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The performance of a membrane-coated voltammetric sensor for propofol (2,6-diisopropylphenol) has been characterized in long term monitoring experiments using an automated flow analytical system (AFAS) and by analyzing human serum and whole blood samples by standard addition. It is shown that the signal of the membrane-coated electrochemical sensor for propofol is not influenced by the components of the pharmaceutical formulation of propofol (propofol injectable emulsion). The current values recorded with the electrochemical propofol sensor in buffer solutions and human serum samples spiked with propofol injectable emulsion showed excellent correlation with the peak heights recorded with an UV-Vis detector during the HPLC analysis of these samples (R² = 0.997 in PBS and R² = 0.975 in human serum). However, the determination of propofol using the electrochemical method is simpler, faster and has a better detection limit (0.08 ± 0.05 µM) than the HPLC method (0.4 ± 0.2 µM). As a first step towards feedback controlled closed-loop anesthesia, the membrane-coated electrochemical sensor has been implemented onto surface of an intravenous catheter. The response characteristics of the membrane-coated carbon fiber electrode on the catheter surface were very similar to those seen using a macroelectrode. [ABSTRACT FROM AUTHOR]

For monitoring of the popular anesthetic drug propofol an automatic flow analytical system (AFAS) has been built that allows the quantitative measurement of electrochemically active compounds in continuous flow, stopped flow and flow injection analysis (FIA) modes. The performance characteristics of the AFAS is demonstrated using a microfabricated planar electrochemical cells in combination with a ∼15 µL volume flow cell. To perform continuous monitoring experiments and the analysis of individual propofol samples an organic membrane-coated voltammetric sensor has been implemented into the AFAS. The membrane coating prevents electrode fouling, provides outstanding detection limit and selectivity for the voltammetric working electrode. [ABSTRACT FROM AUTHOR]

Propofol is a widely used, potent intravenous anesthetic for ambulatory anesthesia and long-term sedation. The target steady state concentration of propofol in blood is 0.25–10 μg/mL (1–60 μM). Although propofol can be oxidized electrochemically, monitoring its concentration in biological matrixes is very challenging due to (i) low therapeutic concentration, (ii) high concentrations of easily oxidizable interfering compounds in the sample, and (iii) fouling of the working electrode. In this work we report the performance characteristics of an organic film coated glassy carbon (GC) electrode for continuous monitoring of propofol. The organic film (a plasticized PVC membrane) improved the detection limit and the selectivity of the voltammetric sensor due to the large difference in hydrophobicity between the analyte (propofol) and interfering compounds of the sample, e.g., ascorbic acid (AA) or p-acetamidophenol (APAP). Furthermore, the membrane coating prevented electrode fouling and served as a protective barrier against electrode passivation by proteins. Studies revealed that sensitivity and selectivity of the voltammetric method is greatly influenced by the composition of the PVC membrane. The detection limit of the membrane-coated sensor for propofol in PBS is reported as 0.03 ± 0.01 μM. In serum-like electrolyte solutions containing physiologically relevant levels of albumin (5%) and 3 mM AA and 1 mM APAP as interfering agents, the detection limit was 0.5 ± 0.4 μM. Both values are below the target concentrations used clinically during anesthesia or sedation. [ABSTRACT FROM AUTHOR]

Abstract: The fabrication and characterization of surface-attached PEG–diacrylate hydrogel structures and their application as sensing platforms for the detection of specific target sequences are reported. Hydrogel structures were formed by a photopolymerization process, using substrate-bound Eosin Y molecules for the production of free radicals. We have demonstrated that this fabrication process allows for control over hydrogel growth down to the micrometer scale. Confocal imaging revealed relatively large pore structures for 25% (v/v) PEG–diacrylate hydrogels, which appear to lie in tightly packed layers. Our data suggest that these pore structures decrease in size for hydrogels with increasing levels of PEG–diacrylate. Surface coverage values calculated for hydrogels immobilized with 21-mer DNA probe sequences were significantly higher compared to those previously reported for 2- and 3-dimensional sensing platforms, on the order of 1016 moleculescm−2. Used as sensing platforms in DNA hybridization assays, a detection limit of 3.9nM was achieved for hybridization reactions between 21-mer probe and target sequences. The ability of these hydrogel sensing platforms to discriminate between wild-type and mutant allele sequences was also demonstrated, down to target concentrations of 1–2nM. A reduction in the hybridization time down to a period of 15min was also achieved, while still maintaining confident results, demonstrating the potential for future integration of these sensing platforms within Lab-on-Chip or diagnostic devices. [Copyright &y& Elsevier]

Abstract: The behaviour of an acridine-functionalised calix[4]arene at the interface between two immiscible electrolyte solutions (ITIES) is reported. Molecular modelling showed that the acridine-calix[4]arene has regions of significant net positive charge spread throughout the protonated acridine moieties, consistent with it being able to function as an anion ionophore. The presence of this compound in the organic phase facilitated the transfer of aqueous phase electrolyte ions. Upon addition of double stranded DNA to the aqueous phase, the transfer of electrolyte anions was diminished, due to DNA binding to the acridine moiety at the ITIES. The behaviour provides a basis for DNA hybridization detection using electrochemistry at the ITIES. [Copyright &y& Elsevier]

