Pencil lead microelectrode and the application on cell dielectrophoresis

A microelectrode was fabricated by electrochemical etching of a pencil lead (0.5 mm in diameter) in 1.0 M NaOH aqueous solution. The pencil lead was dipped into the solution and then an ac voltage (3.0 V_rms for 10 min) was imposed against a stainless plate under mild stirring (450 rpm). The electrochemically sharpened pencil tip was about 10 μm in diameter (12 ± 3 μm, n = 5), and the lateral part was insulated within a polypropylene micro-pipette tip (2–200 μL volume range). The cyclic voltammograms conducted in 2.0 mM ferricyanide/ferrocyanide buffer solution (pH 7.0) are with low capacitive current and a typical sigmoidal signal of micro-sized electrodes.The microelectrode was used to perform dielectrophoresis of polystyrene latex microbeads (nominal diameter of 3 μm) and human red blood cells. A conducting glass (indium tin oxide coated glass, 40 mm × 40 mm × 1 mm) served as the counter electrode (0.5 mm beneath the microelectrode) to generate the asymmetrical electric field and also as the window for microscopic observation. With the sinusoidal bias voltage (30 V_rms) ranged from 20 Hz to 2 MHz, positive and negative dielectrophoretic phenomena were identified.     

The atmospheric corrosion of zinc: The effects of salt concentration, droplet size and droplet shape

The influence of droplet characteristics on the atmospheric corrosion of zinc was investigated using a multi-microelectrode approach. Arrays of close-packed zinc wires, 500 μm in diameter, were coupled such that the net anodic and cathodic current flowing through each electrode interface was measured as a function of time. Droplets in the range of 1–10 μL placed onto the array showed that electrochemical fields are immediately established and can remain unaltered for significant periods of time. The total charge passed was found to be almost identical for 0.6 M NaCl droplets of varying size when compensating for the electrolyte–zinc contact area, however significant differences in current exchange were observed when varying electrolyte concentration.In contrast to studies on other metals, the highest rates of zinc corrosion, as measured by the microelectrode array, did not occur during drying cycles. It was observed that the initial wetting and subsequent holding at high relative humidity led to the highest measured currents. Corrosion damage during drying cycles, however, appears to be enhanced for large droplets with high contact angle and increased electrolyte concentration. The importance of these observations to the modeling of atmospheric corrosion has been discussed and future developments of the technique are outlined.     

Novel method for fast determination of ultra trace amounts of timolol maleate by continuous cyclic voltammetry at Au microelectrode in flowing injection systems

A novel method for easy and fast detection of timolol maleate in flow-injection system has been introduced. It was used for analysis of timolol maleate in pure form as well as in its pharmaceutical formulations. The reported method is simple, precise, accurate, time saving and economic as compared to all previously reported methods. The best performance for measurement of timolol maleate was obtained at, pH 2.0, scans rate 300 V s⁻¹, accumulation potential −500 mV and delay time 0.6 s. The advantages of the proposed detection method are, (1) the removal of oxygen from the test solution is not required any more, (2) the detection limit of the method is sub-micromolar, (3) this method is fast enough for determination of the drug compound, in a wide variety of chromatographic techniques. The potential waveform consists of potential steps for cleaning, accumulation and potential ramp that were continuously applied on an Au disk microelectrode (with a radius of 12.5 μm). The detection limit of the method for timolol maleate was 1.58 ng ml⁻¹. The relative standard deviation of the method at 1.0 × 10⁻⁹ M was 2.3% for 20 runs.     

An Experimental Study on Electro Chemical Machining of Microelectrode

Puts forward a new method in machining microelectrode by electro chemical machining （ECM） and plastic deformed theory. The procedure of this method is to machine the microelectrode according to the basic rule of ECM theory at first. Then, with the change of ECM machining parameters, one of the microelectrode ends is exerted by a load. As a result, the elastic and plastic deformation is produced at the machining section and the microelectrode diameter is reduced. It has been proved that the proposed method can determine the optimum machining parameters to machine the microelectrode of Cu.     

