An implantable Teflon chip holding lithium naphthalocyanine microcrystals for secure, safe, and repeated measurements of pO2 in tissues.

ABSTRACT

Lithium naphthalocyanine (LiNc) is a crystalline material that has significant potential as a probe for EPR (electron paramagnetic resonance)-based biological oximetry (Pandian et al. J. Mater. Chem. 194138-4147, 2009a). However, implantation of LiNc crystals in tissues in raw or neat form is undesirable since dispersion of crystals in tissue may lead to loss of EPR signal, while also exacerbating biocompatibility concerns due to tissue exposure. To overcome these concerns, we have encapsulated LiNc crystals in an oxygen-permeable polymer, Teflon AF 2400 (TAF). Fabrication of TAF films incorporating LiNc particles (denoted as LiNcTAF chip) was carried out using solvent-evaporation techniques. The EPR linewidth of LiNcTAF chip was linearly dependent on oxygen-partial pressure (pO(2)) and did not change significantly relative to neat LiNc crystals. LiNcTAF chip responded to changes in pO(2) reproducibly, enabling dynamic measurements of oxygenation in real time. The LiNcTAF chips were stable in tissues for more than 2 months and were capable of providing repeated measurements of tissue oxygenation for extended periods of time. The results demonstrated that the newly fabricated, highly oxygen-sensitive LiNcTAF chip will enhance the applicability of EPR oximetry for long-term and clinical applications.