CF embedded in sol–gel matrix

Sensors and Actuators B 195 (2014) 259–265

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Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb

Optical fiber sensor for dual sensing of temperature and oxygen based on PtTFPP/CF embedded in sol–gel matrix Cheng-Shane Chu ∗ , Che-An Lin Department of Mechanical Engineering, Ming Chi University of Technology, New Taipei City, Taiwan

a r t i c l e

i n f o

Article history: Received 13 August 2013 Received in revised form 6 January 2014 Accepted 8 January 2014 Available online 21 January 2014 Keywords: Plastic optical fiber Dual sensing Temperature Oxygen PtTFPP CF

a b s t r a c t 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. © 2014 Elsevier B.V. All rights reserved.

1. Introduction While temperature and oxygen are important parameters in optical sensing technologies, the former affects the performance of all opto-chemical sensors [1–6]. It is important to know the, temperature in the fluorescent sensing of oxygen, since quenching by oxygen always is highly temperature dependent [7], and so, there is a need for optical sensors that measure both oxygen and temperature. In optical oxygen sensors, the oxygen concentration is evaluated based upon the reduction in luminescence intensity caused by oxygen quenching of the emitting state. Optical oxygen sensors consist of an oxygen-sensitive dye entrapped in a matrix with a high permeability to oxygen. Many researchers have reported that sol–gel derived glass is a suitable matrix material for oxygen, since it has high oxygen permeability, good mechanical and chemical stability, and superior optical clarity [8–10]. Furthermore, it has been shown that the use of organically modified silicate (ORMOSIL) matrixes improves the response and sensitivity of ruthenium-based oxygen sensors [11–13]. ORMOSILs can accommodate and disperse analyte-sensitive dyes, and also

∗ Corresponding author. Tel.: +886 2 29089899x4535; fax: +886 2 29063269. E-mail address: [email protected] (C.-S. Chu). 0925-4005/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2014.01.032

have a porous structure, which is essential for improving the sensor response. On the other hand, longer-lived, fluorescent oxygen-sensitive dyes are needed to improve the sensitivity of oxygen sensors. Phosphorescent porphyrins of platinum [14–16] such as platinum tetrakis pentrafluoropheny porphine (PtTFPP), have the desirable features of longer lifetimes, convenient excitation and emission wavelengths with large Stokes shifts (100–170 nm), and a reasonable luminescence quantum yield. Recently, our lab developed fiber-optic oxygen sensors based on 3,3,3-trifluoropropyltrimethoxysliane (TFP-TriMOS) or npropyltrimethoxysilane (n-propyl-TriMOS)/tetraethylorthosilane (TEOS)/n-octyltriethoxysilane (Octyl-triEOS) composite xerogel doped with platinum complexes. The resulting fiber-optic oxygen sensors have linear Stern–Volmer plots and show better performance than existing oxygen sensors based on ruthenium dye immobilized in various sol–gel matrixes [17]. Fluorescent temperature sensing is a common approach for the optical determination of temperature, while another optical spectroscopic technology that can be used for this is luminescence quenching [18–20]. In this latter approach, an excited fluorophore molecule can drop back to its ground state through radiation emission (luminescence) or through collision with another molecule. The luminescence emission and collision processes are in equilibrium for a system at a certain temperature. A change in temperature will change the frequency of collision, and thus shift the

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Table 1 Comparison between various optical dual sensors reported in the literature and the one proposed in this work. Oxygen probe

Matrix

ex (nm)

em (nm)

T range (◦ C) O2 range

Signal

Ref.

