Application of hydrophobic micropatterns to centrifugal fluid valve in flow channel

Optimizing the use of micro-flow channels as fluid control mechanisms is an effective means of increasing the sensitivity and selectivity of biosensors. The purpose of this study was to clarify the effectiveness of periodic structure applied to this type of fluid control mechanism to improve the hydrophobicity. We evaluated the functionality of centrifugal fluid valve with micrometer-sized periodic structure in the micro-flow channel. A disposable compact disc-based chip with centrifugal fluid valve was designed for this evaluation. The hydrophobic properties such as transferred volume ratio of the sample solution and the change in the transferred volume ratio with rotational velocity (slope) of the centrifugal fluid valve were investigated. In this case, parallel pillars showed higher hydrophobicity than cross-shaped pillars. The transferred volume ratio increased by 20% compared to that without a micro-periodic structure when a protein solution with a similar concentration to that in saliva and plasma was used. Additionally, a change in rotational velocity of only 49.3 rpm was sufficient to switch a centrifugal fluid valve with parallel pillars, meaning that it makes it possible to have two critical rotation speeds when the fluid begins to move with a rotational velocity of 100 rpm. It was shown that the static hydrophobicity dominates the switching characteristics in the proposed centrifugal fluid valve. Our study suggests that applying periodic structure to fluid control mechanisms is an effective means of realizing hydrophobic surfaces.