DNA-Directed Self-Assembly of Core-Satellite Plasmonic Nanostructures: A Highly Sensitive and Reproducible Near-IR SERS Sensor

Abstract

The excitation of surface plasmons in metallic nanostructures provides an opportunity to localize light at the nanoscale, well below the scale of the wavelength of the light. The high local electromagnetic field intensities generated in the vicinity of the nanostructures through this nanofocusing effect are exploited in surface enhanced Raman spectroscopy (SERS). At narrow interparticle gaps, so-called hot-spots, the nanofocusing effect is particularly pronounced. Hence, the engineering of substrates with a consistently high density of hot-spots is a major challenge in the field of SERS. Here, a simple bottom-up approach is described for the fabrication of highly SERS-active gold core-satellite nanostructures, using electrostatic and DNA-directed self-assembly. It is demonstrated that well-defined core-satellite gold nanostructures can be fabricated without the need for expensive direct-write nanolithography tools such as electron-beam lithography (EBL). Self-assembly also provides excellent control over particle distances on the nanoscale. The as-fabricated core-satellite nanostructures exhibit SERS activities that are superior to commercial SERS substrates in signal intensity and reproducibility. This also highlights the potential of bottom-up self-assembly strategies for the fabrication of complex, well-defined functional nanostructures with future applications well beyond the field of sensing.