Water dispersible cobalt single-atom catalysts with efficient Chemiluminescence enhancement for sensitive bioassay

Self-Illuminating Copper-Luminol Coordination Polymers for Bioluminescence Imaging of Oxidative Damage

Timely detection of reactive oxygen species (ROS) accumulated during inflammation is essential for an early disease diagnosis. Compared to fluorescence probes with limited sensitivity and accuracy, chemiluminescence (CL) imaging offers the potential for highly sensitive molecular visualization of ROS by minimizing background interferences. However, the development of bright and easily manufacturable CL probes for ROS imaging remains challenging. In this study, a novel chemiluminescent nanoprobe named Cu-Lum@NPs for ROS imaging in inflammation was synthesized by using a one-step solvothermal method. The Cu-Lum@NPs, which are composed of coordination polymers containing copper ions and luminol (Lum), demonstrate intrinsic peroxidase-like activity that relies on Cu(I) as the catalytic active center to initiate the Fenton reaction. This catalytic process facilitates the decomposition of hydrogen peroxide (H2O2) into hydroxyl radicals (•OH) and superoxide anion radicals (O2•-), leading to the oxidation of Lum and inducing strong luminescence. Cu-Lum@NPs, displaying nanozyme characteristics, were observed to accelerate and enhance the ROS-responsive luminescence (10-1600-fold in solution and over 100-fold in neutrophils) and notably extend persistent luminescence. The Cu-Lum@NPs allowed for CL imaging of endogenous ROS in living cells and animals with an outstanding signal-to-noise ratio exceeding 96 and facilitated oxidative damage luminescence imaging for tissue-specific detection. The study presents Cu-Lum@NPs, a highly sensitive and easily manufacturable chemiluminescent nanoprobe for ROS imaging both in vitro and in vivo, exhibiting enhanced luminescence and prolonged persistence for ROS-related disease detection.

Ultrasensitive Imaging Assay of Multiple Mycotoxins Using Cobalt DNA-Inorganic Hybrid Superstructure with High Chemiluminescence Catalytic Property

A multiplex assay of mycotoxins in food and medicine is urgently needed and challenging due to synergistic hazards of trace mycotoxins and a lack of sensitive and user-friendly detection approaches. Herein, a cobalt DNA-inorganic hybrid superstructure (Co@DS) was developed through isothermal rolling circle amplification (RCA) for an ultrasensitive chemiluminescence (CL) imaging assay of multiple mycotoxins. Cobalt ions were enriched in the RCA product, endowing the Co@DS with a high CL catalytic property. Experimental studies elucidated the formation and CL catalytic mechanism of Co@DS. Co@DS was facilely integrated with biotinylated DNA to function as a universal platform and combined with a disposable immunosensor array chip. After a competitive immunoassay and biotin-avidin recognition, the CL signals of luminol and hydrogen peroxide, catalyzed by Co@DS captured on each testing zone of the array chip, were imaged simultaneously. Target mycotoxins can be quantitated by CL intensities. To validate the concept, the CL imaging approach was employed for joint determination of aflatoxin B1, ochratoxins A, and zearalenone. Under optimal conditions, it showed advantages including simple sample pretreatment, acceptable throughput, high accuracy, minimal sample consumption, broad linear ranges, and detection limits as low as 0.75, 0.62, and 0.61 pg mL-1, respectively. Furthermore, the approach was applied in analyzing real coix seed samples, showcasing excellent performance in effectively distinguishing qualified and contaminated medicine, revealing the great potential in managing the complex issue of mycotoxins cocontamination in food and medicine.

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.

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.

Recent advances in the synthesis and applications of single-atom nanozymes in food safety monitoring

Nanozymes are synthetic compounds with enzyme-like tunable catalytic properties. The success of nanozymes for catalytic applications can be attributed to their small dimensions, cost-effective synthesis, appreciable stability, and scalability to molecular dimensions. The emergence of single atom nanozymes (SANzymes) has opened up new possibilities in bioanalytical applications. In this regard, this review outlines enzyme-mimicking features of SANzymes for food safety applications in relation to the key variables controlling their catalytic performance. The discussion is extended further to cover the applications of SANzymes for the monitoring of various compounds/biomaterials of significance with respect to food safety (e.g., pesticides, veterinary drug residues, foodborne pathogenic bacteria, mycotoxins/bacterial endotoxin, antioxidant residues, hydrogen peroxide residues, and heavy metal ions). Furthermore, the performance of SANzymes is evaluated in terms of various performance metrics such as limit of detection (LOD), linear dynamic range, and figure of merit (FoM). The challenges and future road map for the applications of SANzymes are also addressed along with their upscaling in the area of food safety.

