Exploiting double exchange Diels-Alder cycloadditions for immobilization of peptide nucleic acids on gold nanoparticles

The generation of PNA-decorated gold nanoparticles (AuNPs) has revealed to be more difficult as compared to the generation of DNA-functionalized ones. The less polar nature of this artificial nucleic acid system and the associated tendency of the neutral poly-amidic backbone to aspecifically adsorb onto the gold surface rather than forming a covalent bond through gold-thiol interaction, combined with the low solubility of PNAs itself, form the main limiting factors in the functionalization of AuNP. Here, we provide a convenient methodology that allows to easily conjugate PNAs to AuNP. Positively charged PNAs containing a masked furan moiety were immobilized via a double exchange Diels-Alder cycloaddition onto masked maleimide-functionalized AuNPs in a one-pot fashion. Conjugated PNA strands retain their ability to selectively hybridize with target DNA strands. Moreover, the duplexes resulting from hybridization can be detached through a retro-Diels-Alder reaction, thus allowing straightforward catch-and-release of specific nucleic acid targets

Hybrid nanoreceptors for high sensitivity detection of small molecules by NMR chemosensing

Self-assembled gold nanoparticles onto colloidal silica nanoparticles exhibited higher magnetization transfer efficiencies in NMR chemosensing experiments, allowing the detection of analytes as low as 10 μM

Toward Supramolecular Nanozymes for the Photocatalytic Activation of Pt(IV) Anticancer Prodrugs

A supramolecular nanozyme for the photocatalytic conversion of a Pt(IV) anticancer complex to cisplatin is described herein. We employed 1.9 nm Au nanoparticles decorated with thiol ligands bearing a TACN (1,4,7-triazacyclononane) headgroup to encapsulate FMN (riboflavin-5'-phosphate). In the presence of an electron donor, flavin-loaded nanoparticles photocatalyzed the reductive activation of the prodrug cis,cis,trans-[Pt(NH3)(2)(Cl-2)(O2CCH2CH2COOH)(2)] to cisplatin, achieving turnover frequency values of 7.4 min(-1).We acknowledge financial support from the Spanish State Research Agency for the grants CTQ2016-80844-R, BIO201677367-R, PID2019-111649RB-I00 and PCI2018-092984. This work was performed under the Severo Ochoa Centres of Excellence and Maria de Maeztu Units of Excellence Program from the Spanish State Research Agency -Grant No. CEX2018-000867-S (DIPC) and MDM-2017-0720 (CIC biomaGUNE). We also thank Fondazione Cariparo (Ricerca Scientifica di Eccellenza Grant "SELECT''). A. M. has received funding from the European Union's Horizon 2020 Research and Innovation Programme under Marie SklodowskaCurie Actions grant no. 793702. We thank the Spanish MultiMetDrugs network (RED2018-102471-T) for fruitful discussion