Abstract: Characterization of the interaction of a urea-functionalized calix[4]arene ionophore and phosphate was undertaken by combination of nuclear magnetic resonance (NMR) spectrometry, potentiometric selectivity coefficient evaluation and voltammetric ion transfer at the interface between two immiscible electrolyte solutions (ITIES). NMR revealed that the urea protons were involved in complexation with the target anion and potentiometric separate solution selectivity data indicated selectivity for phosphate over chloride and sulphate. Voltammetry at the ITIES confirmed that the ionophore-facilitated transfer of monohydrogen phosphate occurred in preference to dihydrogen phosphate transfer. The results correlate with previously reported data on the potentiometric evaluation of this calixarene as an anionophore in PVC-membrane electrodes. The data provide the basis for development of amperometric monohydrogen phosphate sensors based on the ion-transfer principle. [Copyright &y& Elsevier]

Abstract: Ion-selective membrane electrodes doped with the urea- or thiourea-functionalised calix[4]arenes, 5,11,17,23-tetra-tert-butyl-25,27-bis[[4-N′-(phenylureido)butyl]oxy]-26,28-dipropoxy calix[4]arene (I) and 5,11,17,23-tetra-tert-butyl-25,27-bis[[4-(N′-phenylthioureido)-butyl]oxy]-26,28-dipropoxy calix[4]arene (II), were evaluated for anion sensing. Potentiometric results show that these calixarene ionophore-based membrane electrodes exhibit a good sensitivity to aqueous solutions of the monohydrogen orthophosphate species HPO4 2− in the concentration range 5.0×10−5 to 1.0×10−1 M, with near-Nernstian response slopes of −33.0 and −28.0mVdec−1 for ionophores I and II, respectively. Selectivity coefficient values for monohydrogen orthophosphate over a range of common anions were determined by the fixed interference and matched potential methods and indicated that these membrane electrodes exhibit a good selectivity for HPO4 2− with respect to the other anions, including sulfate and nitrate. [Copyright &y& Elsevier]

Goal: Target-controlled infusion of anesthesia is a closed-loop automated drug delivery method with a computer-aided control. Our goal is to design and test an automated drug infusion platform for propofol delivery in total intravenous anesthesia (TIVA) administration. Methods: In the proposed method, a dilution chamber with first-order exponential decay characteristics was used to model the pharmacodynamics decay of a drug. The dilution chamber was connected to a flow system through an electrochemical cell containing an organic film-coated glassy carbon electrode as working electrode. To set up the feedback-controlled delivery platform and optimize its parameters, ferrocene methanol was used as a proxy of the propofol. The output signal of the sensor was connected to a PI controller, which prompted a syringe pump for feedback-controlled drug infusion. Results: The result is a bench-top drug infusion platform to automate the delivery of a propofol based on the measurement of concentration with an organic film-coated voltammetric sensor. Conclusion: To evaluate the performance characteristics of the infusion platform, the propofol concentration in the dilution chamber was monitored with the organic film-coated glassy carbon electrode and the difference between the set and measured concentrations was assessed. The feasibility of measurement-based feedback-controlled propofol delivery is demonstrated and confirmed. Significance: This platform will contribute to high-performance TIVA application of intravenous propofol anesthesia. [ABSTRACT FROM PUBLISHER]

Abstract: 2,6-Diisopropylphenol (propofol) is a potent anesthetic drug with fast onset of the anesthetic effect and short recovery time for the patients. Outside of the United States, propofol is widely used in performing target controlled infusion anesthesia. With the long term vision of an electrochemical sensor for in vivo monitoring and feedback controlled dosing of propofol in blood, different alternatives for the electrochemical quantification of propofol using diverse working electrodes and experimental conditions are presented in this contribution. When the electrochemical oxidation of propofol takes place on a glassy carbon working electrode, an electrochemically active film grows on the electrode surface. The reduction current of the film is proportional to the propofol concentration and the accumulation time. Based on these findings a stripping analytical method was developed for the detection of propofol in acidic solutions between 0 and 30μM, with a detection limit of 5.5±0.4μM. By restricting the scanned potential window between 0.5V and 1.0V in cyclic voltammetric experiments, the formation of the electrochemically active polymer can be prevented. This allowed the development of a direct voltammetric method for assessing propofol in acidic solutions between 0 and 30μM, with a 3.2±0.1μM (n =3) detection limit. The stripping method has a better sensitivity but somewhat worse reproducibility because the electrode surface has to be renewed between each experiment. The direct method does not require the renewal of the electrode surface between measurements but has no adequate selectivity towards the common interfering compounds. [Copyright &y& Elsevier]