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Plasmonic Enhancement of Two-Photon Excitation Fluorescence by Colloidal Assemblies of Very Small AuNPs Templated on M13 Phage
journal contribution
posted on 2020-07-01, 20:29 authored by Esen Sokullu, Maxime Pinsard, Jiawei Zhang, Julien Plathier, Gitanjali Kolhatkar, Amy Szuchmacher Blum, François Légaré, Andreas Ruediger, Tsuneyuki Ozaki, Marc A. GauthierIn this study, an
engineered M13 bacteriophage was examined as
a biological template to create a well-defined spacing between very
small gold nanoparticles (AuNPs 3–13 nm). The effect of the
AuNP particle size on the enhancement of the nonlinear process of
two-photon excitation fluorescence (2PEF) was investigated. Compared
to conventional (one-photon) microscopy techniques, such nonlinear
processes are less susceptible to scattering given that the density
of background-scattered photons is too low to generate a detectable
signal. Besides this, the use of very small AuNPs in 2PEF microscopy
becomes more advantageous because individual “isolated”
AuNPs of this size do not sufficiently enhance 2PEF to produce a detectable
signal, resulting in even less background signal. To investigate the
2PEF of the AuNP–M13 assemblies, a variety of sample preparation
approaches are tested, and surface-enhanced Raman spectroscopy (SERS)
is employed to study the strength of plasmon coupling within the gaps
of AuNPs assembled on the M13 template. Results indicate that assemblies
prepared with 9–13 nm AuNP were able to clearly label Escherichia coli cells and produce a 2PEF signal
that was orders of magnitude higher than the isolated AuNP (below
the threshold of detection). This study thus provides a better understanding
of the opportunities and limitations relevant to the use of such small
AuNPs within colloidal plasmonic assemblies, for applications in biodetection
or as imaging contrast agents.