Plasmonics and Nanophotonics

Plasmonic nanoparticles are discrete metallic nanoparticles that have unique optical properties, and are increasingly being incorporated into commercial products and technologies.  These technologies, which span fields ranging from photovoltaics to biological and chemical sensors, take advantage of the extraordinary efficiency of gold and silver plasmonic nanoparticles at absorbing and scattering light.  Additionally, unlike most dyes and pigments, plasmonic nanoparticles have a color that depends on their size and shape and can be tuned to optimize performance for individual applications without changing the chemical composition of the material. 

Figure 1: (Left) Gold and silver nanoparticles of varying sizes and shapes.  From left to right: 80 nm silver nanospheres, 20 nm silver nanospheres, 40 nm gold nanospheres, 12 nm gold nanospheres, 200 nm silver nanoplates, 120 nm silver nanoplates, 60 nm silver nanoplates. (Right) Plasmonic nanoparticles can simultaneously have large absorption and scattering cross sections.  Here the particles absorb green and red light, causing transmitted light to appear blue, and scatter red light, causing scattered light to appear red.

NanoComposix has developed a number of technologies which take advantage of plasmonic and photonic nanomaterials.  These technologies include ultrabright surface enhanced Raman scattering (SERS) tags for multiplexed and multiparameter cytometry, surface enhanced fluorescence (SEF) nanotags for ultrasensitive detection of biomolecules, and as a new class of photothermal therapeutic materials.  Additionally, we are developing technologies to improve the performance of photovoltaic cells and photonic waveguides.

For more information about nanoComposix’s plasmonics and nanophotonics technologies, please contact us at info@nanocomposix.com, call us at (858) 565-4227, or read about our plasmonic materials below. 

NanoComposix Plasmonic Nanoparticle Product Lines:

Silver Particles 

Spherical: High quality spherical silver nanoparticles have peak wavelengths ranging from 400 nm - 520 nm and absorption/scattering ratios that vary with size.  Available in two formulations:

  • NanoXact (0.02 mg/mL), with peak optical densities (ODs) of up to 2.5 OD/cm
  • BioPure (1 mg/mL), with peak optical densities of up to 130 OD/cm

Plates: Sprix silver nanoplates with extremely high optical efficiencies and peak wavelengths that can be tuned from 550 nm to 950 nm by changing the plate aspect ratio (length:width).  Available in two formulations:

  • 1 mg/mL with peak optical densities of up to 100 OD/cm
  • At custom concentrations with peak optical densities of up to 1000 OD/cm

Wires: Sprix silver nanowires with diameters of <100 nm and lengths up to 20 microns.  Sprix nanowires can be used for plasmonic and photonic applications at both visible and infrared wavelengths.  Available in two formulations:

  • Short Sprix Nanowires: Available with lengths of 2-5 microns
  • Long Sprix Nanowires: Available with lengths of up to 20 microns

Gold Particles 

Spherical: High quality spherical gold nanoparticles have peak wavelengths ranging from 515 nm - 560 nm and absorption/scattering ratios that vary with size.  Available in 2 formulations:

  • NanoXact (0.05 mg/mL), with peak optical densities (ODs) of up to 1.6 OD/cm
  • BioPure (1 mg/mL), with peak optical densities of up to 32 OD/cm

Nanoshells: Gold nanoshells are nanoscale silica cores surrounded by an ultra-thin gold shell that can be tuned to strongly absorb or scatter light at any wavelength in the visible and near-IR regions of the electromagnetic spectrum.

  • NanoXact (0.05 mg/mL) or BioPure (1 mg/mL) concentrations in water
  • Polyvinylpyrollidone (PVP) or Polyethylene Glycol (PEG) surface coatings
  • 800 nm resonant (120 nm silica core with a 15 nm gold shell)

 

More Information

What is a Surface Plasmon?

The remarkable optical properties of plasmonic materials occurs because the conduction electrons on the nanoparticle surface undergo a collective oscillation when excited by light at specific wavelengths (Figure 2, left).  This oscillation, which is known as a surface plasmon resonance (SPR), results in the unusually strong scattering and absorption of light.  In fact, plasmonic nanoparticles can have optical cross sections up to 10 times larger than their physical cross sections, allowing individual nanoparticles to be imaged using dark field microscopy (Figure 2, middle, right).  Interested in learning more?  Please see our the Plasmonics Tutorial in our Knowledge Base.

 

Figure 2: (Left) Schematic of surface plasmonc resonance where the free conduction electrons in the metal nanoparticle are driven into oscillation due to strong coupling with incident light.  (Middle) Dark field microscopy image of 50 nm gold nanoparticles. (Right) Dark field microscopy image of 60 nm silver nanoparticles.

