Superhydrophilic/Superhydrophobic Droplet Microarrays of Low Surface Tension Biofluids for Nucleic Acid Detection

Superhydrophilic/superhydrophobic patterned surfaces can be used to create droplet microarrays. A specific challenge with the liquids needed for various biomedical applications, as compared to pure water, is their lower surface tension and potential for contaminating the surfaces through adsorption. Here, a method is shown to create biofluid droplet microarrays using discontinuous dewetting of pure water, an oil protective layer, and finally biofluid exchange with the water droplet array. With this method, a droplet array of a viscous nucleic acid amplification solution can be formed with a low surface tension of 34 mN m⁻¹ and a contact angle of only 76° with the used hydrophobic coating. This droplet array is applied for nucleic acid detection of SARS-CoV-2 virus using strand invasion-based amplification (SIBA) technology. It is shown that by using an array of 10 000 droplets of 50 µm diameter the limit of detection is 1 RNA copy µL⁻¹. The results demonstrate that SIBA on droplet microarrays may be a quantitative technology.