Dual-polarity MALDI mass spectrometry and imaging of oil binders and fatty acids in artworks using cyanographene as a single matrix.

Matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) and imaging mass spectrometry (IMS) are being increasingly recognized for the detection and visualization of various organic species including lipids and fatty acids. Nevertheless, most MALDI matrices perform optimally in one ionization mode. This study investigates the performance of cyano derivative of graphene (G-CN) as a matrix in two polarities of MALDI MS and IMS for the detection of oil binders and fatty acids in artworks, and compares it with classical MALDI matrices (2,5-dihydroxybenzoic acid, 9-aminoacridine). Results revealed the ability of G-CN to provide high quality positive and negative mass spectra of oils and fatty acids, respectively, with lowest matrix-induced interferences among tested matrices and minimal effects of the presence of inorganic pigments. The newly developed approach makes both oil and fatty acid identifiable in a single spot simply by covering the sample surface with one matrix and switching the polarity in MALDI without any sample manipulation. G-CN offers effective matrix to analyte energy transfer, ability to detect components in less than 100 ng of oil at a MALDI spot and lesser analyte fragmentation than the compared conventional matrices. Furthermore, it enables direct mapping of specific m/z features corresponding to triacylglycerol (TAG), products of TAG oxidation and deprotonated acids using one nanoparticle matrix in MALDI IMS. This research shows potential for technical innovations in the study of art micro-environments and degradation phenomena of historical artworks.

Selective Functionalization Blended with Scaffold Conductivity in Graphene Acid Promotes H2O2 Electrochemical Sensing.

The widespread industrial use of H2O2 has provoked great interest in the development of new and more efficient materials for its detection. Enzymatic electrochemical sensors have drawn particular attention, primarily because of their excellent selectivity. However, their high cost, instability, complex immobilization, and inherent tendency toward denaturation of the enzyme significantly limit their practical usefulness. Inspired by the powerful proton-catalyzed H2O2 reduction mechanism of peroxidases, we have developed a well-defined and densely functionalized carboxylic graphene derivative (graphene acid, GA) that serves as a proton source and conductive electrode for binding and detecting H2O2. An unprecedented H2O2 sensitivity of 525 µA cm-2 mM-1 is achieved by optimizing the balance between the carboxyl group content and scaffold conductivity of GA. Importantly, the GA sensor greatly outperforms all reported carbon-based H2O2 sensors and is superior to enzymatic ones because of its simple immobilization, low cost, and uncompromised sensitivity even after continuous operation for 7 days. In addition, GA-based sensing electrodes remain highly selective in the presence of interferents such as ascorbic acid, paracetamol, and glucose, as well as complex matrices such as milk. GA-based sensors thus have considerable potential for use in practical industrial sensing technologies.

Microwave Energy Drives "On-Off-On" Spin-Switch Behavior in Nitrogen-Doped Graphene.

The established application of graphene in organic/inorganic spin-valve spintronic assemblies is as a spin-transport channel for spin-polarized electrons injected from ferromagnetic substrates. To generate and control spin injection without such substrates, the graphene backbone must be imprinted with spin-polarized states and itinerant-like spins. Computations suggest that such states should emerge in graphene derivatives incorporating pyridinic nitrogen. The synthesis and electronic properties of nitrogen-doped graphene (N content: 9.8%), featuring both localized spin centers and spin-containing sites with itinerant electron properties, are reported. This material exhibits spin-switch behavior (on-off-on) controlled by microwave irradiation at X-band frequency. This phenomenon may enable the creation of novel types of switches, filters, and spintronic devices using sp2 -only 2D systems.

2D Chemistry: Chemical Control of Graphene Derivatization.

Controllable synthesis of graphene derivatives with defined composition and properties represents the holy grail of graphene chemistry, especially in view of the low reactivity of graphene. Recent progress in fluorographene (FG) chemistry has opened up new routes for synthesizing a plethora of graphene derivatives with widely applicable properties, but they are often difficult to control. We explored nucleophilic substitution on FG combining density functional theory calculations with experiments to achieve accurate control over the functionalization process. In-depth analysis revealed the complexity of the reaction and identified basic rules for controlling the 2D chemistry. Their application, that is, choice of solvent and reaction time, enabled facile control over the reaction of FG with N-octylamine to form graphene derivatives with tailored content of the alkylamine functional group (2.5-7.5% N atomic content) and F atoms (31.5-3.5% F atomic content). This work substantially extends prospects for the controlled covalent functionalization of graphene.