Determination of major inorganic ions in blood serum and urine by capillary electrophoresis with contactless conductivity detection

Application of capillary electrophoresis with capacitively contactless conductivity detection for biomedical analysis

The coupling of capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C4 D) has become convenient analytical method for determination of small molecules that do not possess chromogenic or fluorogenic group. The implementations of CE with C4 D in the determination of inorganic and organic ions and amino acids in biomedical field are demonstrated. Attention on background electrolyte composition, sample treatment procedures, and the utilize of multi-detection systems are described. A number of tables summarizing highly developed CE-C4 D methods and the figures of merit attained are involved. Lastly, concluding remarks and perspectives are argued.

Chelate-functionalized magnetic micelles for sequestration of cisplatin

Many cancer patients suffer permanent hearing loss due to accumulation of ototoxic cisplatin in the inner ear. In this study, two types of 100 nm magnetic micelles were developed to sequester cisplatin from aqueous solutions, with the goal of eliminating cochlear ototoxins via magnetic microsurgery. The micellar surface was quantitatively functionalized with anionic S-rich ligands and the micelle core encapsulated superparamagnetic iron oxide nanoparticles. Exceptionally effective sequestration is demonstrated, with removal of greater than 95 and 50% of solution Pt, by means of centrifugal filtration and magnetic extraction. Attraction between negatively charged micellar surfaces and cationic Pt-species played a critical role and was only partially screened by physiologic salt solution. Importantly, magnetic micelles introduce negligible impact on the integrity of inner ear hair cells, demonstrating excellent biocompatibility. This study showcases successful magnetic sequestration of Pt-based ototoxins using highly applicable nano-micellar materials. More generally, these examples highlight features of the micelle-water interfacial environment that are important in developing nanomaterials for metallo-medicinal applications.

Sample plug induced peak splitting in capillary electrophoresis studied using dual backscattered interferometry and fluorescence detection

The appearance of unexpected peaks in capillary electrophoresis (CE) is common and can lengthen the time of method development as assay conditions and experimental parameters are varied to understand and mitigate the effects of the additional peaks. Additional peaks can arise when a single-analyte zone is split into multiple zones. Understanding the underlying mechanism of these phenomena, recognizing conditions that favor its presence, and knowing how to confirm and eliminate the effect are important for efficient method optimization. In this study, we examine how the overlap of analyte zones with the sample plug can lead to peak splitting. This is explored experimentally using dual detection CE, which enables both the sample plug and analyte zones to be independently and simultaneously measured from the same detection volume. Simulations performed via COMSOL Multiphysics confirm the origin of the splitting and help guide experiments to reduce and eliminate the effect. Our findings show that this peak splitting mechanism can arise in separations of both small and large molecules but is, especially, prevalent in separations of slowly migrating macromolecules. This effect is also more prevalent when using a short length-to-detector, as is commonly found in microfluidic applications. A simple diffusion-less model is introduced to develop strategies for reducing peak splitting that avoids modifying the apparatus, such as by lengthening the separation length, which can be difficult. Decreasing the sample plug length and slowing the electroosmotic flow can both reduce this effect, which is confirmed experimentally.

Validation of circular dichroic spectroscopy of synthetic oligonucleotide PS2.M for K + concentration measurements

The single-stranded synthetic oligonucleotide PS2.M is known to provide a basis for developing sensors since it tends to fold into structures called G-quadruplexes (G4) having characteristic topology and orientation with probabilities that depend on the chemical environment. The presence and concentration of cation species are among the key factors that determine the outcome of such a process. PS2.M and other aptamers have been used in several applications in conjunction with various probes, such as hemin, at the cost of increased technical complexity and applicability limitations. We instead validated the application limits of Circular Dichroic spectroscopy (CD) as only measurement method to assay PS2.M asK + sensor in a variety of solutions having different chemical complexity. The tested solutions range from simple NaCl and KCl solutions to chemically complex solutions like DMEM-Dulbecco's Modified Eagle Medium-which is widely used in a biological laboratory. PS2.M was also evaluated in solutions of KHCO 3 and D-ribose (K:D-rib), an antioxidant potassium compound, to compare its response to the simple KCl solution case. Our findings show that, within specific concentration applicability ranges, CD spectra can estimate theK + concentration in the examined water solutions even at high Na + concentrations with respect toK + and in the presence of antioxidant molecules.

