In the last several decades, metal oxide thin films have attracted significant attention for the development of various existing and emerging technological applications, including pH sensors. The mandate for consistent and precise pH sensing techniques has been increasing across various fields, including environmental monitoring, biotechnology, food and agricultural industries, and medical diagnostics. Metal oxide thin films grown using physical vapor deposition (PVD) with precise control over film thickness, composition, and morphology are beneficial for pH sensing applications such as enhancing pH sensitivity and stability, quicker response, repeatability, and compatibility with miniaturization. Various PVD techniques, including sputtering, evaporation, and ion beam deposition, used to fabricate thin films for tailoring materials' properties for the advanced design and development of high-performing pH sensors, have been explored worldwide by many research groups. In addition, various thin film materials have also been investigated, including metal oxides, nitrides, and nanostructured films, to make very robust pH sensing electrodes with higher pH sensing performance. The development of novel materials and structures has enabled higher sensitivity, improved selectivity, and enhanced durability in harsh pH environments. The last decade has witnessed significant advancements in PVD thin films for pH sensing applications. The combination of precise film deposition techniques, novel materials, and surface functionalization strategies has led to improved pH sensing performance, making PVD thin films a promising choice for future pH sensing technologies.

The effect of contact layer on the pH sensing performance of a sputtered RuO2 thin film pH sensor is investigated. The response of pH sensors employing RuO2 thin film electrodes on screen-printed Pt, carbon and ordered mesoporous carbon (OMC) contact layers are measured over a pH range from 4 to 10. Working electrodes with OMC contact layer are found to have Nernstian pH sensitivity (-58.4 mV/pH), low short-term drift rate (5.0 mV/h), low hysteresis values (1.13 mV) and fast reaction times (30 s), after only 1 h of conditioning. A pH sensor constructed with OMC carbon contact layer displays improved sensing performance compared to Pt and carbon-based counterparts, making this electrode more attractive for applications requiring highly-accurate pH sensing with reduced conditioning time.

The feasibility of using a thin-film RuO2 (ruthenium oxide) pH sensor for the detection of Helicobacter pylori is investigated. In particular, we demonstrate the ability of the sensor to measure urease activity between 1.0 and 50 U/mL in less than 30s. The developed sensor exhibited a super-Nernstian response of 77.74mV/pH and excellent reversibility. The pH sensor's ability to detect H. pylori in real time is demonstrated, and found to be much faster than the rapid urease test. (C) 2016 Elsevier B.V. All rights reserved.

We design, develop and demonstrate the principle of a continuous, non-intrusive, low power microfluidics-based lab-ona- chip (LOC) structure for Circulating Tumor Cell (CTC) separation. Cell separation is achieved through 80 cascaded contraction and expansion microchannels of widths 60 μm and 300 μm, respectively, and depth 60 μm, which enable momentum-change-induced inertial forces to be exerted on the cells, thus routing them to desired destinations. The total length of the developed LOC is 72 mm. The LOC structure is simulated using the COMSOL multiphysics software, which enables the optimization of the dimensions of the various components of the LOC structure, namely the three inlets, three filters, three contraction and expansion microchannel segments and five outlets. Simulation results show that the LOC can isolate CTCs of sizes ranging from 15 to 30 μm with a recovery rate in excess of 90%. Fluorescent microparticles of two different sizes (5 μm and 15 μm), emulating blood and CTC cells, respectively, are used to demonstrate the principle of the developed LOC. A mixture of these microparticles is injected into the primary LOC inlet via an electronically-controlled syringe pump, and the large-size particles are routed to the primary LOC outlet through the contraction and expansion microchannels. Experimental results demonstrate the ability of the developed LOC to isolate particles by size exclusion with an accuracy of 80%. Ongoing research is focusing on the LOC design improvement for better separation efficiency and testing of biological samples for isolation of CTCs.

