Carbon Vacancy-Enhanced Activity of Fe-N-C Single Atom Catalysts toward Luminol Chemiluminescence in the Absence of H2O2

Chlorine-functionalized black phosphorus quantum dots induced superoxide anion generation and depletion for efficient chemiluminescence detection

BACKGROUND

Due to their unique optoelectronic properties, environmental friendliness, and excellent biocompatibility, metal-free quantum dots have been a new star in exploring novel chemiluminescence (CL) systems for analytical applications in recent years. However, unknown CL property, relatively weak emission and instability of some of them in water (eg. black phosphorus) often seriously hindered their further applications. Hence, developing a novel QDs-assist CL signal amplification to achieve efficient analyst detection is significant and currently hot topic for researchers.

RESULTS

In this work, we purposely synthesized chlorine-functionalized black phosphorus quantum dots (Cl-BPQDs) with improved stability and rich-hole property, which were demonstrated to exhibit the excellent capability for the activation of ferrate (VI) with large reactive oxygen species generation and leading to enhanced CL signal. The detail mechanism was demonstrated, the unique CL response to the presence of active sites (P-Cl) in Cl-BPQDs, which accelerated ferrate (VI) decomposition and produced a large amount of superoxide anion (•O2-). And then, the radiative recombination of the exogenous electron-donated and existing holes Cl-BPQDs accounting for the strong CL emission. Furthermore, based on the consumption capacity of ascorbic acid (AA) and glutathione (GSH) for •O2-, a direct CL sensing platform of Cl-BPQDs/ferrate (VI) quenching was fabricated to AA and GSH detection. This fabricated assay has broad detection linear ranges (2-200 μM) and low detection limit (GSH: 1.3 μM; AA: 1.7 μM). Compared with the reported CL technique, this new method displayed superior sensitivity and anti-interference capabilities toward transition-metal ions and inorganic anions. The potential analytical application of the new CL system was further demonstrated by the evaluation of total antioxidant capacity (TAC) in diabetic patients.

SIGNIFICANCE

This study proposes a new strategy for enhancing CL signal via Cl-BPQDs triggering •O2- generation and depletion, which provides an innovative tool for ascorbic acid and glutathione detection. This method not only enriches our understanding of the optical characteristics of BP, but also provides a new charge transfer-based path for CL amplification.

Single-Atom Iron Boosts Counter Electrode Electrochemiluminescence for Biosensing

Traditional electrochemiluminescence (ECL) detection makes it difficult to realize the spatial separation of the sensing and reporting sides, which inevitably causes mutual interference between the target and the luminescent substance. By studying the relationship between the luminol luminescence position and electrode potential in a three-electrode system, this work realized spatial separation of the sensing and reporting sides for the first time. Experimental investigations showed that luminol only emitted ECL signals at electrodes with positive polarity, regardless of whether a positive or negative voltage was applied. Inspired by this, we introduced a carbon vacancy-modified iron single-atom catalyst (VC-Fe-N-C SAC) with excellent oxygen reduction reaction (ORR) activity into the working electrode, which can catalyze the reduction of dissolved O2 to produce abundant reactive oxygen species (ROS). ROS diffused to the surface of the counter electrode to oxidize luminol and produce a high-intensity ECL signal at an ultralow trigger potential. As a proof-of-concept application, a sensitive ECL biosensor with spatial separation of the sensing and reporting sides was first constructed for microcystin-LR (MC-LR) detection. This work solved the interference between the target and luminescent substance in the traditional three-electrode ECL system and improved the detection accuracy and sensitivity. Furthermore, the introduction of single-atom catalysts (SAC) avoided the use of the coreactant H2O2 and the tedious electrochemical oxidation process of luminol, which broadened the application of ECL biosensors.

Cu3(HITP)2 with peroxidase- and ascorbic acid oxidase-like catalytic activity for fluorescence/chemiluminescence sensing of ascorbic acid

Nanomaterials with intrinsic enzyme mimicking activity have achieved widespread application. However, developing novel nanomaterials with multienzyme mimicry activity remains challenging. Herein, Cu3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) with ascorbic acid oxidase (AAO)- and peroxidase (POD)-like activity are successfully synthesized. Cu3(HITP)2 exhibits excellent AAO-like activity and can specifically catalyze the oxidation reaction of ascorbic acid (AA). Dehydroascorbic acid (DHAA) obtained from the oxidation of AA is allowed to react with nonfluorescent o-phenylenediamine (OPD) to form 3-(1,2-dihydrox-yethyl) furo[3,4-b]quinoxaline-1-one (DFQ) with strong fluorescence emission. Moreover, Cu3(HITP)2 is able to catalyze the chemiluminescence (CL) reaction of ABEI-H2O2 to generate a strong and glow-type emission based on its POD activity. Inspired by the multienzyme mimicry activity of Cu3(HITP)2, the simple and sensitive fluorescence and chemiluminescence sensing platforms are successfully constructed and applied for the detection of AA. The sensors show high sensitivity and excellent selectivity. We believe that this multienzyme mimicry activity nanomaterial not only can be used to construct the multiple-mode biosensing platform, but also enables the extensive applications in the fields of biomedicine, energy, and environment.

