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Trafficking profiles of pathogens are important in elucidating the mechanisms leading
to their pathogenicity and disease manifestations. Current approaches for such studies
have typically involved the use of conventional fluorophores or fluorescent proteins that
are excited by ultraviolet or visible light. Hence, autofluorescence and photodamage are
the common problems encountered in these studies. Here, we propose the use of unique
luminescent nanomaterial, upconversion nanoparticles (UCNs), for bacterial labeling so
as to circumvent these problems. Excitation wavelengths of these nanoparticles lies in
this near-infrared (NIR) spectral region in which biological materials have low absorption
and scattering coefficients. Thus, the use of UCNs as pathogens? contrast agents could
allow for deeper tissue penetration, low autofluorescence and minimal photodamage.
Moreover, the particles? high photostability and environmental insensitivity mean that
continuous monitoring of the pathogens can be carried out without any diminishing
of the signal intensities. A model pathogen,
Gu?rin (BCG), was surface-labelled with carboxyl-functionalized UCNs by a general
carboiidime-based conjugation strategy in which the bacterial surface amine groups were
linked to the functionalized nanoparticles via a covalent amide bond. Our study showed
that the conjugation process did not drastically affect on the bacterialbiological behavior.
Characterization of the labelled BCG by transmission electron microscopy revealed that
the nanoparticles were attached to the outer capsular layer. Results from the preliminary
time point studies suggest that the UCN-labelled bacteria could be possibly be used to
study outer surface dynamics of BCG during infection.
This work is supported by A*STAR SBIC and National University of Singapore
Ms. Ong has completed her Bachelor of Engineering (Chemical) in the year of 2009 from National
University of Singapore. She is currently pursuing her Ph.D, under the supervision of A/Prof. Yong
Zhang and Dr. Sylvie Alonso, focusing on upconversion nanoparticles and their applications in imaging
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