CE Determination of Creatinine and Uric Acid in Saliva and Urine During Exercise

A simple and reliable method based on capillary electrophoresis with electrochemical detection (CE–ED) was applied to study the effect of aerobic exercises on creatinine and uric acid concertration in saliva and urine. The pH value, the running buffer concentration, the SDS concentration, separation voltage, injection time and the potential applied to the working electrode were investigated to find the optimum conditions. The detection limits (S/N = 3) for creatinine and uric acid were 3.6 μmol L^?1 and 0.86 μmol L^?1, respectively. This method was successfully used in the rapid analysis of creatinine and uric acid in saliva samples. After aerobic exercises, creatinine concentration decreased, and uric acid concentration increased in saliva. In urine, the concentrations of creatinine and uric acid both increased after exercise.     

A novel anti-interference and pH-modulation device: application to enzyme-free glucose detection

We report on a novel anti-interference and pH-modulation device (herein after referred to as ??device??). It is based on electrodialysis and can continuously increase the pH value of the carrier solution and - at the same time - remove interfering analytical signals obtained for ascorbic acid (AA) and uric acid (UA). The ??device?? was coupled to the FIA-amperometric detection of glucose. The linear range is from 1???mol?L^?1 to 0.4?mmol?L^?1, with a sensitivity of 213???A?cm^?2?mM^?1 and a detection limit of 1???mol?L^?1 at a signal-to-noise ratio of 3. The method was used to sucessfully determine glucose in serum. This study represents a novel technique for overcoming analytical interference and is expected to find applications in liquid chromatography, for example in on-line pH-modulation if different pH values are needed for separation and detection.

Chromatographic Properties of Ethanol/Water Mobile Phases on Silica Based Monolithic C18

A simple and reliable method based on capillary electrophoresis with electrochemical detection (CE–ED) was applied to study the effect of aerobic exercises on creatinine and uric acid concertration in saliva and urine. The pH value, the running buffer concentration, the SDS concentration, separation voltage, injection time and the potential applied to the working electrode were investigated to find the optimum conditions. The detection limits (S/N = 3) for creatinine and uric acid were 3.6 μmol L⁻¹ and 0.86 μmol L⁻¹, respectively. This method was successfully used in the rapid analysis of creatinine and uric acid in saliva samples. After aerobic exercises, creatinine concentration decreased, and uric acid concentration increased in saliva. In urine, the concentrations of creatinine and uric acid both increased after exercise.

     

Flow in a Paper‐based Bioactive Channel – Study on Electrochemical Detection of Glucose and Uric Acid

Although paper‐based analysis is known for centuries, only during the last decade this simple substrate became an object of detailed microfluidic studies. In order to obtain optimum performance and separation of the analytes in a microfluidic channel, devices should be optimized, both in terms of architecture and paper properties. Enzyme immobilization methods can not only increase the storage stability but also have an impact on the flow in paper matrix, providing additional charges, and changing the porous structure of paper. Therefore it should be guaranteed that the method of choice will not obstruct the flux in the final device. Paper‐based device proposed in this study was composed of a bioactive channel, Pt working electrode, pencil drawn pseudo‐reference electrode, a buffer filled sponge providing the wicking solution and a stack of wicking pads to guarantee continuous flow. Based on our previous research we chose 4 methods of enzyme immobilization relying on different phenomena (adsorption, covalent linkage, layer‐by‐layer, capsules). Different channel architectures were also evaluated in order to achieve optimum time of the enzymatic reaction, separation of peaks and the time of measurement. Experimental results were compared with computer simulations. Final device could quantify glucose (2.0–10.0 mmol L^?1) and uric acid (0.1–1.2 mmol L^?1) in their clinical range with good repeatability.     

Electrogenerated Chemiluminescence of Tris(2,2′‐bipyridyl)ruthenium(II) Immobilized in Humic Acid‐Silica‐Poly(vinyl alcohol) Composite Films

