Benchtop chemistry for the rapid prototyping of label-free biosensors: Transmission localized surface plasmon resonance platforms

Abstract

Herein, a simple label-free biosensor fabrication method is demonstrated based on transmission localized surface plasmon resonance (T-LSPR). The platform, which consists of a silver nanoparticle array, can be prepared in just a few minutes using benchtop chemistry. The array was made by a templating technique in conjunction with the photoreduction of Ag ions from solution. This metal surface was functionalized with biotin-linked thiol ligands for binding streptavidin molecules from solution. For an array of 19 nm diameter silver nanoparticles, a redshift in the T-LSPR spectrum of 24 nm was observed upon protein-ligand binding at saturation. The binding constant was found to be 2x10(12) M(-1). Platforms were also fabricated with silver nanoparticles of 34, 55, and 72 nm diameters. The maximum LSPR wavelength shift was nanoparticle size dependent and the maximum sensitivity was obtained with the smaller nanoparticles.

Fig. 1

(Color online) Schematic of the process for fabricating monodisperse silver nanoparticle based T-LSPR biosensors. (a) Silver nanoparticle array templated by an alumina membrane on a thin TiO₂ film during the photoreduction process. (b) Monodisperse silver nanoparticle array after alumina membrane lift off. (c) Biotin/PEG modified silver nanoparticle biosensing array. (d) Binding of streptavidin molecules.

Structure 1

Biotin PEG disulfide

Structure 2

PEG propionate disulfide

Fig. 2

UV/visible spectra of (a) a bare TiO₂ background and four different diameter silver nanoparticle arrays fabricated by (b) 18 nm, (c) 35 nm, (d) 55 nm, and (e) 73 nm templates, respectively.

Fig. 3

UV/visible spectra of 19 nm diameter Ag nanoparticle biosensor array (a) before and after incubated with (b) 10^–12 M and (c) 10^–6 M streptavidin solutions, respectively.

Fig. 4

Binding curve of the biotin-streptavidin interaction using a 19 nm diameter Ag nanoparticle sensor array. The solid dots represent experimental points while the curve represents the fit to a Langmuir isotherm.

Fig. 5

UV/visible spectra of different diameter Ag nanoparticle sensor arrays before and after incubated with 1.0 × 10^–6 M streptavidin solutions. The arrays employed (a) 34 nm, (b) 55 nm, and (c) 72 nm diameter Ag nanoparticles. The spectrum after adsorption is redshifted and slightly higher than the one before adsorption in each case.