Use of silver nanoparticles to enhance surface plasmon-coupled emission (SPCE)

Abstract

We report that self-assembled monolayers of colloidal silver nanoparticles can increase the intensity of the surface plasmon-coupled emission (SPCE) signal from sulforhodamine 101 (S101). The S101 was spin coated on a glass slide coated with a layer of continuous silver, and a silica layer upon which the nanoparticle layer was self-assembled. Of the various colloid sizes studied, the 40 nm colloids showed both the highest enhancements in the SPCE signal and the largest extent of plasmon coupling, defined as the ratio of SPCE to Free Space signal. Our findings reveal a new technique that can be potentially employed to increase the sensitivity of SPCE applications.

Fig. 1

(Top) Schematic of the configuration of a film of S101 in PVA spin coated on top of silver colloidal nanoparticles assembled on a ∼42 nm thick silver film. (Bottom) Geometrical scheme for measurement of angle-dependent emission.

Fig. 2

Polar intensity plots showing surface plasmon-coupled emission (SPCE) and Free Space emission of S101 in PVA on ∼42 nm silver films with: (a) control, no Ag colloid, (b) 20 nm Ag colloid, (c) 40 nm Ag colloid and (d) 80 nm Ag colloid. Only one quadrant in both the Free Space and SPCE region is presented for clarity.

Fig. 3

(Top) Emission spectra from S101 in PVA on ∼42 nm silver films with no Ag colloid (control), and with 20 nm, 40 nm and 80 nm Ag colloid. (Inset) S101 emission data from 40 nm Ag colloid sample showing SPCE signal to be completely p-polarized. (Bottom) Enhancement factor for SPCE signal as a function of Ag colloid size. The enhancement factor is defined as the ratio of the SPCE signal of the colloid sample to that of the SPCE signal of the control sample.

Fig. 4

Surface plasmon-coupled emission (SPCE) spectra and Free Space emission spectra from S101 in PVA on ∼42 nm silver films with: (a) control, no Ag colloid, (b) 20 nm Ag colloid, (c) 40 nm Ag colloid, (d) 80 nm Ag colloid and (e) ratio of intensity of SPCE signal to Free Space signal for all the samples. Note 0 nm colloid size denotes the control sample.