Multifunctional microvalves control by optical illumination on nanoheaters and its application in centrifugal microfluidic devices.

Valving is critical in microfluidic systems. Among many innovative microvalves used in lab-on-a-chip applications, phase change based microvalves using paraffin wax are particularly attractive for disposable biochip applications because they are simple to implement, cost-effective and biocompatible. However, previously reported paraffin-based valves require embedded microheaters and therefore multi-step operation of many microvalves was a difficult problem. Besides, the operation time was relatively long, 2-10 s. In this paper, we report a unique phase change based microvalve for rapid and versatile operation of multiple microvalves using a single laser diode. The valve is made of nanocomposite materials in which 10 nm-sized iron oxide nanoparticles are dispersed in paraffin wax and used as nanoheaters when excited by laser irradiation. Laser light of relatively weak intensity was able to melt the paraffin wax with the embedded iron oxide nanoparticles, whereas even a very intense laser beam does not melt wax alone. The microvalves are leak-free up to 403.0 +/- 7.6 kPa and the response times to operate both normally closed and normally opened microvalves are less than 0.5 s. Furthermore, a sequential operation of multiple microvalves on a centrifugal microfluidic device using a single laser diode was demonstrated. It showed that the optical control of multiple microvalves is fast, robust, simple to operate, and requires minimal chip space and thus is well suited for fully integrated lab-on-a-chip applications.