Close-conjugation of quantum dots and gold nanoparticles to sidewall functionalized single-walled carbon nanotube templates

Two types of nanoscale hybrid materials have been synthesized by conjugating CdSe-ZnS quantum dots (QDs) and gold nanoparticles (NPs) to sidewall functionalized single-walled carbon nanotube (SWNT) templates, and examined photoluminescence (PL) properties of the hybrid materials. The two types of hybrid nanoscale materials are SWNT-QD and SWNT-gold-NP conjugates. Excessive sidewall functionalization of SWNT into nitro- and amino-derivatives provided weak PL and water solubility to the SWNT derivatives. Solubility of SWNT derivatives in aqueous media was helpful for efficient conjugation of SWNTs to QDs and gold-NPs. The SWNT-QD and SWNT-gold-NP conjugates were characterized using atomic force microscopy (AFM) imaging. From AFM imaging we identified that the sidewall functionalized SWNTs assisted the formation of one-dimensional close-conjugates of QDs and gold-NPs. Although the nitro- and amino-derivatives of SWNT showed weak PL, conjugation of gold-NPs to the amino-derivative quenched the PL quantitatively. On the other hand, conjugation of luminescent QDs to SWNTs resulted in a partial (similar to 35%) quenching of PL from QDs. We attributed the quenching of PL from SWNTs by gold-NPs to non-radiative energy transfer between SWNTs and gold-NPs or vice versa, and the quenching of PL from QDs is due to non-radiative energy transfer from QDs to SWNTs. In the current work, we demonstrated a simple method of close-packing of QDs and gold-NPs using functionalized SWNT templates. Also, we identified that PL properties of SWNTs and QDs are affected in the close-packed structures. SWNT and NP based hybrid materials show great promise as building blocks for nanoscale devices. In this regard the preparation and understanding of the properties of SWNT-QD and SWNT-gold-NP conjugates would be useful during the design of various hybrid nanoscale materials for device applications. (c) 2006 Elsevier B.V. All rights reserved.