Click and detect: Versatile ampicillin aptasensor enabled by click chemistry on a graphene-alkyne derivative

Tackling the current problem of antimicrobial resistance (AMR) requires fast, inexpensive, and effective methods for controlling and detecting antibiotics in diverse samples at the point of interest. Cost-effective, disposable, point-of care electrochemical biosensors are a particularly attractive option. However, there is a need for conductive and versatile carbon-based materials and inks that enable effective bioconjugation under mild conditions for the develop ment of robust, sensitive, and selective devices. This work describes a simple and fast methodology to construct an aptasensor based on a novel graphene derivative equipped with alkyne groups prepared via fluorographene chem istry. Using click chemistry, an aptamer is immobilized and used as a suc cessful platform for the selective determination of ampicillin in real samples in the presence of interfering molecules. The electrochemical aptasensor displayed a detection limit of 1.36 nM, high selectivity among other antibi otics, the storage stability of 4 weeks, and is effective in real samples. Addi tionally, structural and docking simulations of the aptamer shed light on the ampicillin binding mechanism. The versatility of this platform opens up wide possibilities for constructing a new class of aptasensor based on disposable screen-printed carbon electrodes usable in point-of-care devices.Web of Scienc

Silver covalently bound to cyanographene overcomes bacterial resistance to silver nanoparticles and antibiotics

The ability of bacteria to develop resistance to antibiotics is threatening one of the pillars of modern medicine. It was recently understood that bacteria can develop resistance even to silver nanoparticles by starting to produce flagellin, a protein which induces their aggregation and deactivation. This study shows that silver covalently bound to cyanographene (GCN/Ag) kills silver-nanoparticle-resistant bacteria at concentrations 30 times lower than silver nanoparticles, a challenge which has been so far unmet. Tested also against multidrug resistant strains, the antibacterial activity of GCN/Ag is systematically found as potent as that of free ionic silver or 10 nm colloidal silver nanoparticles. Owing to the strong and multiple dative bonds between the nitrile groups of cyanographene and silver, as theory and experiments confirm, there is marginal silver ion leaching, even after six months of storage, and thus very high cytocompatibility to human cells. Molecular dynamics simulations suggest strong interaction of GCN/Ag with the bacterial membrane, and as corroborated by experiments, the antibacterial activity does not rely on the release of silver nanoparticles or ions. Endowed with these properties, GCN/Ag shows that rigid supports selectively and densely functionalized with potent silver-binding ligands, such as cyanographene, may open new avenues against microbial resistance.Web of Scienceart. no. 200309

Hematene: A sustainable 2D conductive platform for visible-light-driven photocatalytic ammonia decomposition

The emerging class of 2D non-van der Waals (n-vdW) materials, including 2D iron oxides, possesses unique properties and high applicability, making them attractive for various technological applications. However, the synthesis of these materials through a scalable and eco-friendly method remains a challenge, as most known chemical exfoliation processes require toxic organic solvents. In this study, we report a green synthesis of 2D hematene (α-Fe2O3) using an ultrasound-supported exfoliation method of earth-abundant iron oxide ore in a pure aqueous solution. The resulting hematene sheets, only a few nanometers thick, exhibit superior electrochemical performance in terms of charge transfer processes, making them ideal for photocatalytic applications. By doping a conductive hematene substrate with ruthenium, we demonstrate a synergistic effect for generating electrons and holes under visible light irradiation. Using this approach, we successfully decomposed ammonia into hydrogen and nitrogen, highlighting the potential of this novel class of environmentally-friendly photocatalysts for clean energy production. Overall, our water-assisted scalable synthesis of hematene offers a promising strategy for producing efficient and sustainable photocatalysts.Web of Science34art. no. 10188

Magnetic polaron states in photoluminescent carbon dots enable hydrogen peroxide photoproduction

