Smart CuS Nanoparticles as Peroxidase Mimetics for the Design of Novel Label-Free Chemiluminescent Immunoassay

Iron decoration in binary graphene oxide and copper iron sulfide nanocomposites boosting catalytic antibacterial activity in acidic microenvironment against antimicrobial resistance

The strong antimicrobial resistance (AMR) of multidrug-resistant (MDR) bacteria and biofilm, especially the biofilm with extracellular polymeric substance (EPS) protection and persister cells, not only renders antibiotics ineffective but also causes chronic infections and makes the infectious tissue difficult to repair. Considering the acidic properties of bacterial infection microenvironment and biofilm, herein, a binary graphene oxide and copper iron sulfide nanocomposite (GO/CuFeSx NC) is synthesized by a surfactant free strategy and utilized as an alternative smart nanozyme to fight against the MDR bacteria and biofilm. For the GO/CuFeSx NC, the iron decoration facilitates the well distribution of bimetallic CuFeSx NPs on the GO surfaces compared to monometallic CuS NPs, providing synergistically enhanced peroxidase (POD)-like activity in acidic medium (pH 4 ∼ 5) and intrinsic strong near infrared (NIR) light responsive photothermal activity, while the ultrathin and sharp structure of 2D GO nanosheet allows the GO/CuFeSx NC to strongly interact with the bacteria and biofilm, facilitating the catalytic and photothermal attacks on the bacterial surfaces. In addition, the GO in GO/CuFeSx NC exhibits a "Pseudo-Photo-Fenton" effect to promote the ROS generation. Therefore, the GO/CuFeSx NC can effectively kill bacteria and biofilm both in vitro and in vivo, finally eliminating the infections and accelerating the tissue repair when treating the biofilm-infected wound. This work paves a new way to the design of novel nanozyme for smart antibacterial therapy against antimicrobial resistance.

ZnO/Au/GaN heterojunction-based self-powered photoelectrochemical Sensor for alpha-fetoprotein detection

In recent years, the development of miniature and portable sensors has been a major focus of research. PEC self-powered sensors have emerged as a potential solution to the power supply issue, eliminating the need for external power supplies and operating without bias voltage. This study developed a ZnO/Au/GaN sensor for highly sensitive detection of alpha-fetoprotein (AFP). The sensor uses GaN substrates with nanogold films to provide an auxiliary bias voltage, promoting high photogenerated current density. Using ZnO/Au/GaN as a photoanode resulted in significantly higher photocurrent generated by the sensor compared to Au/GaN or ZnO/ITO alone. To enable selective detection of AFP, antibody modification of the ZnO nanorod arrays was employed. The linear range of the sensor response to AFP was determined to be 0.080-5.0 ng/mL, with an impressively low detection limit of 0.027 ng/mL (S/N = 3). These results demonstrate the potential of this self-powered sensor for detecting AFP content in human serum samples. Overall, this study presents a novel approach for developing highly sensitive and selective self-powered sensors for biomarker detection, which could facilitate early detection and clinical diagnosis of various types of cancer.

Synthesis of Two-Dimensional (Cu-S)n Metal-Organic Framework Nanosheets Applied as Peroxidase Mimics for Detection of Glutathione

Facilely synthesized peroxidase-like nanozymes with high catalytic activity and stability may serve as effective biocatalysts. The present study synthesizes peroxidase-like nanozymes with multinuclear active sites using two-dimensional (2D) metal-organic framework (MOF) nanosheets and evaluates them for their practical applications. A simple method involving a one-pot bottom-up reflux reaction is developed for the mass synthesis of (Cu-S)n MOF 2D nanosheets, significantly increasing production quantity and reducing reaction time compared to traditional autoclave methods. The (Cu-S)n MOF 2D nanosheets with the unique coordination of Cu(I) stabilized in Cu-based MOFs demonstrate impressive activity in mimicking natural peroxidase. The active sites of the peroxidase-like activity of (Cu-S)n MOF 2D nanosheets were predominantly verified as Cu(I) rather than Cu(II) of other Cu-based MOFs. The cost-effective and long-term stability of (Cu-S)n MOF 2D nanosheets make them suitable for practical applications. Furthermore, the inhibition of the peroxidase-like activity of (Cu-S)n MOF nanosheets by glutathione (GSH) could provide a simple strategy for colorimetric detection of GSH against other amino acids. This work remarkably extends the utilization of (Cu-S)n MOF 2D nanosheets in biosensing, revealing the potential for 2D (Cu-S)n MOFs.

Fluorometric detection of alpha-fetoprotein based on the use of a novel organic compound with AIE activity and aptamer-modified magnetic microparticles

BACKGROUND

Liver cancer is one of the most common cancers in the world, and it seriously threatens human life and health. Alpha-fetoprotein (AFP), as a carcinogenic glycoprotein, is an important serum marker for detecting liver cancer. Therefore, the accurate and sensitive determination of AFP is crucial for the early diagnosis and treatment of liver cancer. To this end, a label-free fluorescence aptasensor for detecting AFP based on the use of a novel organic Compound D with an aggregation-induced emission activity and aptamer-modified magnetic microparticles was constructed.

RESULTS

Compound D could combine with the complementary short chain of the aptamer (CSC-Apt) of AFP to form the D/CSC-Apt complex and realize the fluorescence enhancement of Compound D. Then, magnetic particles modified by the Apt of AFP (Apt-Fe3O4) were prepared. When AFP (or nontarget substance) and D/CSC-Apt were successively added to the Apt-Fe3O4 solution, Apt-Fe3O4 selectively bound to AFP or the D/CSC-Apt complex. Magnetic separation technology showed the changes in the fluorescence intensity of the supernatant. The research results revealed a good linear relationship between the changes in the fluorescence intensity of the supernatant and concentration of AFP within the concentration range of 10-10000 pg mL-1. The proposed aptasensor could achieve high-sensitivity and high-specificity detection of AFP, and its limit of detection was 3 pg mL-1 (S/N = 3).

SIGNIFICANCE AND NOVELTY

The sensor combines the advantages of high selectivity of Apt, high sensitivity of fluorescence analysis, AIE effect and good water solubility of Compound D, and rapid separation using magnetic separation technology. And it can be directly used for the detection of AFP in actual serum samples with high accuracy, whereas most of the methods reported in the literature can only detect AFP in spiked serum samples.

