Microspectroscopic SERS detection of interleukin-6 with rationally designed gold/silver nanoshells

Abstract

Rationally designed gold/silver nanoshells (Au/Ag-NS) with plasmon resonances optimized for red laser excitation in order to minimize autofluorescence from clinical samples exhibit scattering cross-sections, which are ca. one order of magnitude larger compared with solid quasi-spherical gold nanoparticles (Au-NPs) of the same size. Hydrophilic stabilization and sterical accessibility for subsequent bioconjugation of Au/Ag-NS is achieved by coating their surface with a self-assembled monolayer (SAM) of rationally designed Raman reporter molecules comprising terminal mono-and tri-ethylene glycol (EG) spacers, respectively. The stability of the hydrophilically stabilized metal colloid was tested under different conditions. In contrast to metal colloids coated with a SAM without terminal EG spacers, the hydrophilically stabilized SERS particles do not aggregate under physiologically relevant conditions, i.e., buffer solutions with high ionic strength. Using these rationally designed SERS particles in conjunction with a microspectroscopic acquisition scheme, a sandwich immunoassay for the sensitive detection of interleukin-6 (IL-6) was developed. Several control experiments demonstrate the high specificity of the assay towards IL-6, with a lowest detectable concentration of ca. 1 pg mL À1 . The signal strength of the Au/Ag-NS is at least one order of magnitude higher compared with hydrophilically stabilized, non-aggregated solid quasi-spherical Au-NPs of the same size.

Bioconjugation of SERS nanotags and increasing the reproducibility of results

“…SERS technique with multiplexing capacity is a novel technique for the sensitive and selective detection of biomolecules such as proteins [2]. A typical SERS immunodetection is based on the formation of a direct or sandwich immunocomplex, in which the antibodies are immobilized on SERS substrates.…”

Molecularly linked 3D plasmonic nanoparticle core/satellite assemblies: SERS nanotags with single-particle Raman sensitivity

“…[13][14][15] The assembly process can be mediated and efficiently controlled by molecular linkers. 16 Examples are biomacromolecules with recognition elements such 25 as DNA 17,18 as well as molecules comprising two terminal surface-seeking groups such as dithiols 19 or diamines 20 . Nanodiagnostic applications of highly SERS-active NPs for the selective detection and localization of analytes exploit the characteristic vibrational Raman signature of reporter molecules 30 on the metal surface.…”

“…On the other hand, PVP-capped satellites are not as good for forming assemblies as citrate-capped satellites are. These observations can be explained by the surface affinity of the 25 bifunctional crosslinker. In the case of PVP-capped core particles, the crosslinker binds via the thiol group to the gold surface of the core particles.…”

“…Specifically, we employ 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB) as the actual Raman reporter and conjugate it to a bisamino-diethylene glycol (H 2 N-DEG-NH 2 ) for both hydrophilic stabilization (ethylene glycol) 24,25 and subsequent electrostatic conjugation (amino group) 26,27 . Upon incubation with 80-nm, 55 PVP-capped AuNP cores, the conjugate (DTNB-DEG-NH 2 ) forms a Raman-active (DTNB), positively charged (terminal -NH 3 + ) and hydrophilically stabilized (DEG) self-assembled monolayer (SAM), which replaces PVP by the formation of Au-S bonds 28 (Fig.…”

Enabling Rapid and Specific Surface-Enhanced Raman Scattering Immunoassay Using Nanoscaled Surface Shear Forces

“…11 The assay time was reduced from 24 h to 10 min with a 10-fold improvement in detection limit. Despite these attempts being successful in reducing assay times, 10,11 nonspecific adsorption of nontarget molecules still remains the biggest challenge in immunoassays, 12,13 in particular, SERS-based immunoassays, 3,9 and very few attempts have been reported to address this longstanding problem. To circumvent this problem, herein, we propose an innovative platform that utilizes nanoscaled alternating current electrohydrodynamic (ac-EHD)-induced surface shear forces to enhance the capture efficiency (i.e., increase diffusion of target and SERS particles) as well as B significantly reduce the nonspecific binding of molecules from the electrode surface.…”