Accurate pH monitoring is crucial for many applications, such as, water quality monitoring, blood monitoring, chemical and biological analyses, environmental monitoring and clinical diagnostic. The most common technique for pH measurement is based on the use of conventional glass pH electrodes. Glass electrodes have several limitations, such as mechanical fragility, large size, limited shapes and high cost, making them impractical for implementation as Lab-on-chips and pH sensor capsules. Various metal oxides, such as RuO2, IrO2, TiO2, SnO2, Ta2O5 and PdO have recently been proposed for the realization of pH sensing electrodes. Specifically, ruthenium oxide exhibits unique properties including thermal stability, excellent corrosion resistance, low hysteresis high sensitivity, and low resistivity. In this paper, we demonstrate the concept of a miniaturized ion selective electrode (ISE) based pH sensor for point-of-care urease monitoring. The sensor comprises a thin film RuO2 on platinum sensing electrode, deposited using E-beam and R.F. magnetron sputtering, in conjunction with an integrated Ag/AgCl reference electrode. The performance and characterization of the developed pH/urea sensors in terms of sensitivity, resolution, reversibility and hysteresis are investigated. Experimental results show a linear potential-versus-urea-concentration response for urea concentrations in the range 0 - 180 mg/ml. Experimental results demonstrate super-Nernstian slopes in the range of 64.33 mV/pH - 73.83 mV/pH for RF sputtered RuO2 on platinum sensing electrode using a 80%:20% Ar:O-2 gas ratio. The RuO2 sensor exhibits stable operation and fast dynamic response, making it attractive for in vivo use, wearable and flexible biomedical sensing applications.

A miniaturized pH sensor structure employing an R.F. sputtered ruthenium oxide sensing thin-film electrode in conjunction with an electroplated Ag/AgCI reference electrode is developed and the effect of the temperature of the pH test solution on the performance of the sensor is investigated. Experimental results show that the pH sensor employing 300 nm thick RuO2 sensing electrode exhibits Nernstian slopes of 65.66 mV/pH, 69.16 mV/pH, 72.50 mV/pH, 78.50 mV/pH and 84.50 mV/pH for pH test solution temperatures of 1.5 degrees C, 12 degrees C, 22 degrees C, 37 degrees C and 50 degrees C, respectively. The performance of the pH sensor in terms of sensitivity, response time, stability and reversibility is experimentally evaluated. (C) 2015 Elsevier B.V. All rights reserved.

The influence of the Ar/O2 gas ratio during radio frequency (RF) sputtering of the RuO2 sensing electrode on the pH sensing performance is investigated. The developed pH sensor consists in an RF sputtered ruthenium oxide thin-film sensing electrode, in conjunction with an electroplated Ag/AgCl reference electrode. The performance and characterization of the developed pH sensors in terms of sensitivity, response time, stability, reversibility, and hysteresis are investigated. Experimental results show that the pH sensor exhibits super-Nernstian slopes in the range of 64.33–73.83 mV/pH for Ar/O2 gas ratio between 10/0–7/3. In particular, the best pH sensing performance, in terms of sensitivity, response time, reversibility and hysteresis, is achieved when the Ar/O2 gas ratio is 8/2, at which a high sensitivity, a low hysteresis and a short response time are attained simultaneously.

We demonstrate the concept of a low-cost, rugged, miniaturized ion selective electrode (ISE) comprising a thin film RuO2 on platinum sensing electrode deposited using RF magnetron sputtered in conjunction with an integrated Ag/AgCl and Ag reference electrodes for engine oil acidity monitoring. Model oil samples are produced by adding nitric acid into fresh fully synthetic engine oil and used for sensor evaluation. Experimental results show a linear potential-versus-acid-concentration response for nitric acid concentration between 0 (fresh oil) to 400 ppm, which demonstrate the accuracy of the RuO2 sensor in real-time operation, making it attractive for use in cars and industrial engines.

A miniaturised pH sensor structure employing an R.F. sputtered ruthenium oxide sensing thin-film electrode in conjunction with an electroplated Ag/AgCl reference electrode is developed and the effect of the thickness of the sensing electrode on the measurement accuracy is investigated. Experimental results show that the pH sensor exhibits Nernstian slopes of 66.52 mV/pH, 68.63 mV/pH, 67.73 mV/pH, and 54.83 mV/pH for ruthenium oxide film thicknesses of 425, 300, 175 and 50 nm, respectively. All the pH measurements were carried out at a temperature of 22 degrees C. The performance and characterisation of the pH sensors in terms of sensitivity, response time, pH resolution, stability and reversibility are discussed. (C) 2014 Elsevier B.V. All rights reserved.

