Materials Science and Engineering C 57 (2015) 304–308
Contents lists available at ScienceDirect
Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec
Design of an optically stable pH sensor based on immobilization of Giemsa on triacetylcellulose membrane Saeid Khodadoust a, Narges Cham Kouri b, Mohammad Sharif Talebiyanpoor c,⁎, Jamile Deris b, Arezou Amiri Pebdani d a
Department of Chemistry, Behbahan Khatam Alanbia University of Technology, Behbahan, Iran Abadan School of Medical Sciences, Abadan, Iran Medicinal Plants Research Center, Yasuj University of Medical Science, Yasuj, Iran d Behbahan Faculty of Medical Sciences, Behbahan, Iran b c
a r t i c l e
i n f o
Article history: Received 11 March 2015 Received in revised form 1 July 2015 Accepted 27 July 2015 Available online 2 August 2015 Keywords: pH optical sensor Giemsa Triacetylcellulose membrane
a b s t r a c t In this work a simple, inexpensive, and sensitive optical sensor based on triacetylcellulose membrane as solid support was developed by using immobilization of Giemsa indicator for pH measurement. In this method, the influence variables on the membrane performance including pH concentration of indicator, response time, ionic strength, and reversibility were investigated. At optimum values of all variables the response of optical pH sensor is linear in the pH range of 3.0–12.0. This optical sensor was produced through simultaneous binding of the Giemsa on the activated triacetylcellulose membrane which responded to the pH changes in a broader linear range within less than 2.0 min and suitable reproducibility (RSD b 5%). Stability results showed that this sensor was stable after 6 months of storage in the water/ethanol (50:50, v/v) solution without any measurable divergence in response properties (less than 5% RSD). © 2015 Elsevier B.V. All rights reserved.
1. Introduction In recent years, optical chemical sensors have been investigated for their use in different knowledge fields. Especially, these kinds of sensors suggest many advantages over the traditional systems, because they offer the capacity of operating in hostile and dangerous environments [1–4]. The study of these sensors is attractive since they allow us to perform in vivo analysis and in situ monitoring. Chemical sensor technology involves the key processes of chemical recognition of the analytes of interest and subsequent transduction of the analytical signal. An ideal optical sensor must have the ability to measure the concentration of an analyte continuously and reversibly through changes in the optical properties of the sensing reagents. To date, this ability has been based on the availability of suitable, long-lasting reversible chemical reactions. In recent years, numerous efforts have been directed toward the development of optic pH sensors. pH monitoring is one of the most important parameters in many industrial processes such as in food, pharmaceutical, water and wastewater. Therefore, continuous online pH control in many manufacturing processes is essential [4–7]. pH determination is done using three methods including electrochemical and photochemical sensors and pH test paper strips. Although the pH test paper strip is simple and inexpensive, it was not used in high accuracy cases. In ⁎ Corresponding author. E-mail address:
[email protected] (M.S. Talebiyanpoor).
http://dx.doi.org/10.1016/j.msec.2015.07.056 0928-4931/© 2015 Elsevier B.V. All rights reserved.
recent years, the development of electrochemical and optical sensors has attracted great interest that indicates the importance of this field in various sciences [5–10]. Conventionally, electrochemical devices such as electrolyte-filled glass electrode and semiconductor devices have been utilized. Compared to traditional pH detection methods, an optical pH sensor has many advantages, such as immunity to electrical interference, fast response, safety and possibility of micro-area measurement. Some of the optical pH sensors are based on the immobilization of a pH sensitive organic dye that is deposited on the flat face of the fiber or around a conventional one. The organic dye is supported typically by a sensing membrane. This kind of sensor bases its operation on the evanescent wave absorption when the ions present in the solution under test interact with the organic dye in the sensing membrane. A pH optical sensor is based on pH dependent change of the absorbance or luminescence of certain indicator molecules immobilized on/in certain solids [8–11]. The development of optical pH sensors can provide an accessible and rapid method for routine environmental measurements [12–17]. In this work, Giemsa dye immobilized on activated transparent triacetylcellulose membrane was used as a novel pH optical sensor [18]. Because this complexation reaction is pH dependent, it can be applied as a relatively selective reagent for H3O+ ion and absorbance spectrum of this optical sensor was monitored at different pH levels. Parameters affecting the performance of the sensor, such as pH of dye bonding to triacetylcellulose membrane and dye concentration, were
S. Khodadoust et al. / Materials Science and Engineering C 57 (2015) 304–308
305
Scheme 1. Activation process of triacetylcellulose.
also investigated and optimized. The proposed pH sensor has a linear and reproducible pH response in the pH range from 3.0 to 12.0. 2. Experimental
distilled/deionized water (produced by a Milli-Q system (Millipore, Bedford, MA, USA)) and ethanol (50:50 V/V). The pH buffer solutions were prepared from sodium perchlorate/perchloric acid (0.01 mol L−1 of each). The final pH was adjusted by adding 1.0 mol L−1 hydrochloric acid or sodium hydroxide solutions.