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.

A novel luminol-coordinated silver(I) organic gel with self-enhanced chemiluminescence applied for uric acid detection

A novel silver(I)-based metal-organic gel (AgMOG) consisting of luminol as the ligand was synthesized by a facile strategy, which was found to exhibit self-enhancing chemiluminescence (CL) property. Based on this, a new AgMOG-K₂S₂O₈ CL system without additional catalyst was established. According to the results of CL spectra, electron spin resonance (ESR) spectra as well as the influence of radical scavengers to AgMOG-K₂S₂O₈ system, the possible CL mechanism of this system was discussed. In this CL system, AgMOG exhibited the dual properties of catalysis and luminescence. On the one hand, AgMOG can catalyze K₂S₂O₈ to produce SO₄^•-. The generated SO₄^•- can be converted to hydroxyl radical (OH^•) under alkaline condition, and further converted to other radical oxygen species (ROS, such as ¹O₂ and O₂^•-). Furthermore, the reaction between the K₂S₂O₈ and H₂O can form H₂O₂, which also can be catalyzed by AgMOG to produce ROS. On the other hand, the AgMOG can be oxidized by ROS to emit strong CL signal. Then, based on the quenching effect of uric acid (UA) to this CL system, a method for UA detection was established with a good linearity over the range from 0.08 to 10 µmol·L^-1. In this work, a new CL luminant with catalytic property was synthesized by a simple method, and a self-enhancing AgMOG-K₂S₂O₈ CL system was developed for the first time, providing a novel direction for the application of MOG in the CL field.

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.

Single-atom nanozymes: From bench to bedside

Single-atom nanozymes (SANs) are the new emerging catalytic nanomaterials with enzyme-mimetic activities, which have many extraordinary merits, such as low-cost preparation, maximum atom utilization, ideal catalytic activity, and optimized selectivity. With these advantages, SANs have received extensive research attention in the fields of chemistry, energy conversion, and environmental purification. Recently, a growing number of studies have shown the great promise of SANs in biological applications. In this article, we present the most recent developments of SANs in anti-infective treatment, cancer diagnosis and therapy, biosensing, and antioxidative therapy. This text is expected to better guide the readers to understand the current state and future clinical possibilities of SANs in medical applications.

Atomic Dispersion of Zn2+ on N-Doped Carbon Materials: From Non-Activity to High Activity for Catalyzing Luminol-H2O2 Chemiluminescence

Fe and Co single-atom catalysts (SACs) have been widely explored in many fields, while Zn SACs are still in their infancy stage. Herein, we unexpectedly found that atomically dispersed Zn²⁺ on N-doped carbon material (Zn-N-C) exhibited high catalytic activity on luminol-H₂O₂ chemiluminescence (CL) reaction. The Zn-N-C SACs were readily prepared through simple pyrolyzation of the cheap precursors (dopamine and ZnCl₂). The mechanism of Zn SAC-catalyzed CL reaction of luminol-H₂O₂ was investigated in detail. The activity of Zn SACs originated from the Zn-N sites in the Zn-N-C structure. The monoatomic dispersion makes Zn²⁺ catalytic performance change from no activity to high activity in luminol-H₂O₂ CL reaction. This study demonstrated the particularity of the monatomic metal catalyst over the conventional metal ion. This work provides the unprecedented perspective for design of new metal SACs in CL reaction.

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

Single atom-dispersed catalysts (SADCs) with highly exposed active sites can be used as sensitive signal probes because of their superior catalytic efficiency. However, the dispersed atoms tend to aggregate, restricting the loading capacity of metal atoms. Herein, the defective sites on Zr-oxo clusters of metal-organic frameworks (MOFs) UiO-66-NH₂ were modulated by excessive acetic acid and utilized for confining metal atoms with high loading capacity. To verify the feasibility of the designed strategy, the Co element was loaded onto MOFs UiO-66-NH₂ to prepare SADCs with desirable Fenton-like activity. The prepared Co SADCs at a low concentration of 1.0 μg mL^-1 are found to boost chemiluminescent (CL) emission for 3700 times due to the significantly improved Co content of 5.55 wt %. The superior CL enhancement efficiency is ascribed to reactive oxygen species generated by the accelerated decay of H₂O₂. To verify the application potential in CL assay, they were used as signal probes to establish an immunoassay method for carbendazim with a dynamic range of 1.0 pg mL^-1 to 25 ng mL^-1 and a limit of detection of 0.33 pg mL^-1. This defective site modulation strategy paves an avenue for preparing SADCs with a high CL response by improving the loading capacity of metal atoms.