Microscale
Sensing of Oxygen via Encapsulated Porphyrin
Nanofibers: Effect of Indicator and Polymer “Core” Permeability
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Abstract
Biomimetic
polymer nanofibers integrate sensing capabilities creating
utility across many biological and biomedical applications. We created
fibers consisting of either a poly(ether sulfone) (PES) or a polysulfone
(PSU) core coated by a biocompatible polycaprolactone (PCL) shell
to facilitate cell attachment. Oxygen sensitive luminescent probes
Pt(II) <i>meso</i>-tetra(pentafluorophenyl)porphine (PtTFPP)
or Pd(II) <i>meso</i>-tetra(pentafluorophenyl)porphine (PdTFPP),
were incorporated in the core via single-step coaxial electrospinning
providing superior sensitivity, high brightness, linear response,
and excellent stability. Both PES–PCL and PSU–PCL fibers
provide more uniform probe distribution than polydimethylsiloxane
(PDMS). PSU-based sensing fibers possessed optimum sensitivity due
to their relatively higher oxygen permeability. During exposure to
100% nitrogen and 100% oxygen, PES–PCL fiber displayed an <i>I</i><sub>0</sub>/<i>I</i><sub>100</sub> value of
6.7; PSU–PCL exhibited a value of 8.9 with PtTFPP as the indicator.
In contrast, PdTFPP-containing fibers possess higher sensitivity due
to the long porphyrin lifetime. The corresponding <i>I</i><sub>0</sub>/<i>I</i><sub>100</sub> values were 80.6 and
106.7 for the PES–PCL and PSU–PCL matrices, respectively.
The response and recovery times were 0.24/0.39 s for PES–PCL
and 0.38/0.83 s for PSU–PCL which are 0.12 and 0.11 s faster,
respectively, than the Pt-based porphyrin in the same matrices. Paradoxically,
lower oxygen permeabilities make these polymers better suited to measuring
higher (i. e., ∼20%) oxygen contents than PDMS. Individual
fiber sensing was studied by fluorescence spectrometry and at a sub-micrometer
scale by total internal reflection fluorescence (TIRF). Specific polymer
blends relate polymer composition to the resulting sensor properties.
All compositions displayed linear Stern–Volmer plots; sensitivity
could be tailored by matrix or the sensing probe selection
