Electrowetting-based pH- and biomolecule-responsive valves and pH filters.

An electrowetting-based pH-responsive valve that uses a nonstandard electrochemical three-electrode system is proposed. The system comprises a gold valve electrode and an iridium electrode that act as the working and auxiliary electrodes, depending on the purpose, while an iridium oxide pH-sensitive electrode acts as the reference electrode. To make the valve open at pH higher than a threshold, the gold valve electrode is used as the working electrode and a voltage is applied to it with respect to the pH-sensitive reference electrode. To make the valve open at pH lower than the threshold, the gold valve electrode is used as the auxiliary electrode, while the iridium electrode is used as the working electrode. The wettability of the valve electrode is altered when a voltage is applied to it. When the pH of a solution crosses the threshold, the potential of the gold valve electrode exceeds a threshold potential because of the change in the potential of the pH-sensitive reference electrode. Consequently, the gold valve electrode becomes more hydrophilic, thereby allowing the solution to pass through the valve. Furthermore, by combining two valve electrodes, we realized a pH filter that allows solutions with pH within a limited range to pass through it. Urea- and glucose-responsive valves that opened at concentrations higher than the threshold could also be formed by immobilizing an enzyme on the pH-sensitive reference electrode.

[1]  Wataru Satoh,et al.  Electrowetting-based valve for the control of the capillary flow , 2008 .

[2]  Wataru Satoh,et al.  Electrochemical immunoassay on a microfluidic device with sequential injection and flushing functions. , 2007, Biosensors & bioelectronics.

[3]  Helen Song,et al.  Reactions in droplets in microfluidic channels. , 2006, Angewandte Chemie.

[4]  Robin H. Liu,et al.  Microfluidic tectonics: a comprehensive construction platform for microfluidic systems. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[5]  R. Fair,et al.  An integrated digital microfluidic lab-on-a-chip for clinical diagnostics on human physiological fluids. , 2004, Lab on a chip.

[6]  Hiroaki Suzuki,et al.  Electrochemical techniques for microfluidic applications , 2008, Electrophoresis.

[7]  Peter Woias,et al.  Micropumps—past, progress and future prospects , 2005 .

[8]  Jiri Janata,et al.  Principles of Chemical Sensors , 1989 .

[9]  Asim Nisar,et al.  MEMS-based micropumps in drug delivery and biomedical applications , 2008 .

[10]  E. Delamarche,et al.  Microfluidics for Processing Surfaces and Miniaturizing Biological Assays , 2005 .

[11]  Masayoshi Esashi,et al.  Microflow devices and systems , 1994 .

[12]  Hiroaki Suzuki,et al.  A disposable intelligent mosquito with a reversible sampling mechanism using the volume-phase transition of a gel , 2002 .

[13]  Juan G. Santiago,et al.  A review of micropumps , 2004 .

[14]  Wataru Satoh,et al.  Microanalysis system with automatic valve operation, pH regulation, and detection functions , 2008 .

[15]  Alberto Escarpa,et al.  Real sample analysis on microfluidic devices. , 2007, Talanta.

[16]  Wataru Satoh,et al.  Electrowetting on gold electrodes with microscopic three-dimensional structures for microfluidic devices , 2008 .

[17]  Richard B. Fair,et al.  Digital microfluidics: is a true lab-on-a-chip possible? , 2007 .

[18]  Arianna Menciassi,et al.  Wireless capsule endoscopy: from diagnostic devices to multipurpose robotic systems , 2007, Biomedical microdevices.

[19]  M. Hitchman,et al.  Evaluation of iridium oxide electrodes formed by potential cycling as pH probes. , 1988, The Analyst.

[20]  Isao Karube,et al.  Microfabricated Liquid Junction Ag/AgCl Reference Electrode and Its Application to a One-Chip Potentiometric Sensor , 1999 .

[21]  Lei Wang,et al.  Implementation of radiotelemetry in a lab-in-a-pill format. , 2006, Lab on a chip.

[22]  G. Iddan,et al.  Wireless capsule endoscopy , 2003, Gut.

[23]  A. Murray,et al.  Toward a miniature wireless integrated multisensor microsystem for industrial and biomedical applications , 2002 .

[24]  A sampling mechanism employing the phase transition of a gel and its application to a micro analysis system imitating a mosquito , 2001 .