Functional Zonation Strategy of Heterodimer Nanozyme for Multiple Chemiluminescence Imaging Immunoassay

Although nanozymes with intrinsic enzyme-like characteristics have aroused great interest in the biosensing field, the challenge is to keep high enzyme-like activity of the nanozyme after the modification of biomolecules onto nanozymes. Herein, a functional zonation strategy of a heterodimer nanozyme was proposed to tackle the challenge and further construct a multiple chemiluminescence (CL) imaging immunoassay. Here Fe3O4-Au as a heterodimer nanozyme model was divided into two zones, in which Fe3O4 nanoparticles (NPs) were regarded as a nanozyme zone and AuNPs were defined as an antibody immobilization zone. A signal amplification probe (Fe3O4-Au-Ab2) was prepared by modifying the secondary antibody (Ab2) on AuNPs of the Fe3O4-Au heterodimer owing to the Au-S bond. The exposed Fe3O4 of the Fe3O4-Au-Ab2 probe shows very high peroxidase-like activity and can efficiently catalyze H2O2-luminol to produce strong CL imaging signals for multiple antigens detection. Using chicken interleukin-4 (ChIL-4) and chicken gamma interferon (ChIFN-γ) as models, the proposed CL imaging immunoassay shows wide linear ranges (0.005-0.10 ng/mL for both ChIL-4 and ChIFN-γ) and low detection limits (0.58 pg/mL for ChIL-4, 0.47 pg/mL for ChIFN-γ) with the characteristics of high sensitivity, high specificity, and good stability. This work provides a promising functional zonation concept for nanozymes to construct new types of nanozyme probes for immunoassay of multiple biomolecules.

Cobalt Species-Loaded MOFs as Chemiluminescent Catalysts for Monitoring Carbendazim

The application of active metal-based nanoscale catalysts as signal enhancers for chemiluminescent immunoassay (CLIA) is restricted by poor thermodynamic stability and ease of aggregation. For the present exploration, zirconium-based MOFs UiO-66-NH2 were adopted as supports to load cobalt species by an impregnation-reduction approach. Cobalt species were uniformly distributed in the framework architecture of the MOF materials. The prepared cobalt-loaded MOF hybrids, noted as UiO-66-NH2/Co, display superior chemiluminescence (CL) catalytic activity owing to the introduction of cobalt catalytic centers. The CL catalytic capability of UiO-66-NH2/Co hybrids is about 18 times of that of free cobalt ions at the same cobalt amount. The results of mechanism exploration manifest that the hybrids are capable of accelerating the decay of hydrogen peroxide and promoting the yield of reactive oxygen species. Based on their remarkable CL catalytic capability, a CLIA approach was proposed to monitor carbendazim by adopting the hybrids as signal probes, which showed the merits of high sensitivity and satisfactory selectivity. Carbendazim was quantitated within a concentration range of 0.05 to 60 ng mL-1, with a detection limit of 19.8 pg mL-1. The results for monitoring spiked samples verify the acceptable practicality of the proposed CLIA approach.

Label-Free Detection of Epinephrine Using Flower-like Biomimetic CuS Antioxidant Nanozymes

A biosensor comprising crystalline CuS nanoparticles (NPs) was synthesized via a one-step simple coprecipitation route without involvement of a surfactant. The powder X-ray diffraction method has been used to evaluate the crystalline nature and different phases consist of the formation of CuS NPs. Mainly hexagonal unit cells consist of the formation of CuS NP unit cells. Most of the surfaces are covered with rhombohedral microparticles with a smooth exterior and surface clustering, examined by SEM images, and the shape of NPs was spherical, having an average size of 23 nm, as confirmed by TEM analysis. This study has focused on the peroxidase-mimicking activity, superoxide dismutase (SOD)-mimicking activity, and chemosensor-based colorimetric determination and detection of epinephrine (EP) neurotransmitters with excellent selectivity. The CuS NPs catalyzed the oxidation of the oxidase substrate 3, 3-5, 5 tetramethyl benzidine (TMB) with the help of supplementary H2O2 that followed Michaelis-Menten kinetics with excellent Km and Vmax values calculated by the Lineweaver-Burk plot. Taking advantage of the drop in absorbance upon introduction of EP for the CuS NPs-TMB/H2O2 system, a colorimetric route has been developed for selective and real-time detection of EP. The sensitivity of the new colorimetric probe was vibrant, having a linear range of 0-16 μM, and achieved a low limit of detection of 457 nM. Moreover, the present nanosystem exhibited appreciable SOD-mimicking activity which could effectively remove O2•- from commercial cigarette smoke, along with it acting as a potential radical scavenger as well. The new nanosystem effectively scavenged •OH, O2.-, and metal chelation which were investigated calorimetrically.

Application of Metal-Based Nanomaterials in In Vitro Diagnosis of Tumor Markers: Summary and Prospect

Cancer, which presents with high incidence and mortality rates, has become a significant health threat worldwide. However, there is currently no effective solution for rapid screening and high-quality treatment of early-stage cancer patients. Metal-based nanoparticles (MNPs), as a new type of compound with stable properties, convenient synthesis, high efficiency, and few adverse reactions, have become highly competitive tools for early cancer diagnosis. Nevertheless, challenges such as the difference between the microenvironment of detected markers and the real-life body fluids remain in achieving widespread clinical application of MNPs. This review provides a comprehensive review of the research progress made in the field of in vitro cancer diagnosis using metal-based nanoparticles. By delving into the characteristics and advantages of these materials, this paper aims to inspire and guide researchers towards fully exploiting the potential of metal-based nanoparticles in the early diagnosis and treatment of cancer.

