title: Microencapsulated 3-dimensional sensor for the measurement of oxygen in single isolated pancreatic islets.
abstract: BACKGROUND
  Oxygen consumption reflects multiple processes in pancreatic islets including mechanisms contributing to insulin secretion, oxidative stress and viability, providing an important readout in studies of islet function, islet viability and drug testing. Due to the scarcity, heterogeneity, and intrinsic kinetic properties of individual islets, it would be of great benefit to detect oxygen consumption by single islets. We present a novel method we have developed to image oxygen in single islets.
  
  
  RESULTS
  Using a microfluidics system, individual islets and a fluorescent oxygen-sensitive dye were encased within a thin alginate polymer layer. Insulin secretion by the encapsulated islets was normal. Fluorescent signal from the encased dye, detected using a standard inverted fluorescence microscope and digital camera, was stable and proportional to the amount of oxygen in the media. When integrated into a perifusion system, the sensing system detected changes in response to metabolic substrates, mitochondrial poisons, and induced-oscillations. Glucose responses averaged 30.1±7.1% of the response to a metabolic inhibitor (cyanide), increases were observed in all cases (n = 6), and the system was able to resolve changes in oxygen consumption that had a period greater than 0.5 minutes. The sensing system operated similarly from 2-48 hours following encapsulation, and viability and function of the islets were not significantly affected by the encapsulation process.
  
  
  CONCLUSIONS
  An oxygen-dependent dye situated around and within a pancreatic islet encapsulated by a thin layer of alginate was sensitive to changes in oxygen consumption, and was not harmful to the function or viability of islets over the course of two days. The microcapsule-based sensing method is particularly suited to assessing the effects of compounds (dose responses and time courses) and chronic changes occurring over the course of days. The approach should be applicable to other cell types and dyes sensitive to other biologically important molecules.
authors.affiliation: Department of Mechanical Engineering, University of Washington, Seattle, Washington, United States of America.
authors.forename: Wanyu
authors.initials: W
authors.lastname: Chen
authors.forename: Mark
authors.initials: M
authors.lastname: Lisowski
authors.forename: Gamal
authors.initials: G
authors.lastname: Khalil
authors.forename: Ian R
authors.initials: IR
authors.lastname: Sweet
authors.forename: Amy Q
authors.initials: AQ
authors.lastname: Shen
mesh_terms: D000464:Alginates / Q000737:chemistry; D000818:Animals; D015374:Biosensing Techniques / Q000295:instrumentation / Q000379:methods*; D002462:Cell Membrane / Q000378:metabolism; D005456:Fluorescent Dyes / Q000737:chemistry; D020723:Glucuronic Acid / Q000737:chemistry; D006603:Hexuronic Acids / Q000737:chemistry; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation / Q000379:methods; D008856:Microscopy, Fluorescence; D010100:Oxygen / Q000032:analysis*; D010101:Oxygen Consumption; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results
chemical_list: D000464:Alginates; D005456:Fluorescent Dyes; D006603:Hexuronic Acids; D007328:Insulin; D020723:Glucuronic Acid; D010100:Oxygen