Artur Dybko

Assessment of water quality based on multiparameter fiber optic probe

Abstract A multiparameter fiber optic probe was designed to test drinking water. The probe consists of pH, temperature and calcium ions sensors, which are based on the absorbance changes of an appropriate reagent. The sensors are combined in a form of the head made from Teflon. Light emitting diodes (LEDs) are used as light sources and they are matched to maximum absorbance of the reagents. A measurement system is governed by a special software developed in LabWindows.

Uranyl salophenes as ionophores for phosphate-selective electrodes

Anion selectivities of poly(vinylchloride) (PVC) plasticized membranes containing uranyl salophene derivatives were presented. The influence of the membrane components (i.e. ionophore structure, dielectric constant and structure of plasticizer, the amount of incorporated ammonium salt) on its phosphate selectivity was investigated. The highest selectivity for H2PO4− over other anions tested was obtained for lipophilic uranyl salophene III (without ortho-substituents) in PVC/o-nitrophenyl octylether (o-NPOE) membrane containing 20 mol% of tetradecylammonium bromide (TDAB). Ion-selective electrodes (ISEs) based on these membranes exhibited linear response in the range 1–4 of pH2PO4− with a slope of 59 mV/decade. The introduction of ortho-methoxy substituents in ionophore structure decreased the phosphate selectivity of potentiometric sensors.

Long-term three-dimensional cell culture and anticancer drug activity evaluation in a microfluidic chip.

In this work, we present a microfluidic array of microwells for long-term tumor spheroid cultivation and anticancer drug activity evaluation. The three-dimensional microfluidic system was obtained by double casting of poly(dimethylsiloxane). Spheroids of HT-29 human carcinoma cells were cultured in the microsystem for four weeks. After two weeks of the culture growth slowdown and stop were observed and high cell viability was determined within next two weeks. The characteristics of a homeostasis-like state were achieved. A cytostatic drug (5-fluorouracil) was introduced into the microsystem with different frequency (every day or every second day) and different concentrations. The geometry and construction of the microsystem enables flushing away of unaggregated (including dead) cells while viable spheroids remain inside microwells and decreasing spheroid diameter can be observed and measured as an indicator of decreasing cell viability. The results have shown differences in response of spheroids to different concentrations of 5-fluorouracil. It was also observed, that higher frequency of drug dosing resulted in more rapid spheroid diameter decrease. The presented microfluidic system is a solution for cell-based studies in an in vivo-like microfluidic environment. Moreover, observation of decreasing spheroid dimensions is a low-cost, label-free and easy-to-conduct mean of a quantitative determination of a 3D cellular model response to a applied drug. It is suitable for long-term observation of spheroid response, in a contrary to other viability assays requiring termination of a culture.

Efficient reagent immobilization procedure for ion-sensitive optomembranes

This paper presents an efficient and simple reagent immobilization procedure for ion-sensitive membranes of fiber-optic chemical sensors. The applied procedure combines two well-known types of sensing optrode layers: the surface membrane and the bulk type using a polymer track membrane (PTM). The microporous polymer foil significantly increases the active surface of the membrane for reagent immobilization and allows a larger amount of an indicator dye to be incorporated, which leads to large changes in the measured signal. Additionally, the high porosity of a PTM reduces the barrier of mass transport, which decreases the response time of prepared optomembranes. The preparation and performance of optrodes for redox titration and pH fiber-optic sensors based on cellulose acetate PTMs are described.

Durable phosphate-selective electrodes based on uranyl salophenes

Lipophilic uranyl salophenes derivatives were used as ionophores in durable phosphate-selective electrodes. The influence of the ionophore structure and membrane composition (polarity of plasticizer, the amount of incorporated ionic sites) on the electrode selectivity and long-term stability were studied. The highest selectivity for H2PO4− over other anions tested was obtained for lipophilic uranyl salophene III (with t-butyl substituents) in poly(vinylchloride)/o-nitrophenyl octyl ether (PVC/o-NPOE) membrane containing 20 mol% of tetradecylammonium bromide (TDAB). Moreover, phosphate-selective electrodes based on this derivative exhibited the best long-term stability (2 months). The electrode durability can be improved decreasing the amount of the ammonium salt in membrane to 5 mol%.

Application of optical fibres in oxidation-reduction titrations

Abstract The paper presents recent advances in the development of an optical fibre system for determination of the end-point in redox titration. A new method for reagent immobilization based on the entrapment of the molecules in micropores is described. This method seems to be independent of both the physical and chemical properties of the reagent. As a practical application we have tested an optrode based on the use of a colourimetric indicator. This indicator was N , N ′-diphenylbenzidine. A low-cost optoelectronic system consists of a bifurcated optical fibre bundle with a light emitting diode as a light source and a silicone photodiode as a photodetector.

Towards advanced chemical microsensors—an overview

The paper presents design and performance of miniaturized chemical sensors based on silicon transducers: ion-sensitive field effect transistor (ISFET) and solid-state electrode (SSE). The sensors were fabricated as back-side contact structures, which facilitate their mounting in a flow-cell. The role of an intermediate layer between the transducer and the ion-selective membrane is discussed. Various polymeric matrices were used to manufacture microsensors: polysiloxanes, polyacrylates (polymethacrylates), polyurethanes.

Novel head for testing and measurement of chemical microsensors

Abstract A novel head for measurement of chemical sensors was designed and tested. The head was manufactured in the form of a round module allowing simultaneous measurement of 10 sensors. Low cost materials were used for fabrication of a special reference electrode, the head, and plugs connecting the sensors with an electronic amplifier. The hydrodynamic properties of the head such as air bubble distribution, possibility of de-aeration and flow-rate optimisation were investigated. K + -selective CHEMFETs based on plasticised poly(vinyl chloride) membranes and valinomycine were chosen as model sensors in order to verify the usefulness of the head. The measurements were carried out in a fully computerised flow set-up governed by special software developed under LabView.

Evaluation of photodynamic therapy (PDT) procedures using microfluidic system

A hybrid PDMS/glass microfluidic system for evaluation of the efficiency of photodynamic therapy is presented. 5-aminolevulinic acid (ALA) was used as a precursor of photosensitizer. The geometry of the microdevice presented in this paper enables to test different concentrations of the photosensitizer in a single assay. The viability of the A549 cells was determined 24 h after PDT procedure (irradiation with light which induced a photosensitizer accumulated in carcinoma cells, λ=625 nm). The presented results confirmed the possibility to perform the photodynamic therapy process in vitro in microscale and the possibility to assess its effectiveness. Moreover, because two identical microstructures on a single chip were performed, the microchip can be used for examination simultaneously various cell lines (carcinoma and normal) or various photosensitizers.

Miniaturized back-side contact transducer for potentiometric sensors

A novel type of a miniature transducer for potentiometric sensors was designed and tested. The transducer is made from an ordinary printed circuit board using a typical technology. As a result, a back-side contact structure was obtained, which can be mounted in flow systems. The advantage of the fabrication process is its cheapness and flexibility in designing modified structures. The measurement properties of the transducer were tested as a chloride sensor. Then the structure was covered with polyHEMA and a potassium-selective membrane and tested as a potassium sensor. The performance and the long-term stability of the sensors with plasticized PVC and Siloprene based potassium-selective membranes were compared.