The Excess Polarizability of Single-Stranded DNA Molecules in Solution: A Linear Response Theory in the Polarizable Continuum Model with an Application to Biosensing

The excess polarizability of a molecular solute describes
the interaction
energy between a molecular solute and a macroscopic optical field
that polarizes the solute itself, as compared to the same interaction
process involving solvent molecules. The excess polarizability is
involved in the physical mechanism that triggers the signals in the
whispering gallery mode (WGM), a biosensing technique (denoted as
WGM) for detecting biomolecules. The interpretation of the WGM signals
requires information on the excess polarizability of the biomolecule
of interest, which, until now, could be obtained from experimental
measurements of the refractive index of solutions. Here, we present
a quantum chemical theory for determining the excess polarizability
using the effective linear response theory in the polarizable continuum
model (PCM-eLRT) for solvation. As a proof-of-concept, the PCM-eLRT
is applied at the TD-DFT level of electronic structure methodology
to the calculation of the excess polarizability of single-stranded
DNA molecules constituted up to 14-mer oligonucleotides, showing remarkable
agreement with available experimental data.