Carbon and Silicon Fluorescent Nanomaterials

Abstract

The most known fluorescence nanoparticles are the semiconductor nanocrystals usually called quantum dots (QD) (Smith & Nie, 2010). These nanoparticles, with typical sizes between 1 to 12 nm, are being used in many advanced technological applications, for example in bioimaging (Gerion et al., 2001; Murcia et al., 2008; Williams et al., 2009). However, some of the materials that compose the QD are rare in the earth crust and highly toxic (Lovric et al., 2005). Recently, the elements carbon and silicon, which are among the most abundant elements in the earth crust and are intrinsically non-toxic, become quite important elements in nanochemistry because they originate fluorescent nanostructures with relatively high quantum yield. Bulk carbon and silicon materials are not fluorescent but the corresponding nanomaterials are strongly fluorescent, allow emission colour tuning and are non-blinking nanoparticles with high scientific and technological potential. Carbon nanomaterials are already well known, like for example the fullerenes, carbon nanotubes (CNT), either single-wall (SWNT) or multiple-wall (MWNT), carbon nanofibers and graphene (Liu et al., 2010). Highly fluorescent carbon nanomaterials, here called carbon dots (CD), were only accidently discovered in 2004 during the electrophoretic purification of SWNT derived from arc-discharge soot (Xu et al., 2004). However, in the years 2000 and 2007, studies observed strongly fluorescence shortened MWNT and shortened SWNT (Luo et al., 2007; Riggs et al., 2000). Indeed, CD are carbon based nanomaterials that possesses similar size and surface functionality they constitute different families of nanomaterials and are constituted mainly by carbon with sp2 hybridization characteristic of monocristaline graphite with relatively high oxygen contents (Baker & Baker, 2010; Esteves da Silva & Goncalves, 2011; Fan & Chu, 2010; Xu et al., 2004). CD are different from nanodiamonds because these last nanoparticles are constituted by about 98% carbon with a sp3 hybridization with small amounts of graphitic carbon on the surface that are synthesized from milling microdiamonds, chemical vapour deposition, shockwave or detonation processes (Baker & Baker, 2010). New simplified synthetic pathways are being proposed and the number of potential technological applications of CDs is increasing in the last years (Baker & Baker, 2010; Esteves da Silva & Goncalves, 2011; Fan & Chu, 2010). Another class of potentially non-toxic and biocompatible fluorescent nanoparticles are those of silicon (silicon dots SD). One fluorescent silicon nanoparticle (silicon porous