity of the optical fiber sensor, where I100 and I0 represent the steady-state luminescence intensities in pure carbon dioxide and pure nitrogen environments, respectively. The ratio I100/I0 of this optical fiber sensor is estimated to be 100. These results of the optical sensing method can be used in practice for detection of CO2 and could offer a new approach for developing novel types of optical fiber sensor.

A simple, low-cost technique for fabrication of high performance optical fiber oxygen sensor is described. An organically modified silicate (ORMOSIL) as a matrix for the fabrication of oxygen sensing film was produced. The technique is based on coating the end of an optical fiber with ormosil composite xerogel film sequestered with luminophore palladium (II) meso-tetrakis(pentafluorophenyl)porphyrin (PdTFPP) prepared by a sol–gel process. The composite xerogel studied is n-propyltrimethoxysilane (n-propyl-TriMOS)/tetraethylorthosilane (TEOS)/n-Octyltriethoxysilane (Octyl-triEOS). Result shows that, expect for PdTFPP-doped n-propyl-TriMOS/TEOS/Octyl-triEOS composite xerogel shows a high sensitivity and linear Stern–Volmer relationship which indicates the homogenous environment of the luminophore. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio I N 2 / I O 2 , where I N 2 and I O 2 represent the detected phosphorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental result reveals that the PdTFPP-doped n-propyl-TriMOS/TEOS/Octyl-triEOS oxygen sensor has sensitivity of I N 2 / I 100 O 2 = 263 .

This paper presents a highly sensitive fiber-optic oxygen sensor. The sensor was fabricated using palladium (II) meso-tetrakis (pentafluorophenyl) porphyrin (PdTFPP) and porous silica nanoparticles embedded in a tetraethylorthosilane (TEOS)/n-octyl-triethoxysilane (Octyl-triEOS) composite xerogel present as a coating on the end of the fiber. Sensitivity is quantified in terms of the ratio IN2/IO2, where IN2 and IO2 represent the intensity of fluorescence detected in a pure nitrogen or pure oxygen environment. The experimental results reveal that this PdTFPP-doped oxygen sensor with porous silica nanoparticles has a sensitivity of IN2/I100O2 = 386. The results also show that this sensor has higher sensitivity than an oxygen sensor based on Pd(II) complex immobilized in a sol-gel matrix. Furthermore, the optical oxygen sensor yields a linear Stern–Volmer plot. The proposed optical sensor has the advantages of easy fabrication, low cost, and high sensitivity to oxygen.

This paper presents a high-sensitivity oxygen sensor that comprises an optical fibre coated at one end with tris (4, 7-diphenyl-1, 10-phenanthroline) ruthenium (II) ([Ru (dpp)3]2+) and porous 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 IN2/IO2, where IN2 and IO2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results show that the oxygen sensor has a sensitivity of 26. The experimental results show that compared to oxygen sensor based on Ru (II) complex immobilized in the sol-gel matrix, the proposed optical fibre oxygen sensor has higher sensitivity. In addition to the increased surface area per unit mass of the sensing surface, the porous silica nanoparticles increase the sensitivity because a substantial number of aerial oxygen molecules penetrate the porous silica shell. The proposed optical sensor has the advantages of easy fabrication, low cost, fast response and high sensitivity for oxygen monitoring using a cheap LED as a light source.

A simple, low-cost technique for fabrication of high performance optical fiber oxygen sensor is described. An organically modified silicate (ORMOSIL) as a matrix for the fabrication of oxygen sensing film was produced. The technique is based on coating the end of an optical fiber with ORMOSIL composite xerogel films film sequestered with luminophore platinum (II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) prepared by a sol–gel process. The composite xerogels studied are 3,3,3-trifluoropropyltrimethoxysliane (TFP-TriMOS) or n -propyltrimethoxysilane ( n -propyl-TriMOS)/tetraethylorthosilane (TEOS)/ n -octyltriethoxysilane (Octyl-triEOS). Results show that, expect for PtTFPP-doped TFP-TriMOS or n -propyl-TriMOS/TEOS/Octyl-triEOS composite xerogels show the high sensitivity and linear Stern–Volmer relationship which indicate the homogenous environment of the luminophore. The sensitivities of the two oxygen sensors are quantified in terms of the ratio I N2 / I O2 , where I N2 and I O2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results reveal that the PtTFPP-doped TFP-TriMOS/TEOS/Octyl-triEOS and n -propyl-TriMOS/TEOS/Octyl-triEOS oxygen sensors have sensitivities of 101 and 155, respectively. The experimental results confirm that the current oxygen sensors exhibit the linear Stern–Volmer plots and high-sensitive based on the oxygen indicator embedded in TFP-TriMOS or n -propyl-TriMOS/TEOS/Octyl-triEOS composite xerogels.

