Chemical Sensor : Structure, Circuit, Working, Types, Vs Biosensor & Its Applications

Ideal chemical sensors are portable, inexpensive, and foolproof devices that react with ideal and instant selectivity to a particular analyte in any preferred medium to generate a measurable output signal at any required analyte concentration. Generally, these sensors are devices (or) instruments that decide the concentration, detectable presence (or) analyte quantity. The chemical sensor’s application complexity is connected to the technical complexities connected with these determinations and the specific nature of the chemical material to be analyzed. The selectivity & sensitivity aspects of chemical sensing can be affected by the dimensional, phase & temporal aspects of the preferred determination. The analyte can be available in a liquid or solid phase on different dimensional scales which range from bulk liters to picoliters. This article provides brief information on a chemical sensor, its working, and its applications.

What is a Chemical Sensor?

A sensor that is used to measure & detect chemical quantities within an analyte (composition, existence of a particular element (or) ion, chemical activity, concentration) to convert it into electronic data is known as a chemical sensor. These sensors are utilized mainly in myriad applications which include home detection systems, medical, nanotechnology & automotive.

Chemical Sensor Structure

The chemical sensor structure is shown below. This sensor is made with two significant components; the receptor or sensing material & the transducer. The sensing material interacts with the target analyte in different ways based on the type of sensor. The outcome of this interaction is the transformation of a material property like electrical conductivity & mass.

The next component of this sensor is the transducer, which is responsible for taking the chemical data of the interaction between the receptor & analyte and changing it into an electronic signal. After that, this data is given to a computer (or) a mechanical component.

The chemical sensor works on the principle of electrochemical reaction to convert the composition & concentration of organic & inorganic chemical compounds into electrical signals.

Chemical Sensor Circuit & Its Working

This circuit describes how the carbon monoxide sensor works. This sensor has three electrodes which are immersed within a liquid electrolyte. These three electrodes are mainly the working electrode, the counter electrode & the reference electrode but the most important electrode is the working electrode. This electrode is made of platinum which is a catalytic metal to carbon monoxide backed by a gas-permeable although hydrophobic membrane. The carbon monoxide gas diffuses through the porous membrane and is oxidized electrochemically.

The electrons involved in the flow of electrochemical reaction from the electrode produce the output signal of sensor. The reference electrode provides a stable electrochemical potential within the electrolyte. This electrode is protected simply from exposure to carbon monoxide gas, thus, its thermodynamic potential is always similar & remains stable. In addition, no current is permitted to flow throughout the reference electrode A counter-electrode is provided to complete the electrochemical cell circuit.

This electrode works only as the second half-cell & lets electrons go into or away from the electrolyte. The below circuit controls the working electrode potential & changes the signal current to a voltage known as a potentiostat. The current from the WE (working electrode) is changed to a voltage through the U2 op-amp. So this circuit maintains the working electrode voltage at the bias potential (Vbias). The RE (reference electrode) potential is compared to the constant input voltage (Vbias). The U1 op-amp in the circuit generates a voltage at the CE (counter electrode) which is adequate to generate a current that is precisely equivalent and reverse to the working electrode current. Simultaneously, a constant voltage can be maintained between the working electrode & reference electrode.

The carbon monoxide sensor is also equipped through a chemically selective filter which eliminates potentially interfering gases before they arrive at the working electrode. If the chemically selective filter operates correctly, the chemical sensor will have less response to interfering gases. The technology explained above can be modified to provide sensors that react to the various gases. So this can be accomplished with different working electrodes, chemically selective filters bias potentials.

Chemical Sensor Types

There are different types of chemical sensors which are discussed below.

Breathalyzer

A breathalyzer is a chemical sensor used to estimate BAC (blood alcohol content) from a breath sample. Whenever people drink alcohol, then they breathe out some quantity of alcohol molecules which is directly proportional to the quantity they drink. So this sensor is designed particularly to measure the BAC of a person frequently to decide whether they are driving a vehicle securely or not. Once the molecules of alcohol interact through the receptor, then they encounter one more chemical substance enclosed in the receptor like sulfuric acid, silver nitrate, water, and potassium dichromate. When the chemical dissimilarity between the two chambers is recognized, an electric signal can be generated & indicated through its needle or screen.

Carbon dioxide Sensor

A carbon dioxide sensor is also known as a CO2 sensor which is used for measuring CO2 gas. The common principles for this sensor are infrared gas sensors & chemical gas sensors. So, measuring CO2 gas is significant in observing indoor air quality, the lung’s function in the capnograph device form & various industrial areas.

