Switchable MRI contrast agents based on morphological changes of pH-responsive polymers

Satoshi Okada, Shin Mizukami, Kazuya Kikuchi

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)


Magnetic resonance imaging (MRI) contrast agents are effective tools in both medical diagnosis and life science research. Various smart contrast agents have been developed for the visualization of biological phenomena. These contrast agents have molecular switches that increase or reduce MRI signal intensity in response to the target biological reaction. Therefore, novel approaches to the design of molecular switches for versatile in vivo studies using MRI are eagerly anticipated. Here, we report one such approach for the development of molecular switches based on morphological changes of pH-responsive polymers. We designed and synthesized three types of contrast agents based on a linear homopolymer or spherical copolymers with two different cross-linking degrees. The relaxivity measurements showed that these agents have molecular switches that respond to pH changes, and fluorescence studies indicated that these switches are based on the alteration of the molecular tumbling caused by pH-responsive morphological changes. As a result, the spherical polymers possess promising characteristics for the development of switchable MRI contrast agents.

Original languageEnglish
Pages (from-to)769-774
Number of pages6
JournalBioorganic and Medicinal Chemistry
Issue number2
Publication statusPublished - 2012 Jan 15


  • Contrast agent
  • Molecular switch
  • MRI
  • pH-responsive polymer
  • Rotational correlation time


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