Smart Plasmonic Sensors

Biosensors and Biointerfaces Group - Research Projects

Metal nanoparticle assemblies-based optical sensors for single molecule detection

Plasmonic sensors are nanodevices that are made of metal (mostly gold and silver) nanoparticles. A unique feature of metal nanoparticles is their ability to support resonance oscillation of free electrons (known as surface plasmons) in response to light. The excitation of surface plasmons results in a large electric field in the close vicinity of the metal surfaces (panel a) that is orders of magnitude higher than that of the excitation field. This field enhancement is particularly strong at interparticle gaps of metal nanoparticle assemblies (e.g. core-satellite nanostructures, panel b and c), typically referred to as “hot spots”. Such assemblies enable fluorescence or Raman signals of analytes to be detected at extreme low concentration levels (panel d). The strength of the electric field enhancement provided by a given plasmonic assemblies can be fine-tuned by tailoring the metal nanoparticle shape, interparticle gap, and assembly configuration. This also provides the means to adjust the wavelength at which surface plasmon resonance occurs. Tight control over these parameters is a paradigm for the fabrication of cheap, ultrasensitive and reproducible plasmonic sensors. This project aims to (1) identify plasmonic assemblies with exceptionally high electric field enhancement through modeling, (2) develop nanofabrication methods to produce these assemblies, and (3) push their sensitivity down to single molecule level using Raman spectroscopy.

 

Above: (a) Schematic representation of localised surface plasmons of a metal nanosphere, (b) Spatial distribution of electric field enhancement of a core-satellite assembly, (c) A typical SEM image of core-satellite nanostructures composed of gold nanoparticles, (d) Raman spectra of thiolbenzene adsorbed on core-satellite nanostructures (peaks highlighted with stars are from silicon substrate).

For more information on this project see:

  • Zheng, YH et al. 2013 ‘DNA-directed self-assembly of core-satellite plasmonic nanostructures: a highly sensitive and reproducible near-IR SERS sensor’, Adv. Funct. Mater., vol. 23, pp. 1519.
  • Anstaett, P, Zheng, YH et al. 2013 ‘Synthesis of stable peptide nucleic acid-modified gold nanoparticles and their assembly onto gold surfaces’, Angew. Chem. Int. Ed., vol. 52, pp. 421.
  • Thai, T, Zheng, YH et al. 2012 ‘Self-assembly of vertically aligned gold nanorod arrays on patterned substrates’, Angew. Chem. Int. Ed., vol. 51, pp. 8732.
  • Zheng, YH et al. 2011 ‘Gutenberg-style printing of self-assembled nanoparticle arrays: electrostatic nanoparticle immobilization and DNA-mediated transfer’, Angew. Chem. Int. Ed., vol. 50, pp. 4398.
  • Lalander, CH, Zheng, YH et al. 2010 ‘DNA-directed self-assembly of gold nanoparticles onto nanopatterned surfaces: controlled placement of individual nanoparticles into regular arrays’, ACS Nano, vol. 4, pp. 6153.
  • Zheng, YH et al. 2010 ‘ Nanoscale force induced size-selective separation and self-assembly of metal nanoparticles: sharp colloidal stability thresholds and hcp ordering’, Chem. Commun., vol. 46, pp. 7963.