Detection Of Theophylline Research Articles

Fabrication of electrochemical theophylline sensor based on manganese oxide nanoparticles/ionic liquid/chitosan nanocomposite modified glassy carbon electrode

In this study, the preparation of a glassy carbon (GC) electrode modified with chitosan/NH2-ionic liquid/manganese oxide nanoparticles (Chit/NH2-IL/MnOx) was described for electrocatalytic detection of theophylline (TP). First, chitosan hydrogel (Chit) was electrodeposited on the GC electrode surface at a constant potential (−1.5V) in acidic solution. Then, the previously synthesized amine-terminated 1-(3-Aminopropyl)-3-methylimidazolium bromide ionic liquid (NH2-IL) was covalently attached to the modified electrode via glutaraldehyde (GA) as linking agent. Finally, manganese oxide (MnOx) nanoparticles were electrodeposited onto the Chit/NH2-IL film by potential cycling between −1.0 and 1.7V in Mn(CH3COO)2·4H2O neutral aqueous solution. Electrochemical behavior of the modified electrode was evaluated by cyclic voltammetry (CV) technique. The charge transfer coefficient (α) and electron transfer rate constant (ks) for MnOOH/MnO2 redox couple were calculated to be 0.35 and 1.62s−1, respectively. The resulting system brings new capabilities for electrochemical sensing through combining the advantages of IL and MnOx nanoparticles. The differential pulse voltammetric (DPV) results indicated the high ability of GC/Chit/NH2-IL/MnOx modified electrode to catalyze the oxidation of TP. DPV determination of TP in acetate buffer solution (pH 5) gave linear responses over the concentration range up to 120μM with the detection limit of 50nM and sensitivity of 804nAμM−1. Furthermore, the applicability of the sensor for TP analysis in pharmaceutical samples has been successfully demonstrated.

Gold nanoparticles based colorimetric aptasensor for theophylline

A simple colorimetric aptasensor for the detection of theophylline was investigated using stable RNA aptamer and gold nanoparticles (AuNPs). Theophylline, a purine derivative, structurally similar to caffeine is broadly used in the treatment of respiratory diseases and bronchial asthma. A highly stable RNA aptamer that selectively binds to the theophylline molecule was prepared by structural modification of the 2′-hydroxyl group of ribose to 2′-fluoro (5′GGC GAU ACC AGC CGA AAA GGC CCU UGG CAG CGU C3′) in all the pyrimidines in a 34-mer length aptamer. The RNA aptamer binds to AuNPs by simple electrostatic interactions thereby inhibiting salt induced aggregation. AuNPs are aggregated due to detachment of the theophylline specific RNA aptamer from the surface of the AuNPs as a result of interaction with the target leading to a color change from red to purple. By successfully optimizing the concentration of aptamer, AuNPs, salts and stability of the aptamer, a detection limit of 50 ng mL−1 theophylline was achieved. Analyses of theophylline in samples were carried out, and the observed recovery was 97–98.7% with a relative standard deviation in the range of 2.69–19.4%. The results obtained were compared with those of an HPLC method. This colorimetric aptasensor is advantageous for onsite visual detection.

A method based on electrodeposition of reduced graphene oxide on glassy carbon electrode for sensitive detection of theophylline

Graphene nanosheets were directly electrodeposited onto a glassy carbon electrode (GCE) from the electrolyte solution containing graphene oxide (GO); the resulting electrode (ED-GO/GCE) was characterized with scanning electron microscopy. A simple and rapid electrochemical method was developed for the determination of theophylline (TP), based on the excellent properties of ED-GO film. The result indicated that ED-GO film-modified GCE exhibited efficient electrocatalytic oxidation for TP with relatively high sensitivity and stability. The electrochemical behavior of TP at ED-GO/GCE was investigated in detail. Under the optimized conditions, the oxidation peak current was proportional to the TP concentration in the range of 8.0 × 10−7 to 6.0 × 10−5 mol L−1 with the detection limit of 1.0 × 10−7 mol L−1 (S/N = 3). The proposed method was successfully applied to green tea samples with satisfactory results.