This paper presents a highly sensitive dissolved oxygen sensor comprising an optical fiber coated at one end with core-shell silica nanoparticles and platinum(II) meso-tetrakis (pentafluorophenyl) porphyrin (PtTFPP) embedded in an n-octyltriethoxysilane (Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel. The sensitivity of optical fiber dissolved oxygen sensor is quantified in terms of the ratio I0/I100, where I0 and I100 represent the detected fluorescence intensities in fully deoxygenated and fully oxygenated water, respectively. The experimental results show that the optical fiber dissolved oxygen sensor has a sensitivity of approximately 117 in the range 0–40 mg/L of dissolved oxygen concentrations. The experimental results show that as compared to the other optical dissolved oxygen sensors based on Pt(II) or Ru(II) complexes, the proposed optical fiber dissolved oxygen sensor has the highest sensitivity. In addition to the increased surface area per unit mass in the sensing surface, the dye entrapped in the core of silica nanoparticles also play an important role in the increased sensitivity because of the penetration of substantial amount oxygen molecules through the porous silica shell.

This paper develops a new ratiometric optical dual sensor for Cu2+ ions and dissolved oxygen (DO) incorporating a sol-gel matrix doped with palladium tetrakis pentafluorophenyl porphine as the oxygen-sensitive material, CdSe quantum dots as the Cu2+ ion-sensing material, and 7-amino-4-trifluoromethyl coumarin as the Cu2+ /DO practically independent fluorescent dye. The feasibility of coating an optical fiber with the sensing film to fabricate a ratiometric optical fiber dual sensor is investigated. Using an LED with a central wavelength of 405 nm as an excitation source, it is shown that the emission wavelengths of the Cu2+ ion-sensitive, DO-sensitive dye and the reference dye have no spectral overlap and therefore permit Cu2+ ion and DO concentration to be measured using a ratiometric-based method. The ratiometric optical fiber dual sensor has been tested with regard to monitoring different Cu2+ ion (0-10 μM) and DO concentrations (0-38 mg/L). The results show that the luminescence properties of the Cu2+ ion sensor are independent of the presence of the oxygen sensor and have a uniquely good linear response in the 0-10 μM range. The proposed ratiometric sensing approach presented in this study has the advantage of suppressing spurious fluctuations in the intensity of the excitation source.

In this work, carbon quantum dots (CQD s ) have been synthesized by one step hydrothermal method to detect hydrogen peroxide (H 2 O 2 ). The optical H 2 O 2 sensors were based on the fluorescent quenching of the carbon quantum dots. The optical H 2 O 2 sensors demonstrate capable of detecting H 2 O 2 over the range of 0-88.2 mM and 0-60 mM. The H 2 O 2 sensitivities of wavelength shift to changes in the H 2 O 2 concentration were found to be 0.18 nm/mM and 0.26 nm/mM. These results of the optical sensors showed that the method can be used in practice detection of H 2 O 2 and could offer a new approach for developing a new optical biosensor. The CQDs exhibit good emission property and high stability, as well as excitation-independent emission behavior. Moreover, it is attractive that CQDs can be used as an effective fluorescent probe for the detection of H 2 O 2 with linear Stern-Volmer plot and wavelength shift in an aqueous solution.

A new, simple signal processing, low-cost technique for the fabrication of a portable oxygen sensor based on time-resolved fluorescence is described. The sensing film uses the oxygen sensing dye platinum meso-tetra (pentfluorophenyl) porphyrin (PtTFPP) embedded in a polymer matrix. The experimental results reveal that the PtTFPP-doped oxygen sensor has a sensitivity of 2.2 in the 0-100% range. A preparation procedure for coating the photodiodes with the oxygen sensor film that produces repetitive and reliable sensing devices is proposed. The developed time-resolved optical oxygen sensor is portable, low-cost, has simple signal processing, and lacks optical filter elements. It is a cost-effective alternative to traditional electrochemical-based oxygen sensors and provides a platform for other optical based sensors.

A new, simple signal processing, low-cost technique for the fabrication of a portable oxygen sensor based on time-resolved fluorescence is described. The sensing film uses the oxygen sensing dye platinum meso-tetra (pentfluorophenyl) porphyrin (PtTFPP) embedded in a polymer matrix. The ratio τ0/τ100 measures sensitivity of the sensing film, where τ0 and τ100 represent the detected fluorescence lifetimes from the sensing film exposed to 100% nitrogen and 100% oxygen, respectively. The experimental results reveal that the PtTFPP-doped oxygen sensor has a sensitivity of 2.2 in the 0%–100% range. A preparation procedure for coating the photodiodes with the oxygen sensor film that produces repetitive and reliable sensing devices is proposed. The developed time-resolved optical oxygen sensor is portable, low-cost, has simple signal processing, and lacks optical filter elements. It is a cost-effective alternative to traditional electrochemical-based oxygen sensors and provides a platform for other optical based sensors.

