Optimization of film over nanosphere substrate fabrication for SERS sensing of the allergen soybean agglutinin

Abstract

Metal film over nanosphere (FON) substrates are a mainstay of surface‐enhanced Raman scattering (SERS) measurements because they are inexpensive to fabricate, have predictable enhancement factors, and are relatively robust. This work includes a systematic investigation of how the three major FON fabrication parameters—nanosphere size, deposited metal thickness, and metal choice—impact the resulting localized surface plasmon resonance (LSPR). With these three parameters, it is quite simple to fabricate FONs with an optimal LSPR for SERS experiments with various excitation wavelengths. Some SERS experiments require that the substrates be incubated in organic solvents that have the potential to damage the substrate; as such, this work also explores how solvent incubation impacts the physical and optical properties of the FON substrate. Although no significant increase in physical damage is obvious, the LSPR does shift significantly. Finally, these optimized FONs were employed for the sensing of an important allergen, soybean agglutinin. The FONs were modified with a glycopolymer that has affinity for soybean agglutinin and clear Raman bands demonstrate detection of 10 μg/ml soybean agglutinin. Overall, this work serves the dual purpose of both sharing critical details about FON design and demonstrating detection of an important lectin analyte.

Chemical Enhancement vs Molecule–Substrate Geometry in Plasmon-Enhanced Spectroscopy

“…These MFON SERS surfaces have high dispersion in terms of hotspot size and formation because of the fabrication procedure that does not provide a homogeneous size of the crystallites and spacing. The dispersion in hotspots naturally leads to a very wide LSPR that depends not only on the material but also on the nanosphere size and metal thickness. − We justify neglecting dispersion effects by considering the intensity ratio changes for Raman peaks observed within the same spectral range (<2 nm apart, marked in Figure S22) that are the opposite for Ag and Au FON, which different LSPR responses cannot explain. However, a direct experimental determination of the optical response from these MFON opaque substrates in follow-up work could provide definite evidence on enhancing contributions that do not originate from geometry or charge-transfer effects.…”

Preface to the special issue dedicated to Professor Richard P. Van Duyne (1945–2019)

“…They employ optimized FONs for the sensing of an important allergen, soybean agglutinin with a limit of detection of 10 μg/ml. [22] Zhao et al investigate the Raman enhancement mechanism of the 1,2-bis (4-pyridyl) ethylene (BPE) on the PbI 2 . The results prove that the BPE molecule enters the lattice of PbI 2 and that the PbI 2 is a special adsorbent, demonstrating and providing a better understanding of the Raman enhancement mechanism of PbI 2 .…”

Towards a protein-selective Raman enhancement by a glycopolymer-based composite surface

“…modified the metal film on nanosphere (FON) substrates with glycopolymers, and successfully enhanced the Raman signal of soybean agglutinin. 50 Chia et al designed polyanilinecontaining galactosylated gold nanoparticles, and the Raman signal of bacteria was enhanced by the reaction of the galactoside moiety with b-galactosidase from bacteria. 51 Therefore, the specific interaction between certain proteins (lectin) and glycopolymers can be utilized for the selective adsorption of proteins, thus realizing specific SERS detection.…”