Objective. To develop technique immobilizing antibodies graphene surface of proteins that play a significant role in pathogenesis Alzheimer's disease.Materials and methods. Graphene films were obtained sublimation surface of SiC substrates. Presence graphene monolayer was confirmed spectroscopy spectra. Graphene surface quality was evaluated cyclic voltammetry. Functionalization by amino groups was carried out method based on sorption pyrene derivatives from a solution and phenylnitrogroups electrochemical method. Graphene was kept in solutions monoclonal antibodies to human beta-amyloid peptide 1–42. Preparations were also kept in solution secondary antibodies labeled with FITZ. Results were evaluated fluorescence microscopy. Additionally, samples were kept in solution antibody with peroxidase label, which was detected chemiluminescence.Results. For attachment specific antibodies surface of graphene, quality its surface is great importance. Optimal working concentration of antibodies of human beta-amyloid 1–42 in solution for subsequent manufacture biological sensors is 15 micrograms per 1 ml. Covalent crosslinking antibodies with glutaraldehyde with amino groups on graphene gives a slight gain in the level fluorescence compared with noncovalent sorption on graphene with nitro groups. Functionalization phenylnitrogroups is optimal for further work related to the identification specific antigens.Conclusions. The technique of immobilization on the graphene surface of specific antibodies to beta-amyloid in concentrations detected by fluorescence microscopy and chemiluminescence is investigated. Amount antibodies sufficient to create a biosensor is immobilized on graphene. It was found that functionalization of phenylnitrogroups allows creating optimal conditions for the attachment of antibodies to the graphene surface, as well as washing resulting antibody-antigenic complexes for further reuse of graphene biosensors.

The properties of graphene chips with low reproducibility (LR) after photolithography (PLG) and graphene functionalization have been studied. It is shown that the introduction of additional cleaning after PLG can significantly increase the reproducibility of the parameters of processed graphene in biosensors. The use of dilute PBS solutions for virus detection makes it possible to increase the relative concentration sensitivity of biosensors by several times.

The well-known effect of the local interaction between graphene and photoresist (LIGF) during the creation of biosensors is shown to lead to non-uniform distribution of compressive stresses, which deteriorates the adsorption properties of graphene, parameter reproducibility, and detecting ability of influenza B and SARS-Cov-2 biosensors. It is also shown that controlling the occurrence of LIGF areas on a graphene surface by atomic force microscopy or introducing a protective layer between graphene and photoresist can minimize the non-persistent effect of LIGF. The results of influenza B and SARS-CoV-2 imaging on the graphene surface in biosensor chips in a scanning electron microscope are presented.

The quality of graphene intended for use in biosensors was assessed on manufactured chips using a set of methods including atomic force microscopy (AFM), Raman spectroscopy, and low-frequency noise investigation. It is shown that local areas of residues on the graphene surface, formed as a result of the interaction of graphene with a photoresist at the initial stage of chip development, led to a spread of chip resistance (R) in the range of 1–10 kOhm and to an increase in the root mean square (RMS) roughness up to 10 times, which can significantly worsen the reproducibility of the parameters of graphene chips for biosensor applications. It was observed that the control of the photoresist residues after photolithography (PLG) using AFM and subsequent additional cleaning reduced the spread of R values in chips to 1–1.6 kOhm and obtained an RMS roughness similar to the roughness in the graphene film before PLG. Monitoring of the spectral density of low-frequency voltage fluctuation (SU), which provides integral information about the system of defects and quality of the material, makes it possible to identify chips with low graphene quality and with inhomogeneously distributed areas of compressive stresses by the type of frequency dependence SU(f).

A procedure of synthesis of Pd(II) complexes with 2-phenylquinoline-4-carboxylic acid methyl ester: PdMpqc(μ-Ac)]2 and [PdEnMpqc]BF4, where Mpqc is methyl 2-phenyl-4-quinolinecarboxylate ion, Ac --- acetate ion, En --- ethylenediamine, was developed. The composition and structure of the complexes obtained were established on the basis of IR and polynuclear NMR spectroscopy data, optical and physical properties were described on the basis of UV and fluorescence spectroscopy. The phosphorescence of Pd(II) complexes in the visible region was assigned to the radiative transition from the spin-forbidden intraligand electronically excited state 3(π-π) that is localized on the aromatic Mpqc system. Keywords: Pd(II) complexes, methyl 2-phenyl-4-quinolinecarboxylate, NMR spectroscopy, spectral-luminescence properties.

