Rapid and sensitive detection of Nampt (PBEF/visfatin) in human serum using an ssDNA aptamer-based capacitive biosensor.

A single-stranded DNA (ssDNA) aptamer was successfully developed to specifically bind to nicotinamide phosphoribosyl transferase (Nampt) through systematic evolution of ligands by exponential enrichment (SELEX) and successfully implemented in a gold-interdigitated (GID) capacitor-based biosensor. Surface plasmon resonance (SPR) analysis of the aptamer revealed high specificity and affinity (K(d)=72.52 nM). Changes in surface capacitance/charge distribution or dielectric properties in the response of the GID capacitor surface covalently coupled to the aptamers in response to changes in applied AC frequency were measured as a sensing signal based on a specific interaction between the aptamers and Nampt. The limit of detection for Nampt was 1 ng/ml with a dynamic serum detection range of up to 50 ng/ml; this range includes the clinical requirement for both normal Nampt level, which is 15.8 ng/ml, and Nampt level in type 2 diabetes mellitus (T2DM) patients, which is 31.9 ng/ml. Additionally, the binding kinetics of aptamer-Nampt interactions on the capacitor surface showed that strong binding occurred with increasing frequency (range, 700 MHz-1 GHz) and that the dissociation constant of the aptamer under the applied frequency was improved 120-240 times (K(d)=0.3-0.6 nM) independent on frequency. This assay system is an alternative approach for clinical detection of Nampt with improved specificity and affinity.