Separation of purine and pyrimidine bases by capillary electrophoresis using β-cyclodextrin as an additive

Hybrid Nanomaterial of Graphene Oxide Quantum Dots with Multi-Walled Carbon Nanotubes for Simultaneous Voltammetric Determination of Four DNA Bases

In this proof-of-concept study, a novel hybrid nanomaterial-based electrochemical sensor was developed for the simultaneous detection of four DNA bases. For the modification of the working electrode surface, graphene oxide quantum dots (GOQDs) were synthesized using a solvothermal method. GOQDs were then used for the preparation of a hybrid nanomaterial with multi-walled carbon nanotubes (GOQD-MWCNT) using a solvothermal technique for the first time. Transmission electron microscopy (TEM) was used to characterize the GOQDs-MWCNTs. A glassy carbon electrode (GCE) was modified with the GOQDs-MWCNTs using Nafion™ to prepare a GOQD-MWCNT/GCE for the simultaneous determination of four DNA bases in phosphate buffer solution (PBS, pH 7.0) using differential pulse voltammetry (DPV). The calibration plots were linear up to 50, 50, 500, and 500 µM with a limit of detection at 0.44, 0.2, 1.6, and 5.6 µM for guanine (G), adenine (A), thymine (T) and cytosine (C), respectively. The hybrid-modified sensor was used for the determination of G, A, T, and C spiked in the artificial saliva samples with the recovery values ranging from 95.9 to 106.8%. This novel hybrid-modified electrochemical sensor provides a promising platform for the future development of a device for cost-effective and efficient simultaneous detection of DNA bases in real biological and environmental samples.

Application of Carbon Nanotubes in Chiral and Achiral Separations of Pharmaceuticals, Biologics and Chemicals

Carbon nanotubes (CNTs) possess unique mechanical, physical, electrical and absorbability properties coupled with their nanometer dimensional scale that renders them extremely valuable for applications in many fields including nanotechnology and chromatographic separation. The aim of this review is to provide an updated overview about the applications of CNTs in chiral and achiral separations of pharmaceuticals, biologics and chemicals. Chiral single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) have been directly applied for the enantioseparation of pharmaceuticals and biologicals by using them as stationary or pseudostationary phases in chromatographic separation techniques such as high-performance liquid chromatography (HPLC), capillary electrophoresis (CE) and gas chromatography (GC). Achiral MWCNTs have been used for achiral separations as efficient sorbent objects in solid-phase extraction techniques of biochemicals and drugs. Achiral SWCNTs have been applied in achiral separation of biological samples. Achiral SWCNTs and MWCNTs have been also successfully used to separate achiral mixtures of pharmaceuticals and chemicals. Collectively, functionalized CNTs have been indirectly applied in separation science by enhancing the enantioseparation of different chiral selectors whereas non-functionalized CNTs have shown efficient capabilities for chiral separations by using techniques such as encapsulation or immobilization in polymer monolithic columns.

Containment of bioaerosol infection risk by the Xpert MTB/RIF assay and its applicability to point-of-care settings

The recently introduced Xpert MTB/RIF assay (Xpert) has point-of-care potential, but its capacity for biohazard containment remained to be studied. We compared the bioaerosols generated by the Xpert assay to acid-fast bacillus (AFB) microscope slide smear preparation. The Xpert assay sample treatment reagent (SR) was also studied for its sterilizing capacity, stability, and effect on assay sensitivity after prolonged treatment. During the preparation of AFB smears, sputum samples spiked with Mycobacterium bovis BCG at 5 × 10(8) CFU/ml produced 16 and 325 CFU/m(3) air measured with an Andersen impactor or BioSampler, respectively. In contrast, neither the sample preparation steps for the Xpert assay nor its automated processing produced any culturable bioaerosols. In testing of SR sterilizing capacity, clinical sputum samples from strongly smear-positive tuberculosis patients treated with SR at a 2:1 ratio eliminated Mycobacterium tuberculosis growth in all but 1/39 or 3/45 samples cultured on solid or liquid medium, respectively. These few unsterilized samples had a mean 13.1-day delay in the time to positive culture. SR treatment at a 3:1 ratio eliminated growth in all samples. SR retained a greater than 6-log-unit killing capacity despite storage at temperatures spanning 4 to 45°C for at least 3 months. The effect of prolonged SR sample treatment was also studied. Spiked sputum samples could be incubated in SR for up to 3 days without affecting Xpert sensitivity for M. tuberculosis detection and up to 8 h without affecting specificity for rifampin resistance detection. These results suggest that benchtop use of the Xpert MTB/RIF assay limits infection risk to the user.

