Bioelectronic Systems

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Bioelectronic Systems bioMS_at_ee.iitb

• M B Patil
• Convener Microelectronics Group
• IIT Bombay

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Definitions

• Bioelectronic Systems Systems that utilize a
  bio-object or operate on bio-objects for their
  function.
• BioMS Microfabricated systems (MS) that utilize
  bio-objects or operate on bio-objects for their
  function.

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Concluding Remarks about this area in AIM 2002

• IITB is one of the few places in the country
  which has demonstrated collaborative work in the
  area of bio-instrumentation bio-sensing systems
• These have been demonstrated by student projects
  and modest consultancy and sponsored projects
• Need projects with critical funding levels to
  take these ideas to the field and is actively
  seeking funding and collaboration ? We have got
  this support this year
• The academic-research structure in the institute
  is conducive for the realization of the above
  objective that would create both locally useful
  bioMEMS based diagnostic systems and globally
  appreciated new knowledge

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Projects in this area

• A major sponsored project by NPSM on bioMS for
  Cardiac Markers we have called this sensing
  system iSens
• Smaller and internally funded projects in
  biomolecular electronics and electroporation

FOR MORE INFO...
A site on iSens will soon be up
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iSens Project Goals

• The ultimate goal of the project is to design
  prototype
• A Point of Care Assay System for Molecular
  Markers for Myocardial Infarction
• Would involve
• Design prototype of processes
• Design prototype of structures
• Integration of system for quick assay of cardiac
  markers
• Testing of the devices and systems at various
  stages of the development
• Overall protocol testing
• Team Timeframe
• Multi-departmental team
• Project duration 30 months

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Molecular Markers

• Enzymatic markers
• Creatine kinase-Total (CK)
• Creatine kinase MB (CK-MB)
• Lactate dehydrogenase (LDH)
• Aspartate aminotransferase (AST)
• Glycogen phosphorylase isoenzyme BB (GPBB)
• Protein molecules
• Troponin
• Myoglobin
• Cell-free DNA fragments
• Will try the molecules in blue

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Conventional Approaches

• Sequential assays
• Immunoassays
• ELISA (Enzyme Linked ImmunoSorbant Assay)
• Radioimmunoassay
• Immunoprecipitation
• Chromatography (!)
• Electrophoresis for separating isomers and then
  looking for activity (for lab (skilled labor,
  time consuming))

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New approaches

• Biosensor array based or microfabricated
  sequential assay system based
• General approach is to use affinity sensors
• Some modern direct affinity sensors
• Quartz crystal microbalance
• Surface plasmon resonance
• Affinity cantilevers
• Conducting polymer devices
• EIS capacitors

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Functional Architecture of iSens
Input Filter
Sample
Signal Conditioning Display
Biosensor Array
Reactor
Control Processing Electronics
Reagent
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Flavour of Biosensor Array Affinity Cantilevers

• Based on resonating structure 0r deflection
• ?Attachment changes mass or stiffness of
  resonating structure and thence resonant
  frequency
• ?Attachment changes bending of the cantilever

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Flavour of BiosensorArray Conducting polymer
FETs

• Inter-digitated noble metal electrode covered
  with conducting polymer
• Conductance change occurs with change of state
  (such as change of pH in enzyme catalyzed or
  affinity reaction) that can be used for sensing

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Flavour of Biosensor Array ISFET based

• Attachment of ions to naturally occurring surface
  sites or ionophores attached to the surface of
  the dielectric of a FET-like device
• ? Changes channel charge thence drain current
• Could be used in the constant drain current mode
  or constant gate voltage mode

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Team Resources

• People A team of about 24
• Equipment About Rs 2 crore for equipment,
  includes e-beam lithography, AFM, HWCVD,

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Status

• Have got started working to have the devices
  ready
• This is how a microcantilever looks

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A whiff of a smaller project

• A student project, but with faculty and research
  scholar support form Chemistry Electrical
  Engineering
• Aim Try to see how a gold-single molecule (a
  porphyrin synthesized in Chemistry) behaves as a
  diode
• Deposit gold on SiO2, Deposit a SAM monolayer,
  study IV characteristics with a STM

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Preparation and Characterization of the gold film

• - Prepared using Physical Vapor deposition
  process
• Cleaned using the Piranha solution to remove
  organic impurities
• XRD spectrum taken to analyse the crystal
  structure
• lt111gt crystal structure observed
• STM/AFM pictures taken to gauge surface smoothness

1000nm x 1000nm scan Features height lt 1nm
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Porphyrin Molecules

• Porphyrin Molecule attatched with a thiol group
  protected by an acetate group
• Formation of SAM in-situ cleavage of the S-Ac
  bond
• Metallo-porphyrin selected due to its
  intercalating properties with DNA
• The methyl groups attached make the porphyrin
  water soluble

Tetra Methyl Pyridyl Zinc Porphyrin Thiol
Acetate
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STM Images
Ridges type structure obtained in the first
figure (10nm x 10nm scan) Valley of depth 1nm
observed in the second image (50nm x 50nm scan)
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I-V curves obtained
Diode type characteristics with a barrier
potential Measurements taken on the hill shown
before
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In conclusion

• There is frenetic activity in the bioelectronics
  and bioMS area at IITB
• Need to create more awareness of the
  applications of this new area
• Need to increase interaction with user agencies