Selective, sensitive and fluorometric determination of urinary cytosine with 4-trifluoromethylbenzamidoxime and N,N-dimethylformamide

Dual-Responsive Carbon Quantum Dots for the Simultaneous Detection of Cytosine and 5-Methylcytosine Interpreted by a Machine Learning-Assisted Smartphone

DNA methylation is an epigenetic alteration that results in 5-methylcytosine (5-mC) through the addition of a methyl group to the fifth carbon of a cytosine (C) residue. The methylation level, the ratio of 5-mC to C, in urine might be related to the whole-body epigenetic status and the occurrence of common cancers. To date, never before have any nanomaterials been developed to simultaneously determine C and 5-mC in urine samples. Herein, a dual-responsive fluorescent sensor for the urinary detection of C and 5-mC has been developed. This assay relied on changes in the optical properties of nitrogen-doped carbon quantum dots (CQDs) prepared by microwave-assisted pyrolysis. In the presence of C, the blue-shifted fluorescence intensity of the CQDs increased. However, fluorescence quenching was observed upon the addition of 5-mC. This was primarily due to photoinduced electron transfer as confirmed by the density functional theory calculation. In urine samples, our sensitive fluorescent sensor had detection limits for C and 5-mC of 43.4 and 74.4 μM, respectively, and achieved satisfactory recoveries ranging from 103.5 to 115.8%. The simultaneous detection of C and 5-mC leads to effective methylation level detection, achieving recoveries in the range of 104.6-109.5%. Besides, a machine learning-enabled smartphone was also developed, which can be effectively applied to the determination of methylation levels (0-100%). These results demonstrate a simple but very effective approach for detecting the methylation level in urine, which could have significant implications for predicting the clinical prognosis.

Sensitive and Selective Determination of Orotic Acid in Biological Specimens Using a Novel Fluorogenic Reaction

Orotic acid is an intermediate in the synthesis pathway of uridine-5'-monophosphate, and increases in body fluids of patients suffering from hereditary disorders such as orotic aciduria and hyperammonemia. In this study, we developed a spectrofluorometric method with or without high-performance liquid chromatography for the selective and sensitive quantification of orotic acid in human biological specimens, using 4-trifluoromethylbenzamidoxime (4-TFMBAO) as a fluorogenic reagent. This reagent provided intensive fluorescence for only orotic acid amongst 62 compounds including structurally related bio-substances such as nucleic acid bases, nucleosides, nucleotides, amino acids, vitamins, bilirubin, uric acid, urea, creatine, creatinine and sugars. Under optimized reaction conditions, orotic acid was reacted with 4-TFMBAO, K3[Fe(CN)6] and K2CO3 in an aqueous solution. The fluorescence produced from the orotic acid derivative was measured at an excitation of 340 nm and an emission of 460 nm. A concentration of 1.2 μM orotic acid per 1.0 mM creatinine in normal urine and 0.64 nmol orotic acid per 5.0 × 10(5) HeLa cells were determined by this method. The present method permitted the facile quantification of orotic acid in healthy human urine and cultured HeLa cells by spectrofluorometry and/or high-performance liquid chromatography.