Ethylene diamine functionalized graphitic carbon nitride for highly sensitive and reliable detection of creatine kinase

Early diagnosis of myocardial infarction necessitates the sensitive and reliable detection of cardiac biomarkers in biological fluids. Creatine kinase (CK) serves as a critical enzymatic indicator of myocardial injury that can be detected in various bodily fluids, including serum and saliva. Its concentration increases sharply during the early onset of myocardial cell damage, enabling timely diagnosis and clinical management. In this study, we report a novel electrochemical sensing platform based on ethylenediamine-functionalized graphitic carbon nitride (EDA-GCN), integrated with phosphocreatine (PC) on a gold electrode ( Au|EDA-GCN|PC ), for label-free and direct detection of CK. The carboxyl-functionalized GCN enables covalent linkage of EDA via amide bonds at both edge and basal planes, enhancing surface area and introducing abundant amine groups. These amines facilitate subsequent immobilization of PC through amide bond formation with its carboxyl groups, allowing PC to serve as a CK recognition element via specific phosphoryl group interactions. The sensor exhibits two distinct linear dynamic ranges from 0.1 pg·dL⁻¹ to 1 ng·dL⁻¹ and from 10 ng·dL⁻¹ to 10 mg·dL⁻¹ with respective sensitivities of 7.52 and 1.68 μA·mg⁻¹·dL⁻¹. These ranges reflect the transition from sub-monolayer to monolayer adsorption of CK on the biosensor surface. The lower detection limit was determined to be 0.079 pg·dL⁻¹ within the low-concentration regime. The sensor also demonstrates excellent selectivity against interferents such as myoglobin, tyrosine, immunoglobulin G, and cholesterol, along with high stability (95 % signal retention over seven days). Recovery tests in spiked artificial serum and saliva confirm its applicability as a rapid, accurate, and label-free electrochemical tool for point-of-care diagnostics in cardiovascular disease.