Alkyl-capped silicon quantum dots (alkyl-SiQDs) are chemically-robust, brightly-luminescent nanocrystals with unusual photophysics and spectroscopy. These properties give rise to a number of potential applications for labelling. In particular, we can obtain simultaneous Raman and luminescence spectra and thereby encode more information in these particles than in a mixture of simple fluorophores.[1]

Alkyl-SiQDs can be deposited on surfaces in two ways: (i) by casting/printing from solutions in organic solvents or aqueous dispersions and (ii) by deposition from the vapor phase. Although alkyl-SiQDs are too hydrophobic to dissolve in water, metastable aqueous dispersions can be prepared in the presence of as little as 0.01% organic solvent. The particles are also so thermally stable that they can be evaporated intact at relatively low temperatures (ca. 200 oC) in vacuum.[2]

Fairly sophisticated synthesis can be carried out on the alkyl-SiQDs to produce chemically-modified particles: we have prepared alkyl-SiQD:DNA conjugates by automated solid phase oligosynthesis. Spectroscopic studies of these particles show that they retain bright orange-red luminescence which allows convenient detection/location, but that a Raman spectral fingerprint of the conjugate can also be acquired at the same time if necessary.

[1]. Patent, Newcastle University, GB2433589.

[2]. Y. Chao, L. Siller, S. Krishnamurthy, P. R. Coxon, U. Bangert, M. Gass, L. Kjeldgaard, S. N. Patole, L. H. Lie, N. O’Farrell, T. A. Alsop, A. Houlton and B. R. Horrocks ’Evaporation and deposition of alkyl-capped silicon nanocrystals in ultrahigh vacuum’ Nature Nanotech.2007, 2, 486.