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.

We demonstrate the feasibility of developing a low-cost, rugged, miniaturized ruthenium oxide (RuO2) thin-film pH sensor comprising a RuO2 on platinum sensing electrode deposited using R.F. magnetron sputtered in conjunction with an integrated thick Ag/AgCl reference electrode. A RuO2 thin-film (300nm) is deposited on an alumina substrate using R. F. magnetron sputtering with a RuO2 sputtering target in Argon plasma. Experimental results show a linear pH sensitivity of 58.50mV/pH when the developed sensor is immersed in a standard buffer solution having pH values of 4.0 and 10.0 and lab supply water of pH 7.7 at a temperature of 22°C. These results are in excellent agreement with the theoretical Nernstian response of 58.56mV/pH at 22°C.

We present experimental and simulation results for focused ion beam (FIB) milling of microchannels in lithium niobate in this paper. We investigate two different cuts of lithium niobate, Y- and Z-cuts, and observe that the experimental material removal rate in the FIB for both Y-cut and Z-cut samples was 0.3 μm(3)/nC, roughly two times greater than the material removal rate previously reported in the literature but in good agreement with the value we obtain from stopping and range of ions in matter (SRIM) simulations. Further, we investigate the FIB milling rate and resultant cross-sectional profile of microchannels at various ion beam currents and find that the milling rate decreases as a function of ion dose and correspondingly, the cross-sectional profiles change from rectangular to V-shaped. This indicates that material redeposition plays an important role at high ion dose or equivalently, high aspect ratio. We find that the experimental material removal rate decreases as a function of aspect ratio of the milled structures, in good agreement with our simulation results at low aspect ratio and in good agreement with the material removal rates previously reported in the literature at high aspect ratios. Our results show that it is indeed easier than previously assumed to fabricate nanochannels with low aspect ratio directly on lithium niobate using the FIB milling technique.

Microfluidic channels are fabricated in lithium niobate (LN) by Focused /on Beam (FIB) miffing. 127.68' axis rotated Y-cut (SAW grade) and Z-cut LN wafers are used. Material removal rate is 0.34±0.02 pnJ3/nC for Y-cut sample and 0.30 ± 0.02 prwlnC for Z-cut sample. Experimental results show that the material removal rate decreases at l1igh ion doses and high aspect ratios due to the increased significance of material deposition at these conditions. We also demonstrate the suitability of FIB-miffed nanochannels for micro!nanofluidic applications. INTRODUCTION Lithium niobate (LN) represents the most common piezoelech·ic matetial used in radio frequency telecommunications including mobile phones, television, and wireless transmitters. Machining lithium niobate, an interesting and commonly used piezoelectric material, is difficult, and although Focused Ion Beam (FIB) milling [1-3] has been used to machine LN in the past, all previous works have focused on the development of photonic devices' [ 4-5]. In recent years, piezoelectrically generated acoustic energy using LN [6] has been found to be extremely useful for microfluidics. In this paper, we investigate the use of FIB milling for fabricating a wide range of stmchtrcs and show that FIB milling of nanochannels on lithium niobate can move microfluidics towards V. Rajcndran, P. Paramasivam and K.E. Geckeler (eds.) Admnced Nmw Materials for Industrial Applications, pp. 103-108 (2012). © Blooms~ury Publishing India Pvt. Ltd.