In this paper, we report the first attempt to use humic acid (HA) as modifiers to prepare the organic‐inorganic hybrid modified glassy carbon electrodes based on HA‐silica‐PVA (poly(vinyl alcohol)) sol‐gel composite. Electroactive species of tris(2,2′‐bipyridyl)ruthenium(II) (Ru(bpy) ) can easily incorporate into the HA‐silica‐PVA films to form Ru(bpy) modified electrodes. The amount of Ru(bpy) incorporated in the composite films strongly depends on the amount of HA in the hybrid sol. Electrochemical and electrogenerated chemiluminescence (ECL) of Ru(bpy) immobilized in HA‐silica composite films coated on a glassy carbon electrode have been studied with tripropylamine (TPA) as the coreactant. The analytical performance of this modified electrode was evaluated in a flow injection analysis (FIA) system with a homemade flow cell. The as‐prepared electrode showed good stability and high sensitivity. The detection limits (S/N=3) were 0.050 μmol L^?1 for TPA and 0.20 μmol L^?1 for oxalate, and the linear ranges were from 0.10 μmol L^?1 to 1.0 mmol L^?1 for TPA and from 1.0 μmol L^?1 to 1.0 mmol L^?1 for oxalate, respectively. The resulting electrodes were stable over two months.     

Unadulterated Glucose Biosensor Based on Direct Electron Transfer of Glucose Oxidase Encapsulated Chitosan Modified Glassy Carbon Electrode

Glucose oxidase (GOD) was encapsulated in chitosan matrix and immobilized on a glassy carbon electrode, achieving direct electron transfer (DET) reaction between GOD and electrode without any nano‐material. On basis of such DET, a novel glucose biosensor was fabricated for direct bioelectrochemical sensing without any electron‐mediator. GOD incorporated in chitosan films gave a pair of stable, well‐defined, and quasireversible cyclic voltammetric peaks at about ?0.284 (E_pa) and ?0.338 V (E_pc) vs. Ag/AgCl electrode in phosphate buffers. And the peak is located at the potentials characteristic of FAD redox couples of the proteins. The electrochemical parameters, such as midpoint potential (E_1/2) and apparent heterogeneous electron‐transfer rate constants (k_s) were estimated to ?0.311 V and 1.79 s^?1 by voltammetry, respectively. Experimental results indicate that the encapsulated GOD retains its catalytic activity for the oxidation of glucose. Such a GOD encapsulated chitosan based biosensor revealed a relatively rapid response time of less than 2 min, and a sufficient linear detection range for glucose concentration, from 0.60 to 2.80 mmol L^?1 with a detection limit of 0.10 mmol L^?1 and electrode sensitivity of 0.233 μA mmol^?1. The relative standard deviation (RSD) is under 3.2% (n=7) for the determination of practical serum samples. The biologic compounds probably existed in the sample, such as ascorbic acid, uric acid, dopamine, and epinephrine, do not affect the determination of glucose. The proposed method is satisfactory to the determination of human serum samples compared with the routine hexokinase method. Both the unique electrical property and biocompatibility of chitosan enable the construction of a good bio‐sensing platform for achieved DET of GOD and developed the third‐generation glucose biosensors.     

Disposable Sandwich‐type Electrochemical Sensor for Selective Detection of Glucose Based on Boronate Affinity

A disposable sandwich‐type electrochemical sensor for selective detection of glucose was established. The primary receptor, 3‐aminophenylboronic acid was grafted covalently onto the surface of screen‐printed carbon electrodes through an in situ‐generated diazo‐reaction. Glucose was first captured by boronic acid group on the electrode, followed by captureing an electroactive ferroceneboronic acid (FcBA) as the secondary receptor to form bidentate glucose‐boronic complex. Electrochemical impedance spectroscopy was applied to characterize the construction of sandwich‐type disposable sensor. In the sandwich assay, current response of captured FcBA on the electrode was dependent on the concentration of glucose. The sandwich assay showed higher selectivity for glucose than that for fructose, mannose, galactose and other electroactive interferences including uric acid, ascorbic acid and dopamine, and exhibited a dynamic concentration range of glucose from 0.5 to 20.0 mmol L⁻¹. The disposable sensor demonstrated a good reproducibility with 2.2 % relative standard deviation (RSD). In addition, the disposable glucose sensor was used in detection of the trace glucose in the clinical urine samples.     

Determination of Uric Acid in Human Urine by Ion‐exclusion Chromatography with UV Detection Using Pure Water as Mobile Phase

A simple, rapid and accurate ion‐exclusion chromatographic method coupled with a UV detector for the determination of uric acid in human urine samples has been developed. The separation was carried out on an ion‐exclusion column using only pure water as mobile phase. The detection wavelength was 254 nm and urine sample was injected directly without any pretreatment. Furthermore, the retention behavior of uric acid on the ion‐exclusion column was researched when pure water and 1 mmol·L^?1 HCl were used as mobile phase, respectively. The stability of uric acid was also further investigated within 28 days. In this method, the linear range of the calibration curve for uric acid was 0.25–100 mg·L^?1, and the detection limit calculated at S/N=3 was 0.02 mg·L^?1. The proposed ion‐exclusion chromatographic method has been used for the determination of uric acid in human urine.     

