Graphene-Based Electrochemical Sensing Platform for Rapid and Selective Ferulic Acid Quantification.

Due to the multitude of physiological functions, ferulic acid (FA) has a wide range of applications in the food, cosmetic, and pharmaceutical industries. Thus, the development of rapid, sensitive, and selective detection tools for its assay is of great interest. This study reports a new electroanalytical approach for the quantification of ferulic acid in commercial pharmaceutical samples using a sulphur-doped graphene-based electrochemical sensing platform. The few-layer graphene material (exf-SGR) was prepared by the electrochemical oxidation of graphite, at a low applied bias (5 V), in an inorganic salt mixture of Na2S2O3/(NH4)2SO4 (0.3 M each). According to the morpho-structural characterization of the material, it appears to have a high heteroatom doping degree, as proved by the presence of sulphur lines in the XRD pattern, and the C/S ratio was determined by XPS investigations to be 11.57. The electrochemical performances of a glassy carbon electrode modified with the exf-SGR toward FA detection were tested by cyclic voltammetry in both standard laboratory solutions and real sample analysis. The developed modified electrode showed a low limit of detection (30.3 nM) and excellent stability and reproducibility, proving its potential applicability as a viable solution in FA qualitative and quantitative analysis.

N,S-Decorated graphenes modified with 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine manganese(III) chloride-based 3D needle stochastic sensors for enantioanalysis of arginine: a key factor in the metabolomics and early detection of gastric cancer.

Arginine has an important role in the metabolomics of gastric cancer. Two 3D enantioselective needle stochastic sensors based on the physical immobilization of 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine manganese(III) chloride (solution, 10-3 mol L-1) in graphene paste matrices decorated with N and S atoms were designed, characterized and validated for the enantioanalysis of arginine in whole blood and tissue samples. The signature values obtained for the enantiomers of arginine confirmed that the stochastic sensors are enantioselective. The lowest limit of quantification obtained for both enantiomers of arginine was 1 fmol L-1, while sensitivity of up to 1011 s-1 mol-1 L was recorded for the stochastic sensors. High recoveries were obtained for the determination of one enantiomer in the presence of the other one; moreover, very good correlation was found between the results obtained with the two 3D enantioselective needle stochastic sensors.

Stochastic microsensors based on modified graphene for pattern recognition of maspin in biological samples.

Maspin is a novel serine protease inhibitor differentially expressed in several types of human cancers. It proved to be a key biomarker in the assessment of gastric cancer. Therefore, we design, characterize, and validate two stochastic microsensors based on graphene co-doped with N and S, and modified with α-cyclodextrin and maltodextrin, for the pattern recognition and quantification of maspin in whole blood, gastric tumor tissue, saliva, and urine. While the sensitivities were comparable with magnitude order, the variations were in the wideness of the linear concentration range, when measurements were performed at a pH of 7.40. Very low limits of quantification were recorded at both working pHs: 7.40, and 3.00. High recoveries of maspin in whole blood, gastric tissue tumor, saliva, and urine were also recorded.

Stochastic biosensors based on N- and S-doped graphene for the enantioanalysis of aspartic acid in biological samples.

Metabolomics plays a very important role in cancer mechanism and also in the early diagnosis of cancer. The enantioanalysis of aminoacids found in biological samples may favor the development of new screening tests for the early diagnosis of cancer. Two stochastic biosensors, based on the immobilization of α-hemolysin and hemin in exfoliated reduced graphene modified with nitrogen and sulphur, were proposed for the enantioanalysis of aspartic acid in biological samples (whole blood, urine, saliva, and tissue). The proposed biosensors showed low limits of quantification, high sensitivity, and large linear concentration ranges. The recoveries of d- and l-aspartic acid in biological samples were higher than 95.00%, with a relative standard deviation lower than 1.00%.

Myoglobin-silver reduced graphene oxide nanocomposite stochastic biosensor for the determination of luteinizing hormone and follicle-stimulating hormone from saliva samples.

A silver reduced graphene oxide (Ag-rGO) nanocomposite paste was prepared for the assay of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in children's saliva. The paste was modified with a solution of myoglobin (Myb) to form the stochastic biosensor, to improve the sensitivity of the method. The Ag-rGO powder and Myb-Ag-rGO paste were morphologically and structurally characterized by SEM, TEM and XRD measurements. For the molecular recognition of the hormones, the biosensor based on Myb-Ag-rGO reached determination limits of 8.5 × 10-3 UI L-1 (2.0 × 10-12 g/mL) for luteinizing hormone and 1.4 × 10-2 UI L-1 (1.0 × 10-12 g/mL) for follicle-stimulating hormone. The determination of both hormones in saliva samples collected from children was done with high reliability. Graphical Abstract.

Pattern recognition of 8-hydroxy-2'-deoxyguanosine in biological fluids.

8-Hydroxy-2'-deoxyguanosine (8-OHdG), a product of oxidative DNA damage, which has been used as a sensitive and reliable marker of oxidative stress and carcinogenesis, is found in high levels in biological fluids of leukemia patients. A reliable screening method based on pattern recognition of 8-OHdG using stochastic sensors designed with graphene materials decorated with nanoparticles of TiO2Ag or TiO2Au was developed. 5,10,15,20-Tetraphenyl-21H,23H porphyrin (P), 2,6-bis((E)-2-(furan-2-yl)vinyl)-4-(4,6,8-trimethylazulen-1-yl)pyridine (Py1), and 2,6-bis((E)-2-(thiophen-3-yl)vinyl)-4-(4,6,8-trimethylazulen-1-yl)pyridine (Py2) were used as modifiers of the graphene paste in the design of sensors. The screening method used for pattern recognition was developed for two pH values accordingly with the nature of the biological fluid to be screened: pH = 3.02 for urine samples and pH = 7.49 for whole blood samples. High sensitivities and low limits of determination for 8-OHdG obtained at both pH values favored the early detection of leukemia. Recoveries over 98.00% with RSD (%) values lower than 1.00% proved the reliability of the proposed screening method. Graphical abstract Graphene based sensors detect 8-hydroxy-2'-deoxyguanosine in biological fluids.