Sensitive impedimetric DNA biosensor with poly(amidoamine) dendrimer covalently attached onto carbon nanotube electronic transducers as the tether for surface confinement of probe DNA.

This study demonstrates a new impedimetric DNA biosensor with second-generation poly(amidoamine) dendrimer (G2-PAMAM) covalently functionalized onto multi-walled carbon nanotube (MWNT) electronic transducers as the tether for surface confinement of probe DNA. G2-PAMAM dendrimer was covalently functionalized onto purified MWNTs and the as-formed G2-PAMAM-functionalized MWNT composite (i.e., G2-PAMAM/MWNT) was used both as the support to confine the single-stranded DNA (ssDNA) probe and as the electronic transducer to form the DNA biosensors. Upon the occurrence of hybridization events between surface-confined ssDNA probe with target DNA in solution to form a double-stranded DNA (dsDNA) at electrode surface, the negative charge in the electrode/electrolyte interface and, as such, the interfacial charge-transfer resistance of the electrodes towards the Fe(CN)(6)(3-/4-) redox couple were changed. Such a change was used for the impedimetric DNA biosensing. The use of G2-PAMAM dendrimer attached onto MWNT electronic transducer as the tether for probe DNA provides a large number of amino groups to increase the surface binding of probe DNA, results in the increase the sensitivity of the impedimetric biosensor for the target DNA. Under the conditions employed here, the change in the interfacial charge-transfer resistance was linear with the logarithm of the concentration of the target DNA within a concentration range from 0.5 to 500 pM with a detection limit of 0.1 pM (S/N=3). The excellent analytical properties of the impedimetric DNA biosensors developed here substantially makes them potentially useful for practical applications.