Characterization of a new ionophore-based ion-selective electrode for the potentiometric determination of creatinine in urine.

The optimization, analytical characterization and validation of a novel ion-selective electrode for the highly sensitive and selective determination of creatinine in urine is presented. A newly synthesized calix[4]pyrrole-based molecule is used as an ionophore for the enhanced recognition of creatininium cations. The calculation of the complex formation constants in the polymeric membrane with creatininium, potassium and sodium confirms the strong selective interactions between the ionophore and the target. The optimization of the potentiometric sensor presented here yields an outstanding analytical performance, with a linear range that spans from 1µM to 10mM and limit of detection of 10-6.2M. The calculation of the selectivity coefficients against most commonly found interferences also show significant improvements when compared to other sensors already reported. The performance of this novel sensor is tested by measuring creatinine in real urine samples (N=50) and comparing the values against the standard colorimetric approach (Jaffé's reaction). The results show that this sensor allows the fast and accurate determination of creatinine in real samples with minimal sample manipulation.

Recognition and Sensing of Creatinine.

Current methods for creatinine quantification suffer from significant drawbacks when aiming to combine accuracy, simplicity, and affordability. Here, an unprecedented synthetic receptor, an aryl-substituted calix[4]pyrrole with a monophosphonate bridge, is reported that displays remarkable affinity for creatinine and the creatininium cation. The receptor works by including the guest in its deep and polar aromatic cavity and establishing directional interactions in three dimensions. When incorporated into a suitable polymeric membrane, this molecule acts as an ionophore. A highly sensitive and selective potentiometric sensor suitable for the determination of creatinine levels in biological fluids, such as urine or plasma, in an accurate, fast, simple, and cost-effective way has thus been developed.

Analysis of risk factors for hydrocephalus development in newborn infants with germinal matrix hemorrhage.

AIM: The aim of this study was to analyze risk factors for the development of hydrocephalus in newborn infants with germinal matrix (GM) hemorrhage. METHODS: The study comprised 271 patients admitted to Carlos Haya University Hospital in Malaga with GM hemorrhage. The following data were recorded: gestational age, gender, twin birth, head circumference at birth, weight at birth, and Papile grade. Severe obstetrical (abruption, chorioamnionitis, pregnancy-induced hypertension, tocolytic treatment) and neonatal disorders (respiratory distress syndrome, neonatal infection, coagulation disorder, patent ductus arteriosus, necrotizing enterocolitis) were also recorded. Symptomatic hydrocephalus was diagnosed in the event of a progressive increase in head circumference and ventricular indices requiring shunting. RESULTS: Of the 271 patients, 139 (51%) developed posthemorrhagic ventriculomegaly; 47 patients (17%) developed symptomatic hydrocephalus and needed shunt implantation. We found a significant relationship between the development of symptomatic hydrocephalus and Papile grade, lower gestational age, lower birth weight, twin birth, and neonatal infection. CONCLUSION: Awareness of risk factors for the development of hydrocephalus in newborn infants with GM hemorrhage should be emphasized in order to enable an early diagnosis of ventriculomegaly and symptomatic hydrocephalus and thus make a correct therapeutic decision.

Chloride-selective electrodes based on "two-wall" aryl-extended calix[4]pyrroles: combining hydrogen bonds and anion-π interactions to achieve optimum performance.

The performance of chloride-selective electrodes based on "two-wall" aryl-extended calix[4]pyrroles and multiwall carbon nanotubes is presented. The calix[4]pyrrole receptors bear two phenyl groups at opposite meso-positions. When the meso-phenyl groups are decorated with strong electron-withdrawing substituents, attractive anion-π interactions may exist between the receptor's aromatic walls and the sandwiched anion. These anion-π interactions are shown to significantly affect the selectivity of the electrodes. Calix[4]pyrrole, bearing a p-nitro withdrawing group on each of the meso-phenyl rings, afforded sensors that display anti-Hofmeister behavior against the lipophilic salicylate and nitrate anions. Based on the experimental data, a series of principles that help in predicting the suitability of synthetic receptors for use as anion-specific ionophores is discussed. Finally, the sensors deliver excellent results in the direct detection of chloride in bodily fluids.

