Fused Silica Microcapillaries Used for a Simple Miniaturization of the Electrified Liquid-Liquid Interface

Comparative electrochemical study of veterinary drug danofloxacin at glassy carbon electrode and electrified liquid-liquid interface

This work compares the electroanalytical performance of two electroanalytical systems based on (1) the glassy carbon electrode (GCE), and (2) the electrified liquid-liquid interface (eLLI), for the detection of fluoroquinolone antibiotic-danofloxacin (DANO). Our aim was to define the optimal conditions to detect the chosen analyte with two employed systems, extract a number of electroanalytical parameters, study the mechanism of the charge transfer reactions (oxidation at GCE and ion transfer across the eLLI), and to provide physicochemical constants for DANO. Detection of the chosen analyte was also performed in the spiked milk samples. To the best of our knowledge, this is the first work that directly compares the electroanalytical parameters obtained with solid electrode (in this case GCE) and eLLI. We have found that for DANO the latter provides better electroanalytical parameters (lower LOD and LOQ) as well as good selectivity when the milk was analyzed.

Nitrazepam and 7-aminonitrazepam studied at the macroscopic and microscopic electrified liquid-liquid interface

Two benzodiazepine type drugs, that is, nitrazepam and 7-aminonitrazepam, were studied at the electrified liquid-liquid interface (eLLI). Both drugs are illicit and act sedative in the human body and moreover are used as date rape drugs. Existence of the diazepine ring in the concerned chemicals structure and one additional amine group (for 7-aminonitrazepam) allows for the molecular charging below their pKa values, and hence, both drugs can cross the eLLI interface upon application of the appropriate value of the Galvani potential difference. Chosen molecules were studied at the macroscopic eLLI formed in the four electrode cell and microscopic eLLI formed within a microtip defined as the single pore having 25 μm in diameter. Microscopic eLLI was formed using only a few μL of the organic and the aqueous phase with the help of a 3D printed cell. Parameters such as limit of detection and voltammetric detection sensitivity are derived from the experimental data. Developed methodology was used to detect nitrazepam in pharmaceutical formulation and both drugs (nitrazepam and 7-aminonitrazepam) in spiked biological fluids (urine and blood).

Disposable-micropipette tip supported electrified liquid-organogel interface as a platform for sensing acetylcholine

Sensing acetylcholine has been predominantly based on enzymatic strategies using acetylcholine esterase and choline oxidase because of its electrochemical inertness. Electrified liquid-liquid interfaces are not limited to oxidation/reduction processes, and can be utilized to detect non-redox molecules which cannot be detected using conventional solid electrodes. In this study, a disposable micropipette tip based liquid-organogel interface, in the presence/absence of calixarene has been developed as a platform for sensing acetylcholine. We also explored a liquid-liquid interface approach for sensing acetylcholine using a pre-pulled glass micropipette. In both approaches, the configuration, i.e., liquid-organogel and liquid-liquid interface-current linearly increases during the backward transfer of acetylcholine. The simple and facilitated ion transfer of acetylcholine across the liquid-organogel exhibited a linear range of 10-50 μM and 1-30 μM with a detection limit of 0.18 μM and 0.23 μM and a sensitivity of 9.52 nA μM^-1 and 9.20 nA μM^-1, respectively. Whereas, the detection limit of simple and facilitated ion transfer of liquid-liquid interface using pre-pulled glass micropipette was found to be 0.42 μM and 0.13 μM with a sensitivity of 5 × 10^-3 nA μM^-1 and 3.39 × 10^-2 nA μM^-1. The results indicate that the liquid-organogel configuration supported on a disposable micropipette tip without any pre-fabrication is highly suitable for electrified soft interface sensing applications.

