Defective Site Modulation Strategy for Preparing Single Atom-Dispersed Catalysts as Superior Chemiluminescent Signal Probes

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.

A sensing strategy based on novel pyrene-functionalized MOFs for sVCAM-1 detection and prognostic assessment in coronary heart disease

Coronary heart disease (CHD) remains a significant global health concern, with exercise therapy playing a crucial role in rehabilitation. Optimizing exercise intensity is essential, as both insufficient and excessive exercise may lead to suboptimal or adverse outcomes. In response to this challenge, we developed Adaptive Posture-Balance Cardiac Rehabilitation Exercise (APBCRE), which integrates postural balance training with aerobic exercise. To evaluate its therapeutic efficacy, we designed a novel fluorescent biosensor targeting soluble vascular cell adhesion molecule-1 (sVCAM-1), a key biomarker of endothelial inflammation. The biosensor utilizes pyrene-functionalized metal-organic framework (PCA-UiO-66), synthesized via a one-pot approach. Within the MOF, pyrenecarboxylic acid (PCA) exists primarily in the excimer state, exhibiting stable fluorescence emission, a narrow spectral peak, and a wide Stokes shift. For the purpose of identify sVCAM-1, the sVCAM-1-specific aptamer was functionalized to PCA-UiO-66. When sVCAM-1 is present, the aptamer is competitively stripped from the MOF surface by the target. This process induces π-π stacking interactions between the aptamer's phosphate backbone and PCA molecules, facilitating PCA release and transition from the excimer to the monomer state. By quantifying the fluorescence value of monomer state PCA, the fluorescence response allowed precise quantification of sVCAM-1, with a detection limit of 0.69 ng/mL and a range of 2 ng/mL to 50 μg/mL. We analyzed cardiopulmonary performance and serum sVCAM-1 levels in 20 CHD patients who underwent APBCRE. These findings establish APBCRE as an effective rehabilitation strategy that provides both physiological and molecular benefits while also confirming Apt@PCA-UiO-66 as a robust biosensing tool for monitoring therapeutic efficacy and elucidating CHD pathophysiology.

D-Histidine modulated chiral metal-organic frameworks for discriminating 3,4-Dihydroxyphenylalanine enantiomers based on a chemiluminescence quenching mode

BACKGROUND

Drug enantiomers often display distinguishable or even opposite pharmacological and toxicologic activities. Therefore it is of great necessity to discriminate enantiomers for guaranteeing safetyness and effectiveness of chiral drugs. Facile chiral discrimination has long been a noticeable challenge because of the minimal differences in physicochemical properties of enantiomers. As one of high-performance chirality selection components, chiral metal-organic frameworks (CMOFs) are bringing new opportunities for the establishment of chiral discrimination platform with merits of high enantioselectivity, low cost, and facile operation.

RESULTS

By introducing D-Histidine as a modulator, a CMOFs material termed as D-Histidine-ZIF-8 was prepared on chitosan (CS) with an in-situ growth protocol. The positively charged CMOFs/CS hybrids were adsorbed onto negatively charged polystyrene microplate via electrostatic interaction to form a chiral discrimination interface. This interface can effectively adsorb 3,4-Dihydroxyphenylalanine (DOPA) enantiomers, and the adsorbed molecules can be quantitated based on their quenching behavior on the chemiluminescent (CL) signal of Co2+-catalyzed luminol-H2O2 reaction. The results of contact angle measurements and density functional theory calculations imply that CMOFs/CS have stronger affinity towards D-isomer than L-isomer. Thus the sensitivity for quantifying D-isomer is 2.93 times of that for L-isomer, demonstrating the enantioselectivity of the CMOFs/CS hybrids. The content of D-isomer in nonracemic mixtures of DOPA enantiomers and real samples were assayed with satisfactory results, showing the practicality of this method. The strategy also exhibited discrimination capacity for many other chiral molecules.

