Effect of pH on stability and plasmonic properties of cysteine-functionalized silver nanoparticle dispersion

Edit Csapó, Rita Patakfalvi, V. Hornok, László Tamás Tóth, Áron Sipos, Anikó Szalai, M. Csete, I. Dékány

Research output: Contribution to journalArticle

55 Citations (Scopus)

Abstract

Citrate-stabilized spherical silver nanoparticles (Ag NPs) with d=8.25±1.25nm diameter were prepared and functionalized with l-cysteine (Cys) in aqueous dispersion. The nanosilver-cysteine interactions have been investigated by Raman and 1H NMR spectroscopy. The effect of pH on stability of biofunctionalized Ag NPs was investigated. The cysteine-capped nanosilver dispersions remain stable at higher pH (pH>7), while the degree of aggregation increased as the pH decreased. Below pH ∼7, the characteristic surface plasmon band of bare silver nanoparticles was back-shifted from λmeasuredbareAgNP=391 nm to λmeasured1=387-391 nm, while the presence of a new band at λmeasured2=550-600 nm was also observed depending on pH. Finite element method (FEM) was applied to numerically compute the absorption spectra of aqueous dispersions containing bare and cysteine-functionalized Ag NPs at different pH. Both the dynamic light scattering (DLS) measurements, Zeta potential values and the transmission electron microscopic (TEM) images confirmed our supposition. Namely, electrostatic interaction arose between the deprotonated carboxylate (COO -) and protonated amino groups (NH 3 +) of the amino acid resulting in cross-linking network of the Ag NPs between pH ∼3 and 7. If the pH is measurable lower than ∼3, parallel with the protonation of citrate and l-cysteine molecules the connection of the particles via l-cysteine is partly decomposed resulting in decrease of second plasmon band intensity.

Original languageEnglish
Pages (from-to)43-49
Number of pages7
JournalColloids and Surfaces B: Biointerfaces
Volume98
DOIs
Publication statusPublished - Oct 1 2012

Fingerprint

cysteine
Dispersions
Silver
Nanoparticles
Cysteine
silver
nanoparticles
Protonation
Dynamic light scattering
Zeta potential
Coulomb interactions
Nuclear magnetic resonance spectroscopy
Amino acids
Absorption spectra
Agglomeration
Finite element method
Citric Acid
Molecules
Electrons
citrates

Keywords

  • Biofunctionalized nanosilver
  • PH effect
  • Plasmonic properties

ASJC Scopus subject areas

  • Biotechnology
  • Colloid and Surface Chemistry
  • Physical and Theoretical Chemistry
  • Surfaces and Interfaces

Cite this

Effect of pH on stability and plasmonic properties of cysteine-functionalized silver nanoparticle dispersion. / Csapó, Edit; Patakfalvi, Rita; Hornok, V.; Tóth, László Tamás; Sipos, Áron; Szalai, Anikó; Csete, M.; Dékány, I.

In: Colloids and Surfaces B: Biointerfaces, Vol. 98, 01.10.2012, p. 43-49.

Research output: Contribution to journalArticle

Csapó, Edit ; Patakfalvi, Rita ; Hornok, V. ; Tóth, László Tamás ; Sipos, Áron ; Szalai, Anikó ; Csete, M. ; Dékány, I. / Effect of pH on stability and plasmonic properties of cysteine-functionalized silver nanoparticle dispersion. In: Colloids and Surfaces B: Biointerfaces. 2012 ; Vol. 98. pp. 43-49.
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AB - Citrate-stabilized spherical silver nanoparticles (Ag NPs) with d=8.25±1.25nm diameter were prepared and functionalized with l-cysteine (Cys) in aqueous dispersion. The nanosilver-cysteine interactions have been investigated by Raman and 1H NMR spectroscopy. The effect of pH on stability of biofunctionalized Ag NPs was investigated. The cysteine-capped nanosilver dispersions remain stable at higher pH (pH>7), while the degree of aggregation increased as the pH decreased. Below pH ∼7, the characteristic surface plasmon band of bare silver nanoparticles was back-shifted from λmeasuredbareAgNP=391 nm to λmeasured1=387-391 nm, while the presence of a new band at λmeasured2=550-600 nm was also observed depending on pH. Finite element method (FEM) was applied to numerically compute the absorption spectra of aqueous dispersions containing bare and cysteine-functionalized Ag NPs at different pH. Both the dynamic light scattering (DLS) measurements, Zeta potential values and the transmission electron microscopic (TEM) images confirmed our supposition. Namely, electrostatic interaction arose between the deprotonated carboxylate (COO -) and protonated amino groups (NH 3 +) of the amino acid resulting in cross-linking network of the Ag NPs between pH ∼3 and 7. If the pH is measurable lower than ∼3, parallel with the protonation of citrate and l-cysteine molecules the connection of the particles via l-cysteine is partly decomposed resulting in decrease of second plasmon band intensity.

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