Multifunctionalized flower-like gold nanoparticles with high chemiluminescence for label-free sensing of the hepatitis C virus core protein

Developing functionalized nanomaterials with strong chemiluminescence (CL) properties is highly significant for ultrasensitive bioanalysis. Here, we report chitosan (CS), luminol, and Co²⁺-functionalized flower-like gold nanoparticles (Co²⁺/CS/Lum/AuNFs) with strong CL for the label-free sensing of the HCV core protein (HCVcp). The Co²⁺/CS/Lum/AuNFs exhibited a greatly enhanced CL emission at around 425 nm, which is 50 times stronger than that of CS/Lum/AuNFs, and is superior to other commonly reported CL nanomaterials. The HCVcp aptamer (HCVcp-apt) further functionalized the surface of the Co²⁺/CS/Lum/AuNFs through electrostatic interactions blocked the Co²⁺ catalytic site, depressing the CL. Owing to the high affinity of HCVcp for the HCVcp-apt, the presence of HCVcp predominated its binding and effectively separated the HCVcp-apt from the surface of the Co²⁺/CS/Lum/AuNFs, so that the CL intensity was significantly enhanced. As the results showed, the HCVcp-apt/Co²⁺/CS/Lum/AuNFs were successfully used to detect the HCVcp in human serum samples with a linear range from 0.50 ng mL^-1 to 1.00 μg mL^-1, a detection limit of 0.16 ng mL^-1 and an excellent selectivity over other analogs. The strategy is universal for the development of the ultrasensitive detection of other proteins in the field of early disease diagnostics.

A label-free electrochemical immunosensor based on PtCoCu PNPs/NB-rGO as a dual signal amplification platform for sensitive detection of β-Amyloid1-42

In this work, a label-free electrochemical immunosensor based on popcorn-shaped PtCoCu nanoparticles supported on N- and B-codoped reduced graphene oxide (PtCoCu PNPs/NB-rGO) was constructed to sensitively detect concentration level of β-Amyloid_1-42 oligomers (Aβ). The PtCoCu PNPs exhibits excellent catalytic ability due to its popcorn structure which improves the specific surface area and porosity, resulting in more active sites being exposed and fast transport paths for ion/electron. NB-rGO with large surface area and unique pleated structure could disperse PtCoCu PNPs through electrostatic adsorption and formation of d-p dative bonds between the metal ion and pyridinic N of NB-rGO. In addition, the doping of B atoms enhances the catalytic ability of GO enormously and achieves further signal amplification. Besides, both PtCoCu PNPs and NB-rGO are able to fix abundant antibodies through M(Pt, Co, Cu)-N bonds and amide bonds respectively without any other complex processing procedures such as carboxylation, ect. The designed platform achieved the dual amplification of electrocatalytic signal and effectively immobilization of antibodies. Under the optimum conditions, the designed electrochemical immunosensor presented wide linear rang (50.0 fg/mL ∼ 100 ng/mL) and low detection limits (3.5 fg/mL). The results demonstrated that the prepared immunosensor will be promising in sensitive detection of AD biomarkers.

Strategies to simplify operation procedures for applying labeled antibody-based immunosensors to point-of-care testing

Point-of-care testing (POCT) is an ideal testing format for the rapid and on-site detection of analytes in patients, and facilitates disease diagnosis and monitoring. Molecular recognition elements are required for the specific detection of analytes, and biosensors that use antibodies as the molecular recognition elements are called immunosensors. Traditional immunosensors such as sandwich enzyme-linked immunosorbent assay (ELISA) require complicated procedures to form immunocomplexes consisting of detection antibodies, analytes, and capture antibodies. They also require long incubation times, washing procedures, and large and expensive specialized equipment that must be operated by laboratory technicians. Immunosensors for POCT should be systems that use relatively small pieces of equipment and do not require special training. In this review, to help in the construction of immunosensors for POCT, we have summarized the recently reported strategies for simplifying the operation, incubation, and washing procedures. We focused on the optical and electrochemical detection principles of immunosensors, compared the strategies for operation, sensitivity, and detection devices and discussed the ideal system. Combining detection devices that can be fabricated inexpensively and strategies that enable simplification of operation procedures and enhance sensitivities will contribute to the development of immunosensors for POCT.

Gold Nanowires Array-Based Closed Bipolar Nanoelectrode System for Electrochemiluminescence Detection of α-Fetoprotein on Cell Surface

Inspired by the promising applications of a closed bipolar electrodes (c-BPEs) system in electrochemiluminescence (ECL) detection of cell adhesion and disease-related biomarkers, here, a gold nanowires array-based c-BPEs system was constructed for cell surface protein detection. Regular and uniform gold nanowires array were prepared by intermittent potentiostatic deposition. Then, two poly(dimethylsiloxane) (PDMS) chips with a hole diameter of 2 mm as a reservoir were placed at both sides of Au nanowires array to construct c-BPEs system. Thionine-functionalized silicon dioxide nanoparticles conjugated to antibody (Ab2-Th@SiO₂) were used as the electrochemical probe, while [Ru(bpy)₃]²⁺-wrapped SiO₂ nanoparticles (Ru(II)@SiO₂) were employed as the ECL signal readout. Taking α-fetoprotein (AFP) as model, the gold nanowires array-based c-BPEs system allowed sensitive detection of AFP at a linear range from 0.002 to 50.0 ng/mL and at least 6 living cells ascribing to the synergetic amplification effect at both sensing and reporting chambers. Besides, the amount of AFP expressed by HepG2 cells was calculated to be 6.71 pg/cell. The presented strategy with high sensitivity provided a promising and universal platform for the detection of other cancer cells and disease-related biomarkers (such as proteins, glycan, miRNA).

Ultra-sensitive detection of florfenicol by flow injection chemiluminescence immunoassay based on Nickel/Cobalt bimetallic metal-organic framework nanozymes

The emergence and progress of metal-organic frameworks (MOFs) with high stability, large surface area, and abundant unsaturated active sites, once again promote the development of nanozymes, making nanozymes more advantageous to replace natural enzymes and will increase the applications of chemiluminescence immunoassay. In this study, a flow injection chemiluminescence immunoassay based on Ni/Co metal-organic framework (Ni/Co-MOF) nanozymes was developed, which can quickly and highly sensitively detect florfenicol (FF) in animal-derived food residues. Ni/Co-MOF_0.75 nanospheres can not only form stable immune probes with antibodies but also act as nanozymes to efficiently catalyze H₂O₂ for amplifying the chemiluminescence signal of the luminol-H₂O₂ system. In addition, due to good biocompatibility and large specific surface area, carboxyl-modified resin beads are used as a suitable material for loading more coating antigens. Based on the principle of competitive immunity, FF standard solution will compete with coating antigen loaded on the carboxyl resin beads for the limited binding sites on the FF antibody. Under the best experimental conditions, the detection range of FF is 0.0001-1000 ng mL^-1, and the detection limit (LOD) is 0.033 pg mL^-1 (S/N = 3). Furthermore, this method has been successfully applied to the analysis of actual samples with satisfactory results, which will provide a certain reference for the detection of small molecules in food and environmental analysis.

