A voltammetric peptide biosensor for Cu2+ metal ion quantification in coffee seeds.

A prion-derived copper(II)-binding peptide was assembled onto a gold electrode for the building of a voltammetric biosensor for measuring the Cu2+ metal ion in biological samples. The chosen sequence was H-CVNITKQHTVTTTT-NH2, with an appended cysteine residue for binding to the gold surface as a self-assembled monolayer and a histidine residue as the anchorage point for copper(II) complexation. The biosensor showed a linear range of 10-7 to 10-6 M with an 8.0 × 10-8 M detection limit and a 1.0 × 10-7 M quantification limit, with good precision, trueness, and absence of matrix effect. The quantification of Cu2+ was performed in the presence of other transition metal ions, such as Zn2+, Cd2+, Fe2+, or Ni2+, which indicates the excellent selectivity of the biosensor. When the modified electrode was applied for measuring copper(II) in calcined coffee seeds, a difference in copper amount was observed between two Coffea arabica cultivars that were submitted to a treatment with a copper-based antifungal, showing the applicability of the biosensor in the agricultural field.

Ca(II) -gamma-thionin complex: interaction studies by differential pulse voltammetry and MALDI-TOF/MS.

In this work we investigated the formation of a complex between gamma-thionin SI alpha1 and Ca(2+) using differential pulse voltammetry and MALDI TOF/MS. A stoichiometry rate of one calcium ion per one SI alpha1 molecule was obtained. K(d) values of 1.31 x 10(-9) mol L(-1), 2.63 x 10(-8) mol L(-1) and 2.71 x 10(-8) mol L(-1) were determined for the Ca(2+)- SI alpha1 complex by three different methodologies. These findings contribute to a better understanding of the SI alpha1 inhibition mechanism towards insect and mammalian alpha-amylases.