F. Olcaytug

Thin-Film Multiple Electrode Probes: Possibilities and Limitations

Thin-film multiple electrode probes are produced by means of thin-film techniques. They are successfully employed for potential measurements in brain research. The most advantageous feature of these probes is that the electrodes can be designed and arranged accurately and close together. The geometric size of the electrode areas is usually in the range of between 50 and 10 000 ¿m2. The size limitations of these thin-film probes are mainly determined by the electrode-electrolyte interface and insulation layer qualities. Since medical research problems, as well as surgical requests, are stressing these limitations, some estimates of maximum resolution and probe dimensions are presented.

High-resolution thin-film temperature sensor arrays for medical applications

Abstract Highly sensitive and fast temperature sensors with sensitive areas of 0.14 × 0.1 mm 2 have been arranged in arrays with interdistances of 0.4 mm consisting of thin films of amorphous germanium (a-Ge) to yield a high temperature coefficient of resistance of 2%/K at room temperature. The sensors are passivated by a 3-μm-thick silicon nitride layer and can be placed on glass, alumina and polymer substrates. The sensor noise limits the temperature resolution of 0.1 mK whereas the 90% response time is typically 3 ms. The electrical resistance of the sensor is in the range of 10 5 ohm. A measurement current of 1 μA causes selfheating of the sensor on glass substrates of less than 0.3 mK in water. This corresponds to a measured heat resistance of 3 × 10 3 K/W. Temperature distribution measurements in the cortex of rabbits and enzyme-calorimetric determinations have been accomplished with these devices.

New microminiaturized glucose sensors using covalent immobilization techniques

Abstract Glucose monitoring is at present the most widespread application of the GOD/H 2 O 2 system. This paper deals with a new technique for immobilizing onto electrochemical thin-film electrode cells based on this detection principle. The thin-film structure consists of a 100 nm thick titanium—platinum or —palladium sandwich layer on glass substrates isolated by a 3 μm silicon nitride film. A three-electrode miniaturized electrochemical cell with an outer diameter of 200 μm was produced by means of standard wet and dry etching procedures. The Ag/AgCl reference electrode was produced by depositing and structuring a 1 μm thick silver film which was subsequently chlorinated by FeCl 3 . The Pt or Pd surface was oxidized electrochemically in dilute aqueous oxidizing solutions. The modified surface was derivatized with amino-organic silylating agents. The covalent coupling of glucose oxidase was carried out by introducing a substituted bifunctional 1,4-benzoquinone group between the silylated electrode surface and the enzyme. A sulfonated polymer was used to protect the enzyme layer and to modify the diffusion characteristics of the electrode.

The construction of microcalorimetric biosensors by use of high resolution thin-film thermistors

Abstract A new calorimetric biosensor has been developed using thin-film thermistor arrays and immobilized enzymes. The miniaturized thermistors produced on glass substrates, exhibit a high sensitivity of 2%/K (TCR), a temperature resolution of 0·1 mK, a rise-time of 3 ms and high reproducibility of resistance and TCR. The life time in physiological solution is at least three months. Additionally this device can be miniaturized and integrated on different substrate materials. A Peltier thermostat with a temperature stability of 1 mK was built up containing two thermistor arrays which were inserted into a flow-through system to enable the detection of the heat produced by an enzyme reaction in a differential mode. Covalently immobilized glucose oxidase and catalase on controlled pore glass (CPG) were used to demonstrate the high sensitivity of the produced thermistor arrays.

Microminiaturized thermistor arrays for temperature gradient, flow and perfusion measurements

Abstract This work reports first experiments on novel probes for measuring mass flow, heat conductivity, perfusion and local temperature gradient. Arrays of high quality microminiaturized thin-film thermistors were used. The outstanding features of these thermistors are the high temperature resolution, the small tracking error between the sensors and the small size of a single thermistor, which allows the use of minimized substrate sizes. The results of our experiments to measure mass flow and perfusion with the heat clearance method are very encouraging. The suitability is good, especially for low mass flow in a micro-channel and on-line blood-flow measurements in physiological matter. Further experiments with the heat clearance device show the probe is also feasible for vacuum measurements.

