Biosensors are widely classified based on the molecular recognition elements they use, which include enzymes, microorganisms, cells, tissues, and immunological components. These elements act as sensitive materials that interact with specific analytes, triggering a detectable response. For instance, enzyme-based biosensors rely on catalytic reactions, while microbial biosensors utilize living organisms to detect pollutants or biological compounds.
Additionally, biosensors can be categorized by their transducer types, such as electrochemical, optical, thermal, and piezoelectric sensors. Each transducer converts the biochemical interaction into an electrical signal that can be measured. Electrochemical biosensors, for example, often use electrodes to detect changes in current or voltage, whereas optical biosensors may measure light intensity or fluorescence changes.
Bio-affinity biosensors focus on the specific interactions between the target molecule and the recognition element, such as antigen-antibody or ligand-receptor binding. This specificity is crucial for accurate detection and reduces cross-interference from other substances.
The basic structure of a biosensor includes a molecular recognition component (sensing element) and a transduction unit (signal converter). The recognition part identifies the target analyte, while the transducer translates this interaction into a measurable signal. This combination ensures both selectivity and sensitivity in detecting various substances.
Designing a biosensor requires careful selection of the recognition element and transducer. The choice of material and configuration depends on the nature of the target analyte and the desired detection method. For example, oxygen electrode-based biosensors are commonly used for measuring dissolved oxygen levels, which can indicate biological activity in water samples.
BOD biosensors, for instance, replace traditional dilution methods by using immobilized microorganisms to detect organic pollution in water. When organic matter is introduced, the microorganisms consume oxygen, leading to a measurable decrease in oxygen levels. This allows for rapid and real-time monitoring of water quality without the need for long incubation periods.
A similar approach is used in ammonia biosensors, where nitrifying bacteria are immobilized and used to detect ammonia concentrations by measuring their oxygen consumption. These biosensors are highly selective and can operate under controlled pH and temperature conditions, making them ideal for environmental monitoring applications.
Nitrite biosensors also employ immobilized bacteria that metabolize nitrite, converting it into other compounds that affect oxygen levels. By measuring the change in oxygen concentration, these biosensors can accurately determine nitrite levels in water samples.
Ethanol biosensors use enzymes like ethanol oxidase to convert ethanol into acetaldehyde and hydrogen peroxide. The resulting reaction is detected using a hydrogen peroxide electrode, allowing for precise measurement of alcohol content in liquids.
Methane biosensors work by utilizing methane-oxidizing bacteria that consume oxygen during the assimilation of methane. By comparing the oxygen levels in two separate reaction chambers—one with bacteria and one without—these biosensors can quantify methane concentrations in gas samples with high accuracy and speed.
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