Biosensor's work management and characteristics analysis - Database & Sql Blog Articles

Photocoupler

According to the molecular recognition elements in the biosensor, that is, the sensitive elements can be classified into five types: enzyme sensors, microbial sensors, cell sensors, tissue sensors, and immunosensors. Obviously, the sensitive materials applied are enzymes, microbial individuals, organelles, animal and plant tissues, antigens and antibodies.

According to the transducer of the biosensor, that is, the signal converter, the biosensor sensor, the semiconductor biosensor, the photobiosensor, the thermal biosensor, the piezoelectric crystal biosensor, etc.; the transducer is an electrochemical electrode, a semiconductor, and a photoelectric Converters, thermistors, piezoelectric crystals, etc.

In addition, there are bio-affinity biosensors that classify the interaction between the target and the molecular recognition element.

Biosensor basic structure and working principle

The biosensor consists of a molecular recognition part (sensing element) and a conversion part (transducer), and the molecular recognition part identifies the object to be measured, and is a main functional element that can cause some physical change or chemical change. The molecular recognition moiety is the basis for the selective determination of biosensors.

Among the substances in the organism that can selectively distinguish specific traits are enzymes, antibodies, tissues, cells, and the like. These molecular recognition functional substances can be combined with the target to be combined by the recognition process, such as binding of antibodies and antigens, and binding of enzymes to substrates. When designing a biosensor, it is an extremely important premise to select an identification functional substance suitable for the measurement object; the characteristics of the resulting composite are taken into consideration. Selecting a transducer based on chemical changes or physical changes caused by sensitive components prepared by molecular recognition functional substances is another important step in the development of high quality biosensors. The generation or consumption of light, heat, and chemicals in sensitive components produces a corresponding amount of change. Based on these variations, a photopic transducer can be selected.

The information generated by the biochemical reaction process is diversified, and the results of microelectronics and modern sensing technologies provide a rich means of detecting this information.

BOD biosensor

The BOD standard dilution method is one of the routine monitoring methods for organic pollution in water. It needs to culture the water sample containing microorganisms at 20 ° C for 5 days. It requires skilled operation skills, and the operation process is cumbersome and cannot reflect the water quality in time. In order to determine BOD simply and quickly, a BOD biosensor was produced instead of the standard dilution method.

The microorganism used in the BOD biosensor may be a genus Trichosporon. The cells are adsorbed on the porous membrane, dried at room temperature, and stored for use. The porous membrane with the cells was placed on the Teflon membrane of the oxygen electrode, and the cells were placed between the two membranes. The measuring system consists of a jacketed flow cell (diameter 1.7 cm, height 0.6 cm, volume 1.4 ml), biosensor probes mounted in the flow cell; peristaltic pump; automatic sampler and recorder.

The water temperature in the flow cell jacket was constant at 30 ° C ± 0.2 ° C, and oxygen-saturated phosphate buffer (pH 7.0, 0.1 mol/L) was injected into the flow cell at a flow rate of 1 ml/min. After the current showed a steady state value, the sample solution was injected into the flow cell at a flow rate of 0.2 ml/min, and the sample was injected once every 60 minutes.

When a standard BOD sample solution containing glucose and glutamic acid is injected into a measurement system, these organic compounds are utilized by microorganisms immobilized by a porous membrane. The immobilized microorganisms begin to consume oxygen, causing a decrease in the dissolved oxygen content of the solution near the membrane. As a result, the output current of the oxygen electrode decreases significantly with time, reaching a certain steady state value within 18 minutes. At this time, a new kinetic balance between oxygen consumption and oxygen supply is established between the diffusion of oxygen molecules into the membrane and cellular respiration.

The magnitude of the steady state current value depends on the BOD concentration of the sample solution. After the sample solution has flowed, the buffer is passed into the flow cell to return the sensor's output current to the initial level. The response time of the biosensor (the time required to reach the steady state current) varies depending on the type of sample solution. The response time was 8 min for the sample solution containing acetic acid and 18 min for the sample solution containing glucose. Therefore, the time to inject the sample in the experiment was 20 min.

The biosensor's current difference (the difference between the initial current and the steady state current) is linear with the BOD concentration measured by the five-day standard dilution method. The minimum BOD concentration was 3 mg/L. At a BOD content of 40 mg/L, the current difference can be reproduced in 10 experiments (relative error is within ±6%).

Determination of ammonia biosensor

A biosensor composed of immobilized nitrifying bacteria, a polytetrafluoroethylene gas permeable membrane, and an oxygen electrode can be used for the determination of ammonia. Nitrifying bacteria isolated from activated sludge, including nitrosomonas and Nitrobacter, are adsorbed and fixed on a porous membrane (having a pore size of 0.45 μm and a thickness of 150 μm), and the carrier membrane is attached to the end of the oxygen electrode. An ammonia biosensor is prepared by coating a membrane with a gas permeable membrane. The nitrifying bacteria consume oxygen with ammonia as the sole energy source.

The concentration of ammonia can be determined by detecting the oxygen consumption of the immobilized microorganisms on the oxygen electrode. The measurement was carried out at pH 9.0 and at a temperature of 30 °C. The current reduction value (the difference between the initial current value and the steady state current value) is linear with the ammonia concentration. The maximum detection concentration was 42 mg/L, the maximum current reduction was 4.7 μA, and the detection limit was 0.1 mg/L (reproducibility was ±5%). No response to various volatile substances (such as acetic acid, ethanol, dimethylamine, butylamine, etc.), indicating excellent sensor selectivity. For the 33 mg/L ammonia sample, the sensor output current was almost unchanged for measurements of up to two weeks or more than 1500 times. The ammonia in human urine was measured, and the correlation coefficient between the biosensor method and the ammonia electrode method was 0.9. The biosensor was used to measure ammonia in the fermentation effluent.

