MEVE 018: Unit 12 – Biosensors
UNIT 12:
BIOSENSORS
12.0 Introduction
Environmental
pollution monitoring is critical for ensuring a safe and sustainable ecosystem.
Traditional techniques like chromatography and spectrophotometry, although
effective, often require elaborate procedures, sophisticated instruments, and
skilled personnel. In contrast, biosensors offer a rapid, sensitive,
specific, and often cost-effective alternative for detecting pollutants.
Biosensors combine a biological
recognition element with a transducer to detect specific analytes. They are
increasingly used in environmental monitoring to detect toxins, heavy metals,
pesticides, and microbial contaminants in air, water, and soil.
12.1 Objectives
By the end of
this unit, you should be able to:
- Understand
the concept and significance of biosensors.
- Describe how
biosensors work.
- Classify
different types of biosensors.
- Explain
various biosensor technologies including electrochemical and optical
types.
- Discuss the application
of biosensors in environmental monitoring.
12.2 Environmental Pollution and Conventional Techniques
Environmental
pollution arises from various sources, such as industrial effluents, vehicle
emissions, agricultural runoff, and household waste. Traditional monitoring
involves:
- Chromatographic
methods (e.g., HPLC, GC-MS)
- Spectroscopic
techniques (e.g., AAS, ICP-OES)
- Wet chemical
analysis (e.g., titration, colorimetry)
Limitations of Conventional Techniques:
- Require
large sample volumes
- Time-consuming
- Expensive
instruments
- Require
trained operators
- Inability
for on-site or real-time monitoring
This led to the
evolution of biosensors for fast, portable, and reliable detection.
12.3 Biosensors
A biosensor
is an analytical device that combines a biological sensing element with
a physical transducer to produce a measurable signal proportional to the
concentration of an analyte.
12.3.1 Working of Biosensors
- Biological
element (enzyme, antibody, microorganism, nucleic acid,
etc.) interacts with the target analyte.
- This
interaction produces a change (chemical, electrical, thermal, or optical).
- The transducer
converts this change into a measurable signal.
- The signal
is amplified, processed, and displayed, often via digital output.
12.4 Classification of Biosensors
Biosensors can be
classified based on the type of transducer used.
12.4.1 Electrochemical Biosensors
These biosensors
detect changes in electrical properties during the biological reaction.
a) Amperometric Biosensors
- Measure
current produced by the redox reaction of the analyte.
- Example:
Glucose biosensors.
- Used for
detecting pesticides, heavy metals, and phenols in water.
12.4.2 Cyclic Voltammetry
- A type of electrochemical
analysis where current is measured as voltage is swept cyclically.
- Useful for
studying electron transfer processes in environmental pollutants.
- Helps
understand redox behavior of toxic chemicals.
12.4.3 Conductometric Biosensors
- Measure changes
in electrical conductivity due to the ionic strength of the sample.
- Simple and
inexpensive.
- Applied in
detecting urea, nitrates, and industrial pollutants.
12.4.4 Potentiometric Biosensors
- Measure
changes in voltage at a constant current.
- Involve ion-selective
electrodes (ISEs).
- Applied for
detection of pH, ammonia, heavy metals, and cyanide.
12.4.5 Optical Biosensors
- Detect
changes in light properties (absorbance, fluorescence, or reflectance)
during the interaction.
- Often use
fiber optics for signal transmission.
- Example:
Fluorescence-based detection of pathogens or DNA hybridization.
- Useful for
continuous, remote, or online monitoring of water pollution.
12.4.6 Piezoelectric Biosensors (Optional Extension)
- Use crystals
that generate electric signals in response to mass changes.
- Detect
airborne or waterborne toxins and bacteria.
- Highly
sensitive for VOCs and pathogens.
12.5 Application of Biosensors
Biosensors have
revolutionized real-time, on-site detection of pollutants.
Key Applications:
- Water
Quality Monitoring:
- Detect
pathogens (E. coli), heavy metals (lead, mercury), and pesticides.
- On-site
analysis of river and groundwater.
- Air
Pollution Monitoring:
- Detection
of VOCs, SO₂, and NOₓ gases.
- Enzyme-based
sensors for detecting oxidants.
- Soil
Contamination Analysis:
- Biosensors
for detecting hydrocarbons, nitrates, and heavy metals in soil.
- Toxicity
Detection:
- Whole-cell
biosensors (bacteria/algae) indicate the presence of toxins.
- Bioluminescent
microbes used to detect pollutant-induced stress.
- Pathogen
Detection:
- DNA or
antibody-based biosensors detect bacteria and viruses in environmental
samples.
- Bioremediation
Monitoring:
- Monitor
microbial activity and pollutant degradation in situ.
12.6 Let Us Sum Up
In this unit, we
explored the working principles, types, and environmental applications of
biosensors. These devices have emerged as powerful tools for rapid, sensitive,
and on-site detection of a wide range of environmental contaminants. The
continued advancement in biosensor technology, particularly miniaturization and
integration with digital systems, will further enhance environmental monitoring
and management in the coming years.
Keywords
- Biosensor-A device combining a
biological element with a transducer to detect an analyte.
- Transducer-Converts a biological
response into a measurable signal.
- Amperometric-Biosensors that measure
current during a redox reaction.
- Voltammetry-Measurement of current
as a function of changing voltage.
- Conductometry-Measures changes in
conductivity due to ionic changes.
- Potentiometric-Measures voltage changes
at constant current, using ion-selective electrodes.
- Optical biosensor-Detects changes in light
properties during analyte detection.
- Environmental monitoring-Assessing environmental conditions to detect pollution or degradation.
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