Ultra-sensitive and selective label free electrochemical DNA detection at layer-by-layer self-assembled graphene oxide and vesicle liposome nano-architecture

Liposomes are self-assembled successfully on graphene oxide/reduced graphene oxide (GO/rGO) composite supported on a gold electrode for the ultra-sensitive and selective label free detection of target DNA in presence of gold nanoparticle electrochemically for the first time. This work used the chemically synthesized GO for controlling the bilayer to vesicle structure of cationic DOTAP by the simultaneous control of GO hydrophobic character and oxy functional group spacing. This has been achieved by two different approaches: (i) the traditional physical mixing of ascorbic acid reduced GO with the unreduced GO to form a trilayered rGO/GO/rGO network and (ii) in another method, the rGO was prepared electrochemically by the controlled potential reduction of acid functional groups on the GO in sulphuric acid medium (ErGO). Both these methods produce graphene surfaces with evenly spaced functional groups and low hydrophobic character which are essential to prevent liposome vesicle fusion on the GO surface. Electrochemical and quartz crystal micro balance techniques (QCM) suggest more adsorption of the vesicles on the ErGO than on the GO/rGO assembly. These surfaces are further decorated with gold nanoparticles to anchor single stranded DNA to detect target DNA ultrasensitively in the presence of ferri/ferro cyanide redox probe. When the complementary hybridization decreases the redox peak current in cyclic voltammetry, the non-complementary hybridization does not show any obvious change in the peak currents. The intact spherical liposome on the GO/rGO and ErGO promotes the ultrasensitive detection of target DNA and showed the lowest detection limit of 1.29 x 10(-17) M with a broad linear range 10(-17)-10(-8) M. The bilayered liposome/AuNP structures on the AuE, GO and rGO do not show any selectivity for DNA detection. The constructed sensor is stable, selective and sensitive with fast response time ensuing its applicability in molecular diagnosis.