Colloidal SERS Substrate for the Ultrasensitive Detection of Biotinylated Antibodies Based on Near-Field Gradient within the Gap of Au Nanoparticle Dimers

Abstract

Surface-enhanced Raman spectroscopy (SERS) has demonstrated to be a powerful technique for the ultrasensitive detection of different types of analytes and particularly biomolecules, with the rational design of SERS substrates being one of the most relevant issues for the development of effective detection protocols. In this work, a colloidal SERS substrate consisting of a pair of Au nanorods linked by the molecular bridge biotin/streptavidin/biotin has been obtained and employed for the detection of picomolar quantities of the biotinylated antibodies gliadin IgG and Ara h1 IgG, which is of great interest in food science. As a consequence of the bioconjugation strategy implemented, the SERS substrate, that is, the Au nanorod dimer, presents the advantage of combining in a single nanostructure the capabilities for both direct and indirect detection of the biotinylated antibodies. Furthermore, the experimental results are supported by detailed electrodynamics simulations which takes into account not only the gradient of the near-field enhancements within the hot spot but also the volume occupied by the respective biomolecules. The SERS substrate presented here could be straightforwardly employed for the ultrasensitive detection of other biotinylated biomolecules.

A New Figure of Merit to Assess the SERS Enhancement Factor of Colloidal Gold Nanoparticle Aggregates

“…These phenomena are attributed to the excitation of plasmonic resonances in dimers and larger size aggregates. 41,42 The simulated extinction spectra of the Au NP aggregates, calculated by means of eq 8, are displayed in the respective dashed blue curves shown in Figure 4.…”

“…In these spectra, it can be noted that the LSPR peak is located at around 536 nm, but in contrast with the spectrum of isolated Au NPs, an appreciable decrease of the peak intensity is observed as well as the appearance of shoulders at larger wavelengths between 650 and 750 nm (see Figure S2). These phenomena are attributed to the excitation of plasmonic resonances in dimers and larger size aggregates. , The simulated extinction spectra of the Au NP aggregates, calculated by means of eq , are displayed in the respective dashed blue curves shown in Figure .…”

“…Lastly, it is important to mention that the methodology proposed in this work to assess the SERS enhancement factor of colloidal Au NP aggregates can be applied to different experimental conditions that include nanoparticles of other sizes and metals (for example, silver) as well as other molecules with the capacity to form molecular bridges between two nanoparticles (such as, the streptavidin–biotin pair, , dithiols, , or DNA). The molecule employed in this work (DA) to demonstrate the developed methodology plays the double role of acting as the molecular bridge as well as the analyte.…”

Smart design of high‐performance surface‐enhanced Raman scattering substrates

“…It is well known that the EM field enhancement in nanogaps is more stronger than that of a single particle, 35 and the size of nanogap has a great influence on the electromagnetic field enhancement 36 . The EM field will be amplified at the nanogap between nanoparticles, which are usually called “hot spots.” The interstitial hot spots in the dimer have been studied in detail, such as nanorod dimer, nanosphere dimer, and nanocube dimer 37,38 . Gold nanorods are anisotropic nanoparticles that exhibit two different plasma oscillations: one along the short axis (transverse oscillations) and the other along the long axis (longitudinal oscillations).…”

Theoretical Analysis of Optical Absorption Spectra of Parallel Nanowire Dimers and Dolmen Trimers

“…Experiments have shown enhancements as large as 10–14 orders of magnitude, enabling spectroscopic detection of a single molecule. − Different shapes of nanoparticles have been studied such as nanoshells, , rods, , disks, cubes, cylinders, triangles, and rings . Among them, cylindrical nanowires and nanorods have received a lot of interest because their optical properties are very sensitive to their aspect ratio. − Arrays of nanoparticles are ideal for different applications like biosensing, , nanolasing, and spectroscopy , and as optical waveguides. − In consequence, a number of interesting studies have been performed on ordered arrays of nanoparticles − such as dolmen trimers − and end-to-end and side-by-side arrangements of nanorods. − …”