In Situ Generation of Prussian Blue with Potassium Ferrocyanide to Improve the Sensitivity of Chemiluminescence Immunoassay Using Magnetic Nanoparticles as Label

Multifunctional magnetic tags with photocatalytic and enzyme-mimicking properties for constructing a sensitive dual-readout ELISA

ELISA has become the gold standard for detecting harmful substances due to its specific antibody recognition and sensitive enzyme-catalyzed reactions. In this study, multifunctional magnetic Prussian blue nanolabels (MPBNs) were synthesized using a simple gentle two-step method to achieve a dual-readout mode. The MPBNs provide a sensitive colorimetric signal by efficiently catalyzing the oxidation of TMB and exhibit prominent photocatalytic degradation activity towards Rhodamine B (RhB). Supplemented by the quenching effect of oxTMB, the fluorescence was enabled to serve as a sensitive second signal. The magnetic property of the labels facilitates the separation and enrichment of the target, thereby improving sensitivity. Utilizing the versatile MPBNs, the visual limit of detection (vLOD) for Staphylococcus aureus is as low as 100 CFU/mL, with a quantitative analysis range of 102-108 CFU/mL. The introduction of photocatalytic reactions into immunoassay has opened up a new signal response system with strong momentum for development and application.

Detection technology and clinical applications of serum viral products of hepatitis B virus infection

Viral hepatitis, caused by its etiology, hepatitis virus, is a public health problem globally. Among all infections caused by hepatitis-associated viruses, hepatitis B virus (HBV) infection remains the most serious medical concern. HBV infection particularly affects people in East Asia and Africa, the Mediterranean region, and Eastern Europe, with a prevalence rate of > 2%. Currently, approximately 1 billion people worldwide are infected with HBV, and nearly 30% of them experience chronic infection. Chronic HBV infection can lead to chronic hepatitis B (CHB), liver cirrhosis, and hepatocellular carcinoma (HCC), resulting in the related death of approximately 1 million people annually. Although preventative vaccines and antiviral therapies are currently available, there is no cure for this infection. Clinical testing is not only the gateway for diagnosis of HBV infection, but also crucial for judging the timing of medication, evaluating the effect of antiviral therapy, and predicting the risk of relapse after drug withdrawal in the whole follow-up management of hepatitis B infected persons. With advances in detection technology, it is now possible to measure various viral components in the blood to assess the clinical status of HBV infection. Serum viral products of HBV infection, such as HBV DNA, HBV RNA, hepatitis B surface antigen, hepatitis B e-antigen, and hepatitis B core-related antigen, are non-invasive indicators that are critical for the rapid diagnosis and management of related diseases. Improving the sensitivity of monitoring of these products is essential, and the development of corresponding detection technologies is pivotal in achieving this goal. This review aims to offer valuable insights into CHB infection and references for its effective treatment. We provide a comprehensive and systematic overview of classical and novel methods for detecting HBV serum viral products and discusses their clinical applications, along with the latest research progress in this field.

CRET-based immunoassay on magnetic beads for selective and sensitive detection of Nanog antigen as a key cancer stem cell marker

A method is presented for chemiluminescence resonance energy transfer (CRET) using APTES-Fe3O4 as a highly efficient energy acceptor with strong magnetic effectiveness over extended distances, while an Au@BSA-luminol composite acts as the donor. In order to boost the chemiluminescence reactions, CuO nanoparticles were successfully employed. The distance between the donor and acceptor is a crucial factor in the occurrence of the CRET phenomenon. A sensitive and high-throughput sandwich chemiluminescence immunosensor has been developed accordingly with a linear range of 1.0 × 10-7 g/L to 6.0 × 10-5 g/L and a limit of detection of 0.8 × 10-7 g/L. The CRET-based sandwich immunosensor has the potential to be implemented to early cancer diagnosis because of its high sensitivity in detecting Nanog, fast analysis (30 min), and simplicity. Furthermore, this approach has the potential to be adapted for the recognition of other antigen-antibody immune complexes by utilizing the corresponding antigens and their selective antibodies.

