From FFN Dual Probe Screening to ITO Microdevice for Exocytosis Monitoring: Electrochemical and Fluorescence Requirements

In this work, four different new fluorescent false neurotransmitters (FFN) probes were synthesized to contribute to the rationale of the FFN design. Their electroactive and spectroscopic properties were investigated. Hence, the optimal excitation and emission wavelengths (from 344 to 393 nm and 423 to 474 nm, respectively) make these probes adapted to fluorescence microscopy. Moreover, their electroactivity were demonstrated to occur at relatively low oxidation potentials for three of them (FFN132, FFN145 and FFN122: 0.26, 0.25 and 0.30 V vs. Ag/AgCl, respectively) and at 0.74 V vs. Ag/AgCl for FFN21 on carbon fiber electrodes. However, epifluorescence observations evidenced that the new designed FFN with the best spectroscopic and electrochemical properties (FFN122) did unfortunately not accumulate into secretory vesicles of model BON N13 cells. It thus confirms that FFN42 is currently the best bioelectrofluorescent compromise. This is why total internal fluorescence reflection microscopy measurements were then studied with the model FFN42 and BON N13 cells. Beyond the choice of the appropriate FFN, other analytical requirements are needed. As a consequence, the features of the transparent and conducting indium tin oxide (ITO) microdevice for coupled amperometry-fluorescent measurements were investigated and optimized in terms of effects on the electrochemical performances and reusability. These results pave the way for future coupled investigations of exocytosis with the FFN-ITO device association.

Automated summary

In this study, four new fluorescent false neurotransmitters (FFN) probes were synthesized and their spectroscopic and electrochemical properties were investigated. The results showed that one of the probes (FFN122) had the optimal suitability for fluorescence microscopy. However, it was found that this probe did not accumulate into secretory vesicles of model cells. Therefore, FFN42 is currently the best bioelectrofluorescent compromise. Additionally, the effects of a transparent and conducting indium tin oxide (ITO) microdevice on electrochemical performances and reusability were examined.