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Quantum dot technology has been widely used in our daily life, including energy, solar cells, displays, biomedical and biological applications. Especially in the field of biomedicine, the application of quantum dot technology in fluorescence labeling has greatly improved the imaging quality of cells and in vivo.
Highly sensitive analysis and detection of important biomolecules such as proteins, nucleic acids, and peptides in vivo and in the process of life is an important problem in the field of life science research. Exploring and developing high-sensitivity analysis and detection methods has always been the direction of researchers in this field. Fluorescence analysis is one of the most important methods in biological research, and its detection sensitivity largely depends on the luminescence intensity and photochemical stability of the label. The currently used organic fluorescent dyes have insurmountable fluorescent performance defects: narrow excitation spectrum, wide emission spectrum and tailing, easy photo-bleaching, and their own toxicity, which greatly limits their application in life sciences.
The attention and research on semiconductor fluorescent nanomaterials quantum dots (Quantum dots, QDs) have begun in the late 1970s. As a typical representative of inorganic fluorescent materials, QDs belong to artificially prepared nano-semiconductor materials. The particle size ranges from 1-20 nm and can have different fluorescent colors according to their size. Common types include type II-VI (CdTe, CdSe, CdS), type II-V (InP, InAs), type I-III-VI2 (CuInS2, AgInS2), and type IV-VI (PbSe). These quantum dots play a very important role in various medical applications such as bioimaging, biosensor, and drug delivery.
Biomedical applications of quantum dots
In 1998, Alivisatos and Nie innovatively solved the problem of biocompatibility after quantum dot labeling and realized the combination of biological macromolecules and quantum dots. Then quantum dots began to be widely used in a variety of biotechnologies including DNA detection, immunofluorescence, and cell biology.
- In vivo applications
Nie et al. found that using CdSe quantum dots modified with thioglycolic acid and chemically cross-linked with transferrin, transferrin can enter the cell interior and track the donor-acceptor reaction. Nafiujjaman’s research shows that the diameter of the new Cl-GQDs-N quantum dots is about 30nm. In vitro experiments have shown that QDs have no toxic effects on both cancer cells and normal cells, and have promising applications in cell imaging.
- Bioimaging
NIR light has small background interference and large penetration depth, making NIR quantum dots incomparable advantages in the imaging of living animals. Akerman et al. confirmed that after intravenous injection of biomarker labeled quantum dots in mice, quantum dots can specifically target the specific tissues of mice and be successfully imaged.
- In vitro diagnostics
Quantum dots are used in in vitro diagnostics and are mainly used as fluorescent probes to directly or indirectly detect biomolecules. Azmi et al. reported a new type of fluorescent biosensor in a 96-well microplate format, encapsulated with CdS quantum dots (QDs)-uricase/horseradish peroxidase (HRP) enzyme. The use of quantum dots as a fluorescent indicator reveals the fluorescent signal of the uricase/HRP enzymatic reaction system in the presence of uric acid. The sensor has been successfully applied to the detection of uric acid in human urine, and the result is comparable to the assay kit.
As a new generation of fluorescent nano-markers, quantum dots are a field with extremely broad development prospects in the application of life sciences. With the continuous improvement of quantum dot synthesis and modification technology, the regulation of the size, structure, performance, and dispersion of quantum dots will gradually be realized, and it is expected to be applied to mass screening in the field of proteomics and genomics. The unique fluorescence properties of quantum dots make it possible to study a series of life activities in the dynamic process of living cells.
References:
Bruchez, M., Moronne, M., Gin, P., Weiss, S., & Alivisatos, A. P. (1998). Semiconductor nanocrystals as fluorescent biological labels. Science, 281(5385), 2013-2016.
Chan, W. C., & Nie, S. (1998). Quantum dot bioconjugates for ultrasensitive nonisotopic detection. Science, 281(5385), 2016-2018.
Nafiujjaman, M., Joon, H., Kwak, K. S., & Lee, Y. K. (2018). Synthesis of nitrogen-and chlorine-doped graphene quantum dots for cancer cell imaging. Journal of nanoscience and nanotechnology, 18(6), 3793-3799.
Åkerman, M. E., Chan, W. C., Laakkonen, P., Bhatia, S. N., & Ruoslahti, E. (2002). Nanocrystal targeting in vivo. Proceedings of the National Academy of Sciences, 99(20), 12617-12621.
Azmi, N. E., Rashid, A. H. A., Abdullah, J., Yusof, N. A., & Sidek, H. (2018). Fluorescence biosensor based on encapsulated quantum dots/enzymes/sol-gel for non-invasive detection of uric acid. Journal of luminescence, 202, 309-315.