Noninvasive determination of blood constituents using an array of modulated laser diodes and a photoacoustic sensor head

Using photoacoustic laser spectroscopy, the noninvasive determination of blood constituents like hemoglobin and glucose is feasible. The aim of our investigations is the development of a sensor which is suitable for continuously noninvasive monitoring of blood glucose concentrations in diabetic patients. For this purpose a photoacoustic sensor head was developed and coupled via an optical fiber bundle to an array of 8 laser diodes emitting at various wavelengths in the near infrared region. Applying a special modulation scheme, the tiny changes of the absorption coefficient of whole blood caused by the variations of blood glucose concentrations could be measured. A resolution of 70 mg/dl was achieved, a value which is already close to the clinical requirements for a continuously working glucose sensor.     

Noninvasive determination of blood constituents using an array of modulated laser diodes and a photoacoustic sensor head

Using photoacoustic laser spectroscopy, the noninvasive determination of blood constituents like hemoglobin and glucose is feasible. The aim of our investigations is the development of a sensor which is suitable for continuously noninvasive monitoring of blood glucose concentrations in diabetic patients. For this purpose a photoacoustic sensor head was developed and coupled via an optical fiber bundle to an array of 8 laser diodes emitting at various wavelengths in the near infrared region. Applying a special modulation scheme, the tiny changes of the absorption coefficient of whole blood caused by the variations of blood glucose concentrations could be measured. A resolution of 70 mg/dl was achieved, a value which is already close to the clinical requirements for a continuously working glucose sensor.     

Enzymatic determination of urea in undiluted whole blood by flow injection analysis using an ammonium ion-selective electrode

A flow-injection system is described for the assay of urea in undiluted whole blood. Urea is quantified by means of an ammonium ion-selective electrode covered with a membrane with covalently immobilized urease. The enzymatically generated ammonium ion is directly related to the urea concentration. Interference from potassium is reduced by adjusting the potassium ion concentration in the carrier stream and in the aqueous calibration solutions to 4.0 mM; it can be eliminated by measuring the potassium ion concentration in the sample separately and applying a mathematical correction for the K⁺ contribution to the signal. The linear measuring range is 1–40 mM urea, with an injection frequency of 40 h^?1 and a standard deviation of 1% for whole blood samples. The result of the measurement is obtained within 25 s from the time of injection. Vatiations in the hematocrit level of the sample have no effect on the measurement. The results obtained by the flow-injection method are in excellent agreement with those found routinely at a local hospital. The sensor is stable for more than 25 days.     

Microdialysis SPR: diffusion-gated sensing in blood

Chemical measurements are rarely performed in crude blood due to the poor performance of sensors and devices exposed to biofluids. In particular, biosensors have been severely limited for detection in whole blood due to surface fouling from proteins, the interaction of cells with the sensor surface and potential optical interference when considering optical methods of analysis. To solve this problem, a dialysis chamber was introduced to a surface plasmon resonance (SPR) biosensor to create a diffusion gate for large molecules. This dialysis chamber relies on the faster migration of small molecules through a microporous membrane towards a sensor, located at a specified distance from the membrane. Size filtering and diffusion through a microporous membrane restricted the access of blood cells and larger biomolecules to a sensing chamber, while smaller, faster diffusing biomolecules migrated preferentially to the sensor with limited interference from blood and serum. The affinity of a small peptide (DBG178) with anti-atherosclerotic activity and targeting type B scavenger receptor CD36 was successfully monitored at micromolar concentrations in human serum and blood without any pre-treatment of the sample. This concept could be generally applied to a variety of targets for biomolecular interaction monitoring and quantification directly in whole blood, and could find potential applications in biochemical assays, pharmacokinetic drug studies, disease treatment monitoring, implantable plasmonic sensors, and point-of-care diagnostics.     

