implantable biosensor devices for lactate and glucose detection

Implantable Biosensor Devices
for Glucose and Lactate Detection
Rebecca Davis, Daniel Baron, Erik Dietrich
Outline
I. Device specifics and enzyme function
II. Biocompatability and system integration
III. Detection of analyte and possible drug delivery systems
What makes a good biosensor?
• Sensitivity – detect small changes
• Specificity – minimize effect of interferants
• Simplicity - Lower cost, and less likely to be
incorrectly made
• Response time – Faster reaction to a condition
• Continuous - Close monitoring of analyte levels may
be critical
•Size
• Durability
What analytes can be measured with a biosensor?
• Metabolites- Lactate, other enzyme substrates
• Gases- pCO2, pO2, etc
• Ions
• Oligonucleotides
Immobilization of Enzymes Through Chemical Bonds
ml
• Chemical bonds from enzyme to a surface/self assembling monolayers (SAMs)
• Binding enzyme cofactors
• Anti-enzyme antibody coated beads
• Absorption onto a hyrdrophobic surface
Thiol (R-S-H) groups on gold + amino acid tags

Enzyme Entrapment

• Crosslinking polymer matrixes
• Carbon nanotube matrix
• Capsule of inert material
• Matrixes can be either
electropolymerized or preformed
www-biol.paisley.ac.uk/…/Chapter1/page3a.htm
Implantable lactate sensor
• One sensor is covered in lactate oxidase
enzyme and one is not. Lactate oxidase
converts lactate and oxygen to pyruvate and
H
2
O
2
• Because oxygen is consumed in this reaction,
the difference between the two pO2 sensors is
directly proportional to the lactate
concentration in blood.
Implantable glucose sensor
• Enzymatic oxidation of glucose creates
H
2
O
2
, which generates a current by
electrode reaction.
/>Lactate + O
2
Pyruvate +
O

2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O

2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
Uncoated sensor
Lactate Oxidase
coated sensor
Hydrogen peroxide
Acute myocardial infarctions (AMI)
• Result of a blockage in the coronary arteries, cutting off the supply of blood to the
heart.
• Once an MI begins, time to treatment becomes extremely important. Treatment
should begin within two hours.

• The implantable lactate sensor lead can be easily placed in the coronary sinus.
• A device able to create a response to lactate concentrations passing a threshold
would be useful.
Applications in Medicine
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FILT Lung and Chest Diagnostic Company
• Biosensors for measurement of Lactate, Glucose, pH.
• Biosensor for measurement of Hydrogen Peroxide in low
levels (sensitivity below 50 nmol)
Medtronic MiniMed
• Implanted enzyme-based sensor
• Measures glucose around skin tissue for up to 3 days.
Sensor is wired to a readout device outside the body
Current Research
/>FILT
Medtronic MiniMed
Challenges regarding enzymes as a detection mechanism
• LOC durability and shelf life
• Enzyme selectivity and alternate substrates
• Need to replace power source may require surgery
• Poor stability of SAMs on many surfaces in presence of oxidizing
agents
Solutions under investigation
• Chaperone proteins/Whole cell immobilization
• Directed evolution techniques for more stable/efficient enzymes
• Amperometry could eventually be used to recharge power source
• Use of surfaces that form strong carbon-carbon covalent bonds
with enzymes
Dealing with Biofouling

Challenges and Solutions
Challenges and Solutions
What is Biofouling?
The
The
impairment or degradation
impairment or degradation
of something as
of something as
a result of the growth or activity of
a result of the growth or activity of
living
living
organisms
organisms
.
.
Comparing fabrication and use
Strong Vacuum vs Pressure / Pulse
Strong Vacuum vs Pressure / Pulse
Vibration Isolation vs Repeated Shock
Vibration Isolation vs Repeated Shock
Controlled Chemical Environment vs Highly Variable and
Controlled Chemical Environment vs Highly Variable and
Reactive
Reactive
Biggest Problem: Biological Reactions
Covers Sensors and Electrodes
Covers Sensors and Electrodes
Sugars can't reach enzymes

Sugars can't reach enzymes
Reaction becomes oxygen limited
Reaction becomes oxygen limited
Fragments by
Fragments by
Microstress
Microstress
and Endocytosis
and Endocytosis
Immune cells chemically attack surface
Immune cells chemically attack surface
Fibroblasts attach and stress components
Fibroblasts attach and stress components
Isolates by Fibrous
Isolates by Fibrous
Encapsulization
Encapsulization
Body forms 'bubble' around device
Body forms 'bubble' around device
Chemical environment in bubble not accurate
Chemical environment in bubble not accurate
What Must Be Done
Keep Sensors Clear
Keep Sensors Clear
Prevent material from sticking
Prevent material from sticking
Inhibit cell attachment
Inhibit cell attachment
Prevent Immune Response
Prevent Immune Response

Imitate natural surface
Imitate natural surface
-
-
Camouflage!
Camouflage!
Use non
Use non
-
-
reative
reative
material
material
Integrate into Body Tissue
Integrate into Body Tissue
Present intentional footholds
Present intentional footholds
Use synthetic anchors
Use synthetic anchors
How the Body Does It
Passive Barriers
Passive Barriers
Oligopeptides
Oligopeptides
Lipids
Lipids
Presenting Favorable Tags
Presenting Favorable Tags
Antigens identify cells

Antigens identify cells
Enzymes allow for communication
Enzymes allow for communication
Targeted Attachment Points
Targeted Attachment Points
Protein 'docks' tell cells where to grip
Protein 'docks' tell cells where to grip
Amino acid sequences attract specific proteins
Amino acid sequences attract specific proteins
How Modern Medicine Does It
Polymer Chains
Polymer Chains
Hydrophilic establishes water barrier
Hydrophilic establishes water barrier
Similar to oligosaccharides in structure
Similar to oligosaccharides in structure
Functionalized
Functionalized
Endgroups
Endgroups
Polar
Polar
endgroups
endgroups
can repel certain materials
can repel certain materials
Proteins can have complex function
Proteins can have complex function
Synthetic Attachment Points
Synthetic Attachment Points

