Single-Walled Carbon Nanotubes Probing the Denaturation of Lysozyme

Abstract

Resonance Raman spectroscopy measurements of lysozyme-bound single-walled carbon nanotubes have been made during different stages of the chemically and thermally induced misfolding and of the denaturation process of nanotube-bound lysozymes. Changes to the Raman intensity of single-walled carbon nanotubes (SWNTs) have been observed during the denaturation of lysozyme. The Raman intensity changes are attributed to excitonic transition energy (E_ii ) shifts of the SWNTs during the denaturation of lysozyme. The E_ii shift of SWNTs was confirmed by photoluminescence measurements.

Figure 1

Schematic illustration of structures of a lysozyme-wrapped SWNT and a denatured lysozyme-wrapped SWNT.

Figure 2

(a) Circular dichroism spectra of lysozyme at different GndHCl concentrations. Here, Θ_MRW denotes the ellipticity in the mean residue weight. (b) A denaturation plot shown for LYZ-SWNT. The percent denatured lysozyme is calculated from the ellipticity at 222 nm shown in (a).

Figure 3

Raman spectra of the lysozyme–SWNT dispersion with different GndHCl concentrations: (a) at 532 nm excitation for (9,3) SWNTs and (b) at 647 nm excitation for (7,5) and (8,3) SWNTs. (c) Lorentzian fits of RBM bands of (7,5) and (8,3) nanotubes at different GndHCl concentrations. (d) Plot of the RBM integrated intensity ratio (I_(7,5)/I_(8,3)) for the (7,5) to (8,3) nanotubes vs the GndHCl concentration. (e) PL of the LYZ-SWNT dispersion without any GndHCl (blue line) and with 4 M GndHCl (red line). The excitation wavelength is 658 nm. Emission intensity is normalized at the emission peaks occurring around 1150 nm. (f) Calculated normalized intensity of the Stokes RBM bands for (7,5) (red line) and (8,3) (blue line) at 647 nm (1.916 eV) laser excitation as a function of E₂₂, and the fwhm resonance window width of 65 meV is indicated.

Figure 4

Plot of the RBM intensity ratio I_(7,5)/I_(8,3) of (7,5) to (8,3) nanotubes as a function of heating time at 80 °C (blue solid squares) and 90 °C (red solid circles). The red line is an exponential-decay fit (y = A*exp(−kx) + B) for data taken at 90 °C, and the rate constant k = 0.15 min⁻¹ is obtained for data at 90 °C.