A microchannel immunoassay chip with ferrofluid actuation to enhance the biochemical reaction

This paper presents a novel microchannel immunoassay chip comprised of a nitrocellulose slide and a microchannel film. The microchannel film has a circular channel and four reaction zones and is fabricated using PDMS. An analytical reagent, such as protein, can be immobilized at the reaction zones on a nitrocellulose slide, and the sample to be analyzed is manipulated by ferrofluid to circulate through the reaction zones for immunological tests. The ferrofluid forming plugs in the circular channel was actuated by an external NdFeB permanent magnet affixed to a stepper motor. The purpose of circulative fluid actuation is to produce enough agitation to increase the collision opportunities of molecules and, hence, the reaction rate. After immunoassay, the PDMS microchannel film can be peeled off for fluorescence scanning. In this study, four different concentrations of biotin were immobilized at each zone, respectively. Streptavidin–Cy5 conjugate was driven by ferrofluid. The experimental results showed that adequate fluid actuation was contributive to enhance the immunoassay reactions. The incubation time can be reduced, providing high throughput experiments. Moreover, slow fluid actuation cannot produce enough agitation to increase the reaction rate, while rapid fluid actuation has a negative effect on immunoassay, as the immobilized biotins may be removed from the chip surface.