The term near-infrared (NIR) dye has been put forward before the 1980s. The emission wavelengths of near-infrared (NIR) dyes range from 700 nm to 1200 nm, and the self-fluorescence of biomolecules within this range is weak, which can avoid background interference and obtain high analytical sensitivity. Therefore, near-infrared (NIR) dyes have attracted wide attention in the biological field. At the same time, the extensive application in various fields has further promoted the in-depth study of near-infrared (NIR) dyes. Due to their promising application prospect, near-infrared (NIR) dyes are widely concerned and studied.
- Bioluminescence imaging: Excessively high or low levels of some substances in organisms will seriously affect health, and the effective detection is of great significance to the evaluation of human health and the diagnosis and treatment of diseases. By extinguishing or enhancing the fluorescence, near-infrared (NIR) probes can detect some important substances in cells or tissues, such as reactive oxygen species, reactive nitrogen, mercaptan, metal ions, enzymes, etc.
Figure 1. Near-infrared (NIR) dye applied in bioluminescence imaging.
- Cancer treatment field: As a promising tumor imaging agent and treatment medium, near-infrared (NIR) dyes are of great significance in tumor detection and treatment. After absorbing a specific wavelength of NIR light, near-infrared (NIR) dyes can transfer to the excited singlet state, and part of the energy will be attenuated to form fluorescence. After administration, the targeted tissue will appear a strong fluorescent signal in the tumor area, which can effectively distinguish the tumor from the normal tissue. Furthermore, near-infrared (NIR) dyes can also improve the tumor signal and reduce the background signal.
Figure 2. Near-infrared (NIR) dye applied in cancer treatment.
- Anti-counterfeiting field: Adding near-infrared (NIR) dyes into ink can obtain near-infrared ink, which is an important anti-counterfeiting material. Printing products containing near-infrared (NIR) dyes are invisible to the naked eye under visible light sources, but in the near infrared light source, with the help of detection instruments or special lens, it can be observed.
- The others: In addition, near-infrared (NIR) dyes have important applications in DNA sequencing, immune analysis, optical storage materials, laser protection and absorption dyes, optical disc recording and other fields.
According to chemical structures, near-infrared (NIR) dyes can be classified into many kinds.
- Phthalocyanine near-infrared (NIR) dyes: Phthalocyanine near-infrared (NIR) dyes have been widely used in industry. For most simple phthalocyanine compounds, their maximum absorption wavelengths are not in the near infrared region, but combining a benzene ring to obtain naphthalene phthalocyanine can make the absorption wavelength redshifted and become a near-infrared (NIR) dye.
Figure 3. The molecular structure of phthalocyanine.
- Cyanine near-infrared (NIR) dyes: The chromophore of cyanine near-infrared (NIR) dyes consists of N heterocycle at both ends and a conjugated multi-methine chain in the middle. According to the form of multi-methine chain, cyanine near-infrared (NIR) dyes can be divided into cyanine dyes, square cyanine dyes and the others. Cyanine near-infrared (NIR) dyes have the advantages of strong molecular modifiability, high extinction coefficient and wide adjustable range of absorption wavelength.
Figure 4. The molecular structure of cyanine near-infrared (NIR) dyes.
- The others: Near-infrared (NIR) dyes also include metal-complex dyes, quinone dyes and azo dyes. Among them, quinone dyes were first synthesized in 1978 and can be classified into naphthoquinone dyes and anthraquinone dyes.
- A unique approach toward near-infrared fluorescent probes for bioimaging with remarkably enhanced contrast[J]. Chemical ence, 2016, 7(3).
- Zhang X , Liang X , Ma X , et al. Highly Stable Near-Infrared Dye Conjugated Cerasomes for Fluorescence Imaging-Guided Synergistic Chemo-Photothermal Therapy of Colorectal Cancer[J]. Biomaterials Science, 2019.