Disclosed is a method for the production of a porous polymer membrane suitable for liquid filtration or analyte capture, comprising the steps of: providing a flowable composition (100) on a substrate (220) the composition including at least: photo-activatable monomer molecules, photo activation initiator molecules and photo-activation quencher molecules; providing one or more pulses (L) of laser light at at least one focal point in the composition of sufficient energy to locally polymerise the composition; moving the or each focal point relative to the previously polymerised composition in a continuous or stepwise predetermined manner to a multiplicity of further positions; and repeating the pulse(s) at those further positions such that a three dimensional matrix of the composition is polymerised leaving unpolymerized areas of a size equivalent to conventional polymer membrane pores.