Dual modal improved enzyme-linked immunosorbent assay for aflatoxin B1 detection inspired by the interaction of amines with Prussian blue nanoparticles

This work reports an improved enzyme-linked immunosorbent assay (ELISA) via the interaction between prussian blue nanoparticles (PBNPs) and amines for aflatoxin B1 (AFB1) detection. The effect of different amines on the structure and properties of PBNPs was systematically investigated. Amines with pKb < 7, like ethylenediamine (EDA), can decompose structure of PBNPs, leading to the reduction of extinction coefficient and photothermal effect. Whereas, amines with large pKb > 7, such as o-phenylenediamine (OPD), could undergo catalytic oxidation by PBNPs, resulting in the production of fluorescent and colored oxidation products. Accordingly, EDA and OPD were used to construct improved ELISA. Specifically, silica nanoparticles, on which AFB1 aptamer and amino binding agent (ethylenediaminetetraacetic acid disodium salt, EDTA•2Na) were previously assembled via carboxyl-amino linkage, are anchored to microplates by AFB1 and antibody. EDA concentration can be regulated by EDTA•2Na to affect extinction coefficient and photothermal effect of PBNPs, thereby achieving visual colorimetric and portable photothermal signal readout (Model 1). OPD concentration can also be controlled by EDTA•2Na, thus generating colorimetric and ultrasensitive fluorescent signals through PBNPs catalysis (Model 2). The proposed strategy not only opens new avenue for signal readout mode of biosensing, but also provides universal technique for hazards.

Construction of Magnetic Core-Large Mesoporous Satellite Immunosensor for Long-Lasting Chemiluminescence and Highly Sensitive Tumor Marker Determination

Chemiluminescence immunoassay exhibits high sensitivity and signal-to-noise ratio, thus attracting great attention in the early diagnosis and dynamic monitoring of diseases. However, the collection of conventional flash-type chemiluminescence signal (<5 s) relies heavily on automatic sampling and reading instrument. Herein, a novel core-satellite multifunctional chemiluminescence immunosensor is designed for the efficient enrichment and highly sensitive determination of cancer biomarker carcinoembryonic antigen (CEA) with enhanced and long-lasting output signal that can be conveniently recorded by a simple microplate plate reading instrument. Anti-CEA monoclonal antibody 2 (Ab2) modified Fe3 O4 @SiO2 microspheres (Fe3 O4 @SiO2 -Ab2, 370 nm in diameter) are synthesized as the core for selectively capturing and enriching target CEA in solution, and anti-human CEA monoclonal antibody 1 (Ab1) and horseradish peroxidase (HRP) co-immobilized dendritic large-mesoporous silica nanospheres (MSNs-HRP/Ab1, 80 nm in diameter, pore size: 17 nm) are synthesized as the satellite for efficient immunological recognition and signal amplification. The as-designed core-satellite magnetic chemiluminescence immunosensors exhibit a broad linear range of 0.01-20 ng mL-1 and a low detection limit of 3.0 pg mL-1 for the convenient, highly specific, and sensitive determination of CEA in human serum. Such core-satellite chemiluminescence immunosensors are expected to act as a powerful tool for in vitro detection of various biomarkers, overcome the defect of conventional chemiluminescence relying heavily on expensive and bulky automatic instruments and popularize chemiluminescence analysis to primary medical institutions and remote areas.

A methylene blue-functionalized DNA concatemer for the construction of a turn-off fluorescent immunosensor for the sensitive detection of carcinoembryonic antigen

This study showed a method of synthetization of a methylene blue-functionalized DNA concatemer via hybridization chain reaction (HCR) used for turn-off fluorescence detection of carcinoembryonic antigen (CEA). During the experiments, CEA aptamers and the methylene blue-functionalized DNA concatemer were modified onto the surface of Au nanoparticles (AuNPs). By detecting the signal of remaining methylene blue in the solution that has not been embedded in the DNA concatemer, we obtained an amplified decrease of the fluorescence signal at 695 nm for CEA. The linear range was from 0.1 to 80 ng mL-1 with a limit of detection at 75 pg mL-1 for CEA determination. Our results showed that the proposed method had good selectivity and could generate satisfactory results for clinical serum sample determination. Based on the positive outcomes obtained, we determined that the method provided a sensitive and accurate way for early clinical diagnosis of cancer disease.

