Response
of Villin Headpiece-Capped Gold Nanoparticles
to Ultrafast Laser Heating
- Publication date
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Abstract
The
integrity of a small model protein, the 36-residue villin headpiece
HP36, attached to gold nanoparticles (AuNP) is examined, and its response
to laser excitation of the AuNPs is investigated. To that end, it
is first verified by stationary IR and CD spectroscopy, together with
denaturation experiments, that the folded structure of the protein
is fully preserved when attached to the AuNP surface. It is then shown
by time-resolved IR spectroscopy that the protein does not unfold,
even upon the highest pump fluences that lead to local temperature
jumps on the order of 1000 K of the phonon system of the AuNPs, since
that temperature jump persists for too short a time of a few nanoseconds
only to be destructive. Judged from a blue shift of the amide I band,
indicating destabilized or a few broken hydrogen bonds, the protein
either swells, becomes more unstructured from the termini, or changes
its degree of solvation. In any case, it recovers immediately after
the excess energy dissipates into the bulk solvent. The process is
entirely reversible for millions of laser shots without any indication
of aggregation of the protein or the AuNPs and with only a minor fraction
of broken protein–AuNP thiol bonds. The work provides important
cornerstones in designing laser pulse parameters for maximal heating
with protein-capped AuNPs without destroying the capping layer