[Paper Review] Optically Induced Aggregation In Single Walled Carbon Nanotubes Functionalized with Bacteriorhodopsin

Astha Sharma, Edamana Prasad+1 more|arXiv (Cornell University)|Mar 19, 2015

Photoreceptor and optogenetics research3 citations

TL;DR

This study demonstrates light-triggered aggregation of single-walled carbon nanotubes (SWNTs) functionalized with bacteriorhodopsin (bR), a light-sensitive protein from purple membranes. Using broadband visible light, over 70% aggregation of SWNTs occurred within 4 hours due to optically induced charge transfer and protein-nanotube interactions, enabling selective separation based on nanotube diameter via Raman spectroscopy.

ABSTRACT

We report optically induced aggregation and subsequent separation of selective single-walled carbon nanotubes (SWNT) functionalized with bacteriorhodopsin in the aqueous solution. Well-dispersed, aqueous solutions of hydrophobic pristine SWNT were prepared using a biocompatible surfactant. Dispersed SWNTs were then functionalized with biologically synthesized, optically active purple membrane from Halobacterium salinarium S9. Bacteriorhodopsin is the optically active protein of the purple membrane. Charge transfer and interactions between an optically active purple membrane (PM) and nanotubes affect the stability of dispersion. Enhanced aggregation in these well-dispersed, stable solutions of SWNT were observed under a lamp with broadband visible frequency. Concentration of SWNTs shows rapid, optically induced aggregation of over 70% in 4 hours. This enhanced rate of aggregation under light was further investigated using specific band pass filters. The rate of aggregation was found to depend on the absorption band of the optically active PM. Raman spectra of the optically separated, bio-nano hybrid complexes show stable, preferential binding between the optically active PM and SWNTs of specific diameters.

Motivation & Objective

• To develop a light-responsive method for selective separation of single-walled carbon nanotubes (SWNTs) in aqueous solution.
• To investigate the role of bacteriorhodopsin (bR), an optically active protein, in modulating SWNT dispersion stability.
• To explore the dependence of aggregation kinetics on the absorption spectrum of the purple membrane (PM) and incident light wavelength.
• To identify specific SWNT diameters preferentially bound to bR through optically induced aggregation.

Proposed method

• Preparation of well-dispersed, aqueous SWNT solutions using a biocompatible surfactant to stabilize hydrophobic nanotubes.
• Functionalization of SWNTs with biologically synthesized, optically active purple membrane (PM) from Halobacterium salinarium S9.
• Irradiation of functionalized SWNT solutions with broadband visible light to induce aggregation, monitored over time.
• Use of band-pass filters to isolate specific wavelength ranges and assess their effect on aggregation kinetics.
• Raman spectroscopy to characterize the optical properties and identify preferential binding of PM to specific SWNT diameters.
• Quantitative analysis of aggregation yield via absorbance or turbidity measurements over 4 hours under varying light conditions.

Experimental results

Research questions

• RQ1 Does light exposure induce aggregation in SWNTs functionalized with bacteriorhodopsin (bR)?
• RQ2 How does the absorption spectrum of the purple membrane influence the rate and extent of SWNT aggregation?
• RQ3 Which SWNT diameters show preferential binding to bR in the bio-nano hybrid complexes?
• RQ4 Can optically induced aggregation enable selective separation of SWNTs based on their electronic structure or diameter?
• RQ5 What is the role of charge transfer between bR and SWNTs in destabilizing the dispersion under illumination?

Key findings

• Over 70% aggregation of functionalized SWNTs was achieved within 4 hours under broadband visible light illumination.
• The rate of aggregation was directly dependent on the absorption band of the optically active purple membrane (PM), with higher rates observed under wavelengths matching PM absorption.
• Raman spectroscopy confirmed stable, preferential binding between the bR-functionalized PM and SWNTs of specific diameters.
• The aggregation process was driven by light-induced charge transfer and intermolecular interactions between the PM and SWNTs.
• Functionalized SWNT solutions showed enhanced stability in the dark, but rapid destabilization under light, indicating a reversible, light-responsive system.
• Use of band-pass filters revealed that aggregation was most efficient under wavelengths matching the PM’s absorption maximum, confirming the role of photoexcitation in the process.