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Biosensors???-??????? ??????? ???????? ??????
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• Dr. Ronen Almog

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Outline

• Biosensors
• Detection principles
• Electrochemical
• Optical
• Mechanical
• Lab on a chip/BioMEMS
• Examples
• Diabetes - glucose monitoring
• Water toxicity detection

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Elements of a biosensor
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Biosensor definition

• An integrated device consisting of
• a biological recognition element and
• a transducer
• capable of detecting specific biological/chemical
  compound and converting it into an electronic
  signal.

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Biosensors applications and importance

• Medical/health monitors

• Homeland security

• Pharmaceutical industry

• Food industry

• Simplicity

• Miniaturization

Biosensors Features

• Selectivity

• Rapid

• Sensitivity

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Biological recognition elements

• Enzymes and their substrates
• Antibodies and their antigens
• Nucleic acids and their complementary sequences
• Whole cell

A - T
G - C
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On Size and Scale
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Enzymes

• Large protein molecules.
• Catalyze chemical reactions.
• Used as tools to perform various biochemical
  reactions in the cell.

Participates actively in the transformation of
chemical A (the substrate) to chemical B (the
product) but remains unchanged at the end of the
reaction.
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Immunosensors Antibody Antigen recognition
Antibody - proteins, produced by the immune
system of higher animals in response to the entry
of foreign materials into the body, eg.
viruses, bacteria
Bind tightly to the foreign material (the
antigen) that provoked the response and mark it
for attack by other elements of the immune system.
Antibodies are also very specific- they need to
be, in recognizing and binding to the foreign
substance only and not to materials native to the
organism.
If an antigen is present in that medium, it will
be bound by the antibody to form a larger,
antigen-antibody complex.
This will change some physicochemical parameter
(usually mass or an optical parameter) of the
environment at the transducer surface of the
sensor and that change is subsequently detected.
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Antibody structure
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The transducer
Chemical change
Physical change
The key part of a biosensor is the transducer
which makes use of a physical change accompanying
the reaction.
The most common are
1. Electrochemical-Amperometric Measures
currents generated when electrons are exchanged
between a biological system (in solution) and an
electrode in a constant potential.
2. Optical detection - refractive index change or
fluorescence
3. Mechanical detection
4. Conductometric/Impedimetric detect changes
in conductivity/impedance between two electrodes.
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Transducers - sensing methods in biosensors
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MEMS - MicroElectroMechanichal sensors
Use Bioassay of prostate-specific antigen (PSA)
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Optical sensors - Biacore example
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Reasons for Miniaturization
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Biochips Microelectronic-inspired devices that
are used for delivery, processing, analysis, or
detection of biological molecules and
species. These devices are used to detect cells,
microorganisms, viruses, proteins, DNA and
related nucleic acids, and small molecules of
biochemical importance and interest.
BioMEMS Biomedical or biological applications of
MEMS (micro electro mechanical systems)
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Lab-on-a-chip
Burns et al. Science 282, 484, 1998
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BioChip/BioMEMS Materials

• Silicon
• Glass, Quartz
• Polymers
• Poly (dimethylsiloxane) (PDMS)
• Poly (methyl methacrylate) (PMMA)
• Teflon, etc.

Considerations Biocompatibility, ideal for
biomedical devices Transparent within the
visible spectrum Rapid fabrication
Photo-definable Chemically modifiable
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Biochip - microfluidics
Key Attributes of Biochips 1. Small length
scale 2. Small thermal mass 3. Laminar flow 4.
High surface-to-volume ratio
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The Oxygen electrode
Clarks Glucose electrode
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Biosensors History
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Technology evolution
6 analyses from a drop of blood in about one
minute.
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Diabetes - Glucose Biosensor

• The user carries a wallet sized case that
  contains the testing equipment
• A lancet pierces the skin on the finger
• The user places this blood sample on a test strip
  and inserts it into the reader
• Electrochemical detection

http//www.diabetesuffolk.com/Managing20Diabetes/
Meters/LifeScan20Ultrasmart.asp
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Alcohol Test Drager Alcotest 7110
The Alcotest 7110 Standard is a highly developed
measuring instrument for precise determination of
breath alcohol concentration.

