# Development of Cortisol Sensors with Interdigitated Electrode Platforms Based on Barium Titanate Nanoparticles

## TL;DR

This paper describes a new cortisol sensor using barium titanate nanoparticles and interdigitated electrodes for stress monitoring.

## Contribution

A novel cortisol sensor platform using barium titanate nanoparticles and IDEs is developed and optimized for low cortisol detection.

## Key findings

- BaTiO3 nanoparticles synthesized at 160 °C showed optimal mesoporous structure and high surface area.
- Electrochemical tests showed significant impedance changes with cortisol concentration in saliva samples.
- The sensor effectively detected cortisol at physiological levels, indicating potential for stress monitoring.

## Abstract

Cortisol is a key biomarker for stress detection, and its levels can be monitored using point-of-care devices with sensors such as nanoparticles and interdigitated array electrodes (IDEs). This study developed an IDE platform using barium titanate (BaTiO3) particles synthesized via colloidal precipitation with titanium tetraisopropoxide, barium chloride, and Pluronic® P123. The calcination temperatures varied between 160 °C and 340 °C, with optimal results observed at 160 °C. Scanning electron microscopy revealed particles with an average size of 26 nm, and Fourier transform infrared spectroscopy confirmed the molecular composition after the removal of P123. X-ray diffraction analysis revealed anatase and brookite phases. Brunauer-Emmett-Teller analysis indicated changes in pore morphology, with samples treated at 160 °C exhibiting a type IV(a) mesoporous structure, a surface area of 163 m2/g, and an average pore diameter of 5.24 nm. Higher temperatures led to transitions to type IV(b) at 260 °C and type V at 340 °C, with reduced pore size. Electrochemical impedance spectroscopy was employed to evaluate the performance of the IDE sensor integrated with BaTiO3 nanoparticles and albumin across cortisol concentrations ranging from 5.0 to 20 ng/mL. Impedance measurements revealed a significant decrease in impedance (Z′) with increasing cortisol concentrations, indicating increased conductivity. Specifically, Nyquist plots for a saliva sample containing 5 ng/mL cortisol—within the typical physiological range—exhibited a marked increase in charge-transfer resistance (Rct), confirming the sensor’s ability to detect low hormone levels in biological fluids. These findings underscore the potential of BaTiO3-based IDE platforms at 160 °C for stress biomarker monitoring.