Proximity hybridization induced DNA assembly for label-free surface-enhanced Raman spectroscopic detection of carcinoembryonic antigen

In our research, label-free and surface-enhanced Raman dyes-free Raman spectroscopy which was used to detect carcinoembryonic antigen (CEA) according to poly adenine (Poly A)-regulated self-assembly methods was developed and studied. CEA induced partial hybridization of Ab-H2 and Ab-H1, and Ab-H1-CEA-Ab-H2 (a sandwich proximity CEA-DNA complex) was formed, which unfolded molecular beacon 1 (MB1) and modified the substrate. Subsequently, MB2-AuNPs were hybridized with MB1, and Ab-H1-CEA-Ab-H2 was released via toehold regulated displacements of DNA strands. Therefore, hybridization processes of MB2 and MB1 were induced and promoted by CEA-DNA complexes which worked as catalysts. The misplaced target then induced a next round of strand exchange, and the signals for determination of CEA were amplified by AuNPs absorbed on the substrate. It was indicated that the spectral characteristics of adenine at 736 cm^-1 were consistent with the SERS spectrum of DNA. Adenine acted as an internal marker for label-free SERS detection of CEA. Moreover, satisfactory stability and reproducibility were found. Meanwhile, the antibody could specifically recognize the corresponding antigen. Since adenine was dominant in SERS spectra, which was also proximal to Au surface, the sensitivity of the novel method was high without modifications. The analytical performance of this method in determining serum CEA was satisfactory.

A dual-signal output electrochemical immunosensor based on Au-MoS2/MOF catalytic cycle amplification strategy for neuron-specific enolase ultrasensitive detection

In this work, a dual-signal output electrochemical immunosensor based on the Au-MoS₂/MOF high-efficiency catalytic cycle amplification strategy for the sensitive detection of neuron-specific enolase (NSE). The mixed-valence structure MOF (Fe²⁺/Fe³⁺-MOF) exhibits high-speed charge mobility and excellent electrochemical performance. Notably, nanoflowers-like MoS₂ (MoS₂ NFs), as a co-catalyst, were introduced into Fe²⁺/Fe³⁺-MOF to successfully ensure the stable cycle of Fe²⁺/Fe³⁺ at the electrode interface. The constantly emerging of "fresh" active sites significantly amplified the current signal response. According to the electrochemical behavior, the catalytic cycle mechanism and electron transfer pathways between MoS₂ and Fe²⁺/Fe³⁺-MOF were further discussed. The two output signals of a sample realized the self-calibration of the immunoassay results, which improved the reliability and sensitivity of the immunosensor. Under optimal conditions, the linear range was 1.00 pg/mL∼100 ng/mL, and the low detection limits were 0.37 pg/mL and 0.52 pg/mL. The results suggest that the as-proposed immunosensor will be promising in the biological analysis and early clinical diagnosis of cancer biomarkers.

Direct and Indirect Chemiluminescence: Reactions, Mechanisms and Challenges

Emission of light by matter can occur through a variety of mechanisms. When it results from an electronically excited state of a species produced by a chemical reaction, it is called chemiluminescence (CL). The phenomenon can take place both in natural and artificial chemical systems and it has been utilized in a variety of applications. In this review, we aim to revisit some of the latest CL applications based on direct and indirect production modes. The characteristics of the chemical reactions and the underpinning CL mechanisms are thoroughly discussed in view of studies from the very recent bibliography. Different methodologies aiming at higher CL efficiencies are summarized and presented in detail, including CL type and scaffolds used in each study. The CL role in the development of efficient therapeutic platforms is also discussed in relation to the Reactive Oxygen Species (ROS) and singlet oxygen (1O2) produced, as final products. Moreover, recent research results from our team are included regarding the behavior of commonly used photosensitizers upon chemical activation under CL conditions. The CL prospects in imaging, biomimetic organic and radical chemistry, and therapeutics are critically presented in respect to the persisting challenges and limitations of the existing strategies to date.

Automatic label-free immunoassay with high sensitivity for rapid detection of SARS-CoV-2 nucleocapsid protein based on chemiluminescent magnetic beads

Accurate and efficient early diagnosis is crucial for the control of COVID-19 pandemic. However, methods that can balance sensitivity, high throughput, detection speed and automation simultaneously are still scarce. Here, we report an automatic label-free chemiluminescence immunoassay (CLIA) for rapid SARS-CoV-2 nucleocapsid protein (NP) detection with high sensitivity and throughput. N-(4-aminobutyl)-N-ethylisoluminol and Co²⁺ dual-functionalized chemiluminescent magnetic beads (dfCL-MB) were first applied to the detection of protein by a novel and simple strategy. Sulphydryl polyethylene glycol was coated on the surface of dfCL-MB so as to assemble dfCL-MB and antibody conjugated gold nanoparticles through Au-S bond. Considering the high-risk application scenarios, the immunosensor was integrated with an automatic chemiluminescence analyzer so that the whole testing procedure could be carried out automatically without manual operation. A linear correlation between CL intensities and the logarithm of NP concentration was obtained in the range of 0.1-10,000 pg/mL with a detection limit of 21 fg/mL. The whole process cost 25 min and the sample compartment can bear 24 samples simultaneously. The spiked human serum samples and serum samples from COVID-19 patients were determined with satisfactory recoveries of 91.1-109.4%, suggesting that the proposed label-free CLIA is of great potential for SARS-CoV-2 NP detection in practice.

