Measurement of Cerium with Tyrosine-Functionalized EF-Hand Loop Peptide Bio-Electrochemical Sensor

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The detection of rare earth elements (REEs) holds significant importance in various practical applications, particularly in monitoring industrial waste streams and assessing environmental samples such as urine. EF-hand loop peptide sequences, known for their affinity to REE ions, present a promising avenue for developing user-friendly sensors to support these studies. This study focuses on modifying an EF-hand loop peptide to covalently bond to a gold electrode and incorporate tyrosine as an electrochemically active indicator of REE binding. It is anticipated that as REEs bind to the peptide, a conformational shift will occur, modulating the current exchange between the redox-active tyrosine moiety and the electrode surface.Isothermal titration calorimetry and circular dichroism are employed to evaluate the binding of the modified sensing peptide to REEs, with cerium chosen as a model REE. Utilizing a quartz crystal microbalance and cyclic voltammetry, we demonstrate the binding of the designed peptide to cerium ions while immobilized on a gold surface. Tests conducted in artificial urine and potassium phosphate buffer, mimicking physiological conditions, reveal the sensor's efficacy in detecting cerium ions.The binding affinity of the tyrosine-conjugated peptide to cerium ions in solution is presented by KD to be approximately 4 µM, while the gold-immobilized peptide exhibits an estimated KD for cerium ions of about 1.1 µM. The effectiveness of the redox-active sensing peptide is explored in an electrochemical sensing platform, where the peptide-modified biosensor, created through thiol binding onto gold working electrodes within a screen-printed sensor setup, shows a current response modulated by different concentrations of cerium.The developed biosensor demonstrates good affinity and selectivity for cerium, as evidenced by calibration curves constructed within a biologically relevant range. Overall, this research introduces an innovative electrochemical biosensor capable of detecting REEs using cerium ions as a model. The combination of the electrochemical platform and the designed peptide aptamer allows for the selective detection of cerium in simple buffer solutions and artificial urine, with high affinity, at concentrations relevant to human health.