Simultaneous and direct determination of urea and creatinine in human urine using a cost-effective flow injection system equipped with in-house contactless conductivity detector and LED colorimeter

Additive-manufactured paper-PMMA hybrid microfluidic chip for simultaneous monitoring of creatinine and pH in artificial urine

Nowadays, kidney dysfunction is a common health issue due to the modernized lifestyle. Even though medications are commercially available to treat kidney diseases, early diagnosis is crucial and challenging. Clinically, measuring urine creatinine and pH has gained significant interest as a way to diagnose kidney diseases early. In the present work, we attempted to develop a low-cost, robust, accurate and naked-eye colorimetric method to determine both creatinine levels and pH variations in artificial urine samples using a simple 3D-printed hybrid microfluidic device. Creatinine was detected by the incorporation of the traditional Jaffe test onto the hybrid paper-PMMA microfluidic device and pH (4-8) was measured by a simple anthocyanin test. Notably, the tests were established without employing any sophisticated or costly instrument clusters. The developed 3D-printed microfluidic probe showed a limit of detection (LOD) of 0.04 mM for creatinine over a concentration range of 1-10 mM, with a regression coefficient (R2) of 0.995 in laboratory conditions. Interestingly, the experimental data obtained with artificial urine exhibited a wide linear range from 0.1 mM to 5 mM under different pH values ranging from 4 to 8 in the presence of matrices commonly found in urine samples other than proteins, indicating the potential use of this method in pre-clinical analysis. Since the wide linear range of urine creatinine in artificial urine samples falls well below the clinically relevant concentrations in humans (0.07-0.27 mM), the developed lab-on-chip device is further suitable for clinical evaluation with proper ethical clearance. This 3D-printed hybrid microfluidic colorimetry-based creatinine detection and pH indicator platform can be beneficial in the healthcare sector due to the on-site testing capability, cost-effectiveness, ease of use, robustness, and instrument-free approach.

Innovated single flush on-line solid-phase extraction in bead injection format for flow programming-based determination of creatinine in human urine

Reaction-based assays are commonly automated and miniaturized via flow analysis. However, aggressive reagents can affect or destroy even the chemically resistant manifold during long-term use. Using on-line solid-phase extraction (SPE) can eliminate this drawback and allow for high reproducibility and further advanced automation, as presented in this work. Determination of creatinine in human urine, an important clinical marker, by sequential injection analysis was achieved using bead injection on-line SPE with specific UV spectrophotometric detection, providing the necessary sensitivity and selectivity of the method for bioanalysis. The automated SPE column packing and disposal, calibration, and fast measurement highlighted the improvements in our approach. Variable sample volumes and a single working standard solution eliminated matrix effects, broadened the calibration range, and accelerated the quantification. Our method comprised an injection of 20 μL of 100 × times diluted urine with aqueous acetic acid solution pH 2.4, sorption of creatinine in a strong cation exchanger SPE column, washing out urine matrix with 50% aqueous acetonitrile, and elution of creatinine with 1% ammonium hydroxide. The SPE step was accelerated by a single flush of the column when the eluent/matrix wash/sample/standard zones sequence was created in the pump holding coil, and then the sequence of the zones was flushed into the column at once. The whole process was continually spectrophotometrically detected at 235 nm, subtracted from the signal at 270 nm. A single run duration was less than 3.5 min. Method relative standard deviation was <5.0% (n = 6). A calibration range was linear within the range of 0.02-0.30 μg creatinine (R > 0.999), covering 1.0-15.0 mmol/L creatinine in urine. The standard addition method used two different volumes of a single working standard solution for quantification. Results proved the effectiveness of our improvements in the flow manifold, bead injection, and automated quantification. The accuracy of our method was comparable to the routine enzymatic assay of real urine samples in a clinical laboratory.

Ameliorative effect of Nigella sativa conjugated silver nanoparticles against chromium-induced hepatotoxicity and renal toxicity in mice

