Focus on nanoparticle size and plasmon resonance position
Surface-enhanced Raman spectroscopy (SERS) is a unique technique to study submembrane hemoglobin (Hbsm) in erythrocytes. We report the detailed design of SERS experiments on living erythrocytes to estimate dependence of the enhancemen t factor for main Raman bands of Hbsm on silver nanoparticle (AgNP) properties. We demonstrate that the enhancement factor for 4/A1g, 10/B1g and A2g Raman bands of Hbsm varies from 105 to 107 under proposed experimental conditions with 473 nm laser excitation. For the first time we show that the enhancement of Raman scattering increases with the increase in the relative amount of small NPs in colloids, with the decrease in AgNP size and with plasmon resonance shift to the shorter wavelength region. Obtained results can be explained by the ability of smaller AgNPs to get deeper into nano-invaginations of the plasma membrane than larger AgNPs. This shortens the distance between small AgNPs and Hbsm and, consequently, leads to the higher enhancement of Raman scattering of Hbsm. The enhancement of higher wavenumber bands 10/B1g and A2g is more sensitive to AgNPs' size and the relative amount of small AgNPs than the enhancement of the lower wavenumber band 4/A1g. This can be used for AgNP-controlled enhancement of the desired Raman bands and should be taken into account in biomedical SERS experiments.
Journal of Raman Spectroscopy, 2013, Vol 44, Issue 5, p. 686-694