A. L. Kukla

Ammonia sensors based on sensitive polyaniline films

Abstract We propose a new type of ammonia sensor with polyaniline (electroconducting polymer) as the sensitive element. Such sensors are characterized by high sensitivity, wide range of measured concentrations (1–2000 ppm) and high stability of electrical parameters. The use of polyaniline ensures high chemical stability of the sensors in oxidizing ambients. A sensor design based on a silicon chip custom-packed into a linear plastic case is presented. The chip is provided with a system of heaters and thermometers to check the temperature regime of sensor operation. We have studied I – V curves, temperature, concentration and kinetic characteristics of the sensors, as well as their ageing. The possibility for thermoregeneration of the sensor parameters after long-term functioning in an ammonia ambient is emphasized.

Multienzyme electrochemical sensor array for determination of heavy metal ions

Abstract A multienzyme electrochemical sensor array is developed. It is based on capacitance pH-sensitive electrolyte–insulator–semiconductor (EIS) sensors with silicon nitride ion-sensitive layers and different forms of cholinesterase, urease and glucose oxidase as sensitive elements. With this sensor array, we used a multienzyme analysis to recognize the heavy metal ions in solutions containing a mixture of different metal ions, as well as for determination of their content in the analysed samples. The content of toxic elements was determined by estimation of the residual activity of enzymatic membranes after the injection of analysed samples. The conditions for enzyme sensors operation, such as buffer capacity, substrate concentration, time of incubation and time of response signal measurement, were optimised to reach the maximal sensitivity of multisensor for analysis of heavy metal ions in the investigated solutions. It was shown that multienzyme analysis followed by mathematical processing is an efficient approach to develop sensor arrays for toxic substrates detection.

Calixarene-coated nanoparticle gold films for chemical recognition system

Nanoparticle metal films functionalized with calixarenes offer a novel technology for highly effective, technologically feasible, small and cheap chemical gas sensors. We have designed, manufactured and measured the performance of chemical gas sensor elements, where molecular absorption by the calixarene layer controls the electrical conductivity of a nanoparticle gold film evaporated on a dielectric substrate. The sensors were exposed to several alcohol and water vapors and the dynamic sensor responses were analyzed. Resistance variation of the measured samples achieves 10%. Current-voltage curves, recovery characteristics and temperature dependencies of the sensor elements were investigated. Degradation of the sensitivity due to the aging effect was observed. We show that differences in the sensor recovery time, as well as concavity or convexity of the leading edge of the sensor transition curve could be used as additional information parameters for chemical recognition system.

Computer simulation of transport processes in biosensor microreactors

Abstract Microelectronic ferment reactors are finding increasing employment as base elements of biosensor matrices. In this work, a computer simulation of a microelectronic reactor based on ion-sensitive elements, such as transistor or electrolyte—insulator—semiconductor structure, is presented. Our objective involved elucidation of quantitative relations between the sensor design and its characteristics. The computer simulation is performed for different versions of both enzyme carriers and their positions in the microreactor cell. The results of simulation enabled us to optimise both design and all-over dimensions of the microreactor. The principal sensor parameters (such as response rate, amplitude and time lag) are calculated for the optimum cell. A comparison between the calculated models and the corresponding experimental results obtained with the help of considered types of microreactors is carried out.

Biosensors for in Field Measurements: Optimisation of Parameters to Control Phosphororganic Pesticides in Water and Vegetables

Enzymatic sensors based on the ion sensitive field effect transistor (ISFET) and semiconductor structures for detection of phosphororganic pesticides were developed. Their characteristics were optimised to control these pollutants in field. Acetyl-(AChE), butyril- (BChE) cholinesterase’s (ChE) and crude substances contained both forms of ChE were used as chemically sensitive substances to the phosphororganic pesticides. Detectable phosphororganic components were o,o-diethyl o-3,5,6-trichloro-2 pyridil phosphortionate, 2,2-dichlorovinyl dimethyl phosphate and phasolone. They are irreversible inhibitors for above mentioned ChE’s. It is shown that the usage of replaceable enzymatic membrane is more preferable for repeated analysis than its reactivating. Alginate gel and nitrocellulose (NC) strips are very suitable for creation of replaceable enzymatic membrane. The standard deviation of sensor responses for series measurements and for different membrane castings did not exceed 10%. The working characteristics of enzymatic sensors based on the ISFETs depend on medium condition of samples to be analysed. Vegetable sap influences on the value of sensor response. To prevent dependence of sensor signal on medium of analysed samples, the measurements should be performed in standard solution (3–5 mmo1/1, pH 7.3 tris-HCL buffer, contained 140 mmo1/1 sodium chloride). The sensitivities of enzymatic sensors based on the ISFETs to above mentioned pesticides were within the range 10−5 – 10−7 mol/l. ChE’s are reversible inhibited by heavy metal ions. The activity of ChE’s is significantly reduced at their concentration 10−3mo1/l and higher. To diminish nonspecific signal which is generated by ChE’s in the presence of heavy metal ions, it is necessary to have information from urease sensor. The usage of urease and any ChE as well as transducer in form of Si-SiO2-Si3N4-Ta2O5-electrolyte metal allows to get multichannel sensor for pesticide analysis. The detectable concentration of phasolone by multi-enzymatic sensor was about 10−7 mol/1. The sensitivity of analysis by both developed sensors is significantly higher than permissible limit of pesticide concentration in water and in vegetable food.

Effect of synthesis and doping conditions on the physical and chemical properties of mesoporous tin dioxide

We have studied the effect of doping mesoporous materials and films based on tin dioxide on their physical and chemical properties. We have studied their thermal stability, sorption, acid, and semiconductor properties. We demonstrate the advantages of using nanocomposites to obtain thermally stable layers (thickness ~1 μm) with relatively high porous structural parameters (Vtot = 0.460 cm3/g, SBET = 440 m2/g) and physical and chemical properties that can be varied in a targeted fashion.

Conductivity of HBF/sub 4/-and HCLO/sub 4/-doped emeraldine polyaniline in air and ammonia

Summary form only given. For the emeraldine poiyaniline films doped with HBF/sub 4/ and HClOsub 4/ conductivity in air and ammonia vs both concentration of NH/sub 3/ molecules and temperature was measured at various values of thin film thickness. Polymer films were produced by precipitation from saturated polyaniline solution in dimethyiformamide onto substrates having a system of interdigital contacts. For both types of films the resistivity in the ammonia ambience was shown to grow (sub)linearly with NH/sub 3/ molecules concentration in the range from 100 to 1000 ppm. The conductivity G was exponential in temperature T: G=Goexp[(To/T)/spl and/k]. The values of parameters To and k were determined for cases of both air and ammonia. The obtained results enabled us to suggest the hole hopping to be the dominant mechanism of charge transport in these materials. Physical mechanisms of the effect of adsorbed molecules on charge transfer in polyanilines are discussed.