Disposable electrochemical sensor: Highly sensitive determination of nitrofurazone antibiotic in environmental samples and pharmaceutical formulations.

The study presents the successful development of a new electrochemical sensor with low cost and disposability for application in nitrofurazone detection in environmental and pharmaceutical samples. The sensors were fabricated using materials obtained from local storage and conductive carbon ink. The modification of the screen-printed electrodes with the hybrid nanomaterial based on silver nanoparticles, carbon quantum dots, and carbon nanotubes showed synergistic contributions in the nitrofurazone electrooxidation, as observed in the wide linear range (0.008 at 15.051 µM), with a sensitivity of 0.650 µA/µM. The limit of detection obtained was 4.6 nM. Differential pulse voltammetry, cyclic voltammetry, X-ray photoelectron spectroscopy, X-ray diffraction analysis, and high-resolution transmission electron microscopy were used to evaluate the electrochemical and structural characteristics. Studies of possible interferences were considered with nitrofurazone in the presence of the ions and organic molecules. The results were satisfactory, with a variation of 93.3% ± 4.39% at 100% ± 2.40%. The low volume used in the analyses (50 µL), disposability, high sensibility, selectivity, and low limit of detection are advantages that make the proposed sensor an electrochemical tool of high viability for the NFZ detection in environmental matrices and pharmaceutical formulations.

Non-enzymatic biosensor based on F,S-doped carbon dots/copper nanoarchitecture applied in the simultaneous electrochemical determination of NADH, dopamine, and uric acid in plasma.

This work presents the synthesis and characterization of an innovative F,S-doped carbon dots/CuONPs hybrid nanostructure obtained by a direct mixture between F,S-doped carbon dots obtained electrochemically and copper nitrate alcoholic solution. The hybrid nanostructures synthesized were characterized by absorption spectroscopy in the Ultraviolet region (UV-vis), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and different electrochemical techniques. The fluoride and sulfur-doped carbon dots/CuONPs nanostructures were used to prepare a non-enzymatic biosensor on a printed carbon electrode, exhibiting excellent electrocatalytic activity for the simultaneous determination of NADH, dopamine, and uric acid in the presence of ascorbic acid with a detection limit of 20, 80, and 400 nmol L-1, respectively. The non-enzymatic biosensors were also used to determine NADH, dopamine, and uric acid in plasma, and they did not suffer significant interference from each other.

Fragmenting nanoPutians: Capturing admiration to the rationality, predictability, and beauty of ion chemistry in mass spectrometry.

The fragmentation chemistry of the protonated and ionized nanoPutian 1 has been studied in the gas phase via electrospray ionization and tandem mass spectrometry. A direct analogy was observed between the fragmentation chemistry of this fascinating "humanoid molecule" and "cleavages" at certain parts of the human body. We argue that such direct analogy and illustrative schemes for the fragmentation of molecular ions of 1 offer a ludic and efficient tool to teach and capture attention to ion chemistry in mass spectrometry. Using the changes in mass for the two heavier nanoPutians with different head styles but the same body design, the analogy has also been used to predict mass spectra. The concepts of isotopic labelling and dissociation thresholds have also been illustrated. For many years, the approach has been successfully used by one of us in classes and lectures, mainly when presenting ion chemistry to students and audiences from fields other than Chemistry, most particularly from Biology, Medicine, and Forensic Chemistry.

Rapid Screening of COVID-19 Directly from Clinical Nasopharyngeal Swabs Using the MasSpec Pen.

The outbreak of COVID-19 has created an unprecedent global crisis. While the polymerase chain reaction (PCR) is the gold standard method for detecting active SARS-CoV-2 infection, alternative high-throughput diagnostic tests are of a significant value to meet universal testing demands. Here, we describe a new design of the MasSpec Pen technology integrated to electrospray ionization (ESI) for direct analysis of clinical swabs and investigate its use for COVID-19 screening. The redesigned MasSpec Pen system incorporates a disposable sampling device refined for uniform and efficient analysis of swab tips via liquid extraction directly coupled to an ESI source. Using this system, we analyzed nasopharyngeal swabs from 244 individuals including symptomatic COVID-19 positive, symptomatic negative, and asymptomatic negative individuals, enabling rapid detection of rich lipid profiles. Two statistical classifiers were generated based on the lipid information acquired. Classifier 1 was built to distinguish symptomatic PCR-positive from asymptomatic PCR-negative individuals, yielding a cross-validation accuracy of 83.5%, sensitivity of 76.6%, and specificity of 86.6%, and validation set accuracy of 89.6%, sensitivity of 100%, and specificity of 85.3%. Classifier 2 was built to distinguish symptomatic PCR-positive patients from negative individuals including symptomatic PCR-negative patients with moderate to severe symptoms and asymptomatic individuals, yielding a cross-validation accuracy of 78.4%, specificity of 77.21%, and sensitivity of 81.8%. Collectively, this study suggests that the lipid profiles detected directly from nasopharyngeal swabs using MasSpec Pen-ESI mass spectrometry (MS) allow fast (under a minute) screening of the COVID-19 disease using minimal operating steps and no specialized reagents, thus representing a promising alternative high-throughput method for screening of COVID-19.