SIGNIFICANCE

The CMOFs/CS hybrids prepared with in-situ growth protocol display satisfactory selectivity for discriminating enantiomers. Due to usage of multi-well microplate platform, the method is anticipated to achieve high-throughput assay in the future work. This study paves a pathway for facile chiral discrimination based on a chemiluminescence quenching mode to meet the demand of drug development and manufacture.

Advances in nanozymes with peroxidase-like activity for biosensing and disease therapy applications

Natural enzymes are crucial in biological systems and widely used in biomedicine, but their disadvantages, such as insufficient stability and high cost, have limited their widespread application. Since discovering the enzyme-like activity of Fe3O4 nanoparticles, extensive research progress in diverse nanozymes has been made with their in-depth investigation, resulting in rapid development of related nanotechnologies. Nanozymes can compensate for the defects of natural enzymes and show higher stability with lower costs. Among them, peroxidase (POD)-like nanozymes have attracted extensive attention in biomedical applications owing to their efficient catalytic performance and diverse structures. This review explores different types of nanozymes with POD-like activity and discusses their activity regulation, particularly emphasizing their latest development trends and advances in biosensing and disease treatment. Finally, the challenges and prospects for the development of POD-like nanozymes and their potential future applications in the biomedical field are also provided.

Hybrid Mn Atomic Clusters/Single-Dispersed Atoms with Dual Antioxidant Activities for a Chemiluminescent Immunoassay

Single-dispersed atoms (SDAs) as catalysts have drawn extensive attention due to their ultimate atom utilization efficiency and desirable catalytic capability. Atomic clusters (ACs) with potential multiple enzyme-like activities also display great practicability in catalysis-based biosensing. In this work, hybrid Mn ACs/SDAs were implanted in the frameworks of defect-engineered MIL 101(Cr) modulated by excess acetic acid, with a high loading capability of 13.9 wt %. Distinctively, Mn SDAs display weak superoxide dismutase (SOD)-like activity for specifically eliminating superoxide anion (O2•-), while Mn ACs/SDAs display both catalase-like and SOD-like activities for remarkable elimination of total reactive oxygen species (ROS) due to the cooperative effect of the two atom-scale catalytic sites. Thus, Mn ACs/SDAs can efficiently inhibit the chemiluminescent (CL) emission of multiple ROS-mediated luminol systems with a superior quenching rate of 85.5%. To validate the practicability of Mn ACs/SDAs for a sensitive CL assay, an immunoassay method was established to detect acetamiprid by using Mn ACs/SDAs as signal quenchers, which displayed a quantification range of 10 pg mL-1-25 ng mL-1 and a detection limit of 3.3 pg mL-1. This study paves an avenue for developing ACs/SDAs with multiple antioxidant activities that are suitable for application in biosensing.

Dual-Emission Single Sensing Element-Assembled Fluorescent Sensor Arrays for the Rapid Discrimination of Multiple Surfactants in Environments

Surfactants are considered as typical emerging pollutants, their extensive use of in disinfectants has hugely threatened the ecosystem and human health, particularly during the pandemic of coronavirus disease-19 (COVID-19), whereas the rapid discrimination of multiple surfactants in environments is still a great challenge. Herein, we designed a fluorescent sensor array based on luminescent metal-organic frameworks (UiO-66-NH2@Au NCs) for the specific discrimination of six surfactants (AOS, SDS, SDSO, MES, SDBS, and Tween-20). Wherein, UiO-66-NH2@Au NCs were fabricated by integrating UiO-66-NH2 (2-aminoterephthalic acid-anchored-MOFs based on zirconium ions) with gold nanoclusters (Au NCs), which exhibited a dual-emission features, showing good luminescence. Interestingly, due to the interactions of surfactants and UiO-66-NH2@Au NCs, the surfactants can differentially regulate the fluorescence property of UiO-66-NH2@Au NCs, producing diverse fluorescent "fingerprints", which were further identified by pattern recognition methods. The proposed fluorescence sensor array achieved 100% accuracy in identifying various surfactants and multicomponent mixtures, with the detection limit in the range of 0.0032 to 0.0315 mM for six pollutants, which was successfully employed in the discrimination of surfactants in real environmental waters. More importantly, our findings provided a new avenue in rapid detection of surfactants, rendering a promising technique for environmental monitoring against trace multicontaminants.

