Marta Pokrzywnicka

Miniaturized optical chemosensor for flow-based assays

A cost-effective, highly compact, and versatile optoelectronic device constructed of two ordinary light emitting diodes compatible with optosensing films has been developed. This fibreless device containing chemoreceptor, semiconductor light source, and detector integrated in a miniaturized flow-through cell of low microliter internal volume works as a complete photometric chemical sensor suitable for detection in flow analysis. The operation of the developed device under nonstationary programmable-flow conditions offered by sequential injection analysis has been demonstrated using Prussian Blue film as a model optical chemoreceptor. The unique spectroelectrochemical properties of the sensing material enable its use for optical sensing of redox species, whereby ascorbic acid and hydrogen peroxide have been chosen as model analytes. The reported SI-sensor system features fast and reproducible determination of both analytes in the submillimolar range of concentrations. The construction concept demonstrated in this work can be easily applied to other kinds of optical sensors based on absorbance sensing films.

Towards the development of a miniaturized fiberless optofluidic biosensor for glucose

A miniaturized fiberless optical sensor integrated in an automated sequential injection (SI) manifold for mesofluidic handling of sample, conditioning and regeneration solutions is herein proposed for monitoring glucose (as a model analyte) in human serum. The optofluidic biosensor capitalizes on the co-immobilization of Prussian Blue (PB) and glucose oxidase (GOx) on a polyester film working concomitantly as a chemo- and bioreceptor. The oxidation of β-glucose at the receptor surface by GOx yields hydrogen peroxide whereby reoxidizing the reduced form of PB (the so-called Prussian White) so as to generate a deep blue color. The change in the optical properties of the film was continuously monitored by red paired emitter-detector diodes (PEDDs). A full factorial design followed by a Doehlert matrix-based response surface was exploited for multivariate optimization of the optofluidic PB-GOx-PEDD biosensor. The most significant variables influencing sensors response were the current powering the light emitting diode (LED) emitter and the surface concentration of GOx. The optosensor was proven rugged as the response varies by merely 5% from the optimal value whenever the GOx concentration increases or decreases by 17% or the current powering the LED by 18.5%. Under the optimized physicochemical conditions, the limits of detection and quantification at the 3s(blank) and 10s(blank) levels, respectively, were estimated to be 23.8μmolL(-1) and 79.3μmolL(-1), respectively, with a dynamic working range spanning from 0.1 to 2.5mmolL(-1) of glucose. The trueness of the biosensor measurements was assessed with certified pathological and physiological human serum materials and compared against the spectrophotometric Trinder method. The devised enzymatic biosensor is affordable (less than 0.2€), sturdy, and versatile inasmuch as the chemical composition of the receptor and pair of LEDs might be customized at will.

Low-cost optical detectors and flow systems for protein determination.

Two miniature, fibreless, compact and highly integrated flow-through optoelectronic detectors dedicated for photometric and fluorimetric determination of proteins have been developed. Both detectors operating according to paired-emitter-detector-diode methodology are constructed only of light emitting diodes and therefore their total cost is extremely low. The photometric detector is dedicated for protein determination according to Bradford method based on detection of protein adduct with Coomassie Brilliant Blue. The fluorimetric detector allows determination of proteins after reaction with fluorescamine. Both developed detectors have been incorporated into economic flow systems constructed of microsolenoid valves and pumps. The resulting multicommutated/multipumping flow analysis systems enable detection of albumins and globulins at ppm levels, thus they are useful for protein determination in diluted samples of physiological fluids.

A concept of dual optical detection using three light emitting diodes.

In this paper a concept of very simple measurement system dedicated for simultaneous photometric and fluorometric detection is presented. Only three ordinary unmodified light emitting diodes (LEDs) can be applied in this analytical device: one of them is used in the conventional way as a source of nearly monochromatic light inducing fluorescence, whereas two others are applied as photometric and fluorometric detectors of light. In this study quinine is chosen as a model analyte. The reported device enables simultaneous detection of this analyte in the micromolar range of concentration. The practical utility of prototype dual detector for complex sample analysis is illustrated by its application for determination of quinine in tonic water samples.