PtTFPP

FIB

337

5–50

0–20%

Luminescence decay time

[21]

Ru-phen

PtTFPP

p-tBS-co-TFEM

465

10–50

0–20%

Luminescence intensity

[22]

Magnesium fluoro-germanate

Ru(dpp)3 2+

Sol–gel

470

25–65

0–100%

Luminescence decay time

[23]

Eu-␤-diketonate complex

PtTFPP lactone FIB

390

5–45

0–20%

PdTFPP

Hydrogel

405

1–70

0–20%

Luminescence intensity and decay time Luminescence decay time

[24]

Europium (III) complexes Eudapt

Rudpp

Polymer

400

10–70

0–21%

Luminescence decay time

[26]

Eu(tta)3 dpbt

PtTFPP

405

1–50

1–40%

Ru-phen

C70

Hydrogel two layer Two layer

Epoxy glue

PtTFPP

Sol–gel

380

Core–shell CdSe QDs-silica nanoparticles Ru-phen

PtTFPP

Sol–gel

409

PdTFPP

Hydrogel

Ru-phen

PtTFPP

Polymer

CF

PtTFPP

Sol–gel

470(Ru) 525 (Pd) 475(Ru) 505(Pt) 405

650(Pt complex) 514(T phosphor) 580(Ru complex) 650(Pt complex) 610(Ru complex) 650(T phosphor) 615(Eu complex) 738(Pt complex) 615(Eu complex) 670(Pd complex) 610(Ru complex) 615(Pt complex) 615(Eu complex) 650(Pt complex) 580(Ru complex) 670-70 (C70 ) 497(Epoxy glue) 650(Pt complex) 532(CdSe QDs) 648(Pt complex) 580(Ru complex) 670(Pd complex) 580(Ru complex) 650(Pt complex) 532(CF) 650(Pt complex)

Temperature probe 3+

La2 O2 S:Eu

phosphor

470

equilibrium of the two processes, resulting in changes in the luminescence intensity and lifetime, and optical temperature sensors have been developed based this characteristic [18–20]. In recent years a number of materials have been reported that enable the dual sensing of temperature and oxygen. A comparison between the luminescence-based oxygen-temperature optical dual sensors reported to date and the device proposed in the current study is presented in Table 1. The earlier sensors are based on materials that use a single wavelength [21–30] or two different wavelengths [31,32] for excitation of the sensing indicators. Most of these dual sensing techniques are based on measuring the lifetime of the luminescence signal. Because the emissions of temperature and oxygen sensors have spectral overlap, the lifetimes of their signals are not affected by changes in the light source, drifts in the optical path or changes in the gain of the detection system [33]. In addition, when sensing layers are embedded with multiple indicators then these usually suffer from increased photodecomposition and signal drifts compared to single sensors, particularly when oxygen sensors (which generate singlet oxygen) are present [34]. Recently, Chu and Lo [29] presented a plastic optical fiber sensor for the dual sensing of temperature and oxygen. The sensor features commercially available epoxy glue coated on the side-polished fiber surface for temperature sensing and a fluorinated xerogel doped with platinum tetrakis pentrafluoropheny porphine (PtTFPP) coated on the fiber end for oxygen sensing. A commercial epoxy glue is coated on the side-polished fiber surface. After the epoxy glue dries, a fluorinated xerogel doped with platinum tetrakis pentrafluoropheny porphine (PtTFPP) is coated on the end of the fiber. Therefore, the response to temperature change at different rates. This makes temperature compensation unachievable in an application where there are frequent, shortterm changes in temperature, e.g., breath monitoring. In 2012, Sung and Lo [30] present an optical sensor comprising doped core–shell nanoparticles embedded in a sol–gel matrix for the dual sensing of temperature and oxygen. The nanoparticles comprise a CdSe quantum dot (QD) core and a silica shell doped with platinum(II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP). The process parameter for synthesis of CdSe QDs and preparation of core–shell CdSe/SiO2 nanoparticles are complicated and involves multiple steps. For these reasons, this paper examines how

[25]

[27]

22–73

Luminescence intensity and decay time 0–0.005% Luminescence intensity and decay time 0–100% Luminescence intensity

0–100

0–100%

Luminescence intensity

[30]

1–60

0–100%

Luminescence decay time

[31]

0–50

0–20 kPa

Luminescence decay time

[32]

