An avidin-biotin assay was developed from a voltammetric procedure using biotin labeled with cysteine. Mercury(II) as a marker was used to detect avidin and biotin, because the oxidation wave of mercury decreases when the cysteine part of labeled biotin(LB) complexes with mercury(II).The formation of the mercury(II)-cysteine complex is suppressed when the LB binds to the biotin site of avidin. Accordingly, the concentration of avidin can be estimated from the increasing mercury peak current. Detection of biotin is also carried out by a competitive reaction of biotin and the LB to the binding site on avidin, where the addition of biotin decreases the peak current of mercury. Limits of detection for avidin and biotin were in the 10–9 mol/L range. The length of the spacer between the cysteine and biotin was investigated. It was observed that the strength of binding increased with increasing length of spacer. Size considerations rules out steric influences, so it is suggested that the binding constant depends on hydrophobic interactions in the binding site. 相似文献
Ten synthetic receptors were tested in potentiometric coated wire electrodes. The electrodes were used as sensing devices in classical reversed phase HPLC determinations of dicarboxylic acids present in food materials. All receptors contained amine functionalities. Four of them were podand urea derivatives. The other six were macrocyclic polyamines with lipophilic groups. Three of them had urea functionalities in their side-chains. Glassy carbon (GC) substrate electrodes were coated with PVC-based “liquid membranes” containing plasticizers and receptors. All tested compounds strongly enhanced the detection limits for the dicarboxylic acids (low pg detection limits), in comparison to a non-specific electrode based on methyltridodecylammonium chloride (MTDDACl). Receptors of the podand urea type yielded high sensitivity, but the electrodes had a lower long-time stability (a few weeks) than the electrodes based on macrocyclic polyamines (at least 3 months). 相似文献
A benzthiazole-based receptor 1 has been designed and synthesized for recognition of biotin ester and urea in CHCl3 containing 1% CH3CN. The receptor binds biotin methyl ester and urea with moderate binding constant values and shows significant increase in emission of benzthiazole motif. The emission characteristics of 1 upon complexation clearly distinguishes biotin methyl ester and urea from thiourea and N,N′-dimethylurea. Characterization and sensing properties of the receptor 1 were evaluated by 1H NMR, UV-vis, and fluorescence spectroscopic methods. 相似文献
A two-dimensional array of gold nanotriangles inscribed onto glass coverslips were optimized for the surface-enhanced Raman detection of streptavidin/biotin monolayer assemblies. The nanostructures were fabricated by electron beam lithography, and its optical parameters were optimized to be probed under a Raman microscope with a linearly polarized He-Ne laser with an excitation wavelength of λ = 632.8 nm. The platforms were first tested against a monolayer of biotinylated alkanethiols (BAT) functionalized over the gold nanostructure, showing that good-quality spectra could be acquired with a short acquisition time. The supramolecular interaction of streptavidin (strep) with BAT showed subsequent modification of the Raman spectrum that implies a change in the secondary structure of the host biomolecule (streptavidin). Compared to gold surfaces without nanoscale structures, the local enhancement that results from our nanostructured surfaces allows one to detect the vibrational signal of monolayers within a time on the order of seconds and under modest laser intensity, further demonstrating the utility of using plasmonic metallic nanostructures for molecular recognition. 相似文献
We have measured, by means of NMR titrations, the binding constants for the complexes between hosts N,N′-bis(6-methylpyridin-2-yl)-1,3-benzenedicarboxamide (7) and 4-chloro-N,N′-bis(6-methylpyridin-2-yl)-2,6-pyridinedicarboxamide (8, hydrated) with biotin methyl ester (1), N,N′-dimethylurea (2), 2-imidazolidone (3), N,N′-trimethylenurea (4), barbital (5) and tolbutamide (6) as guests. Molecular Mechanics calculations (Monte Carlo Conformational Search, AMBER and OPLS force fields, MacroModel v.8.1) on the complexes formed between the foregoing guests and hosts 7 and 8, comparatively with 4-oxo-N,N′-bis(6-methylpyridin-2-yl)-1,4-dihydro-2,6-pyridinedicarboxamide (9a) have been carried out in order to determine the correlation between experimental and theoretical results and to understand the behaviour of the designed new hosts. Finally we have performed single point DFT [B3LYP/6-31G(d,p)] calculations on the optimised Molecular Mechanics geometries for the complexes between hosts 7-9 and water. 相似文献
