The present disclosure provides methods for barcoding a plurality of DNA samples using a microarray of barcode-containing transposase complexes. In some embodiments, the DNA samples and transposase complexes are present in aqueous droplets on the surfaces of opposing substrates, which allows a single DNA sample droplet to be combined with a single transposase-complex droplet. The barcoded DNA in the combined droplets can be used for any number of purposes, including as templates for amplification and sequencing.