BIOSENSORS

DEFINITION Self-contained integrated device that is capable of

providing specific qualitative or semi-quantitative analytical information using a biological recognition element which is in direct-spatial contact with a transduction element. (IUPAC,1998)

COMPONENTS

Detector

ELEMENTS OF BIOSENSORS

BIOSENSOR.

Analyte

Sample handling/preparation

Detection

SignalAnalysis

Response

THE ANALYTE.(What do you want to detect?)

MoleculeProtein, toxin, peptide, vitamin, sugar, metal ion

Cholera toxin Glucose

DETECTION/RECOGNITION.(How do you specifically recognise the analyte?)

Antibody Enzyme

Active site

Fc

Cell

Membrane receptors

Polymer/Hydrogel

Competitive binding

Fab

WORKING PRINCIPLEAnalyte diffuses from the solution to the surface of the Biosensor.Analyte reacts specifically & efficiently with the Biological Component of the Biosensor.This reaction changes the physicochmical properties of the Transducer surface.This leads to a change in the optical/electronic properties of the Transducer Surface.The change in the optical/electronic properties is measured/converted into electrical signal, which is detected.

ADVANTAGES

Highly Specific.Independent of Factors like stirring, pH, etc.Linear response, Tiny & Biocompatible.Easy to Use, Durable.Require only Small Sample Volume.Rapid, Accurate, Stable & Sterilizable.

TYPES

Calorimetric/Thermal Detection Biosensors. Optical Biosensors. Resonant Biosensors. Piezoelectric Biosensors. Ion Sensitive Biosensors. Electrochemical Biosensors.

Conductimetric Sensors. Amperometric Sensors. Potentiometric Sensors.

Calorimetric / Thermal Detection Biosensors. Uses Absorption / Production of Heat.

Total heat produced/absorbed. Temp. measured by Enzyme Thermistors.

Advantages:• No need of Frequent recalibration.• Insensitive to the Optical & Electrochemical

Properties of the sample.Uses:Detection of: (1) Pesticides .

(2) Pathogenic Bacteria.

Optical Biosensors. Colorimetric for colour - Measures change in

Light Adsorption. Photometric for Light Intensity - Detects the

Photon output.

Resonant Biosensors. An Acoustic Wave Transducer is coupled with

Bio-element. Measures the change in Resonant Frequency.

Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound.

Piezoelectric Biosensors. A piezoelectric sensor is a device that uses the

piezoelectric effect, to measure changes in pressure, acceleration, temperature, strain, or force by converting them to an electrical charge. The prefix piezo- is Greek for 'press' or 'squeeze'.

Ion Sensitive Biosensors. Are semiconductor FETs with ion-sensitive surface. Surface Electrical Potential changes when the ions &

semiconductors interact. Measures the Change in Potential. Uses:o pH Detection.

Electrochemical Biosensors.Underlying Principle – Many chemical produce or

consume ions or ȇs causing some change in the electrical properties of the solution that can be sensed out & used as a measuring parameter.

Uses:Detection of : o Hybridized DNAo DNA- binding Drugs &o Glucose Concentration.

Conductimetric Sensors. Measures Electrical Conductance/Resistance of the

solution. Conductance Measurements have relatively Low

Sensitivity.

Amperometric Biosensors. High Sensitivity Biosensor. Detects electroactive species present in the

biological test samples. Measured Parameter – Current.

Potentiometric Sensors. Working Principle – When ramp voltage is

applied to an electrode in solution, a current flow occurs because of electrochemical reactions.

Measured Parameter – Oxidation / reduction Potential of an Electrochemical reaction.

In electronics and electrical engineering, a ramp generator is a function generator that increases its output voltage up to a specific value, called a ramp. Among multitude of other uses, it is used in electrical generators or electric motors to avoid jolts when changing a load.

The enzyme electrode is a miniature chemical transducer which functions by combining an electrochemical procedure with immobilized enzyme activity.