Competitive Assay for Theophylline Based on an Abasic Site‐Containing DNA Duplex Aptamer and a Fluorescent Ligand

A fluorescence assay for theophylline, one of the common drugs for acute and chronic asthmatic conditions, has been developed based on an abasic site-containing DNA duplex aptamer (AP aptamer) in combination with an abasic site-binding fluorescent ligand, riboflavin. The assay is based on the competitive binding of theophylline and riboflavin at the abasic (AP) site of the AP aptamer. In the absence of theophylline, riboflavin binds to the receptor nucleotide opposite the AP site, which leads to fluorescence quenching of the riboflavin. Upon addition of theophylline, competitive binding occurs between theophylline and riboflavin, which results in an effective fluorescence restoration due to release of riboflavin from the AP site. From an examination of the optimization of the AP aptamers, the complex of riboflavin with a 23-mer AP aptamer (5'-TCT GCG TCC AGX GCA ACG CAC AC-3'/5'-GTG TGC GTT GCC CTG GAC GCA GA-3'; X: the AP site (Spacer C3, a propylene residue)) possessing cytosine as a receptor nucleotide was found to show a selective and effective fluorescence response to theophylline; the limit of detection for theophylline was 1.1 μM. Furthermore, fluorescence detection of theophylline was successfully demonstrated with high selectivity in serum samples by using the optimized AP aptamer and riboflavin.

Surface Plasmon Resonance (SPR) Detection of Theophylline via Electropolymerized Molecularly Imprinted Polythiophenes

A facile approach to tailor-made, highly selective, and robust ultrathin sensor film for theophylline detection was demonstrated by an electropolymerized molecularly imprinted polymer (E-MIP) film of a terthiophene derivative. The method involved direct electropolymerization of the H-bond complexing terthiophene monomer. A key enabling step in sensor fabrication is the use of an electrochemically mediated washing step of the template. The formation of the E-MIP film was monitored by in situ electrochemical surface plasmon resonance (EC-SPR) spectroscopy, allowing real-time observation of the simultaneous changes in electrochemical and optical properties of the film. Surface characterization techniques for the electropolymerized films include atomic force microscopy (AFM), ellipsometry, static contact angle, X-ray photoelectron spectroscopy (XPS), and quartz crystal microbalance (QCM). A linear calibration curve (R = 0.994) of the E-MIP/SPR sensor for theophylline detection was obtained with a 10−50 μM−1 r...

A label-free electrochemical RNA aptamer for selective detection of theophylline

In this work, we report a novel electrochemical RNA aptamer for the selective detection of theophylline. Firstly, gold nanoparticles were electrodeposited on the surface of glassy carbon (GC) electrode to form a gold nanoparticles modified electrode. Secondly, the designed single-stranded RNA (ssRNA) was immobilized on gold nanoparticles through a thiol linker as a probe RNA. Then, the complement stranded RNA, which can combine with the probe ssRNA to form a double-stranded RNA (dsRNA) with a recognition unit of theophylline, was linked on the probe RNA through a hybrid reaction in the presence of theophylline. Doxorubicin was selected as an electrochemical indicator. The proposed RNA aptamer presents an excellent selectivity for the detection of theophylline. The detectable concentration range of theophylline is from 2.0 to 50.0 μM with a limit of detection of 1.2 μM.

Optimization of the Electrochemical RNA‐Aptamer Based Biosensor for Theophylline by Using a Methylene Blue Redox Label

AbstractThe electrochemical biosensor for theophylline detection in serum based on the RNA molecular beacon approach and methylene blue (MB) as a redox label has been developed. The RNA aptamer for theophylline was immobilized at gold electrodes in its open unfolded state through the alkanethiol linker at its 5′ end, and the MB redox label was attached to the 3′ end of the aptamer. Conformational folding of the aptamer upon theophylline binding increased the electrochemical response from the MB redox probe, then placed closer to the electrode surface. The signal was calibrated versus theophylline concentration within the 2 to 100 μM range, which allows practical determinations of theophylline within therapeutically important 20–100 μM range. The performance of the RNA‐aptamer based biosensor was not inhibited in serum, which was consistent with the absence of detrimental effects of adsorption of serum proteins within the operational potential window of the MB‐labeled biosensor.

