Hunor Sántha

Polytronics for biotronics: unique possibilities of polymers in biosensors and bioMEMS ?

In recent years, sensing polymeric materials have gained a wide theoretical interest and practical application in biomedicine both in sensors and in bio-MEMS. They can be used for very different purposes and may offer unique possibilities. The paper give a broad summary of the polymer films used in these type applications. Polymers offer a lot of advantages for medical and biosensor technologies: they are relatively low cost materials, their fabrication techniques are quite simple, they can be deposited on various types of substrates using methods compatible with all microelectronic and micro fabrication technologies, as well as the wide choice of their molecular structure and the possibility to build in side chains, charged or neutral particles or even grains of specific behavior into the bulk material or on its surface region enables producing films with various physical and chemical properties including also sensing behavior.

Hybridization chain reaction performed on a metal surface as a means of signal amplification in SPR and electrochemical biosensors

A more specific and intense signal is desirable for most kinds of biosensors for biomedical or environmental applications, and it is especially so for label-free biosensors. In this paper, we show that hybridization chain reaction (HCR) can be exploited for the easily detectable accumulation of nucleic acids on metal surfaces as an event triggered by specific recognition between a probe and a target nucleic acid. We show that this process could be exploited to increase the sensitivity in the detection of nucleic acids derived from a pathogenic microorganism. This strategy can be straightforwardly implemented on SPR biosensors (commercial or custom-built) or on label-free electrochemical biosensors. Together with signal amplification, HCR can serve as a confirmation of the specificity of target recognition, as it involves the specific matching with a separate base sequence in the target nucleic acid. Furthermore, the kinetics of the target binding and the HCR can be easily distinguished from each other, providing an additional means of confirmation of the specific recognition.

Amperometric uric acid biosensors fabricated of various types of uricase enzymes

Preparation process of an enzyme-based bipotentiostatic amperometric uric acid sensor has been investigated. The suitability of three different Uricase (EC 1.7.3.3) enzymes (from porcine liver, Candida Utilis, Bacillus Fastidiosus) is described in this paper. The sensor fabricated of Uricase from Candida Utilis showed a linear response to uric acid in the 0-0.9 mM concentration range and the response current range was 0-3.3 /spl mu/A. The sensor fabricated of Uricase from Bacillus Fastidiosus has been saturated at 0.72 mM and the response was not linear above 0.24 mM. The response current range was 0-0.9 /spl mu/A. The sensor fabricated of Uricase from porcine liver has not given detectable electrical signal due to its very low specific activity. The substrate was prepared by screen printing on sintered alumina ceramic sheets using pastes of Au or Pd-Pt as working (W) and counter (C) and Pt-Ag as a reference (R) electrode. Galvanostatic electrocopolymerization of dodecyl sulfate doped poly-N-methyl-pyrrole (pNMPy) layer was used for enzyme immobilization. The layout of the sensor consists of four electrode surfaces (W/sub 1/, W/sub 2/, R, and C). By the bipotentiostatic technique, the two working electrodes (with and without the enzyme) are identically prepared and polarized, while the currents in the two circuits are measured simultaneously; thus, the current of the W/sub 2/-C circuit (I/sub 2/) can be substracted as a nonspecific background noise. The nonspecific oxidation of uric acid on the poly-N-methyl-pyrrole layer at 0.2 V has been demonstrated in oxygen bubbled buffer solution.

Phantom with Pulsatile Arteries to Investigate the Influence of Blood Vessel Depth on Pulse Oximeter Signal Strength

This paper describes a three-layer head phantom with artificial pulsating arteries at five different depths (1.2 mm, 3.7 mm, 6.8 mm, 9.6 mm and 11.8 mm). The structure enables formation of spatially and temporally varying tissue properties similar to those of living tissues. In our experiment, pressure pulses were generated in the arteries by an electronically controlled pump. The physical and optical parameters of the layers and the liquid in the artificial arteries were similar to those of real tissues and blood. The amplitude of the pulsating component of the light returning from the phantom tissues was measured at each artery depth mentioned above. The build-up of the in-house-developed pulse oximeter used for performing the measurements and the physical layout of the measuring head are described. The radiant flux generated by the LED on the measuring head was measured to be 1.8 mW at 910 nm. The backscattered radiant flux was measured, and found to be 0.46 nW (0.26 ppm), 0.55 nW (0.31 ppm), and 0.18 nW (0.10 ppm) for the 1.2 mm, 3.7 mm and 6.8 mm arteries, respectively. In the case of the 9.6 mm and 11.8 mm arteries, useful measurement data were not obtained owing to weak signals. We simulated the phantom with the arteries at the above-mentioned five depths and at two additional ones (2.5 mm and 5.3 mm in depth) using the Monte Carlo method. The measurement results were verified by the simulation results. We concluded that in case of 11 mm source-detector separation the arteries at a depth of about 2.5 mm generate the strongest pulse oximeter signal level in a tissue system comprising three layers of thicknesses: 1.5 mm (skin), 5.0 mm (skull), and >50 mm (brain).

