Ultra-sensitive immunoassay biosensors using hybrid plasmonic-biosilica nanostructured materials

Abstract

We experimentally demonstrate an ultra-sensitive immunoassay biosensor using diatom biosilica with self-assembled plasmonic nanoparticles. As the nature-created photonic crystal structures, diatoms have been adopted to enhance surface plasmon resonances of metal nanoparticles on the surfaces of diatom frustules and to increase the sensitivity of surface-enhanced Raman scattering (SERS). In this study, a sandwich SERS immunoassay is developed based on the hybrid plasmonic-biosilica nanostructured materials that are functionalized with goat anti-mouse IgG. Our experimental results show that diatom frustules improve the detection limit of mouse IgG to 10 pg/mL, which is ˜100× better than conventional colloidal SERS sensors on flat glass. Ultra-sensitive immunoassay biosensor using diatom biosilica with self-assembled plasmonic nanoparticles.

Keywords: diatom biosilica; immunoassay; photonic crystal; surface plasmon; surface-enhanced Raman scattering.

Figure 1

Schematic diagram of the SERS immunoassay using diatom biosilica with self-assembled Ag NPs.

Figure 2

SEM images of a single diatom frustule and its fine features.

Figure 3

Bright-field image of a diatom frustule (A) and Raman mapping image of free DTNB (B) on a single diatom frustule.

Figure 4

SEM images of a diatom frustule with self-assembled Ag NPs (A), and the hybrid plasmonic-biosilica immunoassay with mouse IgG at 1.0 × 10⁻¹⁰ g/mL (B) and 1.0 × 10⁻⁷ g/mL (C).

Figure 5

SERS spectra, offset for clarity, acquired at mouse IgG concentration from 10 μg/mL to 1 pg/mL on diatoms frustules (A) and on glass slides (B). Dose-response curves of the Raman peaks at 1331 cm⁻¹ acquired from the SERS spectra on diatom frustules (C) and glass slides (D). (Average SERS intensities and error bars of human IgG at 10 μg/mL on diatom frustules and on glass slides were indicated as the solid lines and gray ribbon in (C) and (D), and the detection limit on diatom frustules and on glass slides were indicated as the red line in (C) and (D)).

Figure 6

Bright field optical images and Raman mapping images of the hybrid plasmonic-biosilica immunoassay with human IgG at 10 μg/mL (A, D), mouse IgG at 1 pg/mL (B, E), and mouse IgG at 10 pg/mL (C, F).