Stewart Smith Biosensors and Instrumentation Beijing University of Posts and Telecommunications 2019 Chemical Sensors & Biosensors
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Chemical Sensors & Biosensors
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Definition of 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.”
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook.
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
A Typical BiosensorBiosensors produce an output (often electrical) which is proportional to the concentration of biological analytes.
Signal Conditioning
Analyte
Biological Recognition Element
Transducer
Output Signal
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Required Characteristics• Sensitivity
• Low detection limits
• Cost
• Simplicity
• Reliability
• Speed
• Accuracy
• Precision
• Utility
• Field portability
• Ruggedness
• Reproducibility
• Ease of calibration
• Stability
• Room for improvement
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Applications of Biosensors
• Medical Care (both clinical and laboratory use)
• Determination of Food Quality
• Detection of Environmental Pollutants
• Industrial Process Control
• Law Enforcement (e.g., Alcohol, Drugs)
• Military (Biodefence)
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Biosensing PrinciplesType Examples
Electrochemical: Potentiometric Amperometric FET based Conductometric
Glucose Sensor Neurochemical Sensor for Dopamine, Nitric Oxide, etc.
Optical: Spectroscopy, Fluorescence, Polarimetry
Environmental monitoring
MEMS/Piezoelectric: Quartz crystal microbalance
DNA sequence detection
Thermal: Thermistor, Thermopile
Sensing by Enzymatic Catalysis
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Electrochemical Sensors• Potentiometric: Measurement of the emf of an
electrochemical cell at zero current. The emf is proportional to the log. concentration of the analyte.
• Amperometric: An increasing (decreasing) potential is applied to the cell until oxidation (reduction) of the substance to be analyzed occurs. The height of the peak current is directly proportional to the concentration of the electroactive material.
• Conductometric: Most reactions involve a change in the composition of the solution, which can often be measured as a change in its electrical conductivity.
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Optical Biosensors• Principle: Changes in light intensity are linked to changes in mass
or concentration. Hence, fluorescent or colorimetric molecules must be present.
• Methods: Optical fibres, surface plasmon resonance, absorbance, luminescence.
LED
Photodetector
Finger
IR light
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Glucose Sensor (Electrochemical)
• The analyte, glucose, diffuses through a membrane to the GOD enzyme layer - where glucose is converted to hydrogen peroxide and gluconic acid.
• Both oxygen (being consumed) and H2O2 (being produced) can be measured electrochemically (in an amperometric technique), or the local pH change can be monitored (potentiometrically).
Pt Anode (+)
Ag Cathode (-)
Immobilized Glucose Oxidase (GOD)
Polyurethane Membrane
Glucose → H2O2 + gluconic acid
Glucose oxidase (in presence of oxygen)
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Glucose Sensor (Affinity Method)Based on the competitive binding of glucose (plus attached fluorescent label) with receptor sites on an immobilised protein (Concanavalin A). The reduction of fluorescence in the bulk fluid is detected.
3 mm
0.3
mm
Hollow Dialysis Fibre Immobilised Con A
Excitation
Emission
Optical Fiber
Glucose
(Note: Con A has receptor sites that bind specifically to various sugars, glycoproteins
and glycolipids.)
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Glucose Sensor (Zhu et al.)
J. Zhu et al, Planar amperometric glucose sensor based on glucose oxidase immobilised by chitosan film on Prussian blue layer, Sensors 2: 127-136, 2002. doi:10.3390/s20400127
Selection of Operational pH
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Glucose Sensor (Zhu et al.)Effect of Temperature on Response
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Glucose Sensor (Zhu et al.)Response Time
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Glucose Sensor (Zhu et al.)Testing Interference with ascorbic and uric acid
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Glucose Sensor (Zhu et al.)Calibration curve
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Glucose Sensor (Zhu et al.)Long Term Stability
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Glucose Sensor (Zhu et al.)
No. 1 2 3 4 5 6 7 8 9 10 11
I/nA 291 294 298 292 297 295 290 289 299 295 294
AV 294
RSD 3.0%
PrecisionA measurement can be precise but may not be accurate!
Standard deviation σ is a statistical measure of the precision. (N - number of data; xi - each individual measurement; - mean of all measurements.)x̄
σ =∑N
i=1 (xi − x̄)2
N − 1
Stewart SmithBiosensors and InstrumentationBeijing University of Posts and
Telecommunications 2019
Glucose Sensor (Zhu et al.)Accuracy
Correlation and regression line for measurements of 100 human serum samples between spectrophotometry and the glucose sensor.
Correlation Coefficient:
0.996.