LUMINESCENT CARBON NANODOTS EMERGENT NANOLIGHTS PDF

Synthesis and processing Abstract Carbon dots CDs have a wide range of applications in chemical, physical and biomedical research fields. We are particularly interested in the use of CDs as fluorescence nanomaterials for targeted tumor cell imaging. One of the important aspects of success is to enhance the fluorescence quantum yields QY of CDs as well as increase their targetability to tumor cells. However, most of the reported CDs are limited by relative low QY.

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Synthesis and processing Abstract Carbon dots CDs have a wide range of applications in chemical, physical and biomedical research fields. We are particularly interested in the use of CDs as fluorescence nanomaterials for targeted tumor cell imaging. One of the important aspects of success is to enhance the fluorescence quantum yields QY of CDs as well as increase their targetability to tumor cells. However, most of the reported CDs are limited by relative low QY.

In the current study, for the first time, one-step synthesis of highly luminescent CDs by using folic acid FA as single precursor was obtained in natural water through hydrothermal method. The as-prepared CDs exhibited QY as high as The obtained CDs showed excellent photoluminescent activity, high photostability and favorable biocompatibility.

The FA residuals in CDs led to extraordinary targetability to cancer cells and promoted folate receptor-mediated cellular uptake successfully, which holds a great potential in biological and bioimaging studies. Download PDF Introduction Photoluminescence PL nanomaterials, such as carbon dots CDs , semiconductor quantum dots, upconversion nanoparticles and luminescent metal complexes offering unique chemical and physical characteristics 1 , 2 , 3 , 4 , 5 , 6 , have dramatically changed the paradigm of fluorescence in the past decades.

Among them, CDs have emerged as a novel type of PL nanomaterial 7 , which attracted significant and growing interest in both scientific and technology circles due to their excellent chemical and photo-physical properties. However, efficient methods for the synthesis of CDs with high QY are still remaining as a challenge 12 , 13 , Most reported CDs are limited by relative low QY.

Therefore, extensive efforts have been devoted in the development of high fluorescent CDs. Up to now, chemical doping with heteroatoms is the major renowned pathway to tune the intrinsic properties of CDs. Among them, N-doped CDs, which can be inherited from nitrogen rich precursors such as low cost and environment-friendly amino acids, proteins and other nitrogen-containing natural products 19 , 20 , are more attractive due to their excellent optical properties especially increased fluorescence QY.

Folic acid FA , one of the B vitamins, is an essential dietary component that can effectively decrease the risk of several diseases 21 , 22 , such as neural-tube defects and congenital heart defects.

Particularly, FA has a good targetability to cancer cells 23 , Consisting rich nitrogen and functional groups of —OH, —NH2 and —COOH, FA has a great possibility to be sufficiently condensed, polymerized and carbonized to generate N-doped CDs without addition of any additives or passivation agents.

Herein in this study, FA was chosen as a single precursor to prepare N-doped CDs by hydrothermal-assisted method. Moreover, these CDs showed instinctive targetability to cancer cells without the requirement of any additional surface modifications. Figure 1 Schematic illustration of the synthesis of folic acid FA -derived CDs and their application for folate receptor FR -mediated cancer cell targeting.

As can be seen from the TEM image in Fig. Unlike most other reported CDs, Fig. Excitation-independent FL behavior reflects that the surface state of these CDs are mainly single energy level, and almost all excited electrons return to the ground state via a radiative route 27 , 28 , which can enhance the passivation degree of traps on CDs and consequently increase the fluorescence QY 29 , 30 , PL decay curves of the CDs only exhibit a single-exponential function and the fluorescence decay average is Single lifetime of as-prepared CDs reveals the high ratio of radiative-to-nonradiative transition, which benefit the generation of high QY CDs.

Apparently, the Kr 6. Schematic illustration of the synthesis of folic acid FA -derived CDs and their application for folate receptor FR -mediated cancer cell targeting. As shown in Fig. The rich amino groups on the CDs surface might contribute to the ultra-high QY. The amino-groups on the surface of CDs can enhance the conjugation degree of conjugated systems, which increase the electron transition probability from the ground state to the lowest excited singlet state, and finally contribute to higher QY of the CDs indirectly Moreover, compared with the reported fluorescent materials, the as-prepared CDs showed superior photostability.

These results indicate that these CDs have very good photo- and chemostability. Targeted cancer cell imaging by CDs Due to the ultra-high QY, robust stability, favorable biocompatibility and FA-induced targetability, the as-prepared CDs has a great possibility to be utilized for biological and biomedical applications.

As a proof of concept, the aqueous solution of CDs was used for cancer cell imaging in this study. Hela cells, overexpressing folate receptor FR , were selected as a model. As indicated in Fig. Further increment of incubation time, only a slight brightness enhancing was shown. Correspondingly, A cells blocked with FA exhibits no essential change in fluorescence image Fig. Bright field images are shown in b and e. The overlay images are shown in c and f.

Full size image Possible Origins for Photoluminescence Superiority of CDs To further explore the outstanding optical property of ultra-high QY, the influence of pyrolysis temperature was investigated firstly. Meanwhile, Fig. In other words, the strong absorption around nm means that the hydrothermal reaction was incomplete in strong basic or acid condition. In our current work, with the reaction temperature is near the melting point of FA, the hydrothermal reaction in a closed system has higher efficiency that FA-derived CDs would like to possess an ultrahigh QY without further treatment to assist the solubility of FA.

Obviously, the weak acid circumstance of 5. When the experiment was carried out in natural water, partial activity of —OH was shielded 35 , and the dehydration condensation was mainly between the carboxyl and amino groups of FA.

Therefore, circumstance condition of pH is critical valuable for CDs synthesis and directly impact on the fluorescence intensity of the obtained CDs. Full size image Conclusion To summarize, ultrahigh fluorescent FA-derived CDs were synthesized through a facile one-step and green preparation of hydrothermal approach by importing FA as carbon source, nitrogen source and surface passivation agent.

The as-prepared CDs show excellent PL activity and excitation-independent emission. These nanoparticles offer several distinct advantages: 1 the high fluorescence QY reaches up to Overall, these ultra-bright CDs has a great potential to be widely useful in a number of biological studies and biomedical applications.

Fluorescence measurements were recorded by using an F spectrophotometer Hitachi, Japan. The IS consists of a mm spherical cavity. The experimental procedure is described as follows. After this reaction, a clear light yellow-brown solution was obtained. The solution was centrifuged for 10 min at 10, rpm to remove precipitate. Then, the culture media were discarded.

The cells were incubated for another 4 h and then the supernatant was abandoned. Five parallel samples were tested in each group and three independent experiments were performed under identical conditions. The cell dish was placed in the incubator at a desired time. The cells were washed thrice with 0. Finally, the cells were used for fluorescence imaging. References 1. Zhu, S. Nano Res.

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There are still, however, challenges ahead such as blue-biased photoluminescence, spectral broadness, undefined energy gaps and etc. In this report, we chemically modify the surface of C-dots with a series of para-substituted anilines to control their photoluminescence. Our surface functionalization endows our C-dots with new energy levels, exhibiting long-wavelength up to nm photoluminescence of very narrow spectral widths. The roles of para-substituted anilines and their substituents in developing such energy levels are thoroughly studied by using transient absorption spectroscopy.

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