Fluorimetric detector and sensor for flow analysis made of light emitting diodes

Two compact optoelectronic fluorimetric devices operating according to the paired-emitter-detector-diode concept have been developed. The fluorimetric detector, fabricated of three light emitting diodes only, has been applied for the development of fluorimetric optosensor by further integration with sensing solid phase. In these investigations as a model analyte and as a model sensing layer useful for solid phase spectrometry, riboflavin and C18-silica have been chosen, respectively. Both developed analytical devices have been applied for non-stationary fluorimetric measurements performed under conditions of flow injection analysis. The presented flow-through detector and sensor operating under given flow conditions offer riboflavin determination in mg L(-1) and μg L(-1) ranges of concentration, respectively.

Compact optoelectronic flow-through device for fluorometric determination of calcium ions

A low-cost and compact complete fluorometric detector dedicated for measurements under conditions of flow injection analysis has been developed. This device is fabricated by integration of light emitting diodes (LEDs) applied in the double role: as the source of light inducing fluorescence and as the detector of light emitted by excited fluorescent analyte. The device is made of three LEDs only, without any additional fibers, filters and lenses. The LEDs are integrated in the form of flow cell of 0.060 mL internal volume. The developed detector has been tested in simple flow injection manifold dedicated for fluorometric determination of calcium using calcein method. The system offers sensitive and selective determination of calcium at ppm levels with relatively high flow throughput (near 60 injections per hour) and satisfactory reproducibility. The practical utility of developed detector has been confirmed by its application for analysis of mineral waters, medicines as well as physiological fluids.

A multicommutated tester of bioreactors for flow analysis

Enzymes are often used in the modern analytical procedures allowing selective recognition and conversion of target analytes into easily detected products. In flow analysis systems, enzymes are predominantly applied in the immobilized forms as flow-through bioreactors. In this research the multicommutated flow analysis (MCFA) system for evaluation and comparison of analytical parameters of bioreactors has been developed. The MCFA manifold allows simultaneous testing up to four bioreactors, but if necessary their number can be easily increased. The system allows comparison of several parameters of tested bioreactors including activity, repeatability, reproducibility, operational and storage stability. The performance of developed bioreactor tester is presented using urea-urease model system based on plastic open-tubular bioreactor with covalently immobilized enzyme. Product of enzymatic reaction is detected using two different chemical methods and by dedicated optoelectronic ammonium detectors. Moreover, the utility of developed MCFA manifold for evaluation of other enzyme bioreactors is demonstrated.

Disaccharides Determination: A Review of Analytical Methods

ABSTRACT Disaccharides are determined mainly for dietetic purposes, hence the most analyses are carried out for food and drink samples. Its content can also be used to profile groceries in order to identify the origin and quality of the products. They also can be an indicator of the rate of metabolism as well as for the control of some technological and biotechnological processes. Unfortunately most of technological analysis are performed with nonselective polarimetry methods. Sugars due to specific physicochemical properties of compounds are difficult to determine with classical analytical techniques. The most common disaccharides are composed of several types of monomers connected by a different configuration of the glycosidic bond, therefore, there are subject of the same characteristic reactions. This often enforces the need for pre-separation of sample components. Therefore, nowadays the most popular analytical methodologies for disaccharides determination are based on chromatographic and electrophoretic techniques. An alternative is enzymes application that allow both selective recognition of target analyte and its conversion to easy detected product, allowing detection by relatively simple conventional analytical methods. Another approach is the use of advanced chemometric methodologies for computing of data obtained from some spectroscopic techniques. This article is a review of the recent analytical literature devoted to non-selective and selective methods for disaccharide determination in real samples.