Combinatorial-Entropy Driven Aggregation in DNA-Grafted Nanoparticles.

We use computer simulations to study the interactions between a pair of nanoparticles (NP) grafted with DNA strands ending with a sticky palindromic single stranded sequence. This situation is different from the non-palindromic case since the sticky ends can also associate with strands grafted on the same particle. We demonstrate that at low temperature the strength of the attractive interparticle interaction does not depend on the selected DNA sticky sequence but arises purely from a combinatorial entropy contribution. We evaluate theoretically and verify numerically this entropic contribution originating from the number of distinct bonding patterns associated to intra and inter particle binding. This attraction becomes more favorable with decreasing inter-NP distance because more sticky ends can participate in making this choice.