MoS2 quantum dots-based optical sensing platform for the analysis of synthetic colorants. Application to quinoline yellow determination

In this work, a novel fluorescence sensor has been designed to solve the actual need of new fast and inexpensive sensing platforms for the analysis of synthetic colorants. It is based on MoS2 quantum dots obtained by a hydrothermal method and incorporated as fluorophore into the matrix of PVC membranes, which are deposited on quartz substrates by spin-coating. It was proven, as in these conditions, MoS2 quantum dots maintain the fluorescent properties that they present in solution. Experiments carried out in solution displayed a maximum emission when they were excited under 310 nm. This initial fluorescence decreases linearly in presence of increasing concentrations of various synthetic colorants namely quinoline yellow, tartrazine, sunset yellow, allura red, ponceau 4R and carmoisine. The two possible mechanisms that can explain this quenching effect, colorants absorbing photons emitted by quantum dots and/or competing with the nanomaterial for photons coming from the excitation source, were evaluated. The most pronounced effect was observed with quinoline yellow, as a result of a mixed mechanism. The optimized methodology developed for the determination of quinoline yellow showed a linear concentration range between 5.4 and 55.0 µg with a limit of detection of 1.6 µg. The sensor was applied to the determination of quinoline yellow in a food colour paste obtaining results in good agreement with those obtained by HPLC-UV–vis measurementsThe authors acknowledge financial support from projects PID2020- 113142RB-C22 funded by MCIN/AEI/ 10.13039/501100011033 and P2018/NMT-4349 (TRANSNANOAVANSENS-CM) funded by the Comunidad Autónoma de Madrid. We thank A. Redondo and D. García for the profilometer measurement

MoS2 nanosheets for improving analytical performance of lactate biosensors

In this paper, a new 2D lactate electrochemical biosensor was developed. It was based on the incorporation of molybdenum disulfide (MoS2) nanosheets, obtained by an exfoliation method, onto the surface of a glassy carbon (GC) electrode, together with lactate oxidase enzyme (LOx). For the sensor construction, conditions regarding the exfoliation solvent type, as well as both the size and amount of MoS2, were optimized. The biosensor platform (GC/MoS2/LOx) was topographically characterized by atomic force microscopy (AFM) and the charge transfer process occurring at the electrode interface was studied by electrochemical impedance spectroscopy (EIS). The GC/MoS2/LOx biosensor was applied to the determination of lactate in presence of hydroxymethylferrocene (HMF) as a redox mediator. Electrocatalytic effect of the system MoS2/LOx was evaluated by comparing the cyclic voltammetric biosensor response with those obtained for biosensors incorporating only one of the components (MoS2 or LOx) onto the electrode surface. Biosensors containing both components exhibit the best electrocatalytic response. From the calibration curve obtained at +0.30 V, the following analytical parameters were obtained: linear concentration range from 0.056 to 0.77 mM, high sensitivity (6.2 μA mM−1), good detection limit (17 μM) and reproducibility (RSD = 4.7%)The authors would like to thank Ministerio de Economía, Industria y Competitividad (MAT2017-85089-C2-1-R, MAT2017-85089-C2-2-R) and the Comunidad Autónoma de Madrid (S2013/MIT-3029, NANOAVANSENS) for financial suppor

A supramolecular hybrid sensor based on cucurbit[8]uril, 2D-molibdenum disulphide and diamond nanoparticles towards methyl viologen analysis

We develop an electrochemical sensor by using 2D-transition metal dichalcogenides (TMD), specifically MoS2, and nanoparticles stabilized with cucurbit[8]uril (CB[8]) incorporated together with them. Two different nanoparticles are assayed: diamond nanoparticles (DNPs) and gold nanoparticles (AuNp). 0D materials, together with TMD, provide increased conductivity and active surface while the macrocycle CB[8] affords selectivity towards the guest methyl viologen (MV2+), also named paraquat. Glassy Carbon (GC) electrodes are modified by drop-casting of suspensions of MoS2, followed by either a CB[8]-DNPs hybrid dispersion or a CB[8]-AuNp suspension. Atomic force microscopy is employed for the morphological characterization of the electrochemical sensor surface while cyclic voltammetry and electrochemical impedance spectroscopy techniques allow the electrochemical characterization of the sensor. The well-stablished signals of CB[8]-encapsulated MV2+ arise in voltammetric measurements when the macrocycle modifies the 0D-materials. Once the sensor construction and differential pulse voltammetry parameters have been optimized for quantification purposes, calibration procedures are performed with the platform GC/MoS2/CB[8]-DNPs. This sensing platform shows linear relations between peak intensity and the MV2+ concentration in the linear concentration range of (0.73–8.0) · 10−6 M with a limit of detection of 2.2 · 10−7 M. Analyses of river water samples fortified with MV2+ at the μM level shows recoveries of 100% with RSD values of 6.4% (n = 3)The authors acknowledge financial support from the Spanish MINECO ( MAT2017-85089-C2-1-R , MAT2017-85089-C2-2-R , PID2020-113142RB-C21 , PID2020-113142RB-C22 ) and the Comunidad Autónoma de Madrid ( P2018/NMT-4349 , TRANSNANOAVANSENS-CM)

