Photo-responsive graphene and carbon nanotubes to control and tackle biological systems

Photo-responsive multifunctional nanomaterials are receiving considerable attention for biological applications because of their unique properties. The functionalization of the surface of carbon nanotubes (CNTs) and graphene, among other carbon based nanomaterials, with molecular switches that exhibit reversible transformations between two or more isomers in response to different kind of external stimuli, such as electromagnetic radiation, temperature and pH, has allowed the control of the optical and electrical properties of the nanomaterial. Light-controlled molecular switches, such as azobenzene and spiropyran, have attracted a lot of attention for nanomaterial's functionalization because of the remote modulation of their physicochemical properties using light stimulus. The enhanced properties of the hybrid materials obtained from the coupling of carbon based nanomaterials with light-responsive switches has enabled the fabrication of smart devices for various biological applications, including drug delivery, bioimaging and nanobiosensors. In this review, we highlight the properties of photo-responsive carbon nanomaterials obtained by the conjugation of CNTs and graphene with azobenzenes and spiropyrans molecules to investigate biological systems, devising possible future directions in the field

Photochemically Induced Phase Change in Monolayer Molybdenum Disulfide.

Monolayer transition metal dichalcogenide (TMDs) are promising candidates for two-dimensional (2D) ultrathin, flexible, low-power, and transparent electronics and optoelectronics. However, the performance of TMD-based devices is still limited by the relatively low carrier mobility and the large contact resistance between the semiconducting 2D channel material and the contact metal electrodes. Phase-engineering in monolayer TMDs showed great promise in enabling the fabrication of high-quality hetero-phase structures with controlled carrier mobilities and heterojunction materials with reduced contact resistance. However, to date, general methods to induce phase-change in monolayer TMDs either employ highly-hostile organometallic compounds, or have limited compatibility with large-scale, cost-effective device fabrication. In this paper, we report a new photochemical method to induce semiconductor to metallic phase transition in monolayer MoS2 in a benign chemical environment, through a bench-top, cost-effective solution phase process that is compatible with large-scale device fabrication. It was demonstrated that photoelectrons produced by the band-gap absorption of monolayer MoS2 have enough chemical potential to activate the phase transition in the presence of an electron-donating solvent. This novel photochemical phase-transition mechanism advances our fundamental understanding of the phase transformation in 2D transition metal dichalcogenides (TMDs), and will open new revenues in the fabrication of atomically-thick metal-semiconductor heterostructures for improved carrier mobility and reduced contact resistance in TMD-based electronic and optoelectronic devices

A Bioengineered Memory Storage Device Using Bacteriorhodopsin and Graphene

Bacteriorhodopsin (BR) is a photoactive protein, which has been studied as a memory storage device owing to its photochemical and thermal stability. BR photocycle comprises of two distinct stable binary states, bR (0) and Q (1) based on the wavelength of the applied radiation. However, such devices have a limited success due to low quantum yield of the Q state1. Many studies have used genetic and chemical modification as optimization strategies to increase the yield of the Q state compromising the overall photochemical stability of the BR1. Here we come up with a unique way of stabilizing the conformations of BR and thereby the BR and Q states of the protein through its adsorption onto graphene. We have used all-atom molecular dynamics (MD) simulations utilizing NAMD (Nanoscale Molecular Dynamics) and the CHARMM (Chemistry at HARvard Macromolecular Mechanics) force field to understand the interactive events at the interface of BR and a single layer graphene sheet. Based on the stable RMSD (Root Mean Square Deviation) and interactive energies such as Van-der-Waals and electrostatics, we propose that the adsorption of BR onto graphene can stabilize the photochemical behavior of BR. Furthermore, the switching between Cis and Trans conformations of the retinal based on the angular change of the dihedral demonstrates that such an adsorption is beneficial to preserve the binary states

Laser-induced chemical transformation of freestanding graphene oxide membranes in liquid and gas ammonia environments

Laser-induced chemical conversion of graphene oxide (GO) is an effective way to modify its properties and expand its potential use for numerous applications. In this work, a mechanically stable and flexible free-standing GO membrane is synthesized and further processed by ultraviolet laser radiation in gas and liquid ammonia-rich environments. Electron and atomic force microscopy, as well as X-ray photoelectron spectroscopy analysis, reveal that laser irradiation in gas leads to a large defect-induced morphology modification and high deoxygenation process, accompanied by the slight incorporation of nitrogen functionality to the reduced GO structure. Conversely, irradiation in liquid provokes significant integration of nitrogen groups, essentially amines, into a partially reduced GO structure, without evident modification of the morphology. Electrical measurements on the macro- and nano-scale point to a complex contribution of morphology and oxidized regions to the overall resistance of the rGO.The authors acknowledge the financial support of the Spanish Ministry of Economy and Competitiveness under the project ENE2014-56109-C3-3-R, in addition to the Romanian National Authority for Scientific Research and Innovation, CNCS – UEFISCDI, under the Grants PN-II-ID-PCE-2012-4-0292 and PNII- RU-TE-2014-4-1194. ICMAB acknowledges financial support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0496).Peer reviewe

Strategies for the Thermal and Photochemical Modification of Gold Nanoparticles (AuNPs) and the Fabrication of AuNP Hybrid Materials

Among the existing approaches for the functionalization of the gold nanoparticle (AuNP), a direct interfacial organic reaction of terminal functional groups exposed on the surface of template nanoparticles with various reactants has been shown as a promising strategy to incorporate desired functionality onto the AuNP monolayer. In our own attempts to extend the types of reactions that can be utilized for efficient interfacial modifications of AuNPs, we examined uncatalyzed Huisgen 1,3-dipolar click-type cycloaddition of azide-modified AuNPs to terminal alkynes. These particular reactions were found to be generally too slow to be useful at ambient temperatures but it was shown that high pressure conditions (11 000 atm) can be used as an efficient tool to facilitate these reactions on the AuNPs with high yields and with no detrimental effects on the gold core. Photochemical reactions of suitably functionalized gold nanoparticles (AuNPs) can also be utilized to chemically modify AuNPs under mild conditions, given that photoinitiated reactions don’t require high temperature or catalysis. Diazirine, as an excellent carbene precursor, readily generates the reactive carbene intermediate by photoinitiated nitrogen extrusion. In Chapter Three, the synthesis and characterization of diazirine-modified AuNPs are described and it is demonstrated that upon irradiation, intermediate carbene-modified AuNPs are formed and that their subsequent insertion reactions with trapping reagents lead to interfacial modification of the diazirine-modified AuNPs. Furthermore, I show that photo-generation of a carbene on the monolayer of AuNPs in the presence of host materials drives the formation of covalently assembled AuNP-based hybrid materials via carbene insertion/addition reactions. Diazirine-modified AuNPs with different sizes were prepared and irradiated in the presence of a series of substrates including CNTs, diamond, graphene, and glass slide. Upon UV irradiation of diazirines attached onto the AuNPs, intermediate carbenes were generated and the following carbene insertion/addition reactions could occur with the surface functionality of substrates. Using this method, we prepared hybrids including AuNP-CNT, AuNP-Diamond, AuNP-Graphene, and AuNP-Glass. In total, this thesis work reviews my efforts toward chemical modification of AuNPs via thermal and photothermal interfacial reactions. Moreover, it provides an efficient strategy for the synthesis of covalently assembled AuNP-based hybrid materials employing carbene insertion/addition reactions