In-Capillary Photodeposition of Glyphosate-Containing Polyacrylamide Nanometer-Thick Films

The present research reports on in-water, site-specific photodeposition of glyphosate (GLP)-containing polyacrylamide (PAA-GLP) nanometer-thick films (nanofilms) on an inner surface of fused silica (fused quartz) microcapillaries presilanized with trimethoxy(octen-7-yl)silane (TMOS). TMOS was chosen because of the vinyl group presence in its structure, enabling its participation in the (UV light)-activated free-radical polymerization (UV-FRP) after its immobilization on a fused silica surface. The photodeposition was conducted in an aqueous (H₂O/ACN; 3:1, v/v) solution, using UV-FRP (λ = 365 nm) of the acrylamide (AA) functional monomer, the N,N'-methylenebis(acrylamide) (BAA) cross-linking monomer, GLP, and the azobisisobutyronitrile (AIBN) UV-FRP initiator. Acetonitrile (ACN) was used as the porogen and the solvent to dissolve monomers and GLP. Because of the micrometric diameters of microcapillaries, the silanization and photodeposition procedures were first optimized on fused silica slides. The introduction of TMOS, as well as the formation of PAA and PAA-GLP nanofilms, was determined using atomic force microscopy (AFM), scanning electron microscopy with energy-dispersive X-ray (SEM-EDX) spectroscopy, and confocal micro-Raman spectroscopy. Particularly, AFM and SEM-EDX measurements determined nanofilms' thickness and GLP content, respectively, whereas in-depth confocal (micro-Raman spectroscopy)-assisted imaging of PAA- and PAA-GLP-coated microcapillary inner surfaces confirmed the successful photodeposition. Moreover, we examined the GLP impact on polymer gelation by monitoring hydration in a hydrogel and a dried powder PAA-GLP. Our study demonstrated the usefulness of the in-capillary micro-Raman spectroscopy imaging and in-depth profiling of GLP-encapsulated PAA nanofilms. In the future, our simple and inexpensive procedure will enable the fabrication of polymer-based microfluidic chemosensors or adsorptive-separating devices for GLP detection, determination, and degradation.

Heroin detection in a droplet hosted in a 3D printed support at the miniaturized electrified liquid-liquid interface

Simple sensing protocols for the detection of illicit drugs are needed. Electrochemical sensing is especially attractive in this respect, as its cost together with the analytical accuracy aspires to replace still frequently used colorimetric tests. In this work, we have shown that the interfacial transfer of protonated heroin can be followed at the electrified water-1,2-dichloroethane interface. We have comprehensively studied the interfacial behavior of heroin alone and in the presence of its major and abundant cutting agents, caffeine and paracetamol. To maximally increase developed sensing protocol applicability we have designed and 3D printed a platform requiring only a few microliters of the aqueous and the organic phase. The proposed sensing platform was equipped with a cavity hosting a short section of Ag/AgCl electrode, up to 20 µL of the aqueous phase and the end of the micropipette tip being used as a casing of a fused silica capillary having 25 µm as the internal pore diameter. The volume of the organic phase was equal to around 5 µL and was present inside the micropipette tip. We have shown that under optimized conditions heroin can be detected in the presence of caffeine and paracetamol existing in a sample with 10,000 times excess over the analyte of interest. The calculated limit of detection equal to 1.3 µM, linear dynamic range spanning to at least 50 µM, good reproducibility, and very low volume of needed sample is fully in line with forensic demands.

Voltammetric study of cefotaxime at the macroscopic and miniaturized interface between two immiscible electrolyte solutions

The electrochemical behavior of cefotaxime (CTX⁺) was investigated at the polarized macro- and micro-interface between two immiscible electrolyte solutions (ITIES) by cyclic voltammetry and alternating current voltammetry. Miniaturization was achieved with fused silica microcapillary tubing entrapped in a polymeric casing. Scanning electron microscopy (SEM) was employed for the fabricated LLI support characterization. Voltammetric investigation of CTX⁺ at macro- and μ-ITIES allowed the determination of many physicochemical parameters, such as formal Galvani potential of the ion transfer reaction (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\Delta }_{org}^{aq}{\varPhi}^{\prime }$$\end{document}ΔorgaqΦ′), diffusion coefficients (D), formal free Gibbs energy of the ion transfer reaction (∆G^{′aq → org}), and water-1,2-dichloroethane partition coefficient (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\log}{P}_{water/ DCE}^{CTX+}$$\end{document}logPwater/DCECTX+). Additionally, based on the results obtained the analytical parameters including voltammetric sensitivity, limits of detection and the limits of quantification (in micromolar range) were calculated. The applicability of the developed procedures was verified in spiked still mineral and tap water samples.

