Biosensors are categorized based on their molecular recognition elements, which include enzymes, microbes, cells, tissues, and immunological components. These materials interact with specific targets to detect analytes. For example, enzymes bind substrates, while antibodies recognize antigens.
Additionally, biosensors can be classified by their transducers, such as electrochemical, optical, thermal, or piezoelectric devices. These transducers convert the biochemical signal into an electrical or measurable output, enabling accurate detection of biological interactions.
Bio-affinity biosensors focus on the interaction between the target molecule and the recognition element, ensuring high specificity and selectivity in measurements.
The fundamental structure of a biosensor includes a molecular recognition element and a transducer. The recognition component identifies the target, triggering a physical or chemical change that is then converted into a measurable signal by the transducer.
Selecting the right molecular recognition material is crucial for sensor performance. It must be compatible with the target substance and capable of producing a detectable response. The choice of transducer also plays a vital role in ensuring accurate and reliable results.
Modern biosensors benefit from advances in microelectronics and sensing technologies, allowing for real-time and precise monitoring of complex biochemical processes.
BOD Biosensor:
A BOD biosensor replaces traditional dilution methods by using immobilized microorganisms to measure organic pollution in water. This system provides faster and more efficient results compared to conventional methods, which require time-consuming incubation.
The biosensor uses a porous membrane with immobilized Trichosporon microorganisms, placed on an oxygen electrode. When a sample is introduced, the microorganisms consume oxygen, leading to a decrease in current that correlates with BOD levels. This method allows for rapid and accurate determination of BOD in less than 20 minutes.
Ammonia Biosensor:
This biosensor employs nitrifying bacteria immobilized on a gas-permeable membrane and connected to an oxygen electrode. Ammonia is metabolized by the bacteria, causing a reduction in oxygen consumption, which is detected as a current change. The sensor demonstrates high selectivity and sensitivity, with a detection limit of 0.1 mg/L and a linear response up to 42 mg/L.
Nitrite Biosensor:
A nitrite biosensor utilizes nitrifying bacteria and an oxygen electrode to detect nitrite concentrations. The bacteria consume oxygen in the presence of nitrite, and the resulting current change is directly proportional to the nitrite concentration. This system shows excellent stability and reproducibility, with a detection limit of 0.1 mmol/L.
Ethanol Biosensor:
This biosensor combines ethanol oxidase with a hydrogen peroxide electrode. Ethanol is oxidized to acetaldehyde and hydrogen peroxide, which is then detected by the electrode. The sensor exhibits a linear response to ethanol concentrations up to 3.0% (V/V), making it suitable for various applications.
Methane Biosensor:
The methane biosensor uses methane-oxidizing bacteria to detect methane levels. The system measures the difference in oxygen electrode currents between two reactors—one containing bacteria and the other not. This difference reflects the methane concentration, offering a fast and accurate method for gas analysis.
In summary, biosensors provide a powerful tool for detecting a wide range of biological and chemical substances. Their design and functionality continue to evolve, driven by advancements in biotechnology and sensor technology, making them essential in environmental monitoring, medical diagnostics, and industrial applications.
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