Rubber-based substrates modified with carbon nanotubes inks to build flexible electrochemical sensors.

The development of a solid-contact potentiometric sensor based on conducting rubbers using a carbon nanotubes ink is described here. Commercial rubbers are turned into conductive ones by a simple and versatile method, i.e. painting an aqueous dispersion of single-walled carbon nanotubes on the polymer surface. On this substrate, both the working ion-selective electrode and the reference electrode are built in order to form an integrated potentiometric cell. As a proof-of-principle, selective potassium electrodes are fully characterized giving comparable performances to conventional electrodes (sensitivity, selectivity, stability, linear range, limit of detection and reproducibility). As an application of the rubber-based electrodes, a bracelet was constructed to measure potassium levels in artificial sweat. Since rubbers are ubiquitous in our quotidian life, this approach offers great promise for the generation of chemical information through daily objects.

A reference electrode based on polyvinyl butyral (PVB) polymer for decentralized chemical measurements.

A new solid-state reference electrode using a polymeric membrane of polyvinyl butyral (PVB), Ag/AgCl and NaCl to be used in decentralized chemical measurements is presented. The electrode is made by drop-casting the membrane cocktail onto a glassy carbon (GC) substrate. A stable potential (less than 1 mV dec(-1)) over a wide range of concentrations for the several chemical species tested is obtained. No significant influence to changes in redox potential, light and pH are observed. The response of this novel electrode shows good correlation when compared with a conventional double-junction reference electrode. Also good long-term stability (90±33 µV/h) and a lifetime of approximately 4 months are obtained. Aspects related to the working mechanisms are discussed. Atomic Force Microscopy (AFM) studies reveal the presence of nanopores and channels on the surface, and electrochemical impedance spectroscopy (EIS) of optimized electrodes show low bulk resistances, usually in the kΩ range, suggesting that a nanoporous polymeric structure is formed in the interface with the solution. Future applications of this electrode as a disposable device for decentralized measurements are discussed. Examples of the utilization on wearable substrates (tattoos, fabrics, etc) are provided.

A paper-based potentiometric cell for decentralized monitoring of Li levels in whole blood.

A novel approach to monitor Li levels in blood in decentralized (out of the lab) settings is presented. The approach uses a potentiometric cell fully made with filter paper as a support. Electrodes were built using carbon nanotubes ink to create a conductive path and a suitable polymeric membrane. Solid-state ion-selective electrodes for Li and a reference electrode were built and optimized. The results obtained on real samples of serum and whole blood are comparable with those obtained by conventional standard approaches. This platform shows an outstanding performance for the direct, fast and low-cost monitoring of Li levels in blood.

Graphene-based potentiometric biosensor for the immediate detection of living bacteria.

In this communication we present a potentiometric aptasensor based on chemically modified graphene (transducer layer of the aptasensor) and aptamers (sensing layer). Graphene oxide (GO) and reduced graphene oxide (RGO) are the basis for the construction of two versions of the aptasensor for the detection of a challenging living organism such as Staphylococcus aureus. In these two versions, DNA aptamers are either covalently (in the GO case) or non-covalently (in the RGO case) attached to the transducer layer. In both cases we are able to selectively detect a single CFU/mL of S. aureus in an assay close to real time, although the noise level associated to the aptasensors made with RGO is lower than the ones made with GO. These new aptasensors, that show a high selectivity, are characterized by the simplicity of the technique and the materials used for their construction while offering ultra-low detection limits in very short time responses in the detection of microorganisms.

Computer-operated analytical platform for the determination of nutrients in hydroponic systems.

Hydroponics is a water, energy, space, and cost efficient system for growing plants in constrained spaces or land exhausted areas. Precise control of hydroponic nutrients is essential for growing healthy plants and producing high yields. In this article we report for the first time on a new computer-operated analytical platform which can be readily used for the determination of essential nutrients in hydroponic growing systems. The liquid-handling system uses inexpensive components (i.e., peristaltic pump and solenoid valves), which are discretely computer-operated to automatically condition, calibrate and clean a multi-probe of solid-contact ion-selective electrodes (ISEs). These ISEs, which are based on carbon nanotubes, offer high portability, robustness and easy maintenance and storage. With this new computer-operated analytical platform we performed automatic measurements of K(+), Ca(2+), NO3(-) and Cl(-) during tomato plants growth in order to assure optimal nutritional uptake and tomato production.