Determination of quinine in tonic water at the miniaturized and polarized liquid-liquid interface

In this work we report an electrochemical approach to quantitative and qualitative analysis of quinine (QN) at the interface between two immiscible electrolyte solutions (ITIES). This was done at the macroscopic (macroITIES) and microscopic (µITIES) systems using ion transfer voltammetry (ITV). The linear response of the peak current vs. increasing concentrations of QN at the µITIES was from 2.50 µM to 29.13 µM and the corresponding calculated limit of detection (LOD) for the current signals originating from QN transfer from the aqueous to the organic phase was equal to 0.49 µM. Additionally, the influence of pH (2-12) of the aqueous phase on the recorded QN signals was investigated. We have found that our method is fully applicable for QN direct determination in non-treated tonic water, as confirmed on three different real samples from three different manufacturers. Finally, a number of validation parameters for the developed method are provided and discussed.

Electrified liquid-liquid interface as an electrochemical tool for the sensing of putrescine and cadaverine

Putrescine and cadaverine are biogenic amines that serve as potential biomarkers for several types of cancers and monitoring food quality. Electrochemical sensing of putrescine and cadaverine by non-enzymatic routes remains a challenge because of their inertness at unmodified electrode surfaces and hence a liquid-liquid interface strategy has been employed for their detection. In the present study, electrochemical sensing of cadaverine and putrescine has been demonstrated by simple and facilitated ion-transfer processes using a liquid-liquid microinterface supported by a microcapillary. A microinterface was constructed in different configurations by varying the aqueous phase composition in the absence and presence of dibenzo-18-crown-6, and the ion-transfer ability of putrescine and cadaverine was studied in these configurations. A peak shaped voltammogram was observed in the backward scan, due to the linear diffusion of putrescine and cadaverine from the organic to the aqueous phase. The detection ability in the presence of dibenzo-18-crown-6 was observed in the concentration ranges of 0.25-25 μM and 0.25-40 μM for putrescine and cadaverine with detection limits of 0.11 and 0.17 μM respectively. In the presence of dibenzo-18-crown-6, the electrochemical sensing of putrescine and cadaverine was more pronounced compared to the simple ion-transfer process.

Electrochemical study of ephedrine at the polarized liquid-liquid interface supported with a 3D printed cell

In this work, we have examined an electrochemical behavior of the ephedrine at the polarized liquid-liquid interface (water/1,2-dichloroethane). In this respect, we first designed and then 3D printed polyamide-based electrochemical cell that was used as the liquid-liquid interface support during electroanalytical measurements. The protonated ephedrine undergoes a reversible ion transfer reaction with the standard Galvani potential difference equal to +0.269 V. This value was used to calculate the water - 1,2-dichloroethane logP equal to -4.6. Ion transfer voltammetry was used to build the calibration curve and allowed for the ephedrine detection from concentration equal to 20 μM. By varying the pH of the aqueous phase from 2 up to 12 we were able to plot the ion partition diagram that was further analyzed and provided several pharmacochemical information. To further push this work towards practical utility, we have formulated the artificial urine and studied the interfacial behavior of all its components at the polarized liquid-liquid interface. Ephedrine detection from real spiked urine samples was also performed.

The development of a fully integrated 3D printed electrochemical platform and its application to investigate the chemical reaction between carbon dioxide and hydrazine

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An integrated electrochemical platform was manufactured by bi-material 3D printing.

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It was applied to investigate the reaction between hydrazine and carbon dioxide.

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Experimental results were supported by finite-element method numerical simulations.

The combination of computer assisted design and 3D printing has recently enabled fast and inexpensive manufacture of customized ‘reactionware’ for broad range of electrochemical applications. In this work bi-material fused deposition modeling 3D printing is utilized to construct an integrated platform based on a polyamide electrochemical cell and electrodes manufactured from a polylactic acid-carbon nanotube conductive composite. The cell contains separated compartments for the reference and counter electrode and enables reactants to be introduced and inspected under oxygen-free conditions. The developed platform was employed in a study investigating the electrochemical oxidation of aqueous hydrazine coupled to its bulk reaction with carbon dioxide. The analysis of cyclic voltammograms obtained in reaction mixtures with systematically varied composition confirmed that the reaction between hydrazine and carbon dioxide follows 1/1 stoichiometry and the corresponding equilibrium constant amounts to (2.8 ± 0.6) × 10³. Experimental characteristics were verified by results of numerical simulations based on the finite-element-method.