Supplementary Information

The online version supplementary material available at 10.1140/epjp/s13360-022-02581-2.

3D-printed manifold integrating solid contact ion-selective electrodes for multiplexed ion concentration measurements in urine

Urinalysis is a simple and non-invasive approach for the diagnosis and monitoring of various health disorders. While urinalysis is predominantly confined to clinical laboratories the non-invasive sample collection makes it applicable in wide range of settings outside of central laboratory confinements. In this respect, 3D printed devices integrating sensors for measuring multiple parameters may be one of the most viable approaches to ensure cost-effectiveness for widespread use. Here we evaluated such a system for the multiplexed determination of sodium, potassium and calcium ions in urine samples with ion-selective electrodes based on state of the art octadecylamine-functionalized multi-walled carbon nanotube (OD-MWCNT) solid contacts. The electrodes were tested in the clinically relevant concentration range, i.e. ca. 10^-4 - 10^-1 mol L^-1 and were proven to have Nernstian responses under flow injection conditions. The applicability of the 3D printed flow manifold was investigated through the analysis of synthetic samples and two certified reference materials. The obtained results confirm the suitability of the proposed system for multiplexed ion analysis in urine.

Sensing of electrolytes in urine using a miniaturized paper-based device

Analyzing electrolytes in urine, such as sodium, potassium, calcium, chloride, and nitrite, has significant diagnostic value in detecting various conditions, such as kidney disorder, urinary stone disease, urinary tract infection, and cystic fibrosis. Ideally, by regularly monitoring these ions with the convenience of dipsticks and portable tools, such as cellphones, informed decision making is possible to control the consumption of these ions. Here, we report a paper-based sensor for measuring the concentration of sodium, potassium, calcium, chloride, and nitrite in urine, accurately quantified using a smartphone-enabled platform. By testing the device with both Tris buffer and artificial urine containing a wide range of electrolyte concentrations, we demonstrate that the proposed device can be used for detecting potassium, calcium, chloride, and nitrite within the whole physiological range of concentrations, and for binary quantification of sodium concentration.

Quick stabilization of capillary for rapid determination of potassium ions in the blood of epilepsy patients by capillary electrophoresis without sample pretreatment

Mutations in the potassium channel genes may be linked to the development of epilepsy and affect the blood potassium levels. Therefore, accurate determination of potassium in the blood will be critical to diagnose the cause of epilepsy. CE is a competent technique for the fast detection of multiple ions, but complicated matrices of a blood sample may cause significant variation of migration times and the peak shape. In this work, a procedure for rapid stabilization of the capillary inner surface through preflushing of a blood sample was employed. The process takes only 40 min for a capillary and then it can be used for more than 2 weeks. No pretreatment of the blood sample or other surface modification of the capillary is needed for the analysis. The RSDs of the migration time and peak area were reduced to 1.5 and 5.1% from 12.6 and 14.5%, respectively. The proposed method has been successfully applied to the determination of the potassium contents in the blood sample of patients with epilepsy at different stages. The recoveries of potassium ions in these blood samples are in a range from 86.5 to 104.5%.

Analysis of bicarbonate, phosphate and other anions in saliva by capillary electrophoresis with capacitively coupled contactless conductivity detection in diagnostics of gastroesophageal reflux disease

