A Spin-Coated Hydrogel Platform Enables Accurate Investigation of Immobilized Individual Single-Walled Carbon Nanotubes

Abstract

Single-walled carbon nanotubes (SWCNTs) have been used in a variety of sensing and imaging applications over the past few years due to their unique optical properties. In the solution phase, SWCNTs are employed as near-infrared (NIR) fluorescence-based sensors of target analytes via modulations in emission intensity and/or wavelength. In an effort to lower the limit of detection, research has been conducted into isolating SWCNTs adhered to surfaces for potential single molecule analyte detection. However, it is known that SWCNT fluorescence is adversely affected by the inherently rough surfaces that are conventionally used for their observation (e.g., glass coverslip), potentially interfering with fluorescence-based analyte detection. Here, using a spin-coating method with thin films of alginate and SWCNTs, we demonstrate that a novel hydrogel platform can be created to investigate immobilized individual SWCNTs without significantly perturbing their optical properties as compared to solution-phase values. In contrast to the glass coverslip, which red-shifted DNA-functionalized (6,5)-SWCNTs by an average of 3.4 nm, the hydrogel platform reported emission wavelengths that statistically matched the solution-phase values. Additionally, the heterogeneity in the wavelength measurements, as determined from the width of created histograms, was reduced nearly by a factor of 3 for the SWCNTs in the hydrogel platform when compared to glass coverslips. Using long SWCNTs, i.e., those with an average length above the diffraction limit of our microscope, we show that a glass coverslip can induce optical heterogeneity along the length of a single SWCNT regardless of its surface functionalization. This is again significantly mitigated when examining the long SWCNTs in the hydrogel platform. Finally, we show that upon the addition of a model analyte (calcium chloride), the optical response can be spatially resolved along the length of a single SWCNT, enabling localized analyte detection on the surface of a single nanoscale sensor.

Distinguishing Antioxidant Molecules with Near-Infrared Photoluminescence of DNA-Wrapped Single-Walled Carbon Nanotubes

“…Card et al pointed out that SWNTs show heterogeneity in optical characteristics depending on the analytes that they react with. 17 Different analytes produce different variations in optical responses. This may explain why different optical responses of DNA-SWNTs were achieved when saponin and banana solutions were injected.…”

“…Therefore, DNA-SWNTs are useful biosensing tools for distinguishing biomolecules, based on NIR-PL intensities. Card et al pointed out that SWNTs show heterogeneity in optical characteristics depending on the analytes that they react with . Different analytes produce different variations in optical responses.…”

“…Card et al pointed out that SWNTs generally have selective sensitivities to single molecules of analytes. 17 …”

“…The SWNTs’ selectivity of nitrogen oxide molecules, sulfur dioxide molecules, porphyrins, peanut allergy-causing protein ara h1, and pyrene molecules, as well as their interactions have been reported. Card et al pointed out that SWNTs generally have selective sensitivities to single molecules of analytes …”

Hyperspectral Counting of Multiplexed Nanoparticle Emitters in Single Cells and Organelles

“…These advantageous properties have been leveraged to achieve multiplexed optical imaging ,− and sensing − ,, in addition to drug and gene delivery in live cells, , plants, , and animals. , Such uses necessitate their accurate in situ characterization in biological systems; however, the 1-dimensional structure generally makes the direct visualization of individual SWCNTs with appropriate resolution difficult. Although single-SWCNT quantification methods have been developed, − their use has generally been limited in solutions, on devices, or otherwise adsorbed to a substrate.…”