Hexavalent chromium induces oxidative stress in the liver and kidney. Therefore an in vivo study was designed to investigate the modulatory effect of biosynthesized AgNP against Cr (VI) induced hepatotoxicity and nephrotoxicity. The organs index, serum level of ALT, AST, ALP, MDA, total protein and creatinine were measured. The histopathology and micrometry of the liver and kidney were examined. The liver index was significantly increased (0.098 ± 0.13 g) with slight increase in kidney index in Cr exposed group. The serum level of ALT (163.0 ± 5.5 U/L), AST (484.0 ± 10.7 U/L), ALP (337.6 ± 9.6 U/L), MDA (641.2 ± 29.2 U/L), and creatinine (2.9 ± 0.2 mg/dL) were significantly increased (P ≤ 0.05) with significant decrease in total protein level (2.9 ± 0.2 g/dL) (P ≤ 0.05) in chromium treated group. In histopathology, distorted hepatic cords, necrosis, damaged glomerulus and Bowman's capsule were observed. Micrometric studies of the liver and kidney showed significant increase in size of hepatocytes (1188.2 ± 467.7 µ²) and their nuclei (456.4 ± 206.7 µ²), ACSA of Bowman's capsule (11835.5 ± 336.7 µ²) and glomerulus (9051.8 ± 249.8 µ²⁾ in Cr (VI) treated group. The size of brush border (10.1 ± 3.0 µ) was significantly reduced in Cr (VI) treated group however the ACSA of lumen was not significantly changed. With the administration of NSSE and Nigella sativa AgNPs, decreased the oxidative damage caused by Cr (V).

A Study on Double Inputs Direct Contact and Single Output Capacitively Coupled Conductivity Detector

In this paper, an improved double inputs direct contact and single output capacitively coupled conductivity detector (DISODCD) based on traditional contactless capacitively coupled conductivity detector (C⁴D) is developed. The sensor uses double inputs of the contact electrode and capacitively coupled output of the contactless electrode and a lock-in amplifier to reduce interfering noise signals and amplify gain. Parallel circuit counteracts the part of the adverse capacitance reactance introduced by electrode polarization and reduces the effect of the impedance caused by the coupled wall capacitance to measure the resistance of solution. The sensor reduces limit of detection (LOD) of analyte and improves the sensitivity of the device. The LOD of the potassium chloride solution is 1 nM, and the detection range is 0.01 μM to 10 mM in actual testing for a single sample. The ratio of the response of potassium chloride solution to background ultrapure water at low concentrations is better than that of double input capacitively coupled contactless conductivity detector (DIC⁴D) and direct contact conductivity detection (DCD) under the same condition. In the case that the test cell is contaminated with impurities, pollution of impurities has little effect on the response of DISODCD. In practical application, it has a good service life.

On-line 'protein shaker': A multicommutated flow analysis system for fluorometric creatinine determination in deproteinized serum

A fully mechanized multicommutated flow analysis (MCFA) system for fluorometric determination of creatinine in serum samples is introduced in this paper. The flow system was constructed with microsolenoid pumps and valves and with a 3D-printed flow cell. Fluorometric assay relied on creatinine reaction with 3,5-dinitrobenzoic acid and hydrogen peroxide in an alkaline environment. To overcome significant interference from protein, a flow reactor for serum deproteinization was designed and implemented in the flow system. The deproteinization was carried out by precipitation with trichloroacetic acid and the addition of sodium chloride facilitated the precipitate sedimentation. The supernatant representative sample was pumped out and subjected to fluorometric creatinine assay. The obtained linear range was from 1.6 to 500 μmol L^-1 and the precision, expressed as RSD, was below 3%. The proposed MCFA system was used to determine creatinine concentration in control serum samples. The results obtained with flow deproteinization correlated well with results obtained with conventional deproteinization (y = (0.91 ± 0.09) x + (37 ± 28)) with Pearson's r 0.979.

The comparison between light-scattering detectors based on LED and photodiode for immunoprecipitation assays of transferrin and ferritin

Undoubtedly, light-emitting diodes (LEDs) and photodiodes (PDs) are indispensable optoelectronic devices in modern analytical chemistry. LEDs can serve as either light emitters or detectors, thus being an alternative to the most popular detection systems consisted of PD. In this contribution, a comparison between LED-LED and LED-PD detectors, operating in turbidimetric and nephelometric modes, has been carried out for immunoprecipitation detection of transferrin and ferritin. The greatest emphasis was placed on the study of detectors responses under different measurement conditions including current powering an emitter, amplification gain in the case of PD as detector or the construction of detection cells designed for the Multicommutated Flow Analysis (MCFA). The assumption was to obtain the fully-mechanized system with simple but efficient detection system to enable the determination of iron-binding proteins occurring at different concentration ranges in human body. As a result, the optimized arrangements of LED-LED and LED-PD setups were characterized by similar analytical characteristics, enabling the determination of transferrin with the detection limit (LOD) of 0.2 mg/L and RSDs of 2.8-4.8% for LED-LED, and LOD of 0.1 mg/L and RSDs of 0.9-3.6% for LED-PD. In the case of ferritin detection, only the response of the LED-PD detector was statistically distinguishable in the range of 130-198 μg/L of protein with recorded analytical signal change of 20 mV value. The addition of polymer for signal enhancement provided the increase of response range to 107-253 μg/L, enabling the developed system for detection of pathological serum ferritin levels.

