DNA:Au nanosphere bioconjugates have applications in biosensing and in the bottom-up assembly of materials. These bioconjugates can be selectively assembled into three-dimensional aggregates upon addition of complementary DNA oligonucleotides and can be dissociated by heating above a melting transition temperature at which the DNA duplexes are denatured. Herein we describe the impact of polymeric solutes on the thermal denaturation behavior of DNA:Au nanoparticle bioconjugate assemblies. Polymeric solutes can dramatically impact biochemical reactions via macromolecular crowding. Poly(ethylene glycol)s (PEGs) and dextrans of varying molecular weights were used as crowding reagents. While both PEG and dextran increased the stability of DNA:Au aggregates, melting transition temperatures in the presence of PEG were impacted more significantly. Polymer molecular weight was less important than polymer chemistry and weight percent in solution. For a high (15%) weight percent of PEG, aggregation was observed even in the absence of complementary oligonucleotides. These results underscore the importance of polymer chemistry in addition to physical volume exclusion in macromolecular crowding and point to the importance of understanding these effects when designing biorecognition-based nanoparticle assembly schemes in complex matrixes (i.e., any involving polymeric solutes).

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