Amine‐Rich Nitrogen‐Doped Carbon Nanodots as a Platform for Self‐Enhancing Electrochemiluminescence

Abstract

Amine-richn itrogen-doped carbon nanodots (NCNDs) have been successfully used as co-reactant in electrochemiluminescence (ECL) processes.P rimary or tertiary amino groups on NCNDs have been studied as coreactant sites for Ru(bpy) 3 2+ ECL, showing their eligibility as powerful alternatives to tripropylamine (TPrA). We also report the synthesis and ECL behavior of an ew covalently linked hybrid of NCNDs and Ru(bpy) 3 2+.Notably,the NCNDs in the hybrid act both as carrier for ECL labels and as co-reactant for ECL generation. As ar esult, the hybrid shows ah igher ECL emission as compared to the combination of the individual components,s uggesting the self-enhancing ECL of the ruthenium complex due to an intramolecular electron transfer process.Carbon nanodots (CNDs), quasi-spherical nanoparticles with size below 10 nm, [1][2][3] are expected to have ah uge impact in biotechnological and environmental applications, based on their high potential as an ontoxic,f luorescent alternative to the popular semiconductor-based quantum dots (QDs). [4,5] In addition, properties such as water solubility, chemical inertness,facile modification and high resistance to photobleaching [3,4, 6] are important for their analytical and bioanalytical applications. [1,4,5] In this latter fields,e lectrochemiluminescence (ECL) is becoming an increasingly popular biosensing technique.E CL is ar edox-induced light emission in which high-energy species,g enerated at the electrodes,u ndergo ah igh-energy electron transfer reaction forming an excited state that emits light. [7] Thee xcited state can be produced through the reaction of radicals generated from the same chemical species (emitter), in the so-called annihilation mechanism, or from two different precursors (emitter and co-reactant), via co-reactant ECL. [7,8] In the annihilation mechanism, the application of oxidative conditions to al uminophore followed by reductive conditions (or viceversa), generates high-energy species that react with one another producing ECL emission. In contrast, in co-reactant ECL, both luminophore and co-reactant are first oxidized or reduced at the electrodic surface forming radicals and intermediate states.T he co-reactant radical oxidizes or reduces the luminophore producing its excited state.T hus, depending on the nature of the co-reactant, both "oxidativereduction" or "reductive-oxidation" mechanisms are possible.The main advantage of the co-reactant pathway is that the formation of radicals in aqueous solutions,a nd the consequent generation of ECL, is attainable without potential cycling and at less extreme potentials compared to common organic solvents,o pening up aw ide range of bioanalytical applications. [7] Them ost employed ECL luminophore is ruthenium(II) tris(2,2'-bipyridyl) (Ru(bpy) 3 2+

Graphitic Carbon Nitride Nanosheets as Co‐reactants for Tris(2,2′‐bipyridine)ruthenium(II) Electrochemiluminescence

“…Ru(bpy) 3 2 + /tripropylamine (TrPA) co-reactant system is currently the most widely used Ru(bpy) 3 2 + ECL system. [12][13][14][15] Among the new co-reactants, nanomaterials not only work as co-reactants, but also act as scaffold for covalent immobilization of Ru(bpy) 3 2 + to construct self-enhanced ECL probes, [13,16] which are supposed to extend ECL application in biomedical areas due to the elimination of adding additional co-reactant. [6][7] Therefore, the analysts are committed to find alternate biocompatible coreactants for Ru(bpy) 3 2 + ECL.…”

“…The spatiotemporal controllability of luminescence by electrochemical reactions endows ECL with high signal-to-background ratio, making it an excellent analytical method. [12][13][14][15] Among the new co-reactants, nanomaterials not only work as co-reactants, but also act as scaffold for covalent immobilization of Ru(bpy) 3 2 + to construct self-enhanced ECL probes, [13,16] which are supposed to extend ECL application in biomedical areas due to the elimination of adding additional co-reactant. [2][3][4][5] Among the luminophores, Ru(bpy) 3 2 + has attracted extensive attention due to its unique features such as high ECL efficiency, reversible electrochemical reaction, good solubility in both aqueous and nonaqueous solutions, and low biotoxicity.…”

“…[6] Ru(bpy) 3 2 + ECL occurs by means of two pathways: ion annihilation and co-reactant. [12][13][14][15] Among the new co-reactants, nanomaterials not only work as co-reactants, but also act as scaffold for covalent immobilization of Ru(bpy) 3 2 + to construct self-enhanced ECL probes, [13,16] which are supposed to extend ECL application in biomedical areas due to the elimination of adding additional co-reactant. Ru(bpy) 3 2 + /tripropylamine (TrPA) co-reactant system is currently the most widely used Ru(bpy) 3 2 + ECL system.…”

Tris(2,2’‐bipyridyl)ruthenium(II)‐Nanomaterial Co‐Reactant Electrochemiluminescence

“…Self‐enhanced ECL has attracted extensive attention due to the improved intensity and stability of intramolecular ECL as well as the massive functional groups on nanomaterials acting co‐reactant sites. Carrara et al . constructed a novel self‐enhanced ECL probes Ru‐NCDs with strong and stable ECL emission comparable to Ru(bpy) 3 2+ /TPA system.…”

“…Nitrogen-doped CDs (NCDs) can enhance anodic Ru (bpy) 3 2 + ECL as well. [26,27] Carrara et al [27] clarified that amine groups attached to α-carbon with the hydrogen atom on the surface of NCDs were responsible for the enhancement (Figure 2). The conclusion was supported by the finding that conversion of primary amine on NCDs to tertiary amines through an Eschweiler-Clarke methylation reaction could further increase the ECL enhancement.…”