DEVELOPMENT AND CHARACTERIZATION OF CARBON NANOTUBE BASED RAMAN NANOPROBES BY RAMAN HYPERSPECTRAL IMAGING: MULTIPLEXING AND BIODETECTION
The potential of Photon etc. Raman Imaging Platform, RIMA™, was demonstrated by Pr. R Martel’s group at Université de Montréal in a recent publication in Nature Photonics on the development of Raman nanoprobes .
These new kind of nanoprobes are based on single-wall carbon nanotubes and J-aggregated dyes, such as α−sexithiophene (6T), β-carotene (βcar) and phenazine (Ph). Compared to fluorescent probes, Raman probes have the advantages of being more stable over long periods of times (weeks and years) and they produce a unique signature with narrow peaks that allows easy multiplexing of 3 probes or more using the same excitation laser energy. This nanomaterial shows a very high Raman scattering cross-section, without any photobleaching or fluorescence background, even at high laser intensities.
In this work RIMA™ enabled the imaging and multiplexing of three different probes with sensitivity down to the single object as seen in Figure 1. The different probes were deposited on a SiOx/Si surface and characterized by taking a single hyperspectral image. We were able to determine, without a doubt, the position of each isolated probe (diameters: 1.3 ± 0.2 nm), and even identify the co-localized probes (Fig 1b, Ph and βcar). The sensitivity, efficiency and hyperspectral properties of RIMA™ were essential to the development of these probes.
The carbon nanotube, which serves as a capsule for the probe, can be covalently functionalized to selectively target biomolecules, such as streptavidin. We demonstrated RIMA™’s potential in the detection of probes in a biological context by imaging the βcar probe functionalized with PEG-biotin groups that targeted streptavidin.
A pattern of 10 μm spots of streptavidin was created by microcontact printing and then incubated with the probes. The pattern was maintained hydrated under a cover slip during imaging and the probes were detected where streptavidin was located. Figure 2 shows Raman hyperspectral images at 1520 cm-1 of two printed surfaces, where streptavidin was deposited either inside (main figure) or around the dots (inset). With a single acquisition, a sample area of 133 x 133 μm2 was studied using RIMA™ with laser excitation at 532 nm. Damages to the samples were also limited due to a uniform illumination over the portion of the sample in the field of view. In terms of spectral resolution and large surface area imaged, RIMA™ provided hyperspectral images in a much shorter time then conventional point-by-point mapping Raman imagers.
Raman hyperspectral imaging is a powerful technique to study a wide range of materials, from nanopatterned surfaces to biological systems. Because of its high throughput, RIMA™ allows the acquisition of spectrally resolved maps of large area samples, without damaging the surface.
Text by Nathalie Tang and Marc Verhaegen. Images reprinted by permission from:
 E. Gaufrès et al., Giant Raman scattering from J-aggregated dyes inside carbon nanotubes for multispectral imaging, Nature Photonics, 2014, 8 72-78. Copyright 2014 Macmillan Publishers Ltd.
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