Disclosed is a microfluidic device for sequencing a nucleic acid characterised by comprising: €¢ a first zone in which the analyte is contained and progressively digested into a stream of its constituent single nucleotides; €¢ a primary microfluidic pathway connected to the first zone adapted to allow passage of a carrier solvent containing an ordered stream of primary aqueous microdroplets at least some of which contain one of the single nucleotides; €¢ a second zone disposed within the primary microfluidic pathway and comprising a microdroplet injector and/or a coalescence means for sequentially coalescing secondary aqueous microdroplets from a secondary microfluidic pathway into the primary aqueous microdroplets in the ordered stream; €¢ a storage zone connected to the primary microfluidic pathway downstream of the second zone(s) where the primary aqueous microdroplets are stored; €¢ a light source for interrogating the microdroplets at one or more locations downstream of the primary microfluidic pathway and €¢ a photodetector for detecting fluorescence from the primary aqueous droplets at the location(s).