Enantioselective recognition of alanine in solution with modified gold electrodes using chiral PAMAM dendrimers G4.0

Enantiomeric alanine was covalently grafted onto modified gold electrodes with mercaptopropionic acid and PAMAM dendrimers G4.0 with amine terminal groups. Cyclic voltammetric experiments in the presence of monocarboxylic ferrocene as a probe molecule proved that the alanine (Ala) was immobilized as a monolayer on the gold electrodes. Electron transfer to Ru(NH3)6Cl3 in solutions of different pH was studied by cyclic voltammetry (CV). Changes in solution pH resulted in the variation of the charge state of the terminal group and surface pKa values were estimated on the basis of these results. Because of electrostatic interactions between the positive charged groups on the electrode surface and the Ala, enantioselective recognition was possible. The interaction between enantiomers can be proven with molecular simulation. The electro-oxidation peak current was linearly dependent on Ala concentration over the range 0–10 μM with slopes between 143 and 187 μA cm−2/μM. The detection limit (3σ) was 0.4059 μM for PAMAM G4.0-d(+)Ala–l(−)Ala and 0.4172 μM for PAMAM G4.0-l(−)Ala–d(+)Ala.