Functional fluorine-doped tin oxide coating for opto-electrochemical label-free biosensors
Dariusz Burnat, Petr Sezemský, Katarzyna Lechowicz, Marcin Koba, Marta Janczuk-Richter, Monika Janik, Vítězslav Straňák, Joanna Niedziółka‐Jönsson, Robert Bogdanowicz, Mateusz Śmietana
Abstract
Sensors operating in multiple domains, such as optical and electrochemical, offer properties making biosensing more effective than those working in a single domain. To combine such domains in one sensing device, materials offering a certain set of properties are required. Fluorine-doped tin oxide (FTO) thin film is discussed in this work as functional optically for guiding lossy modes and simultaneously electrochemically, i.e. as a conductive material for a working electrode. Performance of the FTO-based optical fiber lossy-mode resonance (LMR) sensor in both optical and electrochemical domains is analyzed. Additionally, to enhance applicability of the sensor, its probe-like reflection configuration has been developed. It is found that FTO may be considered as a promising alternative for other thin conductive oxides (TCO), such as indium tin oxide (ITO) that has been often applied up to date in various dual-domain sensing concepts. In the optical domain, the sensitivity of the FTO-LMR sensor to external refractive index (RI) has reached 450 nm/RIU in the RI range of 1.33–1.40 RIU. In the electrochemical domain, in turn, the response for FTO electrode in 1,1′-Ferrocenedimethanol solution has been reached with RedOx current low peak-to-peak separation. In contrast to the ITO-LMR sensors, the FTO-LMR counterparts exhibit a significant influence of applied potential on LMR wavelength shift in a wide potential range. It is shown using streptavidin as a target biomaterial that label-free biosensing applications of the FTO-LMR approach are possible. The dual-domain functionality allows for cross-verification between readouts received in both the domains, as well as enhancement of optical sensitivity when cross-domain interactions are applied.