Peptide-Induced Chiral Plasmonic Hotspots for Ultrasensitive Chirality-Dependent Raman Analysis of Proteins

Abstract

Highly sensitive chirality-dependent Raman analysis capable of probing protein structural information is important for bioanalytical applications. Although chiral plasmonic nanostructures can generate chirality-dependent electromagnetic fields, efficient localization of proteins within these hotspots under hydrated conditions remains challenging, limiting their application to chirality-dependent Raman analysis. Here, peptide-induced chiral plasmonic hotspots are introduced in gold nanotriangle–hydrogel platforms (c-AuTAG) for ultrasensitive chirality-dependent Raman analysis of proteins. Enantiomeric oligo-proline peptides introduce well-defined chirality into plasmonic nanogaps while minimizing protein adsorption and charge-dependent interactions that would otherwise hinder efficient analyte localization within plasmonic hotspots. The peptide-induced chiral hotspots are integrated with the previously developed GFT delivery strategy. Efficient analyte delivery through antifouling interfaces enables protein accumulation within dynamically tunable plasmonic hotspots. The system exhibits exceptionally large SERS chiral anisotropy factors (gSERS-ChA > 1.8) despite a small far-field optical dissymmetry factor (goptical ≈ 0.001), consistent with strong chirality-dependent plasmonic enhancement. The observed response reflects interactions between localized plasmonic near fields and vibrational-mode-dependent molecular polarizability. Ultrasensitive detection down to fg/mL is achieved within seconds using a conventional Raman spectrometer with linearly polarized excitation, enabling differential vibrational spectral analyses analogous to those used in Raman optical activity (ROA) without circular polarization optics. This platform enables ultrasensitive chirality-dependent Raman analysis of biomolecules in hydrated environments while preserving native structures, providing a practical approach for probing protein secondary structures, conformational changes, and biologically relevant molecular modifications.