One-step nondestructive functionalization of graphene oxide paper with amines

Creation of spin switching in graphene oxide-based hybrid film materials with an anionic Fe(III) 5Cl-salicyaldehyde-thiosemicarbazone complex

The present article describes the synthesis of hybrid composite film materials formed during the self-assembly process through non-covalent interactions of graphene oxide (GO) nanosheets with salt 1, represented by an anionic spin-crossover complex [FeIII(5Cl-thsa)2]- (5Cl-thsa - 5-chlorosalicylaldehyde thiosemicarbazone) and the organic tetraethylammonium cation [Et4N]+. The insertion of the salt 1 molecules into the interlayer space of GO nanosheets with the subsequent formation of a hybrid material GO-1 was observed. The film of the hybrid material GO-1 was characterized by scanning electron and confocal laser microscopy, EDX and XPS analysis, IR, Raman and 57Fe Mössbauer spectroscopy, dc magnetic measurements, and powder X-ray diffraction. Comparison of the magnetic properties of salt 1 and a film of the hybrid material GO-1 demonstrated a significant influence of the GO nanosheets matrix on the completeness of spin transition and showed a slight shift of the hysteresis loop by 1 K in the temperature range of 200-230 K. DFT calculations showed an important role of the organic cation [Et4N]+ in the process of adsorption of the spin-crossover anion [FeIII(5Cl-thsa)2]- on the GO nanosheet surface.

Ultrasensitive biosensing platform for Mycobacterium tuberculosis detection based on functionalized graphene devices

Tuberculosis (TB) has high morbidity as a chronic infectious disease transmitted mainly through the respiratory tract. However, the conventional diagnosis methods for TB are time-consuming and require specialists, making the diagnosis of TB with point-of-care (POC) detection difficult. Here, we developed a graphene-based field-effect transistor (GFET) biosensor for detecting the MPT64 protein of Mycobacterium tuberculosis with high sensitivity as a POC detection platform for TB. For effective conjugation of antibodies, the graphene channels of the GFET were functionalized by immobilizing 1,5-diaminonaphthalene (1,5-DAN) and glutaraldehyde linker molecules onto the graphene surface. The successful immobilization of linker molecules with spatial uniformity on the graphene surface and subsequent antibody conjugation were confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy. The GFET functionalized with MPT64 antibodies showed MPT64 detection with a detection limit of 1 fg/mL in real-time, indicating that the GFET biosensor is highly sensitive. Compared to rapid detection tests (RDT) and enzyme-linked immunosorbent assays, the GFET biosensor platform developed in this study showed much higher sensitivity but much smaller dynamic range. Due to its high sensitivity, the GFET biosensor platform can bridge the gap between time-consuming molecular diagnostics and low-sensitivity RDT, potentially aiding in early detection or management of relapses in infectious diseases.

Design of a novel aptamer/molecularly imprinted polymer hybrid modified Ag-Au@Insulin nanoclusters/Au-gate-based MoS2 nanosheet field-effect transistor for attomolar detection of BRCA1 gene

Early detection of breast cancer, the first main cause of death in women, with robust assay platforms using appropriate biomarkers is of great importance for diagnosis and follow-up of the disease progression. This paper introduces an extra selective and sensitive label-free aptasensor for the screening of BRCA1 gene biomarker by taking advantage of a gate modified with aptamer and molecularly imprinted polymer hybrid (MIP) as a new synthetic receptor film coupled with an electrolyte-gated molybdenum disulfide (MoS2) field-effect transistor (FET). The Au gate surface of FET was modified with insulin stabilized bimetallic Ag-Au@nanoclusters (Ag-Au@InsNCs), after which, the immobilization of the hybridized aptamer and o-phenylenediamine was electropolymerized to form an aptamer-MIP hybrid receptor. The output characteristics of Apta-MIP hybrid modified Au gate MoS2 FET device were followed as a result of change in electrical double layer capacitance of electrolye-gate interface. The magnitude of decrease in the drain current showed a linear response over a wide concentration range of 10 aM to 1 nM of BRCA1 ssDNA with a sensitivity as high as 0.4851 μA/decade of concentration and a limit of detection (LOD) of 3.0 aM while very low responses observed for non-imprinted polymer. The devised aptasensor not only was capable to the discrimination of the complementary versus one-base mismatch BRCA1 ssDNA sequence, but also it could detect the complementary BRCA1 ssDNA in spiked human serum samples over a wide concentration range of 10 aM to 1.0 nM with a low LOD of 6.4 aM and a high sensitivity 0.3718 μA/decade.

