Voltammetric Determination of 2′-Deoxyadenosine and Adenine in Urine of Patients with Hepatocellular Carcinoma Using Fullerene-C60-modified Glassy Carbon Electrode

Simultaneous determination of guanine and adenine in human saliva with graphite sparked screen-printed electrodes

Saliva represents one of the most useful biological samples for non-invasive testing of health status and diseases prognosis and therefore, the development of advanced sensors enabling the determination of biomarkers in unspiked human whole saliva is of immense importance. Herein, we report on the development of a screen-printed graphite sensor modified with carbon nanomaterials generated by spark discharge for the determination of guanine and adenine in unspiked human whole saliva. The designed sensor was developed with a "green", extremely simple, fast (16 s), fully automated "linear mode" sparking process implemented with a 2D positioning device. Carbon nanomaterial-modified surfaces exhibit outstanding electrocatalytic properties enabling the determination of guanine and adenine over the concentration range 5 - 1000 nM and 25 - 1000 nM, while achieving limits of detection (S/N 3) as low as 2 nM and 8 nM, respectively. The sensor was successfully applied to the determination of purine bases in unspiked human whole saliva following a simple assay protocol based on ultrafiltration that effectively alleviates biofouling issues. Recovery was 96-108%.

Detection of Volatile Organic Compounds in a Drop of Urine by Ultrasonic Nebulization Extraction Proton Transfer Reaction Mass Spectrometry

Detection of volatile organic compounds (VOCs) in human urine has potential application value in screening for disease and toxin exposure. However, the current technologies are too slow to detect the concentration of VOCs in fresh urine. In this study, we developed a novel ultrasonic nebulization extraction proton transfer reaction mass spectrometry (UNE-PTR-MS) technology. The urinary VOCs can be rapidly extracted to gaseous VOCs using the UNE system and then delivered using a carrier gas to the PTR-MS instrument for rapid detection. The carrier gas flow and sample size were optimized to 100 mL/min and 100 μL, respectively. The limits of detection (LODs) and response time of the UNE-PTR-MS were evaluated by detecting three VOCs that are common in human urine: methanol, acetaldehyde, and acetone. The LODs determined for methanol (4.47 μg/L), acetaldehyde (1.98 μg/L), and acetone (3.47 μg/L) are 2-3 orders of magnitude lower than the mean concentrations of that in healthy human urine. The response time of the UNE-PTR-MS is 34 s and only 0.66 mL of urine is required for a full scan. The repeatability of this UNE-PTR-MS was evaluated, and the relative standard deviations of 5 independent determinations were between 4.62% and 5.21%. Lastly, the UNE-PTR-MS was applied for detection of methanol, acetaldehyde, and acetone in real human urine to test matrix effects, yielding relative recoveries of between 88.39% and 94.54%. These results indicate the UNE-PTR-MS can be used for the rapid detection of VOCs in a drop of urine and has practical potential for diagnosing disease or toxin exposure.

Detection of Guanine and Adenine Using an Aminated Reduced Graphene Oxide Functional Membrane-Modified Glassy Carbon Electrode

A new electrochemical sensor based on a Nafion, aminated reduced graphene oxide and chitosan functional membrane-modified glassy carbon electrode was proposed for the simultaneous detection of adenine and guanine. Fourier transform-infrared spectrometry (FTIR), transmission electron microscopy (TEM), and electrochemical methods were utilized for the additional characterization of the membrane materials. The prepared electrode was utilized for the detection of guanine (G) and adenine (A). The anodic peak currents to G and A were linear in the concentrations ranging from 0.1 to 120 μM and 0.2 to 110 μM, respectively. The detection limits were found to be 0.1 μM and 0.2 μM, respectively. Moreover, the modified electrode could also be used to determine G and A in calf thymus DNA.

Design and synthesis of novel adenine fluorescence probe based on Eu(III) complexes with dtpa-bis(guanine) ligand

A novel adenine (Ad) fluorescence probe (Eu^III-dtpa-bis(guanine)) was designed and synthesized by improving experimental method based on the Eu(III) complex and dtpa-bis(guanine) ligand. The dtpa-bis(guanine) ligand was first synthesized by the acylation action between dtpaa and guanine (Gu), and the corresponding Eu(III) complex was successfully prepared through heat-refluxing method with dtpa-bis(guanine) ligand. As a novel fluorescence probe, the Eu^III-dtpa-bis(guanine) complex can detect adenine (Ad) with characteristics of strong targeting, high specificity and high recognition ability. The detection mechanism of the adenine (Ad) using this probe in buffer solution was studied by ultraviolet-visible (UV-vis) and fluorescence spectroscopy. When the Eu^III-dtpa-bis(guanine) was introduced to the adenine (Ad) solution, the fluorescence emission intensity was significantly enhanced. However, adding other bases such as guanine (Gu), xanthine (Xa), hypoxanthine (Hy) and uric acid (Ur) with similar composition and structure to that of adenine (Ad) to the Eu^III-dtpa-bis(guanine) solution, the fluorescence emission intensities are nearly invariable. Meanwhile, the interference of guanine (Gu), xanthine (Xa), hypoxanthine (Hy) and uric acid (Ur) on the detection of the adenine using Eu^III-dtpa-bis(guanine) probe was also studied. It was found that presence of these bases does not affect the detection of adenine (Ad). A linear response of fluorescence emission intensities of Eu^III-dtpa-bis(guanine) at 570nm as a function of adenine (Ad) concentration in the range of 0.00-5.00×10^-5molL^-1 was observed. The detection limit is about 4.70×10^-7molL^-1.

Functionalized solid electrodes for electrochemical biosensing of purine nucleobases and their analogues: a review

Interest in electrochemical analysis of purine nucleobases and few other important purine derivatives has been growing rapidly. Over the period of the past decade, the design of electrochemical biosensors has been focused on achieving high sensitivity and efficiency. The range of existing electrochemical methods with carbon electrode displays the highest rate in the development of biosensors. Moreover, modification of electrode surfaces based on nanomaterials is frequently used due to their extraordinary conductivity and surface to volume ratio. Different strategies for modifying electrode surfaces facilitate electron transport between the electrode surface and biomolecules, including DNA, oligonucleotides and their components. This review aims to summarize recent developments in the electrochemical analysis of purine derivatives, as well as discuss different applications.

A carbon ion beam irradiated MWCNT/AuNPs composite sensor for a sensitive assay of purine-nucleosides of DNA

Sensor for purine nucleosides has been developed using irradiation with high energy carbon ion beam.

Voltammetric quantification of anti-hepatitis drug Adefovir in biological matrix and pharmaceutical formulation

Electrochemical reduction behavior of Adefovir was studied using Hanging Mercury Drop Electrode (HMDE) in Britton–Robinson (BR) buffer solution. Voltammetric study showed one well-defined reduction peak in the potential range −1.2 to −1.4 V (vs. Ag/AgCl) due to reduction of C=N bond of the imidazole ring. Solid-phase extraction and protein-precipitation techniques were employed for extraction of Adefovir from human plasma. The proposed method allows quantification of Adefovir in human plasma over the concentration range 0.50–5.00 μg/mL with the detection limit 0.17 μg/mL, whereas in pharmaceutical formulation 0.25–2.25 μg/mL with the detection limit 0.08 μg/mL.