Biomedical Sensors Dr. James A. Smith

What’s Important? Accuracy Operational Range Response Time Sensitivity Resolution Reproducibility

Classification Breakdown into general categories –Physical Goniometer –Electrical EMG (electromyographic) –Chemical Blood oxygen

Sensor Packaging “In vivo” –Inside the organism! –Risky! –Biocompatibility Host can affect the sensor & vice versa Protein absorption / cell. Deposits –Permeability affected Inflamation of tissue (latex!) Sterilization –Steam, ethylene oxide, gamma radiation

Electrolyte / Metal Electrodes Charge distribution at interface Different metals have different potentials

Physical Measurements: Displacement Linear Variable Diff. Transformer Goniometer –Knee & Elbow Strain –Wire length & width –Chest contraction –Force Plates Ultrasonics

Temperature Tightly controlled body variable /- 0.5 C at core –Too high: disease or infection –Too low: trauma / shock Thermistor –Change resistance with temperature –Cavity or closed area

Oxygen Measurement Plasma O 2 : 2% of total oxygen –Clarke Electrode Chem. Reaction with Platinum Electrode Current is prop. To oxygen content Transcutaneous Heat releases oxygen through skin Hemoglobin –Optical oximeter –Light absorption by blood

pH Electrodes Acid: excess hydrogen ions Base: excess hydroxl ions Normal blood pH: 7.4 (basic) –CO 2 removal by lungs –Kidneys acid-base regulation Organic dye strips Electrodes in solution –a battery consisting of two electrodes, each immersed in its respective solution joined by a salt bridge –Glass electrodes –Glass membrane can wear out

CO 2 CO2 in solution: –Weak acid –Carbonic Acid (H 2 CO 3 ) Use electrodes like in pH system

Enzyme Biosensors Biological specific mediators –Reagents for reaction or catalyzing Enzymes –2000 proteins w/ biocatalytic properties –Accelerate reactions in cells Embed in neutral matrix Glucose sensor –Enzyme glucose oxidase –Useful for diabetics –Measure gluconic acid or hydrogen peroxide

Microbial Sensors Assimilation of organic compounds by microorganisms Look for secretions by micros –H 2, CO 2, etc. Need immobilized microbes Examples –Ammonia & Nitrogen Dioxide

EKG / ECG Electrocardiogram (ECG) Electrokardiogram (EKG) Electrode –Polymer & carbon / metal filler –Silver Chloride contact –Electrolytic foam –Motion artifacts!

EMG / EEG Electromyogram (EMG) Nerve & Muscle Surface are like EKG Direct –Needle –Bipolar electrode EEG –Brain –Cups (gel) –Subdermal (10mm, 0.5mm)

EMG & Muscles Source:

EMG: locate muscles Figure 1 Source: Vernier Inc.

Electrode Placement Source: Vernier Inc.

Electrical Patterns Source:

EMG Video