Bicarbonate and phosphate constitute major salivary buffering components, and their importance consists in the neutralization of acidic gastric contents during reflux episodes. In this work, capillary electrophoresis with capacitively coupled contactless conductivity detector was applied for the analysis of bicarbonate, phosphate, and another inorganic (chloride, nitrite, nitrate, sulfate, thiocyanate) and organic anions (acetate, butyrate) to evaluate their levels in saliva. The background electrolytes of different composition and pH between 6.02-9.41 were assessed for the bicarbonate and phosphate determination by comparison of the real analyses of a model solution with the simulation by PeakMaster software. The optimized background electrolyte was composed of 10 mM 2-(N-morpholino)ethanesulfonic acid, 20 mM arginine, and 30 µM cetyltrimethylammonium bromide, pH 8.95. Using this BGE, the anion levels were compared in saliva from 20 patients suffering from gastroesophageal reflux disease (GERD) and saliva from 12 healthy subjects. Bicarbonate levels were significantly elevated in saliva from GERD patients suggesting the possible applicability of bicarbonate as a biomarker in non-invasive diagnostics of GERD by CE-C⁴ D.

Selective Binding and Quantitation of Calcium with a Cobalt-Based Magnetic Resonance Probe

We report a cobalt-based paramagnetic chemical exchange saturation transfer (PARACEST) magnetic resonance (MR) probe that is able to selectively bind and quantitate the concentration of Ca²⁺ ions under physiological conditions. The parent LCo complex features CEST-active carboxamide groups and an uncoordinated crown ether moiety in close proximity to a high-spin pseudo-octahedral Co^II center. Addition of Na⁺, Mg²⁺, K⁺, and Ca²⁺ leads to binding of these metal ions within the crown ether. Single-crystal X-ray diffraction and solid-state magnetic measurements reveal the presence of a cation-specific coordination environment and magnetic anisotropy of Co^II, with axial zero-field splitting parameters for the Na⁺- and Ca²⁺-bound complexes differing by over 90%. Owing to these differences, solution-based measurements under physiological conditions indicate reversible binding of Na⁺ and Ca²⁺ to give well-separated CEST peaks at 69 and 80 ppm for [LCoNa]⁺ and [LCoCa]²⁺, respectively. Dissociation constants for different cation-bound complexes of LCo, as determined by ¹H NMR spectroscopy, demonstrate high selectivity toward Ca²⁺. This finding, in conjunction with the large excess of Na⁺ in physiological environments, minimizes interference from related cations, such as Mg²⁺ and K⁺. Finally, variable-[Ca²⁺] CEST spectra establish the ratio between the CEST peak intensities for the Ca²⁺- and Na⁺-bound probes (CEST_80 ppm/CEST_69 ppm) as a measure of [Ca²⁺], providing the first example of a ratiometric quantitation of Ca²⁺ concentration using PARACEST. Taken together, these results demonstrate the ability of transition metal PARACEST probes to afford a concentration-independent measure of [Ca²⁺] and provide a new approach for designing MR probes for cation sensing.

Application of capillary electrophoresis combined with conductometric and UV detection to monitor meteorite simulant bioleaching by Acidithiobacillus ferrooxidans

The importance of microorganisms and biotechnology in space exploration and future planets colonization has been discussed in the literature. Meteorites are interesting samples to study microbe-mineral interaction focused on space exploration. The chemolithotropic bacterium Acidithiobacillus ferrooxidans has been used as model to understand the iron and sulfur oxidation. In this work, capillary electrophoresis with capacitively coupled contactless conductivity detection and UV detection was used to monitor bacterial growth in a meteorite simulant by measuring the conversion of Fe²⁺ into Fe⁺³ . The effect of Co²⁺ and Ni²⁺ (metals also found in meteorites) on the bacterial growth was also evaluated. The presented method allowed the analyses of all metals in a single run (less than 8 min). The background electrolyte was composted of 10 mmol/L α-hydroxyisobutyric acid/Histidine. For comparison purpose, the samples were also analyzed by UV-Vis spectrophotometry. The Fe²⁺ conversion into Fe³⁺ by A. ferrooxidans was observed up to 36 h with the growth rate constant of 0.19/h and 0.21/h in Tuovinen and Kelly (T&K) and in meteorite simulant media, respectively. The developed method presents favorable prospect to monitor the growth of other chemolithotropic microorganisms for biotechnology applications.