2.1. Chemicals and reagents 2.2. Instrumentation All chemicals were of the best available analytical reagent grade and all solutions were prepared with double distilled water. Giemsa, hydrochloric acid, sodium hydroxide, sodium perchlorate, and methanol were purchased from Merck (Darmstadt, Germany). The stock solution (0.1 M) of Giemsa was prepared in methanol. The working solutions were prepared by appropriate dilution of the stock solution with double
A Metrohm 827 pH-meter with a Metrohm double junction glass electrode was used for monitoring pH adjustment. A double beam spectrophotometer (PG Instruments, model T80+ UK) was used for absorbance determination. Absorbance data were obtained using a designed cell replaced in the cell holder of a spectrophotometer
Scheme 2. Possible scheme of reaction between Giemsa and activated membrane.
306
S. Khodadoust et al. / Materials Science and Engineering C 57 (2015) 304–308
instrument. The pH sensors were placed between the two plates of the cell. The sensing membrane was placed and fixed in the designed cell and all measurements were performed in a batch mode. 2.3. Activation of the triacetylcellulose membrane Triacetylcellulose film was cut into pieces with suitable size and stored in the water/ethanol (50:50, v/v) solution. The transparent triacetylcellulose membranes were produced from waste photographic film tapes that were previously treated with commercial sodium hypochlorite (0.1 mol L−1: activation process) for several seconds in order to remove colored gelatinous layers. The membrane pieces were treated with 1.0 mol L−1 sodium hydroxide (24 h) for its partial deacetylation, and then washed with a large amount of distilled water in order to remove the hydroxide. The partly deacetylated membrane was treated with 0.5 mol L−1 sodium periodate at 4 °C in 0.1 mol L−1 acetate buffer with pH 4.0 for 1 h in the darkness. After that, the membrane was carefully washed with distilled water. The oxidized membrane was further treated with 15% NH2CONH2 for 10 to 10 h in the presence of 0.5% sulfuric acid at 50 °C in a water bath with continuous shaking. The urea derivative formed on the cellulose membrane was stable. After careful washing with distilled water, the membrane was treated with 20% formaldehyde at 40 °C for 10 h in 0.1 mol L−1 phosphate buffer (pH 7.5) in a water bath with continuous shaking [19–21]. After repeated washing with distilled water the activated membrane was used in the subsequent work. The schematic diagram of the activation process is shown in Scheme 1.
(3.0–12.0). Due to the protonation of Giemsa indicator at lower pH than 3.0 and competition of OH− ion with H3O+ ion at basic media, the repeatability of the sensor response to pH was not suitable at lower pH than 3.0 and higher than 12.0. The absorbance maxima of the immobilized Giemsa are located at 711 nm. In order to perform pH monitoring the wavelength of 771 nm was selected for further studies because of higher selectivity and sensitivity at this wavelength. As can be seen in Fig. 1 with the increase in solution pH, the absorbances of sensor and solution were decreased. However, the absorbance changes of the optical sensor by pH variation are greater than by the soluble form. This behavior increases the sensitivity of the optical sensor. On the other hand, Giemsa solution is used as pH indicator in acidic medium while the immobilized Giemsa can be used in a wider pH range (3.0–12.0). Therefore, the optimum pH was selected at pH = 3. However, the absorbance changes of the optical sensor by pH variation are greater than by the soluble form.
2.4. Preparation of the sensor membrane The immobilized indicator on the triacetylcellulose membrane was prepared according to the following procedure. The activated membranes washed with deionized water and then stored in the water/ethanol (50:50, v/v) solution. These films were treated with a clear solution of Giemsa in 10 mL sodium perchlorate (0.01 mol L−1: pH 4) for 2 min at ambient temperature. Then they were washed with water to remove excess sodium perchlorate and the loosely trapped indicator. The membranes were finally washed with detergent solutions and rinsed with water. Prepared membranes were kept under water when not in use. The possible covalent binding mechanism of Giemsa to activated triacetylcellulose membrane is illustrated in Scheme 2. 3. Results and discussion 3.1. Spectra of the sensor's membrane Fig. 1 shows the absorbance spectra of immobilized Giemsa on hydrolyzed triacetylcellulose film and aqueous solution at different pHs
Fig. 1. Absorbance of the proposed optical sensor at 711 nm at different pHs. The dye concentration was 10−8 mol L−1 in solution.
