An Electrocatalysis and Self-Enrichment Strategy for Signal Amplification of Luminol Electrochemiluminescence Systems

Abstract

Numerous strategies have been developed to improve the intensity of a luminol electrochemiluminescence (ECL) system due to the low quantum yield of luminol. Notably, considerable research was carried out to improve luminol ECL intensity relying on increasing the concentration of reactive oxygen species (ROS). Herein, a Co–N x –C electrocatalyst treated with nitric acid or hydrochloric acid (named as Co-POC-O or Co-POC-R, respectively) was in situ prepared on the surface of carbon nanotubes. Surprisingly, compared with Co-POC-R, the Co-POC-O electrocatalyst not only displays excellent oxygen reduction reaction (ORR) performance but also enriches luminol via non-covalent bonds rather than covalent bonds and physical mixing. This method improves the amount of luminol involved in the electrochemical reaction as well as shortens the distance for electron transfer between oxidized luminol and ROS, which significantly enhances the ECL intensity (10-fold higher than that of the bare electrode and 2-fold higher than that of Co-POC-R). The platform realizes highly sensitive dopamine (DA) with a detection limit of 1.0 pM and a linear range from 10 pM to 1.0 nM. In this work, Co-POC-O is both the co-reaction accelerator and carrier material of luminophore species, which provides a new idea to realize ECL signal amplification.

Integration of High-Entropy Oxide with Nitrogen-Doped Graphene for the Ultrasensitive Electrochemiluminescence Detection of Trolox and Dopamine

“…To alleviate this, a supplementary accelerator is generally needed to efficiently convert DO to reactive oxygen species (ROS), to produce a much-enhanced ECL signal. Until now, plenty of materials, such as copper-doped TiO 2 , noble-metal heteronanostructures, ZnO, single-atom catalysts, dual single-atom catalysts, and Co–N x –C, have been applied to achieve this goal. Despite such progress, issues of ambiguous ECL mechanisms, instability, and insensitivity of the relevant luminol-involved ECL systems are still barricading its real analytical and bioanalytical applications.…”

Self-Enhanced Electrochemiluminescence Imaging System Based on the Accelerated Generation of ROS under Ultrasound

“…Electrochemiluminescence (ECL) is a luminescence process in which luminophores undergo high-energy electron transfer and emit photons in the electrochemical reaction. − It has the advantages of no external light source, high sensitivity, and controllable potential. With the high spatiotemporal resolution from microscopy, ECL imaging has been widely applied in immunoassays − and single-particle or cell imaging behavior research. − Most of these cases heavily rely on co-reactants because they can significantly promote the generation of light-emitting excited species. ,, For example, the most famous tris­(bipyridyl)ruthenium (Ru­(bpy) 3 2+ )/tri- n -propylamine (TPrA) ECL system, which has been extensively applied in the commercial ECL immunoassay. , However, TPrA is poorly water-soluble and highly toxic, and a large dose of TPrA (typically 100 mM) is required to gain enough light emission. Thus, the presence of high-concentration co-reactants in solution blocks practical bioanalytical applications.…”

“…9−15 Most of these cases heavily rely on co-reactants because they can significantly promote the generation of lightemitting excited species. 3,16,17 For example, the most famous tris(bipyridyl)ruthenium (Ru(bpy) 3 2+ )/tri-n-propylamine (TPrA) ECL system, which has been extensively applied in the commercial ECL immunoassay. 18,19 However, TPrA is poorly water-soluble and highly toxic, and a large dose of TPrA (typically 100 mM) is required to gain enough light emission.…”

“…These ROS species promote the generation of the excited state of luminol by accelerating the formation of endoperoxides, which emit photons with an enhancement of ECL intensity. 17,30,32 Previously, ultrasound (US), as a nondestructive and biologically friendly technology, can split water into ROS in situ. 33 The US facilitates the generation of co-reactants in situ 34,35 and acting as an agitating pump 36 that accelerates the mass transfer, emitting more photons by boosting the electrochemical reaction rates.…”

“…To maintain more general bioanalytical applicability, the bio-friendly luminol/reactive oxygen species (ROS) system based on dissolved oxygen with better stability would provide a promising strategy. ,− ROS is generated from the electrochemical reduction reaction of dissolved oxygen and water. These ROS species promote the generation of the excited state of luminol by accelerating the formation of endoperoxides, which emit photons with an enhancement of ECL intensity. ,, Previously, ultrasound (US), as a nondestructive and biologically friendly technology, can split water into ROS in situ . The US facilitates the generation of co-reactants in situ , and acting as an agitating pump that accelerates the mass transfer, emitting more photons by boosting the electrochemical reaction rates.…”