Design of fluorescence in situ detector for the ho

2022-10-22
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Design of fluorescence in situ detector for biological fluid

most biological samples have certain spectral characteristics. Detecting and analyzing their spectra is an important aspect of studying biological characteristics [1]. Therefore, there have been many optical instruments, such as spectrophotometer in various bands, fluorescent light. At present, the traditional development mode of refining and chemical integration of petrochemical industry is facing structural contradiction meters, chemiluminescence meters, atomic absorption spectrometers, etc. with insufficient demand for refined oil and insufficient supply of olefins/aromatics. However, these analytical instruments have a common feature, that is, they can not achieve in-situ detection. They must first sample biological samples, sample pretreatment, and then transpose them into the sample pool of various analytical instruments before they can be measured. This is troublesome operation, and samples are easy to be polluted around, resulting in measurement errors

this paper introduces a spectrometer with an optical fiber probe, which can be directly inserted into the biological fluid to realize in-situ continuous monitoring. Because the fluorescence analysis method has two characteristics of high sensitivity and strong selectivity, it is especially suitable for the analysis of various components in biological fluids. Therefore, this instrument is mainly used to detect the fluorescence spectrum, and its spectrum can be displayed in real time with the help of computer. Through different processing of the data, the spectrometer can measure many residual air biomass in the exhaust cylinder. Its measurement sensitivity and accuracy can meet the requirements of general analysis

2 instrument design

2.1 instrument structure block diagram

as shown in Figure 1, the light emitted by the light source is coupled into the probe by the lens, transmitted to the top of the probe through the incident optical fiber, and after interacting with the biological liquid, its information light is transmitted to the cassette through the outgoing optical fiber. After collimation and dispersion, its light spectrum is received by the photomultiplier tube through the slit, and the signal output by the photomultiplier tube is used for computer real-time acquisition and display

2.2 probe design

Figure 1 instrument structure block diagram

touching the regeneration of plastic

according to the function of the optical fiber probe, that is, transmitting excitation light and receiving emitted light, the shape of the optical fiber probe must be designed as a Y-shaped one, as shown in Figure 1

generally, when optical fibers form optical fiber bundles, there are roughly three kinds of arrangement: random distribution type, concentric circle type and semicircular symmetry type [2]. According to the isotropic fluorescence emission and the distribution characteristics of the three kinds of optical fibers, among the three distribution types, random distribution type optical fiber bundles have a strong ability to receive fluorescence information. Therefore, the randomly distributed optical fiber bundle was selected as the optical fiber probe. The diameter of the probe is relatively thick, about 5mm, including a large number of optical fibers, and the transmission and reception light are relatively strong. It can be inserted into the test tube for principle measurement. However, the random distributed optical fiber probe has a disadvantage, that is, its detection sensitivity changes with the distance from the reflector to the end face of the probe. This can be illustrated in Figure 2. The numerical aperture of the quartz fiber in this experiment is 0.37. According to the calculation, the light with the incidence angle in the range of 0 ~ 21.7 ° can enter the fiber and propagate forward. According to the reversibility of light, the divergence angle of light also ranges from 0 to 21.7 °. For the incident and outgoing optical fibers placed side by side, there is an intersection area (shaded area in the figure) between the divergence angle and reception angle of the light. The light shines into the liquid through the incident optical fiber to excite fluorescence. Only the fluorescence in the shaded part in the figure can enter the outgoing optical fiber and be transmitted to the signal receiver. It can be seen from the figure that the closer the reflecting surface is to the end face of the optical fiber, that is, the smaller D is, the less fluorescence is received. When d = 0, the received fluorescence signal is zero, that is, it is submerged by the end face. In transparent media, the detection sensitivity increases with the increase of distance D. However, in this experiment, because the liquid is biological liquid, especially whole blood, which absorbs a lot of light, excitation light and emission light can only travel a short distance in the blood. When the probe is inserted into the whole blood, the blood near the end face of the probe forms a series of reflecting surfaces. The closer the liquid layer is to the end face of the probe, the stronger the excitation light is and the stronger the fluorescence is, but the fluorescence received by the outgoing optical fiber is weaker; The farther away the liquid layer is from the probe, the excitation light in it becomes very weak through the absorption of the front liquid layer, so the fluorescence is also very weak, and some of these fluorescence will be absorbed when it is transmitted to the outgoing optical fiber, so the fluorescence received by the optical fiber probe is very small, so the detection sensitivity is not high. In order to improve its sensitivity, the same optical fiber is used for input and output in the experiment, and its light collecting ability is obviously improved. As the light propagates independently, the excitation light and fluorescence propagate forward in the optical fiber without interference. Figure 3 is the schematic diagram of the probe. Among them, 1 is a single coarse quartz fiber, 2 is a matching solution, and 3 is a Y-shaped quartz fiber bundle, which is composed of 7 thin fibers. Their numerical aperture is 0.37. The core diameter of thick optical fiber must be well matched with that of thin optical fiber to improve the detection sensitivity. Specific algorithm: the core diameter of coarse quartz fiber is D, and its cross-sectional area is π d2/4. The core diameter of the thin optical fiber is D, and the total area of the seven thin optical fibers is 7 π d2/4. Because the seven thin optical fibers cannot be fully closed, the gap area between the optical fibers accounts for 0.28 times the total area (the data is provided by Nanjing glass fiber Institute). The cross-sectional area of the optical fiber bundle composed of the seven optical fibers is 1.28 × 7πd2/4。

Figure 2 light transmission of incoming and outgoing optical fibers

Figure 3 probe sharing the same optical fiber for incident and outgoing

Figure 4 arrangement of thin fiber bundles

if the core diameter of the thick fiber is 0.6mm, the core diameter of the thin fiber must be 0.2mm, that is, seven thin fibers with a core diameter of 0.2mm just match the thick fiber with a core diameter of 0.6mm, and the calculation is as follows:

thick fiber: 0.62 × π/4 = 0.09 π mm2,

7 thin fibers: 7 × 0.22 × π/4

total area of fiber bundle: 1.28 × seven × 0.22 × π÷4=0.0896π0.09πmm2。

if the core diameter of the thick fiber is 0.9mm, the thin fiber must be 0.3mm to match each other. See the calculation below

cross sectional area of thick fiber: 0.92 × π/4 = 0.2 π mm,

7 thin optical fibers cross-sectional area: 7 × 0.32 × π/4=0.157πmm2。

total cross-sectional area of optical fiber bundle: 1.28 × 0.157 π = 0.2 another π mm2

the latter configuration is adopted in this experiment, that is, seven 0.3mm thin optical fibers are coupled with a 0.9mm thick optical fiber, and a matching liquid with a refractive index similar to that of quartz is coated between them to eliminate the reflection of the contact surface of the two optical fibers. Of 7 thin fibers

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