Imprinted Polymer

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• Molecular Imprinting Polymers
• MIPs

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Introduction

• In chemistry, molecular imprinting is a technique
  to create template-shaped cavities in polymer
  matrices with memory of the template molecules.

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Schematic of molecular imprinting
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History of Molecular Imprinting

• Molecular imprinting was used as early as the
  1930's by MV Polyakov to selectively capture
  various additives in a silica matrix.
• In the 1940's Linus Pauling hypothesized that a
  process similar to molecular imprinting could be
  responsible for the selectivity of antibodies to
  their respective antigens.

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Biological systems

• Molecular recognition plays an important role in
  biological systems and is observed in between
  receptor-ligand, antigen-antibody, DNA-protein,
  sugar-lectin, RNA-ribosome, etc

Antigens
Antigen-binding site
Antigen
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History of Molecular Imprinting

• The concept of molecular imprinting was revived
  in the 1970's when Günter Wulff discovered that
  highly crosslinked organic polymers could also be
  used to make molecular imprints with high
  specificity.
• In more recent years, imprinted polymers have
  been used to capture everything from steroids to
  TNT.

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Imprinting methodologies

• Covalent
• Reversible covalent linkage

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Molecular Imprinting Covalent
Wulff Schauhoff J. Org. Chem., 1991, 56,
395-400.
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Imprinting methodologies advantages and
disadvantages

• Covalent Imprinting
• Ability to fix template in place during
  polymerisation - lower dispersity in binding
  sites
• Can be carried out in any solvent flexibility
• Can be difficult to remove template from polymer
  - low recovery of valuable templates and low
  number of binding sites
• Limited number of chemistries for fixing template
  to polymer reversibly - reduction in number of
  templates that can be imprinted
• Poor kinetics of re-binding 

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Imprinting methodologies

• Non-covalent
• Monomer-template complexes

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Molecular Imprinting Non-covalent
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Imprinting methodologies - advantages and
disadvantages

• Non-covalent imprinting
• Easy to remove template from polymer- good
  recovery of valuable templates and accessible
  binding sites
• Very large number of templates amenable to
  non-covalent imprinting
• Rapid kinetics of re-binding
• Inability to fix template in place during
  polymerisation - polydispersity in binding sites,
  poor definition
• Generally requires low-polarity aprotic solvents
  - incompatible with aqueous polymerisations 

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Imprinting methodologies

• Sacrificial spacer (semi-covalent)
• Covalent link during synthesis
• Non-covalent rebinding

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Molecular Imprinting Spacer Approach
CVPC
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Imprinting methodologies - advantages and
disadvantages

• Sacrificial spacer method
• Ability to fix template in place during
  polymerisation - lower dispersity in binding
  sites
• Can be carried out in any solvent flexibility
• Rapid kinetics of re-binding
• Can be difficult to remove template from polymer
  - low recovery of valuable templates and low
  number of binding sites
• Limited number of chemistries for fixing template
  to polymer reversibly - reduction in number of
  templates that can be imprinted

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Target molecules Imprinting matrices

• Target molecules
• Small organic molecules, pesticides, amino
  acids, nucleotide bases, steroids ,sugars ,metal
  ion peptides, proteins and drug,
• Imprinting matrices
• Acrylic and vinyl polymers
• Organic polymers
• Other imprinting matrices

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Preparation MIPs

• Generally MIPs have been prepared as monoliths
  using bulk polymerization of vinylic monomer
  mixtures by free radical initiation
• Consequently, the material requires grinding
  before use (sieving is often also employed to
  fractionate by particle size)

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Preparation MIPs

• In situ polymerization.
• In order to avoid the grinding and packing of
  HPLC columns the polymer is formed inside a
  column as a porous monolith.
• Coated silica particles.
• A polymerizable group was first attached to
  the silica surface and polymerization was then
  carried out using template, cross-linker and
  functional monomer.

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2
1
3
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Molecular imprinting of theophylline immobilized
onto a solid support immobilized template with
monomers (1), composite material after
polymerization (2), imprinted polymer after
dissolution of the support.
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Preparation MIPs

• Precipitation polymerization.
• Precipitation polymerization can be performed
  with similar prepolymerization mixtures as for
  bulk polymers, except that the relative amount of
  solvent present in the mixture is much higher.
  When polymerization progresses, imprinted nano-
  or microspheres precipitate instead of
  polymerizing together to form a polymer monolith.

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Preparation MIPs

• W/O emulsion polymerization.
• Binding sites confined at the interior
  surface of voids within an organic polymer can be
  created by polymerization of the continuous (oil)
  phase of a water-in-oil (W/O) emulsion stabilized
  with an amphiphilic functional surfactant
  complexed with the template molecule at the
  wateroil interface.
• and

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Applications of imprinted polymers

• SeparationChromatographyCapillary electro
  chromatographySolid phase extraction
• Pseudo immunoassays
• Synthesis Catalysis
• Sensors

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Separation chromatography

• MIPs as stationary phases

Imprinted enantiomer retained on column
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Separation Solid phase extraction
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Pseudo immunoassays

• An immunoassay is a biochemical test that
  measures the concentration of a substance in a
  biological liquid, typically serum or urine,
  using the reaction of an antibody or antibodies
  to its antigen. The assay takes advantage of the
  specific binding of an antibody to its antigen.
• A promising application area for MIP development
  is as replacements for biological receptors such
  as antibodies in analogues of immunoassays.

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Imprinted polymers-antibody binding site mimics
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Comparison of MIPs and antibodies
MIPs
Antibodies

• In vivo preparation
• Limited stability
• Limited applicability
• Higher costs

• In vitro preparation
• Unlimited stability
• General applicability
• Lower costs

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Sensors

• a chemical sensor selectively recognizes a
  target molecule in a complex matrix and generates
  an output signal using a transducer that
  correlates to the concentration of the analyte .
• Sensor performance
• selectivity,
• sensitivity,
• stability,

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MIP Sensors

• MIPs have unique properties that make them
  especially suitable for sensor technology. They
  exhibit good specificity for various compounds of
  medical, environmental, and industrial interest
  and they have excellent operational stability.
  Their recognition properties are unaffected by
  acid, base, heat, or organic phase treatment
  making them highly suitable as recognition
  elements in chemical sensors.

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Sensor type

• Quartz-crystal microbalance-based sensing devices
• Optical sensors
• Electrochemical Sensor
• and

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Optical sensors Fluorescent Sensor
strongly fluorescent
Weakly fluorescent
F fluorescent tag
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Typical set of fluorescence emission spectra of
D-fructose imprinted polymer at different
concentrations of D-fructose (?ex370nm)
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REFERENCES

• J. Mol. Recognit. 2006 19 106180
• Analyst, 2001, 126, 747756
• Analytica Chemica Acta 534(2005) 31-39
• Anal Bioanal Chem(2006) 386 1235-1244

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Thanks