Self-assembled gold nanoparticles and amphiphile peptides: a colorimetric probe for copper() ion detection

• Published in: Dalton transactions : an international journal of inorganic chemistry 2020-11, Vol.49 (45), p.16226-16237
• Main Authors: Pelin, Juliane N. B. D, Edwards-Gayle, Charlotte J. C, Martinho, Herculano, Gerbelli, Barbara B, Castelletto, Valeria, Hamley, Ian W, Alves, Wendel A
• Format: Article
• Language: English
• Subjects: Absorption spectra; Agglomeration; Aqueous solutions; Colorimetry; Copper; Copper compounds; Dichroism; Gold; Image transmission; Nanoparticles; Nucleation; Peptides; Phenylalanine; Proline; Raman spectroscopy; Reducing agents; Self-assembly; Small angle X ray scattering; Spectrum analysis; Zeta potential
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d0dt00844c

Morphological, spectroscopic and scattering studies of the self-assembly and aggregation process of hybrids containing gold nanoparticles (AuNPs) and the amyloid peptides [RF] 4 and P[RF] 4 (where R = arginine; F = phenylalanine; P = proline) in aqueous solution were performed. Two methodologies were tested for the AuNP nucleation, using sodium borohydride (NaBH 4 ) or epigallocatechin gallate (EGCG) as a reducing agent. This led to remarkable distinct modes of assembly, AuNP decorated fibrils with NaBH 4 reduction or isolated AuNPs with EGCG reduction. For both methodologies, the presence of spherical AuNPs was observed by plasmonic resonance bands in absorption spectra at ∼520 nm. Zeta potential measurements confirmed stable systems, with a similar aggregation state. Circular dichroism spectra revealed an antiparallel β-sheet conformation of the peptides. The transmission electron microscopy (TEM) images showed the coexistence of nanometer fibers and globular nanoparticles with 20 nm size. The small-angle X-ray scattering (SAXS) results show that the NaBH 4 systems presented large cylindrical structures, while with increasing P[RF] 4 content, a decrease in radius was observed. However, the EGCG-AuNPs were characterized by spherical particles, with a radius of 10-20 nm. Also, the colorimetric efficiency of the hybrids in the capture of Cu 2+ ions in solution was monitored. Raman spectroscopy data confirmed the conformation/structure of self-assembled samples. Moreover, there are indications for a surface-enhanced Raman spectroscopy (SERS) effect for Cu 2+ sites. The set of results indicates that these systems could act as a promising sensitive metal concentration probes. We show that arginine/phenylalanine based peptides can be used to control the aggregation of gold nanoparticles in different ways. The arrangement provides a colorimetric approach to detect Cu 2+ ions in water.