Immunosensors based on Polyaniline:A Conducting polymer

AuthorChetana Saparia

MentorProf. A. Contractor

Conductometric sensors based on conductive polymer like polyaniline as transducers which measure the changes in electrical conductivity of conductive polymer due to antigen

antibody interaction

Master Layout

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1Fig 1:

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1Fig 2:

Biological element(Subtrate/

Analyte)

Receptors

Measurement

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1Fig 3:

© Copyright 2009 Sapidyne Instruments Inc. All rights reserved.

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1Fig 4: Conductometric

Sensor concept

Polycarbonate membraneMembrane pores

Gold deposition

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1Fig 5:

Pores of membrane

Antibody

Compact coil of Polyaniline

Antigen

Expanded coil of Polyaniline

Active Device

Change in conductance

Conductometric Sensor concept

Polycarbonate membrane

Gold line

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Polycarbonate membrane

Pores of membrane

Fig A

Binding

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1Fig 6:

PolyanilinePolyaniline + PSS

Polyaniline + PSS + Antibody Polyaniline + PSS + Antibody + Antigen

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Definitions of the components:

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1 In biochemistry, a receptor is a protein molecule, embedded

in either the plasma membrane or the cytoplasm of a cell, to which one or more specific kinds of signaling molecules may attach. A molecule which binds (attaches) to a receptor is called a ligand, and may be a peptide (short protein) or other small molecule, such as a neurotransmitter, a hormone, a pharmaceutical drug, or a toxin. Each kind of receptor can bind only certain ligand shapes. Each cell typically has many receptors, of many different kinds.

A transducer is a device that converts one type of energy to another. The conversion can be to/from electrical, electro-mechanical, electromagnetic, photonic, photovoltaic, or any other form of energy. While the term transducer commonly implies use as a sensor/detector, any device which converts energy can be considered a transducer.

Biosensors have been defined as analytical device which has tightly combined bio-reorganization elements with physical transducers for detection of the target compounds.

Definitions of the components:

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1 Biosensors that uses antibodies or antigens as the specific

sensing element and provide concentration dependent signal are called immunosensor.

Conducting polymer: are conjugated organic polymers that have an extended P-orbital system, through which electrons can be moved from one end of polymer to other end of polymer.

Examples Polyacetyelene, polyparaphenylene, polypyrrole and polyaninline.

A change in the pH of the microenvironment or change in the conformation of the polymer caused by binding event in the polymer matrix result in change in the electronic conductivity of the polymer.

This property of polyaniline has been widely used in the field of Conductometry sensor device.

Definitions of the components:

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1 Analyte: Biosensors are generally concerned with sensing

and measuring particular chemicals which may or may not be biological themselves. We shall usually refer to such a material as the substrate, although the more general term analyte is sometimes used.

In chemistry, protonation is the addition of a proton (H+) to an atom, molecule, or ion. Protonation is possibly the most fundamental chemical reaction and is a step in many stoichiometric and catalytic processes. Some ions and molecules can undergo more than one protonation and are labeled polybasic. This is true of many biological macromolecules. Molecules which can be deprotonated are acids, or polyacids if more than one proton can be removed.

Oxidation:The combination of a substance with oxygen. A reaction in which the atoms in an element lose electrons and

the valence of the element is correspondingly increased.

Definitions of the components:

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1 In polymer chemistry, polymerization is a process of reacting

monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains. There are many forms of polymerization and different systems exist to categorize them.

Analogy / Scenario / Action1

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Fig 1 the picture of man smelling the flower and howhe receives the smell signal is used as an analogy to explain the biosensor fig 2:

In the diagram the terms receptors and the receptor cells are to be made bold.

Stepwise description of process

The goal of the IDD is to provide instructions to an animator who is not a expert.

You have to describe what steps the animator should take to make your concept come alive as a moving visualization.

Use one slide per step. This will ensure clarity of the explanation.

Add a image of the step in the box, and the details in the table below the box.

You can use any images for reference, but mention about it's copyright status

The animator will have to re-draw / re-create the drawings

Add more slides as per the requirement of the animation

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Step 1: 1

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fig 1 the process of smellwill come here

What we detect with our nose is smell– smell is nothing but small quantity of chemicals

It can distinguish between many different chemical substances.

The chemical to be detected is passed over the receptors that sense the substrate.

This is converted into a electrical signal by the receptor cells which is transmitted to the brain.

• In fig 1 : The person smelling the flower on the left side appears first.

• On the left side the process of odorants attaching to receptors and then going to the receptors cells to be converted into signals for the brain.