Synthesizing Submicron Polyelectrolyte Capsules to Boost Enzyme Immobilization and Enhance Enzyme-Based Immunoassays

Polyelectrolyte capsules (PCs) exhibit attractive superiorities in enzyme immobilization, including providing a capacious microenvironment for enzyme conformational freedom, highly effective mass transfer, and protecting enzymes from the external environment. Herein, we provide the first systemic evaluation of submicron PCs (SPCs, 500 nm) for enzyme immobilization. The catalytic kinetics results show that SPC encapsulation affected the affinities of enzymes and substrates but significantly enhanced their catalytic activity. The stability test indicates that SPC-encapsulated horseradish peroxidase (HRP) exhibits ultrahigh resistance to external harsh conditions and has a longer storage life than that of soluble HRP. The proposed encapsulation strategy enables 7.73-, 2.22-, and 11.66-fold relative activities when working at a pH as low as 3, at a NaCl concentration as high as 500 mM, and at a trypsin concentration as high as 10 mg/mL. We find that SPC encapsulation accelerates the cascade reaction efficiency of HRP and glucose oxidase. Owing to SPCs enhancing the catalytic activity of the loaded enzymes, we established an amplified enzyme-linked immunosorbent assay (ELISA) for the detection of Escherichia coli O157:H7 using HRP-loaded SPCs. The detection sensitivity of SPC-improved ELISA was found to be 280 times greater than that of conventional HRP-based ELISA. Altogether, we provide an elaborate evaluation of 500 nm SPCs on enzyme immobilization and its application in the ultrasensitive detection of foodborne pathogens. This evaluation provides evidence to reveal the potential advantage of SPCs on enzyme immobilization for enzyme-based immunoassays. It has excellent biological activity and strong stability and broadens the application prospect in urine, soy sauce, sewage, and other special samples.

Two kinds of lateral flow immunoassays based on multifunctional magnetic prussian blue nanoenzyme and colloidal gold for the detection of 38 β-agonists in swine urine and pork

Herein, novel multifunctional magnetic prussian blue nanoenzymes (MPBNs) and colloidal gold (CG) were synthesized and used to develop two kinds of lateral flow immunoassays (LFIAs) for the detection of 38 β-agonists. Since MPBNs has a unique three-in-one function of colorimetric magnetic catalytic activities, the signal intensity and coupling ratio are 2 and 8-fold higher than that of the CG. The cut-off values of the CG-LFIA and MPBNs-LFIA for swine urine and pork are 5/5 and 0.3/0.5 μg/kg, the limits of detection are 0.19/0.29 and 0.02/0.03 μg/kg, respectively. The sensitivity of MPBNs-LFIA is 10-fold higher than that of CG-LFIA, and up to 200-fold higher than that of the reported LFIAs. The recoveries of the LFIAs are 80.0%-116.7%, with coefficients of variation of 1.4%-14.3%. Our study proved that the MPBNs have more advantages than CG, and can offer a promising signal label for ultrasensitive immunoassay techniques.

Anthracycline-Functionalized Dextran as a New Signal Multiplication Tagging Approach for Immunoassay

The most used kind of immunoassay is enzyme-linked immunosorbent assay (ELISA); however, enzymes suffer from steric effects, low stability, and high cost. Our research group has been developing quinone-linked immunosorbent assay (QuLISA) as a new promising approach for stable and cost-efficient immunoassay. However, the developed QuLISA suffered from low water-solubility of synthesized quinone labels and their moderate sensitivity. Herein, we developed a new approach for signal multiplication of QuLISA utilizing the water-soluble quinone anthracycline, doxorubicin, coupled with dextran for signal multiplication. A new compound, Biotin-DexDox, was prepared in which doxorubicin was assembled on oxidized dextran 40, and then it was biotinylated. The redox-cycle-based chemiluminescence and the colorimetric reaction of Biotin-DexDox were optimized and evaluated, and they showed very good sensitivity down to 0.25 and 0.23 nM, respectively. Then, Biotin-DexDox was employed for the detection of biotinylated antibodies utilizing avidin as a binder and a colorimetric assay of the formed complex through its contained doxorubicin redox reaction with NaBH₄ and imidazolium salt yielding strong absorbance at 510 nm. The method could detect the plate-fixed antibody down to 0.55 nM. Hence, the application of Biotin-DexDox in QuLISA was successfully demonstrated and showed a significant improvement in its sensitivity and applicability to aqueous assays.

