Understanding and optimising the packing density of perylene bisimide layers on CVD-grown graphene

The non-covalent functionalisation of graphene is an attractive strategy to alter the surface chemistry of graphene without damaging its superior electrical and mechanical properties. Using the facile method of aqueous-phase functionalisation on large-scale CVD-grown graphene, we investigated the formation of different packing densities in self-assembled monolayers (SAMs) of perylene bisimide derivatives and related this to the amount of substrate contamination. We were able to directly observe wet-chemically deposited SAMs in scanning tunnelling microscopy (STM) on transferred CVD graphene and revealed that the densely packed perylene ad-layers adsorb with the conjugated {\pi}-system of the core perpendicular to the graphene substrate. This elucidation of the non-covalent functionalisation of graphene has major implications on controlling its surface chemistry and opens new pathways for adaptable functionalisation in ambient conditions and on the large scale.Comment: 27 pages (including SI), 10 figure

Strong plasmonic enhancement of single molecule photostability in silver dimer optical antennas

Photobleaching is an effect terminating the photon output of fluorophores, limiting the duration of fluorescence-based experiments. Plasmonic nanoparticles (NPs) can increase the overall fluorophore photostability through an enhancement of the radiative rate. In this work, we use the DNA origami technique to arrange a single fluorophore in the 12-nm gap of a silver NP dimer and study the number of emitted photons at the single molecule level. Our findings yielded a 30× enhancement in the average number of photons emitted before photobleaching. Numerical simulations are employed to rationalize our results. They reveal the effect of silver oxidation on decreasing the radiative rate enhancement.We acknowledge funding by a starting grant (SiMBA, EU 261162) of the European Research Council (ERC) and the Deutsche Forschungsgesellschaft (AC 279/2-1 and TI 329/9-1). IK is grateful for the support by the Mobility Plus grant 1269/MOB/IV/2015/0 from the Polish Ministry of Science and Higher Education (MNiSW). CV thanks a scholarship of the Studienstiftung des deutschen Volkes. AIF-D and AC-G acknowledge funding from the Spanish MINECO under Contracts FIS2015- 64951-R and MDM-2014-0377-16-4, respectively. AIF-D also acknowledges funding from EU Seventh Framework Programme under Grant Agreement FP7-PEOPLE- 2013-CIG-630996. GA and PT acknowledge funding of the state ministry for research of lower saxony in the frame of the “Quantum- and Nanometrology” (QUANOMET) strategic research area. Quanomet is part of the LUH-TUBS research allianc

Understanding and optimising the packing density of perylene bisimide layers on CVD-grown graphene

The non-covalent functionalisation of graphene is an attractive strategy to alter the surface chemistry of graphene without damaging its superior electrical and mechanical properties. Using the facile method of aqueous-phase functionalisation on large-scale CVD-grown graphene, we investigated the formation of different packing densities in self-assembled monolayers (SAMs) of perylene bisimide derivatives and related this to the amount of substrate contamination. We were able to directly observe wet-chemically deposited SAMs in scanning tunnelling microscopy (STM) on transferred CVD graphene and revealed that the densely packed perylene ad-layers adsorb with the conjugated π-system of the core perpendicular to the graphene substrate. This elucidation of the non-covalent functionalisation of graphene has major implications on controlling its surface chemistry and opens new pathways for adaptable functionalisation in ambient conditions and on the large scale

Preparation and applications of platforms based on gold nanoparticles and graphene

Dans ce travail de thèse, de nouvelles méthodes de préparation d’interfaces recouvertes de nanoparticules d’or (Au NPs) et/ou d’oxyde de graphène réduit (rGO) ont été développées. La méthode de dépôt des nanoparticules d’or repose sur la technique dite « three phase junction » ou « jonction à trois phases ». Différentes conditions de dépôt par voltampérométrie et chronoampérométrie ont été utilisées pour optimiser la taille et la forme ainsi que la stabilité de ces nanostructures sur l’électrode. Les propriétés catalytiques des électrodes modifiées par les nanostructures métalliques ainsi obtenues ont été exploitées pour l’oxydation du glucose et la réduction d’oxygène. Ces interfaces ont montré une activité catalytique comparable à celle décrite dans la littérature pour d’autres électrodes. Ces interfaces ont été aussi investiguées comme substrats pour la spectroscopie SERS et pour la microscopie en fluorescence. La deuxième partie de la thèse a porté sur la mise au point d’une méthode simple pour la réduction et la fonctionnalisation de feuillets de GO. Deux molécules aromatiques (la dopamine et le tétrathiafulvalène, TTF) ont été utilisées pour la préparation de matériaux nanocomposites : rGO/dopamine et rGO/TTF. Les nanocomposites obtenus ont été caractérisées par différentes techniques d’analyse de surfaces et mesures électrochimiques. Les applications potentielles de ces nanocomposites ont été démontrées dans le domaine de capteurs et interrupteurs chimiques. Finalement, l’influence des Au NPs et/ou de rGO ainsi synthétisées sur les propriétés de fluorescence de biomolécules a été investiguée sur des interfaces modifiées par ces nanoobjets.In this thesis, new methods for the preparation of interfaces covered with gold nanoparticles (AuNPs) and/or reduced graphene oxide (rGO) based materials are introduced. An electrode|aqueous electrolyte|gold precursor solution in toluene three-phase junction was applied for AuNPs electrodeposition. Nanoparticles obtained in various conditions, with cyclic voltammetry or chronoamperometry, were investigated to find optimal conditions for their electrodeposition. To characterize the properties of AuNPs deposited at the electrode surface, electrochemical, spectroscopic and microscopic methods were employed. These modified surfaces were applied as a new catalytic and bioelectrocatalytic material, as well as sensing platform for surface-enhanced Raman spectroscopy and fluorescence microscopy. This allowed to demonstrate some potential applications of AuNPs deposited at the three-phase junction. In the following part, a new and simple method for GO reduction and simultaneous functionalization was proposed. Selected aromatic molecules were employed as reducing agents in reactions carried out under mild conditions. To characterize the new composites, electrochemical, spectroscopic and microscopic techniques were used. These composites were also investigated as potential substrates for sensors and (electro)chemical switches. Finally, AuNPs and/or rGO were applied as new sensors in fluorescence microscopy. Using these materials separately and afterwards hybrid coatings containing both structures, allowed exploring interactions between them. This strategy was also applied to explore fluorescence properties of a selected biomolecule and the influence of both materials on it

