Zbigniew Brzozka

Direct and two-stage data analysis procedures based on PCA, PLS-DA and ANN for ISE-based electronic tongue—Effect of supervised feature extraction

A novel strategy of data analysis for artificial taste and odour systems is presented in this work. It is demonstrated that using a supervised method also in feature extraction phase enhances fruit juice classification capability of sensor array developed at Warsaw University of Technology. Comparison of direct processing (raw data processed by Artificial Neural Network (ANN), raw data processed by Partial Least Squares-Discriminant Analysis (PLS-DA)) and two-stage processing (Principal Components Analysis (PCA) outputs processed by ANN, PLS-DA outputs processed by ANN) is presented. It is shown that considerable increase of classification capability occurred in the case of the new method proposed by the authors.

Microfluidic devices as tools for mimicking the in vivo environment

One of the major branches of microfluidic development is cell engineering. A number of devices for cell cultivation, lysis, single-cell analysis and cell-based toxicity tests have been reported in the literature. The variety of structures that can be created leads to devices more closely mimicking the in vivo environment than classic cell cultures. Studies on this topic will have an effect on the evaluation of methods that can replace animals in biomedical research. The aim of this review is to present latest advancements of “lab-on-a-chip” for cell cultivation and engineering. The authors focus on the achievements leading to in vivo-like methods. The materials and fabrication methods in silicon, glass, PDMS and other polymers were briefly characterized. Microfluidic devices were applied for mimicking the in vivo environment at various levels of mammalian body organization—from the surroundings of single cells to interactions between functional organs. Solutions for “human-on-a-chip”, perfusion cell cultures, extracellular matrix analogues, microscaffolds, spheroid formation and co-cultures were reviewed in this paper. The presented solutions have the potential to become new cellular models for toxicology, drug development and biomedical research.

Novel approach of immobilization of calix[4]arene type ionophore in 'self-plasticized' polymeric membrane

Abstract The design of ion-selective membranes based on the immobilization of the calix[4]arene tetraethyl ester containing at their wider rim one polymerizable group in a linear isodecyl acrylate (IDA)/methyl methacrylate (MM) copolymer is reported. Preliminary studies were focused on an optimization of polymeric matrix based on IDA/MM copolymers to make them suitable for preparing ion-selective membranes. The effect of polymer composition (IDA:MM ratio), matrix features (glass transition temperature and molecular weight) and compatibility with electro-active components was examined. It was found that the copolymer of IDA:MM=3:7 ratio exhibited the best mechanical properties. The feasibility of the application of IDA/MM matrix for ion-selective membranes was examined using as a model ionophore, 4- tert -butyl calix[4]arene tetraethyl ester. Electrodes based on these membranes showed near theoretical sensitivity towards sodium concentration and selectivity similar to reported for classical plasticized PVC-based membranes. Methacrylamide derivative of calixarene was immobilized in IDA/MM polymer of optimized composition. Potentiometric measurements revealed that the selectivity and the slope of the response curve obtained for electrodes employing membranes with immobilized calixarene are essentially the same as for the membranes containing a free ionophore, while the lifetime was improved from 2 to 6 months.

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.

The design of durable Na+-selective CHEMFETs based on polysiloxane membranes

The design of durable sodium-selective CHEMFETs based on the covalent attachment of a sodium-selective ionophore and tetraphenylborate anions to a polysiloxane membrane matrix is described. Simulations of the membrane potential of such CHEMFETs using an extended version of the model developed previously in our group, revealed that a membrane with a reduced mobile ionophore and completely immobilized anionic sites should give a sub-nernstian response owing to a counteracting diffusion potential. CHEMFETs with all possible combinations of free and covalently bound ionophore and borate anions were prepared and the effect of covalent binding on the sensing behaviour was studied. The attachment of both electroactive components to a polysiloxane membrane matrix results in CHEMFETs that respond to Na+ activities in aqueous solution with good selectivity, and an almost nernstian slope (56.7 mV decade?1). The polarity of the membrane plays a crucial role. The durability is improved by the covalent attachment of the electroactive components (more than 90 days).

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%.

Cesium-selective chemically modified field effect transistors with calix[4]arene-crown-6 derivatives

Calix[4]arene-crown-6 derivatives (1–3) in the 1,3-alternate conformation, incorporated in poly(vinylchloride) membranes of CHEMFETs, exhibit good Cs+-selectivity and Nernstian behaviour. The Cs+-selectivity over Na+, i.e., log KpotCs,Na = −3.3, is slightly better than observed for bis(18-crown-6) derivatives (log KpotCs,Na = −3.0). The CHEMFETs respond sub-Nernstian in the presence of NH+4 and K+. Model calculations show that this can be explained by the small difference between the stability constants of the Cs+− and K+-complexes and by the high partition coefficient of NH+4 in favour of the membrane phase, respectively.