On-line cell lysis of bacteria and its spores using a microfluidic biochip

Optimal detection of pathogens by molecular methods in water samples depends on the ability to extract DNA rapidly and efficiently. In this study, an innovative method was developed using a microfluidic biochip, produced by microelectrochemical system technology, and capable of performing online cell lysis and DNA extraction during a continuous flow process. On-chip cell lysis based on chemical/physical methods was performed by employing a sufficient blend of water with the lysing buffer. The efficiency of lysis with microfluidic biochip was compared with thermal lysis in Eppendorf tubes and with two commercial DNA extraction kits: Power Water DNA isolation kit and ForensicGEM Saliva isolation kit in parallel tests. Two lysing buffers containing 1% Triton X-100 or 5% Chelex were assessed for their lysis effectiveness on a microfluidic biochip. SYBR Green real-time PCR analysis revealed that cell lysis on a microfluidic biochip using 5% Chelex buffer provided better or comparable recovery of DNA than commercial isolation kits. The system yielded better results for Gram-positive bacteria than for Gram-negative bacteria and spores of Gram-positive bacteria, within the limits of detection at 103 CFU/ml. During the continuous flow process in the system, rapid cells lysis with PCR-amplifiable genomic DNA were achieved within 20 minutes.

A Novel Point of Care Diagnostic Device: Impedimetric Detection of a Biomarker in Whole Blood

There is an unmet medical need for a more reliable and earlier assessment of patients suspected of having a deep vein thrombosis. We describe a novel approach which is developing a highly reliable, accurate, portable and handheld prototype medical diagnostic device to improve radically the speed, accuracy and reliability with which DVT and related blood clotting conditions can be assessed. The device will measure whole blood concentration of D-dimer, a recognized biomarker of increased blood clotting activity, and through innovation in the development of a novel detection, measurement and reporting system, will offer the opportunity to use the test in the point of care setting. The device combines innovation in antibody bio-engineering for high specificity immunoassay-based diagnostics and nano/micro engineered impedimetric analysis electrodes incorporating a biocompatible polymer substrate with development of a disposable microfluidic manifold specifically enabling diagnostics at the point-of-first-contact.

DNA chip with electronically accelerated processes

In recent years DNA chips are in the focus of research activities in the field of molecular biology. Their principle is based on hybridization, the specific recognition between complementer single-stranded DNA segments. In this paper the preparation of a substrate for DNA chip purposes is described. The substrate material is glass with a thin film Au microelectrode array, which is covered with an insulating layer. A flow injection electrochemical cell with a volume of 250 /spl mu/l has been fabricated, where the working electrodes (w) are Au surfaces with 300 /spl mu/m diameter, the counter electrode (c) is a Pt wire and the reference electrode (r) is an Ag/AgCl wire. The wires are in a symmetrical arrangement. The flow injection chamber can be from the Au covered substrate dismounted. The working substrates are connected to the potentiostat through a standard 1.27mm connector. In case of this DNA chip the electrical acceleration of hybridization and readout can be demonstrated.

A custom-developed SPRi instrument for biosensor research

In this paper we present a custom-developed, small, fixed-angle Surface Plasmon Resonance imaging (SPRi) instrument that enables the biochips to be prepared in an array format providing SPR information simultaneously on up to 100 active sites (spots). Besides the presentation of the hardware and software setup of our device we also demonstrate the application with pilot measurement results on different solutions containing NaCl, sucrose, avidin or DNA. The sensitivity of our instrument is calculated in function of the concentration.

Optimization of microfluidic flow sensors for different flow ranges by FEM simulation

Finite element simulation and post-processing results of calorimetric type microfluidic mass flow sensors are presented. The output characteristics of a calorimetric flow sensor are functions of the geometrical position of the temperature sensor elements. A given flow sensor (with a given technology on a given substrate) can be optimized for different flow ranges by determining the position of the temperature sensor elements. The simplified mathematical model of the steady-state thermal profile along the microfluidic channel is presented. It is also shown how the output characteristics depend on the position of the temperature sensors and the ratio of the convective and conductive heat transfer. The optimal parameters of a silicon substrate based microfluidic flow sensor for low and for high flow ranges were calculated by FEM simulation. Based on the simulation results the silicon substrate based microfluidic flow sensor could be optimized for different flow ranges.

Design Considerations of Small Size Reflective Type Pulse Oximeter Heads in Special Applications

Many pulse oximeter types are available on the market but development of reflective pulse oximeters is still required by health care players. An approach to determine optimal conditions of such measurements by means of objective methods and a pilot experiment is described in this paper. The optimal distance between the light sources and the detector and the optimal force to press a reflective pulse oximeter sensor head onto the skin are characterisable by the presented method and experimental setup. The preferable values are probably between 0.5-2 g/mm2 but the distance between the light sources and the detector shifts this value and changes the length of stabile region of performance as well, however, observed phenomena indicate, that pressure value alone is not enough to normalize results and compare pulse oximetry measuring heads having significant difference in size