Glucose oxidase and ferrocene labels immobilized at Au/TiO₂ nanocomposites with high load amount and activity for sensitive immunoelectrochemical measurement of ProGRP biomarker.

Progastrin releasing-peptide (ProGRP) is a sensitive, specific, and reliable tumor marker with small cell lung cancer (SCLC), which may indicate an early tendency of cancer metastasis, causing high mortality rate. Thus, aiming for a more convenient assay system of SCLC, a novel immunoelectrochemical measurement for sensitive detection of ProGRP was developed in this work via Au nanoparticle/graphene modified immunosensor with ferrocene and glucose oxidase-multifunctionalized Au/TiO2 nanocomposites as a trace label. At first, Au nanoparticles (nano-Au) were attached on the TiO2 nanoparticles surface by using 3-aminopropyltriethoxy silane (APTES) as linkage reagent to obtain Au/TiO2 nanocomposites (nano-Au/TiO2). Next, glucose oxidase (GOD) and ferrocene labeled secondary antibodies (Fc-Ab2) were used to bind Au/TiO2 nanocomposites with high load amount and good biological activity, and because the increased surface area and biocompatibility of nano-Au/TiO2, the electrode can provide amplified signals. On the other hand, the nano-Au functionalized graphene sheets (GS) were used for the biosensor platform for increasing the surface area as well as improving the electronic transmission rate to capture a large amount of primary antibodies (Ab1). Then in presence of glucose, amplified signals can be obtained by an electrochemical sandwich immunoassay protocol. Based on the proposed immunosensor, the current is linear with the concentration of ProGRP being within a concentration range from 10.0 to 500 pg/mL with a limit of detection down to 3.0 pg/mL (S/N=3).