A nano-magnetic electrochemical sensor for the determination of mood disorder related substances.

The simultaneous electrochemical detection of mood disorder related substances, such as amitriptyline, melatonin and tryptophan, was successfully achieved by using a novel nano-magnetic electrochemical sensor design, encompassing Fe3O4 nanoparticles decorated with carbon quantum dots (MagNPs/Cdots). The magnetic composite was characterized using HR-TEM microscopy, XRD and Raman spectroscopy, and was applied onto a glassy carbon electrode using a miniature neodymium magnet. The determination of amitriptyline, melatonin and tryptophan was performed by monitoring oxidation promoted by MagNPs/Cdots in BR-buffer at pH 3.0, which proceeded according to well-defined differential pulse voltammetry peaks, with detection limits of 5.9, 4.4 and 4.2 nmol L-1, respectively. No significant interference was seen from biological interferents such as uric acid, ascorbic acid, dopamine, estriol and 17ß-estradiol. The magnetic hybrid material was highly stable in solution, opening exciting opportunities for the development of low cost and practical electrochemical sensors for the determination of mood disorder related substances in real clinical samples.

Decoration of reduced graphene oxide with rhodium nanoparticles for the design of a sensitive electrochemical enzyme biosensor for 17ß-estradiol.

A novel nanocomposite material consisting of reduced graphene oxide/Rh nanoparticles was prepared by a one-pot reaction process. The strategy involved the simultaneous reduction of RhCl3 and graphene oxide with NaBH4 and the in situ deposition of the metal nanoparticles on the 2D carbon nanomaterial planar sheets. Glassy carbon electrode coated with this nanocomposite was employed as nanostructured support for the cross-linking of the enzyme laccase with glutaraldehyde to construct a voltammperometric biosensor for 17ß-estradiol in the 0.9-11 pM range. The biosensor showed excellent analytical performance with high sensitivity of 25.7AµM-1cm-1, a very low detection limit of 0.54pM and high selectivity. The biosensor was applied to the rapid and successful determination of the hormone in spiked synthetic and real human urine samples.

Electrochemical immunosensor for ethinylestradiol using diazonium salt grafting onto silver nanoparticles-silica-graphene oxide hybrids.

This work describes the preparation of an electrochemical immunosensor for ethinylestradiol (EE2) based on grafting of diazonium salt of 4-aminobenzoic acid onto a glassy carbon electrode modified with silver nanoparticles/SiO2/graphene oxide hybrid followed by covalent binding of anti-ethinylestradiol (anti-EE2) to activated carboxyl groups. A competitive immunoassay was developed for the determination of the hormone using peroxidase-labeled ethinylestradiol (HRP-EE2) and measurement of the amperometric response at -200mV in the presence of hydroquinone (HQ) as redox mediator. The calibration curve for EE2 exhibited a linear range between 0.1 and 50ng/mL (r(2)=0.996), with a detection limit of 65pg/mL. Interference studies with other hormones related with EE2 revealed the practical specificity of the developed method for the analyte. A good reproducibility, with RSD=4.5% (n=10) was also observed. The operating stability of a single bioelectrode modified with anti-EE2 was maintained at least for 15 days when it was stored at 4°C under humid conditions between measurements. The developed immunosensor was applied to the analysis of spiked urine with good results.

Sensitive determination of carbendazim in orange juice by electrode modified with hybrid material.

This paper describes the application of a glassy carbon electrode modified with a thin film of mesoporous silica/multiwalled carbon nanotubes for voltammetric determination of the fungicide carbendazim (CBZ). The hybrid material, (SiO2/MWCNT), was obtained by a sol-gel process using HF as the catalyst. The amperometric response to CBZ was measured at +0.73 V vs. Ag/AgCl by square wave voltammetry at pH 8.0. SiO2/MWCNT/GCE responded to CBZ in the linear range from 0.2 to 4.0 µmol L(-1). The calculated detection limit was 0.056 µmol L(-1), obtained using statistical methods. The SiO2/MWCNT/GCE sensor presented as the main characteristics high sensitivity, low detection limit and robustness, allowing CBZ determination in untreated real samples. In addition, this strategy afforded remarkable selectivity for CBZ against ascorbic and citric acid which are the main compounds of the orange juice. The excellent sensitivity and selectivity yielded feasible application for CBZ detection in orange juice sample.

Simultaneous determination of epinephrine and dopamine by electrochemical reduction on the hybrid material SiO2/graphene oxide decorated with Ag nanoparticles.

