The concept of Thick Film Technology (TFT) involves developing requisite structures on substrates using screen printing technology. Structures are printed by forcing the paste, which contains the main ingredient (metals like gold, silver etc. or non metals such as graphite, glass and ceramic), and some binding material through a screen mesh onto a substrate (alumina, plastics etc.). During the curing process the binding material evaporates and structures from the requisite material is formed. Control of the printing allows the preparation of precisely defined and homogeneous shapes / structures.
An electrode is a conductor on the surface of which the electrochemical reaction takes place. It is also, a system in which a conductor is in contact with a mixture of oxidised and reduced forms of some chemical species. Usually it is in the form of a wire, rod, or plate. Electrodes are made of metal, e.g., copper, lead, platinum, silver and zinc or from a non-metal, commonly carbon.
A classical electrochemical cell / sensor consists of a small glass cell body often jacketed by a thermostatic circuit, which is clamped to a plastic top with ports for electrodes, gas purge tube and thermometer. The electrochemical measurement is based on observation of the processes occurring at the electrode surfaces with the working electrode measuring the electrode processes, the reference electrode establishes the reference potential and the last one, i.e. the auxiliary electrode, creates a current loop and prevents the potential drop between the working electrode and the reference electrode.
A biosensor is a device that converts the biological activity into a quantifiable signal. Biosensors have their origin in work carried out by L.C. Clark and Lyons on the combination of enzymatic actions with polarographic, potentiometric or conductometric electrodes, which resulted in a new field of electroanalytical biochemistry.
The entire classical electrode system can be miniaturised and integrated as an electrochemical sensor using thick film technology. The sensor is formed by screen printing the 3-electrode system onto a substrate i.e. working, reference and auxiliary electrodes. At the end of the sensor there is a contact field connected to the active part by silver conducting paths covered with a dielectric protection layer. TFT biosensors with mediators, immunosensors, amperometric biosensors etc. are created by immobilising suitable substances on the sensor substrates.
All applications based on electrochemical and electro-analytical techniques involving electrode process measurements can be catered for by TFT sensors. The practical applications have a very high significance in the scientific community, medical and pharmaceutical industries, environmental monitoring etc. Some of the examples include environmental pollutant analysis, compound toxicity analysis, trace analysis, detection of different compounds in human blood and urine etc. Based on specific applications different types of TFT based sensors have been developed such as displacement sensors, pressure and temperature sensors, accelerometers and gas sensors, electrochemical sensors and substrates for biosensors.
No special equipment is needed as these sensors can be very easily integrated into the classical arrangement. A few accessories, necessary for connecting the sensors to the measurement equipment, are available from BVT. However, to remove some of the conventional problems of the classical measurement techniques which use external stirrers etc., BVT have also developed a micro flow system. This system has an internal pump for stirring and mixing the cell contents and a special chamber for sensor placement.
Using BVT standard connectors the response of the TFT sensors can be directly measured and analysed using standard polarography equipment. Other data acquisition equipment is also available and will allow direct observation and analysis of results on a PC. The BVT biosensor analyser has a memory capacity which allows usage of these sensors in actual field conditions.
The sensitivity of a TFT sensor depends on the application. In most common applications the range lies between 1µM - 10 mM. There are some sophisticated methods which allow detection in pM range. The accuracy is highly dependent on the accessories used. Using precise thermostating correction to external influences precision up 0.01 % can be achieved. The whole system error lies within a range of 1 - 5 %.
Each of the TFT sensors can be individually calibrated and used for a few measurements with a very high repeatability. The low cost of the sensor allows disposability of the sensor after a few uses. Sensor response value may however vary slightly change between different production batches.
BVT tests show that these sensors are not affected at all in short term period of months. Periods spanning a few years show only a very slight decrease in their sensitivity.
All standard metals such as gold, silver, platinum and non-metals such as graphite as well as as silver / silver chloride are available as electrode materials in TFT sensors. Due to the availability of a wide range of TFT pastes, TFT sensors with different combinations, customised to specific user needs, can be produced.
The TFT sensors are extremely low cost and can be disposed of after a few uses.
You may request prices on the info@bvt.cz e-mail address. Our product forms for both standard products and new products are available for download within the Products
The PetroSense® products incorporate DecisionLink’s patented fiber optic chemical sensor (FOCS®) technology with digital electronics and a microprocessor to make PetroSense® unique in the marketplace. The chemical coating on the fiber optic sensor has a specific affinity for hydrocarbons which makes the FOCS® systems both repeatable and accurate for total petroleum hydrocarbon (TPH) measurements. The PetroSense product line will supply TPH measurements without the use of hydrochloric acid, freon, or any other solvents used for extraction. The PetroSense Technology is available in a hand-held version (PHA-100 series) or in continuous monitoring systems (CMS-4000, CMS-5000 or OilSense®-4000). The PetroSense products are available today, have proven track records in the field, and are competitively priced.
The PetroSense technology is based on the principle of a Fiber Optic Chemical Sensor (FOCSâ). A light emitting diode (LED) sends light through the chemically coated strand of optical fiber depicted below. As the outside of the fiber comes in contact with hydrocarbons, some of the light travelling through the optical fiber escapes. A reference detector at one end and a sense detector (PD) at the other end of the fiber measure that loss of light. This change in the refractive index (loss of light) correlates very well to the concentration of hydrocarbons present.
When using UV, IR or Fluorescence, each technology has limitations. UV and IR rely on the hydrocarbon’s ability to adsorb a specific wavelength of light. Problems can arise when other contaminants in produced water may also adsorb at that same wave length increasing your value of oil in water. This change in turbidity can have a pronounced effect on the accuracy of results. Fluorescence can have the same limitations with a bit of a twist. Because specific filters have to be used for control of the specific wavelength before and after the sample cell, changes in production characteristics can lead to inaccurate results. Fluorescence also has had problems with increases in turbidity similar to the UV and IR. Also, the UV, IR, and Florescence technologies all require an extraction with freon or hexane before the hydrocarbon can be measured. This means handling and disposing of more chemicals for your operations. Finally, in- line systems using these technologies can be cost prohibitive.
You should expect very little interference using the PetroSense technology. Turbidity and typical produced water flocculants and coagulants used to clarify produced water should have no effect on the PetroSense readings. The key to success with your new PetroSense monitoring equipment is to keep it well maintained and clean as discussed in the operation procedures.