Electrochemical impedimetry of electrodeposited poly(propylene imine) dendrimer monolayer

Electrochemical detection of nicotine at a carbon Nanofiber-Poly(amidoamine) dendrimer modified glassy carbon electrode

Development of electrochemical sensors for important drugs such nicotine (an addictive drug) is important for the society. This study reports the electrochemical detection of nicotine at a carbon nanofiber/poly (amidoamine) dendrimer modified glassy carbon electrode. The carbon nanofiber (CNF) modified GCE was prepared by drop-coating followed by the electrodeposition of generation 4 poly (amidoamine) succinamic acid dendrimer (PAMAM) to form the sensor - CNF-PAMAM GCE. Characterization of prepared materials and modified electrodes was carried out using Fourier transmission infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The CNF-PAMAM composite was confirmed by microscopy. A marked reduction in charge transfer resistance and increase in current of the CNF-PAMAM GCE in comparison to the bare electrode showed a synergic improvement electrochemical response because of the CNF-PAMAM nanocomposite. The CNF-PAMAM demonstrated an enhanced performance in the oxidation of nicotine in comparison to the bare GCE by shifting the anodic potential E_pa of nicotine from 0.9 V to 0.8 V. The electrochemical sensor achieved a detection limit (LOD) of 0.02637 μM in the concentration range of 0.4815-15.41 μM of nicotine in 0.1 M PBS at pH 7.5. The sensor ability to determine nicotine in real samples was assessed in cigarettes obtaining recovery percentages of 88.00 and 97.42%. The sensor demonstrated selectivity toward nicotine in the presence of interferences. Finally, the method was validated by ultraviolet-visible spectroscopy analysis.

An Electrochemical Cholesterol Biosensor Based on A CdTe/CdSe/ZnSe Quantum Dots-Poly (Propylene Imine) Dendrimer Nanocomposite Immobilisation Layer

We report the preparation of poly (propylene imine) dendrimer (PPI) and CdTe/CdSe/ZnSe quantum dots (QDs) as a suitable platform for the development of an enzyme-based electrochemical cholesterol biosensor with enhanced analytical performance. The mercaptopropionic acid (MPA)-capped CdTe/CdSe/ZnSe QDs was synthesized in an aqueous phase and characterized using photoluminescence (PL) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), X-ray power diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy. The absorption and emission maxima of the QDs red shifted as the reaction time and shell growth increased, indicating the formation of CdTe/CdSe/ZnSe QDs. PPI was electrodeposited on a glassy carbon electrode followed by the deposition (by deep coating) attachment of the QDs onto the PPI dendrimer modified electrode using 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC), and N-hydroxysuccinimide (NHS) as a coupling agent. The biosensor was prepared by incubating the PPI/QDs modified electrode into a solution of cholesterol oxidase (ChOx) for 6 h. The modified electrodes were characterized by voltammetry and impedance spectroscopy. Since efficient electron transfer process between the enzyme cholesterol oxidase (ChOx) and the PPI/QDs-modified electrode was achieved, the cholesterol biosensor (GCE/PPI/QDs/ChOx) was able to detect cholesterol in the range 0.1⁻10 mM with a detection limit (LOD) of 0.075 mM and sensitivity of 111.16 μA mM-1 cm-2. The biosensor was stable for over a month and had greater selectivity towards the cholesterol molecule.

PAMAM templated N,Pt co-doped TiO2 for visible light photodegradation of brilliant black

This study examined the photocatalytic degradation of an azo dye brilliant black (BB) using non-metal/metal co-doped TiO₂. N,Pt co-doped TiO₂ photocatalysts were prepared by a modified sol-gel method using amine-terminated polyamidoamine dendrimer generation 0 (PG0) as a template and source of nitrogen. Structural, morphological, and textural properties were evaluated using scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy (SEM/EDX), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), Fourier transform infrared (FTIR), Raman spectroscopy (RS), photoluminescence (PL) and ultra-violet/visible spectroscopy (UV-Vis). The synthesized photocatalysts exhibited lower band gap energies as compared to the Degussa P-25, revealing a red shift in band gap towards the visible light absorption region. Photocatalytic activity of N,Pt co-doped TiO₂ was measured by the reaction of photocatalytic degradation of BB dye. Enhanced photodegradation efficiency of BB was achieved after 180-min reaction time with an initial concentration of 50 ppm. This was attributed to the rod-like shape of the materials, larger surface area, and enhanced absorption of visible light induced by N,Pt co-doping. The N,Pt co-doped TiO₂ also exhibited pseudo-first-order kinetic behavior with half-life and rate constant of 0.37 and 0.01984 min^-1, respectively. The mechanism of the photodegradation of BB under the visible light irradiation was proposed. The obtained results prove that co-doping of TiO₂ with N and Pt contributed to the enhanced photocatalytic performances of TiO₂ for visible light-induced photodegradation of organic contaminants for environmental remediation. Therefore, this work provides a new approach to the synthesis of PAMAM templated N,Pt co-doped TiO₂ for visible light photodegradation of brilliant black.

Electrochemical aptasensor for endocrine disrupting 17β-estradiol based on a poly(3,4-ethylenedioxylthiopene)-gold nanocomposite platform

A simple and highly sensitive electrochemical DNA aptasensor with high affinity for endocrine disrupting 17β-estradiol, was developed. Poly(3,4-ethylenedioxylthiophene) (PEDOT) doped with gold nanoparticles (AuNPs) was electrochemically synthesized and employed for the immobilization of biotinylated aptamer towards the detection of the target. The diffusion coefficient of the nanocomposite was 6.50 × 10⁻⁷ cm² s⁻¹, which showed that the nanocomposite was highly conducting. Electrochemical impedance investigation also revealed the catalytic properties of the nanocomposite with an exchange current value of 2.16 × 10⁻⁴ A, compared to 2.14 × 10⁻⁵ A obtained for the bare electrode. Streptavidin was covalently attached to the platform using carbodiimide chemistry and the aptamer immobilized via streptavidin—biotin interaction. The electrochemical signal generated from the aptamer–target molecule interaction was monitored electrochemically using cyclic voltammetry and square wave voltammetry in the presence of [Fe(CN)₆]^−3/−4 as a redox probe. The signal observed shows a current decrease due to interference of the bound 17β-estradiol. The current drop was proportional to the concentration of 17β-estradiol. The PEDOT/AuNP platform exhibited high electroactivity, with increased peak current. The platform was found suitable for the immobilization of the DNAaptamer. The aptasensor was able to distinguish 17β-estradiol from structurally similar endocrine disrupting chemicals denoting its specificity to 17β-estradiol. The detectable concentration range of the 17β-estradiol was 0.1 nM–100 nM, with a detection limit of 0.02 nM.