Quick placement
Quick placement
Allows for body to slowly adjust
Allows for body to slowly adjust
Our Application
Polyethylene oxide Chains
Polyethylene oxide Chains
Heparin
Heparin
Endgroups
Endgroups
Stent/Mechanical Anchor
Stent/Mechanical Anchor
Electrodes
Electrodes


Some common materials used are:
Some common materials used are:


Glassy carbon
Glassy carbon


Platinum
Platinum


Gold

Gold


Voltammetry is used to determine whether a substance of interest
Voltammetry is used to determine whether a substance of interest
is
is
making contact with the electrode
making contact with the electrode


This can be useful in determining whether an analyte of interest
This can be useful in determining whether an analyte of interest
is present
is present
in the system as well as how much of it is present
in the system as well as how much of it is present


They take
They take
voltammetric
voltammetric
measurements based on a three electrode
measurements based on a three electrode
structure:
structure:


A working electrode

A working electrode


A counter electrode
A counter electrode


A reference electrode
A reference electrode


The potential does not change during the measurement
The potential does not change during the measurement
Voltammetry
Voltammetry
How they work
How they work


A potential is applied to the system and the faradaic current
A potential is applied to the system and the faradaic current
response can be determined
response can be determined


The potential is measured between the working electrode
The potential is measured between the working electrode
and the reference electrode
and the reference electrode



The current is measured between the working electrode and
The current is measured between the working electrode and
the counter electrode
the counter electrode


When the analyte is depleted on the surface of the electrode
When the analyte is depleted on the surface of the electrode
the current will increase
the current will increase


Depending on how much of the analyte is in contact with
Depending on how much of the analyte is in contact with
the electrode the current will increase
the electrode the current will increase
Drug Delivery
Drug Delivery


While it will be very beneficial to sense these components
While it will be very beneficial to sense these components
in the blood a drug delivery system would make it a
in the blood a drug delivery system would make it a
complete device
complete device


For glucose sensing insulin could be administered via an

For glucose sensing insulin could be administered via an
insulin pump depending on the blood sugar
insulin pump depending on the blood sugar


This could provide for tighter control of blood sugar decreasing
This could provide for tighter control of blood sugar decreasing
the chances of complications
the chances of complications


For lactate sensing a blood thinner could be administered
For lactate sensing a blood thinner could be administered
when a build up of lactate is detected
when a build up of lactate is detected


This could help to lessen the severity of a heart attack
This could help to lessen the severity of a heart attack


The blood thinner would be administered directly to the site and
The blood thinner would be administered directly to the site and
would act faster than taking aspirin
would act faster than taking aspirin
Insulin Pump
Insulin Pump
www.disetronic.com
Drug Delivery Techniques
Drug Delivery Techniques



Insulin Pump reservoirs
Insulin Pump reservoirs


Helps to control insulin level in the body by delivering a conti
Helps to control insulin level in the body by delivering a conti
nuous basal
nuous basal
rate of insulin and then a bolus rate before eating
rate of insulin and then a bolus rate before eating


Microneedles
Microneedles


Can administer medication into the
Can administer medication into the
skin with little pain
skin with little pain


Micropumps
Micropumps


Microreservoirs
Microreservoirs



Any of these could be coupled with a sensor for a complete devic
Any of these could be coupled with a sensor for a complete devic
e
e
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Complications
Complications


No automatic glucose measuring device has been made to
No automatic glucose measuring device has been made to
eliminate other means of determining blood sugar
eliminate other means of determining blood sugar


When dealing with very small devices, the amount of drugs
When dealing with very small devices, the amount of drugs
that could be administered in a complete device is minimal
that could be administered in a complete device is minimal


There is difficulty in using platinum electrodes because
There is difficulty in using platinum electrodes because
platinum free radicals can cause harm
platinum free radicals can cause harm

References
References


Mascini
Mascini
, M. et al.,
, M. et al.,
“
“
An L
An L
-
-
Lactate Sensor with Immobilized Enzyme for Use in in
Lactate Sensor with Immobilized Enzyme for Use in in
Vivo Studies with an Endocrine Artificial Pancreas.
Vivo Studies with an Endocrine Artificial Pancreas.
”
”
Clinical Chemistry
Clinical Chemistry
31/3, pp
31/3, pp
451
451
-
-
453 (1985).
453 (1985).



Saliterman, Steven S.
Saliterman, Steven S.
BioMEMS and Medical Microdevices
BioMEMS and Medical Microdevices
. Washington: Wiley
. Washington: Wiley
-
-
Interscience, 2006.
Interscience, 2006.


Updike, S. J. et al.,
Updike, S. J. et al.,
“
“
A Subcutaneous Glucose Sensor With Improved Longevity,
A Subcutaneous Glucose Sensor With Improved Longevity,
Dynamic Range, and Stability of Calibration.
Dynamic Range, and Stability of Calibration.
”
”
Diabetes Care
Diabetes Care
23(2), pp 208
23(2), pp 208
-
-

214
214
(2000).
(2000).


Wilson, G. S. et al.,
Wilson, G. S. et al.,
“
“
Progress Towards the Development of an Implantable
Progress Towards the Development of an Implantable
Sensor for Glucose.
Sensor for Glucose.
”
”
Clinical Chemistry
Clinical Chemistry
38/9, pp 1613
38/9, pp 1613
-
-
1617 (1992).
1617 (1992).