A probeless and label-free electrochemical immunosensor for cystatin C detection based on ferrocene functionalized-graphene platform.

A novel electrochemical sensor with inherent redox activity mediated by ferrocene for Cystatin C (CysC), an early kidney failure biomarker, is described. The current response was mediated by graphene oxide-ferrocene nanofilm with redox-activity coming from electroactive species surface-confined. Anti-CysC antibodies were immobilized by their Fc portions on the drop-casting polyethyleneimine (PEI) film for improving the sensitivity and reproducibility. Stepwise modifications of the nanostructured surface were characterized by electrochemical techniques, FT-IR and AFM. FT-IR confirmed the formation of the Fc-GO nanocomposite and PEI deposition on the electrode surface. The AFM micrographs confirmed a nanometric film of Fc-GO and PEI. The sensor platform showed a response from 0.1 to 1000 ng/mL and lower limit of detection (LOD) of 0.03 ng/mL of CysC, with good accuracy, specificity and it was successfully applied for CysC detection. Advantages of this immunosensor include rapid testing with minimal steps by the simple use of an intrinsic redox probe, working in a reduction potential, which avoids potential interferences. This proposal attempts to circumvent amperometric detection limitations and provides a promising candidate for future point-of-care diagnostics without redox probe additional solutions for measurements.

The self-assembly of redox active peptides: Synthesis and electrochemical capacitive behavior.

The present work reports on the synthesis of a redox-tagged peptide with self-assembling capability aiming applications in electrochemically active capacitive surfaces (associated with the presence of the redox centers) generally useful in electroanalytical applications. Peptide containing ferrocene (fc) molecular (redox) group (Ac-Cys-Ile-Ile-Lys(fc)-Ile-Ile-COOH) was thus synthesized by solid phase peptide synthesis (SPPS). To obtain the electrochemically active capacitive interface, the side chain of the cysteine was covalently bound to the gold electrode (sulfur group) and the side chain of Lys was used to attach the ferrocene in the peptide chain. After obtaining the purified redox-tagged peptide, the self-assembly and redox capability was characterized by cyclic voltammetry (CV) and electrochemical impedance-based capacitance spectroscopy techniques. The obtained results confirmed that the redox-tagged peptide was successfully attached by forming an electroactive self-assembled monolayer onto gold electrode. The design of redox active self-assembly ferrocene-tagged peptide is predictably useful in the development of biosensor devices precisely to detect, in a label-free platform, those biomarkers of clinical relevance. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 106: 357-367, 2016.