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Acid-base homeostasis (body pH) inside the body is precisely controlled by the kidneys and lungs and buffer systems, such that even a minor pH change could severely affect many organs. Blood and urine pH tests are common in day-to-day clinical trials and require little effort for diagnosis. There is always a great demand for in vivo testing to understand more about body metabolism and to provide effective diagnosis and therapy. In this article, we report the simple fabrication of microneedle-based direct, label-free, and real-time pH sensors. The reference and working electrodes were Ag/AgCl thick films and ZnO thin films on tungsten (W) microneedles, respectively. The morphological and structural characteristics of microneedles were carefully investigated through various analytical methods. The developed sensor exhibited a Nernstian response of -46 mV/pH. Different conditions were used to test the sensor to confirm their accuracy and stability, such as various buffer solutions, with respect to time, and we compared the reading with commercial pH electrodes. Besides that, the fabricated microneedle sensor ability is proven by in vivo testing in mouse cerebrospinal fluid (CSF) and bladders. The pH sensor procedure reported here is totally reversible, and results were reproducible after several rounds of testing.

The present study is concerned about the development of highly sensitive and stable microfluidic pH sensor for possible identification of circulating tumor cells (CTCs) in blood. The precise pH measurements between silver-silver chloride (Ag/AgCl) reference electrode and zinc oxide (ZnO) working electrode have been investigated in the microfluidic device. Since there is a direct link between pH and cancer cells, the developed device is one of the valuable tools to examine circulating tumor cells (CTCs) in blood. The ZnO-based working electrode was deposited by radio frequency (rf) sputtering technique. The potential voltage difference between the working and reference electrodes (Ag/AgCl) is evaluated on the microfluidic device. The ideal Nernstian response of -43.71165 mV/pH was achieved along with high stability and quick response time. Finally, to evaluate the real time capability of the developed microfluidic device, in vitro testing was done with A549, A7r5, and MDCK cells.

In recent years, mental disorders has become serious problem caused by excessive stress. Globally more than 60% of workers are testified to be in stress during work hours. The common diagnostic tools for measuring stress are an electroencephalogram (EEG), body temperature, an electrocardiogram (ECG) and self-questionnaire. Though thee measurement techniques are sensitive enough to identify stress, they are quite complex and poorly suitable for point of care (POC) testing. In addition, salivary alpha amylase measurement is commonly used for stress evaluation. However, it’s unsuitable for continuous measurement of the enzyme activity. Fortunately there is a link between the pH and stress levels of the body. Therefore in this study we aim to continuously monitor the pH fluctuation in an oral cavity using mouthpiece pH sensor. Although, electrolyte free Ag/AgIO 3 reference electrode method facilitated us to make the miniaturized pH sensor. Initially for calibration experiments were done using standard pH buffer solutions (pH4.01, pH5.00, pH6.00 and pH7,01) using Ag/AgIO 3 reference electrode and antimony (Sb) electrode supplied by Chemical Equipment Co., Ltd. (Part Number M 20 E 16002). The observed sensor response is shown in Figure 1 and the sensitivity was around -58.433 mV/pH. Then the electrodes were attached to the mouthpiece device and measured the real time pH fluctuation in mouth by applying noise induced stress. The measurement procedure was at first both electrodes were immersed in a buffer solution for 5 mins, then hearing white noise and finally when no noise is heard. The stress load and non-stress load measurement result is shown in Figure 2. A standard solution voltage values were taken for conversion factor for pH. When no stress load is applied the measurement, there is no serious fluctuation was observed in pH values. On the other hand during white noise hearing, the pH was significantly decreases than the normal value. Hence it is proved that stress levels directly affected the pH values of the saliva. More investigation is underway for conformation.

The detection of pH/temperature at the single-cell level is hoping for the great level of clinical importance for the early detection of many diseases like cancer, diabetes, etc. In this research work, we have fabricated a micro region pH/temperature sensors by series of processes like electrolytic polishing to create needle structure, deposition of electrode materials using RF magnetron sputtering for pH measurements and finally testing in various biological mediums. Working and reference electrodes were Ag/AgIO3 and Sb/Sb2O3 deposited on microneedles under optimized deposition parameters. The structural, elemental and morphological properties were analyzed using XRD, XPS, EDS and FE-SEM. The fabricated tip of the microneedle probe is around analyzed by FE-SEM which size is comparable with the biological cells. pH testing was initially begin with using fish egg, various biological cells and further in vivo tested in mice cerebrospinal fluid and bladder. The obtained temperature/pH sensing results were adequate with theoretical values. Since the sensor works at micro region, the potential difference is easily disturbed by atmospheric anomalies. Hence, many steps have been taken to improve the stability of the sensor.

This research work is focused on development of solid state electrolyte free pH sensor for biomedical applications. Thin films of silver — silver iodate (Ag/AgIO 3 ) and antimony oxide (Sb 2 O 3 ) was deposited on glass substrates and successfully employed them as reference and working electrodes respectively. The structural, morphological, and electrical properties of the working and reference electrodes were investigated using X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM) and high resistance electrometer respectively. Open circuit potential was measured in a universal pH solutions. The developed sensor exhibited the sensitivity of ∼ 43.1552 mV pH−1. Time domain pH monitoring for continuous usage was recorded over a period of several hours and reported.

Recently, piezoelectric material has a very important potential for functional material which configure Bio-MEMS (Biological Micro Electro Mechanical Systems) actuator and sensor. Specifically, in implementation of piezoelectric material for Bio-MEMS, thin film fabrication by sputtering method is made from the viewpoint of miniaturization. Furthermore, in piezoelectric material, perovskite type material composed of ABO3 has a high piezoelectricity. Then, PZT (Lead Zirconate Titanate) as the perovskite type piezoelectric material is widely used since it is easy to produce and has high piezoelectricity. PZT has zirconium or titanium in the B site of ABO3 structure. PZT has the features such as physical properties to greatly change by change in the B site composition ratio of zirconium and titanium. Thus, the B site greatly influences physical properties and therefore function improvement by additive element is tried widely. However, experimental method to lack in economy and quantitativeness is mainstream. Therefore, application of the result is difficult and new evaluation method of B site additive element for sputtering fabrication is necessary. Accordingly, in this research, search of an additive element at low cost and quantitative from the viewpoint of energy by first-principles calculation. First of all, the additive elements which capable of substituting for a B site of PZT were searched. Next, change of piezoelectricity was evaluated by change of crystal structure in a PZT system was introduced an additive element that substitution of the B site was possible. As a result, additive elements for the PZT B site capable of improving piezoelectricity were determined.

We have focused on MgSiO 3 (Magnesium Silicate) which is a new biocompatible piezoelectric material having large spontaneous polarization. Then, crystal thin film growth prediction method was improved in order to predict growth orientation of the non-preferred orientation direction. Calculated total energy in each orientation of distorted crystal by the buffer layer was compared to the value in the stable structure. Total energy difference between the stable state and each crystal orientation pattern showed a trend similar to that of the X-ray peak intensity. Then, energy difference needed to be below 0.001 eV for crystal to be grown.