Electrochemical Charge Transfer Effects of Detonation Nanodiamonds in Cortisol Immunosensor on Metal Electrodes

Improving the detection of cortisol could enable daily health monitoring to prevent the onset and development of diseases caused by long‐term exposure to stress. Electrochemical immunosensors enable easy preparation, high sensitivity and selectivity, rapid analysis and miniaturization without the need for complex equipment. Here, the effect of nanodiamonds on the voltammetric response of cortisol immunosensors with different metal electrodes is studied. Detonation nanodiamonds (DND) are deposited in various concentrations on gold and platinum working electrodes being part of a screen‐printed electrode (SPE) sensor strip. Working electrodes with and without DNDs were functionalized by EDC/NHS, antibody, and bovine serum albumin incubation. Optical microscopy, scanning electron microscopy, infrared spectroscopy, and differential pulse voltammetry with ferri/ferrocyanide redox probe were used to analyze the sensor morphology and function. With ethanol pretreatment, the DND electrodes were robust during all processing steps. As little as 5% dilution of DND colloid was enough to affect the sensor functionality. During cortisol antigen detection, the Au or Pt reference sensors as well as DND/gold sensors exhibited DPV current decrease whereas DND/platinum sensors showed systematic current increase, indicating enhanced surface interaction or redox activity.