Correlation between gas phase composition of rf plasma of argon diluted tetraethylgermanium and chemical structure of therewith deposited Ge/C films

Quadrupole mass spectrometry (QMS) and optical emission spectroscopy (OES) have been applied to the characterization of rf plasma of tetraethylgermanium‐argon mixture. QMS analysis shows that under low power input conditions, when organogermanium plasma polymer films are deposited, the gas phase consists primarily of monomer molecules and their largest fragments. In contrast, at high power input, under conditions of hydrogenated germanium/carbon alloy film formation, tetraethylgermanium undergoes nearly complete fragmentation forming atomic germanium, atomic and molecular hydrogen, and a number of hydrocarbon species. A dramatic increase of molecular hydrogen concentration with the increasing rf power is confirmed by OES actinometric measurements. Strong dependence of atomic hydrogen concentration in the gas phase on rf power supports the concept of the formation of Ge–H bonding in the films via saturation of germanium dangling bond with hydrogen and, therefore, provides an argument to the hypothesis of a...

Development of a multiple thin-film semimicro DC-probe for intracerebral recordings (during surgery)

A thin-film multiple-electrode probe for measuring DC potentials at eight sites with interdistances of 1 mm was constructed for the investigation of slow potential changes in deep regions of the human brain during surgery. The thin-film electrodes had to be placed on curved cylinder-shaped surgical instruments with dimensions of 2-mm diameter and 33-cm length used with the Freiburg stereotactic equipment. Several technological steps had to be introduced for solving the problems encountered. Structuring of the metal layers on curved substrates was accomplished by using flexible masks. Special feed-through technologies had to be invented in order to obtain reliable connections between the thin-film sensors and the copper wires inside the stereotactic instrument. Thin-film Ag-AgCl electrodes had to be formed in order to obtain satisfying recordings of slow potential changes below 10 Hz. Slow potential changes were recorded form different depths in interdistances of only 1 mm with the new miniaturized thin-film Ag-AgCl electrodes, and bipolar recordings with an electrode interdistance of only 3 mm clearly showed the appearance of Bereitschafts potentials.<<ETX>>

Precise measurement of flow rates of vaporized tetraethylgermanium carried by an inert gas

The ‘‘rate‐of‐rise’’ technique has been applied for the measurement of the flow rate of tetraethylgermanium carried in a stream of argon. A very precise time counter designed and constructed for this purpose is described. A simple model is presented where the flow rate of the vapor is proportional to its partial pressure and to the flow rate of the carrier gas and inversely proportional to the partial pressure of the carrier gas. The assumed applicability of the equation of state of the ideal gas to the discussed system is successfully tested by means of the flow rate dependence on temperature in the range from −19 to 20 °C and its comparison with data computed from the Clausius–Clapeyron equation. Finally thermodynamic properties of tetraethylgermanium namely vaporization enthalpy and saturated vapour pressure at standard temperature are calculated from the results of flow rate measurements.

Ultraviolet light in glow discharges

The use of ultraviolet light has prevailed in investigation of gas breakdown phenomena since Townsend developed the model of gas breakdown discharge carrying his name because ultraviolet light creates the supposedly necessary electrons in the interelectrode space. However, the ultraviolet light influences the gas breakdown characteristics. Therefore, the extent of the influence of the ultraviolet light on the prebreakdown current, the breakdown current, the breakdown voltage, and the Townsend’s coefficients is studied.

Magnetron Enhanced Plasma-Polymerization for Biocompatible Sensor Coatings and Membranes on Polymeric Based Materials

One of the key questions in the application of miniaturized sensors and actuators for acute and/or chronic use in living-body environment is the biocompatibility. In case of gas sensors additionally a very fine balance between the biocompatibility of the device and the gas (e.g. O2, NO, CO) permeability of its coating must be maintained. In many sensor configurations polymeric substrate materials are used. Here, we present the application of a unique deposition technique for nano-films with thickness ranging between 10 and 200 nm on top of flexible polymeric foils used as substrates in the technology of a variety of biosensors and lab-on-chip structures. The method employs a 15 kHz magnetron-enhanced glow discharge plasma-polymerization process using methane as precursor. It is configurable for laboratory scale batch sizes but also for continuous industrial coating lines. Unsurpassed results of this processing technique have been documented with contact lenses already. Hence, we tested depositions with this process on top of PMMA, polyimide and polystyrene foils of different surface morphology. Compatibility of the process and of the coatings with these materials, adherence in dry and aqueous environment were checked. Antibacterial behaviour of the films were tested by immersing the coated samples in a bio-film reactor for 48 hours as well as for 7 days in E-coli bacteria solutions. After the inoculation time samples were rinsed and treated in an ultrasonic bath. Colonies formed on different culture media out of the rinsing water were enumerated. Number of colony forming units, depending on inoculation time and coating conditions, has been investigated. Remarkable reduction of bacterial attachment was proven with film thicknesses as low as about 15 nm, which allows a reasonable gas permeation rate. Hence, the technology provides production of antibacterial and gas permeable membranes for miniaturized sensors and sensor arrays on chip.