pH Sensors

In the field of chemical and biological analysis, pH sensors are essential tools because they measure the concentration of hydrogen ions in solutions, which indicates how acidic or alkaline the solution is. They are essential in a wide range of applications, such as medical diagnostics, food and beverage manufacturing, and environmental monitoring.

Electrochemical Potential Measurement

Measuring a solution's electrochemical potential is the key to determining pH. This entails contrasting the solution's potential with a recognized standard reference electrode. The below defined Nernst equation is shown:

Where:

• E₀ = Standard electrode potential
• R = Gas constant
• T = Temperature (in Kelvin)
• n = Number of electrons
• F = Faraday constant
• a_H+ = The activity of the hydrogen ions in the solution

Glass Electrode Types and ISFETs (Ion-Sensitive Field-Effect Transistors)

Glass Electrodes: The most popular kind of pH sensor is a glass electrode, which is made up of a tiny glass bulb at the end of an electrode stem. The electrochemical potential across the glass membrane is caused by the bulb's sensitivity to the concentration of hydrogen ions in the surrounding fluid. This potential is then measured in relation to a reference electrode.

ISFETs: Glass electrodes can be replaced with more contemporary, smaller Ion-Sensitive Field-Effect Transistors (ISFETs). They use a metal-oxide-semiconductor field-effect transistor (MOSFET), in which an ion-sensitive membrane takes the place of the metal gate, enabling them to convert ion concentrations into electrical signals. The resilience, compactness, and interoperability of ISFETs with integrated circuit technology are all benefits.

Applications

ISFETs and glass electrodes have a wide range of uses. They are essential for maintaining pH levels in a variety of industrial operations, keeping an eye on the quality of the water in the surrounding environment, doing biomedical research, and providing clinical diagnoses.

By measuring the electrochemical potential, pH sensors are essential for determining the chemical composition of solutions in a variety of applications. Each type of pH sensor has its own advantages. The manipulation and comprehension of chemical and biological environments is made easier by developments in pH sensing technology, which can be applied to miniaturization and integration of ISFETs or the selective sensitivity of glass electrodes.

Gas Sensors

Gas sensors play a vital role in the field of chemical and biological sensors since they enable the identification of gas concentrations, quantities, and presence within an environment. They play a crucial role in a number of areas, including environmental analysis, safety and security, and industrial process monitoring. They provide vital information to help avert dangerous situations and enhance process control.

Types of Gas Sensors

Catalytic Gas Sensors: For the purpose of identifying combustible gasses, catalytic sensors, also known as pellistors, are commonly utilized. They operate under the premise that the gas to be detected will burn on the active bead of the sensor, changing the temperature and, in turn, the resistance. It is therefore possible to quantify and connect this change in resistance with the concentration of the gas.

Infrared Gas Sensors: Gas molecules absorb infrared light at particular wavelengths, a property that infrared sensors take advantage of. A gas sample's concentration can be ascertained by measuring the light transmission intensity and comparing it to the light intensity at the reference wavelength. Gases like carbon dioxide and hydrocarbons are the main gases for which they are employed.

Semiconductor Gas Sensors: When a semiconductor material is exposed to a gas, it changes resistance, which is how these sensors function. The conductivity of the semiconductor surface is altered by gas molecules adhering to it. It is possible to identify and measure particular gases because of the unique ways that different gases interact with the semiconductor material.

Detection Principles for Various Gases

Oxygen and Carbon Monoxide Detection: Electrochemical cells are commonly employed in the detection of gases such as carbon monoxide and oxygen. The current generated by the electrode material reacts with the target gas in a proportionate manner to the gas concentration.

Methane and Propane Detection: Owing to their capacity to identify gases at lower explosive limits, catalytic combustion sensors are frequently used for the detection of flammable gases such as propane and methane, offering vital safety measurements in industrial settings.

Volatile Organic Compounds (VOCs) Detection: Due to their sensitivity to organic compounds and capacity for quick, real-time observations, semiconductor gas sensors are frequently utilized for volatile organic compound detection.

Applications

Gas sensors are essential for many uses, such as medical gas monitoring, industrial plant leak detection, hazardous environment safety monitoring, and air quality monitoring.

With their varied types and operating principles, gas sensors act as the eyes and noses in a variety of applications, maintaining environmental quality, improving process efficiency, and guaranteeing safety. Depending on the target gas and the necessary sensitivity and selectivity of detection, the choice of sensor type and detection principle is critical.

Biosensors

The ability of biosensors to specifically and sensitively detect biological molecules has led to their rise in popularity in the field of chemical and biological sensors. Biosensors translate a biological response into an electrical signal by fusing a transducer and a biological recognition element. This process yields both qualitative and quantitative analytical data.

Enzyme-Based and Antibody-Based Detection

Enzyme-Based Biosensors: Enzyme-based biosensors use the selectivity of enzyme reactions to find the concentration and existence of particular chemicals. The target molecule's contact with the enzyme initiates a biochemical reaction that modifies the solution's characteristics, which can then be transformed into an electrical signal. To track blood glucose levels, for instance, glucose oxidase is frequently employed in enzyme-based biosensors.

Antibody-Based Biosensors: The mechanism of detection in antibody-based biosensors is based on the particular binding of an antibody to its corresponding antigen. A wide variety of chemicals can be identified and quantified thanks to this extremely specific interaction. These biosensors frequently provide a detectable signal, typically optical or electrochemical, proportionate to the antigen concentration using a tagged secondary antibody.

Applications

Medical Diagnostics: Biosensors are essential for on-site, quick identification of biomarkers associated with a wide range of illnesses in medical diagnostics. They play a crucial role in the identification of infectious organisms, the monitoring of cardiac biomarkers, and glucose monitoring for the management of diabetes, allowing for prompt and well-informed clinical decisions.

Environmental Monitoring: Biosensors are also useful to the environmental field, which uses them to identify toxins and pollutants in soil, water, and the air. They help in the prompt reaction to environmental risks and guarantee the health of ecosystems by monitoring pesticide levels, identifying diseases in water supplies, and evaluating air quality.

Due to the exceptional ability to identify biological entities with a high degree of precision and sensitivity, biosensors are becoming indispensable in many different disciplines. A wide range of applications are served by enzyme- and antibody-based biosensors, which provide small, effective, and user-friendly solutions. The creation of cutting-edge environmental monitoring systems and diagnostic tools is made possible by the field's advancements, which enhance public health and protect the environment.