Advantages and drawbacks of the use of immobilized 'green-synthesized' silver nanoparticles on gold nanolayer for near-field vibrational spectroscopic study of riboflavin

摘要

Nanoscopic near-field techniques are powerful tools in the chemical nanoanalysis thanks to their lateral resolution and the ability to detect trace amounts limiting to the single-molecule level and study molecular interactions at the same level. To achieve these goals, a gap mode is preferred, in which a large-scale plasmonic enhancing substrate with the adsorbed analyte is used and the Au/Ag scanning tip is approached to obtain high enhancement of the local electric field and form the hot-spot between the Au/Ag tip and the Au/Ag plasmonic surface. The appropriate enhancing substrate is crucial considering the enhancement factor and the optical response quality. This study focused on the riboflavin detection by tip-enhanced Raman scattering (TERS) and scanning near-field infrared microscopy (SNIM), immobilized Ag nanoparticles (NPs), synthesized by flavonoids reduction were employed. AgNPs immobilized on Au nanolayer via a dithiol-linker represent effective substrate exhibiting appropriate morphology and optical properties. SNIM provided insight into the intensity distribution of the riboflavin optical response. The optical amplitude and phase images indicate better adsorption of riboflavin on the AgNP-coated surface than on the Au-coated glass. TERS shows interferences of flavonoid residues on some substrates, but the riboflavin limit of detection was improved compared to surface-enhanced Raman scattering.