Colloidal gold and silver possess plasmonic properties that increasingly are studied for a variety of applications including sensing and optical imaging.  Colloidal particles functionalized with biomacromolecules that interact specifically can be used as single particle sensors or programmed to assemble into multi-particle nanostructures. If the molecular tethers that link multi-particle plasmonic nanostructures are responsive to a stimulus of interest, then the plasmonic properties of the structures can be used to transduce the response. Here, we report pH-driven modulation of the plasmonic properties of multi-particle assemblies linked by pH-sensitive oligonucleotide tethers.  Modulation of plasmon coupling in the reconfigurable nanoassemblies is monitored through spectroscopy of both single assemblies and bulk samples. We demonstrate the reversibility of the nanoassembly reconfiguration through multiple cycles of pH variation without loss in the optical signal.  The sub-100 nm structures offer promise for applications that require real-time measurement of pH in various microenvironments, such as cellular compartments and tumors.

Figure 1: Nano pH sensor