Empirical design for gold nanoparticle arrays for nano-biosensor

Maher Z. Ahmed

Department of Physics & AstronomyThe University of Western Ontario

ES 530b

Glass substrate

Choosing the substrate for nano gold particles

Absorption Characterization for the glass substrate

Absorption peak @ 379 nm

Typical LSPR peak and sensing shift

Flat is the most suitable

Electrodynamics calculations

E extinction coefficient of metal nanoparticle εr real components of the metal dielectric functionεi imaginary components of the metal dielectric functionεout dielectric constant of the external environment.χ shape paramter, 2 for sphere -> 20 spheroids a radius of spherical nanoparticleN areal density of the nanoparticles

discrete dipole approximation (DDA) for other shapes

Plasmonic Materials for Surface-Enhanced Sensing and SpectroscopyAmanda J. Haes, Christy L.Haynes et al. MRS Bulletin 30 (2005) 368-375

Material

Environment

shape

Size

Mie theory for sphericalResonance condition εr = - x εout

A. J. Haes et al. MRS Bulletin 30 (2005) 368-375

LSPR for Ag nanoparticles (labeled A–H) fabricated by Nanosphere Lithography (NSL) in-plane width a out-of-plane height b

Effect of size the LSPR peak wavelength

K.-H. Su, et al. Nano Lett., Vol. 3, No. 8, 2003 p. 1087-1090

(a) Scattering spectra of elliptical Au particles fabricated by E-beam lithography (EBL)

short axis lengths of 84, 91, 96,

102, and 104 nm.

The long/short axis aspect ratio is kept at about 1.55.

(b) Measured plasmon resonant wavelength as a function of the particle short-axis length.

3.7% shift for cylinder

Effect of shape on the LSPR peak wavelength

(a) Extinction efficiency (ratio of cross section to effective area) of silver nanoparticles in vacuum. Each particle has the same volume of a sphere with a radius of 50 nm.

|E|2 contours (E is electric field) for a (b) sphere, cube, and (d) pyramid, plotted for wavelengths corresponding to the plasmon peak in (a)

A. J. Haes et al. MRS Bulletin 30 (2005) 368-375

K.-H. Su, et al. Nano Lett., Vol. 3, No. 8, 2003 p. 1087-1090

Comparison of computer-simulated (□, O) and experimentally (∆) measured resonant wavelength shifts as a function of the gap between two particles.

Effect of interparticle distance on the LSPR peak wavelength

0.016

sphere of diameter 30 nm

5.13 maximum absorption @ λ= 356.51 n m

NanoSphere Optics Lab Field SimulatorUsing Mie theory for nano spherical particle in air

simplification interparticle distance 30 nmthe shift in peak 0.015 for one direction for 4 4 x 0.015 x 356.5= 21

expected peak λ= 377 n m + cylindrical shift 15nm = 392

www.nanohub.org

Absorption 0.047% @ λ= 377 n m

Absorption 0.042% @ λ= 392 n m

Absorption peak @ 379 nm

Absorption 0.042% @ λ= 392 n m

max

max maxmax

, ,

( , )

V

V

d dV dV

Simulation using Mie Theory to LSPR wavelength nano gold spheres of different volumes