Measurement of blood analytes, such as pH and glucose, provide crucial information about a patient's health. Some such
analytes, such as glucose in the case of diabetes, require long-term or near-continuous monitoring for proper disease
management. However, current monitoring techniques are far from ideal: multiple-per-day finger stick tests are
inconvenient and painful for the patient; implantable sensors have short functional life spans (i.e., 3-7 days). Red blood
cells serve as an attractive alternative for carriers of analyte sensors. Once reintroduced to the blood stream, these
carriers may continue to live for the remainder of their life span (120 days for humans). They are also biodegradable and
biocompatible, thereby eliminating the immune system response common for many implanted devices. The proposed
carrier system takes advantage of the ability of the red blood cells to swell in response to a decrease in the osmolarity of
the extracellular solution. Just before the membranes lyse, they develop small pores on the scale of tens of nanometers.
Analyte-sensitive dyes in the extracellular solution may then diffuse into the perforated red blood cells and become
entrapped upon restoration of physiological temperature and osmolarity. Because the membranes contain various analyte
transporters, intracellular analyte levels rapidly equilibrate to those of the extracellular solution. A fluorescent dye has
been loaded inside of red blood cells using a preswelling technique. Alterations in preparation parameters have been
shown to affect characteristics of the resulting dye-loaded red blood cells (e.g., intensity of fluorescence).