Functionalized Ag nanoparticles with tunable optical properties for selective protein analysis

Abstract

We present a preparation procedure for small sized biocompatibly coated Ag nanoparticles with tunable surface plasmon resonances. The conditions were optimised with respect to the resonance Raman signal enhancement of heme proteins and to the preservation of the native protein structure.

Novel Approaches for SER Spectroscopic Analysis of Protein Cofactors

“…To achieve this, a defined concentration of silver nitrate (AgNO 3 ) and ascorbic acid is added to the seeds. This seeding method was established for AuNPs (Jana et al, 2001) but also for AgNPs an almost linear correlation between growth solution concentration and either particle size or aspect ratio can be obtained (Sivanesan et al, 2011). As a consequence the SPR position of the nanoparticle ensemble is red-shifted as a function of growth solution concentration.…”

“…The use of Ag NPs is less common since they have to be prepared individually and it is much more difficult to obtain a narrow size distribution (Le Ru & Etchegoin, 2009). For selective enhancement of heme cofactors AgNPs are designed with SPRs that match exactly the Soret band transition of the heme (Sivanesan et al, 2011).…”

Tailored silica coated Ag nanoparticles for non-invasive surface enhanced Raman spectroscopy of biomolecular targets

“…We have shown previously that both diameters as well as their aspect ratio (d long /d short ) are increased upon increasing the growth solution concentration. 7 It is known that these two effects lead to a controlled red shift of the SPR position. 14,15 A further red shift of 8-10 nm was introduced by coating with SiO 2 .…”

“…S1{), which is in very good agreement with our previously published data. 7 From Fig. 1 A, the successful Cyt c is a small soluble redox protein that binds electrostatically to negatively charged surfaces via its lysine rich binding patch.…”

“…We have shown in our previous work that the SPR of AgNPs can be precisely tuned to match the molecular resonance of the model heme protein cytochrome c (Cyt c). 7 Protein denaturation was prevented by replacing the initially surface bound citrate ions with a self assembled monolayer of 11-mercaptoundecanoic acid (MUA). Cyt c was strongly bound to these Ag@MUA NPs, which resulted in a high Raman signal intensity but made it impossible to further study the interactions of the protein with other reaction partners.…”