Fig. 2. Effect of salt concentration on the sensor response at three pH levels (3.0, 5.5 and 8.0), a) NaCl b) Na3PO4 and c) NaH2PO4.
S. Khodadoust et al. / Materials Science and Engineering C 57 (2015) 304–308
307
Fig. 5. Repeatability, reversibility optical sensor at pH buffer 3.0, 8.0 and 12.0 at 711 nm. Fig. 3. Calibration curve of the optical sensor at 711 nm.
3.4. Response time and reproducibility 3.2. Effect of ionic strength One of the most important characteristics of an optical membrane sensor is its relative response toward other ions that are present in the solution. For this purpose, the effect of salt concentration on the sensor response was examined at three pH levels (3.0, 5.5 and 8.0) using sodium chloride, sodium phosphate, and sodium dihydrogen phosphate concentrations in the range of 0.0 to 1.0 mol L−1. The obtained results (Fig. 2) indicated that the sensor response was approximately constant with increasing the ionic strength in the range of 0.0-1.0 mol L− 1 of mention electrolytes. 3.3. Calibration curve Fig. 3 shows a typical calibration curve derived from absorbance measurement of the activated membrane at 711 nm in pH range of 3.0–12.0. As the pH increases, the absorbance decreases. The absorbance of triacetylcellulose membrane varies almost linearly, with an equation of y ¼ ‐0:0801x þ 1:1559 and the coefficient of determination (R2) is 0.9973. It shows that triacetylcellulose membrane has a wide dynamic range with straight line fitted to the experimental data. We also measured the absorbance of triacetylcellulose membrane at pH value lower than 3.0 and higher than 12.0. Both the absorbances of these two regions at 711 nm did not match the tendency mentioned above.
An important analytical feature of any optode is its response time and reproducibility. The response time of the present optode is controlled by the time required for the analyte to diffuse from the bulk of the solution to the membrane interface and to interact with the indicator [15–19]. Response time of the optical sensor was determined using absorption data at 711 nm and obtained results are shown in Fig. 4. As shown in Fig. 4, the absorbance reaches 90% of the steady-state signal in about 2 min. Therefore, 2 min was selected as the response time of this optical sensor. Reproducibility of the sensor was examined by using six similarly constructed sensors under the optimum conditions. The result showed good reproducibility in response of the proposed sensor (RSD ≤ 5%). Fig. 5 shows the results obtained for a period of 15.0 min. Relative standard deviations (RSDs) of results were less than 5%. In order to investigate the lifetime of the sensor membranes, they were maintained in water/ethanol (50:50, v/v) for 6 months. No significant variation in sensor response was observed during this period, which indicated that the membrane was stable over this period. 4. Conclusion In the present study, the application of Giemsa indicators immobilized on the activated triacetylcellulose membrane as a suitable pH sensor was investigated. This sensor exhibits advantages over many existing optical pH sensors including wider dynamic pH range, ease of fabrication, good reversibility and stability. Stability results showed that the sensor was stable after 6 months of storage in the water/ethanol (50:50, v/v) solution with RSD ≤ 5%. The calibration curve of this sensor was linear in the pH range of 3.0–12.0; high stability and good repeatability were the other distinctive features of this sensor. Acknowledgments The authors would like to acknowledge the support of Medicinal Plants Research Center, Yasuj University of Medical Science. References
Fig. 4. Response time of the proposed optical sensor at different pHs (3.0–12.0).
[1] Z. Liu, J. Liu, T. Chen, Phenol red immobilized PVA membrane for an optical pH sensor with two determination ranges and long-term stability, Sensors Actuators B 107 (2005) 311–316. [2] A. Anderson, J. Phair, J. Benson, B. Meenan, J. Davis, Investigating the use of endogenous quinoid moieties on carbon fibre as means of developing micro pH sensors, Mater. Sci. Eng. C 43 (2014) 533–537. [3] H. Hisamato, M. Tsubuku, T. Enomoto, K. Watanabe, H. Kawaguchi, Y. Koike, K. Suzuki, Theory and practice of rapid flow-through analysis based on optode detection and its application to pH measurement as a model case, Anal. Chem. 68 (1996) 3871–3878. [4] M. Hosseini, R. Heydari, M. Alimoradi, A novel pH optical sensor using methyl orange based on triacetyl cellulose membranes as support, Spectrochim. Acta A 128 (2014) 864–867.