Recent advancements in urea biosensors for biomedical applications

The quick progress in health care technology as a recurrent measurement of biochemical factors such as blood components leads to advance development and growth in biosensor technology necessary for effectual patient concern. The review wok of authors present a concise information and brief discussion on the development made in the progress of potentiometric, field effect transistor, graphene, electrochemical, optical, polymeric, nanoparticles and nanocomposites based urea biosensors in the past two decades. The work of authors is also centred on different procedures/methods for detection of urea by using amperometric, potentiometric, conductometric and optical processes, where graphene, polymer etc. are utilised as an immobilised material for the fabrication of biosensors. Further, a comparative revision has been accomplished on various procedures of urea analysis using different materials-based biosensors, and it discloses that electrochemical and potentiometric biosensor is the most promise one among all, in terms of rapid response time, extensive shelf life and resourceful design.

Novel approaches for colorimetric measurements in analytical chemistry - A review

Colorimetric techniques have been developed and used in routine analyses for over a century and apparently all their potentialities have been exhaustively explored. However, colorimetric techniques have gained high visibility in the last two decades mainly because of the development of the miniaturization concept, for example, paper-based analytical devices that mostly employ colorimetric reactions, and by the advances and popularity of image capture instruments. The impressive increase in the use of these devices was followed by the development and enhancement of different modes of color detection to meet the demands of making qualitative, semi-quantitative, and fully quantitative analyses of multiple analytes. Cameras, scanners, and smartphones are now being used for this purpose and have become suitable alternatives for different approaches to colorimetric analysis; this, in addition to advancements in miniaturized devices. On the other hand, recent developments in optoelectronics technologies have launched more powerful, more stable and cheaper light-emitting diodes (LEDs), which once again have become an interesting tool for the design of portable and miniaturized devices based on colored reactions. Here, we present a critical review of recent developments and challenges of colorimetric detection in modern analytical chemistry in the last five years, and present thoughts and insights towards future perspectives in the area to improve the use of colorimetric detection in different application approaches.

Capacitively coupled contactless conductivity detection for analytical techniques - Developments from 2018 to 2020

The developments of analytical contactless conductivity measurements based on capacitive coupling over the two years from mid-2018 to mid-2020 are covered. This mostly concerns applications of the technique in zone electrophoresis employing conventional capillaries and to a lesser extent lab-on-chip devices. However, its use for the detection in several other flow-based analytical methods has also been reported. Detection of bubbles and measurements of flow rates in two-phase flows are also recurring themes. A few new applications in stagnant aqueous samples, e.g. endpoint detection in titrations and measurement on paper-based devices, have been reported. Some variations of the design of the measuring cells and their read-out electronics have also been described.

Application of Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection (CE-C4D): 2017-2020

Capacitively coupled contactless conductivity detection (C⁴D) has emerged as influential to detect analytes that do not have chromogenic or fluorogenic functional group. Since our last review several new capillary electrophoresis (CE) methods coupled with (CE-C⁴D) have been communicated. The aim of this review is to give an update of the almost all the new applications of CE-C⁴D in the field of pharmaceutical, food and biomedical analysis covering the period from 2017 to April 2020. The utilization of CE with C⁴D in the areas of pharmaceutical, food and biomedical analysis is presented. Finally, concluding remarks and outlooks are discussed.

Dual-Purpose Photometric-Conductivity Detector for Simultaneous and Sequential Measurements in Flow Analysis

This work presents a new dual-purpose detector for photometric and conductivity measurements in flow-based analysis. The photometric detector is a paired emitter-detector diode (PEDD) device, whilst the conductivity detection employs a capacitively coupled contactless conductivity detector (C4D). The flow-through detection cell is a rectangular acrylic block (ca. 2 × 2 × 1.5 cm) with cylindrical channels in Z-configuration. For the PEDD detector, the LED light source and detector are installed inside the acrylic block. The two electrodes of the C4D are silver conducting ink painted on the PEEK inlet and outlet tubing of the Z-flow cell. The dual-purpose detector is coupled with a sequential injection analysis (SIA) system for simultaneous detection of the absorbance of the orange dye and conductivity of the dissolved oral rehydration salt powder. The detector was also used for sequential measurements of creatinine and the conductivity of human urine samples. The creatinine analysis is based on colorimetric detection of the Jaffé reaction using the PEDD detector, and the conductivity of the urine, as measured by the C4D detector, is expressed in millisiemens (mS cm-1).