Transcript Biosensors
Biosensors Presented by: Dr. Manouchehr Bahrami Prepared by MEMS group University of Tabriz Department of Electrical and computer Eng. Outline 1) Introduction to Biosensors 2) Bioreceptors 3) Immobilization of Bioreceptors 4) Transduction methods and example devices Introduction to Biosensors A biosensor is an analytical device which is used to determine the presence and concentration of a specific substance in a biological analyte Desired molecule Bioreceptor Transducer Biosample Biosensor Signal Processing Transduction Recognition Signal Processing Display Introduction to Biosensors Bioreceptor Antibody Transducer Optical Enzyme Electrochemical Nucleic Acid (DNA) Mass based Cell Temperature based MIP Electric & Magnetic Absorption Fluorescence Interference potentiometric amperometric conductimetric Dielectric properties Permeability properties Voltage or Current Bioreceptors Antibody Antibodies are biological molecules that exhibit very specific binding capabilities for specific structure (antigens). membrane Antigen It can be recognized by antibody. Bioreceptors Bioreceptor Display Bioreceptors Enzyme Enzyme is a large protein molecule that acts as a catalyst in chemical reactions. Enzymes are often chosen as bioreceptors based on their specific binding capabilities as well as their catalytic activity Bioreceptors Bioreceptor Display Bioreceptors DNA structure Another biorecognition mechanism involves hybridization of deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), which are the building blocks of genetics. Four chemical bases: • adenine(A), guanine (G), • cytosine (C), and thymine (T) Bioreceptors Principles of DNA biosensors Nucleic acid hybridization (Target Sequence) ssDNA (Probe) (Hybridization) (Stable dsDNA) Bioreceptors Bioreceptor Display Bioreceptors Living Cell Nourishment Product Bioreceptors Bioreceptor Display Bioreceptors MIP (Molecular Imprinted Polymer) Bioreceptors MIP as a bioreceptor Bioreceptors Bioreceptor Display Immobilizatiom The immobilization is done either by physical entrapment or chemical attachment. Physical Entrapment Bioreceptor (Antibody, Enzyme, Cell, …) + polymer solution → polymerization Adsorption adsorptive interactions such as ionic, polar or hydrogen bonding and hydrophobic interaction. Immobilizatiom Covalent bounding formation of a stable covalent bond between functional groups of the bioreceptor components and the transducer Cross-linking bridging between functional groups on the outer membrane of the receptor by multifunctional reagents to transducer. The cells can be bounded directly onto the electrode surface or on a removable support membrane, which can be placed on the transducer surface conductimetric Transducers- Optical methods Concept: Capture analyte and detect binding by optical tag or binding-sensitive optical phenomenon Absorption I1/I0 = e−αlc l is the pass length C is the concentration of absorbing material α is the absorption coefficient Transducers- Optical methods- Absorption A device to determine a patient’s blood oxygen content: “the oximeter” The absorption spectra (α) of haemoglobin (Hb) and oxyhaemoglobin (HbO2) differ, which makes it possible to measure the ratio of both concentrations in blood by measuring the absorption of light of two different wavelengths, e.g. 660 nm and 805 nm. Transducers-Optical methods- Florescence Fluorescence is a molecular absorption of light at one wavelength and its instantaneous emission of at longer wavelengths. Some molecules fluoresce naturally and others such as DNA can be modified for fluorescence detection by attachment of special fluorescent dyes An optical system for Florescence measurement Transducers-Optical methods- Florescence Grating Antigens modified by florophor dye Evanescent-field. Planer waveguide Excitation light Florescence detector A device for florescence measurement Transducers-Optical methods- Florescence Taq-Man probe in its preliminary condition for real time PCR devive T 55 c Hybridisation of primer and Taq-Man probe at annealing temperature T 72 c Releasing fluorophore dye during extension Transducers-Optical methods- Florescence Real time Chamber PCR device with integrated fluorescence detection Photodiode pattern to reduce direct illumination Optical fibre used to introduce excitation energy Pyrex Si Photodiode implanted at the bottom of the chamber and CdS film covers the photodiode Pyrex Si Temperature sensor and heaters Transducers-Optical methods-refractive index Mach-Zehnder interferometer Transducers-Optical methods-refractive index The reflected wavelength (λB), called the Bragg wavelength, is defined by Transducers-Optical methods-refractive index Optical waveguide based biosensor Transducers-Electrochemical methods The underlying principle for this class of biosensors is that many chemical reactions produce or consume ions or electrons which in turn cause some change in the electrical properties of the solution which can be sensed out and used as measuring parameter Transducers-Electrochemical methods-amperometric amperometric glucose biosensors Transducers-Electrochemical methods-amperometric amperometric glucose biosensors Transducers-Electrochemical methods-potentiometric Schematic diagram of an integrated enzyme-based flow-through glucose sensor. Transducers-Electrochemical methods-potentiometric Transducers-Electric methods Concept: Capture analyte and detect changes in electrical parameters of sample Immunosensing at micro-sized Au electrodes based on the change of conductivity between the Au strips upon binding of Au nanoparticles Transducers-Electric methods Capacitive sensor by MIP dielectric Variation of Transducers-Electric methods F= 20KHz, AC amplitude of 40 mV peak to peak Transducers-Mass based methods The principle is to change in the frequency of vibrating element. when the mass increases due to binding of chemicals, the oscillation frequency of the device changes and the resulting change can be measured electrically and be used to determine the additional mass. Transducers-Mass based methods Detection by cantilevers Transducers-Mass based methods Detection by cantilevers Change in the resonance frequency: AcV1 antibody (green) and baculovirus particles (red). Transducers-Mass based methods Detection by cantilevers (a) A mechanical cantilever resonator containing an embedded microfluidic channel. (b) Decrease in resonant frequency as the density inside the embedded channel increases. (c) Frequency modulation by single particle movment Transducers-Mass based methods Detection by cantilevers Microcantilever technology: a) with immobilised protein for a specific bacterium b) bending after adsorption of bacteria to the protein Transducers-Mass based methods Transducers-Temperature methods This type of biosensor is exploiting one of the fundamental properties of biological reactions, namely absorption or production of heat, which in turn changes the temperature of the medium in which the reaction takes place. They are constructed by combining immobilized enzyme molecules with temperature sensors. When the analyte comes in contact with the enzyme, the heat reaction of the enzyme is measured and is calibrated against the analyte concentration. The total heat produced or absorbed is proportional to the mola r enthalpy and the total number of molec ules in the reaction Transducers-Temperature methods A three-dimensional schematic representation of the proposed microcalorimeter with integrated microfluidic channels.