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BIOMEDICAL TRANSDUCERS

BIOSENSORS

Dra. Rossana Madrid

LAMEIN – Dpto. de Bioingeniería

FACET-UNT / INSIBIO-CONICET

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INDEX

Introduction
Applications
General Characteristics
Biosensor

Enzymatic
Microbiological
Inmunological

Bioreceptors. Immobilization Methods
1º, 2º y 3º generation Amperometric Sensors

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INTRODUCTION

To locate nutrients
To find the females
To distance itself from poisons

Chemical

Receptors

One can use these receptors to sense (measure) substances

They exchange information with their environment

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Physical Biodetection

Chemical Reactions

The information is transmitted through a set of physicochemical reactions

Recognition Tools

Physical principles

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Through these receptors events are transduced in measurable quantities

One can use:

Cells
Tissues
Proteins
Enzymes

To build

the biosensor

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A brief history

1962 Clark and Lyons
1967 Updike and Hicks

Electrodo

de O₂

Enz

Glu

O₂

Glucose + O₂ Gluconic Acid + H₂O₂

Glucose oxidase

pO₂Reduction

∝ [Glu]

BIOSENSOR

Existing Sensor + Biological System

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Selectively recognizes the chemical information present in the sample

Signal recognized by the transducer

Conversion

Recognizes the signal from the bioreceptor

Actionable electrical signal

Conversion

CARACTERISTICS

Repeatability
Reproducibility
Selectivity
Sensitivity
Linear response
Good time response
LOD: 3.3 σ_B/S
LOQ: 10 σ_B/S

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“Specificity” is sought in a biosensor

That recognizes only 1 analyte among many

Very difficult to obtain

So we talk about “selectivity ”

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CLASSIFICATION

According to the type of receiver used

According to the immobilization methodology used

According to the principle of transduction used�

Electrochemical

Potentiometric
Amperometric

Photometric
Masics
Thermometers

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Electrochemical Detection�Potentiometric Technique

It measures the potential difference between two electrodes immersed in a solution
Nernst equation

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Electrochemical Detection�Amperometric Technique

I ∝ [activ electrochemcial species]
Example: glucose electrode

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Electrochemical Detection�Amperometric Technique

FETs, ISFETs solve the problem of high Zout.
I _drenaje∝ pH
The Biological System is immobilized on the SiO₂layer

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Thermometric Detection

The enthalpy of the reaction is detected
Methods

Optical
Mechanical
Electrical

Thermocuples
Thermistors
Rapid response

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Piezoelectric Detection

Small variations in mass

Examples

enzyme-inhibitor association
antigen-antibody coupling

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Optical Sensors

Optical fibers are used to measure:�

Absorption�Fluorescence�Bio / chemiluminescence

Very low concentrations can be detected

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Microbial Biosensors

Microorganisms Enzymatic systems

ADVANTAGE

Maintains the enzyme in its natural environment ensuring regeneration of any cofactor�

DISADVANTAGES

Permanent fresh culture medium
Low specificity

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BIOSENSORS - CONSTRUCTION

Immobilization of

the bioreceptor

Transducer

Selection

Bioreceptor

Selection

Molecular

recognition “device”

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SELECTION OF THE TRANSDUCER

It depends on:

the type of reaction and the substances released or consumed

That meet biocompatibility criteria (environment)

Chemical interferents

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Advantages and disadvantages of using biological materials in biosensors

TYPE OF BIOLOGICAL MATERIAL	ADVANTAGES	DISADVANTAGES
Enzyme	Coordinate the substrate High selectivity High sensitivity Shows catalytic activity Reacts quickly	Very expensive They lose activity when immobilized They deactivate in short periods of time
Animal or vegetable tissues	Enzymes are kept in their natural environment Enzyme activity stabilizes They work where pure enzymes fail They are cheaper than pure enzymes	Pérdida de selectividad Son mezclas de enzimas, las cuales algunas veces desactivan el sensor
Microorganisms	Low overall costs Less likely to be inhibited More tolerant to changes in pH and temperature. Shelf life > than enzymes	They take longer to generate responses They have a longer reuse time Loss of selectivity x the variety of enzymes present
Nucleic Acids	Highly selective They can be used for detection of genetic flaws, diseases, infect. virals etc They can identify similar genes by tagging techniques	Very expensive technology Insulated and certified material is required Requires specialized personnel for its use

