Electrochemical genosensor for Klotho detection based on aliphatic and aromatic thiols self-assembled monolayers

Changes in expression of Klotho gene are associated with chronic kidney disease and its potential as early biomarker is being studied. We report, for the first time, the detection of Klotho gene by a biosensor platform. Self-assembled mixed monolayers (SAMs) as DNA immobilization method in screen-printed gold electrodes and a sandwich format detection were used in the development of an electrochemical genosensor for the detection of a 100-mer DNA fragment, copy of the partial region of the mRNA Klotho gene. The use of different binary and ternary SAMs based on aliphatic (mercaptohexanol, MCH, and hexanedithiol, HDT) and aromatic (mercaptophenylacetic acid, MPAA) thiol diluents and capture probe (CP) as sensing phases was evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. Multiple configurations were studied, changing the order of component addition and comparing co-immobilization and two-step immobilization processes. The procedure for binary SAM preparation consisting of sequential addition of a thiol diluent followed by CP was found to have the least detrimental impact on electrochemical performance. The signal-to-blank ratios increased considerably in the case of thioaromatic binary DNA monolayers, MPPA/CP, compared to the values obtained for aliphatic SAMs. Ternary monolayers formed by MCH and HDT rendered good fractional coverage levels and generated more reversible redox reactions at the surface, mostly when CP was firstly immobilized, CP/HDT/MCH. A significant reduction of the blank and non-specific (non-complementary sequence) signals was obtained with this ternary SAM, compared to binary SAMs and an increase of 2.42-fold of the S/B ratio (10 nM of target) compared with MPAA/CP SAMs. A linear response in the range of 5·10^-10 to 5·10^-8 M was obtained with CP/HDT/MCH monolayer, with a detection limit of 0.5 nM and RSD of 8.10%.