Supramolecular chemosensors for the detection of phenethylamines

In this work I described and discussed the results of a research project which focused on both development and application of the NMR-chemosensing technique. This technique is based on the combination of gold nanoparticles 2 nm in diameter coated with specific thiols and particular NMR experiments, and it allows to “extract” from the NMR spectrum of a mixture of substances the single NMR spectrum of the analyte bound by the nanoparticle. Specifically, the main goal of my work was to demonstrate how this technique can be successfully used for designer-drug detection. The majority of the new drugs that appear on the market every year belong to this category, i.e. they are structural analogs of already well-known drugs. Designer drugs represent a big health issue, because no studies on them are available, therefore the risks and potential long-term adverse effects are not known. Moreover, as reference standards are not available, their sensing with routine techniques is difficult. The technique that I will describe also works on real street samples, with no pretreatment, thus giving the possibility to get from the seizure of the powder to the characterization of the substance in a few hours. I’ll also show that to improve the potentialities of NMR chemosensing in terms of detection limit and sensitivity one can work from two sides. First, it is possible to improve the design of the coating thiol, obtaining a monolayer with different affinities and different capability of magnetization transfer, both crucial aspects for the technique. On the other hand, it is possible to im-prove sensitivity by acting directly on the type of NMR experiment used as well, also in combination with tricks that exploit magnetization enhancement, such as using the water trapped in the monolayer as an additional magnetization source or using the capability of gold nanoparticles to self-assemble on silica nanospheres, in order to enhance the nanoreceptor’s size. Combining all the various things, I will demonstrate how it is possible to sense inorganic species too, such as K+, which do not have an NMR signal per se. Finally, as NMR is not, as of now, a technique that is easy to apply for on-field analysis, in the last part of this paper I propose a point-of-care sensor developed in the form of an indicator strip in which a self-assembled supramolecular receptor composed of a cucurbituril and a dye can selectively sense the presence, or not, of a drug in a quick, safe and cheap way.In questa tesi ho descritto e discusso i risultati ottenuti nell’ambito di un progetto di ricerca focalizzato sull’applicazione e lo sviluppo della tecnica dell’NMR-chemosensing. Questa tecnica è basata sulla combinazione di nanoparticelle d’oro da 2 nm di diametro passivate con opportuni tioli e di particolari esperimenti NMR e consente di “estrarre” dallo spettro NMR di una miscela di composti lo spettro NMR dell’analita riconosciuto dalla nanoparticella. In particolare, lo scopo primario del mio lavoro è stato dimostrare come questa tecnica possa essere usata con successo per il rilevamento delle cosiddette “designer drugs”. La maggior parte delle nuove droghe immesse sul mercato ogni anno altro non sono che analoghi strutturali di droghe già diffuse. Ciò rappresenta un grave problema di salute pubblica, perché non essendo queste nuove sostanze mai state studiate, non se ne conoscono i potenziali rischi e gli effetti a lungo termine. In più, non esistendo standard di riferimento, la loro rilevazione con tecniche tradizionali risulta difficoltosa. La tecnica che verrà descritta è stata testata e funziona anche su campioni reali, senza bisogno di pretrattamento del campione, e dà la possibilità di arrivare dal sequestro alla caratterizzazione strutturale della sostanza stupefacente nel giro di poche ore. Dimostrerò anche che per migliorare le potenzialità dell’NMR-chemosensing in termini sia di sensibilità che versatilità si può agire su un doppio fronte. Da un lato, è possibile migliorare la struttura del tiolo che ricopre le nanoparticelle, ottenendo un monostrato con maggior affinità e maggior capacità di trasferimento della magnetizzazione, entrambi aspetti fondamentali della tecnica. Dall’altro, è possibile migliorare la sensibilità agendo direttamente sul tipo di esperimento utilizzato, anche in abbinamento ad astuzie che possano aumentare l’efficienza del trasferimento di magnetizzazione, quali ad esempio usare l’acqua intrappolata nel monostrato come fonte supplementare di magnetizzazione oppure sfruttare la capacità delle nanoparticelle d’oro di autoassemblarsi su nanosfere di silice per aumentare le dimensioni del nanorecettore. Combinando tutte queste accortezze, dimostrerò come sia possibile analizzare con questa tecnica anche specie inorganiche, come K+, che di per sé non possiedono alcun segnale NMR. Infine, visto che l’NMR non è, per ora, una tecnica di facile applicazione per analisi sul campo, nell’ultima parte di questo lavoro di tesi mi sono occupato anche un sensore point-of-care sviluppato sotto forma di cartina indicatrice, in cui un recettore supramolecolare autoassemblato composto da un cucurbiturile e un colorante può indicare selettivamente la presenza o meno di sostanza stupefacenti in modo rapido, sicuro ed economico

Supramolecular chemosensors for the detection of phenethylamines

In this work I described and discussed the results of a research project which focused on both development and application of the NMR-chemosensing technique. This technique is based on the combination of gold nanoparticles 2 nm in diameter coated with specific thiols and particular NMR experiments, and it allows to “extract” from the NMR spectrum of a mixture of substances the single NMR spectrum of the analyte bound by the nanoparticle. Specifically, the main goal of my work was to demonstrate how this technique can be successfully used for designer-drug detection. The majority of the new drugs that appear on the market every year belong to this category, i.e. they are structural analogs of already well-known drugs. Designer drugs represent a big health issue, because no studies on them are available, therefore the risks and potential long-term adverse effects are not known. Moreover, as reference standards are not available, their sensing with routine techniques is difficult. The technique that I will describe also works on real street samples, with no pretreatment, thus giving the possibility to get from the seizure of the powder to the characterization of the substance in a few hours. I’ll also show that to improve the potentialities of NMR chemosensing in terms of detection limit and sensitivity one can work from two sides. First, it is possible to improve the design of the coating thiol, obtaining a monolayer with different affinities and different capability of magnetization transfer, both crucial aspects for the technique. On the other hand, it is possible to im-prove sensitivity by acting directly on the type of NMR experiment used as well, also in combination with tricks that exploit magnetization enhancement, such as using the water trapped in the monolayer as an additional magnetization source or using the capability of gold nanoparticles to self-assemble on silica nanospheres, in order to enhance the nanoreceptor’s size. Combining all the various things, I will demonstrate how it is possible to sense inorganic species too, such as K+, which do not have an NMR signal per se. Finally, as NMR is not, as of now, a technique that is easy to apply for on-field analysis, in the last part of this paper I propose a point-of-care sensor developed in the form of an indicator strip in which a self-assembled supramolecular receptor composed of a cucurbituril and a dye can selectively sense the presence, or not, of a drug in a quick, safe and cheap way