NMR titrations and Monte Carlo conformational searches have been used to study the molecular recognition features of five urea derivatives with two synthetic hosts. We have improved the binding constant (Kb) values for all the studied guests and measured the largest binding constant of a complex involving a biotin derivative (biotin methyl ester) bound to a synthetic host by means of several interaction points and not only through the urea moiety. 相似文献
Adenine-based receptors 1 and 2 are designed and synthesized for selective sensing of iodide over the other halides and carboxylate anions. Both the receptors 1 and 2 use the urea motif for binding carboxylates and halides. Emissions of the naphthalene and the anthracene in 1 and 2, respectively, are monitored in CHCl3 in detecting the anions. While carboxylates, fluoride, chloride, and bromide increase the emissions of naphthalene and anthracene in both the receptors 1 and 2 during complexation, iodide quenches the emission. Such selective quenching allows iodide to be discriminated from other halides and carboxylate anions. 相似文献
For the recognition and sensing of anionic analytes, comparative studies were carried out on the anion bindings of pyrophosphate, H2PO4−, and dicarboxylates to the anthracene derivatives bearing two urea groups on the 1,8 and 9,10-positions as fluorescent chemosensors for anions. Their binding properties were compared using fluorescence and 1H NMR, and the results were rationalized with an ab initio study. 相似文献
The photometric detection of urea with the use of p-dimethylaminobenzaldehyde as a reagent has been develeped. The method allows one to reliably determine 10 mg/L of urea with
the volume of an aliquot of 10 mL. The method has been applied for the determination of urea in river water. 相似文献
The novel colorimetric receptors 2,3-bis-N-(9,10-diaza-anthracen-1-yl)-N′-phenylurea and 2,3-bis-N-(9,10-diaza-anthracen-1-yl)-N′-phenylthiourea have been prepared by the reaction of 2,3-diaminophenazine with phenylisocyanate and phenylisothiocyanate, respectively, in quantitative yields. The interaction and colorimetric sensing properties of receptor = 2 and 3 with different anions were investigated by naked eye, UV-vis and fluorescence spectroscopy in DMSO. The receptors effectively and selectively recognized biologically important F−, CH3COO−, H2P in the presence of other anions, such as Cl−, Br−, I− and HS in DMSO. 相似文献
The neutral receptors 1 and 2 are designed and synthesized for the recognition of biotin, a biologically significant molecule, in chloroform to bind completely both of its functional groups simultaneously, i.e., cyclic urea and the carboxyl groups. The truncated receptor 3 binds only the cyclic urea moiety. 相似文献
Fluorogenic probes enable imaging biomolecular targets with high sensitivity and maximal signal-to-background ratio under non-wash conditions. Here, we focus on the molecular design of biotinylated dimeric squaraines that undergo aggregation-caused quenching in aqueous media through intramolecular H-type dimerization, but turn on their fluorescence in apolar environment due to target-mediated disaggregation. Our structure–property study revealed that depending on the linkers used to connect the squaraine dyes, different aggregation patterns could be obtained (intramolecular dimerization versus intermolecular aggregation) leading to different probing efficiencies. Using a relatively short l-lysine linker we developed a bright fluorogenic probe, Sq2B, displaying only intramolecular dimerization-caused quenching properties in aqueous media. The latter was successfully applied for imaging biotin receptors, in particular sodium-dependent multivitamin transporter (SMVT), which are overexpressed at the surface of cancer cells. Competitive displacement with SMVT-targets, such as biotin, lipoic acid or sodium pantothenate, showed Sq2B targeting ability to SMVT. This fluorogenic probe for biotin receptors could distinguish cancer cells (HeLa and KB) from model non-cancer cell lines (NIH/3T3 and HEK293T). The obtained results provide guidelines for development of new dimerization-based fluorogenic probes and propose bright tools for imaging biotin receptors, which is particularly important for specific detection of cancer cells.Rational design of self-quenched squaraine dimers bearing biotin yielded a bright fluorogenic probe that can distinguish cancerous from non-cancerous cells.相似文献