Surface Oxygen Vacancy-Rich Co3O4 Nanowires as an Effective Catalyst of Luminol-H2O2 Chemiluminescence for Sensitive Immunoassay

Oxygen vacancy is one intrinsic defect in metal oxide materials. Interestingly, we herein found that the surface oxygen vacancy can significantly enhance the catalytic activity of Co3O4 nanowires in the luminol-H2O2 chemiluminescence (CL) reaction. 0.1 ng/mL Co3O4 nanowires containing 51.3% surface oxygen vacancies possessed ca. 2.5-fold catalytic activity of free Co2+ (the best metal ionic catalyst for the luminol-H2O2 CL reaction). The superior catalytic efficiency is attributed to the enhanced adsorption of H2O2 by surface oxygen vacancies, which in turn accelerates the cleavage of O-O bonds and generates •OH radicals. More importantly, the surface oxygen vacancy-rich Co3O4 nanowires retained about 90% catalytic activity after modification with antibodies. The surface oxygen vacancy-rich Co3O4 nanowires were used to label the secondary antibody, and one sandwich-type CL immunoassay of carcinoembryonic antigen was established. The detection limit was 0.3 ng/mL with a linear range of 1-10 ng/mL. This proof-of-concept work proves that surface oxygen vacancy-rich Co3O4 nanowires are suitable for labeling biomolecules in CL bioanalysis and biosensing.

Preparation of Co dual atomic site catalysts loaded on defect-engineered MOFs material with superb chemiluminescent enhancement effect for sensitive detection of bacteria

BACKGROUND

Dual atomic site catalysts (DASCs) have aroused extensive interest in analytical chemistry on account of the superb catalytic activity caused by the highly-exposed active centers and synergistic effect of adjacent active centers. The reported protocols for preparing DASCs usually involve harsh conditions such as acid/base etching and high-temperature calcination, leading to unfavorable water dispersity and restricted application. It is crucial to develop DASCs with satisfactory water dispersity, improved stability, and mild preparation procedures to facilitate their application as signal probes in analytical chemistry.

RESULTS

Formic acid was adopted as a modulator for preparing MOF-808 with abundant defective sites, which was used as the carrier for implanting Co atoms. Co DASCs with a special coordination structure of Co2-O10 and a high loading efficiency of 11.1 wt% were prepared with a mild solvothermal protocol. The resultant Co DASCs can significantly accelerate decay of H2O2 for forming numerous reactive oxygen radicals and boost chemiluminescent (CL) signal. Co DASCs at 1.0 μg mL-1 can enhance the CL signal of luminol-H2O2 system by about 5800 times. Thanks to their satisfactory water dispersity and excellent CL enhancement performance, they were used as ultra-sensitive CL signal probes for monitoring methicillin-resistant Staphylococcus aureus. The method shows a detection range of 102-107 CFU mL-1 and a detection limit of 47 CFU mL-1. Antibiotic susceptibility test was performed with the established CL method to prove its practicality.

SIGNIFICANCE

The water dispersible Co DASCs prepared with facile and mild solvothermal protocol exhibit prominent peroxidase-like activity and can promote the production of reactive oxygen radicals for boosting CL signal. Therefore, this study paves an avenue for implanting DASCs in defect-engineered carrier to prepare signal probes suitable for development of ultra-sensitive CL analytical methods.