Phase-transfer catalysis of transmitters and pharmaceuticals at K+-valinomycin- and NH4+-nonactin-PVC-membranes of solid-state contact sensors

Summary As it is known that macrocyclic polyethers also complex substituted ammonium ions for PVC-membranes with the ammonium-selective nonactin and the potassium-selective valinomycin as carriers, the selectivity against transmitters and pharmaceuticals was determined. The tests were made with solid-state contacts independent of oxygen. With regard to the haemoanalysis the influence of pharmaceuticals on serum potassium measurements was determined with clinically significant concentrations of the pharmaceuticals. Apart from promethacine the greatest difference observed was 0.96%. Using the example of continuous monitoring of potassium in the heparinized blood of rats under the influence of epinephrine, it is shown that the decrease of potassium is clearly due to a metabolic effect of the catecholamine and does not represent an epinephrine interference at the sensor.     

A Powder Based Polyaniline Carbon Paste Electrode for Urea Analysis

A new polyaniline carbon paste electrode prepared by mixing polyaniline (emeraldine), nafion, graphite powder and urease for urea analysis was exploited. The ratio of polyaniline, nafion, urease and graphite for the construction of the electrodes and the optimal conditions for urea determination were studied. The detection limit of this sensor for urea is 5 μM and the linearity from 5 μM to 7.5 mM is obtained in FIA. This sensor has a response time of 90s and shows good reproducibility and stability (RSD, 6.3%, n = 43). The blood samples from a patient during blood dialysis were taken and analyzed. The urea concentrations in blood obtained from this sensor are comparable with urea test kit method.     

A potentiometric multisensor system for determining lysine in aqueous solutions containing potassium and sodium chloride

A potentiometric multisensor system has been developed for the determination of lysine in aqueous solutions containing sodium and potassium chlorides. The sensor array includes a cross-sensitive sensor, the response of which is the Donnan potential at the ion-exchange polymer/test solution interface, a set of ion-selective electrodes, and a silver-silver chloride reference electrode. Multidimensional regression analysis has been employed for the calculation of component concentrations. The relative error of determining lysine, potassium, and sodium did exceed 10% in the tested solutions.     

Glucose Clamp Experiments With Electrochemical Biosensors

Abstract

Glucose, lactate and potassium ions have been continuously measured in whole blood using two extracorporeal electrochemical biosensors and a new flow through potassium electrode using the glucose clamp technique. Experiments were carried out with a properly modified endocrine artificial pancreas “Betalike” by connecting this instrument in series with the lactate and potassium probes. the results showed that it is possible to monitor all three metabolites with accuracy and precision, allowing an improved control in diabetes care.     

Ultrafast and high-throughput mass spectrometric assay for therapeutic drug monitoring of antiretroviral drugs in pediatric HIV-1 infection applying dried blood spots

Kaletra® (Abott Laboratories) is a co-formulated medication used in the treatment of HIV-1-infected children, and it contains the two antiretroviral protease inhibitor drugs lopinavir and ritonavir. We validated two new ultrafast and high-throughput mass spectrometric assays to be used for therapeutic drug monitoring of lopinavir and ritonavir concentrations in whole blood and in plasma from HIV-1-infected children. Whole blood was blotted onto dried blood spot (DBS) collecting cards, and plasma was collected simultaneously. DBS collecting cards were extracted by an acetonitrile/water mixture while plasma samples were deproteinized with acetone. Drug concentrations were determined by matrix-assisted laser desorption/ionization-triple quadrupole tandem mass spectrometry (MALDI-QqQ-MS/MS). The application of DBS made it possible to measure lopinavir and ritonavir in whole blood in therapeutically relevant concentrations. The MALDI-QqQ-MS/MS plasma assay was successfully cross-validated with a commonly used high-performance liquid chromatography (HPLC)–ultraviolet (UV) assay for the therapeutic drug monitoring (TDM) of HIV-1-infected patients, and it showed comparable performance characteristics. Observed DBS concentrations showed as well, a good correlation between plasma concentrations obtained by MALDI-QqQ-MS/MS and those obtained by the HPLC-UV assay. Application of DBS for TDM proved to be a good alternative to the normally used plasma screening. Moreover, collection of DBS requires small amounts of whole blood which can be easily performed especially in (very) young children where collection of large whole blood amounts is often not possible. DBS is perfectly suited for TDM of HIV-1-infected children; but nevertheless, DBS can also easily be applied for TDM of patients in areas with limited or no laboratory facilities.     