Electrochemical Morphine Sensor Based on Gold Nanoparticles Metalphthalocyanine Modified Carbon Paste Electrode

Composites of gold nanoparticles (Au) electrochemically deposited and different metal phthalocyanines (Co, Ni, Cu, and Fe) were chemically prepared. The composites were used as modifiers for carbon paste electrodes and were used for the determination of morphine in presence of ascorbic acid and uric acid. Central metal atoms of phthalocyanine moiety affected the rate of electron transfer. Thus, the electroactivity of different modifiers were evaluated towards morphine oxidation. Au‐CoPcM‐CPE possessed the highest rate for charge transfer rate in all studied pH electrolytes. Limit of detection was 5.48×10^?9 mol L^?1 in the range of 4.0×10^?7 to 9.0×10^?4 mol L^?1.     

Magnetite NPs@C with Highly‐Efficient Peroxidase‐Like Catalytic Activity as an Improved Biosensing Strategy for Selective Glucose Detection

This work reports the novel application of carbon‐coated magnetite nanoparticles (mNPs@C) as catalytic nanomaterial included in a composite electrode material (mNPs@C/CPE) taking advantages of their intrinsic peroxidase‐like activity. The nanostructured electrochemical transducer reveals an enhancement of the charge transfer for redox processes involving hydrogen peroxide. Likewise, mNPs@C/CPE demonstrated to be highly selective even at elevated concentrations of ascorbic acid and uric acid, the usual interferents of blood glucose analysis. Upon these remarkable results, the composite matrix was further modified by the addition of glucose oxidase as biocatalyst, in order to obtain a biosensing strategy (GOx/mNPs@C/CPE) with enhanced properties for the electrochemical detection of glucose. GOx/mNPs@C/CPE exhibit a linear range up to 7.5×10^?3 mol L^?1 glucose, comprising the entirely physiological range and incipient pathological values. The average sensitivity obtained at ?0.100 V was (1.62±0.05)×10⁵ nA L mol^?1 (R²=0.9992), the detection limit was 2.0×10^?6 M while the quantification limit was 6.1×10^?6 mol L^?1. The nanostructured biosensor demonstrated to have an excellent performance for glucose detection in human blood serum even for pathological values.     

An amperometric uric acid biosensor based on chitosan-carbon nanotubes electrospun nanofiber on silver nanoparticles

A novel amperometric uric acid biosensor was fabricated by immobilizing uricase on an electrospun nanocomposite of chitosan-carbon nanotubes nanofiber (Chi–CNTsNF) covering an electrodeposited layer of silver nanoparticles (AgNPs) on a gold electrode (uricase/Chi–CNTsNF/AgNPs/Au). The uric acid response was determined at an optimum applied potential of ?0.35 V vs Ag/AgCl in a flow-injection system based on the change of the reduction current for dissolved oxygen during oxidation of uric acid by the immobilized uricase. The response was directly proportional to the uric acid concentration. Under the optimum conditions, the fabricated uric acid biosensor had a very wide linear range, 1.0–400 μmol L^?1, with a very low limit of detection of 1.0 μmol L^?1 (s/n?=?3). The operational stability of the uricase/Chi–CNTsNF/AgNPs/Au biosensor (up to 205 injections) was excellent and the storage life was more than six weeks. A low Michaelis–Menten constant of 0.21 mmol L^?1 indicated that the immobilized uricase had high affinity for uric acid. The presence of potential common interfering substances, for example ascorbic acid, glucose, and lactic acid, had negligible effects on the performance of the biosensor. When used for analysis of uric acid in serum samples, the results agreed well with those obtained by use of the standard enzymatic colorimetric method (P?>?0.05).

