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

Abstract

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 (∼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.