Continuous monitoring of biochemical analytes is of interest in biomedicine to provide insight into physiology and health. Implantable, optical sensors paired with a wearable reader present an opportunity to report on a biomarker of interest without the need to implant any electronics. Specifically, being able to optically sense tissue oxygenation continuously in real-time could be of interest for the management of a number of medical conditions, including metabolic diseases, sepsis, various cancers, critical limb ischemia, and pulmonary diseases. Compared to pulse oximetry, optical methods of sensing oxygen directly detect tissue oxygenation (as opposed to blood saturation levels), can readily assess hyperoxia (heightened tissue oxygenation) in addition to normoxia and hypoxia (decreased tissue oxygenation), and may be resistant to motion artifacts.
In this work, implantable, optical sensors for tissue oxygenation were created via the incorporation of a Pd (II) benzoporphyrin into biodegradable matrices, including synthetically derived electrospun polymers and bio-derived films/sponges. The use of biodegradable matrices allows the implanted sensor to degrade over time, preventing the need for a permanent implant or retrieval surgery and, thereby, increasing user acceptance of the technology. The incorporated chromophore absorbs (~630 nm) and phosphoresces (~810 nm) within the optical tissue window, the 600-1300 nm regime where tissue penetration depths are the greatest due to relatively low degrees of scattering and absorption. The long-lived, near-infrared emission in these materials is readily quenched by dissolved oxygen. A custom in situ fluorimeter setup was constructed and used to characterize the in vitro sensor performance under physiologically relevant conditions. Multiple demonstrated sensor compositions exhibited approximately monoexponential lifetime decays, linear Stern-Volmer plots, and favorable sensitivities. These characteristics indicate excellent interpretability for continuously monitoring tissue oxygenation. These optical oxygen sensors can be used in vivo without the need for any implanted electronics through the use of an external, miniaturized wearable reader. These compositions maintain oxygen sensing function in vivo and demonstrate real-time sensing capabilities throughout various physiological states, comprising hyperoxia, normoxia, and hypoxia.
