Label-Free Capacitive Immunosensing of Lactate Dehydrogenase and Interleukin-6 Using a Protein-Passivated Graphene Interface

Lactate dehydrogenase (LDH) and interleukin-6 (IL-6) serve as two critical biomarkers for assessing disease progression and cellular model status, providing comprehensive pathological insights from the perspectives of cellular metabolism and immunomodulation, respectively. The most widely used method for LDH detection is a colorimetric assay utilizing nicotinamide adenine dinucleotide (NAD) as a coenzyme and lactate as the substrate, which quantifies LDH activity by measuring formazan dye. Although this method offers high sensitivity, its reliance on sophisticated instrumentation limits its applicability in resource-constrained settings. In this study, we developed a capacitive sensing electrode functionalized with specific antibodies for the simultaneous detection of LDH and IL-6 using electrochemical capacitance spectroscopy (ECS). Unlike label-based methods such as ELISA, this label-free strategy enables direct target recognition without the need for labeling reagents or additional procedural steps. A one-step modification process was employed to construct a protein-passivated graphene bioelectrochemical interface, enabling covalent immobilization of antibodies on the electrode surface. This sensor operates based on a coplanar ITO three-electrode system, exhibiting a significant signal response over a broad concentration range spanning 5 orders of magnitude for the target molecules. These results underscore the potential of ECS for the quantification of LDH and IL-6, supporting its promising application in the development of point-of-care (PoC) biosensors.