Development of an Insertable Enzymatic Sensor Towards in vivo Optical Measurements of Amino Acids

In this study, an insertable chemo-optical sensor was designed for the purpose of monitoring in vivo levels of amino acids. To sense amino acids using a platform previously demonstrated for other enzymatic substrates (glucose, lactate, uric acid), the oxidative enzyme L-amino acid oxidase (LAAO) was selected. Initially, LAAO was characterized to quantify its utility as a potential amino acid sensor; it was found to be responsive to 14 of the 20 L-amino acids found in the body. LAAO was then incorporated into alginate microparticles along with oxygen-quenched phosphorescent ethyl cellulose nanoparticles to form an optically responsive sensing domain. Increases in analyte concentration were found to decrease the oxygen concentration as the LAAO reacted oxidatively with the amino acids, inducing the phosphorescent nanoparticles to emit longer lifetimes. Microparticles were coated with polyelectrolyte nanofilms and encapsulated into hydrogels to tune the sensitivity and response range. Prototype sensors tested at the conditions expected in subcutaneous tissue (37°C and 30 μM O₂) displayed a dynamic range of 90 μs over 0-52 mg/dL of amino acids. These results confirm the suitability of LAAO incorporated into this platform as an insertable sensor for real time amino acid measurements.