聚合物驱结合井网调整技术剩余油实验研究

过室内物理实验模拟研究聚合物驱结合井网调整技术的开发效果,从宏观和微观两方面分析了改变井网的聚合物驱油的开发效果及剩余油分布。宏观室内物理实验应用微电极技术,研究改变注采井网系统的聚合物驱调整技术的开发效果和剩余油分布。微观室内物理实验应用核磁共振技术,研究聚合物驱前后剩余油在高低渗岩心孔隙中的微观分布规律。结果表明,通过改变注采井网系统的聚合物驱调整技术,一方面可以有效的改善驱替前缘推进不均匀的情况,扩大波及体积;另一方面可以改善吸水剖面,在聚合物后续水驱阶段提高中低渗层大孔隙产量。同时,由于井网调整后减小了注采井距,可以在减少注入量的同时提高产油量。驱替结束后,剩余油主要分布在中低渗层未波及到的区域,以及低渗层中、小孔隙。     

Electronic chip based on self-oriented carbon nanotube microelectrode array to enhance the sensitivity of indoor air pollutants capacitive detection

Highly sensitive capacitive detection is reported for indoor air pollutants, e.g. formaldehyde, toluene, and ammonia gas, at room temperature using an electronic chip with self-oriented carbon nanotube microelectrode array. A remarkable capacitive response is observed owing to the dense entanglement of CNTs and the highly porous 3D structured CNT network on the surface of gold electrode. Such kind of nanotubes can be considered as extended and oriented electrodes. As compared with the effect of spray-casting MWCNTs, the relative capacitance change of the above-mentioned electronic chip is found to increase from 1.8 to 70 by taking ammonia as an example. A model is proposed to explain qualitatively the sensing mechanism of electronic chip.     

Averaging in vitro cardiac field potential recordings obtained with microelectrode arrays

Extracellular field potential (FP) recordings with microelectrode arrays (MEAs) from cardiomyocyte cultures offer a non-invasive way of studying the electrophysiological properties of these cells at the population level. Several studies have examined the FP properties of cardiomyocytes of various origins, including stem cell-derived cardiomyocytes. This focus reflects growing importance and interest in the field of MEA. High-quality cardiac FP signals are often difficult to obtain, especially from stem cell-derived cardiomyocyte cultures, which represent an important new field in cardiac electrophysiology. One way to improve the quality of these recordings is to average the cardiac FP signals. To date, however, no studies have examined the effect of averaging on cardiac FP signals. We report here that cardiac FP averaging can yield higher-quality signals than original individual FPs, and therefore promise more accurate detection of different phases and analysis of the cardiac FP signal. Averaged signals improved the signal-to-noise ratio (SNR), and obtaining reliable averages required approximately 50 cardiac cycles. We therefore propose that routine cardiac FP averaging can serve as a tool to compare the effects of different experimental conditions or stimuli on the properties of cardiac FPs.     

Plasma assisted thermal bonding for PMMA microfluidic chips with integrated metal microelectrodes

Fracture of integrated metal microelectrodes likely happens during the thermal bonding process of PMMA [poly (methylmethacrylate)] microfluidic chips. In this paper, the fracture behaviors are studied. The fracture is mainly caused by the plastic deformation of the electrode plate (the PMMA plate with microelectrodes) and the thermal stress of microelectrodes, which is due to the high bonding temperature. To decrease the bonding temperature, a plasma assisted thermal bonding method is evaluated and first used to eliminate the fracture of microelectrodes. In this process, the surface of the cover plate (the PMMA plate with microchannels) is modified using oxygen plasma before the electrode plate is thermally bonded to the cover plate. The parameters of the oxygen plasma treatment are optimized, and the contact angle is decreased from 71.7° to 43.6°. The thermal bonding temperature is optimized, which decreases the temperature from 100 °C to 85 °C. Testing of bonding strength shows an average failure pressure of 1.75 MPa, which is comparable to the bonding strength of 1.46 MPa for chips bonded at 100 °C without plasma modification. In order to demonstrate this bonding method, a PMMA microfluidic chip with integrated copper interdigitated microelectrode arrays for AC electroosmotic pump is fabricated.     

微电极技术

介绍了微电极在加速传质、加快响应速度、降低欧姆压降、提高信噪比等几方面的优点及原理，微电极按照形状、材料、用途等几种分类方法，以及微盘、微柱电极和微阵列电极的制作方法。最后结合微电极的优点对微电极在微量分析、机理研究、工业模拟、电沉积过程、电化学动力学参数的测量和生物电化学等６个方面的用途进行了介绍。文中共引用文献２８篇。     

Biocompatibility assessment of next generation materials for brain implantable microelectrodes

Proper interfacing between the microelectrode device and the cells is very important for functional stimulation of brain; the microelectrodes need to be in close proximity to the cells. The materials currently being used in device or research (silicon, polymer, platinum) do not support neuronal attachment on their surfaces. Here, we investigated primary neuronal cell attachment on Pyrex glass, sapphire, and iridium oxide as promising alternative materials. Sapphire was found to be an excellent substrate to support neuron attachment in serum free condition. Using micro-patterning, sapphire was shown to have great potential as a substrate for next generation neural implants.