A novel droplet dosing strategy-based versatile microscale biosensor for detection of DNA, protein and ion

•Channel-fouling, which is a negative phenomenon, is exploited in droplet platform.•A novel droplets dosing strategy, contact-induced droplets dosing (CIDD) is developed.•A microscale biosensor based on CIDD is built for multiple biosensing.•This biosensor possesses excellent practicability and potential high-throughput. Channel-fouling is a pervasive problem which is wanted to be avoided in microfluidic system. Herein, by making good use of this negative phenomenon, a novel and simple droplets dosing strategy, contact-induced droplets dosing (CIDD) is developed based on the adsorption and desorption of PDMS surface. As a proof-of-concept demonstration, a DNA intercalating reagent (SYBR Green I) is prefilled in the section of main channel and non-specifically adsorbed on the channel wall. When the droplets that contained double-stranded DNA (dsDNA) pass through the dosing region, SYBR Green I is removed from the channel wall and transferred into droplets rapidly due to the stronger interaction of aqueous droplets with SYBR Green I caused by the contact between droplets and channel wall. Thus, significant fluorescence responses of droplets are observed. Since this CIDD-based microfluidic platform is capable to perform a variety of biosensing through translating into the detection of dsDNA. In this article, the analytical targets, ranging from protein to DNA, and to a toxic metal ion were successfully quantified in this sensing platform. The satisfactory results in the analysis of dsDNA in human serum and Hg2+ in real water samples demonstrate that this droplet-based biosensor possesses great potential for detecting real samples.