2D-ReS2 & diamond nanoparticles-based sensor for the simultaneous determination of sunset yellow and tartrazine in a multiple-pulse amperometry FIA system

We present a flow injection system with a multiple pulse amperometric detection (FIA-MPA)-based methodology for the simultaneous analysis of sunset yellow and tartrazine. As transducer, we have developed a novel electrochemical sensor based on the synergistic effect of ReS2 nanosheets and diamond nanoparticles (DNPs). Among several transition dichalcogenides for the sensor development, we have selected ReS2 nanosheets since it yields a better response towards both colourants. Scanning probe microscopy characterization shows that the surface sensor is composed by scattered and stacked ReS2 flakes and large aggregates of DNPs. With this system, the gap between the oxidation potential values of sunset yellow and tartrazine is wide enough to allow the simultaneous determination of both dyes. Under the optimum potential pulse conditions (0.8 and 1.2 V) during 250 ms, a flow rate of 3 mL/min and a volume injection of 250 μL, detection limits of 3.51 × 10− 7 M and 2.39 × 10− 7 M for sunset yellow and tartrazine, respectively, were obtained. This method exhibits good accuracy and precision with Er minor than 13% and RSD lower than 8% with a sampling frequency of 66 samples per hour. Pineapple jelly samples were analyzed by the standard addition method, obtaining 53.7 mg/kg and 29.0 mg/kg of sunset yellow and tartrazine, respectively. From the analysis of fortified samples, recoveries of 94% and 105% were obtainedThe authors acknowledge financial support from projects PID2020- 113142RB-C21 and PID2020-113142RB-C22 and TED2021-129416 AI00 funded by MCIN/AEI/10.13039/501100011033 and P2018/NMT4349 (TRANSNANOAVANSENS-CM) funded by the Comunidad Autonoma ´ de Madrid. We thank L. Chico for fruitful discussion

Synergistic effect of manganese (II) phosphate & diamond nanoparticles in electrochemical sensors for reactive oxygen species determination in seminal plasma

In this work, we explore the ability of manganese (II) phosphate (MnP) as a catalytic element for the determination of reactive oxygen species (ROS) in seminal plasma, when MnP is employed as modifier of a glassy carbon electrode. The electrochemical response of the manganese (II) phosphate-modified electrode shows a wave at around +0.65 V due to the oxidation of Mn2+ to MnO2+, which is clearly enhanced after addition of superoxide, the molecule considered as the mother of ROS. Once proved the suitability of manganese (II) phosphate as catalyst, we evaluate the effect of including a 0D (diamond nanoparticles) or a 2D (ReS2) nanomaterial in the sensor design. The system consisting of manganese (II) phosphate and diamond nanoparticles yielded the largest improvement of the response. The morphological characterization of the sensor surface was performed by scanning electron microscopy and atomic force microscopy, while cyclic and differential pulse voltammetry were employed for the electrochemical characterization of the sensor. After optimizing the sensor construction, calibration procedures by chronoamperometry were performed, leading to a linear relation between peak intensity and the superoxide concentration in the range of 1.1 10−4 M − 1.0 10−3 M with a limit of detection of 3.2 10−5 M. Seminal plasma samples were analysed by the standard addition method. Moreover, the analysis of samples fortified with superoxide at the μM level leads to recoveries of 95%The authors acknowledge financial support from projects PID2020- 113142RB-C21 and PID2020-113142RB-C22 and TED2021-129416AI00 funded by MCIN/AEI/10.13039/501100011033 and P2018/NMT4349 (TRANSNANOAVANSENS-CM) funded by the Comunidad Autonoma ´ de Madrid. We thank I. Ballesteros for the SEM measurements and Noemí Gonz´ alez Díaz from the Interdepartmental Research Service (SIDI) of the Universidad Autonoma ´ de Madrid for the XRD measurement

Fluorescence enhancement of fungicide thiabendazole by van der Waals interaction with transition metal dichalcogenide nanosheets for highly specific sensors

