Abstract
Fluorescence imaging of biological systems down to the single-molecule level has generated many advances in cellular biology. For applications within intact tissue, single-walled carbon nanotubes (SWCNTs) are emerging as distinctive single-molecule nanoprobes, due to their near-infrared photoluminescence properties. For this, SWCNT surfaces must be coated using adequate molecular moieties. Yet, the choice of the suspension agent is critical since it influences both the chemical and emission properties of the SWCNTs within their environment. Here, we compare the most commonly used surface coatings for encapsulating photoluminescent SWCNTs in the context of bio-imaging applications. To be applied as single-molecule nanoprobes, encapsulated nanotubes should display low cytotoxicity, and minimal unspecific interactions with cells while still being highly luminescent so as to be imaged and tracked down to the single nanotube level for long periods of time. We tested the cell proliferation and cellular viability of each surface coating and evaluated the impact of the biocompatible surface coatings on nanotube photoluminescence brightness. Our study establishes that phospholipid-polyethylene glycol-coated carbon nanotube is the best current choice for single nanotube tracking experiments in live biological samples.
Highlights
Over recent years, the numerous improvements in optical microscopy that allowed robust single-molecule detection has generated novel knowledge of various biological paradigms
We first evaluated the cytotoxicity of single-walled carbon nanotubes (SWCNTs) encapsulated with different moieties
Surfactants like sodium dodecylbenzene sulfonate or bile salts are known to provide the best luminescing SWCNTs in aqueous environments [24,25,26], their use for cellular applications should be avoided because these surfactants inherently alter the integrity of cellular membranes
Summary
The numerous improvements in optical microscopy that allowed robust single-molecule detection has generated novel knowledge of various biological paradigms. Fluorescence microscopy has been the ubiquitous approach for performing single-molecule detection and SPT experiments because of its high sensitivity, specificity, and spatiotemporal resolution [2]. Since biological samples strongly scatter light [6] and display substantial auto-fluorescence at visible wavelengths [7], SPT studies in intact tissues are challenging with most common visible single-molecule probes. Because the biological transparency window lies in the near-infrared (NIR) range where absorption, scattering, and auto-fluorescence are minimized [8], the identification of stable luminescent nanoscale emitters in the NIR is the preferred route toward deep tissue investigations at the single-molecule level
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