Cholesterol oxidase-immobilized MXene/sodium alginate/silica@n-docosane hierarchical microcapsules for ultrasensitive electrochemical biosensing detection of cholesterol

Electrochemical biosensors usually suffer from the deterioration of detection sensitivity and determination accuracy in a high-temperature environment due to protein denaturation and inactivation of their biological recognition elements such as enzymes. Focusing on an effective solution to this crucial issue, we have developed cholesterol oxidase-immobilized MXene/sodium alginate/silica@n-docosane hierarchical microcapsules as a thermoregulatory electrode material for electrochemical biosensors to meet the requirement of ultrasensitive detection of cholesterol at high temperature. The microcapsules were first fabricated by microencapsulating n-docosane as a phase change material (PCM) in a silica shell, followed by depositing a biocompatible sodium alginate layer, wrapping with electroactive MXene nanosheets and then immobilizing cholesterol oxidase as a biological recognition element for electrochemical biosensing. The fabricated composites not only exhibited a layer-by-layer hierarchical microstructure with the desired chemical and biological components, but also obtained a high latent-heat capacity of over 133 J g-1 for thermal management through reversible phase transitions of its PCM core. A bare glassy carbon electrode was modified with the developed composites to serve for the cholesterol biosensor. This enables the modified electrode to obtain an in situ thermoregulatory ability to regulate the microenvironmental temperature surrounding the electrode, effectively preventing the protein denaturation of cholesterol oxidase and minimizing heat impact on biosensing performance. Compared to conventional cholesterol biosensors without a PCM, the developed biosensor achieved a higher sensitivity of 4.63 μA μM-1 cm-2 and a lower limit of detection of 0.081 μM at high temperature, providing highly accurate and reliable detection of cholesterol for real biological samples over a wide temperature range.