308
S. Khodadoust et al. / Materials Science and Engineering C 57 (2015) 304–308
[5] M. Fritzsche, G. Barreiro, G. Hitzmann, B. Scheper, Optical pH sensing using spectral analysis, Sensors Actuators B 128 (2007) 133–137. [6] W. Gao, J. Song, Polyaniline film based amperometric pH sensor using a novel electrochemical measurement system, Electroanalysis 21 (2009) 973–978. [7] S. Zaman, M.H. Asif, A. Zainelabdin, G. Amin, O. Nur, M. Willander, CuO nanoflowers as an electrochemical pH sensor and the effect of pH on the growth, J. Electroanal. Chem. 662 (2011) 421–425. [8] X. Yang, Y. Gao, Z. Huang, X. Chen, Z. Ke, P. Zhao, Y. Yan, R. Liu, J. Qu, Fluorescent probe based on heteroatom containing styrylcyanine: pH-sensitive properties and bioimaging in vivo, Mater. Sci. Eng. C 52 (2015) 97–102. [9] H.X. Chena, X.D. Wanga, X.H. Songa, T.Y. Zhoua, Y.Q. Jianga, X. Chen, Colorimetric optical pH sensor production using a dual-color system, Sensors Actuators B 146 (2010) 278–282. [10] N. Raoufi, F. Surre, T. Sun, M. Rajarajan, K.T.V. Grattan, Wavelength dependent pH optical sensor using the layer-by-layer technique, Sensors Actuators B 169 (2012) 374–381. [11] C.R. Zamarreño, M. Hernáez, I. Del Villar, I.R. Matías, F.J. Arregui, Optical fiber pH sensor based on lossy-mode resonances by means of thin polymeric coatings, Sensors Actuators B 155 (2011) 290–297. [12] A. Safavi, M. Sadeghi, Development of an optode membrane for high pH values, Spectrochim. Acta A 66 (2007) 575–577. [13] J.I. Peterson, S.R. Goldstein, R.V. Fitzgerald, Fiber optical pH probe for physiological use, Anal. Chem. 52 (1980) 864–869.
[14] G. Beltrán-Pérez, F. López-Huerta, S. Muńoz-Aguirre, J. Castillo-Mixcóatl, R. Palomino-Merino, R. Lozada-Morales, O. Portillo-Moreno, Fabrication and characterization of an optical fiber pH sensor using sol-gel deposited TiO2 film doped with organic dyes, Sensors and Actuators B 120 (2006) 74–78. [15] M. Ghaedi, J. Tashkhourian, M. Montazerozohori, A. Amiri Pebdani, S. Khodadoust, Design of an efficient uranyl ion optical sensor based on 1′-2,2′-(1,2-phenylene) bis(ethene-2,1-diyl)dinaphthalen-2-ol, Mater. Sci. Eng. C 32 (2012) 1888–1892. [16] O.B. Miled, H.B. Ouada, J. Livage, pH sensor based on a detection sol–gel layer onto optical fiber, Mater. Sci. Eng. C 21 (2002) 183–188. [17] P. Hashemi, R. Afzari Zarjani, M.M. Abolghasemi, Agarose film coated glass slides for preparation of pH optical sensors, Sensors Actuators B 121 (2007) 396–400. [18] C.J.W. Meulenberg, M. Cemazar, Low-magnification image analysis of Giemsa stained, electroporation and bleomycin treated endothelial monolayers provides reliable monolayer integrity data, Toxicol. in Vitro 28 (2014) 502–509. [19] Y. Kostov, S. Tzonkov, Membranes for optical pH sensors, Anal. Chim. Acta 280 (1993) 15–19. [20] A. Abbaspour, L. Baramakeh, Novel zirconium optical sensor based on immobilization of Alizarin Red S on a triacetylcellulose membrane by using principle component analysis artificial neural network, Sensors Actuators B 114 (2006) 950–956. [21] A. Afkhami, N. Sarlak, A novel cyanide sensing phase based on immobilization of methyl violet on a triacetylcellulose membrane, Sensors Actuators B 122 (2007) 437–441.
