Dorota G. Pijanowska

The pH-detection of triglycerides

Abstract This paper presents an indirect method of triglycerides determination based on pH-detection. The system consisted of a microreactor containing silica gel beads with surface immobilised lipase and the pH-sensor of ISFET type. Three methods of lipase immobilisation: (1) the chemical bond to the surface of glass beads coated with keratin, (2) entrapment within alginate gel beads and (3) adsorption onto nitrocellulose sheets were compared. All methods of lipase immobilisation, except the second one, were found to be effective. The systems consisting of microreactors packed with surface immobilised lipase were calibrated for different substrates. The highest sensitivity was obtained for tributyrin (0.478 pH/mM for concentration

OPTIMISATION METHODS OF ENZYME INTEGRATION WITH TRANSDUCERS FOR ANALYSIS OF IRREVERSIBLE INHIBITORS

Abstract Manufacturing and application of biosensors cause some problems, the main of which are: (1) optimisation of enzyme immobilisation process to preserve bio-molecular enzyme structures and maximal value of enzyme activity and (2) development of approaches to accomplish a repeated analysis of substances which are irreversible inhibitors of the above mentioned molecules. In this paper both problems are analysed. For stabilisation of the structure of β-glucose oxidase, urease and cholinesterases during their immobilisation, the following approaches were examined: (1) application of one or a combination of the following chemical substances: protein, saccharose, glycerol, and specific substrates or their analogues; (2) optimisation of crosslinking methods including application of bi-functional reagents in aqueous and vaporous phases and (3) proper adjustment of technological operation times. Optimisation of these processes allows to preserve about 70–80% of initial enzyme activity. For the repeated analysis of organophosphorus pesticides and heavy metal ions, which are irreversible inhibitors of enzymes, the following approaches were applied: (1) treatment of enzyme membrane by special reactivating reagents and (2) application of easily replaceable enzymatic membrane. Methods of preservation of enzymatic sensors with use of sodium azide, EDTA and DTT were tested. Optimal conditions of sensor’s preservation and reactivation were chosen.

Drift and Hysteresis Effects Improved by RTA Treatment on Hafnium Oxide in pH-Sensitive Applications

Rapid thermal annealing (RTA) treatment in N 2 ambient is applied to optimize the drift and hysteresis effects of HfO 2 -based sensing membrane. The drift coefficient of the 8 nm thick HfO 2 -electrolyte-insulator-semiconductor (EIS) structure was 1.4 mV/h. After being treated with RTA at 900°C, the drift coefficient and hysteresis width of the 8 nm thick HfO 2 layer was reduced to 0.65 mV/h and 1.7 mV, respectively. For the HfO 2 -EIS structure treated with RTA at 500°C, the drift coefficient was increased to 3.25 mV/h because of the crystallization of the HfO 2 layer and was improved by 900°C annealing due to the densification of the HfO 2 layer. Therefore, the drift coefficient of the HfO 2 -EIS structure was reduced to 0.65 mV/h by RTA treatment at 900°C. With excellent pH sensitivity and stability, an HfO 2 layer with proper RTA processing can be used as pH sensing material in ion-sensitive field-effect transistor-type sensors. Moreover, to easily control capacitance-voltage measurements and automatically calculate parameters such as pH sensitivity, drift coefficient, and hysteresis width of an HfO 2 -EIS structure, a program based on LabVIEW was developed.

Optimization of urea-EnFET based on Ta2O5 layer with post annealing.

In this study, the urea-enzymatic field effect transistors (EnFETs) were investigated based on pH-ion sensitive field effect transistors (ISFETs) with tantalum pentoxide (Ta2O5) sensing membranes. In addition, a post N2 annealing was used to improve the sensing properties. At first, the pH sensitivity, hysteresis, drift, and light induced drift of the ISFETs were evaluated. After the covalent bonding process and urease immobilization, the urea sensitivity of the EnFETs were also investigated and compared with the conventional Si3N4 sensing layer. The ISFETs and EnFETs with annealed Ta2O5 sensing membranes showed the best responses, including the highest pH sensitivity (56.9 mV/pH, from pH 2 to pH 12) and also corresponded to the highest urea sensitivity (61 mV/pCurea, from 1 mM to 7.5 mM). Besides, the non-ideal factors of pH hysteresis, time drift, and light induced drift of the annealed samples were also lower than the controlled Ta2O5 and Si3N4 sensing membranes.