Cell separation in microcanal coated with electrically charged phospholipid polymers

To separate the cell population in whole blood using microcanal, the surface was covered with a polyion complex (PIC) composed of electrically charged phospholipid polymers. The phospholipids polymers were prepared by the polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) and n-butyl methacrylate with 3-(methacryloyloxypropyl)-trimethyl ammonium iodide as the cationic unit or potassium 3-methacryloyloxypropyl sulfonate as the anionic unit. The PIC was formed at the solid-liquid interface, that is, first, the cationic polymer was coated on the substrate and an aqueous solution containing the anionic polymer with different concentrations was applied to the polymer-coated substrate. The formation of the PIC was followed using a quartz crystal microbalance (QCM), and the PIC surfaces were analyzed by both zeta-potential measurement and X-ray photoelectron spectroscopic measurement. The surface electrical potential on the PIC was controllable from +40 to -40 mV by increasing the amount of the adsorbed anionic polymer. The PIC surface was prepared in microcanal. The surface electrical potential was sequentially changed. When the whole blood was introduced into the microcanal, the cells adhered on the positively charged surface, but could not adhere to the negatively charged surface. Even when the cells adhere to the surface, the morphology of cells was maintained. This is due to MPC units at the surface, which show a good biocompatibility. These results indicated that the change in the surface electrical potential will be a useful method to separate the cells from whole blood.     

Biosensor system for continuous glucose monitoring in fish

A biosensor system was developed for continuous estimation of blood glucose in fish. Because it is difficult to measure blood components in real-time due to decreased sensor output resulting from blood coagulation and coalescing blood proteins at the sensor placement site, we used the eyeball scleral interstitial fluid (EISF) as the site of sensor implantation. Evaluation of the relationship between EISF and blood glucose concentrations revealed that the blood glucose concentration correlated closely with the EISF glucose concentration (y = 2.2996 + 0.9438x, R = 0.960, n = 112). To take advantage of the close correlation between blood and EISF glucose, we prepared a needle-type enzyme sensor for implantation in the fish sclera using a flexible wire electrode. The sensor provided a rapid response, good linearity, and reproducibility. Continuous glucose monitoring could be carried out by implanting this needle-type glucose sensor onto the eye. The findings indicated that the glucose concentration increased with sensor output current over time, and that changes in the blood glucose were continuously reflected in the EISF. The glucose concentration was estimated based on the one-point or two-point calibration methods. The two-point calibration method yielded the most accurate glucose monitoring (blood glucose range of 70-420 mg dL⁻¹) over 160 min. Sensor-estimated glucose and whole blood glucose values were highly correlated (y = 0.4401 + 0.8656x, R = 0.958).     

Direct detection of low-concentration NO in physiological solutions by a new GaAs-based sensor

Nitric oxide (NO) acts as a signal molecule in the nervous system, as a defense against infections, as a regulator of blood pressure, and as a gate keeper of blood flow to different organs. In vivo, it is thought to have a lifetime of a few seconds. Therefore, its direct detection at low concentrations is difficult. We report on a new type of hybrid, organic-semiconductor, electronic sensor that makes detection of nitric oxide in physiological solution possible. The mode of action of the device is described to explain how its electrical resistivity changes as a result of NO binding to a layer of native hemin molecules. These molecules are self-assembled on a GaAs surface to which they are attached through a carboxylate binding group. The new sensor provides a fast and simple method for directly detecting NO at concentrations down to 1 microM in physiological aqueous (pH=7.4) solution at room temperature.     