CuS nanoparticles-enhanced luminol-O2 chemiluminescence reaction used for determination of paracetamol and vancomycin

A new chemiluminescence (CL) method was proposed to measure two widely used drugs, including paracetamol (PCM) and vancomycin (VAN). The CL reaction used was the CuS nanoparticles (CuS NPs)-luminol-O₂ system. In this system, CuS NPs played the role of catalyst and increased the CL intensity. CuS NPs were easily synthesized by quick-precipitation. CuS NPs were characterized by spectroscopic techniques, and the mean size of NPs was estimated to be about 9 nm. In the developed CL methods, PCM and VAN decreased the CL intensity. In the proposed method, the linear concentration ranges were 4.0 × 10^-5-4.0 × 10^-4 mol L^-1 of PCM and 2.0 × 10^-5-6.0 × 10^-4 mol L^-1 of VAN. The limit of detections were 2.9 × 10^-5 mol L^-1 and 8.9 × 10^-6 mol L^-1 for PCM and VAN, respectively. The relative standard deviations (RSD) of the CL method were 2.99 and 4.31 (n = 6) for the determination of 3.0 × 10^-4 mol L^-1 PCM and VAN, respectively. It was also shown that the CL methods can measure PCM and VAN concentrations in various real samples.

Nanozymes in Tumor Theranostics

Nanozymes, a new generation of enzyme mimics, have recently attracted great attention. Nanozymes could catalyze chemical reactions as biological enzymes under physiologically mild conditions with higher-efficiency catalytic activities. Moreover, nanozymes could overcome the shortcomings of natural enzymes, such as easy inactivation, high cost, and low yield. With the development of more and more smart and multi-functional nanosystems, nanozymes display great achievement in tumor biology. In this review, we outline the recent advances of nanozymes in tumor and tumor microenvironment diagnosis, therapy, and theranostics.

An ultrasensitive chemiluminescent biosensor for tracing glutathione in human serum using BSA@AuNCs as a peroxidase-mimetic nanozyme on a luminol/artesunate system

In this work, a nanosensor chemiluminescent (CL) probe for sensing glutathione (GSH) was developed, for the first time, based on its inhibition of the intrinsic peroxidase-mimetic effect of BSA@AuNCs. The endoperoxide linkage of artesunate could be hydrolyzed by BSA@AuNCs resulting in the release of reactive oxygen species (ROS), and the consequent generation of strong CL emission. By virtue of the strong covalent interactions of -S⋯Au-, GSH could greatly suppress the peroxidase-mimetic effect of BSA@AuNCs, leading to a drastic CL quenching. The CL quenching efficiency increased proportionally to the logarithm of GSH concentration through the linearity range of 50.0-5000.0 nM with a limit of detection of 5.2 nM. This CL-based strategy for GSH tracing demonstrated the advantages of ultrasensitivity, high selectivity and simplicity. This strategy was successfully utilized to measure GSH levels in human serum with reasonable recovery results of 98.71%, 103.18%, and 101.68%, suggesting that this turn-off CL sensor is a promising candidate for GSH in biological and clinical samples.

Singlet-oxygen generated by a metal-organic framework for electrochemical biosensing

Enzyme-based electrochemical biosensors have been widely employed for analyte detection for several years. However, for wide application, there are many challenges to overcome, such as the sensitivity of the catalytic activity, and the reproducibility and stability of enzymes. In this work, an enzyme-free sensing strategy based on two-dimensional (2D) metal-organic frameworks (MOFs) as photosensitizers and singlet-oxygen (1O2) as the oxidant has been designed via photocatalysis and electrochemical analysis. To be specific, MOF sheets (Zn-ZnMOF) were prepared with Zn as the node and zinc(ii)tetraphenylporphyrin (TCPP(Zn)) as the ligand, which could generate 1O2 from air under light illumination, and sequentially the generated 1O2 could oxidize analytes to form their oxidation state which could be detected and reduced on the electrode, completing a redox cycle and amplifying electrochemical signals. Thanks to the morphology and superior quantum yield of 1O2 of the Zn-ZnMOF, this method could overcome the limitation of enzymes and afford selective detection, such as of hydroquinone with a detection limit of 0.8 μM in 0.1 M PBS (pH = 7.4). Furthermore, the method does not require additional reactive reagents but only with air and on/off light switching. Thirdly, the method detects the target without washing and enzyme-labelled. With these merits, this work provides a new platform for MOFs as photosensitizers for electrochemical sensors and further development of sensitive, selective, and stable electroanalytical devices for bio-application.

Metal enhanced chemiluminescence nanosensor for ultrasensitive bioassay based on silver nanoparticles modified functional DNA dendrimer

A novel metal enhanced chemiluminescence (MEC) nanosensor was developed for ultrasensitive biosensing and imaging, based on functional DNA dendrimer (FDD), proximity-dependent DNAzyme and silver nanoparticles (AgNPs). The FDD containing two split G-quadruplex structures was prepared through an enzyme-free and step-by-step assembly strategy, and then reacted with AgNPs and hemin molecules to form the FDD/hemin/AgNPs facilely. Such a MEC nanosensor consisted of three modules: FDD (scaffold), the generated G-quadruplex/hemin DNAzyme (signal reporter) and AgNPs (chemiluminescence enhancer). The MEC effect was achieved by controlling the length of DNA sequences between AgNPs on the periphery of FDD and DNAzymes inside it. Such nanosensor exhibited 9-fold amplification and another 6.4-fold metal enhancement in chemiluminescence intensity, which can be easily applied into trace detection of multiple protein markers using a disposable protein immunoarray. The FDD/hemin/AgNPs-based multiplex MEC imaging assay showed wide linear ranges over 5 orders of magnitude and detection limits down to 5× 10^-5 ng L^-1 and 1.8 × 10^-4 U mL^-1 for cardiac troponin T and carcinoma antigen 125, demonstrating a promising potential in application to protein analysis and clinical diagnosis. Moreover, the MEC nanosensor can be effectively delivered into cells with excellent biocompatibility and outstanding stability, offering a new tool for detection of intracellular targets and suggesting wide applications in bioassay.

Chemiluminescence of the Ce(IV)/CDP-Star System Based on the Phosphatase-like Activity of Ce(IV) Ions

The phosphatase-like activity of Ce(IV) ions was applied for chemiluminescence (CL) analysis for the first time. Ce(IV) can catalyze the hydrolysis of CDP-star, which is a phosphatase substrate, to produce strong CL emission. The CL performance of the Ce(IV)/CDP-star system can be significantly improved by the addition of ionic liquids. In the presence of 1-butyl-3-methylimidazolium tetrafluoroborate, the selective and sensitive CL detection of Ce(IV) ions was achieved with a detection limit of 460 nM. The proposed CL system was also used for the detection of ascorbic acid and ClO-. It is based on the phenomenon that Ce(IV) can catalyze the hydrolysis of CDP-star, while Ce(III) cannot. The introduction of reductive ascorbic acid into the mixture of Ce(IV)/CDP-star can turn off the CL signal, while the addition of oxidative ClO- into the solution of Ce(III)/CDP-star can turn on the CL emission. Finally, Ce(IV)/CDP-star CL was successfully applied for evaluating the total antioxidant capacity in commercial fruit juice samples.

