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

A Novel Poly(cytosine)-Based Electrochemical Biosensor for Sensitive and Selective Determination of Guanine in Biological Samples

The novel poly(cytosine)-modified glassy carbon electrode-based electrochemical sensor was fabricated potentiodynamically for the detection of Guanine (G) in clinical and biological samples. The surface of the electrode was successfully activated by electropolymerization, and about a 7.5-fold current improvement due to modification was achieved. From the analysis of the dependence of peak current and peak potential on a scan rate, a higher R 2 for the peak current on the square root of scan rate (R 2 = 0.999) than the dependence of peak current on scan rate (R 2 = 0.982) indicated that the oxidation of G at poly(cytosine)/GCE was predominantly diffusion controlled. The oxidative peak response of the electrode revealed a high linear range of G concentration (0.1-200 μM) under optimized conditions. The detection limit and limit of quantification were 6.10 and 20.13 nM, respectively, associated with the %RSD of under 1%. The validation of the developed electrochemical sensor for the determination of G was investigated by analyzing human urine DNA and serum samples with spike recovery results in the range of 98.20-103.70% with the interferent recovery percentage in the range of 97.86-103.10% containing 50-300% of potential interferents. The newly designed sensor demonstrated the highest level of performance for the G detection in real samples.

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%.

Integrated Microfluidic Device with Carbon-Thread Microelectrodes for Electrochemical DNA Elemental Analysis

Evidently, any alternation in the concentration of the essential DNA elements, adenine (A), guanine (G), cytosine (C), and thymine (T), leads to several deformities in the physiological process causing various disorders. So, to realize a simple and precise technique for simultaneous determination of the DNA elements continue to remain a challenge. Microfluidic devices offer numerous advantage, such as low volume consumption, rapid response, highly sensitive and accurate real time analysis, for point of care testing (POCT). Herein, a microfluidic electrochemical device has been developed with three electrodes fabricated using a carbon-thread microelectrode (CTME) for DNA elemental detection. CTME, functionalized with graphitize mesoporous carbon (GMC), worked as a working electrode, bare CTME functioned as an auxiliary electrode while CTME coated with Ag/AgCl ink performed as a reference electrode. The developed device was used for evaluating individual DNA elemental base pairs simultaneously using various electrochemical techniques. The anodic peak current obtained for the DNA bases were 0.56 ± 0.04 V (G), 0.92 ± 0.02 V (A), 1.09 ± 0.05 V (T) and 1.24 ± 0.04 V (C) in a potential window of 0.2 V to 1.5 V. The device was corroborated for simultaneous sensing, and detection limits were found to be 36.73 μM (G), 20 μM (A), 22 μM (T) and 19.78 μM (C) in the linear range of 50 μM - 500 μM. Finally, the device was successfully used for instantaneous determination of DNA bases in the human blood serum sample. Overall, this work demonstrates the use of a simple microfluidic device with CTMEs for electrochemical determination of DNA bases amenable for POCT.

Selective Fluorescent Sensing of Adenine Via the Emissive Enhancement of a Simple Cobalt Porphyrin

Porphyrins absorb strongly in the visible region and are also excellent fluorophores that emit in the visible region that make them excellent candidates for fluorescence sensing and in vivo imaging. This work describes the fluorescence determination of adenine using cobalt complex of a simple porphyrin. Tetraphenylporphyrin (TPP) and tetraphenylpophyrinatocobalt(II) (CoTPP) were synthesized and characterised. TPP on metallation with cobalt resulted in the red shift of fluorescence emission in the region 652 nm and 716 nm and showed an enhancement in the emission peaks with the addition of the nucleobase, adenine. CoTPP is found to be an efficient fluorescent sensor for adenine in DMF solvent. The fluorescence enhancement is due to the formation of the ground state complex formation between adenine and CoTPP, which is supported by experimental evidences from UV- visible spectra, time resolved fluorescence life time measurements etc. The detection limit of adenine was found to be 4.2 μM using the CoTPP fluorescent probe. The proposed sensor is found to be highly selective for adenine in presence of other nitrogen bases like guanine, cytosine, uracil, thymine, alanine, histidine etc. in 1:1 concentration.

