Manipulating the hydrophobicity of DNA as a universal strategy for visual biosensing.

Current visual biosensing methods, including colorimetric-based, fluorescence-based and chemiluminescence-based methods, are inappropriate for the hundreds of millions of people affected by color blindness and color weakness. Compared with these available methods, a droplet motion-based strategy might be a promising protocol for extension to a wider user base. Here we report a protocol for manipulating the hydrophobicity of DNA, which offers a droplet motion-based biosensing platform for the visual detection of small molecules (ATP), nucleic acids (microRNA) and proteins (thrombin). The protocol starts with target-triggered rolling-circle amplification that can readily generate short single-stranded DNA (ssDNA) fragments or long ssDNA. By exploiting macroscopic wetting behavior and molecular interaction, one can tailor the conformation of ssDNA on the water-oil interface to control the relevant DNA hydrophobicity. The wettability of DNA can be translated into visual signals via reading the sliding speed or the critical sliding angle. The time range for the entire protocol is ∼1 d, and the detection process takes ∼1 min.