Endoscopic third ventriculostomy: can we predict success during surgery?

Endoscopic third ventriculostomy (ETV) is widely used as an alternative technique for hydrocephalus treatment. ETV success or failure may be influenced by numerous factors. In this study, we have analyzed preoperative and intraoperative risk factors and suggest an intraoperative scale to predict etV failure. Fifty-one patients (27 adults and 24 children) underwent an etV at Carlos Haya University Hospital, Malaga. Intraoperative video records were assessed and the following intraoperative findings were recorded: (1) abnormal ventricular anatomy, (2) intraoperative incident, (3) Liliequist membrane opening in a second endoscopic maneuver, (4) thickened or scarred membranes in the subarachnoid space, (5) absence or "weakness" of pulsation of third ventricle floor at etV completion, and (6) floppy premammillary membrane that needs edge coagulation. An intraoperative scale ranging from 0 to 6 points was performed. A significant relation was found between a higher result on the prognosis scale and etV failure (p < 0.0001). An absence or weakness of pulsation of the third ventricle floor at etV completion was significantly related to etV failure (p < 0.0001). The presence of thickened or scarred membranes in the subarachnoid space was significantly related to etV failure (p < 0.04) as well as the Liliequist membrane opening in a second endoscopic maneuver (p < 0.008). Intraoperative factors should be taken into account for prediction of etV success. More studies with larger case series are needed to determine the influence of all intraoperative factors over etV success.

Ventriculoperitoneal shunt as a primary neurosurgical procedure in newborn posthemorrhagic hydrocephalus: report of a series of 47 shunted patients.

PURPOSE: Intraventricular hemorrhage is the most common cause of infantile acquired hydrocephalus. Our objective is to determine if the implantation of ventriculoperitoneal shunt in posthemorrhagic hydrocephalus as a primary and definitive neurosurgical treatment, with no previous temporary procedures, would decrease complication rates with good functional outcomes. METHODS: Two hundred seventy-one patients with germinal matrix hemorrhage were diagnosed at the Carlos Haya Hospital between 2003 and 2010. Forty-seven patients underwent ventriculoperitoneal shunt after developing symptomatic hydrocephalus. The minimum weight required for shunt implantation was 1,500 g. We recorded complications related to the surgical procedure and analyzed functional state with a self-developed four-grade scale. RESULTS: One hundred thirty-nine (51.3 %) patients with intraventricular hemorrhage developed ventricular dilatation, but only 47 patients (17.34 %) needed shunting. In seven cases, temporary neurosurgical procedures were performed, but in all of them, this was followed by ventriculoperitoneal shunt implantation. The infection rate was 4.25 %, and shunt obstruction rate was 4.25 %. More than 80 % of patients were classified as good or excellent functional state. Mean follow-up period was 38.75 months (SD, 27.09; range, 1-102 months). CONCLUSIONS: Ventriculoperitoneal shunting as a primary neurosurgical treatment in posthemorrhagic hydrocephalus would decrease surgical morbidity with good functional outcome.

Paper-based chemiresistor for detection of ultralow concentrations of protein.

A new paper-based chemiresistor composed of a network of single-wall carbon nanotubes (SWCNTs) and anti-human immunoglobulin G (anti-HIgG) is reported herein. SWCNTs act as outstanding transducers because they provide high sensitivity in terms of resistance changes due to immunoreaction. As a result, the resistance-based biosensor reaches concentration detection as low as picomolar. The resulting paper-based biosensor is sensitive, selective and employs low-cost substrate and simple manufacturing stages. Since chemiresistors require low-power equipment and are able to detect low concentrations with inexpensive materials, the present approach may pave the way for the development of resistive biosensors at very low-cost with high performances.

