Electrochemical sensors

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What is an electrochemical sensor

The role of electrochemical sensors

·Electrochemical sensors not only expand the research field of analytical chemistry, but also significantly simplify the operational flow of multiple complex analytical tests;

· At the same time, they have promoted technological advances in automatic detection instruments and analytical instruments, providing important support for real-time monitoring and

 accurate analysis.

Classification of chemical sensors

·According to the working principle, electrochemical sensors can be divided into the following categories: ① Electrochemical formula; ② Optical formula; ③ Thermal formula; ④ Mass formula, 

 etc. Among them, the electrochemical sensor is based on the principle of electrochemical, and converts the concentration changes of the components to be measured into electrical signals,

 thereby reflecting the information of the components to be tested in real time. This type of sensor can provide fast, sensitive and accurate detection results, and is widely used in environmental

 monitoring, medical diagnosis, industrial control and other fields.

Types of electrochemical sensors

·Potential sensor

- Introduction to potential sensors：

 Potential sensors are mainly represented by ion sensors, among which the earliest research is pH sensors; ion sensors are also called ion selective electrodes, and their core components are

 ion selective membranes. Such membranes are able to specifically respond to specific ions, and the membrane potential changes with the concentration of the ion being measured.

- Take the pH glass electrode as an example, it is a hydrogen ion selective electrode that is sensitive to H⁺ ions, and its sensitive film is made of glass. Similar to other ion selective electrodes,

 electron transfer does not occur on the sensitive film of the pH glass electrode, but instead forms a film potential through ion exchange reaction on the surface of the film. This principle also 

 applies to other types of ion selective electrodes, and their sensitive membranes also generate potential changes through a similar ion exchange mechanism.

·Current sensor

- A current sensor is a detection device that can sense the information of the measured current and convert it into electrical signals that comply with standards or other required forms of 

information  output in accordance with specific rules to meet the needs of information transmission, processing, storage, display, recording and control. Current sensors are also called magnetic 

sensors.

- The performance indicators of current-type gas sensors mainly include: sensitivity, accuracy, selectivity, measurement range, response time, temperature coefficient, bottom current and 

 noise, service life, and requirements for the working environment. In low-concentration gas detection, indicators such as sensitivity, selectivity, bottom current and noise are particularly critical,

 which directly affect the accuracy and reliability of the detection.

·Conductivity sensor

 A conductivity sensor is an instrument used to detect the conductivity of a liquid or solution. It is widely used in water quality monitoring, industrial process control, and food and beverage

 production, providing important conductivity data support for related industries.

·Bioelectrochemical sensors

 Biosensor is a chemical sensor (bioseensor) that uses organisms to selectively identify specific substances. Its structure is mainly composed of two parts:

- Molecular recognition element (receptor): consists of biologically active substances with molecular recognition capabilities, such as enzymes, microorganisms, animal and plant tissue 

sections,antigens or antibodies.

- Signal converter (base electrode or internal sensor): Usually an electrochemical or optical detection element that converts the recognition reaction into a measurable signal.

 Working principle: When the molecular recognition element specifically binds to the substrate (object to be tested), the generated complex or generated light, heat and other signals are

 converted  into output electrical or optical signals through a signal converter, thereby achieving the purpose of analysis and detection.

·Enzyme sensor

- In organisms, many complex chemical reactions, such as the synthesis and decomposition of proteins, fats and carbohydrates, are almost all reactions catalyzed by enzymes.

- Enzyme catalyzed reaction

 The enzyme (E) first binds to the reactant (also known as substrate, S) to form an intermediate compound (ES). Subsequently, the intermediate compound (ES) is further broken down into 

 product (P) and the enzyme (E) is released.

 Features: Enzyme catalytic reaction has extremely high catalytic efficiency and high selectivity.

- Sensors developed based on this characteristic of enzymes are called enzyme sensors.

The main working principle of electrochemical sensors

·The working principle of an electrochemical sensor is based on chemical reaction with the gas being tested and generating an electrical signal proportional to the gas concentration. 

 A typical electrochemical sensor consists of a sensor electrode (working electrode) and a counter electrode, separated by a thin electrolytic layer. The gas first enters the sensor through

 tiny capillary openings, passes through the hydrophobic barrier layer and reaches the electrode surface. This design not only ensures that the right amount of gas reacts with the sensing

 electrode to generate sufficient electrical signals, but also prevents electrolyte leakage.

·After the gas diffuses through the barrier to the sense electrode, an oxidation or reduction reaction occurs, which is catalyzed by the electrode material designed for the target gas. By 

 connecting the resistor between the electrodes, a current proportional to the measured gas concentration will be generated between the positive electrode and the negative electrode.

 The gas concentration can be determined by measuring the current. Since this process involves the generation of current, electrochemical sensors are also called current gas sensors or

 micro fuel cells.

·In practical applications, due to the continuous electrochemical reaction on the surface of the sensor electrode, its potential cannot be kept constant, and long-term use will lead to a 

 degradation of sensor performance. To improve performance, a reference electrode is introduced into the sensor. The reference electrode is placed in the electrolyte close to the sensing 

 electrode, which can provide a stable fixed potential for the sensing electrode. The reference electrode itself does not participate in the current flow, and its main function is to maintain 

 a constant voltage on the sensing electrode. After the gas molecules react with the sensor electrode, the signal of the counter electrode is measured, and the results are usually directly

 related to the gas concentration. By adjusting the voltage applied to the sensing electrode, the sensor can be made more selective to a specific target gas.