Blood analyte sensing using fluorescent dye-loaded red blood cells

Abstract

Measurement of blood analytes provides 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). Due to analyte transporters on red blood cell (RBC) membranes that equilibrate intracellular and extracellular analyte levels, RBCs serve as an attractive alternative for encapsulating analyte sensors. Once reintroduced to the blood stream, the functionalized RBCs may continue to live for the remainder of their life span (120 days for humans). They are biodegradable and biocompatible, thereby eliminating the immune system response common for many implanted devices. The proposed sensing system utilizes the ability of the RBCs to swell in response to a decrease in the osmolarity of the extracellular solution. Just before lysis, they develop small pores on the scale of tens of nanometers. While at low temperature, analyte-sensitive dyes in the extracellular solution diffuse into the perforated RBCs and become entrapped upon restoration of temperature and osmolarity. Since the fluorescent signal from the entrapped dye reports on changes in the analyte level of the extracellular solution via the RBC transporters, interactions between the RBCs and the dye are critical to the efficacy of this technique. In this work, we study the use of a near infrared pH sensitive dye encapsulated within RBCs and assess the ability to measure dye fluorescence in vivo.

Erythrocytes as Carriers: From Drug Delivery to Biosensors

“…Carrier erythrocytes (CEs) can be used both in therapy and the diagnosis of some diseases, for example, as carriers of contrast agents for magnetic resonance imaging (MRI) or as biosensors that respond to changes in the concentration of metabolites or pH in the blood [33][34][35]. In therapy, depending on the drug that is loaded, the erythrocytes can be used as carriers with a gradual drug release, as bioreactors or a system for targeted drug delivery, primarily to the reticuloendothelial system (RES), liver and spleen [36].…”

“…However, it turned out that for pH measurements in vivo in the physiological range, the sensitivity of such a system is too low. Thus, the next step to facilitate the use of RBCs as biosensor carriers should be the development a fluorescent sensor with higher sensitivity and optimization of RBCs loading to obtain a higher signal level [35].…”