POCT Topics｜Quantum dots-a new generation of high-efficiency fluorescent markers

In recent years, POCT has developed rapidly and has become the fastest growing market segment in the IVD industry, attracting many IVD companies to enter the POCT field.

In the field of immunity, the current mainstream POCT on the market is mainly based on immunofluorescence chromatography. Compared with chemiluminescence, it is still slightly insufficient in sensitivity and stability. Therefore, many companies have begun to introduce small chemiluminescence for POCT. Usually immunofluorescence uses fluorescein as a marker. Fluorescein is a type of organic dye with fluorescence characteristics. However, organic dye markers are easily decomposed under light, and are prone to photobleaching. They have the characteristics of concentration quenching, which affects the analysis. For the accuracy and reliability of the results, it is particularly important to seek a fluorescent marker that is stable and efficient, has a long fluorescence lifetime, and has strong resistance to photobleaching.

Quantum dots (QDs for short, also known as semiconductor nanoparticles) are semiconductor nanocrystalline materials developed in the past 20 years. They are composed of elements of groups II to VI or III to V. The radius is smaller than or close to the laser Bohr radius. A class of semiconductor nanoparticles that receive excitation light to produce fluorescence. Among them, CdX (x=S, Se, Te), with a diameter of about 2nm-6nm, has a significant quantum size effect and surface effect, and has conventional materials. The lack of light absorption characteristics makes its application fields more and more extensive, especially the potential application value in immunobiology and clinical laboratory science research, which has attracted great attention from the majority of scientific workers. From the application of cell markers to the detection and diagnosis of multiple fields. Quantum dots, as fluorescent reagent probes to label biological macromolecules, are one of the important applications of nanomaterials in the field of biological analysis. At present, many domestic in vitro diagnostic companies have begun to use this material as a marker for their fluorescent immunochromatographic platform.

Compared with ordinary fluorescent dyes, quantum dots have the following characteristics:

The laser band of organic dye fluorescent molecules is narrow, and each fluorescent molecule must be excited by light of appropriate energy, and the fluorescence peaks produced are broad, asymmetric, and somewhat tailed. This makes it difficult to distinguish different probe molecules, and it is difficult to use organic dye molecules to detect multiple components at the same time. Due to the quantum confinement effect, quantum dots have a wide range of excitation wavelengths, which can be excited by light with a wavelength shorter than the emitted light (generally shorter than 10 nm), and produce a narrow (half-wave width of about 13 nm) and symmetrical emission spectrum, thus Avoid crosstalk between adjacent detection channels.

Quantum dots have the function of "coloring". Quantum dots of different particle sizes have different colors. The excitation wavelength range for exciting quantum dots is wide and continuously distributed, so it can be obtained by exciting quantum dots of different sizes with light of the same wavelength. Multi-color labeling is an ideal fluorescent probe.

Quantum dots have strong fluorescence intensity, good stability, strong anti-bleaching ability, can withstand multiple excitations, and have little effect on the physiological activity of biological macromolecules after labeling, so it provides the possibility to study the long-term effects of biological macromolecules .

It has good biocompatibility, especially after various chemical modifications, it can be specifically connected, has low cytotoxicity, and has little harm to organisms. It can be labeled and detected in vivo, while traditional organic fluorescent dyes are generally more toxic. Poor biocompatibility.

Long fluorescence lifetime. The fluorescence lifetime of typical organic fluorescent dyes is only a few nanoseconds (ns), which is equivalent to the autofluorescence decay time of many samples. The fluorescence lifetime of quantum dots can last up to tens of nanoseconds (20ns-50ns). ), after a few nanoseconds of light excitation, most of the autofluorescence background has decayed, but the quantum dot fluorescence still exists, at this time, the fluorescence signal without background interference can be obtained.

Quantum dot immunochromatography technology uses quantum dot fluorescent probes as markers, which not only fully embodies the advantages of simplicity, speed and specificity of immunochromatography, but also demonstrates the high sensitivity of quantum dots and its fluorescence characteristics , Showing great development potential and broad application prospects. At present, the new POCT platform of Xiamen Bosheng Company adopts this quantum dot immunochromatography technology. The immunofluorescence on this platform has the characteristics of high sensitivity, high stability, and comparable to chemiluminescence.

As its application becomes more and more extensive, the quantum dot immunochromatography technology is also continuously developed and improved. At present, the following improvements have been achieved:

The preparation of quantum dot fluorescent probes is optimized to obtain QDs with high fluorescence intensity. The detection signal will be greatly increased with the fluorescence enhancement of QDs, which can greatly improve the detection sensitivity and is beneficial to signal detection.

Realize quantitative detection. At present, the fluorescence immunoassay platform is equipped with quantitative detection equipment, which can quantitatively detect the concentration of the analyte, breaking the limitation that the traditional colloidal gold immunochromatography technology cannot quantify. The application of quantum dot immunochromatography technology can greatly improve the quantitative detection. Accuracy and stability.

Multicolor detection of quantum dots. One of the advantages of QDs is that they have precisely adjustable emission wavelengths. Different emission fluorescent QDs can be obtained by adjusting the particle size without changing the composition and surface properties of the particles, so that quantum dots can be used for multi-color labeling of multiple components. To achieve simultaneous detection of multiple components, this will show greater advantages than the multiple detection of traditional colloidal gold immunochromatographic technology, reduce cross-reactions between different antibodies, have stronger specificity, and will not interfere with each other.

With the rapid development of POCT today, users have higher and higher requirements for detection accuracy, sensitivity, and stability. Fluorescence immunochromatography technology not only meets rapid detection and easy operation, but also needs to further improve user requirements for performance. . With the continuous development of quantum dot immunochromatography technology, the performance distance between fluorescence immunoassay and chemiluminescence will be further reduced, and the competitiveness of this technology platform will continue to be improved in the POCT market.

Rapid immunochromatography technology suitable for detection in the grassroots community is receiving more and more attention. It is foreseeable that the emergence of quantum dot immunochromatography technology will further enhance the level of primary medical examination in my country and promote the healthy development of medical undertakings.

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