Microchimica Acta

, Volume 171, Issue 3–4, pp 211–216 | Cite as

Opto-chemical micro-capillary clocks

  • Stefan Wilhelm
  • Otto S. WolfbeisEmail author
Original Paper


Opto-chemical capillary clocks are presented that are based on the measurement of a colored segment in a microchannel (a capillary). Color is created by a chromogenic chemistry involving the oxidation of a (virtually colorless) leuco-dye. Poly(ethylene glycol) (PEG) is used as a solvent, and indigo and thioindigo (in their reduced leuco forms) act as oxygen-sensitive dyes. The clock is started by removing one seal at the end of the capillary. A visible color change occurs as air diffuses into the microchannel due to an irreversible color reaction. The length of the colored segment is proportional to the time elapsed. PEGs of different average molar mass affect the diffusion rate of oxygen in the microchannel and thereby affect the rate of the migration of the color front. Both temperature and relative humidity exert a strong effect. Six types of such clocks are described that enable times to be determined in the range from 1 day to 6 months, possibly of even decades.

Optical clocks are presented where elapsed time is indicated by the length of the colored segment of a micro-capillary.


Optical timer Chromogenic chemistry Indigo Oxygen Clock Poly(ethylene glycol) 


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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  1. 1.Institute of Analytical Chemistry, Chemo- and BiosensorsUniversity of RegensburgRegensburgGermany

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