This paper describes the synthesis, characterization and applications of a new hybrid material composed of mesoporous silica (SiO2) modified with graphene oxide (GO), SiO2/GO, obtained by the sol-gel process using HF as the catalyst. The hybrid material, SiO2/GO, was decorated with silver nanoparticles (AgNPs) with a size of less than 20 nanometres, prepared directly on the surface of the material using N,N-dimethylformamide (DMF) as the reducing agent. The resulting material was designated as AgNP/SiO2/GO. The Ag/SiO2/GO material was characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and high-resolution transmission electron microscopy (HR-TEM). A glassy carbon electrode modified with AgNP/SiO2/GO was used in the development of a sensitive electrochemical sensor for the simultaneous determination of epinephrine and dopamine employing electrocatalytic reduction using squarewave voltammetry. Well-defined and separate reduction peaks were observed in PBS buffer at pH 7. No significant interference was seen for primarily biological interferents such as uric acid and ascorbic acid in the detection of dopamine and epinephrine. Our study demonstrated that the resultant AgNP/SiO2/GO-modified electrode is highly sensitive for the simultaneous determination of dopamine and epinephrine, with the limits of detection being 0.26 and 0.27 µmol L(-1), respectively. The AgNP/SiO2/GO-modified electrode is highly selective and can be used to detect dopamine and epinephrine in a human urine sample.

Sol-gel thin-film based mesoporous silica and carbon nanotubes for the determination of dopamine, uric acid and paracetamol in urine.

This work describes the preparation, characterization and application of a hybrid material composed of disordered mesoporous silica (SiO2) modified with multiwalled carbon nanotubes (MWCNTs), obtained by the sol-gel process using HF as the catalyst. This hybrid material was characterized by N2 adsorption-desorption isotherms, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission microscopy (HR-TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). This new hybrid material was used for the construction of a thin film on a glassy carbon electrode. The modified electrode using this material was designated SiO2/MWCNT/GCE. The electrocatalytic properties of the electrode toward dopamine, uric acid and paracetamol oxidation were studied by differential pulse voltammetry. Well-defined and separated oxidation peaks were observed in phosphate buffer solution at pH 7.0, in contrast with the ill-defined peaks observed with unmodified glassy carbon electrodes. The electrode had high sensitivity for the determination of dopamine, uric acid and paracetamol, with the limits of detection obtained using statistical methods, at 0.014, 0.068 and 0.098 µmol L(-1), respectively. The electrode presented some important advantages, including enhanced physical rigidity, surface renewability by polishing and high sensitivity, allowing the simultaneous determination of these three analytes in a human urine sample.

Simultaneous electroanalytical determination of hydroquinone and catechol in the presence of resorcinol at an SiO2/C electrode spin-coated with a thin film of Nb2O5.

This paper describes the development, characterization and application of an Nb(2)O(5) film formed on the surface of a carbon ceramic material, SiO(2)/C, obtained by a sol-gel method, using the spin-coating technique. The working electrode using this material will be designated as SiCNb. Hydroquinone and catechol can be oxidized at this electrode in the presence of resorcinol, allowing their simultaneous detection. The electrochemical properties of the resulting electrode were investigated using cyclic and differential pulse voltammetry techniques. Well-defined and separated oxidation peaks were observed by differential pulse voltammetry in Tris-HCl buffer solution at pH 7 containing 1 mol L(-1) KCl in the supporting electrolyte solution. The SiCNb electrode exhibited high sensitivity in the simultaneous determination of hydroquinone and catechol in the presence of resorcinol, with the limits of detection for hydroquinone and catechol being 1.6 µmol L(-1) and 0.8 µmol L(-1), respectively. Theoretical calculations were performed to determine the ionization energies of hydroquinone, catechol and resorcinol; the results were used to explain the simultaneous determination of species by differential pulse voltammetry. The presence of resorcinol did not produce any interference in the simultaneous detection of hydroquinone and catechol on the surface of the modified electrode.

SiO2/SnO2/Sb2O5 microporous ceramic material for immobilization of Meldola's blue: application as an electrochemical sensor for NADH.

The mixed oxide SiO(2)/SnO(2), containing 25 wt% of SnO(2), determined by X-ray fluorescence, was prepared by the sol-gel method and the porous matrix obtained was then grafted with Sb (V), resulting the solid designated as (SiSnSb). XPS indicated 0.7% of Sb atoms on the surface. Sb grafted on the surface contains Brønsted acid centers (SbOH groups) that can immobilize Meldola's blue (MB(+)) cationic dye onto the surface by an ion exchange reaction, resulting the solid designated as (SiSnSb/MB). In the present case a surface concentration of MB(+)=2.5×10(-11) mol cm(2) on the surface was obtained. A homogeneous mixture of the SiSnSb/MB with ultra pure graphite (99.99%) was pressed in disk format and used to fabricate a working electrode that displayed an excellent specific electrocatalytic response to NADH oxidation, with a formal potential of -0.05 V at pH 7.3. The electrochemical properties of the resulting electrode were investigated thoroughly with cyclic voltammetric and chronoamperometry techniques. The proposed sensor showed a good linear response range for NADH concentrations between 8×10(-5) and 9.0×10(-4) mol L(-1), with a detection limit of 1.5×10(-7) mol L(-1). The presence of dopamine and ascorbic acid did not show any interference in the detection of NADH on this modified electrode surface.