Applications

Plasmonic nanoparticles have numerous applications including:

  • Diagnostic Applications: Gold and silver nanospheres are used as reagents in numerous assays (including lateral flow assays) where the nanoparticles are used for qualitative or quantitative detection.
  • BioSensing and Chemical Sensing Applications: Plasmonic nanoparticles including gold and silver nanospheres and Sprix silver nanoplates can be used to create surface-enhanced Raman scattering (SERS) tags for highly multiplexed biosensing1-3, and surface enhanced fluorescence (SEF, sometimes called metal enhanced fluorescence, MEF) tags for ultrasensitive detection4.  Particles can also be engineered to detect ultralow concentrations of chemical agents by enhancing the intrinsic Raman scattering signal by up to 14 orders of magnitude.
  • Optical Applications/Light Harvesting:  Gold and silver nanospheres, silver nanoplates, and silver nanowires are used as nanoscale optical antennas to improve light harvesting in solar cells and other devices5.
  • Therapeutics: Plasmonic nanoparticles are used to thermally ablate tumors where the extremely high absorption efficiency of the nanoparticles results in rapid particle heating that can selectively destroy targeted cancerous cells. 

Detailed Description of Plasmonic Nanoparticle Optical Properties

NanoXact and BioPure Silver Nanospheres:  The optical properties of silver nanospheres are a function of the nanoparticle diameter.  As the diameter increases, the peak extinction (scattering + absorption) shifts to longer wavelengths and broadens, and the nanoparticle albedo (a ratio of scattering to total extinction) increases (Figure 3).  At diameters greater than 80 nm, a second peak becomes visible at shorter wavelengths than the primary peak.  This secondary peak is due to a quadrupole resonance that has a different electron oscillation pattern than the primary dipole resonance.

Figure 3: (Left) Extinction (the sum of scattering and absorption) spectra of NanoXact silver nanoparticles with diameters ranging from 10 - 100 nm at mass concentrations of 0.02 mg/mL.  BioPure nanoparticles have optical densities that are 50-times larger. (Right) Plot of silver nanosphere albedo (a ratio of scattering to total extinction) as a function of nanoparticle diameter.

Sprix Silver Nanoplates:  The optical properties of silver nanoplates is a function of the aspect ratio (length:width), with plates with larger aspect ratios having peaks at longer wavelengths.  By precisely controlling the plate diameter and thickness, the nanoplate’s optical resonance can be tuned to peak at specific wavelengths in the visible and near-IR spectral regions (Figure 4).   This allows plates to be tuned to interact with specific laser lines, including 532 nm, 632.8 nm, 660 nm, 785 nm, 808 nm, and 1064 nm lasers.

Figure 4: (Left) Extinction spectra of silver nanoplates with varying aspect ratios. (Right) TEM image of silver nanoplates.

Sprix Silver Nanowires:  Plasmonic silver nanowires support resonances in the mid to long range infrared, with wires with larger aspect ratios (a ratio of wire length:width) supporting resonances at longer wavelengths.  Additionally, because Sprix wires have lengths longer than the wavelengths of visible light, visible light propagates through silver nanowires, and can couple through crossed nanowires, and to other nearby plasmonic nanoparticles (Figure 5).  

Figure 5: (Left) White light dark field microscopy image of Sprix nanowires with lengths of 20 microns.  Because the nanowires have lengths much longer than the wavelengths of visible light, they scatter all wavelengths of visible light and appear white/gold. (Right) Dark field microscopy image of Sprix nanowires with lengths of 4 microns.  When illuminated with a red laser, the wires efficiently scatter the incident light and therefore appear red.

NanoXact and BioPure Gold Nanospheres:  The optical properties of gold nanospheres is a function of the nanoparticle diameter.  As the diameter increases, the peak plasmon resonance shifts to longer wavelengths and broadens, and the nanoparticle albedo (a ratio of scattering to total extinction) increases (Figure 6).  Additionally, as the particles get larger, the particle scattering peak moves to longer wavelengths than the absorption peak (This can be observed by modeling different sized gold nanospheres using our Online Mie Theory Simulator).

Figure 6: (Left) Extinction (the sum of scattering and absorption) spectra of NanoXact gold nanoparticles with diameters ranging from 10 - 100 nm at mass concentrations of 0.05 mg/mL.  BioPure nanoparticles have optical densities that are 20-times larger. (Right) Plot of gold nanosphere albedo (a ratio of scattering to total extinction) as a function of nanoparticle diameter.

References

  1. D.S. Sebba, D.A. Watson, J.P. Nolan.  High Throughput Single Nanoparticle Spectroscopy.  ACS Nano, 2009, 3 (6) 1477-1484.
  2. R.T. Hill, J.J. Mock, D.S. Sebba, S.J. Oldenburg, S.Y. Chen, A.A. Lazarides, A. Chilkoti, D.R. Smith.  Leveraging Nanoscale Plasmonic Modes to Achieve Reproducible Enhancement of Light.  Nano Letters, 2010, 10 (10) 4150-4154.
  3. Willets, K.A. and R.P. Van Duyne, Localized Surface Plasmon Resonance Spectroscopy and Sensing. Annual Review of Physical Chemistry, 2007, 58 (1) 267-297.
  4. J.R. Lakowicz, C.D. Geddes, I. Gryczynski, J. Malicka, Z. Zhang, R. Badugu, J. Huang.  Advances in Surface Enhanced Fluorescence.  Journal of Fluorescence, 2004, 14 (4) 425-441.
  5. A.P. Kulkarni, K.M. Noone, K. Munechika, S.R. Guyer, D.S. Ginger.  Plasmon-Enhanced Charge Carrier Generation in Organic Photovoltaic Films Using Silver Nanoprisms.  Nano Letters, 2010, 10 (4) 1501-1505.