To analyze the modification of the functionalized surface of graphene by protein molecules, a chemiluminescent enzyme-linked immunosorbent assay based method was proposed. Using the example of functionalized graphene (FG) purification, the possibilities of chemiluminescent control of the state of its surface are shown. Methods for purifying FG from protein molecules with the restoration of the ability to resorb protein molecules are discussed. It has been shown that the FG surface can be cleaned from sorbed proteins, and a biosensor can be designed again based on such purified graphene, including with a different specificity. Therefore, the graphene sensor can be used repeatedly. Keywords: functionalized graphene, 1-pyrenemethylamine hydrochloride, cyclic voltammetry, chemiluminescence, monoclonal antibodies, biosensors

The well-known effect of the local interaction between graphene and photoresist (LIGF) during the creation of biosensors is shown to lead to non-uniform distribution of compressive stresses, which deteriorates the adsorption properties of graphene, parameter reproducibility, and detecting ability of influenza B and SARS-Cov-2 biosensors. It is also shown that controlling the occurrence of LIGF areas on a graphene surface by atomic force microscopy or introducing a protective layer between graphene and photoresist can minimize the non-persistent effect of LIGF. The results of influenza B and SARS-CoV-2 imaging on the graphene surface in biosensor chips in a scanning electron microscope are presented.

To analyze the modification of the functionalized surface of graphene by protein molecules, a chemiluminescent enzyme immunoassay method was proposed. Using the example of functionalized graphene (FG) purification, the possibilities of chemiluminescent control of the state of its surface are shown. Methods for purifying FG from protein molecules with the restoration of the ability to resorb protein molecules are discussed. It has been shown that the FG surface can be cleaned from sorbed proteins, and a biosensor can be designed again based on such purified graphene, including with a different specificity. Therefore, the graphene sensor can be used repeatedly.

In this study, we discuss the mechanisms behind changes in the conductivity, low-frequency noise, and surface morphology of biosensor chips based on graphene films on SiC substrates during the main stages of the creation of biosensors for detecting influenza viruses. The formation of phenylamine groups and a change in graphene nano-arrangement during functionalization causes an increase in defectiveness and conductivity. Functionalization leads to the formation of large hexagonal honeycomb-like defects up to 500 nm, the concentration of which is affected by the number of bilayer or multilayer inclusions in graphene. The chips fabricated allowed us to detect the influenza viruses in a concentration range of 10−16 g/mL to 10−10 g/mL in PBS (phosphate buffered saline). Atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed that these defects are responsible for the inhomogeneous aggregation of antibodies and influenza viruses over the functionalized graphene surface. Non-uniform aggregation is responsible for a weak non-linear logarithmic dependence of the biosensor response versus the virus concentration in PBS. This feature of graphene nano-arrangement affects the reliability of detection of extremely low virus concentrations at the early stages of disease.

This work is devoted to the development and optimization of the parameters of graphene-based sensors. The graphene films used in the present study were grown on semi-insulating 6H-SiC substrates by thermal decomposition of SiC at the temperature of ~1700 °C. The results of measurements by Auger and Raman spectroscopies confirmed the presence of single-layer graphene on the silicon carbide surface. Model approach to the theory of adsorption on epitaxial graphene is presented. It is demonstrated that the Green-function method in conjunction with the simple substrate models permit one to obtain analytical results for the charge transfer between adsorbed molecules and substrate. The sensor structure was formed on the graphene film by laser. Initially, a simpler gas sensor was made. The sensors developed in this study demonstrated sensitivity to the NO2 concentration at the level of 1–0.01 ppb. The results obtained in the course of development and the results of testing of the graphene-based sensor for detection of protein molecules are also presented. The biosensor was fabricated by the technology previously developed for the gas sensor. The working capacity of the biosensor was tested with an immunochemical system constituted by fluorescein and monoclonal antibodies (mAbs) binding this dye.

In this work, the modification of the surface parameters of graphene chips after electrolysis treatment in a NaClO 4 aqueous solution has been studied. Two electrolysis modes have been analysed. In the first one, a negative potential (-0.2 V) is applied to the graphene chips, while in the second one the potential is positive (0.8 V). Investigation using a number of techniques including atomic force microscopy, Kelvin probe force microscopy, Raman spectroscopy, measurements of current-voltage characteristics and low-frequency noise has shown that the electrolysis mode with application of a positive potential on graphene chips decreases the 1/ f noise and allows one to obtain a uniform surface potential distribution while leaving the graphene structure undamaged. The results of this study help to understand the efficiency and reproducibility of the procedure for electrolysis treatment of graphene chips.

A procedure of synthesis of Pd (II) complexes with 2-phenylquinoline-4-carboxylic acid methyl ester: [PdMpqc(μ-Аc)]2 and [PdEnMpqc] BF4, where Mpqc is methyl 2-phenyl-4-quinolinecarboxylate ion, Ac - acetate ion, En - ethylenediamine, was developed. The composition and structure of the complexes obtained were established on the basis of IR and polynuclear NMR spectroscopy data, optical and physical properties were described on the basis of UV and fluorescence spectroscopy. The phosphorescence of Pd (II) complexes in the visible region was assigned to the radiative transition from the spin-forbidden intraligand electronically excited state 3(π-π) that is localized on the aromatic Mpqc system.