Audio NarrationDescription of the actionAction

fig 1 man smelling the flower will be

shown here

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Identify the receptors and the transducers in this analogy

• The olfactory sense receptors are similar to the Molecular Recognizing Element that receive the substrate or analyte.

• The receptor cells are similar to transducers in the biosensors, converting sense into electric signals.

• In fig 1 : The person smelling the flower on the left side appears first.

Refer to the terms (receptors and transducers) in the glossary

Audio NarrationDescription of the actionAction

fig 1 the process of smellwill come here

fig 1 man smelling the flower will be

shown here

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• Biosensors are analytical devices which are capable of providing either qualitative or quantitative results.

• Biosensors combine the selectivity of biology with the processing power of modern microelectronics and optoelectronics to offer powerful new analytical tools with major applications in medicine, environmental diagnostics ,food and processing industries.

• In fig 2 appears entirely

Audio NarrationDescription of the actionAction

Fig 3 appear here

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• Biosensors are analytical devices in which the recognition molecule such as enzymes, microorganisms, antibodies are coupled to the transducer in such way that it responds to the corresponding anaylte concentration like substrate, receptors, antigen by measuring the change in signal output.

• Enzymes, nucleic acid, antibodies, tissue slice, binding proteins, whole cells or other bio receptors have been used as sensing probes in biosensors fabrication. It is the first component of the biosensor that has intimate contact with the transducer.

• The term immunosensor is often used to describe biosensors which use antibodies as their biorecognition system. They consist of two processes

1. A molecular recognition process for sensing the Ag-Ab interaction and

2. signal transfer process for responding to change in an electrochemical, optical, spectroscopic or electrical parameter of the receptor caused by specific binding.

• In addition to enzymes and antibodies, the bio-recognition systems can also include nucleic acids, bacteria and single cell organisms and even whole tissues of higher organisms.

• In fig 2: Analyte of the substrate appear.

• They get attached to the receptors

• Passing through the Molecular reorganization Element they reach the Signal transducers

Click on the beginning of the biosensor process

Audio NarrationDescription of the

actionAction

Fig 2 appear here

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• Specific interactions between the target analyte and the complementary bio-recognition layer produces a physico-chemical change which is detected and converted to proportional output by the transducer.

• The transducer can take many forms depending upon the parameters being measured - electrochemical, optical, mass and thermal changes are the most common.

• Transducer converts the biological recognition step to a measurable electrical signal, which is proportional to the concentration of analytes.

• In fig 2: Analyte of the substrate appear.

• They get attached to the receptors

• Passing through the Molecular reorganization Element they reach the Signal transducers to produce electric signal that is then measured.

Click on the beginning of the biosensor process

Audio NarrationDescription of the

actionAction

Fig 2 appear here

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Conductometric sensors (a type of biosensors) based on conductive polymer like polyaniline as a matrix and a transducer. As a matrix it acts as a support for immobilization of antibody and as a transducer, it measures the changes in electrical conductivity of conductive polymer due to changes in microenvironment around conducting polymer.

2. For conductometric sensor application polyaniline is synthesized by electrochemical oxidation of aniline under acidic condition within the pores of micro porous membrane (eg. Polycarbonate membrane) coated with inert metal like gold.

• In fig 4 :White Polycarbonate membrane is shown with text 2.

• Then show it being coated with gold.

• The pores of the membrane remain open.

Audio NarrationDescription of the

actionAction

Fig 4 appear here

Step 4:contd..1

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• Electro polymerization of aniline is carried out inside the micro pores of polycarbonate membrane due to which nanotubes of polyaniline formed, bridges the gold working electrode.

• Polyaniline exhibit different conductivity depending on oxidation and protonation state.

• The emeraldine state of the polymer in its salt exhibits higher conductivity due to formation of polaron conduction band & is widely used.

• Conductivity of polyaniline is highly depended on pH & is high in acidic pH. But treatment of conducting polymer with ionizing agent leads to an increase in its conductivity.

• In fig 5 (fig A): polyaniline nanotubes are added and they enter the pores and are seen in the blue area.

• The blue area get highlighted

• Phase I image is shown.

• As student clicks on any nanotude the electric current passes through the polyaniline nanotubes as shown and the nanotubes get attached to the gold lining and text appears.

Click on the blue area to see what to the polyaniline nanotubes

Click on the nanotube to see binding.

Audio NarrationDescription of the actionAction

Fig 5 (fig A and phase I) appear here

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• This process is known as doping and nature of dopant decides the type of conduction in the resulting conducting polymer chain.