25–66

0–100%

Luminescence intensity

Present study

0–120

[28] [29]

to design a simple, low cost optical dual sensor for sensing temperature and oxygen based on the luminescence intensity, without any spectral overlap. To achieve this, we present a simple, low cost technique to fabricate a plastic optical fiber sensor for the dual sensing of temperature and oxygen. More specifically, this work uses CF as the temperature indicator, PtTFPP as the oxygen sensitive dye, and tetraethylorthosilane (TEOS)/n-octyltriethoxysilane (Octyl-triEOS) as the support matrix. Both indicators are embedded in a sol–gel matrix, coated on the end of a plastic optical fiber, and excited using a single wavelength of 405 nm. The sensing scheme is intended for use in the temperature compensated sensing of oxygen. 2. Experimental 2.1. Materials 5(6)-Carboxyfluorescein (CF, 95%), n-octyltriethoxysilane (Octyl-triEOS, 97.5%) and tetraethylorthosilane (TEOS, 99.5%) were purchased from Aldrich. Triton-X100 (analytical grade) was purchased from Fluka. Finally, platinum(II) mesotetrakis(pentafluorophenyl)porphyrin (PtTFPP) was purchased from Frontier Scientific. All of the chemicals were used in the as-received condition without further purification. 2.2. Preparation of temperature and oxygen sensing material The tetraethylorthosilane (TEOS)/n-octyltriethoxysilane (OctyltriEOS) composite sols used as the matrix material in the current oxygen sensors were prepared by mixing Octyl-triEOS (0.2 mL) and TEOS (4 mL) to form a precursor solution. Adopting a similar approach to that employed by Yeh et al. [14], EtOH (1.25 mL) and HCl (0.4 mL of 0.1 M HCl) were then added to the sol solution to catalyze the ORMOSIL reaction. The resulting solution was then capped and stirred magnetically for 1 h at room temperature. During the mixing process, Triton-X-100 (0.1 mL) was added to the solution to improve the homogeneity of the silica sol, resulting in a crack-free monolith. The sensor dye solution was prepared by dissolving 2 mg of PtTFPP and CF into 10 mL of tetrahydrofuran (THF). PtTFPP and CF

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(Fiber Diameter: 1000 ␮m) coated with the PtTFPP/CF-doped TEOS/Octyl-triEOS composite xerogel on the fiber end. The relative luminescence intensity was measured at a pressure of 101.3 kPa using a USB4000 spectrofluorometer. Six different oxygen concentrations were obtained by mixing oxygen and nitrogen, and this process was controlled by gas flowmeters. The mixed gas was heated to temperatures ranging from 24.8 to 65.6 ◦ C in a Hot Circulator Standard Oven (RISEN Co., LTD, D9LR-RHD452). The mixed gas temperature was measured with a thermometer (Lutron Electronic Co., Ltd., Model TM-925). 3. Results and discussion 3.1. Temperature sensing properties of the optical dual sensor

2.3. Instrumentation Fig. 1 illustrates the experimental setup used to characterize the performance of the plastic optical fiber sensor for dual sensing of temperature and oxygen. The dual sensor was excited by an LED light source (Ocean Optics, Model LS-450, 405 nm wavelength) driven by a 10 kHz Arbitrary Waveform Generator (Thurlby Thandar Instruments Ltd, Model TGA1240). The fiber-optic sensing system consisted of a plastic optical fiber

12000 10000 8000 6000

Temperature Sensing Signal

4000

R² = 0.9997

1500 1000 500 0 20

30

40 50 Temperature (° C)

24.8 34.9 44.8 54.8

2000

65.6

0

60

70

Fig. 3. Variation of peak relative luminescence intensity at 540 nm with temperature.

RelativeLuminescence Intensity(a.u.)

16000 14000

2000

5000

Oxygen Sensing Signal Increasing Temperature

RelativeLuminescence Intensity(a.u.)

18000

2500

4500 Temperature Sensing Signal

4000 3500 3000

Oxygen Sensing Signal

2500 2000

Increasing Temperature

dissolved thoroughly in THF, resulting in a highly homogenous dye solution and hence improved temperature and oxygen sensitivity. The luminophore-doped sol solutions were prepared by mixing the CF/PtTFPP/THF solutions into the sol solution. The sol mixtures were then capped and stirred mechanically for 10 min. Finally, PtTFPP/CF-doped TEOS/Octyl-triEOS composite xerogels were prepared using a sol–gel process performed at room temperature. Prior to the dip-coating process, the plastic optical fiber was cleaned by rinsing it with copious amounts of de-ionized water and EtOH, and then drying it at room temperature for 10 min. The composite xerogels sensing film was deposited on the end of the fiber by using a dip-coating process with a dipping velocity of 0.25 mm/s. Finally, the coated fiber was dried at room temperature and left to stabilize under ambient conditions for 1 week.

