Michal Borecki

Optoelectronic capillary sensors in microfluidic and point-of-care instrumentation.

This paper presents a review, based on the published literature and on the authors’ own research, of the current state of the art of fiber-optic capillary sensors and related instrumentation as well as their applications, with special emphasis on point-of-care chemical and biochemical sensors, systematizing the various types of sensors from the point of view of the principles of their construction and operation. Unlike classical fiber-optic sensors which rely on changes in light propagation inside the fiber as affected by outside conditions, optical capillary sensors rely on changes of light transmission in capillaries filled with the analyzed liquid, which opens the possibility of interesting new applications, while raising specific issues relating to the construction, materials and instrumentation of those sensors.

A Method of Examination of Liquids by Neural Network Analysis of Reflectometric and Transmission Time Domain Data From Optical Capillaries and Fibers

This paper presents the construction and working principles of an intelligent fiber-optic sensor used for liquid examination using time domain data. The sensing elements consisted of a length of optical fiber or a short section of optical capillary and worked either on the reflection intensity basis or on transmission intensity basis. The changes of the monitored signal are caused mainly by the variation in light propagation conditions at the interfaces of liquid and gaseous phases and formation of drops of liquids or lenses at liquid-vapor interfaces. The physical effects on which depends the formation of a drop of liquid or a lens are surface tension, viscosity, boiling point, vapor pressure of liquid and its heat capacity. They provide information allowing determining the type of the liquid by a procedure which includes submerging, submersion, emerging and emergence of the sensing head from the examined liquid, or by local heating of the liquid sample. The measured data were analyzed using neural networks.

Capillaries as the components of photonic sensor micro-systems

Optical capillaries are used in gas and liquid chromatography, electrophoresis, absorbance spectroscopy, Raman spectroscopy, etc. The use of optical capillaries in these micro-fluidic techniques emerged in the 1990s and generated new applications in biotechnologies, medical diagnostic, drug discovery and environmental sciences. The wide range of possible capillary constructions allows them to be tailored advantageously to specific applications. In the present work we discuss some aspects of integration of the photonic heads that use optical capillaries in micro-fluidic systems. The field of research is multidisciplinary, comprising certain aspects of physics of micro fluid sample motion, optical detection and the adaptation of the technology to practical applications. To make it possible to analyze small volumes of fluids, we analyzed the light guidance in capillary tubing. We examined both theoretically and experimentally the phenomena of light propagation, under various conditions, in optical capillaries partially filled with a liquid. We have shown that the light propagation depends on the construction of the capillary, its length and the position of the inserted drop of liquid. We designed and constructed structures built of silicon substrates and thin wall capillaries, and then examined theoretically and experimentally how, on heating the capillary locally, the vapor phase of the micro liquid sample forms in the structures. The results obtained show that, using small liquid samples with volumes below 10−8 cm3, the micro-fluidic systems equipped with capillary tubing can be used as the sensors of the surface tension, viscosity, boiling point and vapor pressure of the liquid and its heat capacity. The proposed system provides information that allows determination of the type of the liquid especially when the data are analyzed using neural networks.

Technology and characterization of 4H-SiC p-i-n junctions

Silicon Carbide (SiC) photodiodes have been proposed in recent years for ultraviolet (UV) light detection because of their robustness even in harsh environments, high quantum efficiency in all the UV range (200nm-400nm), excellent visible and infra-red blindness excluding UV filters implementation, low dark current and high speed. 4H-SiC has a bandgap three times larger (3.26eV) than Si and, thus, SiC detectors should have much higher sensitivity than Si detectors. In this paper, we present an overview of results on 4H-SiC p-i-n junctions fabrication and characterization. We used implantation technique to obtain p-region of the investigated structure. The ohmic contacts were formed using evaporation, etching and lift-off. Current-voltage, contact resistance and electroluminescence are the main characteristics of the presented devices. All the diodes showed excellent rectification with leakage current density of less than 10-9A/cm2.

Short capillary tubing as fiber optic sensor of viscosity of liquids

Optical capillaries are used in capillary gas and liquid chromatography, capillary electrophoresis, absorbance spectroscopy, Raman spectroscopy etc. These micro-fluidic methods find applications in biotechnologies, medical diagnostic, drug discovery and environmental sciences. In the presented work we discuss some aspects of light guidance in capillary tubing made from silica glass or Teflon AF. The wide range of capillary constructions allows them to be used advantageously in specific applications. We have analyzed both theoretically and experimentally partially liquid filled optical capillaries as fiber optic sensor elements in laser light transmission and reflection conditions at 670, 1310 and 1550 nm. We have shown that the light transmission properties and signal in the reflectometric mode of work depend on capillary construction, their length and position of inserted liquid drop. The results obtained by us show that capillary tubing can be used as sensing elements in optical fiber sensors of surface tension and viscosity of small liquid samples with volume below 10-8 cm3.

Light transmission characteristics of silica capillaries

The paper discusses certain aspects of the light guidance in capillary tubing and the possibilities of its utilization in fibre optic sensors heads.

A method of examination of liquids by neural network analysis of reflectometric time domain data from optical capillaries and fibers

This paper presents the construction and working principles of a reflectometric intelligent fiber-optic sensor used for liquid examination. Unlike other well-known fiber optical sensors which use information from optical wavelength variations, the proposed system uses time domain data. The sensing element consists of a length of optical fiber and a short section of optical capillary and works on the reflection intensity basis. The reflected signal level depends on the optical construction of the sensor element. The changes of the monitored signal are caused mainly by variation in light propagation conditions at the interfaces of liquid and gaseous phases. The physical effects involved are Fresnel reflection, local numerical aperture variation and liquid lenses formation. It is possible to call out across the changes of those effects by introducing a measuring procedure which includes submerging, submersion, emerging and emergence of the sensing head from the examined liquid or by local heating of the liquid sample.

Plastic optical fibers in sensors: a review

Basic properties of thermoplastic optical fibers are described. Resulting possibilities and limitations of polymer fiber use in optical sensors are discussed. As an example the idea of the integrated alarm system head, containing smoke, temperature and humidity sensors, is shown.

Automatic detection of characteristic points and form of optical signals in multiparametric capillary sensors

The time series sequence of data readings are the input for computer aided analysis of signal from the multiparametric optical capillary sensor. The time series signals have characteristic points and forms. Their analysis by trained human operators is time consuming and sometimes lacks of precision because of the presence of signal noise. The noises can be mostly rejected with advanced electronic signal processing, but the output analog signal is often modified by the electromagnetic environment and by the noise generated by electronic elements. We propose and analyze an algorithm that can be used as an automatic detector of characteristic points and form of the time series signals that are produced by the measuring head and the analog electronic units of the biodiesel fuel quality test sensor.

Large-area transparent in visible range silicon carbide photodiode

This paper describes the construction, fabrication and properties of large-area ultra violet detector that is transparent in the visible range. The device was made on n-type 4H SiC substrate with a double epitaxial layer in which aluminum was implanted to form a p-n junction close to the surface, and a SiO2 layer was formed for passivation, without a guard ring. The design of the top and bottom electrodes of 4mm diameter UV sensitive area allows not less than 20% visible range transmission. This transmission was measured across sensitive area of examined devices and was only 5% lower than that of the substrate before implantation and electrodes deposition.