Carbon nanotube-based aptasensors for the rapid and ultrasensitive detection of bacteria.

In this paper we present a new generation of potentiometric biosensors based on carbon nanotubes (transducer layer of the biosensor) and aptamers (sensing layer of the biosensor) for the ultralow and selective detection of microorganisms. We show that with these aptasensors we were able to detect a few CFU of the target bacteria almost in real-time, both in buffered and in real samples.

A novel miniaturized radiofrequency potentiometer tag using ion-selective electrodes for wireless ion sensing.

Instrumental approaches to remotely and wirelessly monitoring chemical species are increasingly needed. Together with the electronic developments, efforts to optimize and validate the performance of these new devices are required. In this work, the analytical performance of a recently developed potentiometer-radiofrequency tag connected to ion-selective electrodes is evaluated. This credit card sized and extremely low power consumption device yield results that are comparable to those obtained with more sophisticated, lab-based tools. Advantages such as portability and autonomy, together with unique features, such as the ability to be read through the walls in a closed vessel are demonstrated. Future perspectives opened by this new generation of devices, such as their use in wearable devices and in decentralized settings are discussed.

Potentiometric sensors using cotton yarns, carbon nanotubes and polymeric membranes.

A simple and generalized approach to build electrochemical sensors for wearable devices is presented. Commercial cotton yarns are first turned into electrical conductors through a simple dyeing process using a carbon nanotube ink. These conductive yarns are then partially coated with a suitable polymeric membrane to build ion-selective electrodes. Potentiometric measurements using these yarn-potentiometric sensors are demonstrated. Examples of yarns that can sense pH, K(+) and NH4(+) are presented. In all cases, these sensing yarns show limits of detection and linear ranges that are similar to those obtained with lab-made solid-state ion-selective electrodes. Through the immobilization of these sensors in a band-aid, it is shown that this approach could be easily implemented in a wearable device. Factors affecting the performance of the sensors and future potential applications are discussed.

Protein detection with potentiometric aptasensors: a comparative study between polyaniline and single-walled carbon nanotubes transducers.

A comparison study on the performance characteristics and surface characterization of two different solid-contact selective potentiometric thrombin aptasensors, one exploiting a network of single-walled carbon nanotubes (SWCNTs) and the other the polyaniline (PANI), both acting as a transducing element, is described in this work. The molecular properties of both SWCNT and PANI surfaces have been modified by covalently linking thrombin binding aptamers as biorecognition elements. The two aptasensors are compared and characterized through potentiometry and electrochemical impedance spectroscopy (EIS) based on the voltammetric response of multiply charged transition metal cations (such as hexaammineruthenium, [Ru(NH3)6](3+)) bound electrostatically to the DNA probes. The surface densities of aptamers were accurately determined by the integration of the peak for the reduction of [Ru(NH3)6](3+) to [Ru(NH3)6](2+). The differences and the similarities, as well as the transduction mechanism, are also discussed. The sensitivity is calculated as 2.97 mV/decade and 8.03 mV/decade for the PANI and SWCNTs aptasensors, respectively. These results are in accordance with the higher surface density of the aptamers in the SWCNT potentiometric sensor.

A potassium sensor based on non-covalent functionalization of multi-walled carbon nanotubes.

Non-covalent functionalization of multi-walled carbon nanotubes (MWCNTs) by a pyrene based benzo-18-crown-6 ether 1 leads to nanostructure assemblies that play both the role of an ion-to-electron transducer and a selective recognition element in solid-contact ion-selective-electrodes (SC-ISEs). The high loading capacity (36 wt%) as well as the suitable dispersion character of the MWCNT hybrid in the ion-selective membrane (ISM) confirmed the benefit of this approach over the covalent one. The sensor has been applied successfully to the detection of potassium. Nernstian response (56.9 ± 0.9 mV per decade) was obtained (10(-5) and 10(-2) M K(+)) and the selectivity pattern was not altered by the immobilization of the ionophore on the MWCNTs. Leakage of the ionophore from the polymeric matrix is therefore avoided while the sensor construction was simplified and the analytical performances were maintained.