María Isabel Encinar del Pozo

The use of cucurbit[8]uril host–guest interactions in the development of an electrochemical sensor: characterization and application to tryptophan determination

The host–guest properties of cucurbit[8]uril have been employed to modify a conventional electrode surface in order to increase its analytical performance. The new electrode surface has been characterized, and the influence of different experimental parameters on complex formation has been investigated in detail using different electrochemical techniques. The results of electrochemical spectroscopic impedance studies are in good agreement with the electrochemical behaviour shown by this electrode material in terms of the molecular-recognition properties of this nanosize receptor to positively or negatively charged guests. The electrode developed herein has enhanced sensitivity and selectivity, as demonstrated by its application to the determination of tryptophan in real samples, with a good accuracy and precision and no need for any additional sample treatment.

New supramolecular interactions for electrochemical sensors development: different cucurbit[8]uril sensing platform designs

Three different strategies for cucurbit[8]uril immobilization on a glassy carbon electrode have been assayed. The electrochemical properties of the resulting modified electrodes in solutions containing neutral, positively and negatively charged potential cucurbit[8]uril guests were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The comparison of the electrochemical behaviour exhibited by the unmodified electrodes against various probes, with respect to that of each modified electrode, resulted in an appropriate method to choose among different strategies for the development of electrochemical sensors. These sensors are based on the incorporation of the cucurbit[8]uril molecular selection properties that depend on the chemical characteristics of the potential analytes. Furthermore, atomic force microscopy was employed for the characterization of the different surfaces developed.

Graphene in combination with cucurbit[n]urils as electrode modifiers for electroanalytical biomolecules sensing

Cucurbit[n]urils have been supported on graphene to develop sensitive and selective electrodes. The electrochemical response of modified electrodes containing graphene or graphene plus cucurbiturils has been studied for three probe molecules including hydroxymethylferrocene, ferrocyanide and methylviologen. It was found that the properties of these modified electrodes are derived from an increase in electron mobility and catalytic activity imparted by graphene and the selective complexation and molecular recognition due to cucurbit[n]urils. These properties of the graphene/cucurbit[n]urils modified electrodes have been applied for the electrochemical detection of relevant biomolecules as tryptophan at 0.69×10(-7) M concentration.

On-line competitive host-guest interactions in a turn-on fluorometric method to amantadine determination in human serum and pharmaceutical formulations

A competitive assay between the antiviral Amantadine and the dye Thionine for the Cucurbit[8]uril cavity was carried out in a flow injection analysis system for the indirect fluorescence detection of Amantadine. Both, Cucurbit[7]uril and Cucurbit[8]uril Thionine complexes were evaluated for the competitive assay. The use of a 12-port injection valve allows the on-line reaction in the flow system. Once optimized all the experimental variables, the methodology developed allows the detection of Amantadine at the 0.16µM level with excellent accuracy (Er ≤ 8.2%) and reproducibility (RSD ≤ 6.3%) for all the concentration range assayed. This one-step turn-on fluorescence methodology allows reaching sampling frequencies of 68 samples per hour. The selectivity of the method was evaluated against different antiviral drugs. Moreover, the performance of the methodology proposed was tested by the Amantadine determination in human serum and pharmaceutical formulations samples. The results demonstrated that the method can be applied to Amantadine determination in real samples of different nature with excellent recoveries, ranging from 83% to 98% depending on the matrix assayed.

Synergistic effect of MoS 2 and diamond nanoparticles in electrochemical sensors: determination of the anticonvulsant drug valproic acid

AbstractThe authors describe an electrochemical sensor based on the use of diamond nanoparticles (DNPs) and molybdenum disulfide (MoS2) platelets. The sensor was applied to the voltammetric determination of the anticonvulsant valproic acid which was previously derivatized with ferrocene. The MoS2 platelets were obtained by an exfoliation method, and the DNPs were directly dispersed in water and subsequently deposited on a glassy carbon electrode (GCE). The sensor response was optimized in terms of the solvent employed for dispersing the MoS2 nanomaterial and the method for modifying the GCE. Sensors consisting of a first layer of MoS2 dispersed in ethanol/water and a second layer of DNPs give better response. The single steps of sensor construction were characterized by atomic force microscopy and electrochemical impedance spectroscopy. The differential pulse voltammetric response of the GCE (measured at +0.18 V vs. Ag/AgCl) was compared to that of sensors incorporating only one of the nanomateriales (DNPs or MoS2). The formation of a hybrid MoS2-DNP structure clearly improves performance. The GCE containing both nanomaterials exhibits high sensitivity (740 µA ⋅ mM−1 ⋅ cm−2), a 0.27 μM detection limit, and an 8% reproducibility (RSD). The sensor retained 99% of its initial response after 45 days of storage. Graphical abstractElectrochemical sensor by co-immobilization of MoS2 and diamond nanoparticles (DNP). The formation of a hybrid MoS2-DNP structure enhances the performance of the sensor towards valproic acid derivatized with a ferrocene group, when compared with sensors incorporating only DNP or MoS2.