Strong plasmonic enhancement of single molecule photostability in silver dimer optical antennas

Photobleaching is an effect terminating the photon output of fluorophores, limiting the duration of fluorescence-based experiments. Plasmonic nanoparticles (NPs) can increase the overall fluorophore photostability through an enhancement of the radiative rate. In this work, we use the DNA origami technique to arrange a single fluorophore in the 12-nm gap of a silver NP dimer and study the number of emitted photons at the single molecule level. Our findings yielded a 30× enhancement in the average number of photons emitted before photobleaching. Numerical simulations are employed to rationalize our results. They reveal the effect of silver oxidation on decreasing the radiative rate enhancement

Extended-gate field-effect transistor (EG-FET) with molecularly imprinted polymer (MIP) film for selective inosine determination

A novelrecognitionunitofchemicalsensorforselectivedeterminationoftheinosine,renaldisfunction biomarker,wasdevisedandprepared.Forthatpurpose,inosine-templatedmolecularlyimprinted polymer (MIP) film wasdepositedonanextended-gate field-effect transistor(EG-FET)signaltransducing unit. TheMIP film waspreparedbyelectrochemicalpolymerizationofbis(bithiophene)derivatives bearing cytosineandboronicacidsubstituents,inthepresenceoftheinosinetemplateandathiophene cross-linker.AfterMIP film deposition,thetemplatewasremoved,andwasconfirmed byUV\u2013visible spectroscopy.Subsequently,the film compositionwascharacterizedbyspectroscopictechniques,andits morphology andthicknessweredeterminedbyAFM.The finally MIP film-coated extended-gate fieldeffect transistor(EG-FET)wasusedforsignaltransduction.Thiscombinationisnotwidelystudiedinthe literature,despitethefactthatitallowsforfacileintegrationofelectrodepositedMIP film withFET transducer. The lineardynamicconcentrationrangeofthechemosensorwas0.5\u201350 \u3bcM withinosinedetect- ability of0.62 \u3bcM. Theobtaineddetectabilitycompareswelltothelevelsoftheinosineinbody fluids which areintherange0\u20132.9 mM forpatientswithdiagnoseddiabeticnephropathy,goutorhyperur- icemia, andcanreach25 mM incertaincases.Theimprintingfactorforinosine,determinedfrompie- zomicrogravimetricexperimentswithuseoftheMIP film-coated quartzcrystalresonator,wasfoundto be 5.5.Higherselectivityforinosinewithrespecttocommoninterferentswasalsoachievedwiththe present molecularlyengineeredsensingelement.Theobtainedanalyticalparametersofthedevised chemosensor allowforitsuseforpracticalsamplemeasurements

Strong Plasmonic Enhancement of a Single Peridinin–Chlorophyll <i>a</i>–Protein Complex on DNA Origami-Based Optical Antennas

In this contribution, we fabricate hybrid constructs based on a natural light-harvesting complex, peridinin–chlorophyll <i>a</i>–protein, coupled to dimer optical antennas self-assembled with the help of the DNA origami technique. This approach enables controlled positioning of individual complexes at the hotspot of the optical antennas based on large, colloidal gold and silver nanoparticles. Our approach allows us to selectively excite the different pigments present in the harvesting complex, reaching a fluorescence enhancement of 500-fold. This work expands the range of self-assembled functional hybrid constructs for harvesting sunlight and can be further developed for other pigment–proteins and proteins

Nano–bio interactions of upconversion nanoparticles at subcellular level: biodistribution and cytotoxicity

Background: Modern medicine requires intensive research to find new diagnostic and therapeutic solutions. Recently, upconverting nanoparticles (UCNPs) doped with lanthanide ions have attracted significant attention. Methods: The efficient internalization of UCNPs by cells was confirmed, and their precise cellular localization was determined by electron microscopy and confocal studies. Results: UCNPs colocalized only with specific organelles, such as early endosomes, late endosomes and lysosomes. Furthermore, experiments with chemical inhibitors confirmed the involvement of endocytosis in UCNPs internalization and helped select several mechanisms involved in internalization. Exposure to selected UCNPs concentrations did not show significant cytotoxicity, induction of oxidative stress or ultrastructural changes in cells. Conclusion: This study suggests that UCNPs offer new diagnostic options for biomedical infrared imaging.</p