Introduction to Biosensors

1. Introduction to Biosensors 2007 Mattias Rudh www.realtimebiosensor.com

2. Definition of a biosensor A biosensor: A device that uses specific biochemical reactions mediated by isolated enzymes, immunosystems, tissues, organelles or whole cells to detect chemical compounds usually by electrical, thermal or optical signals. Source: PAC, 1992, 64, 148 (Glossary for chemists of terms used in biotechnology.)

3. Biosensor breakdown Analyte Response Detection Sample handling/preparation Analysis Signal

4. The Analyte What do you want to detect? MoleculeProtein, toxin, peptide, vitamin, sugar, metal ion Cholera toxin Glucose

5. Sample handling How to do deliver the analyte to the sensitive region? • (Micro) fluidics • Concentration (increase/decrease) • Filtration/selection

6. Example: Biosensor Application How to do deliver the analyte to the sensitive region? Collection wand

7. Detection/Recognition How do you specifically recognize the analyte? Fab Active site Membrane receptors Competitive binding Fc Antibody Enzyme Cell Polymer/Hydrogel

8. Signal How do you know there was a detection? Specific recognition? Common signaling principles Optical (SPR, ELM, IR) Electrical (Voltammetry, Potentiometry, Conductivity) Electromechanical (QCM) Thermal Magnetic Pressure Often the detector is immobilized on a solid support/sensor

9. Avoiding false signals False specific recognition? Specific recognition Non specific signal

10. Improving performance Secondary signal amplifier Highly specific detection Magnectic bead, fluorecent dye, enzyme etc Inert background v v v

11. Regeneration or single use? Break binding Low and high pH buffers pH~1 and pH~13 v v v

12. Data Analysis R t Response variable (R) vs time(t):Example of response variables:Refractive indexPotentialCurrentFrequencyMassPressureTemperature

13. Baseline Should be stable when there is no binding Drift baseline Stable baseline t t Quantifying DriftShift in the baseline (RMS) shown as response units per time Quantifying NoiseRoot mean square (RMS) of a sample of data points for a given time

14. Sensitivity Signal-to-noise ratio Per time unit t Spikes Rapid (1 datapoint!) shift in signal Baseline shift Rapid (1 datapoint!) shift in baseline (offset) t t

15. Common signal error sources Inhomogenous sample Bubbles/flow artifacts Temperature Electromagnetic interferance Electronic unstability Unstable chip/detection layer

16. Improved sensitivity Output signal R=R1-R2 or R=R1/R2 The reference is exposed to the same kind of disturbances as the active sensor. These effects are cancelled out by taking the difference between the two sensors Reference sensorCoated with inert material does not detect the analyte Active sensordetects the analyte R1 R2 Sample t R R1 R2 t t

17. Signal interpretation Visual (example pregnancy test) Automatic (Software) Manual (Research Biosensor)

18. Kinetic evaluation Binding / no binding Affinity (Ka / Kd and k_on and k_off)

19. Example of biosensors Pregnancy test Detects the hCG protein in urine. Interpretation and data analysis performed by the user Glucos monitoring device (for diabetes patients) Monitors the glucose level in the blood. Interpretation and data analysis performed by a microprocessor.

20. Example of biosensors Infectous disease biosensor from RBS Data analysis and interpretatoin performed by a microprocessor Old time coal miners’ biosensor Data analysis and interpretation performed by the coal miner.

21. Research Biosensors Biacore Biosensor platform General and flexible, good tool for development of specific biosensors For a comprehensive list of research biosensor suppliers see: www.realtimebiosensor.com