Carbon Monoxide Detector

A carbon monoxide detector is a device used to sense the presence of CO gas to avoid the poisoning of carbon monoxide. Carbon monoxide gas is a colorless, odorless & tasteless gas produced by partial ignition of carbon-containing materials. High levels of this gas can be very hazardous to humans based on the quantity present & exposure length. These detectors are mainly designed to measure the levels of CO eventually & give an alarm before hazardous CO levels build up in surroundings, providing people sufficient warning to securely freshen the area or leave.

Electronic Nose

An electronic nose or e-nose is a device used for detecting flavors or odors. This is capable of reproducing human senses with sensor arrays & pattern recognition systems. So the recognition process stages are related to human olfaction & are performed for, comparison, identification, quantification & other applications like; data storage & retrieval. The stages of the recognition process are similar to human olfaction and are performed for identification, comparison, quantification, and other applications, including data storage and retrieval.

Zinc Oxide Nanorod Sensor

A zinc oxide nanorod sensor (ZnO nanorod sensor) is an optical or electronic device used to detect the presence of liquid molecules or certain gases within the ambient atmosphere. This chemical sensor utilizes enhanced surface area for all nano-sized materials like ZnO nanorods. Molecule absorption on the nanorods can be detected through differences in the nanorods’ properties, like photoluminescence, vibration frequency, electrical conductivity, mass, etc. The simplest & most popular method is to pass electrical current throughout the nanorods & monitor its changes on exposure to gas.

Potentiometric Sensor

A potentiometric sensor is a kind of chemical sensor used to find out the analytical concentration of some components in the analyte gas (or) solution. This sensor measures the electrical potential of an electrode when there is no voltage is present. This sensor has many benefits like simplicity and cost-effectiveness as compared to conventional analytical instruments. So, these sensors can be used in different fields like food, healthcare, agriculture, food quality monitoring, water quality monitoring, health monitoring, environmental monitoring, etc.

Hydrogen Sensor

A hydrogen sensor is a type of sensor; used to detect the presence of hydrogen gas in various fields. These sensors are low-cost, durable, compact, and very simple to maintain as compared to other gas sensors. Hydrogen is colorless, tasteless & an odorless gas. This sensor must be used for detecting the hydrogen content in the environment & monitor gas leakage. This sensor is used in hydrogen gas detectors to detect gas leaks.

Fluorescent Chloride Sensor

The fluorescent chloride sensor is a type of chemical sensor used for chemical analysis, to measure chloride transport across cell membranes to adjust cell volume, charge balance, membrane excitability, and resting potential. These are also used mainly for the cystic fibrosis diagnosis. The chloride (Cl−) participation discoveries within physiological processes stimulate the intracellular Cl− measurements within live cells & the fluorescent tools development.

Difference B/W Chemical Sensor and Biosensor

The difference between chemical sensors and biosensors includes the following.

Advantages & Disadvantages

The advantages of chemical sensors include the following.

• The chemical sensor gives quick responses to various gases & vapors.
• These are affordable.
• Chemical sensors are very simple to use & portable
• These are not expensive.

The disadvantages of a chemical sensor include the following.

• These sensors are narrow (or) their temperature range is limited.
• This sensor cannot meet all ecological monitoring necessities.
• It has a limited shelf life.

Chemical Sensors Applications

The applications of chemical sensors include the following.

• Chemical sensors have significant applications in medical detection, environmental monitoring the food industry, bioengineering, defense safety & the mining industry.
• The chemical sensor applications mainly include safety, critical care, industrial hygiene, product quality controls, process controls, etc.
• This sensor helps measure and detect chemical qualities within an analyte.
• These are used in medicine, home security, environmental pollution, etc.
• Chemical sensing is used in a wide range of disciplines like; electrochemical analysis, biomedical measurement, pollution monitoring & industrial control.
• These sensors have various applications to monitor pollution & contaminants detection.

Please refer to this for more chemical sensors and their interfacings;

• MQ4 Methane Gas Sensor.
• MQ8 Hydrogen Gas Sensor.

Thus, this is an overview of a chemical sensor, structure, working, circuit, types, differences, advantages, disadvantages, and applications. These sensors are devices, used for converting a chemical signal to an analytic one. Here, the chemical signal can be formed through a selective interaction between a sensing material located in the sensor & a target analyte. Examples of chemical sensors are; Carbon monoxide detectors, Glucose detectors, Mosquito, Pregnancy tests, etc. Here is a question for you, what is a biosensor?