Impedimetric Sensor of ss-HSDNA/Reduced Graphene Oxide Aerogel Electrode toward Aflatoxin B1 Detection: Effects of Redox Mediator Charges and Hydrodynamic Diffusion

Here, an impedimetric biosensor for determination and quantification of an aflatoxin B1 (AFB1) level using a reduced graphene oxide aerogel labeled with a single strand DNA (ss-HSDNA/rGO_ae) modified on a rotating disk electrode (RDE) is presented. Owing to the large biomolecule biding on the electrode, an electron transfer is interrupted and not easily accessible to a target molecule. To address this issue, we aim to study two effects; one considers electro-redox mediators and the other considers the hydrodynamic effect. By observing a cyclic voltammetric response from the ss-HSDNA/rGO_ae electrode in three different charges of the redox mediators (i.e., neutral FcCH₂OH, cationic Ru­(NH₃)₆³⁺, and anionic Fe­(CN)₆^4–) in a phosphate buffer solution (PBS) containing AFB1, the magnitude of anodic current at 50 mV s^–1 is 825, 615, and 550 mA cm^–1, respectively, which is significant dominated by the charge of the redox probe. The effect of hydrodynamic diffusion of the ss-HSDNA/rGO_ae rotating disk electrode (RDE) toward AFB1 detection using FcCH₂OH as the redox mediator was recorded by applying a range of rotating speed from 500 to 4000 rpm. Increasing rotating speed reduces the charge transfer resistance resulting in the lower detectable level for AFB1 quantification. In the case of 4000 rpm, the AFB1 can be detected with a limit of detection of 0.04 ng/mL and a linear range of 1 × 10^–10 to 7 × 10^–8g/mL

Data from: Antifungal activity of water-stable copper-containing metal–organic frameworks

Although metal-organic frameworks (MOFs) or porous coordination polymers have been widely studied, their antimicrobial activities have not yet been fully investigated. In this work, antifungal activity of copper-based benzene-tricarboxylate MOF (Cu-BTC MOF), which is water stable and industrially interesting, is investigated against Candida albicans, Aspergillus niger, Aspergillus oryzae and Fusarium oxysporum. The Cu-BTC MOF can effectively inhibit the growth rate of C. albicans and remarkably inhibit the spore growth of A. niger, A. oryzae and F. oxysporum. This finding shows the potential of using Cu-BTC MOF as a strong biocidal material against representative yeasts and moulds that are commonly found in the food and agricultural industries

Comparing the effect of different surfactants on the aggregation and electrical contact properties of graphene nanoplatelets

We report the influence of different surfactants, Triton X-100, sodium dodecyl sulfate (SDS) and cetrimonium bromide (CTAB), on the suspended graphene nanoplatelets (GNPs) in aqueous solution studied via a single entity electrochemical technique. This method simply requires recording the current responses resulting from the impacts of individual and aggregated GNPs with an interdigitated gold electrode array. Upon impact the nanomaterial can bridge across two interdigitated gold microbands creating an electrical contact. The current magnitude reflects both the agglomeration state of the material and the contact resistance between the gold array and the carbon nanomaterial. The sensitivity of the magnitude of the current steps to the identity of the used surfactant was further evidenced, indicating the influence of these surfactants upon the electrical connectivity of the nanomaterial to the electrode substrate

Electrolyte induced electrical dis-connection between single graphene nanoplatelets and an electrode

We report the influence of electrolyte on the electrical contact between graphene nanoplates (GNPs) and an electrode via a single entity electrochemical technique. The current 'steps' were observed in the absence of electrolyte due to the GNPs impacting on and bridging across an interdigitated gold electrode array (IDE), in contrast current spikes of short duration were obtained in the presence of electrolyte. This result indicates that in the latter case the constant short circuit bridging current was switched off and replaced solely by impacts of GNPs with single electrodes. These observed current spikes measured in the presence of electrolyte are evidenced to be of a capacitative nature, demonstrating the high sensitivity of the electronic properties of the GNPs/metal junction to the ionic strength of the electrolytic solution

