β-Cyclodextrin/Fe3O4 hybrid magnetic nano-composite modified glassy carbon electrode for tryptophan sensing

A glassy carbon electrode (GCE) was first modified with β-cyclodextrin functionalized Fe3O4 magnetic nanoparticles (β-CD-MNPs), which was fabricated by the combination of 3-aminopropyl triethoxysilane coated magnetic Fe3O4 nanoparticles (APTES-MNPs) with 6-O-toluenesulfonyl-β-cyclodextrin (6-TsO-β-CD). The β-CD-MNPs grafting was confirmed by TEM, FTIR and thermogravimetric analysis (TGA). Electrochemical behaviors of tryptophan (Trp) at the β-CD-MNPs modified electrode were confirmed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), which indicated that β-CD-MNPs efficiently improved the electron transfer between solution and electrode interface. Some parameters, including pH of electrolyte, the amount of β-CD-MNPs and scan rate of voltammetric sweeping segments have been optimized. Under the optimum conditions, the oxidation peak current displayed a calibration response for tryptophan over a wide concentration range from 8.0 × 10−7 to 3.0 × 10−4 M with a detection limit of 5.0 × 10−7 M (S/N = 3). The relative standard deviation (RSD) of 8 successive scans was 4.2% for 1.0 × 10−4 M tryptophan. The proposed procedure was successfully applied to the determination of tryptophan in a commercial amino acid injection.