  We propose a new strategy to improve the self-assembly properties of
DNA-functionalised colloids. The problem that we address is that
DNA-functionalised colloids typically crystallize in a narrow temperature
window, if at all. The underlying reason is the extreme sensitivity of
DNA-mediated interactions to temperature or other physical control parameters.
We propose to widen the window for colloidal crystallization by exploiting the
competition between DNA linkages with different nucleotide sequences, which
results in a temperature-dependent switching of the dominant bond type.
Following such a strategy, we can decrease the temperature dependence of
DNA-mediated self assembly to make systems that can crystallize in a wider
temperature window than is possible with existing systems of DNA functionalised
colloids. We report Monte Carlo simulations that show that the proposed
strategy can indeed work in practice for real systems and specific, designable
DNA sequences. Depending on the length ratio of the different DNA constructs,
we find that the bond switching is either energetically driven (equal length or
`symmetric' DNA) or controlled by a combinatorial entropy gain (`asymmetric'
DNA), which results from the large number of possible binding partners for each
DNA strand. We provide specific suggestions for the DNA sequences with which
these effects can be achieved experimentally.
