Assessing oxygen carrying properties of MPs using RuDPP
In our previous studies, PFC conjugated chitosan hydrogels were tested
for oxygen transport properties using commercial phosphorescent dots[23] and needle sensors.[24]Our investigations showed these hydrogels enhanced oxygen transport in
aqueous conditions and allowed oxygen tensions to reach higher
equilibrium states compared to controls not integrating PFCs. In this
study, we were interested in understanding the impact of our PFC-MPs on
oxygen tensions using RuDPP in finer detail and at a cellular level.
RuDPP has a long fluorescence lifetime and a long Stokes-shift. It
quenches in the presence of oxygen and thus is a suitable probe dye for
determining dissolved oxygen.[25] A mixture of MP
solution and RuDPP in PBS was injected into a sealed, custom-built
chamber and exposed to gases (Figure 2A) . We measured the
fluorescence intensity after flowing pure N2 and pure
O2 gasses to create oxygen partial pressures at the
extremes of 0% oxygen and 100% oxygen in solution. A solution without
any MPs was used as a control. As shown in Figure 2B , when
switching from pure N2 to pure O2, the
fluorescent intensity decreased due to oxygen quenching of RuDPP. We
also observed a decrease in fluorescence intensity in the presence of
MPs which can be attributed to increased dissolved oxygen concentration.
The sensitivity of the optical oxygen sensor with (I) and without
(I 0) a quencher (here oxygen) was quantified in
term of the ratio I 0/I 100,
as shown in Figure 2C at equilibrium. Our results indicated
that the solution containing PFC-MPs exhibited the highest sensitivity
to oxygen with the maximum quenching ratio ofI 0/I 100 =1.1. Following
saturation, we then stopped oxygen flow and studied the release
kinetics. We observed that the control group showed complete RUDPP
recovery within 3 min whereas MPs slowed the RuDPP recovery process to
10 min (Figure 2D) . This can be explained by MPs’ ability to
uptake oxygen and then release it gradually into a low oxygen tension
aqueous environment. These results confirm that PFC-MPs can act as both
an oxygen absorbing material as well as a reservoir to release oxygen
gradually in an aqueous environment. This finding is in agreement with
our earlier work with PFC-modified hydrogels where we examined their
ability to deliver and sustain biological levels oxygen for enhancing
cellular functions essential in wound
healing.[26,27] Most recent evidence from another
research group shows the potential of PFC nanoemulsions as artificial
oxygen carriers.[28] In this study, PFC
nanoemulsions exhibited five times higher dissolved
O2 concentration compared to water, as measured by a
submerged O2 probe.