3D Graphene Oxide-Polyethylenimine Scaffolds for Cardiac Tissue Engineering

The development of novel three-dimensional (3D) nanomaterials combining high biocompatibility, precise mechanical characteristics, electrical conductivity, and controlled pore size to enable cell and nutrient permeation is highly sought after for cardiac tissue engineering applications including repair of damaged heart tissues following myocardial infarction and heart failure. Such unique characteristics can collectively be found in hybrid, highly porous tridimensional scaffolds based on chemically functionalized graphene oxide (GO). By exploiting the rich reactivity of the GO's basal epoxydic and edge carboxylate moieties when interacting, respectively, with NH2 and NH3+ groups of linear polyethylenimines (PEIs), 3D architectures with variable thickness and porosity can be manufactured, making use of the layer-by-layer technique through the subsequent dipping in GO and PEI aqueous solutions, thereby attaining enhanced compositional and structural control. The elasticity modulus of the hybrid material is found to depend on scaffold's thickness, with the lowest value of 13 GPa obtained in samples containing the highest number of alternating layers. Thanks to the amino-rich composition of the hybrid and the established biocompatibility of GO, the scaffolds do not exhibit cytotoxicity; they promote cardiac muscle HL-1 cell adhesion and growth without interfering with the cell morphology and increasing cardiac markers such as Connexin-43 and Nkx 2.5. Our novel strategy for scaffold preparation thus overcomes the drawbacks associated with the limited processability of pristine graphene and low GO conductivity, and it enables the production of biocompatible 3D GO scaffolds covalently functionalized with amino-based spacers, which is advantageous for cardiac tissue engineering applications. In particular, they displayed a significant increase in the number of gap junctions compared to HL-1 cultured on CTRL substrates, which render them key components for repairing damaged heart tissues as well as being used for 3D in vitro cardiac modeling investigations.

The local electric field effect of onion-like carbon nanoparticles for improved laser desorption/ionization efficiency of saccharides

It is still a challenge to improve ionization efficiency of saccharides in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Herein, the highly curved onion-like carbon nanoparticles (OCS) were synthesized from the low-price candle raw via a facile strategy. The unique nanostructure of OCS showed large surface area with plentiful mesoporous architecture, highly curved sp² carbon with regulating electronic effect, and good hydrophilicity, which could be beneficial to facilitate the desorption and ionization efficiency in MS process. The prepared OCS material as MALDI matrix exhibited the superior performance for the detection of xylose, glucose, maltose monohydrate, and raffinose pentahydrate in positive-ion mode with low background noise, enhanced ion intensities, uniform distribution, excellent reproducibility, good salt-tolerance, and high sensitivity compared to control candle soot (CS) and traditional α-cyano-4-hydroxycinnamic acid (CHCA) matrices. This highly effective LDI of OCS matrix was attributed to its enhancing local electric field effect, strong UV absorption ability, and high photo-thermal conversion performance. Furthermore, the OCS-assisted LDI MS approach was employed to quantitatively detect glucose in rat serum. This LDI MS platform may have valuable for the analysis of metabolites in clinical research.

