BSA has an interesting property of unfolding in a step-wise manner as a function of temperature. The protein remains stable up to a temperature of 40 °C, undergoes reversible changes in conformation from 40–50 °C, followed by irreversible unfolding of α helices and β sheets above 60 and 80 °C, respectively.

To follow the temperature-dependent conformational changes in BSA molecules adsorbed on CNTs, the team used a combination of spectroscopic tools such as infrared and ultraviolet fluorescence spectroscopy.

Heating the mixture

In the study, the researchers found that a random dispersion of CNTs in native BSA at 35 °C is triggered to assemble progressively over the temperature range 40–65 °C, and returns to a random configuration at 80 °C.

Using zeta potential measurements, electron microscopy and binding of sodium cholate, the strong adsorption of BSA on CNT was ascribed to hydrophobic interactions and self-assembly patterns were linked to electrostatic interactions between protein-bound CNTs.

The work demonstrates that the unfolding pattern of BSA can be used as an ON/OFF switch for CNT assembly under ambient conditions – a concept that could be extended to pattern CNTs on protein-modified substrates for various biomedical, sensing and nanotechnology applications. Also, the connection between the folding/unfolding of a protein and the assembly of nanotubes could lead to the nanotechnology-enabled therapy of diseases related to protein misfolding.

Full details can be found in the journal Nanotechnology.