Photoactivation of aspartic acid-based carbon dots (Asp-CDs) induces the generation of spin-separated species, including electron/hole (e−/h+) polarons and spin-coupled triplet states, as uniquely confirmed by the light-induced electron paramagnetic resonance spectroscopy. The relative population of the e−/h+ pairs and triplet species depends on the solvent polarity, featuring a substantial stabilization of the triplet state in a non-polar environment (benzene). The electronic properties of the photoexcited Asp-CDs emerge from their spatial organization being interpreted as multi-layer assemblies containing a hydrophobic carbonaceous core and a hydrophilic oxygen and nitrogen functionalized surface. The system properties are dissected theoreti cally by density functional theory in combination with molecular dynamics simulations on quasi-spherical assemblies of size-variant flakelike model sys tems, revealing the importance of size dependence and interlayer effects. The formation of the spin-separated states in Asp-CDs enables the photoproduc tion of hydrogen peroxide (H2O2) from water and water/2-propanol mixture via a water oxidation reaction.Web of Science1932art. no. 220658

Graphene nanobeacons with high-affinity pockets for combined, selective, and effective decontamination and reagentless detection of heavy metals

Access to clean water for drinking, sanitation, and irrigation is a major sustainable development goal of the United Nations. Thus, technologies for cleaning water and quality-monitoring must become widely accessible and of low-cost, while being effective, selective, sustainable, and eco-friendly. To meet this challenge, hetero-bifunctional nanographene fluorescent beacons with high-affinity pockets for heavy metals are developed, offering top-rated and selective adsorption for cadmium and lead, reaching 870 and 450 mg g(-1), respectively. The heterobifunctional and multidentate pockets also operate as selective gates for fluorescence signal regulation with sub-nanomolar sensitivity (0.1 and 0.2 nm for Pb2+ and Cd2+, respectively), due to binding affinities as low as those of antigen-antibody interactions. Importantly, the acid-proof nanographenes can be fully regenerated and reused. Their broad visible-light absorption offers an additional mode for water-quality monitoring based on ultra-low cost and user-friendly reagentless paper detection with the naked-eye at a limit of detection of 1 and 10 ppb for Pb2+ and Cd2+ ions, respectively. This work shows that photoactive nanomaterials, densely-functionalized with strong, yet selective ligands for targeted contaminants, can successfully combine features such as excellent adsorption, reusability, and sensing capabilities, in a way to extend the material's applicability, its life-cycle, and value-for-money.Web of Science1833art. no. 220100

N-doped graphene and N-doped graphene acid: Heteroatom doping for very efficient broad-band optical limiting performance from UV to NIR

The present work reports on the exceptional optical limiting performance of some recently synthesized nitrogen-doped graphene derivatives (NGs) by substitutional heteroatom doping. In particular, the optical limiting performance of NGs having different nitrogen contents and some NG-based quantum dots is investigated in a broad-band spectral range, from 355 to 1850 nm, using 4 ns laser pulses. The obtained results show that the present N-doped graphene derivatives exhibit very efficient broad-band optical limiting performance, attaining record low values of optical limiting onset (OLon), in particular for NIR wavelengths, significantly lower than those of other previously studied graphene derivatives and other families of benchmark materials for optical limiting. The present results demonstrate that tuning the N-doping of graphene acid is a very powerful and efficient strategy for the enhancement of the OL action of graphene, rendering it the strongest currently known optical limiting material, improving dramatically its potential for various optoelectronic and photonic applications.Web of Science12633143451433

Metal-free cysteamine-functionalized graphene alleviates mutual interferences in heavy metal electrochemical detection

Heavy metal pollutants are of great concern to environmental monitoring due to their potent toxicity. Electrochemical detection, one of the main techniques, is hindered by the mutual interferences of various heavy metal ions in practical use. In particular, the sensitivity of carbon electrodes to Cd 2+ ions (one of the most toxic heavy metals) is often overshadowed by some heavy metals (e.g. Pb 2+ and Cu 2+). To mitigate interference, metallic particles/films (e.g. Hg, Au, Bi, and Sn) typically need to be embedded in the carbon electrodes. However, these additional metallic materials may face issues of secondary pollution and unsustainability. In this study, a metal-free and sustainable nanomaterial, namely cysteamine covalently functionalized graphene (GSH), was found to lead to a 6-fold boost in the Cd 2+ sensitivity of the screen-printed carbon electrode (SPCE), while the sensitivities to Pb 2+ and Cu 2+ were not influenced in simultaneous detection. The selective enhancement could be attributed to the grafted thiols on GSH sheets with good affinity to Cd 2+ ions based on Pearson's hard and soft acid and base principle. More intriguingly, the GSH-modified SPCE (GSH-SPCE) featured high reusability with extended cycling times (23 times), surpassing the state-of-art SPCEs modified by non-covalently functionalized graphene derivatives. Last, the GSH-SPCE was validated in tap water. A metal-free thiol-modified graphene derivative introduces a reusable approach to alleviate mutual interference in electrochemical heavy metal detection