Development of signal multiplication system for quinone linked immunosorbent assay (Multi-QuLISA) by using poly-l-lysine dendrigraft and 1,2-naphthoquinone-4-sulfonate as enzyme-free tag

A sensitive and stable signal multiplied quinone-linked immunosorbent assay (Multi-QuLISA) was developed. In Multi-QuLISA, an oligomerized quinone linked to biotin, namely biotin-8mer-naphthoquinone (Bio8mer-NQ), is used as a signal-generating label. Bio8mer-NQ is formed from a dendrigraft poly-l-lysine generation 1 (DPLL G1), a controlled branched oligomer composed of eight lysine moieties with nine free amino groups as a backbone. One of the nine amino groups of DPLL G1 is attached to biotin moiety, while the other eight are attached to 1,2-naphthoquinone-4-sulfonate (NQS). Bio8mer-NQ labels a biotinylated detection antibody using avidin as a co-binder. Then, multi-quinones in Bio8mer-NQ undergo a redox cycle with dithiothreitol and luminol, generating strong chemiluminescence. Standard ELISA uses a label enzyme that suffers from vulnerability in different conditions and poor stability. Bio8mer-NQ showed better stability than the enzyme (biotin-HRP) under different drastic pH and temperature conditions, hydrolytic enzymes, etc. Furthermore, Bio8mer-NQ was used as both chemiluminescence and colorimetric label based on the redox cycle of quinone, and it had LODs of 1.5 and 6.5 nM, respectively. The method could detect biotinylated immunocomplex in an in-house designed immunoassay down to 0.2 nM, which is about 25 times more sensitive than biotin HRP. Eventually, Bio8mer-NQ was applied successfully in Multi-QuLISA for detecting β-casein with a sensitivity of 3.2 ng/mL, while the conventional ELISA had an LOD of 35 ng/mL. Overall, Bio8mer-NQ is a stable compound that could be used as an excellent replacement for the enzyme in immunoassay and can be used in both colorimetric and chemiluminescence assays with good sensitivity.

Derivatization-free determination of carbonyl compounds using bifunctional chemiluminescence coreactant thiourea dioxide

Uniquely, thiourea dioxide not only can reduce carbonyl compounds but also generate an oxidant to trigger luminol chemiluminescence. Herein, derivatization-free carbonyl compound detection using bifunctional chemiluminescence coreactant thiourea dioxide has been developed for the first time with the second most crucial flavor benzaldehyde as a representative.

Enhancement effect of 2, 3-dimethyl maleic acid on luminol chemiluminescence reactions and its application in detection of sequence-specific DNA related to hepatitis B virus

2, 3-dimethyl maleic acid (DMMA) was found to enhance luminol-H₂O₂ chemiluminescent (CL) reactions, among which the strongest enhancement effect was observed by using polyethyleneimine-templated gold nanoclusters (PEI-Au NCs) as the catalyst. With the addition of DMMA, the CL signal of the PEI-Au NCs-catalyzed luminol-H₂O₂ reaction enhanced about 630-fold, and a flash-type CL profile was obtained. Mechanism studies showed that the luminophore was still 3-aminophthalate anions in the excited state (3-APA*), and superoxide radical (O₂^·-) played an important role during the CL process. Under the optimized experimental conditions, the lowest concentration of PEI-Au NCs can be detected was 0.168 nM which was 82-fold lower than that without an enhancer. Furthermore, the catalytic activity of biotinylated PEI-Au NCs in the DMMA-enhanced luminol system was similar to PEI-Au NCs, providing a good opportunity for the development of CL bioanalysis platforms using PEI-Au NCs as the label. Thus, the DMMA-enhanced luminol-H₂O₂ system was applied to the CL detection of sequence-specific DNA related to the hepatitis B virus (HBV) using PEI-Au NCs as the label. The CL platform exhibited linearly enhanced CL response with the increasing amount of target DNA ranging from 0.0025 to 0.5 pmol. As low as 0.002 pmol of HBV DNA could be sensitively detected, which was superior to the previously reported methods.

Single-Atom Iron Enables Strong Low-Triggering-Potential Luminol Cathodic Electrochemiluminescence

The conventional cathodic electrochemiluminescence (ECL) always requires a more negative potential to trigger strong emission, which inevitably damages the bioactivity of targets and decreases the sensitivity and specificity. In this work, iron single-atom catalysts (Fe-N-C SACs) were employed as an efficient co-reaction accelerator for the first time to achieve the impressively cathodic emission of a luminol-H₂O₂ ECL system at an ultralow potential. Benefiting from the distinct electronic structure, Fe-N-C SACs exhibit remarkable properties for the activation of H₂O₂ to produce massive reactive oxygen species (ROS) under a negative scanning potential from 0 to -0.2 V. The ROS can oxidize the luminol anions into luminol anion radicals, avoiding the tedious electrochemical oxidation process of luminol. Then, the in situ-formed luminol anion radicals will directly react with ROS for the strong ECL emission. As a proof of concept, sensitive detection of the carcinoembryonic antigen was realized by glucose oxidase-mediated ECL immunoassay, shedding light on the superiority of SACs to construct efficient cathodic ECL systems with low triggering potential.

