Biosensors for medical students

1. Dr.S.Sethupathy,
Rajah Muthiah Medical College,
Annamalai University

2. Biosensor” – Any device
that uses specific
biochemical reactions to
detect chemical
compounds in biological
samples.

3. Biosensor
 Integrated device
 Quantitative or semi quantitative
 Biological recognition element
 Transduction element (transducer)
 Electronic signal
 detector

5. A sensor that integrates a
biological element with a
physiochemical transducer
to produce an electronic
signal proportional to a
single analyte which is
then conveyed to a
detector.

6. Medical Diagnostics
 Doctors increasingly rely on testing
 Needs: rapid, cheap, and “low tech”
 Done by technicians or patients
 Some needs for in-vivo operation, with feedback

7. electrode
substrate product
Enzyme
Apply voltage Measure current prop.
to concentration of substrate
Principle of Electrochemical Biosensors

8. • Blood glucose estimation
Most sensors use enzyme called glucose oxidase (GO)
• Most sensors are constructed on electrodes, and use a
mediator to carry electrons from enzyme to GO
Fc = mediator, ferrocene, an iron complex
These reactions occur in the sensor:
Fc
Fc+ + e- (measured)
GOR + 2 Fc + --> GOox + 2 Fc
GOox + glucose --> GOR + gluconolactone

9. Glucose biosensor test strips
Meter
Read glucose
Dry coating of GO + Fc
Patient adds drop of blood,
then inserts slide into meter
Output:
amperometry
I
t
Patient reads glucose level on meter
e’s
electrodes

10. Research on glucose sensors
 Non-invasive biosensors - skin, saliva
 Implantable glucose sensors to accompany
artificial pancreas - feedback control of insulin
supply
 3-4 weeks for implantable sensor in humans

11. Other biosensors
 Cholesterol - based on cholesterol oxidase
 Antigen-antibody sensors - toxic substances,
pathogenic bacteria
 Small molecules and ions in living things: H+, K+,
Na+, CO2, H2O2
 DNA hybridization and damage
 Micro or nanoarrays, optical abs or fluor.

12. Mutagen monitor

13. Components of a Biosensor
Detector

14. 1. LINEARITY Linearity of the sensor should be high
for the detection of high substrate
concentration.
2. SENSITIVITY Value of the electrode response per
substrate concentration.
3. SELECTIVITY Chemicals Interference must be
minimized for obtaining the correct
result.
4.RESPONSE TIME Time necessary for having 95%
of the response.
Basic Characteristics of a
Biosensor

15. Biosensor
Analyte
Sample
handling/
preparation
Detection
Signal
Analysis
Response

16. 1. The Analyte (What do you want to detect)
Molecule - Protein, toxin, peptide, vitamin, sugar,
metal ion
2. Sample handling (How to deliver the analyte to the sensitive region?)
(Micro) fluidics - Concentration increase/decrease),
Filtration/selection
Biosensor

17. 4. Signal
(How do you know there was a detection)
3. Detection/Recognition
(How do you specifically recognize the analyte?)
Biosensor

18. Example of biosensors
Pregnancy test
Detects the hCG protein in urine.
Glucose monitoring device (for diabetes patients)
Monitors the glucose level in the blood.

19. Example of biosensors
Infectous disease biosensor
from RBS
Old time coal miners’ biosensor

20. Fluorescence
DNA Microarray
SPR - Surface plasmon resonance
Impedance spectroscopy
SPM (Scanning probe microscopy, AFM,
STM)
QCM (Quartz crystal microbalance)
SERS (Surface Enhanced Raman
Spectroscopy)
Electrochemical
Typical Sensing Techniques
for Biosensors

21. Piezo-Electric Biosensors
 Piezo-electric devices use gold
 To detect the specific angle at which electron
waves are emitted
 when the substance is exposed to laser light or
crystals, such as quartz,
 which vibrate under the influence of an
electric field.
 The change in frequency is proportional to the
mass of absorbed material.

22. Electrochemical Biosensors
• For applied current:
• Movement of e- in redox reactions
detected
• when a potential is applied
between two electrodes.

23. Potentiometric Biosensor
For voltage:
Change in distribution of
charge is detected
using ion-selective
electrodes
such as pH-meters.

24. Optical Biosensors
• Colorimetric for color
 Measure change in light absorption
• Photometric for light intensity
 Photon output for a luminescent or
fluorescent process can be detected with
photomultiplier tubes or photodiode
systems.

25. Calorimetric Biosensors
 If the enzyme catalyzed reaction is
exothermic,
 two thermistors may be used to
measure the difference in resistance
between reactant and product
 hence, the analyte concentration.

26. Electrochemical DNA Biosensor
 Steps involved in electrochemical DNA
hybridization biosensors:
 Formation of the DNA recognition layer
 Actual hybridization event
 Transformation of the hybridization event
into an electrical signal

27. Motivated by the application to clinical diagnosis
and genome mutation detection
Types DNA Biosensors
 Electrodes
 Chips
 Crystals
DNA biosensor

28. Application of Biosensor
1. Medical diagnosis (both clinical and
laboratory use)
2. Food Analysis
3. Drug Development
4. Crime detection
5. Environmental field monitoring
6. Quality control
7. Industrial Process Control
8. Detection systems for biological warfare agents
9. Pharmaceuticals and replacement organs

29. Biosensors play a part in
identifying the material and
the degree of concentration
present in the biological
samples and environmental
field.