Photoelectrochemical aptasensing of thrombin based on multilayered gold nanoparticle/graphene-TiO2 and enzyme functionalized graphene oxide nanocomposites

A new ternary plasmonic photocatalyst based on multilayered gold nanoparticles decorated graphene (GR)-TiO2 heteronanostructure ((AuNPs)x/GR-TiO2) was fabricated via a simple poly(diallyldimethylammonium chloride) (PDDA) assisted calcination process in combination with the layer-by-layer (LbL) assembly technique. A remarkably enhanced charge separation efficiency of TiO2 was obtained due to the synergistic effect of electron-conducting GR sheets and plasmonic AuNPs. Compared with bare TiO2 and GR-TiO2, the as-prepared (AuNPs)2/GR-TiO2 showed significantly enhanced photocurrent intensity (6-fold of bare TiO2 and 3-fold of GR-TiO2). A sandwich thrombin photoelectrochemical aptasensor was fabricated by using (AuNPs)2/GR-TiO2 immobilized aptamer 1 as the capture probe and graphene oxide, horseradish peroxidase (HRP), and AuNPs triple-labeled aptamer 2 (GO-HRP-AuNPs-apt 2) as the detection probe. On the basis of HRP catalyzed oxidation of 4-chloro-1-naphthol by H2O2 to yield an insulating product on the transducer surface that obstructs the electron transfer of the electron donor (ascorbic acid) to the electrode surface, the detection of thrombin can be carried out by the decrement of photocurrent intensity. The covalent immobilization of HRP on GO can effectively improve the HRP enzyme loading and thus the sensitivity of the sensor. Under the optimum conditions, a linear response was obtained over the range of 0.05-110 pM, with a limit of detection (LOD) of 0.02 pM (S/N = 3). The sensor was successfully used for detection of thrombin in serum samples.