A General Route for Chemiluminescence of n-Type Au Nanocrystals

The photoluminescence, electroluminescence, and electrochemiluminescence from nanocrystals (NCs) have been extensively exploited for both fundamental and applied investigation over two decades, while the understanding of chemiluminescence (CL) from NCs is still far from clear by now. Herein, a general route for triggering CL from NC luminophore is proposed by extensively exploiting the charge transfer between n-type NCs and oxidants. Oxidants, such as K₂S₂O₈, H₂O₂, KMnO₄, and NaClO, can chemically inject the hole onto the valence band (VB) of methionine-capped n-type AuNCs (Met@AuNCs) and enable the occurrence of efficient radiative-charge-recombination between the chemically injected exogenous VB hole and the pre-existed endogenous conduction band (CB) electron, which eventually results in single-color and defect-involved CL with the maximum emission wavelength around 824 nm. The CL of Met@AuNCs/oxidant is qualified for ultrasensitive CL immunoassay in a similar procedure to the biotin-avidin and magnetic separation involved commercial CL immunoassay and exhibits acceptable performance for linearly determining carcinoembryonic antigen from 50 pg/mL to 100 ng/mL with a limit of detection of 10 pg/mL (S/N = 3). This strategy provides a general route to develop nanoparticulate CL luminophores and might eventually enable CL multiplexing assay via extensively exploiting the CL of different wavebands.

Enzyme-controllable just-in-time production system of copper hexacyanoferrate nanoparticles with oxidase-mimicking activity for highly sensitive colorimetric immunoassay

Nanozymes are a series of elaborately designed nanomaterials that can mimic the catalytic sites of natural enzymes for reactions. Bypassing the tedious design and preparation of nanomaterial, in this work, we report on a novel just-in-time production system of copper hexacyanoferrate nanoparticles (CHNPs), which act as an oxidase-mimicking nanozyme. This system can rapidly produce CHNPs nanozyme on demand by simply mixing Cu(II) with potassium hexacyanoferrate(III) (K₃[Fe(CN)₆]). It is found that once K₃[Fe(CN)₆] is reduced to K₄[Fe(CN)₆], the formation of CHNPs is inhibited. Therefore, the just-in-time production system of CHNPs was coupled with alkaline phosphatase (ALP) to construct an enzyme-controllable just-in-time production (ECJP) system, in which ALP could inhibit the production of by catalyzing the hydrolysis of ascorbic acid 2-phosphate (AAP) to generating ascorbic acid (AA). The ECJP system is then used to probe the activity of ALP by employing 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) as the chromogenic substrate, and a detection limit of 0.003 U L^-1 was achieved. Moreover, by adapting ALP as the enzyme label, an ECJP system-based colorimetric immunoassay protocol was established for sensitive detection of aflatoxin B₁ (AFB₁), and a detection limit as low as 0.73 pg mL^-1 was achieved. The developed immunoassay method is successfully applied to the detection of AFB₁ in peanut samples. The operation of ECJP system is quite simple and the coupling of ALP with CHNPs nanozyme can arouse dual enzyme-like cascade signal amplification. So, we believe this work can offer a new perspective for the development of nanozymes-based biodetection methods and colorimetric immunoassay strategies.

Recent developments on nanomaterial-based optical biosensor as potential Point-of-Care Testing (PoCT) probe in carcinoembryonic antigen detection: A review

For the past decades, several cancer biomarkers have been exploited for rapid and accurate prognosis or diagnosis purposes. In this review, the optical biosensor is targeted for carcinoembryonic antigen (CEA) detection. The CEA level is a prominent parameter currently used in clinical cases for the prognosis of cancer-related diseases. Many nanomaterial-based biosensors are invented as alternatives for the commonly used enzyme-linked immunosorbent assays (ELISA) immunoassay method in CEA detection as the traditional approach but they possess certain drawbacks such as tedious procedure, high technical demand, and costly. Nevertheless, the effort appears to be wasted as none of them are being actualised. Generally, the sensor function was carried out by converting bio-signals generated upon the interface of the receptor into light signals. These sensors were popular due to specific advantages such as sensitivity, being free from chemical and electromagnetic interferences, wide dynamic range, and being easy to be monitored. The features of PoC diagnostics are discussed and associated with the various applications of colorimetric-based and chemiluminescent-based biosensors. The roles of nanomaterials in each application were also summarised by comparing the modification, incubation period, lowest detection limit (LOD) and linear range of detection amount. The challenges and future perspectives were highlighted at the end of the review.

