Reagentless and Label-Free Electrochemical Aptasensor Using Polyaniline Incorporated with a Battery-Free NFC Potentiostat for One-Step Detection of Cortisol

Cortisol serves as a vital biomarker for stress levels, but current evaluation methods are complex and resource-intensive. Traditional detection approaches require elaborate procedures and sophisticated equipment, limiting their accessibility and practical application. There is a pressing need for user-friendly, cost-effective, and portable technologies that can efficiently monitor cortisol levels in real-world settings. We developed a reagentless and label-free electrochemical aptasensor for one-step detection of salivary cortisol utilizing polyaniline (PANI) as an active conductive polymer and integrating it with a battery-free near-field communication (NFC) potentiostat. The PANI-modified screen-printed electrode exhibited excellent conductivity and surface-enhancing properties, facilitating efficient aptamer immobilization and enabling reagentless electrochemical detection of cortisol without the need for additional redox reagents. The battery-free NFC integration enables seamless data transfer to mobile devices, providing real-time analysis capabilities. The proposed sensor achieved a low detection limit of 27 pM within 33 min of analysis time and exhibited high selectivity for cortisol, which makes it suitable for patients with Addison's disease. Also, the matrices in artificial saliva were not affected by cortisol detection. A performance comparison between commercial EmStat4s and our NFC-based potentiostat in artificial saliva validated the accuracy of the system. This innovative platform represents a significant advancement in point-of-care diagnostics by combining advanced conductive materials with modern electronics. The system's portability, cost-effectiveness, and user-friendly design make it particularly valuable for noninvasive stress monitoring through salivary analysis, opening new possibilities for accessible bioanalysis and personalized health monitoring.