An apparatus is provided for analysing a polynucleotide. The apparatus includes: a support having an impermeable surface; porous material attached to the impermeable surface; and an array of oligonucleotides with predetermined sequences attached to the porous material. The array includes at least two defined cells, the sequence of the oligonucleotides of a first cell being different from the sequence of the oligonucleotides of a second cell, and the oligonucleotides being shorter than the polynucleotide.