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Detection of thermoresponsive polymer phase transition in dilute low-volume format by microscale thermophoretic depletion.

Authors
  • 1
  • 1 Systems Biophysics, Ludwig-Maximilians-Universität , D-80799 Munich, Germany. , (Germany)
Type
Published Article
Journal
Analytical Chemistry
1520-6882
Publisher
American Chemical Society
Publication Date
Volume
86
Issue
14
Pages
6797–6803
Identifiers
DOI: 10.1021/ac5008283
PMID: 24820008
Source
Medline
License
Unknown

Abstract

Environmentally responsive polymers are becoming increasingly important in the biomaterials field for use as diagnostic reagents, drug carriers, and tissue engineering scaffolds. Characterizing polymer phase transitions by cloud point curves typically requires large milliliter volumes of sample at high micromolar solution concentrations. Here we present a method based on quantification of thermophoretic Soret diffusion that allows determination of polymer phase transitions using only ~1 μL of liquid at dilute nanomolar concentrations, effectively reducing the amount of sample required by a factor of 10(6). We prepared an oligo(ethylene glycol) (OEG) methyl ether methacrylate copolymer via RAFT polymerization. End-group modification with fluorescent BODIPY-maleimide provided a dye-labeled pOEG-BODIPY conjugate with a lower critical solution temperature (LCST) in the range of ~25-35 °C. Thermophoresis measurements in dilute solution demonstrated a marked change in polymer thermodiffusion in the vicinity of the LCST. We measured the temperature dependence of thermodiffusion and transformed these data sets into sigmoidal curves characterizing the phase transition of the polymer. Finite element modeling suggested a correction to the measured values that brought the transition temperatures measured by thermophoresis into accord with the cloud point curves. Our results demonstrate that observation of polymer thermodiffusion in a low volume dilute format is a facile method for determining polymer phase transition temperatures.

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