1 H NMR Chemosensing of Potassium Ions Enabled by Guest-Induced Selectivity Switch of a Gold Nanoparticle/Crown Ether Nanoreceptor

A sensing protocol to detect potassium ions in water by 1 H NMR spectroscopy is described. The method exploits the K + -modulated affinity of 18-crown-6 functionalized gold nanoparticles towards organic ions, combined with NOE magnetization transfer. Binding of K + to the crown ether moieties switches the nanoreceptor preference (and its ability to transfer magnetization) from organic cations (tyramine) to organic anions (phloretate). In this way, a ratiometric NMR signal is produced with a detection limit of 0.6 mM. Detection can be performed in 20 min with standard instruments and with little interference from other alkali and alkaline earth metal ions present in the sample

Intracluster ligand rearrangement: an NMR-based thermodynamic study

Ligand and metal exchange reactions are powerful methods to tailor the properties of atomically precise metal nanoclusters. Hence, a deep understanding of the mechanisms behind the dynamics that rule the ligand monolayer is crucial for its specific functionalization. Combining variable-temperature NMR experiments and dynamic-NMR simulations, we extract the thermodynamic activation parameters of a new exchange reaction: the intracluster ligand rearrangement between the two symmetry-unique positions in [Ag25(DMBT)18]− and [Ag24Au(DMBT)18]− clusters. We report for the first time that this peculiar intracluster modification does not seem to proceed via metal–sulphur bond breaking and follows a first-order rate law, being therefore a process independent from the well-described collisional ligand exchange.</p

Detection and identification of designer drugs by nanoparticle-based NMR chemosensing

Properly designed monolayer-protected nanoparticles (2 nm core diameter) can be used as nanoreceptors for selective detection and identification of phenethylamine derivatives (designer drugs) in water. The molecular recognition mechanism is driven by the combination of electrostatic and hydrophobic interactions within the coating monolayer. Each nanoparticle can bind up to 30-40 analyte molecules. The affinity constants range from 105 to 106 M-1 and are modulated by the hydrophobicity of the aromatic moiety in the substrate. Detection of drug candidates (such as amphetamines and methamphetamines) is performed by using magnetization (NOE) or saturation (STD) transfer NMR experiments. In this way, the NMR spectrum of the drug is isolated from that of the mixture, allowing broad-class multianalyte detection and even identification of unknowns. The introduction of a dimethylsilane moiety in the coating monolayer allows performing STD experiments in complex mixtures. In this way, a detection limit of 30 \u3bcM is reached with standard instruments

Selective NMR detection of N-methylated amines using cavitand-decorated silica nanoparticles as receptors

We report a strategy for the realization of NMR chemosensors based on the spontaneous self-assembly of lower rim pyridinium-functionalized tetraphopshonate cavitands on commercial silica nanoparticles. These nanohybrids enable the selective detection of physiologically relevant N-methylated amines, with a limit of detection of 31 mu M, via STD-based NMR experiments, achieving for the first time fine structural selectivity in nanoparticle-assisted NMR chemosensing

Selective NMR detection of N-methylated amines using cavitand-decorated silica nanoparticles as receptors

We report a strategy for the realization of NMR chemosensors based on the spontaneous self-assembly of lower rim pyridiniumfunctionalized tetraphopshonate cavitands on commercial silica nanoparticles. These nanohybrids enable the selective detection of physiologically relevant N-methylated amines, with a limit of detection of 31 mM, via STD-based NMR experiments, achieving for the first time fine structural selectivity in nanoparticle-assisted NMR chemosensing