Sulfur speciation by HPLC-ICPQQQMS in complex human biological samples: taurine and sulfate in human serum and urine

The advent of the triple quadrupole technology to the inductively coupled plasma mass spectrometry (ICPMS) technique has allowed a strong improvement in the accuracy and detection limits of ICPMS for non-metal elements such as sulfur by removing major polyatomic interferences. Up to now, there has been no report utilizing this development for sulfur speciation in complex human biological matrices. In the present report, we show the success of HPLC-ICPQQQMS for the simultaneous determination of two major sulfur metabolites, taurine and sulfate, in human urine and serum, by direct injection without the need for sample clean-up. The optimized chromatographic method was validated, tested for robustness, and applied for investigating the intra-individual variability in taurine urinary excretion in eight healthy volunteers over a period of 8 weeks. The limit of detection and limit of quantification for taurine determination was found to be 0.2 and 0.7 pmol, respectively. The concentrations found in the analyzed group of urine samples (n = 64) had a range, mean, and SD of 0.6-99, 20.4, and 23.2 μg mL-1 for taurine, and 115-1373, 616, and 259 μg mL-1 for sulfate. Taurine was found to exhibit a much higher intra-individual variability than sulfate. The developed method can be applied in large-scale epidemiological studies and clinical studies in order to establish the potential cardioprotective effects of taurine. Graphical abstract ᅟ.

Paper-based assays for urine analysis

A transformation of the healthcare industry is necessary and imminent: hospital-centered, reactive care will soon give way to proactive, person-centered care which focuses on individuals' well-being. However, this transition will only be made possible through scientific innovation. Next-generation technologies will be the key to developing affordable and accessible care, while also lowering the costs of healthcare. A promising solution to this challenge is low-cost continuous health monitoring; this approach allows for effective screening, analysis, and diagnosis and facilitates proactive medical intervention. Urine has great promise for being a key resource for health monitoring; unlike blood, it can be collected effortlessly on a daily basis without pain or the need for special equipment. Unfortunately, the commercial rapid urine analysis tests that exist today can only go so far-this is where the promise of microfluidic devices lies. Microfluidic devices have a proven record of being effective analytical devices, capable of controlling the flow of fluid samples, containing reaction and detection zones, and displaying results, all within a compact footprint. Moving past traditional glass- and polymer-based microfluidics, paper-based microfluidic devices possess the same diagnostic ability, with the added benefits of facile manufacturing, low-cost implementation, and disposability. Hence, we review the recent progress in the application of paper-based microfluidics to urine analysis as a solution to providing continuous health monitoring for proactive care. First, we present important considerations for point-of-care diagnostic devices. We then discuss what urine is and how paper functions as the substrate for urine analysis. Next, we cover the current commercial rapid tests that exist and thereby demonstrate where paper-based microfluidic urine analysis devices may fit into the commercial market in the future. Afterward, we discuss various fabrication techniques that have been recently developed for paper-based microfluidic devices. Transitioning from fabrication to implementation, we present some of the clinically implemented urine assays and their importance in healthcare and clinical diagnosis, with a focus on paper-based microfluidic assays. We then conclude by providing an overview of select biomarker research tailored towards urine diagnostics. This review will demonstrate the applicability of paper-based assays for urine analysis and where they may fit into the commercial healthcare market.

Ratiometric quantitation of redox status with a molecular Fe2 magnetic resonance probe

We demonstrate the ability of a molecular Fe2 complex to enable magnetic resonance (MR)-based ratiometric quantitation of redox status, namely through redox-dependent paramagnetic chemical exchange saturation transfer (PARACEST). Metalation of a tetra(carboxamide) ligand with FeII and/or FeIII in the presence of etidronate ion affords analogous FeII2, FeIIFeIII, and FeIII2 complexes. Both FeII2 and FeIIFeIII complexes give highly-shifted, sharp, and non-overlapping NMR spectra, with multiple resonances for each complex corresponding to exchangeable carboxamide protons. These protons can be selectively irradiated to give CEST peaks at 74 and 83 ppm vs. H2O for the FeIIFeIII complex and at 29, 40 and 68 ppm for the FeII2 complex. The CEST spectra obtained from a series of samples containing mixtures of FeII2 and FeIIFeIII are correlated with independently-determined open-circuit potentials to construct a Nernstian calibration curve of potential vs. CEST peak intensity ratio. In addition, averaged intensities of phantom images collected on a 9.4 T MRI scanner show analogous Nernstian behavior. Finally, both the FeII2 and FeIIFeIII forms of the complex are stable to millimolar concentrations of H2PO4-/HPO42-, CO32-, SO42-, CH3COO-, and Ca2+ ions, and the FeIII2 form is air-stable in aqueous buffer and shows >80% viability in melanoma cells at millimolar concentration. The stability suggests the possible application of this or related complexes for in vivo studies. To our knowledge, this concentration-independent method based on a single Fe2 probe provides the first example of MR-based ratiometric quantitation of redox environment.