Single gold nanoparticle-driven heme cofactor nanozyme as an unprecedented oxidase mimetic

The catalytic diversity of heme enzymes is a perpetuating pursuit for biomimetic chemistry, but heme nanozymes exhibit catalytic activity only reminiscent of peroxidases. Miraculously, the oxidase-like catalytic function of a heme cofactor is elicited with the help of gold nanoparticles (AuNPs) by maintaining heme with a low-valence state (ferrous) in a confined configuration.

CuS nanoparticles decorated MoS2 sheets as an efficient nanozyme for selective detection and photocatalytic degradation of hydroquinone in water

Cost effective and efficient CuS–MoS₂ nanocomposite with enhanced peroxidase enzyme mimetics and photocatalytic activity was synthesized by simple hydrothermal method and successfully utilized for sensing and detection of toxic hydroquinone molecules in aqueous medium.

Effect of proteins on the oxidase-like activity of CeO2 nanozymes for immunoassays

Protein adsorption inhibits the oxidase-like activity of CeO₂ nanoparticles. Coating a partial shell of silica on CeO₂ and subsequent conjugation of antibodies allow highly sensitive and selective detection of fenitrothion.

Nanomaterial-enhanced chemiluminescence reactions and their applications

Chemiluminescence (CL) analysis is a trace analytical method that possesses advantages including high sensitivity, wide linear range, easy operation, and simple instruments. With the development of nanotechnology, many nanomaterial (NM)-enhanced CL systems have been established in recent years and applied for the CL detection of metal ions, anions, small molecules, tumor markers, sequence-specific DNA, and RNA. This review summarizes the research progress of the nanomaterial-enhanced CL systems the past five years. These CL reactions include luminol, peroxyoxalate, lucigenin, ultraweak CL reactions, and so on. The CL mechanisms of the nanomaterial-enhanced CL systems are discussed in the first section. Nanomaterials take part in the CL reactions as the catalyst, CL emitter, energy acceptor, and reductant. Their applications are summarized in the second section. Finally, the challenges and opportunities are discussed.

Dual-Plasmonic Gold@Copper Sulfide Core-Shell Nanoparticles: Phase-Selective Synthesis and Multimodal Photothermal and Photocatalytic Behaviors

Although the intriguing plasmonic properties of noble metal nanoparticles originate from the collective oscillations of free electrons in the conduction band, nanoparticles of doped semiconductors may also exhibit metal-like, plasmonic features that are dictated by the resonantly excited free hole oscillations in the valence band. Here, we combine Au, a representative free electron metal, with copper sulfides, a class of plasmonic p-type semiconductors, in a core-shell nanoparticle geometry to construct dual-plasmonic hetero-nanostructures displaying unique multiplex optical characteristics dominated by plasmonic hole oscillations in the semiconductor shells, plasmonic electron oscillations in the metallic cores, and interband electronic transitions from the valence to conduction bands. Through deliberately designed colloidal synthesis, we are able to selectively grow nanoshells comprising copper sulfides of specifically targeted crystalline phases and Cu/S stoichiometries, such as covellite (CuS), digenite (Cu_1.8S), and nonstoichiometric Cu_2-xS, on the surfaces of Au nanoparticle cores. Our synthetic approach enables us not only to finely control the core and shell dimensions but also to systematically adjust the free hole concentrations in the semiconductor shells, which forms the keystone for the fine tuning of multiple optical resonance modes supported by these hybrid hetero-nanostructures. The dual-plasmonic Au@copper sulfide core-shell nanoparticles exhibit unique multimodal photothermal and photocatalytic behaviors upon selective photoexcitations of different optical transitions at their characteristic resonant frequencies, allowing us to quantitatively evaluate and rigorously compare the intrinsic photothermal and photocatalytic efficacies of multiple types of hot charge carriers, all photoexcited in the same hybrid nanoparticles but with distinct photophysical origins, excited-state lifetimes, energy distributions, and transfer pathways.

Coupling Two Sequential Biocatalysts with Close Proximity into Metal-Organic Frameworks for Enhanced Cascade Catalysis

The encapsulation of multiple enzyme/nanoenzyme systems within mental-organic frameworks (MOFs) shows great promise for a myriad of practical applications. Herein, two sequential biocatalysts, oxidase and hemin, were coupled together with close proximity using a bifunctional polymer, poly(1-vinylimidazole) (PVI), and encapsulated into MOFs. As a demonstration of the power of such a protocol, glucose oxidase&PVI-hemin encapsulated in ZIF-8 showed significant enhancement of bioactivity for a cascade reaction compared to its counterpart without PVI. For the colorimetric assay of glucose, it showed a low limit of detection of 0.4 μM (S/N = 3), high selectivity, and excellent stability. Because there are numerous biocatalysts that can readily be coupled and encapsulated into MOFs, a myriad of interesting properties can be simply realized by encapsulating different sequential biocatalysts.

Co Single-Atom Catalysts Boost Chemiluminescence

Co single-atom catalysts (SACs) with good aqueous solubility and abundant labelling functional groups were prepared in Co/Fe bimetallic metal-organic frameworks by a facile solvothermal method without high-temperature calcination. In contrast to traditional chemiluminescence (CL) catalysts, Co SACs accelerated decomposition of H₂ O₂ to produce a large amount of singlet oxygen (¹ O₂ ) rather than superoxide (O₂ ^.- ) and hydroxyl radical (OH^. ). They were found to dramatically enhance the CL emission of the luminol-H₂ O₂ reaction by 1349 times, and, therefore, were employed as very sensitive signal probes for conducting CL immunoassay of cardiac troponin I. The detection limit of the target analyte was as low as 3.3 pg mL^-1 . It is the first time that employment of SACs for boosting CL reactions has been validated. The Co SACs can also be employed to trace other biorecognition events with high sensitivity.

