Distinctly Different Morphologies of Bimetallic Au-Ag Nanostructures and Their Application in Submicromolar SERS-Detection of Free Base Porphyrin

Abstract

Core-shell Au-Ag nanostructures (Au-AgNSs) are prepared by a seed-meditated growth, i.e., by a two-step process. The synthetic parameters greatly influence the morphologies of the final bimetallic Au-AgNSs, their stability and application potential as surface-enhanced Raman scattering (SERS) substrates. Direct comparison of several types of Au NPs possessing different surface species and serving as seeds in Au-AgNSs synthesis is the main objective of this paper. Borohydride-reduced (with varying stages of borohydride hydrolysis) and citrate-reduced Au NPs were prepared and used as seeds in Au-AgNSs generation. The order of reactants in seed-mediated growth procedure represents another key factor influencing the final Au-AgNSs characteristics. Electronic absorption spectra, dynamic light scattering, zeta potential measurements, energy dispersive spectroscopy and transmission electron microscopy were employed for Au-AgNSs characterization. Subsequently, possibilities and limitations of SERS-detection of unperturbed cationic porphyrin, 5,10,15,20-tetrakis(1-methyl-4-pyridyl)21H,23H-porphine (TMPyP), were investigated by using these Au-AgNSs. Only the free base (unperturbed) SERS spectral form of TMPyP is detected in all types of Au-AgNSs. It reports about a well-developed envelope of organic molecules around each Au-AgNSs which prevents metalation from occuring. TMPyP, attached via ionic interaction, was successfully detected in 10 nM concentration due to Au-AgNSs.

Ag-coated tetrapod gold nanostars (Au@AgNSs) for acetamiprid determination in tea using SERS combined with microfluidics

“…As Ag + gradually increased, covering the entire surface of tetrapod AuNSs, the whole charge of core-shell Au@AgNSs became positive. 48 The particle size distribution plot (Fig. 3D) signies that the synthesized core-shell Au@AgNSs demonstrated a relatively uniform distribution, with a diagonal size of about 300 nm.…”

Recent progress of gold nanostructures and their applications

“…It is the LSPR, which results from d-d band transitions, that makes Au and Ag nanostructures so well-suited for use in the medical field. 106 Experimentally, metal nanostructure colloids are a highly dispersed object system, and their colour or spectrum shows the average effect of light response of a large number of nanoparticles. Therefore, the homogeneity of the sample in terms of morphology and size is very important.…”

“…It is the LSPR, which results from d–d band transitions, that makes Au and Ag nanostructures so well-suited for use in the medical field. 106…”