C-DOTS: SYNTHESIS, CHARACTERIZATION AND PROSPECTS

CAIRES. Anderson, J1, C. R. Chaves1, B. B. A. Costa1, M. G. Silva1, L. S. Jardim1, S. M. Carvalho2, L. T. L. Vasconcelos3, A. Cury1, A. M. de Paula1, L. O. Ladeira1

1 Department of Physics,2 Department of Metallurgical and Materials Engineering,

Federal University of Minas Gerais, Belo Horizonte-MG, Brazil3INMETRO - National Institute of Metrology, Quality and Technology

e-mail: caires@fisica.ufmg.br

Introduction

Carbon nanoparticles (CNPs) are a new class of carbon-based fluorescent nanomaterials with sizes below 10 nm that were first obtained during the purification of single-walled carbon [1]. Analogous to their well-known cousins, fullerenes and carbon nanotubes, carbon nanoparticles exhibit interesting optical and electronic properties that may be exploited for diverse applications such as optoelectronics, chemical sensing and biological labeling [2,3]. CNPs have drawn increasing attention due to their high photostability, tunable excitation and emission wavelength, excellent biocompatibility and environmental friendliness. The applications of fluorescent biomaterials have been the focus of intense research in many biological areas, such as in cellular imaging and biosensing [4,5]. In this work, we report a method to synthesize fluorescent CNPs by hydrothermal carbonization of chitosan. The synthesis process occurs in aqueous solution and has the advantage of being very cheap and biocompatible

Experimental Procedure

In this work, we report a one-step synthesis method to obtain highly amino functionalized fluorescent CNPs by hydrothermal carbonization of chitosan at a mild temperature (200o). The carbonization and functionalization occur through the dehydration of the chitosan, which leads to the formation of the fluorescent carbon nanoparticles. A characteristic feature of this method is that neither a strong acid solvent nor a surface passivation reagent is needed. The synthetic process occurs in aqueous solution and has the advantage of being very cheap. C-Dots were characterized by transmission electron microscopy of TEM / STEM and EELS. The fluorescent emission was characterized by confocal microscopy.

Results and Discussion

High-resolution transmission electron microscopy (HRTEM) images revealed that theCNPs were monodisperse nanoparticles and had a narrow size distribution of 3-5 nm in diameter. The optical properties of the CNPs showed a strong UV-vis absorption feature centered at 280 nm. The inset photograph of the CNPs solution is yellowish, transparent and clear under daylight and exhibited strong blue luminescence under UV excitation (Figure 1a). The photoluminescence spectra of the carbon dots are generally broad and dependent on the excitation wavelengths. For 410 nm excitation, we observed a maximum photoluminescence about 510 nm and for 375 nm excitation, the observed quantum yields were from about 2.5-7.0%.

(a) (b)

(d)

Figure 1: Photograph of the solution of carbon nanoparticles at daylight and its fluorescence under UV excitation (a), the absorption and photoluminescence emission spectra of CNPs (excitation at 410 nm) and EELS (c) Transmission electron microscopy (TEM).

Conclusions

The yield of the fluorescent CNPs is about 7.0% and the sample is readily soluble in water to form a stable aqueous solution. Our preparation method presents a simple approach to produce highly amino-functionalized fluorescent CNPs on a large scale. The functional groups on its surface improve its water solubility and reduce its potential biotoxicity, which is essential for biologically motivated work.

Acknowledgments

This work was supported by CNPq, Fapemig, Capes and INCT of CarbonNanomaterials.

References

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