Studies on bis(crown ether)-based ion-selective electrodes for the potentiometric determination of sodium and potassium in serum

Bis(crown ether)-based ion-selective electrodes for sodium and potassium are described, based on the bis[(12-crown-4)-2-ylmethyl]-2-dodecyl-2-methyl malonate sensor(I) for sodium and the bis[(benzo-15-crown-5)-15-ylmethyl] pimelate sensor(II) for potassium. The best results were obtained when the sensors were used in association with 2-nitrophenyl octyl ether as plasticising solvent mediator and potassium tetrakis(4-chlorophenyl)borate as anion excluder in poly(vinyl chloride) matrices. Electrode slopes were near-Nernstian, with detection limits of less than 10(-5) M. The electrode features are compared with those of a sodium glass membrane electrode, for sensor I, and with a valinomycin-based potassium electrode, for sensor II. The electrodes are also discussed in relation to others reported for sensors I and II and are shown to be superior. However, although the electrodes described offer promising alternatives to glass electrodes for sodium and valinomycin electrodes for potassium, data for sodium and potassium measurements in blood serum indicate a need for further research in order to improve the correlation with flame photometric measurements.     

A microfluidic glucose sensor incorporating a novel thread‐based electrode system

An electrochemical sensor for the detection of glucose using thread‐based electrodes and fabric is described. This device is relatively simple to fabricate and can be used for multiple readings after washing with ethanol. The fabrication of the chip consisted of two steps. First, three thread‐based electrodes (reference, working, and counter) were fabricated by painting pieces of nylon thread with either layered silver ink and carbon ink or silver/silver chloride ink. The threads were then woven into a fabric chip with a beeswax barrier molded around the edges in order to prevent leaks from the tested solutions. A thread‐based working electrode consisting of one layer of silver underneath two layers of carbon was selected to fabricate the final sensor system. Using the chip, a PBS solution containing glucose oxidase (GOx) (10 mg/mL), potassium ferricyanide (K₃[Fe(CN)₆]) (10 mg/mL) as mediator, and different concentrations of glucose (0‐25 mM), was measured by cyclic voltammetry (CV). It was found that the current output from the oxidation of glucose was proportional to the glucose concentrations. This thread‐based electrode system is a viable sensor platform for detecting glucose in the physiological range.     

An Electrochemical Biosensor Architecture Based on Protein Folding Supports Direct Real-Time Measurements in Whole Blood

The ability to monitor drug and biomarker concentrations in the body with high frequency and in real time would revolutionize our understanding of biology and our capacity to personalize medicine. The few in vivo molecular sensors that currently exist, however, all rely on the specific chemical or enzymatic reactivity of their targets and thus are not generalizable. In response, we demonstrate here an electrochemical sensing architecture based on binding-induced protein folding that is 1) independent of the reactivity of its targets, 2) reagentless, real-time, and with a resolution of seconds, and 3) selective enough to deploy in undiluted bodily fluids. As a proof of principle, we use the SH3 domain from human Fyn kinase to build a sensor that discriminates between the protein's peptide targets and responds rapidly and quantitatively even when challenged in whole blood. The resulting sensor architecture could drastically expand the chemical space accessible to continuous, real-time biosensors.     

Amperometric biosensor for rapid measurement of 3-hydroxybutyrate in undiluted whole blood and plasma

A simple, rapid (< 30 s) electrochemical method for the determination of 3-hydroxybutyrate in whole blood or plasma is described, which uses NAD⁺-dependent d-3-hydroxybutyrate dehydrogenase immobilized at novel platinized carbon electrodes. The steady-state oxidation current produced by enzymatically generated NADH is measured at + 150 mV vs. Ag/AgCl. Enzyme electrodes produced by direct adsorption were stable for at least 3 months. Undiluted whole blood measurement with the sensor was compared with routine spectrophotometric analysis of plasma and perchloric acid extracts of whole blood.     