Microfluidic channels are fabricated in thick polycarbonate (PC) substrates by hot embossing using soft poly(dimethylsiloxane) (PDMS) stamps. The embossing force is in the range of 2.5--3 kN for a 4-inch diameter substrate, and the embossed microchannel is 70 Jim deep. We investigate the influence of soft stamp precursor and curing agent mix ratio, and post thermal treatment on embossing conditions. Experimental results show that a soft stamp fabricated with 5:1 mix ratio and post-annealed at 150'0 results in better embossing properties than conventional un-annealed stamps. INTRODUCTION In recent years, many polymer-based microfabrication techniques have been explored for application in bio-MEMS and microfluidics. Current major polymer microfabrication techniques include hot embossing,[!) injection molding [2) and soft lithography.[3] Among them, hot embossing is the most attractive as it offers high replication accuracy for micron-scale features. 1l1e basic principle of hot embossing is heating a polymer substrate above its glass tt·ansition temperature (Tg), pressing it with a mold or master stamp and gradually cooling it well below the glass transition temperature where patterns from the mold are completely transferred to tlie p~lymer substrate. The mold pattern is then permanently transferred to the substrate upon cooling. The hot embossing process exploits differenceS in thermomechanical prope1ties between the stamp and the substrate. Typically, stamps can be either hard or soft. For hard stamps, which are made of silicon or nickel, fragility, thermal mismatch and cost are V. Rajendran, P. Prabu and K.E. Geckeler (eds.) Nano Biomaterials, pp. 39--42 (2012). ©Bloomsbury Publishing India Pvt. Ltd.

The microfluidic applications of a ZnO/Sapphire based layered surface acoustic wave structure are being investigated. Properties of the ZnO/Sapphire layered SAW device including surface wave velocity and propagation loss were measured and correlated to the fluidic behavior of micro droplets. Acoustic streaming was observed in the form of two vortices. Micro particles were also observed to concentrate in the vortices within 4 seconds of device activations.

An optimized capacitively coupled contactless conductivity detector for microchip electophoresis is presented. The detector consists of a pair of top bottom excitation electrodes and a pair of pickup electrodes disposed onto a very thin plastic microfluidic chip The detection cell formed by the electrodes is completely encased and shielded in a metal housing These approaches allow for the enhancement of signal coupling and extraction from the detection cell that result in an improved signal-to-noise-ratio and detection sensitivity The improved detector performance is illustrated by the electrophoretic separation of six cations (NH4+, K+, Ca2+, Na+, Mg2+, Li+) with a detection limit of approximately 0.3 mu M and the analysis of the anions (Br-, Cl-, NO2-, NO3-, SO42, F-) with a detection limit of about 0 15 mu M. These LODs are significantly improved compared with previous reports using the conventional top top electrode geometry The developed system was applied to the analysis of ions in bottled drinking water samples

The fundamental building blocks of typical electrowetting-on-dielectric (EWOD) actuation and their importance in the EWOD mechanism are introduced and reviewed, respectively. The emphasis in this experimental study of EWOD is on dielectric materials, upon which the performance of EWOD devices is heavily dependent. Dielectric breakdown of several typical polymeric and inorganic insulators employed as dielectrics for EWOD has been analytically investigated, which is forced to occur between the electrodes and conductive liquids under certain threshold potential. The electric breakdown occurring in both dielectric layer and surrounding medium (air or silicon oil) has been studied to build up a mathematical model of breakdown voltage as a function of dielectric thickness. Contact angle measurement of some polymeric materials and self-assembled monolayer using pure water has been carried out to demonstrate the contact angle tunability and reversibility, respectively, upon EWOD actuation.

In this paper, we review the approaches developed in our laboratory to fabricate polymer-based microfluidic devices to suit a range of applications in bio- or chemical analysis. Thermoplastic materials such as polycarbonate (PC) and poly(methyl methacrylate) (PMMA) are used to fabricate microfluidic devices via hot embossing. To emboss microchannels, we use hard stamps fabricated in silicon or soft stamps molded on poly(dimethylsiloxane) (PDMS). Hard stamps are fabricated on silicon wafers through photolithography and deep reactive ion etching (DRIE). Soft stamps are fabricated by casting PDMS prepolymer on silicon molds. To enclose the fluidic channels, direct fusion bonding was found to produce the highest bond strength with minimal structural deformation. One-step photolithographic methods have also been explored to produce via photochemical patterning microfluidic structures in photocurable materials. We use the photocurable capabilities of a PDMS copolymer, which incorporates a methacrylate crosslinker. Microfluidic channels are produced via one step-photopatterning processes by crosslinking the prepolymer mixture through a photomask. The smaller feature size attainable was 100 microm. Structures with higher spatial resolution are fabricated through a photoimprinting process whereby a mold is pressed against the precured mixture during UV crosslinking exposure. The application of the fabricated fluidic devices in electrophoretic ion analysis is also presented.