Chiral analysis of anti-acquired immunodeficiency syndrome drug, 9-(R)-[2-(phosphonomethoxy)propyl]adenine (tenofovir), and related antiviral acyclic nucleoside phosphonates by CE using beta-CD as chiral selector

A new CZE method has been developed for chiral analysis of an important anti-acquired immunodeficiency syndrome drug, 9-(R)-[2-(phosphonomethoxy)propyl]adenine ((R)-PMPA, tenofovir), and six related antiviral acyclic nucleoside phosphonates using beta-CD as a chiral selector. The influence of the composition, concentration and pH of the BGE and the type and concentration of chiral selector on enantiomer resolution was investigated. Complete separations of (R,S)-enantiomers of PMPA with very good resolution (R(s)=1.50-3.64) were achieved within a short time (4-15 min) in 20-50 mM sodium borate or sodium tetraborate BGEs, pH 10.0, at 20 mg/mL concentration of beta-CD. (R,S)-enantiomers of five similar PMPA analogs containing purine bases (adenine, diaminopurine or guanine) and hydroxyl or fluor substituents at C3 carbon atom of propyl chain were baseline separated within 10-17 min in 35 mM sodium tetraborate BGE, pH 10.0, at 20 mg/mL beta-CD concentration. Another important antiviral used by acquired immunodeficiency syndrome patients, derived from pyrimidine base cytosine, 1-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine (cidofovir), and the (R)-enantiomer of this drug were successfully separated in 50 mM sodium tetraborate BGE, pH 10.5, at 20 mg/mL beta-CD concentration within 45 min. Using the UV-absorption detection at 206 nm, the concentration detection limits of the analyzed acyclic nucleoside phosphonates were determined in the submicromolar to micromolar range (0.15-2.51 microg/mL level).

Hydrophilic interaction chromatography of nucleotides and their pathway intermediates on titania

Nucleotides and their pathway intermediates play important roles in all living species. They are essential cellular components in energy transfer, metabolic regulatory processes and biosynthesis. Titania (TiO(2)) has strong Lewis acid sites which have an affinity for the strongly electronegative phosphonate group of nucleotides. Herein a bare titania column (150 mm x 4.6 mm I.D., 3 microm) with UV detection at 254 nm was used for the separation of a set of nucleotides (AMP, ADP, ATP, UMP, UDP, UTP, GMP, GDP, GTP, CMP and CTP) and their intermediates (NAD, NADH, UDP-Glu and UDP-GluNAc). Addition of phosphate to the eluent suppresses the ligand-exchange interactions with the titania surface such that hydrophilic interaction chromatography (HILIC) separations may be performed. Increasing the %ACN resulted in increasing retention and efficiency (up to 13,000, 9500 and 4500 plates/m for AMP, ADP and ATP, respectively). The effects of pH, buffer concentration and other eluent anions (fluoride and acetate) were also studied. Fifteen nucleotides and their intermediates were separated in 26 min (R(minimum)>1.3) using an one-step gradient.

