PAMAM dendrimer-enhanced DNA biosensors based on electrochemical impedance spectroscopy

A novel, simple and sensitive DNA biosensor based on DNA-poly(amidoamine) (PAMAM) dendrimer nanoconjugates was developed by using the electrochemical impedance spectroscopy (EIS) technique. In this context, the assay relies on the hybridization of the single-stranded DNA (ssDNA) probe covalently conjugated on a mercaptoacetic acid self-assembled monolayer on gold electrodes, with the generation 4.5 (G-4.5) PAMAM-target DNA complex in solution. Once the double-stranded DNA (dsDNA) formed on the gold electrodes, G-4.5 PAMAM bearing carboxyls on the periphery was anchored on the hybrids; the changes of interfacial electron-transfer resistance (R-et) of the electrodes were measured using an Fe(CN)(6)(3-/4-) redox probe by electrochemical impedance spectroscopy. The results showed that only a complementary sequence could form a dsDNA PAMAM with the DNA-PAMAM probe and give an obviously enlarged Ret value. The non-complementary and three-base mismatched sequence exhibited negligible impedance change compared with the blank measurement (the blank measurement means: ssDNA probe-modified gold electrode was directly measured by EIS). The unique spherical structure combining with more negative charges on the G-4.5 PAMAM periphery anchored on the hybrids could significantly amplify the hybridization signal (R-et value), and the detection limit for measuring the full complementary sequence is down to pM level.