Relative Luminescence Intensity (a.u.)

Fig. 1. Experimental setup for the optical fiber dual sensor system.

The CF was used as the temperature indicator in this work, and it is sensitive to temperatures in the tested range from 24.8 to around 65.6 ◦ C, as shown in Fig. 2. Although not investigated, this optical fiber dual sensor could also respond to temperatures beyond the tested range. As the temperature increased, the luminescence intensity of the optical fiber dual sensor decreased. The relationship between the temperature and the luminescence intensity at peak wavelength (540 nm) of the CF was obtained by plotting the related data from Fig. 2. The resulting calibration curves, shown in Fig. 3, indicate that these can be used for temperature measurement in the tested range. A linear calibration curve for measuring

1500

24.8 34.9 44.8 54.8

1000 500

65.6

0

450

550 650 Wavelength (nm)

(a)

750

450

550 650 Wavelength (nm)

750

(b)

Fig. 2. Emission spectra of the optical dual sensor as function of temperature, 540 nm for the temperature sensor and 650 nm for oxygen sensor both at (a) 0% and (b) 100% oxygen concentration.

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18 16

23.4oC

23.4oC

21500

R² = 0.9909

20500

42.3oC

20000

Increasing Temperature

12

32.3oC

32.3oC

42.3oC

I0 /I

21000

R² = 0.9972

10

R² = 0.9989

51.9oC

34.9 44.8

8 6

51.9oC

24.8

R² = 0.9892

14

R² = 0.9765

54.8

4

19500

65.6

2 0

19000 2000 Time (s)

3000

0

4000

Fig. 4. Reversibility and total signal change of the optical temperature sensor.

temperature using the optical fiber dual sensor developed in this work can be obtained by using the attenuation of the relative luminescence signal as a sensing signal. Fig. 3 shows the linear calibration curve using the data from Fig. 2. Fig. 4 illustrates the response of the CF based optical temperature sensor. As shown in Fig. 4, the changes in relative luminescence intensity correlate directly with temperature and are fully reversible between the temperature range of 23–52 ◦ C for two cycles. 3.2. Oxygen sensing properties of the optical dual sensor

18000

Oxygen Sensing Signal

16000

0%

14000

20%

12000 10000 8000 6000

Temperature Sensing Signal

Increasing O2

Relative Luminescence Intensity (a.u.)

Fig. 5 shows the relative luminescence spectra of the plastic optical fiber dual sensor, under five different temperatures and six different oxygen concentrations. Note that in recording the luminescence intensity, the integration time of the CCD spectrometer was set to 80 ms. As can be seen in the figure, the spectral separation of the emission band occurred at 540 nm of the CF (temperature indicator) and 650 nm of the PtTFPP-doped sensor (oxygen indicator). The optical fiber dual sensor is excited by a 405 nm LED, and the two emissions of the temperature and oxygen sensors have no spectral overlaps or cross-talk. Fig. 4 shows that the two emissions are very well resolved, and thus the temperatures and oxygen concentrations can be independently monitored. Fig. 5 also shows that the emission spectrum of PtTFPP at 650 nm is highly sensitive to the concentration of oxygen, with nearly complete quenching at 100% oxygen, while the emission of the CF temperature sensor at 540 nm has no oxygen sensitivity, even at 100% oxygen.

40% 60% 80%

4000 2000

100%

20

40 60 80 Oxygen Concentration (%)

100

Fig. 6. Stern–Volmer plots for optical dual sensor with the oxygen concentration ranging from 0% to 100% and the temperature from 24.8 to 65.6 ◦ C.

