Voltammetric detection of vitamin D employing Au-MoS hybrid as immunosensing platform.

A voltammetric immunosensor based on molybdenum sulphide (MoS) and gold nanoparticles (Au NPs) for the determination of 25-hydroxy vitamin D (25(OH)D) is reported. Anti-vit D (Ab-25(OH)D) was immobilized onto the cysteamine-modified MoS and Au NPs which were deposited onto a fluoride tin oxide (FTO) electrode (Ab/Cys/Au/MoS/FTO). The MoS sheets were prepared by hydrothermal method followed by an in situ growth of Au film onto the MoS/FTO surface. Self-assembled monolayer (SAM) of cysteamine was synthesized onto the Au/MoS/FTO which acts as a linker to covalently bind Ab-25(OH)D. The Ab-25(OH)D-immobilized Cys/Au/MoS/FTO was used to detect 25(OH)D using differential pulse voltammetry. The electrochemical system provided an anodic peak current at a potential of +0.21 V vs. Ag/AgCl (satd. KCl) of ferricyanide/ferrocyanide redox couple. The detection principle relies on the inhibition of electron transfer at the electrode surface owing to the hindrance caused by the formation of immune complex between Ab-25(OH)D and 25(OH)D. The immunosensor shows linear response from 1 pg mL to 100 ng mL 25(OH)D and a sensitivity of 189 μA [log (pg mL)] cm along with a low limit of detection (LOD) of 0.38 pg mL. The immunosensor is highly selective towards 25(OH)D and presented a long shelf life of 28 days. Also, the immunosensor exhibits satisfactory performance towards spiked human serum samples with recovery between 95.1 and 102% (RSD 1.15-3.22%).