Direct Fluorescent Detection of Blood Potassium by Ion-Selective Formation of Intermolecular G-Quadruplex and Ligand Binding

G-quadruplex analogues have been widely used as molecular tools for detection of potassium ion (K(+)). However, interference from a higher concentration of sodium ion (Na(+)), enzymatic degradation of the oligonucleotide, and background absorption and fluorescence of blood samples have all limited the use of G-quadruplex for direct detection of K(+) in blood samples. Here, we reported, for the first time, an intermolecular G-quadruplex-based assay capable of direct fluorescent detection of blood K(+). Increased stringency of intermolecular G-quadruplex formation based on our screened G-rich oligonucleotide (5'-TGAGGGA GGGG-3') provided the necessary selectivity for K(+) against Na(+) at physiological ion level. To increase long-term stability of oligonucleotide in blood, the screened oligonucleotide was modified with an inverted thymine nucleotide whose 3'-terminus was connected to the 3'-terminus of the upstream nucleotide, acting as a blocking group to greatly improve antinuclease stability. Lastly, to avoid interference from background absorption and autofluorescence of blood, a G-quadruplex-binding, two-photon-excited ligand, EBMVC-B, was synthesized and chosen as the fluorescence reporter. Thus, based on selective K(+) ion-induced formation of intermolecular G-quadruplex and EBMVC-B binding, this approach could linearly respond to K(+) from 0.5 to 10 mM, which matches quite well with the physiologically relevant concentration of blood K(+). Moreover, the system was highly selective for K(+) against other metal ions, including Na(+), Ca(2+), Mg(2+), Zn(2+) common in blood. The practical application was demonstrated by direct detection of K(+) from real blood samples by two-photon fluorescence technology. To the best of our knowledge, this is the first attempt to exploit molecular G-quadruplex-based fluorescent sensing for direct assay of blood target. As such, we expect that it will promote the design and practical application of similar DNA-based sensors in complex real systems.

Microfluidic chip-capillary electrophoresis device for the determination of urinary metabolites and proteins

Microfluidic chip-CE (MC-CE) devices have caught recent attention for diagnostic applications in urine. This is due to the successes reported in handling real urine samples by integrating microfluidic chips (MC) with analyte enrichment and sample cleanup to CE with high separation efficiency and sensitive analyte detection. Here, we review the determination of urinary metabolites and proteins by MC-CE devices within the past 7 years. The application scope for MC-CE integrated devices was found to exceed the use of either technique alone, showing comparable performance to laser-induced fluorescence detection using less sensitive UV detectors, offering the flexibility to handle difficult urine samples with on-chip dilution and online standard addition and delivering enhanced performance as compared with commercial microfluidic chip electrophoresis chips.

Determination of urine ionic composition with potentiometric multisensor system

The ionic composition of urine is a good indicator of patient's general condition and allows for diagnostics of certain medical problems such as e.g., urolithiasis. Due to environmental factors and malnutrition the number of registered urinary tract cases continuously increases. Most of the methods currently used for urine analysis are expensive, quite laborious and require skilled personnel. The present work deals with feasibility study of potentiometric multisensor system of 18 ion-selective and cross-sensitive sensors as an analytical tool for determination of urine ionic composition. In total 136 samples from patients of Urolithiasis Laboratory and healthy people were analyzed by the multisensor system as well as by capillary electrophoresis as a reference method. Various chemometric approaches were implemented to relate the data from electrochemical measurements with the reference data. Logistic regression (LR) was applied for classification of samples into healthy and unhealthy producing reasonable misclassification rates. Projection on Latent Structures (PLS) regression was applied for quantitative analysis of ionic composition from potentiometric data. Mean relative errors of simultaneous prediction of sodium, potassium, ammonium, calcium, magnesium, chloride, sulfate, phosphate, urate and creatinine from multisensor system response were in the range 3-13% for independent test sets. This shows a good promise for development of a fast and inexpensive alternative method for urine analysis.