LTCC Enzymatic Microreactor

A novel three dimensional LTCC (Low Temperature Co-fired Ceramics) based microreactor with immobilized enzyme (urease) is presented in this paper. The microreactor consists of two chambers separated by a threshold. The shape of the chambers was optimized by the Finite Elements Method. The modeling has brought a better understanding of the microflow of chemically modified glass or polymeric beads through the microreactor. The modeling results are verified by the observation of the fluid movement inside the real structure via a top transparent polymer layer. Moreover, immobilization techniques of enzymes on polymeric beads are investigated. Finally, the properties of the LTCC microreactor are compared with the properties of a similar one made in silicon.

Analysis of the cytotoxicity of carbon-based nanoparticles, diamond and graphite, in human glioblastoma and hepatoma cell lines.

Nanoparticles have attracted a great deal of attention as carriers for drug delivery to cancer cells. However, reports on their potential cytotoxicity raise questions of their safety and this matter needs attentive consideration. In this paper, for the first time, the cytotoxic effects of two carbon based nanoparticles, diamond and graphite, on glioblastoma and hepatoma cells were compared. First, we confirmed previous results that diamond nanoparticles are practically nontoxic. Second, graphite nanoparticles exhibited a negative impact on glioblastoma, but not on hepatoma cells. The studied carbon nanoparticles could be a potentially useful tool for therapeutics delivery to the brain tissue with minimal side effects on the hepatocytes. Furthermore, we showed the influence of the nanoparticles on the stable, fluorescently labeled tumor cell lines and concluded that the labeled cells are suitable for drug cytotoxicity tests.

Immobilisation of bioreceptors for microreactors

In this paper, immobilisation techniques of bioreceptors for microsystems are presented. A method of silicon surface modification for biomolecules immobilisation under mild conditions was analysed. The method is based on the alkilation reaction between amino groups of the biomolecule and epoxy terminal on the surface. For chemical immobilisation of the bioreceptors, glycidoxypropylethoxysilane and 3-glycidoxypropylmethoxysilane were used. Evaluation of the immobilisation procedures was performed in a flow system.

Na+-selective ChemFETs based on a novel ionophore: bis(phenylbenzo)-13-azocrown-5

Abstract This paper presents performances of ChemFETs based on a novel sodium ionophore bis(phenylbenzo)-13-azocrown-5. The main feature of the ionophore is its increased lipophilicity. This study shows that ChemFETs based on the novel ionophore exhibit a relatively high selectivity coefficient for sodium over lithium ions K (Na + /Li + ) pot , and that it is elevated for ChemFETs with PVC membrane containing o -nitrophenyl octyl ether ( o NPOE) as a plasticizer. Moreover, a significant difference in selectivity coefficients for Na + over Ca 2+ ions, also depending on a plasticizer, was observed. In addition, procedure of synthesis of the ionophore is also described. A good stability of the output signal was obtained for Na + -ChemFETs based on Siloprene membrane.

Temperature compensation electronics for ISFET readout applications

This paper presents temperature compensation electronics for ion sensitive field effect transistor (ISFET) sensors. It consists of a bridge-type floating-source ion sensing circuit and a VT extractor centigrade temperature sensor accompanied with a temperature coefficient (TCF) cancellation method. Using LabVlEW packages has developed an extended measurement system including compensation algorithms programming. Experimental results show that the temperature dependence of the Si/sub 3/N/sub 4/-gate ISFET sensor improved from 8mV//spl deg/C to near 0mV//spl deg/C with the proposed temperature compensation circuitry. This system allows a wide range of high accurate pH-level measurements. The method of temperature compensation may also be valid for other biosensors or bioFETs.

Hysteresis effect on traps of Si3N4 sensing membranes for pH difference sensitivity

Abstract The mechanism of different pH sensitivities on single and stacked layer silicon nitride (Si3N4)-electrolyte insulator semiconductor (EIS) structures was investigated for the application of an inorganic ion sensitive field effect transistor (ISFET) and reference field effect transistor (REFET) pair. The capacitance–voltage (C–V) hysteresis effect of the EIS structures was measured. In addition, pH sensitivity was evaluated with different sweep directions and ranges of the substrate bias. Based on the hysteresis results, a pH-dependent trapping effect was found to decrease the pH sensitivity on a single Si3N4 sensing membrane EIS structure.