Electrocatalytic application for gold nanoparticles decorated sulfur-nitrogen co-doped graphene oxide nanosheets and nanosized cobalt tetra aminophenoxy phthalocyanine conjugates

Interfacial assembly of zinc(II) phthalocyanines on graphene oxide (GO): Stable "turn-off-on" nanoplatforms to detect G-quadruplexes (G4)

HYPOTHESIS

The aggregation of phthalocyanines (Pcs) enfeebles their suitability as G-quadruplex (G4) ligands over time. It is hypothesized that the interfacial assembly of Pcs on graphene oxide (GO) influences intermolecular interactions, thereby affecting their physicochemical properties and inducing stabilization of Pcs in solution. Hence, the stacking of Pcs on GO could be tuned to create nanosystems with the ability to detect G4 for longer periods through a slow release of Pcs.

EXPERIMENTS

Four cationic structurally-related zinc(II) phthalocyanines (ZnPc) were non-covalently assembled on GO by ultrasonic exfoliation. A comprehensive characterization of ZnPcs@GO was carried out by spectroscopic techniques and electron microscopy to understand the organization of ZnPcs on GO. The fluorescence of ZnPcs@GO was studied in the presence of G4 (T₂G₅T)₄ and duplex ds26 through spectrofluorimetric titrations and monitored along time.

FINDINGS

GO induced a re-organization of the ZnPcs mostly to J-aggregates and quenched their original fluorescence up to 98 % ("turn-off"). In general, ZnPcs@GO recovered their fluorescence ("turn-on") after the titrations and showed affinity to G4 (K_D up to 1.92 μM). This is the first report that highlights the contribution of GO interfaces to assemble ZnPcs and allow their slow and controlled release to detect G4 over longer periods.

Subnanomolar detection of promethazine abuse using a gold nanoparticle-graphene nanoplatelet-modified electrode

A simple, sensitive, and effective adsorptive stripping voltammetric sensor for the detection of trace-level promethazine was created based on a gold nanoparticle-graphene nanoplatelet-modified glassy carbon electrode (AuNP-GrNP/GCE). AuNP-GrNP nanocomposites were synthesized using an electroless deposition process, and the morphology was characterized using UV-vis spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The electrochemical behavior and detection of promethazine at the AuNP-GrNP/GCE were investigated utilizing cyclic voltammetry and adsorptive stripping voltammetry. The AuNP-GrNP/GCE showed outstanding synergistic electrochemical activity for promethazine oxidation, a highly active surface area, great adsorptivity, and outstanding catalytic properties. The electrolyte pH, amount of AuNP-GrNP nanocomposite, preconcentration potential (vs. Ag/AgCl), and time were optimized to obtain a high performance electrochemical sensor. Under optimal conditions, the proposed sensor displayed two linear concentration ranges from 1.0 nmol L^-1 to 1.0 μmol L^-1 and from 1.0 to 10 μmol L^-1. The limits of detection and quantitation were 0.40 and 1.4 nmol L^-1, respectively. This sensor displayed high sensitivity, a capability for rapid analysis, and excellent repeatability and reproducibility. The developed sensor was effective and practical for promethazine detection in biological fluids and forensic samples, and the obtained results exhibited excellent agreement with the results obtained using the method described in the British Pharmacopoeia. Graphical abstract.

Enhanced electrocatalytic activity of cobalt phthalocyanines when “clicked” to graphene oxide nanosheets

Alkyne-terminated Co phthalocyanine (CoPc) derivatives are linked to reduced graphene oxide nanosheets (GONS) via click chemistry and the conjugates are used for the electrocatalytic oxidation of 2-mercaptoethanol. CoPc derivatives where the alkyne group is separated from the Pc ring by an aliphatic and benzene ring (complex 3) showed the best catalytic activity (in terms of oxidation potential) in comparison to when only aliphatic chains were employed without the benzene ring (complex 2) and when there were no substituents (complex 1). The anodic oxidation of 2-mercaptoethanol on 3-GONS (linked) occurred at the least positive oxidation potential (-0.22 V vs. Ag|AgCl). 3-GONS (linked) was found to have the highest sensitivity with the lowest limit of detection of 0.08 [Formula: see text]M. When the CoPc derivative and GONS were not linked but placed sequentially on the electrode, the electrocatalytic activity (in terms of LOD) was poorer than when linked. The electrodes modified with CoPc clicked to GONS are highly promising electrochemical sensors in terms of stability, sensitivity, good catalytic activity and ease of fabrication.