Biotin is a vitamin of the B-complex, which plays an important biochemical role in every living cell. In the recent years, the interest in this vitamin has been rekindled, mainly due to its association with serious human disorders, such as the inherited syndrome multiple carboxylase deficiency, which can be successfully treated with biotin administration. Diagnosis of biotin deficiency as well as monitoring of biotin levels in biological fluids of patients receiving biotin treatment is crucial. Equally important is the determination of biotin levels in pharmaceutical preparations as well as in food and food supplement products, which constitute the main source of biotin in humans. Several analytical methods for measuring biotin in various samples, e.g. human fluids, pharmaceutical formulations, food material etc., have been reported in the literature. In this review, the most representative of these methods are presented, and their characteristics are evaluated. 相似文献
Nickel oxide (NiO) nanosheets (NSs) deposited on different amounts (0.025, 0.05, 0.1, and 0.2 wt%) of reduced graphene oxide (rGO) are synthesized through hydrothermal method. The NiO NSs on rGO (rGO-NiO) are characterized by using X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) analyses, and electrochemical analysis. Electrocatalytic activity of rGO-NiO nanocomposite modified glassy carbon (GC/rGO-NiO) electrode is examined towards electrocatalytic oxidation of urea in 0.1 M NaOH using cyclic voltammetry and amperometry techniques. The GC/rGO0.1-NiO nanocomposite modified electrode shows enhanced electrocatalytic oxidation of urea than that of other modified electrodes due to the incorporation of NiO NSs on an optimum amount of rGO. The GC/rGO0.1-NiO modified electrode is used for designing electrochemical sensor for urea, and the detection limit is estimated as 0.47 μM using the amperometry technique. The sensitivity of GC/rGO0.1-NiO modified electrode is found to be 2450 μA mM−1 cm−2. In addition to good electroanalytical performance, the present urea sensor displayed good stability and acceptable anti-interference ability in the presence of 20-fold excess concentration of relevant interferents. The GC/rGO0.1-NiO nanocomposite modified electrode is successfully used for the determination of urea in water sample.
Schematic representation of electrocatalytic oxidation of urea at GC/rGO-NiO nanocomposite modified electrode.
A highly selective and rapid electrochemical assay of the improvised explosive urea nitrate (UN) is reported. The method involves a short ( approximately 10 s) acid-catalyzed reaction of UN with 4-nitrotoluene (NT) followed by a rapid ( approximately 2 s) square-wave voltammetric (SWV) detection of the 2,4-dinitrotoluene (DNT) product. The new protocol offers great promise for a reliable field detection of UN, with significant advantages of speed, sensitivity, portability, simplicity, and cost. 相似文献
This study presents a new microfluidic system capable of precise measurements of two important biomarkers, urea and creatinine, automatically. In clinical applications, high levels of these two biomarkers are early indicators of nephropathy or renal failure and should be monitored on a regular basis. The microfluidic system is composed of a microfluidic chip, a control circuit system, a compressed air source and several electromagnetic valves to form a handheld system. The microfluidic chip is fabricated by using micro-electromechanical systems and microfluidic techniques comprising electrochemical sensor arrays and polydimethylsiloxane-based microfluidic structures such as micropumps/micromixers, normally closed valves and microchannels. The microfluidic system performs a variety of critical processes including sample pretreatment, mixing, transportation and detection on a single chip. The experimental results show that the entire procedure takes approximately 40 min, which is much faster than the traditional method (more than 6 h). Furthermore, the total sample volume consumed in each operation is only 0.1 mL, which is significantly less than that required in a large system (5 mL). The developed automatic microfluidic system may provide a powerful platform for further clinical applications. 相似文献