Electrochemical enhancement using iron oxide-gold nanocomposite for detection of tuberculosis based on rGO-APTES modified screen printed electrode

A new electrochemical immunosensor based on Fe3O4-Au nanocomposite (NC) as signal enhancement was proposed for the detection of Mycobacterium Tuberculosis ESAT-6-like protein EsxB. In this study, Fe3O4-Au NC was synthesis via coprecipitation method and size of NC was viewed under high resolution transmission electron microscopy (HRTEM) with average diameter of 1.629-1.915 nm. Meanwhile, X-ray diffraction (XRD) analysis confirmed that Fe3O4-Au NC exhibited all possible peaks of Fe3O4 and new peaks at 38.37° (111) and 44.63° (200) are belongs to crystal plane of metallic gold. Additionally, UV-Vis absorption study shows peak at 545 nm was appeared indicating that Au shell was successfully coated on Fe3O4 NC. Characterization by FTIR demonstrated that the peak at 1670 cm-1 assigned to C=O group and peak at 3280 cm-1 indicated O-H group. The peak at 710 cm-1 represented CS stretching. The IR spectra confirms successful functionalization of the Fe3O4-Au NC with ME-MDDA linker. In this study, rGO-APTES have been used to modify screen printed electrode (SPE) to serve as immobilization matrix for immunoassay interaction. The result from RAMAN spectroscopy, Field Emission Scanning Electron Microscope (FE-SEM) and Energy Dispersive X-ray Spectroscopy (EDX) confirmed rGO-APTES modified SPE successfully reduced. Additionally, the morphology of rGO-APTES modified SPE also revealed smoother surface and ready for immobilization of capture antibody (Ab). The effective surface area value of rGO-APTES modified SPE also has increase about 20 times larger compared to bare SPE of based on cyclic voltammetry (CV) studies. Moreover, the ratio of Ipc/Ipa = 0.9867 showed electron transfer process is towards reversible kinetics. The rGO-APTES modified SPE was further explored as immunoassays matrix for Ab1 tagged with Fe3O4-Au NC (Ab1- Fe3O4-Au) and further interact with Mycobacterium Tuberculosis ESAT-6-like protein EsxB were monitored by differential pulse voltammetry (DPV) technique using 0.1 M PBS as electrolyte. As a result, the decreased of peak current of Ab from 3.996 μA to 3.863 μA occurs after immobilization on rGO-APTES modified SPE confirmed that electron transfer resistance increased. At optimal condition, the DPV was studied in different concentration of Mycobacterium Tuberculosis ESAT-6-like protein EsxB. The DPV current of immunosensor electrode increased as the Mycobacterium Tuberculosis ESAT-6-like protein EsxB increased. In this study, the lowest TB concentration that could be determined statistical by resulting immunosensor was calculated as 1.32 ng/mL. The Relative Standard Deviation (RSD) of the measurements for five electrodes was 6.4% suggesting the precision and reproducibility of the immunosensor was quite good