Fig. 6 presents the Stern–Volmer plots for the oxygen sensitivity in the optical dual sensor system, and these were obtained by determining the relative luminescence intensity at six different oxygen concentrations (0–100%) and five different temperatures (ranging from 24.8 to 65.6 ◦ C). The relative luminescence intensity is dependent on both oxygen and temperature. However, in the simplest scenario of a luminophore in a homogeneous microenvironment, quenching takes place in accordance with the Stern–Volmer equation [35], i.e. I0 = 1 + Ksv [O2 ] I

(1)

where I0 and I represent the steady-state luminescence intensities in the absence and presence of O2 , respectively; Ksv is the Stern–Volmer quenching constant; [O2 ] is the O2 concentration. For this ideal case, a plot of I0 /I vs. [O2 ] will be linear with a slope equal to Ksv and an intercept of unity. Moreover, the Stern–Volmer plots in this study provide an indication of the relative sensitivity of the sensor to O2 quenching, and these are linear. As shown in Fig. 6, the ratio I0 /I (where I0 and I are the luminescence intensities in the absence of oxygen and in the presence of oxygen, respectively) is plotted for six different oxygen concentrations ranging from 0 [% vol] to 100 [% vol] and five different temperatures, ranging from 24.8 to around 65.6 ◦ C. It can be seen that the sensitivity of optical oxygen sensor increases along with the ambient temperature. The PtTFPP-doped sensor has a dynamic quenching behavior. Dynamic quenching depends upon 10000 9000

Oxygen Sensing Signal

8000

0%

7000

20%

6000 5000 4000 3000

Temperature Sensing Signal

Increasing O2

1000

0

Relative Luminescence Intensity (a.u.)

Relative Luminescence Intensity (a.u.)

22000

40% 60%

2000

80%

1000

100%

0

0 450

550 650 Wavelength (nm)

(a)

750

450

550 650 Wavelength (nm)

750

(b)

Fig. 5. Emission spectra of the optical fiber dual sensor as a function of oxygen concentration, 540 nm for the temperature sensor and 650 nm for oxygen sensor both at (a) 24.8 ◦ C and (b) 65.6 ◦ C.

Relative Fluorescence Intensity (a.u.)

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4000 3500

100% N2

3000 2500 2000 1500 1000

100% O2

500 0 0

200

400

600

800

1000

1200

Time (s) Fig. 7. Variation of relative luminescence intensity decay of the optical dual sensor with ambient temperature as function of oxygen concentration.

Fig. 8. Changes in the response time and luminescence intensity of the optical fiber dual sensor for oxygen sensing when switching between 100% nitrogen and 100% oxygen.

3.3. Photostability and long-term stability of optical dual sensor diffusion. Since higher temperatures result in enhanced diffusion coefficients, the bimolecular quenching constants increase with increasing temperature [35]. The luminescence of the CF temperature sensor is clearly not oxygen dependent, in contrast to the strong oxygen dependence of the luminescence of PtTFPP. The dependence of the luminescence intensity of the PtTFPP on the ambient temperature as a function of oxygen concentration for the PtTFPP/CF-doped TEOS/Octyl-triEOS sensor is shown in Fig. 7. It can be seen that the relative luminescence intensity of PtTFPP decreases with increasing temperature and oxygen concentration. This relationship between the temperature and the luminescence intensity decay enables the oxygen measurements to be corrected at different temperatures. Fig. 8 demonstrates the typical dynamic response of the optical fiber dual sensor for oxygen sensing when switching between fully oxygenated and fully de-oxygenated gases. In order to follow the dynamic behavior of the optical fiber dual sensor probe, the integration time for the CCD spectrometer was set at 10 ms. The response times t95 of the PtTFPP film were 6.7 s upon switching from nitrogen to oxygen and 46.6 s when moving from oxygen to nitrogen. As illustrated in Fig. 8, stable and reproducible signals were obtained when the optical fiber dual sensor was used for oxygen sensing.