Efficient degradation of organic pollutants without any external assistance over a wide pH range using carbon vacancy-modified Fe-N-C catalysts

Currently, water treatment usually requires additional light illumination or oxidants for the degradation of organic pollutants, which increases the costs and is not conducive to practical application. In this study, carbon vacancy-modified Fe-N-C single-atom catalysts (Cv-Fe-N-C SACs) were prepared through one simple acid-etching and pyrolysis process. Interestingly, we found that Cv-Fe-N-C SACs could degrade organic pollutants without any external assistance (such as oxidants or light illumination). The Cv-Fe-N-C SACs could remove over 99% of Rhodamine B (RhB) within 10 min at room temperature. The degradation of organic pollutants with the Cv-Fe-N-C SACs was attributed to their ability to activate dissolved oxygen for producing superoxide (O2˙-). In addition, the catalysts showed high activity over a broad pH range (3-11) and held rather good stability after 5 recycles. This study proved that the Cv-Fe-N-C SACs are highly efficient catalysts for degrading organic pollutants. These catalysts have the potential to make sewage treatment more efficient and less expensive.

VS4 Nanodendrites with Narrow Bandgaps in Activating Dissolved Oxygen for Boosted Chemiluminescence and Hemin Detection by Unexpected Quenching

Chemiluminescence (CL)-based analytical methods utilize luminophores that need to be activated with an oxidizing agent to trigger CL emission. Despite its susceptibility to decomposition when exposed to external light or trace metals, hydrogen peroxide (H2O2) has been widely used to develop chemiluminescent methods due to the limited number of suitable alternatives for activating chemiluminescent luminophores. Also, analytical methods based on the well-known luminol/H2O2 CL system have low sensitivity. Dissolved oxygen (DO) is a naturally abundant and environmentally benign alternative oxidant for luminol and other CL luminophores. However, DO alone is inactive and needs an efficient catalyst or a coreaction accelerator for its activation. Because of the narrow bandgap of VS4 (ca. 1.12 eV), it can facilitate fast electron-transfer kinetics with an acceptor molecule such as DO. Here, we introduce vanadium tetrasulfide (VS4) to boost CL for the first time. Under the optimized conditions, VS4 nanodendrite catalyzes the generation of reactive oxygen species by activating DO which subsequently reacts with luminol to generate intense CL. It enhances the CL intensity of luminol/DO by about 10,000 times. Surprisingly, hemin remarkably quenches the generated CL of luminol/DO/VS4 nanodendrites, which is completely opposite to its typical enhancement of luminol CL. Based on the remarkable concentration-dependent quenching of the luminol/DO/VS4 nanodendrite CL by hemin, we have developed a sensitive CL method that can selectively detect hemin in the linear concentration range of 1-250 nM and achieved a limit of detection of 0.11 nM. The practical utility of the developed method was demonstrated by the determination of hemin in a pharmaceutical drug for the treatment of acute intermittent porphyria and in human serum. This study demonstrates that VS4 holds great promise in analytical method development.

Facile Estimation of Surface Oxygen Vacancies in Co3O4 Catalysts with a Colorimetric Method

Oxygen vacancy (Ov) is known to act as an active center of the metal oxide. Quantification of surface Ov is vital for understanding the quantitative structure-activity relationship. Facile quantification characterization of surface Ov is highly desirable but still challenging. In this study, we presented a simple colorimetric method for rapidly quantifying surface Ov. As an example of metal oxide nanoparticles, Co3O4 was used to catalyze the 3,3',5,5'-tetramethylbenzidine (TMB)-H2O2 colorimetric reaction. It was found that the absorbance of the TMB-H2O2 system was dependent on the surface Ov amount in Co3O4. The investigation of the mechanism showed that the Ov-dependent absorbance would be attributed to the activity of surface Ov to easily adsorb and dissociate H2O2 into a hydroxyl radical (•OH). The absorbance signal of the TMB-H2O2 system acted as a probe to estimate the surface Ov. This colorimetric measurement could be completed in less than 20 min. The Ov concentrations obtained by the proposed colorimetric method matched well with those obtained by X-ray photoelectron spectroscopy. This method does not require any complex operation and expensive equipment and can be performed in any ordinary chemical laboratory. So, this colorimetric method is expected to become an alternative approach for quantifying the surface Ov in metal oxide nanoparticles. This method will provide essential insights into the rational design and application of Ov.

N-doped TiO2/Ti3C2-driven self-photocatalytic molecularly imprinted ECL sensor for sensitive and steady detection of dexamethasone

The conventional luminol-based electrochemiluminescence (ECL) biosensor suffers from hampered signal stability due to the self-decomposition of the H2O2 co-reactant. Here, we propose an N-doped TiO2/Ti3C2 heterojunction driven self-photocatalytic platform for ECL signal amplification and then combine it with molecular imprinting technology for sensitive and steady detection of dexamethasone (DXM). Unlike traditional cases involving specific catalysts or external electron injection, the initial luminescence of luminol in this new system is utilized as the excitation light of N-doped TiO2/Ti3C2 photocatalyst to promote the conversation of dissolved oxygen to H2O2, supplying more co-reactants to improve ECL of luminol in turn. Thanks to the heterojunction and self-photocatalytic cyclic amplification, this molecularly imprinted ECL sensor exhibits a wide linear range (1.0 × 10-6-1.0 × 101 μg mL-1) and a low detection limit, as well as excellent anti-interference capability, sensitivity, and stability. This work contributes to more reliable and steady detection of DXM and brings new insights into developing exogenous co-reactant-free self-enhancement ECL models for biosensor applications.