Abstract
This paper describes a label free sensor for the sensitive detection of certain, basic primary amino acids containing free ethyl and methyl amino acids. The control of interfacial electron transfer of a G-quadruplex DNA aptamer, using a Fe(CN)63–/4− redox probe responds rapidly to variations in arginine and lysine concentrations, but not to histidine, using non-labelled, impedance spectroscopy (EIS) detection. Two binding aptamer binding regimes were observed. At the low concentration range (0–0.15μg/mL), selectivity between lysine and arginine was apparent with limits of detection at approximately 0.5pMand 1.6pM respectively. At higher levels of concentrations, 0.15–10μg/mL, selectivity was limited. The aptamer was immobilised on gold substrates ensuring optimal probe density which was monitored by Atomic Force Microscopy. Initial studies indicate that the relative change in charge transfer resistance (Rct) values can be used as a parameter for monitoring free lysine to arginine ratios and free total lysine and arginine for direct detection of total lysine and arginine in food samples (milk, egg white and yoghurt) in Tris/HCl buffer, demonstrating its potential in many applications.
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