Propionic-Acid-Terminated Silicon Nanoparticles:  Synthesis and Optical Characterization

Abstract

Photoinitiated hydrosilylation was used to attach acrylic acid to the surface of photoluminescent silicon nanoparticles, thereby producing water-dispersible, propionic-acid-terminated particles. From transmission electron microscope (TEM) observations, the average diameters of the synthesized nanocrystals were 1.9-2.4 nm. It is likely that smaller particles (<1.5 nm) were also present but could not be imaged. As the nanocrystal size decreased, both the optical absorption edge and photoluminescence (PL) emission peak blue-shifted, whereas the photoluminescence excitation (PLE) spectrum changed very little and showed a sharp onset indicative of direct interband absorption at Γ. After prolonged ultrasonication in water, the Si nanoparticles showed strong blue PL. This can tentatively be attributed to the formation of radiative centers related to incomplete oxidation of the nanocrystals. The silicon nanocrystals could be transferred into water or methanol by dialysis without inducing this oxidation. The PA-terminated Si nanoparticles were stably dispersed in acrylic acid, water, and methanol and showed essentially the same optical properties in all three solvents. The approach used here provides a general means of producing water-dispersible silicon nanocrystals with size-dependent photoluminescence tunable over a wide range of the visible spectrum.

Soft X‐ray induced oxidation on acrylic acid grafted luminescent silicon quantum dots in ultrahigh vacuum

“…The third at 102.21 eV (III) is a sub-oxide state and the fourth at 103.24 eV (IV) from SiO 2 at surface of Si-QDs, respectively [42,43]. The existence of a Si-C component here infers that the silicon atoms at the nanoparticle surfaces have changed from H-to a PA-termination and provides compelling evidence of the successful synthesis of acrylic acid grafted luminescent water dispersible Si-QDs [16]. A broadened peak at 103.24 eV (IV) was observed, confirming the sample surface has been oxidized under the soft X-ray irradiation.…”

“…Thus they are of limited use in a wide range of biological applications. Several groups have attempted to make the QDs water soluble by various routes [14][15][16][17][18]. Warner et al [19] produced allylamine-capped Si-QDs using a Pt catalyst.…”

“…These photo stable propionic acid (PA) terminated Si-QDs were alleged to have great potential in biological imaging. In a subsequent contribution by Sato and Swihart [16], water-dispersible PA-terminated Si-QDs were prepared by photoinitiated hydrosilylation. This work demonstrated that the Si-QDs size and corresponding PL emission colour could be controlled by varying the etching time and allowed a high density of carboxylic acid moieties to be used to covalently immobilize molecules containing amines groups, such as proteins [20,21].…”

“…A simplified synthesis method has been used to prepare samples of water-dispersible luminescent Si-QDs in this work. The acrylic acid grafted method has been adopted [15,16], but [22]. Figure 1a shows the schematic structure of the Si-QD product.…”

Quantum Dots-Based Biological Fluorescent Probes for In Vitro and In Vivo Imaging

“…As a comparison, the photoluminescence from rhodamine 6G dropped by 60% under the same illumination conditions. Sato and Swihart utilized photoinitiated hydrosilylation to successfully attach propionic acid (PA) to the surface of SiQDs, thereby producing water-dispersible, PA-terminated SiQDs with average diameter of less than 2.4 nm [58]. Compared to the former two reports showing water-dispersed SiQDs of a single emission color (red or blue), this work is significant because the size and corresponding PL emission color of SiQDs could be controlled by varying conditions.…”