The photostability of optical oxygen sensors with respect to dye leaching is always a major concern to practical applications. To evaluate the photostability of the optical dual sensor developed herein, the optical dual sensor was continuously illuminated using an LED light source with 405 nm wavelength in the gas and aqueous phases. Note that in acquiring the relative phosphorescence intensity data, the integration time of the CCD spectrometer was set at 80 ms. After continuous illumination for around 14 h, the relative luminescence intensities of PtTFPP and CF sensing signal in the gas phase are 8529 ± 102 and 3330 ± 75, respectively. Fig. 9(a) shows that the proposed optical dual sensor using the PtTFPP/CF film is highly stable in the gas phase. Fig. 9(b) shows that the relative luminescence intensity of PtTFPP sensing signal in aqueous phase decreased by almost 6% after continuous illumination for around 11 h. Taking such photostability into consideration, the optical dual sensor is photostable enough over its operational timescale in the real experiments. The interference from other gaseous species to performance of the optical dual sensor is investigated. Fig. 10 shows the optical dual sensor exposed to the HCl gas. After continuous illumination for around 11 h, the relative luminescence intensity of PtTFPP sensing signal in HCl gas decreased by almost 86%. However, there is no

Fig. 9. Photostability of optical dual sensor in (a) gas and (b) aqueous phase.

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the relative luminescence intensity for temperature sensing has a linear relationship with temperature in the tested range. As compared to the existing schemes, the sensor’s sensing signals are well resolved and the luminescence of the CF temperature sensor has no oxygen dependence, in contrast to the strong oxygen dependence of the luminescence of PtTFPP. Nevertheless, the plastic optical fiber dual sensor can only be operated up to around 70 ◦ C. In conclusion, the plastic optical fiber sensor developed in this paper enables simultaneous and contactless sensing of temperature and oxygen, and may be used, for example, for the temperature compensated sensing of oxygen, in high resolution oxygen profiling, and in a variety of biological and medical applications. Acknowledgement

Fig. 10. Photostability of optical dual sensor in HCl gas.

References

14 12 10 IN2 / IO2

The authors gratefully acknowledge the financial support provided to this study by the National Science Council of Taiwan under Grant No. NSC102-2221-E-131-013.

8 6 4 2 0 0

2

4

6

8 10 12 14 16 18 20 22 24 26 28 Aging time (weeks)

Fig. 11. Effects of aging on the average optical sensor response stability.

luminescence intensity change of CF sensing signal was observed when the PtTFPP/CF-doped sensor is exposed to HCl gas. Thus, the present optical dual sensor is interfered from the acid gas such as HCl gas. Fig. 11 shows the effects of aging time on the optical sensors’ response stability. After being stored without light for 28 weeks, no significant change of quenching properties could be observed. This sol–gel sensor benefits from the excellent mechanical properties and high stability of the inorganic glass matrix. Especially because the acid-catalyzed sol–gel is superior to the base-catalyzed gel in mechanical stability, stable and reproducible signals can be obtained with the former [36]. The results show that the PtTFPP/CFdoped sensor based on the Octyl-triEOS/TEOS composite xerogels exhibit good long-term stability. 4. Conclusions In this work we presented that a simple, low cost technique to fabricate a plastic optical fiber sensor for dual sensing of temperature and oxygen. The optical fiber dual sensor was constructed by using CF and platinum complex (PtTFPP) as the fluorescent indicators for temperature and oxygen, respectively. Both indicators can be excited by the same 405 nm LED, and their bright luminescence has no spectral overlaps or cross-talk, and thus the temperature and oxygen concentrations can be independently monitored. The typical Stern–Volmer plot of the optical fiber dual sensor for oxygen sensing shows linearity, and the attenuation of

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Biographies Cheng-Shane Chu received his M.S. and Ph.D. degrees from the Mechanical Engineering Department at National Cheng Kung University, Taiwan, ROC, in 2004 and 2009, respectively. He has been a member of the Mechanical Engineering Department, Ming Chi University of Technology, since 2010, where he is now an assistant professor. His research interests include the optical techniques in precision measurements, development, optimization, and characterization of novel optical sensors for industrial, biological, and environmental applications. Che-An Lin received his B.S. degree in Mechanical Engineering from Tungnan University, Taiwan, in 2011. He is currently working toward the M.S. degree in mechanical engineering from Ming Chi University of Technology, Taipei, Taiwan. His research interests in the areas of optical fiber sensors and optical measurement.