Many molecules quench their fluorescence upon adsorption on surfaces. Herein we show that the interaction of thiabendazole, a widespread used fungicide of the benzimidazole family, with nanosheets of transition metal dichalcogenides, particularly of WS2, leads to a significant increase, more than a factor of 5, of the fluorescence yield. This surprising effect is rationalized by DFT calculations and found to be related to the inhibition of the intramolecular rotation between the benzimidazole and thiazole groups due to a bonding rigidization upon interaction with the MoS2 surface. This non-covalent adsorption leads to a redistribution of the molecular LUMO that blocks the non-radiative energy dissipation channel. This unusual behaviour does not operate either for other molecules of the same benzimidazole family or for other 2D materials (graphene or graphene oxide). Moreover, we found that a linear dependence of the emission with the concentration of thiabendazole in solution, which combined with the specificity of the process, allows the development of a highly sensitive and selective method towards thiabendazole determination that can be applied to real river water samples. An excellent detection limit of 2.7 nM, comparable to the best performing reported methods, is obtained with very good accuracy (Er ≤ 6.1%) and reproducibility (RSD ≤ 4.1%) in the concentration range assayedThe authors acknowledge financial support from the Spanish MINECO (MAT2017-85089-C2-1-R, MAT2017-85089-C2-2-R) and the EU via the ERC-Synergy Program (grant ERC-2013-SYG-610256 NANOCOSMOS) and Horizon 2020 Research and Innovation Program (Graphene Flagship-core2 – 785219) and the Comunidad Autónoma de Madrid (P2018/NMT-4349, TRANSNANOAVANSENS-CM and P2018/NMT-4367 FOTOART). J. I. M. acknowledges the support by the “Ramón y Cajal” Program of MINECO (grant RYC-2015-17730

Unveiling the collaborative effect at the cucurbit[8]urilMoS2 hybrid interface for electrochemical melatonin determination

Host-guest interactions are of paramount importance in supramolecular chemistry and in a wide range of applications. Particularly well known is the ability of cucurbit[n]urils (CB[n]) to selectively host small molecules. We show that the charge transfer and complexation capabilities of CB[n] are retained on the surface of 2D transition metal dichalcogenides (TMDs), allowing the development of efficient electrochemical sensing platforms. We unveil the mechanisms of host-guest recognition between the MoS2- CB[8] hybrid interface and melatonin (MLT), an important molecular regulator of vital constants in vertebrates. We find that CB[8] on MoS2 organizes the receptor portals perpendicularly to the surface, facilitating MLT complexation. This advantageous adsorption geometry is specific to TMDs and favours MLT electro-oxidation, as opposed to other 2D platforms like graphene, where one receptor portal is closed. This study rationalises the cooperative interaction in 2D hybrid systems to improve the efficiency and selectivity of electrochemical sensing platform

Estudio electroanalítico de dihidrozeatina y dihidrozeatina ribosa

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Analítica. Fecha de lectura: 15-06-199

Lactate biosensing based on covalent immobilization of lactate oxidase onto chevron-like graphene nanoribbons via diazotization-coupling reaction

We have designed and prepared an electrochemical biosensor for lactate determination. Through a diazotation process, the enzyme lactate oxidase (LOx) is anchored onto chevron-like graphene nanoribbons (GNR), previously synthesized by a solution-based chemical route, and used as modifiers of glassy carbon electrodes. In a first step, we have performed the grafting of a 4-carboxyphenyl film, by electrochemical reduction of the corresponding 4-carboxyphenyl diazonium salt, on the GNR-modified electrode surface. In this way, the carboxylic groups are exposed to the solution, enabling the covalent immobilization of the enzyme through the formation of an amide bond between these carboxylic groups and the amine groups of the enzyme. The biosensor design was optimized through the morphological and electrochemical characterization of each construction step by atomic force microscopy, scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy.The cyclic voltammetric response of the biosensor in a solution of hydroxymethylferrocene in presence of Llactate evidenced a clear electrocatalytic effect powered by the specific design of the biosensing platform with LOx covalently attached to the GNR layer. From the calibration procedures employed for L-lactate determination, a linear concentration range of 3.4 ⋅ 10− 5 – 2.8 ⋅ 10− 4 M and a detection limit of 11 μM were obtained, with relative errors and relative standard deviations less than 6.0% and 8.4%, respectively. The applicability of the biosensor was tested by determining lactate in apple juices, leading to results that are in good agreement with those obtained with a well-established enzymatic spectrophotometric assay kitThe authors acknowledge financial support from the European Union’s Horizon 2020 research and innovation programme (Project SPRING, grant agreement No 863098), the European Research Council (ERC) (Project MolDAM, grant agreement No 951519), Ministerio de Ciencia e Innovacion ´ of Spain (Grants MAT2017-85089-C2-1-R, MAT2017-85089-C2-2-R, PID2020-113142RB-C21, PID2020- 113142RB-C22) funded by MCIN/AEI/10.13039/501100011033, the Comunidad Autonoma ´ de Madrid (S2018/NMT-4349TRANSNANOAVANSENS-CM), the Xunta de Galicia (Centro singular de investigacion ´ de Galicia accreditation 2019–2022, ED431G 2019/03) and the European Union (European Regional Development Fund - ERDF). J. Castro thanks the Spanish MINECO and the European Social Fund for the predoctoral grant BES-2017-081094. We want to thank Ismael Ballesteros for the SEM measurement