Electrochemiluminescence from hydrophilic thin film Ru(bpy)32+-modified electrode prepared using natural halloysite nanotubes and polyacrylamide gel

Highly Active Electrochemiluminescence of Ruthenium Complex Co-assembled Chalcogenide Nanoclusters and the Application for Label-Free Detection of Alkaline Phosphatase

Rational design of electrochemiluminescence (ECL) reagents is essential for the development of ECL biosensors with superior performances. In this work, the assembly of tris(1,10-phenanthroline)ruthenium(II) [Ru(phen)₃²⁺] and tetrahedral chalcogenide nanoclusters of [Cd₃₂S₁₄(SC₆H₅)₃₈]^2- in the formation of complex nanoclusters (CdS-Ru) was developed, in which Ru(phen)₃²⁺ was uniformly encapsulated and dispersed at a molecular level in the chalcogenide nanocluster via multiple noncovalent interactions. It was observed that the promoted ECL emission was realized by the charge transfer between the tetrahedral CdS nanocluster and Ru(phen)₃²⁺ by the formation of the assembly complex, which was elucidated by cyclic voltammetry curves, ECL-potential curves, and in situ dynamic ECL spectra. Taking advantages of the facile charge transfer in the open framework CdS-Ru, a high ECL efficiency has been achieved with remarkable stability. Moreover, a solid-state ECL sensor based on the CdS-Ru modified electrode was fabricated for label-free detection of alkaline phosphatase (ALP) activity with a detection limit as low as 0.35 U/L and superior reproducibility. This solid-state ECL sensor also displayed favorable selectivity among various interferences and was applied for ALP activity analysis in human serum samples. These results implicated the potential applications of CdS-Ru for sensitive ECL analysis in complicated reaction systems and enlightened the rational design for self-enhanced and highly efficient ECL materials.

Novel poly-dopamine adhesive for a halloysite nanotube-Ru(bpy)(3)2+ electrochemiluminescent sensor

Herein, for the first time, the electrochemiluminescent sensor based on Ru(bpy)₃²⁺-modified electrode using dopamine as an adhesive was successfully developed. After halloysite nanotube slurry was cast on a glassy carbon electrode and dried, an alkaline dopamine solution was added on the electrode surface. Initially, polydopamine belts with dimensions of tens to hundreds of nanometers formed via oxidization of the dopamine by ambient oxygen. As the incubation time increased, the nanobelts became broader and then united with each other to form a polydopamine film. The halloysite nanotubes were embedded within the polydopamine film. The above electrode was soaked in Ru(bpy)₃²⁺ aqueous solution to adsorb Ru(bpy)₃²⁺ into the active sites of the halloysite nanotubes via cation-exchange procedure. Through this simple procedure, a Ru(bpy)₃²⁺-modified electrode was obtained using only 6.25 µg Ru(bpy)₃²⁺, 15.0 µg dopamine, and 9.0 µg halloysite nanotubes. The electrochemistry and electrochemiluminescence (ECL) of the modified electrode was investigated using tripropylamine (TPA) and nitrilotriacetic acid (NTA) as co-reactants. The different ECL behaviors of the modified electrode using NTA and TPA as well as the contact angle measurements reflected the hydrophilic character of the electrode. The results indicate that halloysite nanotubes have a high loading capacity for Ru(bpy)₃²⁺ and that dopamine is suitable for the preparation of modified electrodes.