Bubble-free diatoms polymerase chain reaction.

Polymerase chain reaction (PCR) in small fluidic systems not only improves speed and sensitivity of deoxyribonucleic acid (DNA) amplification but also achieves high-throughput quantitative analyses. However, air bubble trapping and growth during PCR has been considered as a critical problem since it causes the failure of DNA amplification. Here we report bubble-free diatom PCR by exploiting a hierarchically porous silica structure of single-celled algae. We show that femtoliters of PCR solution can be spontaneously loaded into the diatom interior without air bubble trapping due to the surface hydrophilicity and pore structure of the diatom. We discover that a large pressure gradient between air bubbles and nanopores rapidly removes residual air bubbles through the periodically arrayed nanopores during thermal cycling. We demonstrate the DNA amplification by diatom PCR without air bubble trapping and growth. Finally, we successfully detect DNA fragments of SARS-CoV-2 with as low as 10 copies/µl by devising a microfluidic device integrated with diatoms assembly. We believe that our work can be applied to many PCR applications for innovative molecular diagnostics and provides new opportunities for naturally abundant diatoms to create innovative biomaterials in real-world applications.