A method for writing data including a sequence of bits, the data being written in a form of DNA, by in-vitro enzymatically producing memory DNA from a strand of memory writing substrate DNA is disclosed. In one aspect, the method includes repeating of: receiving a sub-sequence of the sequence of bits, the sub-sequence including at least one bit; selecting memory nucleotides based on the sub-sequence; contacting, in liquid medium including the strand of memory writing substrate DNA contacted with an enzyme, the selected memory nucleotides and the enzyme; and synthesizing a portion of the memory DNA from a portion of the strand of memory writing substrate DNA by the enzyme and at least one of the memory nucleotides of the solution, thereby producing memory DNA including memory nucleotides corresponding to bits of the sequence of bits. The disclosed technology further relates to a micro-fluidic system including a microfluidic chip and a controller.