Łukasz Tymecki

Simplified paired-emitter–detector-diodes-based photometry with improved sensitivity

Paired emitter-detector diodes (PEDDs) coupled with potentiometric pH-meter or multimeter have been characterized as complete instruments for common photometric measurements as well as optical flow-through detectors. The analytical characteristics of investigated devices have been illustrated by the use of two paired red LEDs for the determination of bromothymol blue (BTB) as a model analyte. The developed devices allow rapid and sensitive BTB detection in the ppm range of concentration. Measurements with pH-meter resulted in a wide linearity of PEDD response, whereas PEDDs coupled with ordinary voltmeter offer a significant enhancement of sensitivity. Some practical applications of developed detector for the analytical and bioanalytical measurements have been indicated.

Strip thick-film silver ion-selective electrodes

Abstract Miniaturized, planar silver ion-selective electrodes based on thick film of silver sulfide are described. The sensors were fabricated entirely by screen-printing, using low-temperature-curing polymer pastes and polyester substrate in form of flexible foils. Application of the thick-film technology results in highly reproducible and economic fabrication of the electrodes. These strip sensors exhibit analytical characteristics comparable with those for conventional ion-selective electrodes. The electrodes enable fast and reproducible potentiometric measurements with near-nernstian sensitivity. The sensors exhibit low detection limit and therefore, are useful as indicating electrodes in argentometric titrations as well as sensors for free silver ions in complexing media. The electrodes are also useful for determination of silver cations as well as halide anions under flow injection analysis regime.

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.

A single standard calibration module for flow analysis systems based on solenoid microdevices

Only two computer-controlled microsolenoid devices, namely two micropumps or one micropump and one microvalve, are sufficient for the construction of on-line dilution modules useful in several flow analytical systems for the calibration using single standard. Three simple constructions of such modules were tested and compared. The most promising is the one based on the concept of a microvalve controlling dilution ratio of the standard and a solenoid micropump playing a double role: solution pumping device and mixing segments homogenizer. All investigated modules were tested with paired emitter detector diode (PEDD) as photometric flow-through detector and bromothymol blue as a model analyte. The best module was implemented into more advanced flow-injection system dedicated for optical detection of alkaline phosphatase activity using UV-PEDD-based flow-through detector for the enzyme reaction product.

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.

Hemoglobin determination with paired emitter detector diode

Two ordinary green light-emitting diodes used as light emitter and detector coupled with simple voltmeter form a complete, cost-effective prototype of a photometric hemoglobinometer. The device has been optimized for cuvette assays of total hemoglobin (Hb) in diluted blood using three different chemical methods recommended for the needs of clinical analysis (namely Drabkin, lauryl sulfate, and dithionite methods). The utility of developed device for real analytics has been validated by the assays of total Hb content in human blood. The results of analysis are fully compatible with those obtained using clinically recommended method and clinical analyzer.

POTENTIOMETRIC THICK-FILM GRAPHITE ELECTRODES WITH IMPROVED RESPONSE TO COPPER IONS

Thick-film graphite electrodes produced by screen-printing have been investigated as inexpensive disposable potentiometric sensors for determination of heavy metal ions. The modification of graphite paste with copper sulfides caused an improvement of the analytical characteristics of the sensors. The electrodes based on Cu2S-doped graphite film are useful for reproducible, fast, and selective determination of copper ions with Nernstian sensitivity in a wide range of concentration.

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.

Multicommutated flow analysis system for determination of creatinine in physiological fluids by Jaffe method.

For the needs of photometric determination of creatinine according to Jaffe protocol a dedicated paired emitter detector diode (PEDD) detector has been developed. This PEDD device has been constructed in the compact form of flow-through cell (30 μL total volume and 7 mm optical pathlength) integrated with 505 nm LED-based emitter and 525 nm LED-based detector compatible with multicommutated flow analysis (MCFA) system. This fully mechanized MCFA system configured of microsolenoid valves and pumps is operating under microprocessor control. The developed analytical system offers determination of creatinine in the submillimolar range of concentrations with detection limit at ppm level. The throughput offered by the system operating according to multi-point fixed-time procedure for kinetic measurements is 15-40 samples per hour depending on the mode of measurements. The developed PEDD-based MCFA system has been successfully applied for the determination of creatinine in real samples of human urine as well as serum. The developed sampling unit used the system is free from effects caused by differences in sample viscosity.