A method of preparing a nucleic acid library in droplets in contact with oil, including: (a) blunt ending nucleic acid fragments in a droplet in the oil to yield blunt-ended nucleic acid fragments; (b) phosphorylating the blunt-ended nucleic acid fragments in a droplet in the oil to yield 5 phosphorylating nucleic acid fragments; coupling A-tails to the phosphorylated nucleic acid fragments in a droplet in the oil to yield A-tailed nucleic acid fragments; and (d) coupling nucleic acid adapter to the A-tailed nucleic acid fragments in a droplet in the oil to yield the nucleic acid library comprising adapter-ligated nucleic fragments.