Synergistic Effect of Graphene and Multiwalled Carbon Nanotubes on a Glassy Carbon Electrode for Simultaneous Determination of Uric Acid and Dopamine in the Presence of Ascorbic Acid

A poly(diallyldimethylammonium chloride)-graphene-multiwalled carbon nanotube modified glassy carbon electrode was fabricated and evaluated by cyclic voltammetry and differential pulse voltammetry. The modified electrode offered high sensitivity, selectivity, excellent long-term stability, and electrocatalytic activity for uric acid and dopamine. This sensor showed wide linear dynamic ranges of 5.0 to 350.0 µmol L^?1 for uric acid and 10.0 to 400.0 µmol L^?1 for dopamine in the presence of 500 µmol L^?1 ascorbic acid. The limits of detection were 0.13 for uric acid and 0.55 µmol L^?1 for dopamine. This functionalized electrode has potential application in bioanalysis and biomedicine.     

Enantioselective,Potentiometric Membrane Electrodes Based on Cyclodextrins for the Assay of L‐ and D‐2‐Hydroxyglutaric Acid

Abstract

Enantioselective, potentiometric membrane electrodes (EPMEs) based on immobilization of β‐, γ‐cyclodextrin (CD) or 2‐hydroxy‐3‐trimethylammoniopropyl‐β‐cyclodextrin (as chloride salt) (β‐CD‐derivative) in carbon paste have been designed. The β‐CD and β‐CD‐derivative‐based electrodes were applied in the 10^?8–10^?6 and 10^?7–10^?5 mol/L concentration ranges for the determination of L‐2‐hydroxyglutaric acid (L‐2‐HGA), whereas γ‐CD‐based electrode was applied for the determination of D‐2‐hydroxyglutaric acid (D‐2‐HGA) in the concentration range 10^?6–10^?4 mol/L. The β‐CD‐based EPME showed the lowest detection limit (1×10^?9 mol/L). The enantioselectivity and selectivity of the proposed electrodes for the assay of L‐2‐HGA and D‐2‐HGA, respectively, were determined over D‐2‐HGA/L‐2‐HGA, creatine, and creatinine. The proposed EPMEs can be applied for the enantioanalysis of 2‐hydroxyglutaric acid in urine samples.     

Lactate biosensor based on human erythrocytes

An amperometric lactate biosensor based on human erythrocytes is described. The erythrocyte suspension is retained near the platinum electrode by means of a semipermeable membrane. The response is based on lactate dehydrogenase activity in the erythrocytes and uses the oxidation of NADH by hexacyanoferrate(III) and amperometric detection of the resulting hexacyanoferrate(II). The limit of detection is 2.8 × 10^?5 mol l^?1, and the response is linear up to 1 mmol l^?1 lactate in the analyzed solution (11 mmol l^?1 in a blood sample). The response time is 7 min, and the useful lifetime is 2 weeks. The response is influenced only by reducing substances (uric acid) and malic acid. The effect of uric acid is readily compensated, and there is insufficient malic acid in blood to affect the results.     

Dermal Tattoo Biosensors for Colorimetric Metabolite Detection

Tattooing is a ubiquitous body modification involving the injection of ink and/or dye pigments into the dermis. Biosensors in the form of tattoos can be used to monitor metabolites in interstitial fluid. Here, minimally invasive, injectable dermal biosensors were developed for measuring pH, glucose, and albumin concentrations. The dermal pH sensor was based on methyl red, bromothymol blue, and phenolphthalein, which responded to a pH range from 5.0 to 9.0. The dermal glucose sensor consisted of glucose oxidase, 3,3′,5,5′‐tetramethylbenzidine, and peroxidase that detected concentrations up to 50.0 mmol L^?1. The dermal albumin sensor consisted of 3′,3′′,5′,5′′‐tetrachlorophenol‐3,4,5,6‐tetrabromosulfophthalein to measure concentrations up to 5.0 g L^?1. The sensors were multiplexed in ex vivo skin tissue and quantitative readouts were obtained using a smartphone camera. These sensors can be used to manage of acid–base homeostasis, diabetes, and liver failure in point‐of‐care settings.     

Simultaneous Determination of Dopamine and Uric Acid by Electrocatalytic Oxidation on a Carbon Paste Electrode Using Pyrogallol Red as a Mediator

A sensitive and selective electrochemical method for the simultaneous determination of dopamine (DA) and uric acid (UA) was developed using a pyrogallol red modified carbon paste electrode. Under the optimized conditions, the peak current was linearly dependent on 1.0–700.0 μmol L^?1 DA and 50.0–1000.0 μmol L^?1 UA. The detection limits for DA and UA were 0.78 μmol L^?1 and 35 μmol L^?1, respectively. Finally, this method was also examined for the determination of DA and uric acid in real samples such as drugs and urine.     