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The biological material (enzyme) must remain active
Must allow repetitive determinations
In some cases immobilization of more than one enzyme is required
In some cases the cofactor needs to be co-immobilized

IMPORTANT (By immobilizing biological material)

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BIORECEPTOR IMMOBILIZATION

In polyacrylamide gels
In dialysis membranes
Electromagnetic immobilization

Physical Methods:

Chemical Unions:

Cross-linking
Covalent Unions
Others

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PHYSICAL IMMOBILIZATION

In membranes

Electromagnetic

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CROSS-LINKING

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CROSS-LINKING

IMMERSION METHOD

DIRECT UNION METHOD

USE OF SPRAYS

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MICROORGANISMS IMMOBILIZATION

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BIOMEDICAL APPLICATIONS

Most are enzyme sensors

Biosensors to measure metabolites: Urea, creatinine, cholesterol, acetylcholine, lactate

Immunological sensors:

Not used in-vivo they need the addition of reagents
Very slow Ag-AC complex formation

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Amperometric Sensors

Amperometry electrochemical method
Signal of interest I [Analyte]

The direction of the electron flow depends on the properties of the analyte

Can be controlled with the

voltage applied to the

work electrode

Pt or Au

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Amperometric Sensors

Bipolar or tripolar measurements can be performed

WE: Au, C o Pt

Ref: Ag/AgCl

CE: Pt, Acero

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Amperometric Sensors

According to the transfer processes of e- :

1^st generation biosensors

The product of the reaction diffuses into the transducer and produces the electrical response

2^nd generation biosensors

They involve specific "mediators" between the reaction and the transducer for better responses

3^rd generation biosensors

The reaction itself causes the response and there is no directly involved product diffusion or mediator.

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1º, 2º and 3º generation Biosensors

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Substrate, products or cofactors must have electrochemical properties
1st biosensor (Clark & Lions, 1953)

GOx +Buff retained in dyalisis Monted over the gas membrane

membrane of an O2 sensor

Glucose + O₂ Gluconic Acid + H₂O₂

O₂ + 4H⁺ 2 H₂O

1º generation Biosensors

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1973 Guibault and Lubrano

H₂O₂ O₂ + 2H⁺ + 2e-

An adequate electro-oxidation potential of H₂O₂ is applied

Redox reaction of H₂O₂ 900 mV vs. Ag/AgCl

1º generation Biosensors

Interferents

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“Electronic Mediation”. A Mediator is incorporated

e- transference

GOx Active site Electrode Surface

Low molecular weight redox pairs

They can be used free in solution or immobilized together with the Enzymes

2º generation Biosensors

Mediators

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ADVANTAGES

Greater selectivity
Less susceptible to interferers

DISADVANTAGES

E-protein-electrode transfer impossible, slow or irreversible
Decreases exponentially with distance
Proteins tend to denature by contact with the surface

3º generation Biosensors

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BIBLIOGRAPHY

Madrid, R; Chehín, R.; Chen, T-H and Guiseppi-Elie. Biosensors and Nanobiosensors. 2017. In: Further Understanding the Human Machine. Ed.: Max Valentinuzzi. World Scientific Publisher (WSP), Singapore.
Tran Minh Canh. 1993. Biosensors. Chapman & Hall and Masson. The British Library.
Alegret, S.; del Valle, M.; Merkoci, A. 2004. Sensores electroquimicos, ed. Universidad Autonoma de Barcelona-Servei de Publicacions.
Wang, J. 2001. Glucose biosensors: 40 years of advances and challenges. Electroanalysis, vol. 13(12), 983-988.
State of the Art in Biosensors - General Aspects. Edited by Toonika Rinken, ISBN 978-953-51-1004-0, 351 pages, Publisher: InTech, Chapters published March 13, 2013 under CC BY 3.0 license. DOI: 10.5772/45832. OPEN ACCESS BOOK