Rational Design of Amphiphilic Diblock Copolymer/MWCNT Surface Modifiers and Their Application for Direct Electrochemical Sensing of DNA

We demonstrate the application of amphiphilic ionic poly(n-butylmethacrylate)-block- poly(2-(dimethylamino)ethyl methacrylate) diblock copolymers (PnBMA₄₀-b-PDMAEMA₄₀, PnBMA₄₀-b-PDMAEMA₁₂₀, PnBMA₇₀-b-PDMAEMA₁₂₀) for dispersing multiwalled carbon nanotubes (MWCNTs) in aqueous media, a subsequent efficient surface modification of screen-printed electrodes (SPEs), and the application of the modified SPEs for DNA electrochemistry. Stable and fine aqueous dispersions of MWCNTs were obtained with PnBMA_x-b-PDMAEMA_y diblock copolymers, regardless of the structure of the copolymer and the amount of MWCNTs in the dispersions. The effect of the diblock copolymer structure was important when the dispersions of MWCNTs were deposited as modifying layers on surfaces of SPEs, resulting in considerable increases of the electroactive surface areas and great acceleration of the electron transfer rate. The SPE/(PnBMA_x-b-PDMAEMA_y + MWCNT) constructs were further exploited for direct electrochemical oxidation of the guanine (G) and adenine (A) residues in a model salmon sperm double-stranded DNA (dsDNA). Two well-defined irreversible oxidation peaks were observed at about +600 and +900 mV, corresponding to the electrochemical oxidation of G and A residues, respectively. A multi-parametric optimization of dsDNA electrochemistry enables one to get the limits of detection (LOD) as low as 5 μg/mL (0.25 μM) and 1 μg/mL (0.05 μM) for G and A residues, respectively. The achieved sensitivity of DNA assay enables quantification of the A and G residues of dsDNA in the presence of human serum and DNA in isolated human leukocytes.

Simultaneous Determination of Four DNA bases at Graphene Oxide/Multi-Walled Carbon Nanotube Nanocomposite-Modified Electrode

In this study, we developed a modified glassy carbon electrode (GCE) with graphene oxide, multi-walled carbon nanotube hybrid nanocomposite in chitosan (GCE/GO-MWCNT-CHT) to achieve simultaneous detection of four nucleobases (i.e., guanine (G), adenine (A), thymine (T) and cytosine (C)) along with uric acid (UA) as an internal standard. The nanocomposite was characterized using TEM and FT-IR. The linearity ranges were up to 151.0, 78.0, 79.5, 227.5, and 162.5 µM with a detection limit of 0.15, 0.12, 0.44, 4.02, 4.0, and 3.30 µM for UA, G, A, T, and C, respectively. Compared to a bare GCE, the nanocomposite-modified GCE demonstrated a large enhancement (~36.6%) of the electrochemical active surface area. Through chronoamperometric studies, the diffusion coefficients (D), standard catalytic rate constant (K_s), and heterogenous rate constant (K_h) were calculated for the analytes. Moreover, the nanocomposite-modified electrode was used for simultaneous detection in human serum, human saliva, and artificial saliva samples with recovery values ranging from 95% to 105%.

One-Step Synthesis of Tunable Zinc-Based Nanohybrids as an Ultrasensitive DNA Signal Amplification Platform

Herein, we demonstrated a one-step route for the manufacturing of polypyrrole (PPy)/zinc nanohybrids with tunable elemental composition and nanoscale component mixing resolution by using an ultrafast (within tens of seconds) microwave approach for ultrasensitive DNA biosensors. The zinc-based nanoparticles (i.e., MWPPy/ZnO and MWPPy/ZnS) were produced by loading zinc acetate (ZnAc₂) on PPy under the electromagnetic environment of a microwave with or without sulfur powder in one pot. Then, the signal amplification platforms were fabricated by modifying the glassy carbon electrode (GCE) with the obtained nanohybrids. It was found that both of the resultant MWPPy/ZnO and MWPPy/ZnS were suitable for ultrasensitive DNA molecule detection of the gastric carcinoma related PIK3CA gene ascribing to their unique hybrid nanostructures and surface characteristics. Experimental results revealed that the proposed GCE/MWPPy/ZnO sensor showed a linear range of 1.0 × 10^-10 to 1.0 × 10^-13 M. Notably, the GCE/MWPPy/ZnS sensor was endowed with promising DNA hybrid selection with a minimum concentration response of 1.0 × 10^-18 M. The corresponding detection limit was, respectively, found to be 2.90 × 10^-11 and 7.73 × 10^-21 M for MWPPy/ZnO- and MWPPy/ZnS-based biosensors. Furthermore, reliable determination of single-base and two-base mismatched DNA are more attractive, which greatly supported the application of the constructed zinc-based nanohybrids for the detection of single nucleotide polymorphism in genetic diseases, biological infectious pathogens, or warning against bio-warfare agents.

Graphene and Graphene-Based Nanomaterials for DNA Detection: A Review

DNA detection with high sensitivity and specificity has tremendous potential as molecular diagnostic agents. Graphene and graphene-based nanomaterials, such as graphene nanopore, graphene nanoribbon, graphene oxide, and reduced graphene oxide, graphene-nanoparticle composites, were demonstrated to have unique properties, which have attracted increasing interest towards the application of DNA detection with improved performance. This article comprehensively reviews the most recent trends in DNA detection based on graphene and graphene-related nanomaterials. Based on the current understanding, this review attempts to identify the future directions in which the field is likely to thrive, and stimulate more significant research in this subject.