A flexible pH sensor based on the iridium oxide sensing film

Huang, Wendeng; Cao, Hung; Deb, Sanchali; Chiao, Mu; Chiao, Jung-Chih

doi:10.1016/j.sna.2011.05.016

Cited by 301 publications

(223 citation statements)

References 45 publications

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“…Changes in the absorbance spectra of the PAni coatings as different pH solutions flushed inside the microchannel were 80 recorded using two fiber-optic light guides connected to a Miniature Fiber Optic Spectrometer (USB4000 -Ocean Optics)…”

Section: Measurement Of Absorbance Spectra Of Pani Coatingsmentioning

confidence: 99%

Dynamic pH mapping in microfluidic devices by integrating adaptive coatings based on polyaniline with colorimetric imaging techniques

et al. 2013

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In this paper we present a microfluidic device that has integrated pH optical sensing capabilities based on polyaniline. The optical properties of polyaniline coatings change in response to the pH of the solution that is flushed inside the microchannel offering the possibility of monitoring pH in continuous flow over a wide pH range throughout the entire channel length. This work also features an innovative detection 10 system for spatial localisation of chemical pH gradients along microfluidic channels through the use of a low cost optical device. Specifically, the use of a microfluidic channel coated with polyaniline is shown to respond colorimetrically to pH and that effect is detected by the detection system, even when pH gradients are induced within the channel. This study explores the capability of detecting this gradient by means of imaging techniques and the mapping of the camera's response to its corresponding pH after a 15 successful calibration process. The provision of an inherently responsive channel means that changes in the pH of a sample moving through the system can be detected dynamically using digital imaging along the entire channel length in real time, without the need to add reagents to the sample. This approach is generic and can be applied to other chemically responsive coatings immobilised on microchannels. Introduction 20Conventional glass-type electrodes have been widely used for pH measures for many years in both industry and academic areas. However, in terms of specific applications (e.g. in vivo, food industry, or for clinical applications), they posses several disadvantages due to their size constraints, rigidity, and the 25 inflexibility of the glass electrode. In recent years, a wide number of pH sensors have been developed to overcome these limitations, including ion sensitive field-effect transistor (iSFET) pH sensors 1-4 , optical pH sensors based on pH responsive dyes 5-8 , hydrogel film pH sensors 9, 10 , and solid-state metal oxides pH sensors 11-13 . 30 In particular, optical pH sensors present several advantages over the traditional pH electrodes as such their low costs, immunity from electromagnetic field, absence of electric contacts, possibility of reference electrode removal and a high degree of miniaturisation 14 . Optical fiber-based pH sensors have been 35 particularly popular, as the fibre allows the optical signal to be transported over long distances, which can facilitate applications in remote sensing 15 .Usually, these optical pH sensors (or optrodes) employ a dye or an indicator that requires immobilisation onto a solid support 40 material. There are several critical issues related to this approach: firstly, the dye should retain its optical properties after the immobilisation process 16 and secondly, it should not leach into the solution 17. A third issue of practical importance is their inherently narrow dynamic response range which is usually 45 around 3-4 pH-units centred on the dye´s pKa 18 .Therefore, the further improvement of such sensors focuses...

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Section: Measurement Of Absorbance Spectra Of Pani Coatingsmentioning

confidence: 99%

Dynamic pH mapping in microfluidic devices by integrating adaptive coatings based on polyaniline with colorimetric imaging techniques

et al. 2013

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“…The electrochemical potentials at the same pH level may be different due to various factors, such as different oxidation states and the degree of hydration on the film surfaces, which may establish a new equilibrium of ions every time in the redox reactions at different times of testing [5,64]. In potentiometric measurements, it is represented in mV.…”

Section: Hysteresismentioning

confidence: 99%

“…To evaluate the reversibility, the pH sensor potential is measured in different pH solutions in the acid-to-base direction and vice versa [5,21].…”

Section: Reversibilitymentioning

confidence: 99%

“…The well-known glass electrode is the most commonly used pH sensor because of desirable characteristics, such as good sensitivity, stability, and long lifetime [5,6]. However, traditional glass electrodes have many disadvantages, such as high cost, mechanical fragility, difficult to miniaturize, need for wet storage, large size and limited shape.…”

Section: Introductionmentioning

confidence: 99%

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Recent Developments in R.F. Magnetron Sputtered Thin Films for pH Sensing Applications—An Overview

2014

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pH sensors are widely used in chemical and biological applications. Metal oxides-based pH sensors have many attractive features including insolubility, stability, mechanical strength, electrocatalyst and manufacturing technology. Various metal oxide thin films prepared by radio frequency (R.F.) magnetron sputtering have attractive features, including high pH sensitivity, fast response, high resolution, good stability and reversibility as well as potential for measuring pH under conditions that are not favourable for the commonly used glass electrodes-based pH sensors. In addition, thin film pH sensors prepared by R.F. magnetron sputtering offer many advantages, such as ease of packaging, low cost through the use of standard microfabrication processes, miniaturisation, capability of measuring pH at high temperatures, ruggedness and disposability. In this paper, recent development of R.F. magnetron sputtered thin films for pH sensing applications are reviewed.

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“…Concerning potentiometric sensors, Iridium/Iridium oxide (IrO x ) electrodes showed promising results in aqueous solution [12][13][14][15] in terms of high stability in a broad pH range, accuracy, and insensitivity to the oxygen content. Moreover, the size of the sensors is relatively small, i.e., wire diameters are <1mm, and thus permit high spatial resolution for the application in concrete.…”

Section: Introductionmentioning

confidence: 99%

PH-monitoring in mortar with thermally-oxidized iridium electrodes

2017

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The pH of the concrete pore solution plays a vital role in protecting the reinforcing steel from corrosion. Here, we present results from embeddable pH sensors that permit the continuous, in-situ monitoring of the pH in the concrete pore solution. These are potentiometric sensors, based on thermallyoxidized iridium/iridium oxide (IrO x ) electrodes. We propose an iterative calculation algorithm taking into account diffusion potentials arising from pH changes, thus permitting the reliable, non-destructive determination of the pore solution pH over time. This calculation algorithm forms an essential part of the method using IrO x electrodes. Mortar samples were exposed to accelerated carbonation and the pH was monitored at different depths over time. Comparative tests were also performed using thymolphthalein pH-indicator. The results from the pH sensors give insight in the carbonation process, and can, in contrast to thermodynamic modelling and titration experiments, provide insight in kinetic processes such as transport and phases transformations. It was found that the front at which the pH is decreased from initially 13-14 down to 12.5 can be significantly ahead of the common carbonation front corresponding to pH 9-10. This has major implications for laboratory testing and engineering practice.

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A flexible pH sensor based on the iridium oxide sensing film

Cited by 301 publications

References 45 publications

Dynamic pH mapping in microfluidic devices by integrating adaptive coatings based on polyaniline with colorimetric imaging techniques

Dynamic pH mapping in microfluidic devices by integrating adaptive coatings based on polyaniline with colorimetric imaging techniques

Recent Developments in R.F. Magnetron Sputtered Thin Films for pH Sensing Applications—An Overview

PH-monitoring in mortar with thermally-oxidized iridium electrodes

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