DOI: 10.5281/zenodo.15657328
title: Dataset for the article "Electrochemical charge transfer effects of detonation nanodiamonds in cortisol immunosensor on metal electrodes"

description: Dataset for the article "Electrochemical charge transfer effects of detonation nanodiamonds in cortisol immunosensor on metal electrodes "

Daniel Vítek, Chakavak Esmaeili, Markéta Šlapal Bařinková, Bohuslav Rezek*

Faculty of Electrical Engineering, Czech Technical University in Prague, Technická 2, 16627 Prague, Czechia

Figure 1. Optical and SEM microscopic images of Au SPE sensors: a,b) bare sensor with prior to DND deposition, c,d) sensor after the DND deposition on the central working electrode. e) FTIR spectra of DND before and after biofunctionalization with EDC-NHS and antibody (Ab).Figure 2. Typical electrochemical analysis profiles on Au electrode during DND deposition (from 20% dilution), biofunctionalization and cortisol antigen sensing steps: a) cyclic voltammetry (CV), b) differential pulse voltammetry (DPV). Figure 3. Graphs summarizing mean values and standard deviation (as error bar) of relative  DPV currents  on SPE metal electrode after a DND layer deposition and after each biofunctionalization and antigen sensing step (yellow). The relative response is calculated vs. the intial DPV peak current on a bare metal electrode (100%). Reference SPE sensor data without a DND layer are also shown for comparison (green). The labels show actual % value of the data point. The lines connect the data points as guide for an eye. The arrows denote the trend of sensor response to antigen exposure. The graphs are shown for: a) 2 mm Au electrode with DND layer deposited from 20% dilution,  b) 2 mm Au electrode with DND layer deposited from 50% dilution, c) 2 mm Pt electrode with DND layer deposited from 20% dilution, and d) 2 mm Pt electrode with DND layer deposited from 50% dilution.Figure.4: CV (left) and DPV (right) graphs of 2 mm Au electrode with 20% DNDs layer.Figure 5. (A) Cyclic voltammograms and (B) Differential Pulse Voltammetry of (a) Au bare electrode, (b) EDC NHS/ Au electrode (c) Ab / EDC NHS/ Au bioelectrode, (d) Ag/BSA/Ab / EDC NHS/ Au bioelectrode pH 7.0, containing 250 mM KCl and 5 mM K3[Fe(CN)6] and 5 mM K4[Fe(CN)6], Scan rate 0.1Vs−1.Figure 6. (A) Cyclic voltammograms and (B) Differential Pulse Voltammetry of (a) Pt bare electrode, (b) EDC NHS/ Pt electrode (c) Ab / EDC NHS/ Pt bioelectrode, (d) Ag/BSA/Ab / EDC NHS/ Pt bioelectrode pH 7.0, containing 250 mM KCl and 5 mM K3[Fe(CN)6] and 5 mM K4[Fe(CN)6], Scan rate 0.1Vs−1.Figure.7: SEM images of Au (left) and Pt (right) bare working electrode at 5,000x magnification. The images reveal distinct structural details of each metal layer.

Figure S1. Optical microscopy images of SPE electrodes on Au after DND and water rinsing in the case: a) without surface pre-treatment, b) after ethanol washing. The insets show different resulting SEM surface morphology of the sensors.Figure S2. Optical microscopy images of SPE with Au and Pt working electrode after DND deposition (from 20% dilution), rinsing, bio-functionalization and cortisol antigen sensing steps.Figure S3. Photographs of a) SEM machine Zeiss EVO 10, b) SEM sample holder with SPE sensors, and c) optical microscope Zeiss Stemi 508 with Axiocam 208 color camera and LED illumination in our laboratory.Figure S4. Photograph of the experimental cortisol sensor setup using SPE with deposited nanodiamonds and EmStat pico USB potentiostat.

Table S1. Example of one set of electrochemical analysis: CV and DPV currents on Au and Pt working electrodes in 2 mm size before and after deposition of DNDs from various dilutions (5-100%), in quadruplicates.Table S2. CV and DPV peak currents on 2 mm gold working electrodes (in quadruplicates) with 20% DND layer after each step of functionalization.Table S3. CV and DPV peak currents on 2 mm gold working electrodes (in quadruplicates) with 50% DND layer after each step of functionalization.Table S4. CV and DPV peak currents on 2 mm platinum working electrodes (in quadruplicates) with 20% DND layer after each step of functionalization.Table S5. CV and DPV peak currents on 2 mm platinum working electrodes (in quadruplicates) with 50% DND layer after each step of functionalization.

Abstract: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 need of complex equipment. Here, the effect of nanodiamonds on the voltammetric response of cortisol immunosensors with different metals 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 BSA incubation. Optical microscopy, scanning electron microscopy, infrared spectroscopy, and differential pulsed voltammetry with ferri/ferrocyanide redox probe were used to analyze the sensor morphology and function. With ethanol pre-treatment, 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.

Keywords: nanodiamond, immunosensor, electrochemistry, charge transfer