• Two different and independent measuring systems
• Infrared spectroscopy ?9.5µm
• Electrochemical measurement

/www.draeger-safety.com
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Example - insect MEMS hybrid
A radio-controlled beetle
6 electrodes affixed to the brain and muscles
1.3g electronic module
Max weight 3g
The University of California, Berkeley
IEEE MEMS, January 2009
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Example Toxichip
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Water toxicity detection - motivation
1. Homeland security
THE THREAT Intentional poisoning of a drinking
water source
2. Enviromental pollution
THE NEED A rapid early toxicity warning device
3. Pharmaceutical screening applications
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Toxicity detection systems
Toxicity bioassays
The only question need to be asked is Is the
sample toxic?
Standard toxicity bioassays, mostly designed for
environmental purposes, are unsuitable for our
needs size, response time.
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The goal To develop a portable system that can
detect the presence of unknown acute toxicity
chemicals in drinking water within 20 minutes.
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Whole-cell biosensor The biological material is
an intact, living, functioning cell.
E. Coli bacteria

• Toxichip whole cell biosensors
• Bacterial cells
• Genetically modified
• Bioluminescent
• Tailored to respond to different cell stress
  factors

Three elements in the solution
1. Reporter cells live cells tailored to
detect toxicity. We use Escherichia coli (E.
coli) bacteria as a whole cell sensor.
2. Biochips disposable, credit card size,
containing the cells.
3. Analyzer a small mobile instrument into which
the chip will be inserted, and which will provide
the reading.
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E. Coli bacteria
Biochip array
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Bioluminescence
The emission of light by a living organism as the
result of a chemical reaction. Chemical energy
is converted to light energy.
Insects
Marine organisms
Fungee
Emission spectrum Visible - blue-green (490-500
nm)
Bacteria
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Bioluminescence
At least two chemicals are required
The one which produces the light is generically
called a "luciferin.
The one that drives or catalyzes the reaction is
called a "luciferase."
Each organism has its own luciferin and
luciferase compounds.
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Bacteria engineering for toxins detection
Two types of biochemical response to toxins
Type I
Normally doesnt emit light.
Toxin exposure induces light emission.
Sensitive to low concentration of toxins with a
dose-dependent signal.
Type II
Constitutive test
Normally emits light.
In the presence of a toxin, the signal intensity
decreases.
Respond to high concentration of toxins
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Type I - bacteria engineering for toxins
detection
The fusion of two genetic elements inside a host
E. coli bacteria
Sensing element A promoter of a gene involved in
the response to the desired target.
Reporting element A Bioluminescent gene.
generates the Luciferin and Luciferase when
experssed
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Toxins list
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Example - cell bioluminescence response
Bacteria response to mitomycin C -
chemotherapeutic agent
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Effect of toxin concentration
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• We use Nalidixic Acid (NA) as the model toxin

Measurement of the bacterial bioluminescence
response to different NA concentrations under
static condition (no flow). Here the bacteria
were suspended in LB.
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PDMS Biochip
Elastomer, Simple, fast, modular, cheap,
reproducible, disposable
Single Photon Avalanche photoDiode
Microfluidics interface system for the PDMS
biochip
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The biochip layout
4 strains
4 main channels sample, positive, negative and
constitutive.
The sample, positive and negative channels
consist of four different bacteria strains
immobilized in agar.
The constitutive channel consists of Normally
On bacteria.
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Bacteria panel
2 toxins Nitrogen mustard, Potassium cyanide
2 strains (promoters) nhoA, grpE
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Acknoledgments

• HUJI - Shimshon Belkins group
• Sharon Yagur-kroll
• Tal Elad
• Sahar Melamed

• Prof. Yosi Shacham
• Ramiz Daniel
• Klimentiy Levkov
• Matan Peer
• Yaniv Chen
• Ragini Raj Singh
• Sefi Vernick
• Amit Ron
• Mordechai Aharonson
• Tsvi Shmilovich
• Arthur Rabner

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The end
Thank you!
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E. Coli bacteria
Biochip array
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Optical sensors - Biacore example