Serine-Grafted Cu2O Electrode Enabling Specific β-Hydroxybutyrate Detection by Surface Sensitization-Promoted Electrolysis in Amperometry

As the global prevalence of diabetes continues to rise, the home health testing market has experienced rapid growth. Although blood glucose monitoring is widespread among diabetic patients, there remains a significant lack of testing methods for diabetic ketoacidosis. The present study developed a feasible electrochemical technique for ketoacid detection using serine-immobilized copper(I) oxide nanoparticles (Cu₂O NPs) as the primary electrode material. Given that the serine on the nanoparticle surface enables conjugation with β-hydroxybutyrate (β-HBA) through an esterification reaction between the hydroxyl group of serine and carboxylic acid of β-HBA and another intramolecular nucleophilic acyl substitution between amine and ester groups to form irreversible amide bonding, thus resulting in the β-HBA deposition on the surface of the Cu₂O NP-coated electrode. The quantification of β-HBA can be determined through current variations in amperometry measurement. The results showed a highly linear relationship between reductive current and β-HBA concentration at 0–20 mM, with a reasonable detection limit of 0.1 mM. Moreover, a reasonable mechanism involving the NP surface covering-mediated electrolysis enhancement was proposed. The present method reveals a promising direction in developing sensors for small molecule detection with high specificity and sensitivity.