Introduction
Liposomes are the most successful drug delivery system with over fifteen FDA-approved liposomal formulations. Traditionally, liposomes are loaded with therapeutic cargo and used to prolong drug half life and increase drug accumulation in the target tissue [1]. Recent advances demonstrated applications of lipid and polymer vesicles beyond drug delivery such as in diagnostics and biodetoxification [2,3]. In this lecture, I am focusing on using vesicles in diagnostics, and will show the development of polymersomes for the detection of ammonia, a key neurotoxic metabolite in liver disease, and a liposomal reaction compartment for blood lactate sensing, a widely used biomarker in sepsis [3,4]. Combined with a portable fluorometer, these diagnostic systems promise to provide easy-to-use, rapid, and versatile point-of-care assays for metabolites, drugs, and toxic substances.


Methods
Pyranine-loaded transmembrane pH gradient poly(styrene)-b-poly(ethylene oxide) polymersomes were prepared by emulsification. The ammonia-sensing capacity of this system was optimized in buffers, and validated in the plasma of hyperammonemic bile duct-ligated rats. Liposomes containing lactate oxidase, horseradish peroxidase, and the near-infrared fluorescent dye sulfo-cyanine 7 were prepared and optimized in human arterial blood. In an IRB-approved human volunteer study, the lactate sensing properties were tested in fresh capillary blood.

Results
Transmembrane pH gradient polymersomes sensed ammonia with high selectivity and linearity in a clinically relevant range, and showed comparable results to commercial assays in the plasma of hyperammonemic rats. In lactate-spiked arterial human blood, the liposomal lactate sensor exhibited a linear response to lactate in a clinically relevant range, and quantified lactate-spiked blood samples with high precision and accuracy in fresh capillary blood from healthy subjects.

Conclusion/Implications
We are developing lipid and polymeric vesicles as versatile diagnostic systems. Transmembrane pH gradient vesicles selectively quantified ammonia in plasma of hyperammonemic rats, and are under development as a point-of-care blood ammonia assay. An enzymatic liposomal reaction compartment rapidly quantified lactate in fresh capillary blood from healthy subjects, and is developed as a bedside lactate assay in patients with sepsis.