Intensive and Persistent Chemiluminescence System Based on Nano-/Bioenzymes with Local Tandem Catalysis and Surface Diffusion

A chemiluminescence (CL) system with long persistent and intensive emission is essential for accurate CL quantitative analysis and imaging assay. However, with most known CL systems being flash-type, it is still a great challenge to develop long-lasting CL systems. Here, by combining an iron porphyrin metal-organic frameworks (FePorMOFs) based peroxidase mimic with natural glucose oxidase (GOx), an intensive and persistent CL system is presented on the basis of local tandem catalysis and surface diffusion of the nano-/bioenzymes (FePorMOF/GOx). FePorMOF synthesized by iron porphyrin linker and zirconium ion node possesses high peroxidase catalytic activity and stability. Using luminol and glucose as substrate, the FePorMOF/GOx CL system can produce intensive CL emission containing a plateau period of 7.5 h. The strong CL signal is due to the local tandem generation and reaction of H₂O₂ by GOx and FePorMOF, which avoids the diffusion-limited kinetics and leads to a high catalytic efficiency of the nano-/bioenzymes. On the other hand, the long persistent CL emission is attributed mainly to the enzymatic reaction-controlled H₂O₂ supply and surface diffusion-controlled CL reaction. The proposed CL system is explored for CL imaging sensing of glucose and homogeneous immunoassay of α-fetoprotein. The nano-/bioenzymes CL system exhibits intensive and long constant CL emission in physiological condition, showing promising applications in real-time bioassay and bioimaging.

One-step fabrication of trimetallic alloy nanozyme catalyzer for luminol-H2O2 chemiluminescence and its application for miRNA-21 detection coupled with miRNA walking machine

PtCuCo trimetallic alloys (PtCuCo-TAs) are synthesized by one-step reduction. The chemiluminescence (CL) properties of PtCuCo-TAs are studied systemically. PtCuCo-TAs show good catalyzing for luminol-H₂O₂ system. A CL platform is developed for the detection of miRNA-21 using PtCuCo-TAs as nanozyme catalyzer. In the CL detection platform, H1 (Hairpin DNA1) is immobilized onto magnetic beads (MBs) firstly. In the presence of miRNA-21, H1 is opened. H2 (Hairpin DNA2) then hybridizes with H1. Meanwhile, a "cleat" in the end of miRNA-21 with a fewer bases complementary is formed to prevent miRNA-21 dissociating from H1. This miRNA-21 hybridizes to another H1. When cpDNA-PtCuCo-TAs which consisted with cDNA (Complementary strand of probe DNA) and pDNA-PtCuCo-TAs (PtCuCo-TAs labeled with probe DNA) are added, the ssDNA region of H1 reacts with the toehold domain of probe DNA and cDNA is released resulting pDNA-PtCuCo-TAs being captured. With this process repeatedly, a lot of pDNA-PtCuCo-TAs are captured onto MBs. After separation and washing, the precipitate and H₂O₂ are put into the 96-well and luminol solution is injected. The CL signal is produced by PtCuCo-TAs catalyzing luminol-H₂O₂ system. The amount of miRNA-21 is detected with CL signal. This CL platform performs with limit of detection 0.167 fM and has good selectivity over other RNA.

A Novel Cell-Assisted Enhanced Chemiluminescence Strategy for Rapid and Label-Free Detection of Tumor Cells in Whole Blood

In this study, an interesting phenomenon was found where cells (including tumor and normal cells) managed to significantly enhance chemiluminescence (CL) signals. The possible reaction mechanism may be that cells can be severely damaged by CL substrates, and the released contents, possibly proteins (such as cytochrome c), can remarkably magnify CL owing to the increased production of singlet oxygen. More importantly, based on the above phenomena, a novel cell-assisted enhanced CL strategy was proposed for the rapid and label-free detection of tumor cells. The complexes of aptamer sgc8c and streptavidin-modified magnetic beads were employed to recognize and isolate target tumor cells from whole blood. The enhanced CL intensity, which was triggered directly by the captured cells, was measured. The proposed strategy exhibited a good detection performance with a linear range from 200 to 10,000 cells/mL. The analysis can be finished in ∼30 min, and the limit of detection was down to 100 cells/mL. The recoveries and relative standard deviations were 97.81-102.71% and 3.46-12.71%, respectively. Moreover, the established method can successfully distinguish the leukemia patients from healthy people. Therefore, it provides a novel, rapid, and simple method for the determination of tumor cells, which can be used in further practice.

Protein-mediated sponge-like copper sulfide as an ingenious and efficient peroxidase mimic for colorimetric glucose sensing

Strenuous efforts have been made to develop nanozymes for achieving the performance of natural enzymes to broaden their application in practice, but the fabrication of high-performance and biocompatible nanozymes via facile and versatile approaches has always been a great challenge. Here, sponge-like casein-CuS hybrid has been facilely synthesized in the presence of amphiphilic protein-casein through a simple one-step approach. Casein-CuS hybrid exhibits substrates-dependent peroxidase-like activity. Casein-CuS hybrid exhibits well peroxidase-like activity with 3,3′,5,5′-tetramethylbenzidine (TMB) and 1,2-diaminobenzene (OPD) as substrates, and the affinity of OPD towards the hybrid nanozyme is much higher than that of TMB. More importantly, due to the high affinity of OPD and the well biocompatibility of the hybrid nanozyme, a superior enzyme cascade for glucose based on the well cooperative effect of casein-CuS hybrid and glucose oxidase is developed. The proposed glucose sensor exhibits a wide linear range of 0.083 to 75 μM and a detection limit of 5 nM. This suggests the promising utilization of protein–metal hybrid nanozymes as robust and potent peroxidase mimics in the medical, food and environmental detection fields.

Strenuous efforts have been made to develop nanozymes for achieving the performance of natural enzymes, but the fabrication of high-performance and biocompatible nanozymes via facile and versatile approaches has always been a great challenge.

Facile synthesis of novel reduced graphene oxide@polystyrene nanospheres for sensitive label-free electrochemical immunoassay

Nanosized reduced graphene oxide@polystyrene nanospheres were first synthesized and further exploited for highly sensitive label-free electrochemical immunoassay applications.

