Visual analysis of biomolecules is an integral avenue of basic and applied biological research. Quantum dots (QDs) are emerging as alternative tools to the organic fluorescent dyes currently used in bioimaging. Although these QDs have great potential as probes for bioimaging, certain limitations may restrict their applications. Cytotoxicity strongly influencing is one of the major limiting factors for the application of II-VI QDs in efficient in vivo imaging. We propose silicon carbide (SiC) QDs for bioimaging in order to eliminate numerous disadvantages of traditional QDs. Biocompatibility of bulk SiC and SiC QDs have been proven by several research teams [1]. SiC is also promising material for quantum information processing as a source of single photon emitter [2]. We developed a two-step experimental routine based on SHS synthesis and whet chemical etching for producing luminescent SiC QDs with high quantum yield [3]. While the synthetized SiC nanpowder with size of about 100 nm was bright single photon source [3], SiC QDs with size of 3 nm in diameter made from this powder have high quantum yield and make stable colloid sol in polar solvents without the need of any surfactant or capping layer thanks to the surface termination [4]. The optical properties of SiC QDs are highly influenced by the chemical surface groups according to our ab initio calculations [6]. We successfully developed synthesis methods for different surface terminated SiC-QDs. Carboxyl terminated SiC QDs were synthetized by changing the properties of the SiC precursors, thus no further chemicals or physical processes were needed to increase the concentration of carboxyl groups [7]. We found a clear experimental evidence for the role of carboxyl groups in the luminescence of SiC-QDs that confirm our calculations. Temperature dependent infrared spectroscopy showed anhydride formation from neighboring carboxyl groups on SiC QDs which represents a new possibility of selective engineering of new hybrid materials involving SiC-QDs using the reactivity of anhydrides.

References:

[1] D. Beke, Z. Szekrényes, D. Pálfi, G. Róna, I. Balogh, P. A. Maák, G. Katona, Z. Czigány, K. Kamarás, B. Rózsa, L. Buday, B. Vértessy, and A. Gali, J. Mater. Res., 28(02), 205, (2012).

[2] S. Castelletto, B. C. Johnson, V. Ivády, N. Stavrias, T. Umeda, A. Gali, and T. Ohshima, Nat. Mater., 13(2), 151, (2014).

[3] S. Castelletto, Br. C. Johnson, C. Zachreson, D. Beke, I. Balogh, T. Ohshima, I. Aharonovich, and A Gali, submitted

[4] D. Beke, Z. Szekrényes, I. Balogh, Z. Czigány, K. Kamarás, and A. Gali, J. Mater. Res. 28(01), 44, (2013).

[5] D. Beke, Z. Szekre?nyes, I. Balogh, M. Veres, E. Fazakas, L. K. Varga, K. Kamara?s, Z. Cziga?ny, and A. Gali, Appl. Phys. Lett., 99(21), 213108 (2011).

[6] M. Vörös, P. Deák, T. Frauenheim, and A. Gali, J. Chem. Phys., 133(6), 064705, (2010).

[7] Zs. Szekrényes, B. Somogyi, D. Beke Gy. Károlyházy, I. Balogh, K. Kamarás, A. Gali, submitted

David Beke

Wigner Research Centre for Physics, Budapest University of Technology and Economics, University of P

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