Talanta 78 (2009) 1063–1068 Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta Self-assembled monolayer of nickel(II) complex and thiol on gold electrode for the determination of catechin Sally Katiuce Moccelini a , Suellen Cadorin Fernandes a , Tiago Pacheco de Camargo b , Ademir Neves b , Iolanda Cruz Vieira a,∗ a Departamento de Química, LaBios - Laboratório de Biossensores, Universidade Federal de Santa Catarina, CEP 88040-900 Florianópolis, SC, Brazil b Departamento de Química, LABINC - Laboratório de Bioinorgânica e Cristalografia, Universidade Federal de Santa Catarina, CEP 88040-900 Florianópolis, SC, Brazil article info Article history: Received 25 September 2008 Received in revised form 28 November 2008 Accepted 13 January 2009 Available online 24 January 2009 Keywords: Self-assembled monolayer Gold electrode Nickel(II) complex Catechin abstract Self-assembled monolayers of a nickel(II) complex and 3-mercaptopropionic acid on a gold electrode were obtained for determination of catechin by square wave voltammetry. The complex [Ni II L] with L = [N-(methyl)-N ′ -(2-pyridylmethyl)-N,N ′ -bis(3,5-di-tert-butyl-2-hydroxybenzyl)- 1,3-propanediamine[nickel(II)] was synthesized and characterized by 1 H NMR, IR, and electronic spectroscopies and electrochemical methods. The optimized conditions obtained for the electrodes were 0.1 mol L -1 phosphate buffer solution (pH 7.0), frequency of 80.0 Hz, pulse amplitude of 60.0 mV and scan increment of 10.0mV. Under these optimum conditions, the resultant peak current on square wave voltammograms increases linearly with the concentration of catechin in the range of 3.31 × 10 -6 to 2.53 × 10 -5 mol L -1 with detection limits of 8.26 × 10 -7 mol L -1 . The relative standard deviation for a solu- tion containing 1.61 × 10 -5 mol L -1 catechin solution was 2.45% for eight successive assays. The lifetime of the Ni(II) complex–SAM-Au electrode was investigated through testing every day over 4 weeks. The results showed apparent loss of activity after 20 days. The results obtained for catechin in green tea samples using the proposed sensor and those obtained by electrophoresis are in agreement at the 95% confidence level. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The formation of self-assembled monolayers (SAMs) of alka- nethiols on gold surfaces continues to be a focus for research interests due to their importance in chemistry, biology and supramolecular nanotechnology. The chemisorption of thiolates on gold is the most important class of SAM from the electrochemical point of view. Among the reasons why gold is the preferred metal are its relative inertia and the fact that it has a strong specific inter- action with sulfur that allows the formation of monolayers in the presence of many other functional groups. The SAM technique is simple, reproducible and the molecules are chemically bound to the electrode. The SAM-modified electrodes have advantages such as selectivity, sensitivity, stability, short response time, the pos- sibility of introducing different chemical functionalities, ease of preparation and highly ordered molecules on the electrode [1,2]. The advantages of SAM-gold electrodes using different metalloph- thalocyanine complexes have been reported by Nyokong’s research group for the determination of several analytes [3–7]. ∗ Corresponding author. Tel.: +55 48 3721 6844; fax: +55 48 3721 6850. E-mail address: iolanda@qmc.ufsc.br (I.C. Vieira). Several mimetic complexes have been prepared to produce a system capable of mimicking enzymatic catalysis and used in the construction of biomimetic sensors [8–13]. Recently, Caovilla et al. [8] studied the catalytic oxidation of limonene, -pinene and -pinene by the complex [Fe III (BPMP)Cl(m-O)Fe III Cl 3 ], a biomimetic for the methane monooxygenase enzyme. In a study described by Sotomayor et al. [9], an iron tetrapyridinopor- phyrazine complex was used as a biomimetic catalyst of the P450 enzyme and applied in the construction of a sensor for paracetamol determination in pharmaceutical samples. Wollen- berger et al. [10] developed a sensor based on the combination of a screen-printed peroxidase electrode and an iron porphyrin complex iron(III)-meso-tetrakis-(penta-fluorophenyl)--tetra sul- fonatoporphyrin chloride for aliphatic hydrocarbons. Santhiago et al. [11] developed a biomimetic sensor based on a heterodinu- clear Fe III Zn II mimetic complex which mimics the active site of the hydrolytic enzyme red kidney bean purple acid phosphatase and employed it in the determination of rosmarinic acid. Oliveira et al. [12,13] developed biomimetic sensors based on an Fe III Fe II and a dinuclear copper(II) complex for the determination of dopamine in pharmaceutical products and hydroquinone in cosmetics, respec- tively. Green tea, a plant of Asiatic origin, is produced from Camellia sinensis belonging to the Theaceae family [14] and is popular in 0039-9140/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2009.01.038