Application of CE for determination of DNA base composition

DNA base composition expressed as mol% of guanine plus cytosine (% GC) or GC content is a key parameter of bacterial taxonomy and genomic analyses. Direct chemical determination methods such as HPLC as well as indirect methods based on physical properties of deoxyribonucleic acid (DNA), melting point (T(m)), and buoyant density (B(d)) have been conventionally applied to determine the GC content. However, these methods require relatively large amounts of sample DNA, time, and labor. We have developed a protocol to determine the GC content by fine separation of nucleosides with CZE. Genomic DNAs with known GC content from 23 bacterial strains were determined by CE at the optimized conditions of 27 degrees C, 20 kV in 50 mM of NaHCO(3) (pH 9.0) and 70 mM SDS added. Nucleosides from <1 microg of DNA hydrolyzed with nuclease-P1 and bacterial alkaline phosphatase were separated in a 75 microm wide and 80 cm long silica capillary. The nucleoside peak areas were determined at 254 nm in less than 12 min. The CE-based determination of GC content requires only small amounts of DNA, and thus should be applicable to environmental genomics (metagenomics), as >90% of environmental micro-organisms are nonculturable and produce only small amounts of genomic DNA.

Contemporary sample stacking in CE: A sophisticated tool based on simple principles

Sample stacking is a general term for methods in CE which are used for on-line concentration of diluted analytes. During the stacking process, analytes present at low concentrations in a long injected sample zone are concentrated into a short zone (stack). The stacked analytes are then separated and individual zones are detected. Thus stacking provides better separation efficiency and detection sensitivity. Many papers have been published on stacking till now, various procedures have been described, and, many names have been proposed for stacking procedures utilizing the same principles. This contribution brings an easy and unified view on stacking, describes the basic principles utilized, makes a list of recognized operational principles and brings an overview of principal current procedures. Further, it surveys selected recent practical applications ordered according to their operational principles and includes the terms, nicknames, and acronyms used for these actual stacking procedures. This contribution may help both newcomers and experts in the field of CE to orient themselves in the already quite complex topic of sample stacking.

Enhanced separation of purine and pyrimidine bases using carboxylic multiwalled carbon nanotubes as additive in capillary zone electrophoresis

This paper describes the enhanced separation of adenine (A), hypoxanthine (HX), 8-azaadenine (8-AA), thymine (T), cytosine (C), uracil (U) and guanine (G) by CZE dispersing carboxylic multiwalled carbon nanotubes (c-MWNTs) into the running buffer. The effect of important factors such as c-MWNT nanoparticle concentration, the acidity and concentration of running buffer, and separation voltage were investigated to acquire the optimum conditions. The seven purine and pyrimidine bases could be well separated within 16 min in a 35 cm effective length fused-silica capillary at a separation voltage of +8.0 kV in a 23 mM tetraborate buffer (pH 9.2) containing 8.0 x 10(-5) g/mL c-MWNTs. Under the optimal conditions, the linear ranges were of 2-250 microg/mL for A (R2 = 0.995), 3-200 microg/mL for U (R2 = 0.990) and G (R2 = 0.992), 3-250 microg/mL for T (R2 = 0.998), 2-200 microg/mL for C (R2 = 0.985) and 4-200 microg/mL for HX (R2 = 0.988) and 8-AA (R2 = 0.990). The detection limits were 0.9 microg/mL for A (S/N = 3), 2.4 microg/mL for U, 2.0 microg/mL for T, 1.5 microg/mL for C, 2.5 microg/mL for G and 3.0 microg/mL for HX and 8-AA. The proposed method was successfully applied for determining five purine and pyrimidine bases in yeast RNA.

A novel flow-injection chemiluminescence system for the determination of guanine

A novel flow-injection chemiluminescence (CL) method for the determination of guanine was developed. The procedure is based on the CL reaction of guanine with hydrogen peroxide in borax buffer (pH 8.5) with Co2+ as a catalyst. The calibration graph is linear within the range of 3 x 10(-7)-9 x 10(-5) g/mL. A detection limit of 1 x 10(-7) g/mL, along with a relative standard deviation of 2.23% (3 x 10(-7) g/mL guanine, n = 11), were obtained. The present procedure was applied to the measurement of guanine in urine with recoveries of 97.5-107.5%. A possible CL mechanism of the reaction system is proposed.