In fig 5:Phase I fig is shown and the active device with the arrow.

Audio NarrationDescription of the

actionAction

Fig 5 and phase I appear here

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• Doping of polyaniline with poly styrene sulphonate (PSS) tends to entrap proton inside the film. So the conductivity of polymer remains unaffected by external pH at a certain pH range, thus maintaining the conductivity at neutral pH.

• Primary dopant for Conductometric polymer is a substance of relatively small quantity which drastically changes the electronic, optical, magnetic and structural properties of the polymer and is accompanied by large increase in the conductivity.

• Similarly De-doping results in a reversal of the newly induced properties.

• In fig 5: Phase II of the fig 5 (labeled) appears.

• Antibodies indicated in blue get attached to the coiled structure of polyaniline.

Audio NarrationDescription of the

actionAction

Fig 5 and phase II appear here

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• Secondary dopant is an apparently inert substance which is applied to a primary doped polymer inducing still further changes in the conductivity.

• It differs from primary dopant in a way that the newly enhanced properties may persist even upon complete removal of the secondary dopant.

• Effect of secondary dopant are based primarily on changes in molecular conformation of the polyaniline from ‘compact coil’ to ‘expanded coil’ during secondary doping process.

• In fig 5: Phase III of the fig 5 (labeled) appears.

• Secondary dopant (antigen) added and attatches to the anitgens in blue and polymer become expanded coiled.

• Change in the conductivity reduces. Move arrow to left.

Audio NarrationDescription of the

actionAction

Fig 5 and phase III appear here

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• In the immunosensors interaction of antigen with antibody are expected to act as a secondary dopant .This causes change in conductivity of polyaniline due to conformation changes.

Audio NarrationDescription of the

actionAction

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• This shows how exactly conformation changes in structure of polyaniline takes place due to binding event between antigen-antibody.

• In fig 6:

• Picture one appears the nanotobes (white) are to be shown green

• Then PSS is added and the black wave like line appears.

• Then picture 3. the antibodies (blue) are added.

• Then picture 4 antigens (red) are added the nanotubes separated out.

Audio NarrationDescription of the

actionAction

Fig 6 appear here

Interactivity and Boundary limits

In this section, you will add the ‘Interactivity’ options to the animation.

Use the template in the next slide to give the details.

Insert the image of the step/s (explained earlier in the Section 3) in the box, and provide the details in the table below.

The details of Interactivity could be: Types: Drop down, Slider bar, Data inputs etc. Options: Select one, Multiple selections etc Boundary Limits: Values of the parameters, which won’t

show results after a particular point Results: Explain the effect of the interaction in this column

Add more slides if necessary

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INSTRUCTIONS SLIDE

Questionnaire to test the user A small, (5 questions) questionnaire can be created in the

next slide, to test the user's comprehension. This can be an objective type questionnaire. It can also be an exercise, based on the concept taught in

this animation. Please give the answer key also.

Questionnaire1. Which state of polyaniline exhibit the higher conductivity.

Answers: a)leucocoemeraldine b) emeraldine

c) pernigraniline d) protoemeraldine

2. Polyaniline in conductometic sensors act as

Answers: a) tranducer b) matrix

c) both d) none

3. Conductivity of polyaniline is higher in

Answers: a) acidic pH b) Basic pH

c) neutral d) none

4. Antigen in immunosensors (antibody immobilized) act as

Answers: a) primary dopant b) secondary dopant

c) dedopant d) dopant

5. In immunosensors the interaction is between

Answers: a) antigen-antibody b) Enzyme-substrate

c) Cell-receptor d) legend-drug

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Links for further reading

Reference websites:http://www.jaist.ac.jp/~yokoyama/biosensor.html

http://www.mdpi.org/sensors/papers/s8096015.pdf

http://www.biosensing.net/iaeac/Posters/ENV18.PDF http://biosensing.files.wordpress.com/2009/05/biosensors-basics_pdf-file1.pdf http://www.springerimages.com/Images/LifeSciences/1-10.1385_1-59259-846-3_029-1http://www.jaist.ac.jp/~yokoyama/biosensor.html

Research papers:

Mandakini Kanungo, Divesh N. Srivastava, Anil Kumar and A.Q.Contractor; Chem. Commun., 2002, 680-681.

V. V. R. Sai, Sumeet Mahajan, Aliasgar Q. Contractor, and Soumyo Mukherji; Anal. Chem. 2006, 78, 8368-837

Books:

• Conducting Polymers, Fundamentals and application 1999, Prasanna Chandrasekhar