A microfluidic nucleic acid sequencing device characterised by comprising: • a first zone comprising an attachment site contained therein to which the nucleic acid to be sequenced is attached; first microfluidic tubing for causing a first aqueous pyrophosphorolysing medium to flow over the attachment site thereby allowing the nucleic acid to be progressively pyrophosphorolysed into its constituent nucleotide triphosphates and second microfluidic tubing for removing a flowing second aqueous medium containing the nucleotide triphosphates from around the attachment site; • a means to create microdroplets of the second aqueous medium in a water immiscible carrier solvent at least some of which contain one of said nucleotide triphosphates downstream of the first zone; • contact means arranged to introduce consecutively into the second aqueous medium from which the microdroplets are comprised one or more of a pyrophosphatase, a ligase, a polymerase, a capture system labelled with fluorophores in an undetectable state selective for at least one of the nucleotide triphosphates derived from the nucleic acid and an exonuclease or polymerase having exonuclease activity for releasing detectable fluorophores from any used capture system by exonucleolysis; • an array of microdroplet holding sites at which each microdroplet is incubated until detectable fluorescence occurs; • third microfluidic tubing for delivering each microdroplet in turn to one of the holding sites; • a fluorescence-detection system comprising a light-source adapted to impinge on each holding site in turn after incubation, and; • a detector for detecting fluorescence emitted therefrom. • a first zone comprising an attachment site contained therein to which the nucleic acid to be sequenced is attached; first microfluidic tubing for causing a first aqueous pyrophosphorolysing medium to flow over the attachment site thereby allowing the nucleic acid to be progressively pyrophosphorolysed into its constituent nucleotide triphosphates and second microfluidic tubing for removing a flowing second aqueous medium containing the nucleotide triphosphates from around the attachment site; • a means to create microdroplets of the second aqueous medium in a water immiscible carrier solvent at least some of which contain one of said nucleotide triphosphates downstream of the first zone; • contact means arranged to introduce consecutively into the second aqueous medium from which the microdroplets are comprised one or more of a pyrophosphatase, a ligase, a polymerase, a capture system labelled with fluorophores in an undetectable state selective for at least one of the nucleotide triphosphates derived from the nucleic acid and an exonuclease or polymerase having exonuclease activity for releasing detectable fluorophores from any used capture system by exonucleolysis; • an array of microdroplet holding sites at which each microdroplet is incubated until detectable fluorescence occurs; • third microfluidic tubing for delivering each microdroplet in turn to one of the holding sites; • a fluorescence-detection system comprising a light-source adapted to impinge on each holding site in turn after incubation, and; • a detector for detecting fluorescence emitted therefrom.