Simultaneous Fluorescence and Raman Scattering from Single Carbon Nanotubes

Abstract

Single-molecule fluorescence spectroscopy was used to determine the electronic properties of individual single-walled carbon nanotubes. Carbon nanotube structure was determined simultaneously from Raman spectroscopy. Fluorescence spectra from individual nanotubes with identical structures have different emission energies and linewidths that likely arise from defects or the local environment. Unlike most other molecules studied to date, the fluorescence intensity or spectrum from a single nanotube unexpectedly did not fluctuate.

Photophysics of Individual Single-Walled Carbon Nanotubes

“…170 Ensemble studies benefit significantly from the clarification of fundamental photophysical behavior that is exposed on the single particle level, which has catalyzed single molecule studies for many fluorescent systems including dyes, 171-174 polymer chains, 175,176 proteins, [177][178][179] semiconductor quantum dots, 170,180,181 and single-walled carbon nanotubes. 72,77,182 The observation of fluorescence from individual SWNTs was first reported in 2003 and, importantly, confirmed spectral assignments of (n,m) made on the ensemble level. 72 Importantly, single molecule spectroscopy intrinsically avoids the need for difficult separation techniques by enabling the examination of one molecule at a time, which is particularly useful for studying non-uniform SWNT samples.…”

“…71 SWNTs fluoresce in the near-infrared (NIR) region of the electromagnetic spectrum and exhibit narrow line widths. [72][73][74] The particular wavelength of fluorescence emission varies for each nanotube structure, and so the desired emission energy can be selected by simply tuning the nanotube diameter and chirality. Most known fluorophores suffer from photoinduced bleaching and fluorescence intermittency on the single particle level (i.e., blinking), but strikingly, emission from nanotubes remains steady and uninterrupted over hours of continuous excitation at room temperature.…”

“…Most known fluorophores suffer from photoinduced bleaching and fluorescence intermittency on the single particle level (i.e., blinking), but strikingly, emission from nanotubes remains steady and uninterrupted over hours of continuous excitation at room temperature. 72,75,76 Still, the luminescence efficiency, or fluorescence quantum yield (QY), for ensembles of SWNTs is extremely poor, typically <0.1%. 77 Due to their unique optical properties, SWNTs may satisfy a long-standing need for superior fluorophores required for in vivo single biomolecule imaging and single particle tracking (Figure 1 -5).…”

“…87,96 Single molecule studies directly confirmed spectral assignments. 72 The fluorescence quantum yield provides a measure of the luminescence efficiency for a fluorescent molecule. Importantly, the fluorescence quantum yield offers insight into the rates of radiative and nonradiative relaxation processes (k r and k nr , respectively), which are related to the lifetime () of a molecule in an excited state.…”

Visualizing the Local Optical Response of Semiconducting Carbon Nanotubes to DNA-Wrapping

“…[10][11][12][13][14] As a result, the emission energy of nanotubes is modulated by the dielectric constant, which can be expected to be nonuniform along nanotubes, leading to nonuniform emission energies in single nanotube measurements. 8,15,16 The use of DNA for hybridization of carbon nanotube sidewalls has facilitated sorting nanotubes and building chemical sensors. 9,[17][18][19] Single-strand DNA-wrapping introduces DNA segments with finite length, while the details of the secondary DNA structure will be determined by a complex interplay between π-π stacking interactions between DNA bases and nanotube surface as well as electrostatic interactions of the phosphate backbone.…”