Detection of luminescent single ultrasmall silicon nanoparticles using fluctuation correlation spectroscopy

Abstract

We dispersed electrochemical etched Si into a colloid of ultrasmall blue luminescent nanoparticles, observable with the naked eye, in room light. We use two-photon near-infrared femtosecond excitation at 780 nm to record the fluctuating time series of the luminescence, and determine the number density, brightness, and size of diffusing fluorescent particles. The luminescence efficiency of particles is high enough such that we are able to detect a single particle, in a focal volume, of 1 pcm3. The measurements yield a particle size of 1 nm, consistent with direct imaging by transmission electron microscopy. They also yield an excitation efficiency under two-photon excitation two to threefold larger than that of fluorescein. Detection of single particles paves the way for their use as labels in biosensing applications.

Second harmonic generation in microcrystallite films of ultrasmall Si nanoparticles

“…The substrates were ͑100͒ oriented, 1-10 ⍀ cm resistivity, p-type boron doped silicon, laterally anodized in hydrogen peroxide and HF acid 5,6,9 while advancing the wafer in the etchant at a reduced speed of ϳ1 mm per hour. Subsequent immersion in an ultrasound acetone or water bath crumbles the top film into ultrasmall particles.…”

“…Silicon was dispersed into a suspension nanoparticle colloid of ϳ1 nm across. 5,6 The particles were then reconstituted to create large, thick, uniform, and under control layers of microcrystallites on device quality Si substrates. The film is excited by near-infrared femtosecond two photon process at 750-830 nm.…”

Global analysis of fluorescence fluctuation data

“…FCS measurements of molecules in solution include the observation of translational diffusion , rotational diffusion (Ehrenberg and Rigler 1974;Pecora 1975, 1976), intersystem crossing (Widengren et al 1995), chemical reactions (LaClair 1997, conformational dynamics of DNA hairpins (Bonnet et al 1998), photobleaching (Eggeling et al 2001), flavins and flavoproteins ; Van den Berg et al 2001), viscosity and photodynamics of red fluorescent proteins (Schenk et al 2004). FCS has also proved to be a suitable technique to detect nanoparticles and flowing particles (Akcakir et al 2000;Kunst et al 2002) and to study membrane-mimetic systems (Bastiaens et al 1994;Hink and Visser 1998;Hink et al 1999;Korlach et al 1999;Schwille et al 1999a;Fradin et al 2003). In addition, special studies have been addressed to investigate the flickering dynamics of variants of green fluorescent protein (GFP) (Haupts et al 1998;Schwille et al 2000;Heikal et al 2000), the hybridisation of DNA and RNA sequences (Walter et al 1996;Oehlenschla¨ger et al 1996), ligand-receptor interactions (Rauer et al 1996) and the binding of single-chain antibodies to gramnegative bacteria .…”

Biocompatible fluorescent silicon nanocrystals for single-molecule tracking and fluorescence imaging

“…However, despite all the aforementioned developmental efforts, the application of SiNCs to cell-biological and biomedical research has been extremely limited (Choi et al, 2008;Erogbogbo et al, 2008Erogbogbo et al, , 2011a. No serious application has been made for single fluorescent molecule imaging and tracking (Akcakir et al, 2000). This is largely caused by the following three difficulties: (1) in producing SiNCs, (2) in producing particle populations with uniform size and properties in aqueous media (particularly redemitting SiNCs), and (3) in conjugating them to biomolecules at a 1:1 mol ratio.…”

“…Inspired by the work of Yamani et al (1998), Akcakir et al (2000), and Belomoin et al (2002), we developed an easier protocol that specifically generates red-emitting SiNCs (see Materials and methods subsections Preparation of SiNC on the wafer through Recovery and purification of mSiNC; Fig. 1, A-C).…”