π‐Conjugated Carbon Radicals at Graphene Oxide to Initiate Ultrastrong Chemiluminescence

Abstract

Graphene oxide has widely been employed in various fields, but its structure and composition has still not been fully understood. Here we report that freshly prepared graphene oxide exhibits a large number of π-conjugated carbon radicals at its π-network plane, which result from the addition reaction of hydroxyl radicals from H2O2 onto the conjugated double bonds of graphene oxide. The π-conjugated carbon radicals can directly initiate the long-lasting visible chemiluminescence of luminol, which is even stronger than that obtained when horseradish peroxidase and H2O2 are used. Previously, graphene oxide was mainly reported to be a quencher of chemiluminescence instead. Remarkably, the reacted radicals can be regenerated, thereby enabling the repetitive initiation of chemiluminescence by re-treatment of graphene oxide. The results reported here provide a new understanding of the structure, properties, and applications of graphene oxide.

Graphene Oxide: From Tunable Structures to Diverse Luminescence Behaviors

“…We believed that excess H 2 O 2 might be decomposed to ·OH radicals in the presence of KMnO 4 , and ·OH radicals immediately added to the double bonds at the GO plane, leading to form π-conjugated carbon radicals ( Figure 1C). [22] This work provided a new insight into the structure and properties of freshly prepared GO. The single electron was mobile among the conjugated CC bonds, significantly prompting its oxidizing capability and the reaction efficiency with the target molecules adsorbed on the basal plane of GO, such as luminol molecules ( Figure 9B).…”

“…[39] This model is named Lerf-Klinowski model (Figure 1A), and is widely adopted in literatures. [22] We believed that a large number of π-conjugated carbon radicals were formed by the addition of hydroxyl radicals to the carbon double bonds on the disrupted π-network plane of GO ( Figure 1C). [40] Ajayan and co-workers considered the Lerf-Klinowski model as base structure, and further offered experimental support for a peripheral structure containing five-and six-membered ring lactols and possibly an occasional 2-hydroxynaphthalic anhydride or 1,3-dihydroxyxanthone ( Figure 1B).…”

“…DNA, peptides, conjugated polymer chains can be adsorbed onto GO surface through noncovalent π-π interactions or electrostatic interactions. [22] Copyright 2014, Wiley-VCH. For example, carboxyl groups at the edge of GO nanosheets can react with amino groups or hydroxyl groups through acyl reactions, epoxy groups in GO planes also provide active sites for ring-opening reactions with amino groups, adjacent dihydroxy groups react with borate compounds.…”

“…[2] Moreover, hand, oxidative or reductive cutting of GO nanosheets into 0D quantum dots (QDs) can further create discrete energy levels. [22] Additionally, a series of progresses on luminescent GO nanomaterials and their sensing applications have been made during these years. For example, we have proposed an alkylamine modification method to greatly improve GO luminescent quantum yield for the first time, [7] developed a novel peroxidation strategy to enrich GO luminescent colors, [21] and recently found that ultrastrong chemiluminescence (CL) could be initiated by GO.…”

Fluorescent Nanomaterials for Color‐Multiplexing Test Papers toward Qualitative/Quantitative Assays

“…ii) In comparison, fluorescent CDs have other unique advantages including low cost, low toxicity, high chemical stability, rich raw material in nature, and a large number of carboxyl, hydroxyl, or amide groups at their surfaces for further chemical modification (Figure B) . iii) Similarly, 2D GOs have a large π‐conjugated plane bearing numerous phenol hydroxyl, epoxy, and carboxylic groups to specifically bind chemical/biological species: based on this we have synthesized fluorescent GOs by chemical modification of the surface for the first time (Figure C) . iv) Alternatively, lanthanide ions (Ln 3+ ) with abundant f‐orbital configurations are widely used as emitting species in many phosphors, and Ln 3+ ‐integrated upconversion nanocrystals with exciting‐power‐dependent emissive colors were first demonstrated recently in our research (Figure D) .…”