Bio/abiotic interface constructed from nanoscale DNA dendrimer and conducting polymer for ultrasensitive biomolecular diagnosis.

For sensors detecting immobilized biomarkers, the interface between the surface and the fluid medium plays an important role in determining the levels of signal and noise in the electrochemical detection process. When protein is directly immobilized on the metal electrode, denaturation of the protein by surface-protein interaction results in low activity and low signal level. A conducting polymer-based interface can prevent the protein conformation change and alleviate this problem. A DNA dendrimer is introduced into the interfacial film on the sensor surface to further improve the sensor performance. DNA dendrimer is a nanoscale dendrite constructed of short DNA sequences, which can be easily incorporated into the abiotic conducting polymer matrix and is biocompatible with most biological species. In this work, DNA dendrimer and polypyrrole (DDPpy) form the bio/abiotic interface on electrochemical sensors. Detection of two salivary protein markers (IL-8 and IL-1beta) and one mRNA salivary marker (IL-8) is used to demonstrate the efficiency of the DDPpy sensor. A limit of detection (LOD) of protein of 100-200 fg mL(-1) is achieved, which is three orders of magnitude better than that without the DNA dendrimer interface. An LOD of 10 aM is established for IL-8 mRNA. The typical sample volume used in the detection is 4 microL, thus the LOD reaches only 25 target molecules (40 yoctomole).