Surface-enhanced Raman detection of hemo-proteins with silver nanocubes

Surface enhanced Raman spectroscopy (SERS) is now widely used for detection and analysis of proteins at low concentration. SERS of proteins in a liquid environment is mainly based on the use of plasmonic nanoparticles, which are frequently aggregated by chemical or physical methods, leading to the formation of random hot-spots. However, without controlling size, shape and distribution of the nanoparticles, a high variability in the SER signal is typically observed. Moreover, uncontrolled clustering of plasmonic nanoparticles suffers from high photo-instability, inducing photothermal and photodegradation processes and affecting the Raman signal. In this work, we investigated the use of stable isolated silver nanocrystals in from of cubes for hemoprotein detection in aqueous medium at physiological pH. A highly resolved TEM analysis of the nanocubes revealed a quantitative gathering of molecules onto the their free corner areas, where the enhancement is the largest. SERS results showed an intense and very reproducible Raman signal upon using both resonant and non-resonant laser excitations. Furthermore, similar nanocubes with few nm pores as obtained by galvanic replacement demonstrated more efficiency as SERS substrates thanks to the presence of additional SERS active areas inside the nanopores. The observed behavior confers these nanoparticles with potential for reliable detection of proteins at low concentration in physiological condition.