Electrolyte induced electrical dis-connection between single graphene nanoplatelets and an electrode

We report the influence of electrolyte on the electrical contact between graphene nanoplates (GNPs) and an electrode via a single entity electrochemical technique. The current 'steps' were observed in the absence of electrolyte due to the GNPs impacting on and bridging across an interdigitated gold electrode array (IDE), in contrast current spikes of short duration were obtained in the presence of electrolyte. This result indicates that in the latter case the constant short circuit bridging current was switched off and replaced solely by impacts of GNPs with single electrodes. These observed current spikes measured in the presence of electrolyte are evidenced to be of a capacitative nature, demonstrating the high sensitivity of the electronic properties of the GNPs/metal junction to the ionic strength of the electrolytic solution

Palladium Nanoparticles Decorated on Reduced Graphene Oxide Rotating Disk Electrodes toward Ultrasensitive Hydrazine Detection: Effects of Particle Size and Hydrodynamic Diffusion

Although metal nanoparticle/graphene composites have been widely used as the electrode in electrochemical sensors, two effects, consisting of the particle size of the nanoparticles and the hydrodynamic diffusion of analytes to the electrodes, are not yet fully understood. In this work, palladium nanoparticles/reduced graphene oxide (PdNPs/rGO) composites were synthesized using an in situ polyol method. Palladium­(II) ions and graphene oxide were reduced together with a reducing agent, ethylene glycol. By varying the concentration of palladium­(II) nitrate, PdNPs with different sizes were decorated on the surface of rGO sheets. The as-fabricated PdNPs/rGO rotating disk electrodes (RDEs) were investigated toward hydrazine detection. Overall, a 3.7 ± 1.4 nm diameter PdNPs/rGO RDE exhibits high performance with a rather low limit of detection of about 7 nM at a rotation speed of 6000 rpm and provides a wide linear range of 0.1–1000 μM with <i>R</i>² = 0.995 at 2000 rpm. This electrode is highly selective to hydrazine without interference from uric acid, glucose, ammonia, caffeine, methylamine, ethylenediamine, hydroxylamine, <i>n</i>-butylamine, adenosine, cytosine, guanine, thymine, and l-arginine. The PdNPs/rGO RDEs with larger sizes show lower detection performance. Interestingly, the detection performance of the electrodes is sensitive to the hydrodynamic diffusion of hydrazine. The as-fabricated electrode can detect trace hydrazine in wastewater with high stability, demonstrating its practical use as an electrochemical sensor. These findings may lead to an awareness of the effect of the hydrodynamic diffusion of analyte that has been previously ignored, and the 3.7 ± 1.4 nm PdNPs/rGO RDE may be useful toward trace hydrazine detection, especially in wastewater from related chemical industries

The solution phase aggregation of graphene nanoplates

The occurrence of particle aggregation, especially for two-dimensional (2D) nanoparticles, in the solution phase is an important practical problem. Aggregation influences the materials’ properties and behavior. This work studies the re-stacking process of graphene nanoplates (GNPs) in colloids and suspensions by a simple and highly sensitive technique in which the current responses resulting from the impacts of individual and aggregated particles which bridge across two interdigitated gold microbands are detected. The magnitude of the steps in current varies as a function of time and yield clear in situ information regarding the formation of GNP aggregation

Antifungal activity results of CuBTC againt Fungi

Antifungal activity results of CuBTC againt Fung

The solution phase aggregation of graphene nanoplates

The occurrence of particle aggregation, especially for two-dimensional (2D) nanoparticles, in the solution phase is an important practical problem. Aggregation influences the materials’ properties and behavior. This work studies the re-stacking process of graphene nanoplates (GNPs) in colloids and suspensions by a simple and highly sensitive technique in which the current responses resulting from the impacts of individual and aggregated particles which bridge across two interdigitated gold microbands are detected. The magnitude of the steps in current varies as a function of time and yield clear in situ information regarding the formation of GNP aggregation