CIOMP has recently demonstrated a new approach to impart carbon dots with the added near-infrared (NIR) absorption band

Prof. Songnan Qu’s group at CIOMP, China has recently demonstrated a new approach to impart carbon dots (CDs) with the added near-infrared (NIR) absorption band. Under the excitation of 732 nm laser, the CDs display an efficient NIR emission (maxima of about 760 nm) with a high quantum yield of 10%.

 

Taking the advantages of NIR-excitation and –emission properties, the CDs have been applied in the in vivo fluorescence imaging. Moreover, the NIR emission of CDs can be obtained under the excitation of not only NIR-I window laser (732 nm), but also NIR-II window laser (1400 nm) through two-photon and even three-photon excitation process. Thus, this work should significantly advance the study of carbon based nanomaterials in the viewpoint of basic knowledge of structure-property relationship as well as the potential bioimaging application.

 

These results are published in the journal Advanced Materials (DOI: 10.1002/adma.201705913) and highlighted as the inside back cover. The first author Di Li and the corresponding author Songnan Qu are the members of Youth Innovation Promotion Association of Chinese Academy of Sciences. This work is supported by the Program of the Young Scientific and Technological Innovation Leader and Team in Jilin Province, and the Jilin Province Science and Technology Research projects, et al.

 

Fluorescent CDs have significant potential for use in biomedicine, owing to their non-toxic and good biocompatibility. Because the low levels of photon scattering, light absorption, and autofluorescence of biological tissues occur in the NIR region (700?1700 nm), in vivo fluorescence imaging is preferred to perform in the NIR window to promote the large tissue-penetration depths and thus their potential clinical applications. To date, strong absorption and photoluminescence of CDs have mostly been demonstrated in the ultraviolet-visible regions. The realization of strong absorption and efficient emission for CDs at NIR wavelengths remains difficult. This seriously limits the application of carbon nanodots in fluorescence bioimaging, especially in vivo NIR fluorescence imaging.

 

Since 2012, Prof. Qu’s team has carried out investigations on the bandgap modulation and applications of CDs. The team’s achievements include the development of a new type of water-soluble green emissive CDs (Angew. Chem. Int. Ed., 2012, 51, 12215, IF:13.45, ESI hot paper), the realization of optical pumped green lasers from CDs (Adv. Funct. Mater., 2014, 24, 18, IF:10.3), the development of water-jet printing based on CDs (Adv. Mater., 2015, 27, 1389, IF:19.7), the achievement of strong orange emissive carbon nanodots with a highest fluorescent quantum yield then (Adv. Mater., 2016, 28, 3516, IF:19.7,ESI hot paper), and the construction of supra-CDs with high photothermal conversion efficiency (Light: Sci. Appl., 2016, 5, e16120, IF:14.6). Two of these papers are selected as ESI (Essential Science Indicator) highly cited papers, which enter the list of the best one-thousandth papers. In order to solve the problem of inefficient excitation and emission of CDs in the NIR region, Qu’s group has developed a surface engineering approach exploiting electron-acceptor groups on red emissive CDs.

 

These groups are attached to the outer layers and the edges of the CDs, thereby resulting in the disruption of the ordered layer structure and the nonconjugation of the outer layers and inner layers, and inducing the occurrence of bandgap in the NIR region. Efficient NIR emission for CDs excited in an NIR window is realized with photoluminescence quantum yield up to 10%, which is the highest record for the reported NIR emissive CDs.

 

The surface-modified CDs are successfully applied for in vivo NIR fluorescence imaging of the stomach of a living mouse after gavage and around the body after tail intravenous injection (Figure 1-2). Meanwhile, multiphoton excitation in an NIR-II window can induce red/NIR fluorescence of CDs. Two photon-induced NIR emission and three-photon-induced red emission are first-ever simultaneously observed for CDs under excitation of 1400 nm fs-laser (Figure 3).

 

This work provides a rational design approach for modulating the optical properties of CDs in the long wavelength regions and developing CD-based NIR imaging agents. 

Article link: http://onlinelibrary.wiley.com/doi/10.1002/adma.201705913/full

 


Figure 1. Schematic of structure and energy level alignments of non-treated CDs (left column) and CDs modified with S=O/C=O-rich molecules (right column)(Photo by CIOMP).

 

Figure 2. a) Absorption and PL spectra of CD/PVP film. b) Photograph of characters “CIOMP” written by using CD/PVP ink in daylight (upper) and a fluorescence image through an 800-nm longpass optical filter under excitation of a 732-nm laser (lower). In vivo NIR fluorescence images of a mouse after c) gavage injection and d) tail intravenous injection of CDs in PVP aqueous solution (Ex: 671 nm, Em: 750-nm longpass optical filter) (Photo by CIOMP)

 

Figure 3. Fluorescence spectra obtained for multi-photon excitation associated with incident intensities at a) 1200-nm excitation (inset: photograph showing excitation at 1200 nm and 22 mW) and c) 1400-nm excitation (inset: photograph showing excitation at 1400 nm and 46 mW). Power dependence of emission (shown on logarithmic scales) at b) 1200-nm excitation and d) 1400-nm excitation.(Phtoto by CIOMP)

 

 

Contact:

Prof. Songnan Qu, Changchun Institute of Optics, Fine Mechanics and Physics

Email: qusn@ciomp.ac.cn

 

 

 

 

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