Cyanine dyes are a class of dyes that can increase the sensitivity of photosensitive materials and are often referred to as spectral sensitizers or sensitizing dyes. The addition of cyanine dye to silver bromide emulsion can make the emulsion produce new photosensitivity in the spectral region absorbed by the dye, so it is widely used in the photosensitive material industry such as black and white film, color film and infrared film. In addition, the spectrum of anthocyanin dyes is very sensitive to the changes of external microenvironment, so it is also very suitable for the analysis and study of biological and environmental samples. Squarylium dye is a kind of cyanine dye, which has excellent photoelectrochemical performance and stability. Squarylium dyes are generally divided into two categories: symmetrical and asymmetrical. As a near-infrared dye, squarine dye is widely used in optical information storage, laser printing, bioanalysis, organic solar cells and other fields. In addition, because the oxygen atom and terminal nitrogen atom in the central quaternary ring become the potential sites for the complexation reaction between squaricine and metal, squaricine can also be widely used in ion recognition and detection.
Figure 1. The structural formula of symmetrical squarylium dye.
- Molecular sensing: During the biological reaction, many active small molecule metabolites with unique chemical properties will be produced. The markers of these small molecules can infer whether life activities are proceeding normally. The fluorescence properties of various cyanine dyes with small-molecule recognition groups will change dramatically after being combined with small molecules, thus enabling the detection of small molecules. For example, Sulfo-Cyanine7-based near-infrared fluorescence enhancement strategy can be used for the detection of specific analytes. The detection mechanism is mainly to deprotect the quinone protecting group in Sulfo-Cyanine7 through a specific analyte to realize the formation of quinone and promote the enhancement of fluorescence. The probe can be used to label the endogenous H2O2 produced in the inflammatory response induced by LPS in the abdominal cavity of mice.
Figure 2. The structural formula of Sulfo-Cyanine7.
- Cell markers: Precise labeling of subcellular organelles (such as cell membranes, nuclei, mitochondria, and lysosomes) helps to understand life processes and cell states from a microscopic perspective. Cyanine-based Subcellular labeling probes have also been extensively studied. Some researchers have reported a bifunctional cyanine dye that can simultaneously label the cell membrane and nucleus. It can label both the cell membrane of living cells and the nucleus of apoptotic cells to achieve the specific labeling of different cell structures by the same dye. Therefore, this bifunctional cyanine dye is an important new multifunctional dye, which can be used in the research of life medicine and other fields to mark and identify some apoptotic cells in living tissue. This dye also has good application prospects in distinguishing live cells from dead cells.
- In vivo imaging: Near-infrared light has strong tissue penetration ability, so near-infrared dye imaging has been widely used in the field of in vivo diagnosis. The absorption and emission of cyanine dyes (Cyanine 5.5 and Cyanine 7.5) can reach the near-infrared region, so they can be used for in vivo fluorescence imaging and photoacoustic imaging.
Figure 3. Cyanine 5.5 and Cyanine 7.5 for fluorescence imaging.
- Li J, Guo K, Shen J, et al. (2014) "A difunctional squarylium indocyanine dye distinguishes dead cells through diverse staining of the cell nuclei/membranes." Small. 10(7):1351-1360.
- Zhu H, Fan J, Du J, et al. (2016) "Fluorescent probes for sensing and imaging within specific cellular organelles." A. Chem. Res. 49(10):2115-2126.