An Overview for the Nanoparticles-Based Quantitative Lateral Flow Assay

The development of the lateral flow assay (LFA) has received much attention in both academia and industry because of their broad applications to food safety, environmental monitoring, clinical diagnosis, and so forth. The user friendliness, low cost, and easy operation are the most attractive advantages of the LFA. In recent years, quantitative detection has become another focus of LFA development. Here, the most recent studies of quantitative LFAs are reviewed. First, the principles and corresponding formats of quantitative LFAs are introduced. In the biomaterial and nanomaterial sections, the detection, capture, and signal amplification biomolecules and the optical, fluorescent, luminescent, and magnetic labels used in LFAs are described. The invention of dedicated strip readers has drawn further interest in exploiting the better performance of LFAs. Therefore, next, the development of dedicated reader devices is described and the usefulness and specifications of these devices for LFAs are discussed. Finally, the applications of LFAs in the detection of metal ions, biotoxins, pathogenic microorganisms, veterinary drugs, and pesticides in the fields of food safety and environmental health and the detection of nucleic acids, biomarkers, and viruses in clinical analyses are summarized.

Chemiluminescent magnetic nanoparticles with good catalytic activity and rapid separation capability and sensitive sensing for H2O2

It is of considerable importance to develop chemiluminescent functionalized nanomaterials (CF-NMs) with good catalytic activity, high chemiluminescence (CL) efficiency and good stability, and rapid magnetic separation capability, achieving excellent performance in CL biosensing. In this study, N-(4-aminobutyl)-N-ethylisoluminol (ABEI)-functionalized CuFe2O4 magnetic nanomaterial (ABEI/CuFe2O4) with high catalytic activity was synthesized by virtue of a solvothermal and post-functionalization method. ABEI/CuFe2O4 showed outstanding CL properties, superior to ABEI-CuFe2O4 in liquid phase. This reveals that the immobilization of ABEI on the surface of CuFe2O4 exhibits unique heterogeneous catalytic property. The catalytic ability of CuFe2O4 was better than that of CoFe2O4, ZnFe2O4, MnFe2O4, and NiFe2O4. It is suggested that the peroxide-like activity as well as Cu2+ and Cu0 enriched on the surface of ABEI/CuFe2O4 opened up a dual route for synergistic catalysis of H2O2. ABEI/CuFe2O4 also demonstrated good superparamagnetism and magnetic separation could be carried out in 2 min, which is advantageous for the separation and purification of ABEI/CuFe2O4 during the synthetic procedures and bioassays. Owing to the sensitive response of ABEI/CuFe2O4 to H2O2, an enzyme-free sensor was developed for the detection of H2O2 with a wide linear range over 5 orders of magnitude of H2O2 concentrations and a low detection limit of 5.6 nM. The as-developed sensor is sensitive, stable, and convenient. This work provides a new family member of nanomaterials with good magnetism and CL activity as well as good stability. The developed ABEI/CuFe2O4 shows great prospects in biocatalysis, bioassays, biosensing, and bioimaging, etc.

Sonochemiluminescence Using Apertureless USB Piezoelectric Ultrasonic Transducer and Its Applications for the Detection of Hydrogen Peroxide, Glucose, and Glucose Oxidase Activity