Expanding the scope of chemiluminescence in bioanalysis with functional nanomaterials

Nanomaterial-enabled chemiluminescence (CL) detection has become a growing area of interest in recent years. We review the development of nanomaterial-based CL detection strategies and their applications in bioanalysis. Much progress has been achieved in the past decade, but most attempts still remain in the proof-of-concept stage. This review highlights recent advances in nanomaterials in CL detection and organizes them into three groups based on their role in detection: as a sensing platform, as a signal probe, and applications in homogeneous systems. Furthermore, we have discussed the critical challenges we are facing and future prospects of this field.

Chemiluminescence Immunoassays for Simultaneous Detection of Three Heart Disease Biomarkers Using Magnetic Carbon Composites and Three-Dimensional Microfluidic Paper-Based Device

Chemiluminescence (CL) immunoassays for simultaneous detection of early acute myocardial infarction (AMI) biomarkers, including copeptin, heart-type fatty acid binding protein (h-FABP), and cardiac troponin I (cTnI), were developed by using Co²⁺/N-(aminobutyl)-N-(ethylisoluminol) (ABEI) functionalized magnetic carbon composite (Co²⁺-ABEI-Fe₃O₄@void@C) as an interface and a three-dimensional microfluidic paper-based device (3D μPAD) as a detection system. For CL immunoassays, Co²⁺-ABEI-Fe₃O₄@void@C was assembled with chitosan (CS) and gold nanoparticle-conjugated antibody (Au-Ab) sequentially to form the sensing platform (Co²⁺-ABEI-Fe₃O₄@void@C-CS/Au-Ab). In the presence of antigen (Ag), Ag was captured by the sensing interface to form an immunocomplex, leading to an increase in CL intensity due to the catalysis of -COO^- existing in Ag. A 3D μPAD with three detection zones for simultaneous detection of copeptin, h-FABP, and cTnI was designed and fabricated to obtain time-resolved CL signals. Three kinds of immunocomplexes formed with copeptin, h-FABP, and cTnI were added to three detection zones of 3D μPAD, respectively. After injecting H₂O₂, three time-resolved CL signals were generated in one CL detection run by virtue of time-delayed transport of H₂O₂ to different detection zones. The three time-resolved CL signals were used for the simultaneous determination of copeptin, h-FABP, and cTnI. The detection limit of copeptin, h-FABP, and cTnI was 0.40 pg/mL, 0.32 pg/mL, and 0.50 pg/mL, respectively, which is at least 1 order of magnitude lower than most of the reported immunoassays. The immunoassays could be directly used for the detection of copeptin, h-FABP, and cTnI in human serum samples. The proposed immunoassays are simple, fast, sensitive, and selective, and are of great application potential in early diagnosis and treatment of AMI.

Chitosan-mediated green synthesis and folic-acid modification of CuS quantum dots for photoacoustic imaging guided photothermal therapy of tumor

CuS nanomaterials capped with artificial organic-molecules or polymers have been well demonstrated as efficient photothermal nanoagents for the therapy of tumor, but their biocompatibility and target ability should be improved. To address these problems, we have used chitosan (CS) as the biomacromolecule model and surface ligands to prepare CuS quantum dots (QDs) via a simple co-precipitation method. CuS-CS QDs are then conjugated with folic acid (FA). The resulting CuS-CS-FA QDs are composed of hexagonal phase nanodots with sizes of about 4 nm. FA modification process has no apparent influence on the size, phase and composition of the QDs. Furthermore, the zeta potential and infrared spectroscopy confirm the efficient conjugation of FA. CuS-CS-FA QDs exhibit strong near-infrared photoabsorption and high photothermal efficiency (47.0%). As a result of the presence of CS ligand and FA modification, CuS-CS-FA QDs have good biocompatibility and relatively high cellular uptake efficacy. When CuS-CS-FA QD dispersion is injected intravenously into the tumor-bearing mice, the photoacoustic imaging reveals that CuS-CS-FA QD can be efficiently targeted and accumulated in the tumor and reach the peak dose at 60 min. The irradiation of 1064-nm laser (1.0 W cm^-2, 10 min) results in the efficient inhibition of tumor growth, without treatment-induced toxicity. Therefore, CuS-CS-FA QDs have great potential to become biocompatible multifunctional nanoagents for imaging guided therapy of tumor.

Cu-Doped Carbon Dots as Catalysts for the Chemiluminescence Detection of Glucose

Development of metal-doped carbon dots (CDs) to effectively modulate their electronic properties and surface chemical reactivities is still in its early stage. In this paper, a facile solid-phase synthesis strategy was developed to synthesize Cu-doped CDs (Cu-CDs) using citric acid as the carbon source and Cu(NO₃)₂·3H₂O as the dopant, respectively. The as-prepared Cu-CDs exhibited superior peroxidase-like activity to horseradish peroxidase and were stable under a wide range of pH and temperatures. Consequently, the Cu-CD-based chemiluminescence sensing was applied to sensitively detect glucose with a low detection limit of 0.32 μM, and the recoveries and the relative standard deviation of the serum sample are 87.2-112.2 and 8.16% (n = 6), respectively. Notably, the proposed chemiluminescence sensing was also successfully applied for label-free detection of glucose in complex biological samples, which envisioned its potential applications in clinical diagnosis and other analytical assays.

Electrochemiluminescence-Based Capacitance Microscopy for Label-Free Imaging of Antigens on the Cellular Plasma Membrane

Electrochemiluminescence (ECL)-based capacitance microscopy using a square-wave voltage is established unprecedentedly to realize the label-free visualization of species on electrode surfaces and cellular plasma membranes. The drop in the local capacitance upon the binding of species to the surface or to a cellular membrane is derived to induce a relatively larger potential drop ( V_dl) across the double layer on the local electrode surface, which is utilized to prompt enhanced ECL at the binding position. The square-wave voltage with a frequency of as high as 1.5 kHz is proven to be favorable for the discrimination of the local ECL from the surrounding signal. Using this new detection principle and resultant capacitance microscopy, carcinoembryonic antigens (CEA) at amounts of as low as 1 pg can be visualized. Further application of this approach permits the direct imaging of CEA antigens on single MCF-7 cells through the capacitance change after the formation of the antigen-antibody complex. Successful visualization of the analyte without any ECL tag will allow not only special capacitance microscopy for label-free bioassays but also a novel ECL detection approach for the sensitive detection of biomolecules.