Application and analysis of structure-switching aptamers for small molecule quantification

Modern tools for the analysis of cellular function aim for the quantitative measurement of all members of a given class of biological molecules. Of the analyte classes, nucleic acid measurements are typically the most tractable, both on an individual analyte basis and in parallel. Thus, tools are being sought to enable measurement of other cellular molecules using nucleic acid biosensors. Of the variety of potential nucleic acid biosensor strategies, structure-switching aptamers (SSAs) present a unique opportunity to couple sensing and readout of the target molecule. However, little has been characterized about the parameters that determine the fidelity of the signal from SSA biosensors. In this study, a small molecule biosensor based on a SSA was engineered to detect the model small molecule, theophylline, in solution. Quantitative theophylline detection over nearly three orders-of-magnitude was achieved by scintillation counting and quantitative PCR. Further analysis showed that the biosensor fidelity is primarily controlled by the relative stability of the two conformations of the SSA.

2-Aminopurine-Modified Abasic-Site-Containing Duplex DNA for Highly Selective Detection of Theophylline

2-Aminopurine-modified abasic-site-containing duplex [DNA 5'-TCTGC GTCCT PXT TAACG CACAC-3'/3'-AGACG CAGGA TCA ATTGC GTGTG-5'; P = 2-aminopurine, X = abasic site (Spacer-C3), C = receptor base] is capable of selectively binding to the bronchodilator theophylline with a dissociation constant of 10 microM (5 degrees C, pH 7.0, I = 0.11 M) and is applicable to monitoring serum theophylline concentrations.

Validated stability indicating HPLC method for estimation of theophylline from a novel microsphere formulation

A new, simple, specific, precise and robust isocratic reversed-phase (RP) stability-indicating high-performance liquid chromatographic (HPLC) method was developed and validated for determination of theophylline from a novel formulation. The liquid chromatographic separation was achieved isocratically using a mobile phase of acetonitrile: 50 mM sodium acetate buffer (15:85) adjusted to pH 6.5 using dilute hydrochloric acid. The analysis was carried out using Hi-Q-Sil C18 column [250 mm x 4.6 mm, 5 μm] at flow rate of 1 ml/min and the UV detection at 270 nm. The method was validated for accuracy, precision, linearity, range, selectivity, and robustness. The linearity of the proposed method was investigated in the range of 1 to 24 μg/ml (r2 = 0.9995). The drug was subjected to oxidation, hydrolysis, heat, and photolysis to apply stress conditions. The method provided good peak parameters with retention time of 8.6 ± 0.3 min. Degradation products resulting from stress studies did not interfere with the detection of theophylline and the assay can thus be considered as stability-indicating.

Capacitive Detection of Theophylline Based on Electropolymerized Molecularly Imprinted Polymer

The capacitive sensor was prepared by electropolymerization of phenol onto the surface of gold electrode. By using AC impedance measurements, the sensor is based on the decrease in capacitance caused by the analyte used as the template in the formulation of an electropolymerized molecularly imprinted polymer as receptor layer. Improvement of the insulating properties of the sensor was investigated in detail. Electrochemical impedance (EI) was used to characterize the modified gold electrodes. Unlike the capacitive sensors reported previously, the present sensors were not treated with alkanethiol after the electropolymerization and show even more satisfactory performance.