The mesh-type USB piezoelectric ultrasonic transducer (USB-PUT) used in household humidifiers and inhalation therapy devices is very cheap, small, and energy saving. It holds great promise for sonochemistry. However, the microtapered apertures in the center of the stainless steel substrate of mesh-type USB-PUT can lead to rapid atomization of solution, leakage of solutions containing surfactants and organic solvent through the apertures, and high background emission. Herein, we design a new type of USB-PUT by replacing the meshed stainless steel substrate with an apertureless stainless steel substrate. We have found that this apertureless USB-PUT can not only induce intense sonochemiluminescence (SCL) but can also enable sensitive luminol SCL detection of hydrogen peroxide which is practically impossible using mesh-type PUT because of the strong background SCL emission. By using this apertureless device to induce SCL and using smart phone as a detector, a visual hydrogen peroxide SCL detection method with a linear range of 0.5-50 μM and a detection limit of 0.32 μM is established. Moreover, the device can achieve the detection of glucose oxidase (GOD) activity and glucose by enzymatic conversion of glucose to hydrogen peroxide. The linear range of GOD detection is 1-200U/L with a detection limit of 0.86 U/L. The linear range of glucose detection is 0.5-70 μM with a detection limit of 0.43 μM. The cheap (a few dollars) and user-friendly apertureless USB-PUT is promising for sonochemistry applications and chemical education.

Recent advances in enzyme-enhanced immunosensors

Among the products for rapid detection in different fields, enzyme-based immunosensors have received considerable attention. Recently, great efforts have been devoted to enhancing the output signals of enzymes through different strategies that can significantly improve the sensitivity of enzyme-based immunosensors for the need of practical applications. In this manuscript, the significance of enzyme-based signal transduction patterns in immunoassay and the central role of enzymes in achieving precise control of reaction systems are systematically described. In view of the rapid development of this field, we classify these strategies based on the combination of immune recognition and enzyme amplification into three categories, namely enzyme-based enhancement strategies, combination of the catalytic amplification of enzymes with other signal amplification methods, and substrate-based enhancement strategies. The current focus and future direction of enzyme-based immunoassays are also discussed. This article is not exhaustive, but focuses on the latest advances in different signal generation methods based on enzyme-initiated catalytic reactions and their applications in the detection field, which could provide an accessible introduction of enzyme-based immunosensors for the community with a view to further improving its application efficiency.

An In Situ Generated Prussian Blue Nanoparticle-Mediated Multimode Nanozyme-Linked Immunosorbent Assay for the Detection of Aflatoxin B1

This work aims to develop a novel multimode (photothermal/colorimetric/fluorescent) nanozyme-linked immunosorbent assay (NLISA) based on the in situ generation of Prussian blue nanoparticles (PBNPs) on the surface of magnetic nanoparticles (MNPs). Being considered the most toxic among the mycotoxins, aflatoxin B1 (AFB1) was chosen as the proof-of-concept target. In this strategy, MNPs, on which an AFB1 aptamer was previously assembled via streptavidin-biotin linkage, are anchored to 96-well plates by AFB1 and antibody. In the presence of HCl and K₄Fe(CN)₆, PBNPs formed in situ on the MNP surface, thereby achieving photothermal and colorimetric signal readout due to their photothermal effect and intrinsic peroxidase-like activity. Based on fluorescence quenching by MNPs, Cy5 fluorescence was recovered by the in situ generation of PBNPs to facilitate ultrasensitive fluorescence detection. Photothermal and colorimetric signals allow portable/visual point-of-care testing, and fluorescent signals enable accurate determination with a detection limit of 0.54 fg/mL, which is 6333 and 28 times lower than those of photothermal and colorimetric analyses, respectively. We expect that this proposed multimode NLISA can not only reduce the false-positive/negative rates through the multisignal crossdetection in AFB1 monitoring but also provide a universal way of sophisticated instrumentation-free, easy-to-use, cost-effective, and highly sensitive detection of other food hazards.

MWCNTs-CoP hybrids for dual-signal electrochemical immunosensing of carcinoembryonic antigen based on overall water splitting

Great efforts have been made to search for highly active catalysts toward electrochemical water splitting, but double-signal immunosensors have not been reported based on bifunctional water splitting electrocatalysts. We report here a dual-signal electrochemical immunosensor for detecting carcinoembryonic antigen (CEA) using multi-wall carbon nanotubes (MWCNTs)-cobalt phosphide (CoP) as an electrocatalytic label. The preparation of MWCNTs-CoP involves the growth of Co₃O₄ nanoparticles on MWCNTs and low-temperature phosphatization of Co₃O₄ nanoparticles. The MWCNTs-CoP catalyst shows excellent electrocatalytic activities in a neutral medium toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), enabling MWCNTs-CoP as the electrocatalytic label for sensitive immunosensing. The linear range of the sandwich-type immunosensor for detecting CEA based on the HER signal is from 10^-4-100 ng mL^-1, whereas a linear range for detecting CEA based on the OER signal is achieved from 10^-4 to 10 ng mL^-1. The detection limits for detecting CEA using HER and OER signals are 10 and 12 fg mL^-1, respectively. This work can provide a new double-signal immunosensing platform based on a bifunctional water splitting electrocatalyst.

