  Oxygen (O2)-sensing matrices are promising tools for the live monitoring of
extracellular O2 consumption levels in long-term cell cultures. In this study,
ratiometric O2-sensing membranes were prepared by electrospinning, an easy,
low-cost, scalable, and robust method for fabricating nanofibers.
Poly({\epsilon}-caprolactone) and poly(dimethyl)siloxane polymers were blended
with tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) dichloride, which was
used as the O2-sensing probe, and rhodamine B isothiocyanate, which was used as
the reference dye. The functionalized scaffolds were morphologically
characterized by scanning electron microscopy, and their physicochemical
profiles were obtained by Fourier transform infrared spectroscopy,
thermogravimetric analysis, and water contact angle measurement. The sensing
capabilities were investigated by confocal laser scanning microscopy,
performing photobleaching, reversibility, and calibration curve studies toward
different dissolved O2 (DO) concentrations. Electrospun sensing nanofibers
showed a high response to changes in DO concentrations in the
physiological-pathological range from 0.5 to 20% and good stability under
ratiometric imaging. In addition, the sensing systems were highly biocompatible
for cell growth promoting adhesiveness and growth of three cancer cell lines,
namely metastatic melanoma cell line SK-MEL2, breast cancer cell line MCF-7,
and pancreatic ductal adenocarcinoma cell line Panc-1, thus recreating a
suitable biological environment in vitro. These O2-sensing biomaterials can
potentially measure alterations in cell metabolism caused by changes in ambient
O2 content during drug testing/validation and tissue regeneration processes.