Photoluminescent properties of liposome-encapsulated amine-functionalized nanodiamonds

In the present work, amine-functionalized nanodiamonds (NDs) have been encapsulated in liposomes and studied in order to observe the modification of their photoluminescence properties. NDs were functionalized with aromatic amines such as 1-aminopyrene and 2-aminofluorene, and the aliphatic amine 1-octadecylamine. Morphology, structural and optical properties of NDs and amine-modified NDs were analyzed by transmission electron microscopy, atomic force microscopy, scanning electron microscopy, and photoluminescence. The amine-functionalized NDs were successfully encapsulated in lecithin liposomes prepared by the green and conventional methods. The obtained results show significant changes in photoluminescent properties of functionalized NDs, and were more potentialized after liposome encapsulation. Our findings could be applied in the development of new kinds of water-dispersible fluorescent hybrids, liposome-NDs, with the capability of drug encapsulation for use in diagnostics and therapy (theragnostic liposomes). All-optical sensors with possibilities for tailoring their response for other biomedical applications can be also contemplated.

From 2D Graphene Nanosheets to 3D Graphene-based Macrostructures

The combination of exceptional functionalities offered by 3D graphene-based macrostructures (GBMs) has attracted tremendous interest. 2D graphene nanosheets have a high chemical stability, high surface area and customizable porosity, which was extensively researched for a variety of applications including CO₂ adsorption, water treatment, batteries, sensors, catalysis, etc. Recently, 3D GBMs have been successfully achieved through few approaches, including direct and non-direct self-assembly methods. In this review, the possible routes used to prepare both 2D graphene and interconnected 3D GBMs are described and analyzed regarding the involved chemistry of each 2D/3D graphene system. Improvement of the accessible surface of 3D GBMs where the interface exchanges are occurring is of great importance. A better control of the chemical mechanisms involved in the self-assembly mechanism itself at the nanometer scale is certainly the key for a future research breakthrough regarding 3D GBMs.

A Facile Method for the Non-Covalent Amine Functionalization of Carbon-Based Surfaces for Use in Biosensor Development

Affinity biosensors based on graphene field-effect transistor (GFET) or resistor designs require the utilization of graphene's exceptional electrical properties. Therefore, it is critical when designing these sensors, that the electrical properties of graphene are maintained throughout the functionalization process. To that end, non-covalent functionalization may be preferred over covalent modification. Drop-cast 1,5-diaminonaphthalene (DAN) was investigated as a quick and simple method for the non-covalent amine functionalization of carbon-based surfaces such as graphene, for use in biosensor development. In this work, multiple graphene surfaces were functionalized with DAN via a drop-cast method, leading to amine moieties, available for subsequent attachment to receptor molecules. Successful modification of graphene with DAN via a drop-cast method was confirmed using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and real-time resistance measurements. Successful attachment of receptor molecules also confirmed using the aforementioned techniques. Furthermore, an investigation into the effect of sequential wash steps which are required in biosensor manufacture, on the presence of the DAN layer, confirmed that the functional layer was not removed, even after multiple solvent exposures. Drop-cast DAN is thus, a viable fast and robust method for the amine functionalization of graphene surfaces for use in biosensor development.

Highly Conductive Graphene Paper with Vertically Aligned Reduced Graphene Oxide Sheets Fabricated by Improved Electrospray Deposition Technique

Because of its notable electrical and mechanical properties, the highly conductive graphene paper has great potential applications in future flexible electronics. In this study, we report a simple and effective method to prepare vertically aligned graphene oxide papers from graphene oxide suspensions by an improved electrospray deposition technique with a moving stage, which is controlled by computer. Then, the flexible reduced graphene oxide papers are successfully synthesized after reduction by using hydroiodic acid. The obtained reduced graphene oxide paper has an electrical conductivity as high as 6180 S/m, which is more than one and a half times of the reduced graphene oxide paper film, which was fabricated by using the electrospray deposition technique without the moving stage. The experimental results approved for the first time that the degree of alignment of reduced graphene oxide sheets can affect the conductivity of the reduced graphene oxide papers. Further electrochemical measurements for a symmetrical supercapacitor device based on the prepared reduced graphene oxide paper indicate that it has great capacitive performance and electrochemical stability. It exhibited relatively high specific capacitance (174 F·g^-1) at a current density of 1 A·g^-1 in 6 M KOH aqueous solution, and its capacitance can retain approximately 86% after 1000 cycles. In addition, patterned freestanding reduced graphene oxide papers, which have potential applications in many fields such as stretchable electronics and wearable devices, also can be fabricated by using this method.