Electron-transfer properties of different carbon nanotube materials,and their use in glucose biosensors

Different types of carbon nanotube material (single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) of different internal diameter) have been used for preparation of CNT-modified glassy-carbon electrodes. Redox reactions involving ferricyanide and hydrogen peroxide were examined at the CNT-modified electrodes. Electrodes modified with SWCNTs usually had better electron-transfer properties than MWCNT-modified electrodes. Glucose biosensors were also prepared with electropolymerized polyphenylenediamine films, CNT materials, and glucose oxidase. Amperometric behavior in glucose determination was examined. SWCNT-modified glucose biosensors usually had a wider dynamic range (from 0.1 to 5.5 mmol L⁻¹) and greater sensitivity in glucose determination. The detection limit was estimated to be 0.05 mmol L⁻¹.     

Glucose biosensor based on graphite electrodes modified with glucose oxidase and colloidal gold nanoparticles

The electrochemistry of glucose oxidase (GOx) immobilized on a graphite rod electrode modified by gold nanoparticles (Au-NPs) was studied. Two types of amperometric glucose sensors based on GOx immobilized and Au-NPs modified working electrode (Au-NPs/GOx/graphite and GOx/Au-NPs/graphite) were designed and tested in the presence and the absence of N-methylphenazonium methyl sulphate in different buffers. Results were compared to those obtained with similar electrodes not containing Au-NPs (GOx/graphite). This study shows that the application of Au-NPs increases the rate of mediated electron transfer. Major analytical characteristics of the amperometric biosensor based on GOx and 13 nm diameter Au-NPs were determined. The analytical signal was linearly related to glucose concentration in the range from 0.1 to 10 mmol L^?1. The detection limit for glucose was found within 0.1 mmol L^?1 and 0.08 mmol L^?1 and the relative standard deviation in the range of 0.1–100 mol L^?1 was 0.04–0.39%. The τ_1/2 of V _max characterizes the storage stability of sensors: this parameter for the developed GOx/graphite electrode was 49.3 days and for GOx/Au-NPs/graphite electrode was 19.5 days. The sensor might be suitable for determination of glucose in beverages and/or in food.     

Determination of cadmium, chromium and copper in high salt samples by LA-ICP-OES after electrodeposition—preliminary study

A novel method is presented for determination of heavy metal ions in a high-saline matrix. It is based on the electrodeposition of the ions and subsequent laser ablation coupled to inductively coupled plasma optical emission spectrometry (LA-ICP-OES). Three arrangements for electrodeposition were worked out, two of them with stationary working electrodes. Materials for use in the working electrodes, and conditions for electrodeposition of Cd, Cr and Cu (pH, deposition current, time of electrolysis) were studied. Nickel was found to be the best electrode material. The metals accumulate on the surface of electrode and were then evaporated/ablated with a Nd:YAG laser focused into the ICP-OES spectrometer. The detection limits are 0.13 mg?L^?1 for Cd, 0.15 mg?L^?1 for Cu, and 1.9 mg?L^?1 for Cr in case of a stationary bottom working electrode, and 0.25 mg?L^?1 for Cd, 0.05 mg?L^?1 for Cu, 0.8 mg?L^?1 for Cr when using a rotating electrode. The relative standard deviation is in range from 3.8 to 10.3%. Waste water was analyzed in this way by the standard addition method.     

Kinetic Determination of Uric Acid in Human Serum by Using the Uncatalyzed BZ Reaction in Non‐equilibrium Steady State

A novel kinetic method for determination of uric acid in human serum by means of an uncatalyzed BZ system consisting of potassium bromate and p‐hydroxybenzaldehyde (p‐HBA) in sulfuric acid medium was proposed, in which the analyte perturbation to the system was recorded close to the bifurcation point. The potential change was directly proportional to the logarithm of concentration of uric acid in the range of 3.73×10^?8–7.48×10^?4 mol·L^?1 (r=0.9983) with a detection limit of 7.45×10^?9 mol·L^?1 and a recovery from 98.9% to 101.1%. A comparison between the proposed technique and other methods indicated that results obtained were in agreement with those in clinical detection. In addition, the possible mechanism of action of uric acid on the uncatalyzed BZ reaction was also discussed briefly.