Metal-free cysteamine-functionalized graphene alleviates mutual interferences in heavy metal electrochemical detection

Heavy metal pollutants are of great concern to environmental monitoring due to their potent toxicity. Electrochemical detection, one of the main techniques, is hindered by the mutual interferences of various heavy metal ions in practical use. In particular, the sensitivity of carbon electrodes to Cd2+ ions (one of the most toxic heavy metals) is often overshadowed by some heavy metals (e.g. Pb2+ and Cu2+). To mitigate interference, metallic particles/films (e.g. Hg, Au, Bi, and Sn) typically need to be embedded in the carbon electrodes. However, these additional metallic materials may face issues of secondary pollution and unsustainability. In this study, a metal-free and sustainable nanomaterial, namely cysteamine covalently functionalized graphene (GSH), was found to lead to a 6-fold boost in the Cd2+ sensitivity of the screen-printed carbon electrode (SPCE), while the sensitivities to Pb2+ and Cu2+ were not influenced in simultaneous detection. The selective enhancement could be attributed to the grafted thiols on GSH sheets with good affinity to Cd2+ ions based on Pearson's hard and soft acid and base principle. More intriguingly, the GSH-modified SPCE (GSH-SPCE) featured high reusability with extended cycling times (23 times), surpassing the state-of-art SPCEs modified by non-covalently functionalized graphene derivatives. Last, the GSH-SPCE was validated in tap water.Grant MAT2017-87202-P funded by MCIN/AEI/ 10.13039/501100011033. ICN2 is funded by CERCA programme, Generalitat de Catalunya. Grant SEV-2017-0706 funded by MCIN/AEI/ 10.13039/501100011033. Q. Y. thanks the funding of the Chinese scholarship council. D. P., V. Š. and V. H. thank the Internal Student Grant Agency of the Palacký University (IGA_PrF_2022_019). C.C.C.S. acknowledges funding through CAPES – PRINT (Programa Institucional de Internacionalização; grant #88887.310281/2018-00 and 88887.467442/2019-00) and Mackpesquisa-UPM. A. B. and M. O. acknowledge support by the project Nano4Future (no. CZ.02.1.01/0.0/0.0/16_019/0000754) financed from the ERDF and ESF. M. O. acknowledges the ERC grant 2D-CHEM, No 683024 from H2020.Peer reviewe

Label-free and reagentless electrochemical genosensor based on graphene acid for meat adulteration detection

Altres ajuts: CERCA Programme/Generalitat de CatalunyaWith the increased demand for beef in emerging markets, the development of quality-control diagnostics that are fast, cheap and easy to handle is essential. Especially where beef must be free from pork residues, due to religious, cultural or allergic reasons, the availability of such diagnostic tools is crucial. In this work, we report a label-free impedimetric genosensor for the sensitive detection of pork residues in meat, by leveraging the biosensing capabilities of graphene acid - a densely and selectively functionalized graphene derivative. A single stranded DNA probe, specific for the pork mitochondrial genome, was immobilized onto carbon screen-printed electrodes modified with graphene acid. It was demonstrated that graphene acid improved the charge transport properties of the electrode, following a simple and rapid electrode modification and detection protocol. Using non-faradaic electrochemical impedance spectroscopy, which does not require any electrochemical indicators or redox pairs, the detection of pork residues in beef was achieved in less than 45 min (including sample preparation), with a limit of detection of 9% w/w pork content in beef samples. Importantly, the sample did not need to be purified or amplified, and the biosensor retained its performance properties unchanged for at least 4 weeks. This set of features places the present pork DNA sensor among the most attractive for further development and commercialization. Furthermore, it paves the way for the development of sensitive and selective point-of-need sensing devices for label-free, fast, simple and reliable monitoring of meat purity

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