Urine analysis in microfluidic devices

Microfluidics has attracted considerable attention since its early development in the 1980s and has experienced rapid growth in the past three decades due to advantages associated with miniaturization, integration and automation. Urine analysis is a common, fast and inexpensive clinical diagnostic tool in health care. In this article, we will be reviewing recent works starting from 2005 to the present for urine analysis using microfluidic devices or systems and to provide in-depth commentary about these techniques. Moreover, commercial strips that are often treated as chips and their readers for urine analysis will also be briefly discussed. We start with an introduction to the physiological significance of various components or measurement standards in urine analysis, followed by a brief introduction to enabling microfluidic technologies. Then, microfluidic devices or systems for sample pretreatments and for sensing urinary macromolecules, micromolecules, as well as multiplexed analysis are reviewed, in this sequence. Moreover, a microfluidic chip for urinary proteome profiling is also discussed, followed by a section discussing commercial products. Finally, the authors' perspectives on microfluidic-based urine analysis are provided. These advancements in microfluidic techniques for urine analysis may improve current routine clinical practices, particularly for point-of-care (POC) applications.

Determination of potassium, sodium, calcium and magnesium in total parenteral nutrition formulations by capillary electrophoresis with contactless conductivity detection

A simple method based on capillary electrophoresis with a capacitively coupled contactless conductivity detector (CE-C(4)D) was developed for the determination of potassium, sodium, calcium and magnesium in parenteral nutrition formulations. A hydro-organic mixture, consisting of 100 mM Tris-acetate buffer at pH 4.5 and acetonitrile (80:20, v/v), was selected as the background electrolyte. The applied voltage was 30 kV, and sample injection was performed in hydrodynamic mode. All analyses were carried out in a fused silica capillary with an internal diameter of 50 microm and a total length of 64.5 cm. Under these conditions, complete separation between all cations was achieved in less than 4 min. The CE-C(4)D method was validated, and trueness values between 98.6% and 101.8% were obtained with repeatability and intermediate precision values of 0.4-1.3% and 0.8-1.8%, respectively. Therefore, this method was found to be appropriate for controlling potassium, sodium, calcium and magnesium in parenteral nutrition formulations and successfully applied in daily quality control at the Geneva University Hospitals.

Evaluation of microchip capillary electrophoresis with external contactless conductivity detection for the determination of major inorganic ions and lithium in serum and urine samples

The determination of inorganic ions in clinical samples in less than 90 seconds was demonstrated for microchip capillary electrophoresis using capacitively coupled contactless conductivity detection (C(4)D). Bare electrophoresis chips were used in combination with external electrodes which were part of the chip holder. In order to achieve the required selectivity and sensitivity, an optimization of the electrode layout was carried out. Limits of detection (LOD) of 1 microM for K(+), 1.5 microM for Ca(2+), 3 microM for Na(+), 1.75 microM for Mg(2+) and 7.5 microM for Li(+) were achieved. The determination of inorganic cations (NH(4)(+), K(+), Na(+), Ca(2+), Mg(2+)) and anions (Cl(-), NO(3)(-), SO(4)(2-), phosphate) in blood serum and urine samples was possible in one common electrolyte solution containing 15 mM L-arginine, 10.75 mM maleic acid and 1.5 mM 18-crown-6 at pH 5.90 by simply switching the separation voltage from positive to negative polarity. Lithium, present at significant levels when used for therapeutic purposes, can also be determined in blood serum using a slightly modified background electrolyte solution.