MIL-88B(Fe)-reduced graphene oxide as an artificial enzyme for gold nanorod etching and its application to develop...

An immunosensor based on gold nanorods (AuNRs) etchant activity of a metal-organic framework (MOF): MIL-88B(Fe)-reduced graphene oxide (rGMOF) was developed for the determination of prostate-specific antigen (PSA). Several techniques, including FTIR, UV-Vis spectrophotometry, XRD, and electron microscopy, were employed to characterize the MOFs containing iron-oxygen clusters on the surface of reduced graphene oxide. Enzyme mimetic activity of rGMOF before and after bioconjugation with antibodies was calculated as 8.4 and 2.5 U mg^-1, respectively. The primary anti-PSA was conjugated to a magnetic bead and used as PSA-specific capturing. Then, the secondary anti-PSA was grafted to the rGMOF. In the presence of antigen, an immuno-sandwich was formed between the conjugations mentioned above. Afterward, AuNRs were etched by rGMOF, and the related spectrum was recorded in the wavelength range 350 to 900 nm. By progressing the etching procedure, the longitudinal LSPR peak of AuNRs was gradually blue-shifted with a linear correlation with the PSA concentration from 0.1 pg mL^-1 to 100 ng mL^-1. The detection limit was 0.09 pg mL^-1. The proposed immunosensor was successfully employed to determine PSA levels in real samples. Since the obtained results showed an excellent correlation with those acquired by the chemiluminescence gold standard method, it has the potential for PSA determination in clinical assays.