This particular model uses glucose oxidase immobilized on a gel to measure the concentration of glucose in biological solution and in the tissue in vitro.

ENZYME ELECTRODE

IMMUNOELECTRODES

IMMUNOELECTRODES

The enzyme horseradish peroxidase (HRP)

MICROBIAL BIOSENSORS

APPLICATIONS

The DNA capture element instrument- for hereditary diseases

Glucometer- for measurement of glucose in blood.

Pregnancy Test.•Detects the hCG protein in urine.• Interpretation and data analysis performed by the user.

Infectious Disease Biosensor.•Data analysis and interpretation performed by a microprocessor.

BIOSENSOR FOR DETECTION OF POLLUTION & OF THE CHEMICALS PRESENT IN THE ENVIRONMENT.

Luminescence is emission of light by a substance not resulting from heat; it is thus a form of cold body radiation. It can be caused bychemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a substance as a result of heating. Historically, radioactivity was thought of as a form of "radio-luminescence", although it is today considered to be separate since it involves more than electromagnetic radiation. The term 'luminescence' was introduced in 1888 by Eilhard Wiedemann.[1][2]

•Chemiluminescence, a result of a chemical reaction

• Bioluminescence, emission as a result of biochemical reaction by a living organism

• Electrochemiluminescence, a result of an electrochemical reaction

Luminescence is "cold light" that can be emitted at normal and lower temperatures.

Fluorescence and Photoluminescence are luminescence where the energy is supplied by electromagnetic radiation

Fireflies and glow-wormsFireflies and glow-worms (their larvae) are the best-known examples of bioluminescent creatures. They use a complex reaction to make light from a pair of chemicals called luciferin and luciferase stored in their tails. Bioluminescence is a special kind of chemoluminescence that happens inside living things.

FLUORESCENCE

Cytokines are a large group of proteins, peptides or glycoproteins that are secreted by specific cells of immune system. Cytokines are a category of signaling molecules that mediate and regulate immunity, inflammation and hematopoiesis.

Multiplex (Bioplex) or cytokines analyzer

Similar to ELISA, a majority of assays are designed according to a capture sandwich immunoassay format. Briefly, the capture antibody-coupled beads are first incubated with antigen standards or samples for a specific time. The plate is then washed to remove unbound materials, followed by incubation with biotinylated detection antibodies. After washing away the unbound biotinylated antibodies, the beads are incubated with a reporter streptavidin-phycoerythrin conjugate (SA-PE). Following removal of excess SA-PE, the beads are passed through the array reader, which measures the fluorescence of the bound SA-PE

Multiplex Assay Beads

The substrate for the antibody sandwich is the bead. Bead characteristics define instrument compatibility and workflow and can be classified into two basic categories, nonmagnetic and magnetic. The nonmagnetic beads are smaller in size (5.6 μ) and are used with the vacuum workflow; they are not compatible with certain instruments that utilize magnets for imaging purposes. Nonmagnetic beads utilize a vacuum workflow requiring filter plates and vacuum filtration to wash the beads. Magnetic beads are coated with magnetite and are therefore larger in size (6.5 μ); they can be used with the magnetic workflow as well as vacuum workflows. These magnetic beads (6.5 μ) are compatible with all currently available life science instruments from any Luminex partner. In the magnetic workflow the beads are washed in the well with dispense and aspiration washing.

xMAP assays may contain nonmagnetic or magnetic beads as substrates. Magnetic COOH beads are the newest core components of xMAP assays. They are unique in that they exhibit both fluorescent and magnetic properties. The beads are stained with a fluorescent dye formulation proprietary to Luminex (Figure 2). The staining process involves swelling the bead particles in a dye containing solvent, which allows the dye molecules to infuse into the coating or the polymer layer. Removal of the solvent in a subsequent step shrinks the beads and traps the dye molecules within the bead particles. The magnetite layer of the bead is one important feature that allows many of the newer assays to be automated with robotic wash stations.