Coumarine-Tagged Mixed-Monolayer Protected Gold Nanoparticles for the Detection of ATP

This project's aim is to create a supramolecular system capable of detecting ATP. Such scope is possible with a system consisting of gold nanoparticles coated with a mixed layer of receiver and transducer thiols. The receiver thiols bear a TACN • Zn (II) moiety, capable of binding ATP; the transducer ones have both a fluorophore and a negatively charged group - namely a carboxylate - and are able to interact with the receiver thiols, but with a lower affinity compared to ATP. The interaction between the carboxylate group and the TACN • Zn(II) brings the fluorophore closer to the nanoparticle, leading to a quenching of its fluorescence. When ATP is present, its ability to displace the carboxylate ion (due to its higher affinity for the TACN • Zn(II) moiety) allows the fluorophore to move apart from the nanoparticle, restoring the fluorescence. A proof-of-concept system like the aforementioned one has been previously developed, using L-Tryptophan both as a fluorophore and as a negatively charged group. While the underlying mechanism was proved to be effective, the use of Tryptophan gave rise to a few problems with its employment in a biomedical environment, from the low sensitivity of the sensor to the background fluorescence noise of the naturally occurring amino acid in biological tissues. With these issues in mind a thiol tagged with a coumarine fluorophore and an aspartate linker - which allows to bind TACN • Zn(II) - has been developed and implemented on gold nanoparticles as described before to yield a sensor more effective and more suitable for its intended use.