Potassium-based algorithm allows correction for the hematocrit bias in quantitative analysis of caffeine and its major metabolite in dried blood spots

Although dried blood spot (DBS) sampling is increasingly receiving interest as a potential alternative to traditional blood sampling, the impact of hematocrit (Hct) on DBS results is limiting its final breakthrough in routine bioanalysis. To predict the Hct of a given DBS, potassium (K⁺) proved to be a reliable marker. The aim of this study was to evaluate whether application of an algorithm, based upon predicted Hct or K⁺ concentrations as such, allowed correction for the Hct bias. Using validated LC-MS/MS methods, caffeine, chosen as a model compound, was determined in whole blood and corresponding DBS samples with a broad Hct range (0.18–0.47). A reference subset (n?=?50) was used to generate an algorithm based on K⁺ concentrations in DBS. Application of the developed algorithm on an independent test set (n?=?50) alleviated the assay bias, especially at lower Hct values. Before correction, differences between DBS and whole blood concentrations ranged from ?29.1 to 21.1 %. The mean difference, as obtained by Bland-Altman comparison, was ?6.6 % (95 % confidence interval (CI), ?9.7 to ?3.4 %). After application of the algorithm, differences between corrected and whole blood concentrations lay between ?19.9 and 13.9 % with a mean difference of ?2.1 % (95 % CI, ?4.5 to 0.3 %). The same algorithm was applied to a separate compound, paraxanthine, which was determined in 103 samples (Hct range, 0.17–0.47), yielding similar results. In conclusion, a K⁺-based algorithm allows correction for the Hct bias in the quantitative analysis of caffeine and its metabolite paraxanthine. Graphical Abstract

Percentage differences between uncorrected DBS and whole blood paraxanthine concentrations (upper panel) and between corrected and whole blood paraxanthine concentrations (lower panel) (n = 103)     

Application of an ion-selective field effect transistor with a photocured polymer membrane in nephrology for determination of potassium ions in dialysis solutions and in blood plasma

Application of a potassium ion sensor based on an ion sensitive field effect transistor (ISFET) for ion control of a dialysis solution in an artificial kidney and in blood plasma of patients treated by hemodialysis is presented. Sensors and their long-term stability were characterised in constant contact with test solutions. Test results are compared to those obtained with conventional ion-selective electrodes and commercial blood ion analyser. Tested ISFET sensors showed high reliability in potassium ion measurements in the physiologically significant concentration range which, along with low cost of their production, makes them promising for cited application.     

Photochromic polyoxometalate–based enzyme-free reusable sensors for real-time colorimetric detection of alcohol in sweat and saliva

This study describes a new strategy for real-time detection of alcohol in saliva and sweat. Phosphotungstic acid (PTA) is a colorless, photoelectrochromic heteropoly acid that can be reduced by ethanol under ultraviolet (UV) radiation to produce an intense blue color. This system has useful properties in the development of a new alcohol sensor: (1) the blue color can be detected by the naked eye or mobile camera, even at low ethanol concentrations; (2) color intensity is proportional to ethanol concentration; and (3) once exposed to air, reduced PTA is subsequently oxidized and returns to its colorless state offering sensor reusability. Based on these properties, we developed a simple device consisting of a PTA-impregnated non-woven material and a low-cost UV lamp that can be used to evaluate the alcohol concentration in saliva and sweat. We further enhanced the practical applicability of this sensor by demonstrating the integration of digital image analysis, multivariate analysis, and mobile camera technology with this sensor. This device can be potentially used in vehicles as a convenient, reusable alcohol sensor for drivers.     

Determination of cadralazine in human whole blood using reversed-phase high-performance liquid chromatography: utilizing a salting-out extraction procedure

A rapid, selective, and sensitive ion-paired reversed-phase high-performance liquid chromatographic method for determination of the new carbazate type of antihypertensive vasodilator agent cadralazine in human whole blood has been developed. Cadralazine was extracted from whole blood by adding 0.5 ml of acetonitrile to 1.0 ml of whole blood followed by salting-out of acetonitrile by the addition of potassium carbonate in excess. An aliquot of the salted-out acetonitrile was injected into the chromatographic system. A column packed with 3-microns octyl (C8) particles was used with an isocratic elution of 1% acetic acid and 5 mM hexanesulfonic acid-acetonitrile (70:30, v/v). The cadralazine was measured using ultraviolet detection at 250 nm and the assay was completed in less than 20 min and had a limit of quantitation of 10 ng/ml for a 100-microliters injection volume.