Nitrite biosensor

Nitrifying bacteria use nitrite as the sole source of energy for respiration and oxygen consumption. The reaction process is as follows:

Nitrite can be determined using a biosensor consisting of immobilized nitrifying bacteria and an oxygen electrode.

The porous membrane with immobilized nitrifying bacteria was cut into discs and carefully attached to the Teflon membrane on the surface of the oxygen electrode, and then covered with a gas permeable membrane (0.5 μm pore size) and fixed with a rubber ring. A nitrite sensor probe, its measurement system consists of a jacketed flow cell (diameter 23mm, height 10mm, liquid volume lml), biosensor probe placed in it; peristaltic pump; amplifier and recorder.

The temperature of the flow cell was maintained at 30 ° C ± 1 ° C by a water bath. The oxygen-saturated buffer solution (pH 2.0) was fed into the flow cell at a flow rate of 1.6 mi/min. After the electrode current reached a certain steady state value, the sample solution was sent to the flow cell at a flow rate of 0.4 ml/min. It lasted 2 minutes.

After the sample solution (sodium nitrite solution) is sent to the flow cell, the nitrite ion is converted to nitrogen dioxide under the condition of pH 2.0, and then the nitrogen dioxide passes through the gas permeable membrane. In the nitrifying bacteria layer, nitrogen dioxide is converted into nitrite ions. Nitrite ions are metabolized by nitrifying bacteria as the sole source of energy. The dissolved oxygen consumption of the solution in the vicinity of the bacterial membrane is measured by an oxygen electrode, and the concentration of the nitrite can be indirectly determined from the current reduction value of the oxygen electrode.

The current of the sensor is significantly reduced over time up to a certain steady state value. Steady-state current is available within 10 min.

There is a linear relationship between the difference between the initial current and the steady state current and the concentration of nitrite (below 59 mmol/L). The minimum detectable concentration of nitrite is 0.1 mmol / L. When measured with a 0.25 mmol/L sodium nitrite solution, the standard deviation of the 25 experiments was 0.01 mmol/L with a relative error of ±4%.

The presence of various substances in the solution does not affect the measurement of this biosensor. The same concentration sample was repeatedly measured over 400 times in less than 21 days, and the current output of the sensor was almost unchanged.

Ethanol biosensor

In the presence of ethanol oxidase, water and oxygen, the reaction of ethanol to acetaldehyde and hydrogen peroxide is as follows:

The ethanol biosensor can be composed of an immobilized enzyme membrane and a hydrogen peroxide electrode.

350 units of ethanol oxidase was mixed with 1 ml of 5% (v/v) polyethyleneimine and 3 mg bovine serum albumin solution, and 0.2 ml of a 15% (v/v) glutaraldehyde solution was added. Store at 5 ° C for 4 hours. This mixture of enzymes was further wrapped between a polycarbonate film and a cellulose acetate film and air-dried at 5 ° C for 24 hours. These membranes were again treated with a 0.02% (v/v) glutaraldehyde solution and washed with phosphate buffer (0.05 mol/L, pH 7.0) to obtain a probe for the sensor. Its measurement system mainly includes: a jacketed flow cell, a peristaltic pump, an autosampler, an amplifier and a recorder.

The current increase observed in the concentration range of 0 to 3.0% (V / V) is linear with the ethanol concentration. However, above 3.0% (V / V) concentration, it is nonlinear.

Methane biosensor

Methane oxidizing bacteria consume oxygen when breathing assimilation of methane. The reaction formula is as follows:

The bacteria used to prepare this sensor is Methylomonas. The measuring system consists of two oxygen electrodes, two reactors, a current amplifier, two vacuum pumps and a recorder. Both reactors have a volume of 55 ml each containing 41 ml of culture medium. One reactor carries bacterial cells and the other reactor has no bacterial cells. The two oxygen electrodes are installed in two measuring cells, and the measuring cell is connected to the entire system by a glass tube or a Teflon tube. One vacuum pump is used to evacuate the gas in the tube, and the other pump is used to deliver a gas sample to the system. The entire system remains rigorous and airtight, and the design line maintains the symmetry of the measurement and reference lines. The reaction cell was controlled at 30 ° C ± 0.1 ° C with a constant temperature water bath.

The methane sensor measures the difference in oxygen electrode currents in the two reaction cells, and the difference in current value is caused by the difference in oxygen content. When a gas sample containing methane flows through a reaction cell with bacteria, methane is assimilated by the bacteria, causing an increase in bacterial respiration, so that the oxygen electrode current in the reaction cell is reduced to a minimum steady state. The other oxygen electrode does not contain bacteria in the reaction cell, and the oxygen content and current value are not reduced, so the maximum difference between the two electrode currents is related to the methane content in the gas sample.

The sensor system has a good linear relationship with the current difference in the range of methane concentration of 0-6.6mmol/L. The current difference range is 0-3.5μA, the lowest detectable concentration is 5μmol/L, and the determination is 0.66mmol/ For the L sample (25), the reproducibility of the current difference was within 5% with a standard deviation of 9.40 nA. The response time for the determination of methane returned to the original equilibrium value within 60 seconds, so the total time for determining one sample was 2 min.