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

The classic luminol-H2O2 chemiluminescence (CL) systems suffer from easy self-decomposition of H2O2 at room temperature, hindering the practical applications of the luminol-H2O2 CL system. In this work, unexpectedly, we found that the carbon vacancy-modified Fe-N-C single atom catalysts (VC-Fe-N-C SACs) can directly trigger a luminol solution to generate strong CL emission in the absence of H2O2. The Fe-based SACs were prepared through the conventional pyrolysis of zeolitic imidazolate frameworks. The massive carbon vacancies were readily introduced into Fe-N-C SACs through a tannic acid-etching process. Carbon vacancy significantly enhanced the catalytic activity of Fe-N-C SACs on the CL reaction of luminol-dissolved oxygen. The VC-Fe-N-C SACs performed a 13.4-fold CL enhancement compared with the classic luminol-Fe2+ system. It was found that the introduction of a carbon vacancy could efficiently promote dissolved oxygen to convert to reactive oxygen species. As a proof of concept, the developed CL system was applied to detect alkaline phosphatase with a linear range of 0.005-1 U/L as well as a detection limit of 0.003 U/L. This work demonstrated that VC-Fe-N-C SAC is a highly efficient CL catalyst that can promote the analytic application of the luminol CL system.

Mn Single-Atom Nanozymes with Superior Loading Capability and Superb Superoxide Dismutase-like Activity for Bioassay

Single-atom nanozymes (SANs) with highly exposed active sites and remarkable catalytic activity have shown noteworthy practicability in heterogeneous catalysis-based bioassay. Nevertheless, most of them were reported with peroxidase-like activity and ordinary loading capability. It is still a challenge to prepare high-loading SANs with desirable superoxide dismutase (SOD)-like activity. In this work, Mn SAN was successfully confined in the frameworks of Prussian blue analogues formed on Ti₃C₂ MXene sheets with the assistance of massive surfactants, which show a superior loading efficiency of 13.5 wt % (typically <2.0 wt %). The prepared Mn SAN exhibits desirable superoxide radical anion elimination capability because of its SOD-like activity. Moreover, due to the wide-spectrum absorption behavior of the carriers, Mn SAN shows a synergistically quenching efficiency up to 98.89% on the emission of the reactive oxygen species-mediated chemiluminescent (CL) system. Inspired by these features, a CL quenching method was developed on a lateral flow test strip platform by utilizing Mn SAN as a signal quencher and acetamiprid as a model analyte. The method for detecting acetamiprid shows a detection range of 1.0-10,000 pg mL^-1 and a limit of detection of 0.3 pg mL^-1. Its accuracy has been validated by detecting acetamiprid in medicinal herbs with acceptable recoveries. This work opens an avenue for preparing SANs with a surfactant-assisted protocol and pioneers the study of SANs with SOD-like activity in bioassay.

Smartphone-Based Pressure Signal Readout Device Combined with Bidirectional Immunochromatographic Test Strip for Dual-Analyte Detection

Pressure has been a facile signal readout mode for developing point-of-care testing devices due to the attractive features of portability, accessibility, rapidity, and affordability. Herein, a pressure signal readout device was designed by integrating two homemade needle-type piezoresistive transducers, a controller for a thin-film piezoresistive sensor and a smartphone. Meanwhile, a bidirectional immunochromatographic test strip was designed as an immunoreaction platform for dual-analyte detection. Using PdCuPt nanoparticles with catalase-mimic activity as signal tags, the pressure signals triggered by catalyzed aerogenous reaction were monitored by the pressure signal readout device and read on a smartphone with the Bluetooth module. In this proof-of-principle work, imidacloprid and carbendazim were detected as model analytes. The dynamic ranges for quantitating imidacloprid and carbendazim are 20 pg mL^-1 to 50 ng mL^-1 and 50 pg mL^-1 to 50 ng mL^-1, respectively. The whole immunoassay process was completed within 16 min. The recovery values for imidacloprid and carbendazim spiked into herbal medicines are 82.0-110.0 and 84.0-116.0%, respectively, verifying its reliability for real sample detection. As the smartphone APP and controller for a thin-film piezoresistive sensor contain 12 signal channels, the system can be easily extended to meet the demand for high-throughput screening.