Near-field Raman spectroscopy of biological nanomaterials by in situ laser-induced synthesis of tip-enhanced Raman spectroscopy tips

Abstract

We report a new approach in tip-enhanced Raman spectroscopy (TERS) in which TERS-active tips with enhancement factors of ∼10(-5)× can be rapidly (1-3 min) produced in situ by laser-induced synthesis of silver nanoparticles at the tip apex. The technique minimizes the risks of tip contamination and damage during handling and provides in situ feedback control, which allows the prediction of the tip performance. We show that TERS tips produced by this technique enable the measurement of spatially resolved TERS spectra of self-assembled peptide nanotubes with a spatial resolution of ∼20 nm.

Raman spectroscopy: techniques and applications in the life sciences

“…Similar measurements were also done on insulin fibrils, with TERS able to distinguish variations in α-helix to β-sheet regions as before, but was also able to distinguish between flat, twisted and proto-filaments [367]. TERS measurements have also been demonstrated on model peptide fibrils which form ordered crystal structures, showing spectral variations across the fibril [353].…”

“…Other approaches for TERS tip fabrication include photochemical nanoparticle growth localized to the tip using a nanoparticleseed precursor solution in-situ [353], the fabrication of solid silver cantilevers to avoid loss of enhancement due to wear of the silver films [354], and focused-ion-beam milling of grooves into a metallic wire to engineer specific tip-plasmon resonances [355,356]. Recently nanoparticle attachment methods using dielectrophoresis have also been explored by several groups [357][358][359].…”

“…Copyright 2009 American Chemical Society. ), (h) oxidized silicon tip with silver deposited as in (g) (modified from Hayazawa et al [349]), (i) solid Ag TERS cantilever (after TERS experiment, modified from Rodriguez et al [354]), (j) photochemically grown Ag TERS tips prepared in-situ (modified from Sinjab et al [353]), (k) Ag nanowire attached via dielectrophoresis [357], (l) plasmonic grating TERS tip (Ag) [355] (Reprinted (adapted) with permission. Copyright 2007 American Chemical Society.…”

“…Wood et al demonstrated measurement of hemozoin crystals in sectioned erythrocytes which had been infected with malaria parasites [374], and were also able to identify nano-oxidation sites with TERS [375]. [353]). …”

“…Other biologically relevant samples measured by TERS include alginates in biofilms [376] and self-assembled peptide nanotubes [353]. TERS has also been attempted in liquids, which would be very beneficial for measuring biological systems in more realistic environments [377].…”