A method was developed for the synthesis of a new palladium(II) complex with N,N,N′,N′′,N′′- pentamethyldiethylene triamine. Its structure, electrochemical and optical properties were studied.

Abstract. The response of the chips based on graphene films on SiC substrates (the relative change of the chip resistance) on fluorescein (C20H12O5) in a wide range of its concentrations in phosphate-buffered solution from 1 • 10-3 ng/ml, to 1 • 10+4 ng/ml (7 orders of magnitude) is studied. Detection of fluorescein seems to be a simple and cheap model experiment to study a sensing capability of the graphene in the production of biosensors. It was shown that graphene chips with wide terraces on the surface (1000-nm width and 5-nm height) made it possible to plot calibration dependences of the response of the chips on the concentration of fluorescein.

Graphene is considered as a promising candidate for manufacturing of sensors due to its extreme sensitivity to molecule absorption. In this work, we show the connection between the electrical and optical properties of epitaxial graphene chips grown on 4 H -SiC and intended for the production of protein-based sensors. Using of a complex of techniques, including Raman spectroscopy, atomic force microscopy, Kelvin probe microscopy, study of I-V characteristics and low-frequency noise, it is shown that the character of frequency dependence of the spectral density of voltage fluctuations and its value at a frequency of 1 Hz can be used for classification and selection of graphene chips for their application as sensors. Classification of the graphene chips will allow more efficient development of graphene-based biosensors.

We have studied the response of graphene-film-based chips on SiC substrates (the relative change in the chip resistance) to coming into contact with fluorescein (C 20 H 12 O 5 ) in a wide range of its concentrations in a phosphate-buffered saline solution: from 1 × 10 –3 to 1 × 10 4 ng/mL (seven orders of magnitude). Fluorescein detection seems to be a simple and cheap model experiment to study the sensory ability of graphene in the way of biochips manufacturing. It has been shown that chips with wide terraces on a surface with a step width of about 1000 nm and heights of up to 5 nm made it possible to construct the calibration dependences of chip response on fluorescein concentration.

The spectral and luminescent properties of N 2 O 2 -type aromatic azomethines, N , N '-bis(salicylidene)-1,4-butylenediamine, N , N '-bis(5-bromosalicylidene)-1,4-butylenediamine, and their complexes with Zn(II), have been studied. All compounds at 293 K fluoresce in solutions and in a polycrystalline state. An increase in the fluorescence intensity of the azomethines in alcohol solutions occurs upon their conversion to the quinoid form. The main photoluminescent parameters of solutions of the compounds in DMF and DMSO have been determined. Depending on the presence of bromoaryl substituents in the structure of the ligands and the solvent properties, the zinc complexes fluoresce with quantum yields up to 50%.

We discuss graphene-on-SiC dies for blood-type sensing. For the sensor application, chemical species to be detected adsorb on the graphene surface and act as electron donors or acceptors resulting in resistance changes of the graphene channel. In this work, graphene films were formed on 4H-SiC substrates by thermal decomposition of the (0001) silicon surface in Ar ambient at a high temperature of 1800–2000 oC. The graphene functionalization was performed by the covalent bonding of a nitrophenyl group (C6H5NO2) followed by its reduction to a phenylamine group (C6H5NH2) by using a cyclic voltammetry process. There was a clear and prompt response (current change) of the antibody-coated graphene/SiC dies when the blood antigen matched the antibody. No response occurred when the antibody on the graphene surface mismatched the blood antigen. The experiments demonstrated that a functionalized graphene-on-SiC die has capability in blood sensing, opening a way to manufacture biosensors for detecting blood types and for other applications.

We discuss graphene-on-SiC dies for blood-type sensing. For the sensor application, chemical species to be detected adsorb on the graphene surface and act as electron donors or acceptors resulting in resistance changes of the graphene channel. In this work, graphene films were formed on 4H-SiC substrates by thermal decomposition of the (0001) silicon surface in Ar ambient at a high temperature of 1800-2000 degrees C. The graphene functionalization was performed by the covalent bonding of a nitrophenyl group (C6H5NO2) followed by its reduction to a phenylamine group (C6H5NH2) by using a cyclic voltammetry process. There was a clear and prompt response (current change) of the antibody-coated graphene/SiC dies when the blood antigen matched the antibody. No response occurred when the antibody on the graphene surface mismatched the blood antigen. The experiments demonstrated that a functionalized graphene-on-SiC die has capability in blood sensing, opening a way to manufacture biosensors for detecting blood types and for other applications.