Bioelectrocatalytic detection of theophylline at theophylline oxidase electrodes

Bioelectrocatalytic oxidation of theophylline was studied at gold and graphite electrodes modified with microbial theophylline oxidase (ThOx), a multi-cofactor redox enzyme capable of selective oxidation of theophylline. Gold electrodes were additionally modified with self-assembled monolayers (SAMs) of (–OH)- and (–NH 2)-terminated alkanethiols of different chain lengths, to achieve compatibility between ThOx and the electrode surface. On graphite, ThOx was either physically co-adsorbed with a surfactant didodecyldimethylammonium bromide (DDAB), or entrapped within an Os-redox-polymer film. At all electrodes, ThOx was bioelectrocatalytically active; direct electrochemistry of ThOx in the absence of theophylline was followed only at the SAM-modified gold electrodes. Direct electrochemistry of ThOx correlated with redox transformations of the heme domain of ThOx, with a E o/of −110 ± 2 mV versus Ag|AgCl, at pH 7. Bioelectrocatalytic oxidation of theophylline was optimal at mixed (–OH)/(–NH 2)-terminated SAMs; co-adsorption of ThOx with DDAB improved the bioelectrocatalytic performance of the ThOx-electrode. In both cases, the response to theophylline was within the mM range. Alternatively, a reagentless ThOx-electrode based on ThOx cross-linked within the Os-redox-polymer matrix demonstrated a linear response to theophylline within the physiologically important 0.02–0.6 mM (3.6–72 mg l −1) concentration range with a sensitivity of 52.1 ± 7.8 mA cm −2 M −1.

Poly(methylene green) employed as molecularly imprinted polymermatrix for electrochemical sensing

This paper describes the development of a molecularly imprinted polymer (MIP) for theophylline that can be used for electrochemical sensing. Theophylline is a commonly used medication for the treatment of asthma. Due to its very narrow therapeutic index, it may have toxic and potentially fatal effects on the individual. Electrochemical detection of theophylline is difficult, because its molecular structure and standard reduction potential are very similar to that of caffeine. A new method for fabricating molecularly imprinted polymers is proposed utilizing methylene green. Poly(methylene green)(PMG), prepared by electropolymerization of an azine, methylene green, was imprinted for theophylline. PMG-based MIP-coated electrodes showed sensitivity towards the presence of the imprint molecule in solutions, as well as selectivity for the imprint over the interferent molecule caffeine. The PMG-based MIP-coated electrode described in this paper had an improved selectivity factor and reproducibility compared to other theophylline-imprinted MIP-coated electrodes in literature.

Highly sensitive and rapid determination of theophylline, theobromine and caffeine in human plasma and urine by gradient capillary high-performance liquid chromatography-frit-fast atom bombardment mass spectrometry.

A sensitive and reliable analytical procedure has been established for the detection of theophylline (TH), theobromine (TB) and caffeine (CA) in human plasma and urine by gradient capillary high-performance liquid chromatography (HPLC)-frit-fast atom bombardment mass spectrometry (FAB-MS) (LC-frit-FAB-MS). Two capillary columns and a column-switching valve were used in this LC system to allow all of the sample injected to be introduced into the MS system. 7-Ethyltheophylline was used as the internal standard (I.S.). The xanthines in the specimen were extracted with an Extrelut column. The lowest detected amount was ca. 5 ng/ml using this method.

Liposome immunosensor for theophylline

A new simple, sensitive liposome immunosensor (LIS) has been developed by combining the advantages of spin membrane immunoassay (SMIA) and enzyme immunosensor (EIS). The LIS system is composed of an oxygen electrode and sensitized liposomes. It records liposome lysis induced by specific anti-theophylline antibodies and complement which is monitored by the release of entrapped enzymes instead of spin labeles. A sensitive detection was performed because of the amplification of antigen-antibody reaction by liposome lysis and enzymatic reaction. The method offers a simple and sensitive quantitative detection of theophylline down to 4 × 10 −9 M (0.7 ng/ml).

Detection of theophylline and theobromine by reactions with mercury(II) cyanide

Detection of theophylline and theobromine by reactions with mercury(II) cyanide