Valency and bonding on a larger scale: In molecular systems, valency describes the number of bonds an atom can make with its neighbors. Larger objects such as colloids can be linked together to make connected structures in which the number of connections, or valency, is controlled by the central object. Jones et al. review the two main approaches to creating stiff bonds, based on DNA-based materials synthesis. These approaches allow the construction of molecular-like objects from building blocks much larger than single atoms. Science , this issue 10.1126/science.1260901

Color is everything: Hg²⁺ in aqueous media is detected by the formation of thymidine–Hg²⁺–thymidine coordination complexes, which raises the melting temperature of the DNA‐hybridized gold nanoparticle probes and thus the temperature at which the probes disperse and effect a purple‐to‐red color change. The method has very high sensitivity and selectivity, and it provides a simple and fast colorimetric readout (see picture).

Design rules allow the synthesis of nanoparticle-DNA superlattices in nine different lattices.