implantable biosensor devices for lactate and glucose detection

Immobilization of Enzymes Through Chemical Bondshttp://www2.hmc.edu/~vanryswyk/research.html • Chemical bonds from enzyme to a surface/self assembling monolayers SAMs • Binding enzyme co

Implantable Biosensor Devices for Glucose and Lactate Detection

Rebecca Davis, Daniel Baron, Erik Dietrich

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

http://www2.hmc.edu/~vanryswyk/research.html

• 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

http://www.ncsr.ie.com

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

H2O2

• 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

H2O2, which generates a current by electrode reaction

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

http://www.fda.gov/OHRMS/DOCKETS/AC/04/

b i fi /4018B1 01 ht

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

http://www.sciencemag.org/cgi/content/full/297/5583/962

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

What is Biofouling?

a result of the growth or activity of living

organisms.

Comparing fabrication and use

Strong Vacuum vs Pressure / Pulse Vibration Isolation vs Repeated Shock Controlled Chemical Environment vs Highly Variable and

Reactive

Biggest Problem: Biological Reactions

Covers Sensors and Electrodes

Sugars can't reach enzymes Reaction becomes oxygen limited

Immune cells chemically attack surface Fibroblasts attach and stress components

Isolates by Fibrous Encapsulization

Body forms 'bubble' around device Chemical environment in bubble not accurate

What Must Be Done

Keep Sensors Clear

Prevent material from sticking

Inhibit cell attachment

Prevent Immune Response

Imitate natural surface - Camouflage!

Use non-reative material

Integrate into Body Tissue

Present intentional footholds

Use synthetic anchors

How the Body Does It

Passive Barriers

Oligopeptides

Lipids

Presenting Favorable Tags

Antigens identify cells

Enzymes allow for communication

Targeted Attachment Points

Protein 'docks' tell cells where to grip

Amino acid sequences attract specific proteins

How Modern Medicine Does It

Polymer Chains

Hydrophilic establishes water barrier

Similar to oligosaccharides in structure

Functionalized Endgroups

Polar endgroups can repel certain materials

Proteins can have complex function

Synthetic Attachment Points

Quick placement

Allows for body to slowly adjust

Our Application

Polyethylene oxide Chains

Heparin Endgroups

Stent/Mechanical Anchor

„ Voltammetry is used to determine whether a substance of interest is

making contact with the electrode

„ This can be useful in determining whether an analyte of interest is present

in the system as well as how much of it is present

„ They take voltammetric measurements based on a three electrode

Voltammetry

How they work

response can be determined

and the reference electrode

the counter electrode

the current will increase

the electrode the current will increase

Drug Delivery

in the blood a drug delivery system would make it a

complete device

insulin pump depending on the blood sugar

the chances of complications

when a build up of lactate is detected

would act faster than taking aspirin

Insulin Pump

www.disetronic.com

Drug Delivery Techniques

rate of insulin and then a bolus rate before eating

skin with little pain

http://www.s3.kth.se/mst/researc h/projects/transdermal/NeedleIm age.gif

http://www.jhu.edu/ch be/gracias/porousconta inerl.jpg

eliminate other means of determining blood sugar

that could be administered in a complete device is minimal

platinum free radicals can cause harm

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

„ Saliterman, Steven S BioMEMS and Medical Microdevices Washington: Interscience, 2006.

Wiley-„ Updike, S J et al., “A Subcutaneous Glucose Sensor With Improved Longevity, Dynamic Range, and Stability of Calibration.” Diabetes Care 23(2), pp 208-214 (2000).

„ Wilson, G S et al., “Progress Towards the Development of an Implantable

Sensor for Glucose.” Clinical Chemistry 38/9, pp 1613-1617 (1992).