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 http://www2.hmc.edu/~vanryswyk/research.ht 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 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 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. http://www.cfdrc.com/bizareas/biomedlife/labchip_biomems/biosensor.html 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 http://www.fda.gov/OHRMS/DOCKETS/AC/04/ b i fi /4018B1 01 ht http://www.ncsr.ie.com 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 Challenges and Solutions [...]... the blood a drug delivery system would make it a complete device For glucose sensing insulin could be administered via an insulin pump depending on the blood sugar This could provide for tighter control of blood sugar decreasing the chances of complications For lactate sensing a blood thinner could be administered when a build up of lactate is detected This could help to lessen the severity of a heart... 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 Fragments by Microstress and Endocytosis Immune cells chemically attack surface Fibroblasts attach and stress components... 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: WileyInterscience, 2006 Updike, S J et al., “A Subcutaneous Glucose Sensor With Improved Longevity, Dynamic Range, and Stability of Calibration.” Diabetes Care 23(2), pp... sensor for a complete device Complications No automatic glucose measuring device has been made to eliminate other means of determining blood sugar When dealing with very small devices, the amount of drugs that could be administered in a complete device is minimal There is difficulty in using platinum electrodes because platinum free radicals can cause harm References Mascini, M et al., “An L -Lactate. .. potential does not change during the measurement Voltammetry How they work A potential is applied to the system and the faradaic current response can be determined The potential is measured between the working electrode and the reference electrode The current is measured between the working electrode and the counter electrode When the analyte is depleted on the surface of the electrode the current will increase... severity of a heart attack The blood thinner would be administered directly to the site and would act faster than taking aspirin Insulin Pump www.disetronic.com Drug Delivery Techniques Insulin Pump reservoirs Helps to control insulin level in the body by delivering a continuous basal rate of insulin and then a bolus rate before eating Microneedles Can administer medication into the skin with little pain... 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) ... enzymes Reaction becomes oxygen limited Fragments by Microstress and Endocytosis 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... 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 Electrodes Some common materials used are: Glassy carbon Platinum Gold Voltammetry is used . 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. 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. /4018B1 01 ht http://www.ncsr.ie.com FILT Lung and Chest Diagnostic Company • Biosensors for measurement of Lactate, Glucose, pH. • Biosensor for measurement of Hydrogen Peroxide in low levels