Droplet-based protein chip with Ni-Co coated surface

This Letter describes the implementation of a droplet-based protein chip with an Ni-Co alloy layer for conducting immunoassays. The proposed chip consists of a substrate of a printed circuit board and a microchannel layer. On the substrate surface, an Ni-Co coating was fabricated by electrodeposition to immobilise the histidine-tagged protein. Through droplet fusion and mixing, the fused droplets aligned at the downstream position of the microchannel and were immobilised by the Ni-Co layer for further incubation and fluorescence detection. The experimental results showed that the sample which is encapsulated by the carrier fluid does not have evaporation and contamination problems. Therefore strong fluorescence intensity proportional to the sample concentration can be obtained. The fluorescence intensity is also related to the droplet size. An extremely low concentration of encapsulated content in a smaller droplet might result in arduous fluorescence detection. This proposed droplet-based protein chip allows the operation sequence of the immunoassay to be conducted automatically through the manipulation of droplets. Moreover, the fabrication process is simple and the chip can be implemented to immobilise any functional proteins with His-tag attached.