Biosensor Types and Working Principles: Optical, Electrochemical, Piezoelectric

This article explores biosensor types and their working principles, focusing on optical, electrochemical, and piezoelectric biosensors.

Definition: A biosensor is an analytical device used to detect an analyte, combining it with a physicochemical detector or transducer.

Figure 1 illustrates the working principle of a typical biosensor.

Figure-1: Working principle of Biosensors

The following biosensor types will be discussed:

• Piezoelectric sensor
• Electrochemical sensor
• Optical sensor

Biosensor Working Principle

A biosensor typically consists of the following components integrated onto a single chip:

1. Bioreceptor
2. Transducer element
3. Electronics circuit and display

Typical steps involved in the operation of a biosensor are:

• Detection of a physical change resulting from a biological element’s interaction with the analyte.
• The transducer converts this physical change into an appropriate electrical signal.
• The electrical signal is then amplified, processed, and displayed in a user-friendly format.

The biological material is immobilized using conventional methods, ensuring it’s in direct contact with the transducer. The analyte binds to this immobilized biological material, forming a bound analyte. This binding subsequently produces an electronic response that can be measured.

All biosensors are characterized by several key parameters, including:

• Sensitivity
• Selectivity
• Range
• Response time
• Reproducibility
• Detection limit
• Lifetime
• Stability

These parameters are critical when selecting biosensors for specific applications.

The development of different types of biosensors involves these steps:

• Selection of the appropriate bioreceptor and recognition molecule.
• Selection of a suitable immobilization method.
• Selection and design of the transducer.
• Design of the biosensor based on the aforementioned parameters.
• Packaging of all components into a single device.

Different Types of Biosensors | Working of Biosensors

Biosensors can be categorized based on the biological element or transducing element used. Common biological elements include enzymes, microorganisms, antibodies, biological tissue, and organelles.

The transduction method depends on the type of physicochemical change resulting from the sensing event. Primarily, biosensors are classified based on the transducer element as mass-based, electrochemical, and optical biosensors.

Different types of Biosensors

• Mass-based Biosensors: Include magnetoelectric and piezoelectric sensors (e.g., QCM - Quartz Crystal Microbalance, SAW - Surface Acoustic Wave).

• Electrochemical Biosensors: Include potentiometric, amperometric, impedimetric, and conductometric sensors.

• Optical Biosensors: Include SPR (Surface Plasmon Resonance), Raman & FTIR, and Fiber optics.

The following sections detail different types of biosensors and their working principles.

Piezoelectric Biosensors

These mass-based biosensors operate on the principle of acoustics, utilizing sound vibrations. These sensors generate an electrical signal in response to an applied mechanical force. Sensor modules are attached to a piezoelectric surface, facilitating interactions between the analyte and sensing molecules, which in turn generate mechanical vibrations.

Here, the piezoelectric sensor acts as a mass-to-frequency transducer, translating the electrical signal proportionally to the amount of analyte present.

Piezoelectric biosensors are utilized for detecting and quantifying various biomarkers in clinical samples, such as proteins, hormones, nucleic acids, and infectious agents. They are also applied in drug discovery and screening, environmental monitoring, and food quality control.

Electrochemical Biosensors

In this type of biosensor, a membrane holds the sensing molecules, preventing interfering species from the analyte solution from reaching the transducer.

The sensing molecules react with the compounds to be detected, generating an electrical signal proportional to the analyte concentration. Based on this principle, electrochemical biosensors employ potentiometric, amperometric, and impedimetric transducers. These transducers convert chemical information into a measurable amperometric signal.

Electrochemical biosensors, such as amperometric glucose sensors, are used to monitor blood glucose levels for diabetes management. They also find applications in environmental analysis, biomedical research, and point-of-care testing.

Optical Biosensors

In this biosensor type, optical fibers enable the detection of analytes based on absorption, fluorescence, or light scattering.

Optical biosensors allow the detection of multiple analytes by utilizing different monitoring wavelengths. Various parameters such as changes in wavelength, time, wave propagation, intensity, spectrum distribution, or the polarity of light are used for measurement purposes in optical biosensors.

Optical biosensors are widely used in medical diagnostics for detecting infectious diseases, cancer biomarkers, and genetic disorders. They are used to monitor environmental pollutants such as heavy metals, pesticides and toxins. Furthermore, they facilitate the rapid detection of foodborne pathogens, allergens, and contaminants in food products, and find applications in monitoring and optimizing bioprocesses.

Other types of biosensors include magnetic, thermal, conductive, and acoustic biosensors.

Biosensor Manufacturers

The table below lists popular manufacturers of biosensors and equipment developers used in biosensor development and related activities.