An optical sensor for the dual sensing of oxygen (Osub2/sub) and carbon dioxide (COsub2/sub) based on sensing films coated on filter paper is proposed. Ethyl cellulose (EC) doped with platinum(II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) and 7-amino-4-trifluoromethyl coumarin serve as the oxygen sensing material and reference blue emission dye for the pH indicator, respectively. The COsub2/subsensing layer includes the pH-sensitive fluorescent indicator 1-hydroxy-3,6,8-pyrenetrisulfonic acid trisodium salt immobilized within the EC. The Osub2/sub- and COsub2/sub-sensitive materials can both be excited with a 405 nm LED, and the two emission wavelengths can be detected separately. The experimental result reveals that the optical Osub2/suband COsub2/subsensors have sensitivities of IsubNsub2/sub/sub/Isub100%Osub2/sub/sub=22.8 and IsubNsub2/sub/sub/Isub100%COsub2/sub/sub=3.6, respectively. The response times of the optical Osub2/subsensor were 15 s upon switching from nitrogen to Osub2/suband 41 s when moving from Osub2/subto nitrogen (Nsub2/sub). The response times of the optical COsub2/subsensor were 7 s upon switching from 100% Nsub2/subto 100% COsub2/suband 39 s when moving from 100% COsub2/subto 100% Nsub2/sub. The proposed optical dual sensor can be used for the simultaneous sensing of Osub2/suband COsub2/subconcentrations in environmental applications.

In this paper, the multicolor photoluminescence carbon quantum dots (CQDs) have been synthesized by one step hydrothermal method to analyze hydrogen peroxide (H2O2). These CQDs exhibited multicolor emission under a single wavelength excitation for the quantification of H2O2. Using an LED with a central wavelength of 365 nm as the excitation source, it is shown that the red emission CQDs capable of detecting H2O2 over the linear range of 0-88.2 mM and the H2O2 sensitivity of wavelength shift to changes in the H2O2 concentration was found to be 0.18 nm/mM. These results of the optical sensing method can be used in practice detection of H2O2 and could offer a new approach for developing a new biosensor. The CQDs exhibit good emission property and high stability, as well as excitation-independent emission behavior. Moreover, it is attractive that CQDs can be used as an effective fluorescent probe for the detection of H2O2 with linear Stern-Volmer plot and wavelength shift in an aqueous solution.

This paper presents a high-sensitivity oxygen sensor that comprises an optical fiber coated at one end with tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) ([Ru(dpp)3]2+) and porous 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 IN2 /IO2 , where IN2 and IO2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental results show that the oxygen sensor has a sensitivity of 26. The response time was 2 s when switching from pure nitrogen to pure oxygen, and 7.7 s when switching in the reverse direction. The experimental results show that compared to an oxygen sensor based on Ru(II) complex immobilized in the solgel matrix, the proposed optical fiber oxygen sensor has higher sensitivity. In addition to the increased surface area per unit mass of the sensing surface, the porous silica nanoparticles increase the sensitivity because a substantial number of aerial oxygen molecules penetrate the porous silica shell. The proposed optical sensor has the advantages of easy fabrication, low cost, fast response, and high sensitivity for oxygen monitoring using a cheap LED as a light source.

A simple low-cost technique for the fabrication of portable optical oxygen sensors is described. The sensing film is based on the oxygen sensing dye tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) {[Ru(dpp)3] 2 + } and dye-entrapped core-shell silica nanoparticles embedded in a sol-gel matrix. The feasibility of coating a photodiode with the oxygen sensing film to fabricate a portable optical sensing device is investigated. The sensitivity of the sensor is quantified in terms of the ratio IN2 /I O2 , where I N2 and I O2 represent the detected fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. The experimental result reveals that the portable optical oxygen sensor has sensitivity of 41. The sensor exhibits a linear response for oxygen concentrations in the range 0 to 60%. A preparation procedure for coating photodiodes with the oxygen film that produces repetitive and reliable sensing devices is proposed. The developed optical oxygen sensor is portable, low-cost, highly sensitive, and lacks optical filter elements. The proposed sensor is a cost-effective alternative to traditional electrochemical-based oxygen sensors and provides a platform for other optically based sensors.

Oxygen and carbon dioxide sensors are involved in many chemical and biochemical reactions. Consequently, considerable efforts over years have been devoted to discover and improve suitable techniques for measuring gas concentrations by optical fiber sensors. Optical gas sensors consist of a gas-sensitive dye entrapped in a matrix with a high permeability to gas. With such sensors, gas concentration is evaluated based upon the reduction in luminescence intensity caused by gas quenching of the emitting state. However, the luminescence quenching effect of oxygen is highly sensitive to temperature. Thus, a simple, low-cost plastic optical fiber sensor for dual sensing of temperature and oxygen is presented. Also, a modified Stern-Volmer model is introduced to compensate for the temperature drift while the temperature is obtained by above dual sensor. Recently, we presented highly-sensitive oxygen and dissolved oxygen sensors comprising 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. Also, two-dimensional gas measurement for the distribution of chemical parameters in non-homogeneous samples is developed and is of interest in medical and biological researches.