Fabrication of a needle-type pH sensor by selective electrodeposition

Abstract

Abstract. This manuscript reports on the development of a needle-type sensor for in situ on-site measurement of pH. Conventional pH microelectrode sensors are fabricated by pulling glass pipettes and applying ion-selective films at the tip. However, these sensors suffer from low fabrication yields and short sensor lifetime due to disruption or loss of the ion-selective membrane after repeated use. The developed needle-type sensor is fabricated by meniscus etching and takes advantage of the MEMS batch fabrication techniques. The sensor is based on the ion-selective properties of iridium oxide film, which was deposited at the sensor tip by electrodeposition. The sensor exhibited a Nernstian response with sensitivity of ∼62 mV/pH in the pH 2 to 12 range. The sensor also exhibited a fast 5 s response and a lifetime of ∼2 months when stored in a pH7 buffer solution, which is substantially longer than that of the conventional pulledpipette sensors. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

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“…Iridium oxide (IrOx) was electrochemically deposited onto the gold microneedles using a slight modification of a previously reported protocol. 40,41 In practice, 62.7 mg of K 3 IrCl 6 were dissolved in 30 mL of deionized water, then 87.0 mg of oxalic acid were added to the mixture followed by 331.7 mg of K 2 CO 3 . The mixture was stirred at 800 rpm and heated up using a water bath maintained at 60 °C.…”

Microneedle pH Sensor: Direct, Label-Free, Real-Time Detection of Cerebrospinal Fluid and Bladder pH

“…Besides that, the small dimensions of the sensor could be used for more-precise pH measurements in controlled environments such as brain fluid and the intestine and bladder without taking out the samples externally. 12 In recent days, microneedle-type sensors fabricated in number of ways, such as laser micromachining, selective electrodeposition, 13 reactive ion−wet−dry etching, laser ablation, laser cutting, etc. 14 So far, most of the microneedles based on various nanostructures have been developed for drug delivery and glucose sensors.…”

“…Choi et al developed needle-type pH sensors by selective electrodeposition and used iridium oxide as the sensing element. 13 In addition, a boron-doped diamond microelectrode developed by Fierro et al could be used to identify stomach disorders. 15 These fabrication methods exhibit a number of inherent disadvantages such as poor reproducibility, difficulty in making contacts, fragility, etc.…”

“…However, recent works shows that microneedle-based electrodes can be used for pH detection too. Choi et al developed needle-type pH sensors by selective electrodeposition and used iridium oxide as the sensing element . In addition, a boron-doped diamond microelectrode developed by Fierro et al could be used to identify stomach disorders .…”