Recent advances in visual detection for cancer biomarkers and infectious pathogens

It is an urgency to detect infectious pathogens or cancer biomarkers using rapid, simple, convenient and cost-effective methods in complex biological samples. Many existing approaches (traditional virus culture, ELISA or PCR) for the pathogen and biomarker assays face several challenges in the clinical applications that require lengthy time, sophisticated sample pre-treatment and expensive instruments. Due to the simple and rapid detection manner as well as no requirement of expensive equipment, many visual detection methods have been considered to resolve the aforementioned problems. Meanwhile, various new materials and colorimetric/fluorescent methods have been tried to construct new biosensors for infectious pathogens and biomarkers. However, the recent progress of these aspects is rarely reviewed, especially in terms of integration of new materials, microdevice and detection mechanism into the visual detection systems. Herein, we provide a broad field of view to discuss the recent progress in the visual detection of infectious pathogens and cancer biomarkers along with the detection mechanism, new materials, novel detection methods, special targets as well as multi-functional microdevices and systems. The novel visual approaches for the infectious pathogens and biomarkers, such as bioluminescence resonance energy transfer (BRET), metal-induced metallization and clustered regularly interspaced short palindromic repeats (CRISPR)-based biosensors, are discussed. Additionally, recent advancements in visual assays utilizing various new materials for proteins, nucleic acids, viruses, exosomes and small molecules are comprehensively reviewed. Future perspectives on the visual sensing systems for infectious pathogens and cancers are also proposed.

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.

Hollow Magnetic Nanocatalysts Drive Starvation-Chemodynamic-Hyperthermia Synergistic Therapy for Tumor

Magnetic hyperthermia therapy (MHT) has been considered as an excellent alternative for treatment of deep tumor tissue; however, up-regulation of heat shock proteins (HSPs) impairs its hyperthermal therapeutic effect. Reactive oxygen species (ROS) and competitive consumption of ATP are important targets that can block excessive HSP generation. We developed a magnetic nanocatalytic system comprised of glucose oxidase (GOD)-loaded hollow iron oxide nanocatalysts (HIONCs) to drive starvation-chemodynamic-hyperthermia synergistic therapy for tumor treatment. The Fe²⁺ present in HIONCs contributed to ROS generation via the Fenton reaction, relieving thermo-resistance and inducing cell apoptosis by chemodynamic action. The Fenton effect was enhanced through the conditions created by increased MHT-related temperature, GOD-mediated H₂O₂ accumulation, and elevated tumor microenvironment acidity. The HIONCs catalase-like activity facilitated conversion of H₂O₂ to oxygen, thereby replenishing the oxygen levels. We further demonstrated that locally injected HIONCs-GOD effectively inhibited tumor growth in PC3 tumor-bearing mice. This study presents a multifunctional nanocarrier system driving starvation-chemodynamic-magnetic-thermal synergistic therapy via ROS and oxygen modulation for prostate tumor treatment.

Bimetallic CuCo2 S4 Nanozymes with Enhanced Peroxidase Activity at Neutral pH for Combating Burn Infections

Peroxidase-mimicking nanozymes that can generate toxic hydroxyl radicals (^. OH) hold great promise as antibacterial alternatives. However, most of them display optimal performance under strongly acidic conditions (pH 3-4), and are thus not feasible for many medical uses, including burn infections with a wound pH close to neutral. Herein, we report a copper-based nanozyme (CuCo₂ S₄ ) that exhibits intrinsic peroxidase-like activity and can convert H₂ O₂ into ^. OH at neutral pH. In particular, bimetallic CuCo₂ S₄ nanoparticles (NPs) exhibited enhanced peroxidase-like activity and antibacterial capacity, superior to that of the corresponding monometallic CuS and CoS NPs. The CuCo₂ S₄ nanozymes possessed excellent ability to kill various bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). Furthermore, this CuCo₂ S₄ nanozymes could effectively disrupt MRSA biofilms in vitro and accelerate MRSA-infected burn healing in vivo. This work provides a new peroxidase mimic to combat bacteria in neutral pH milieu and this CuCo₂ S₄ nanozyme could be a promising antibacterial agent for the treatment of burn infections.

Sonochemiluminescence Based on a Small, Cheap, and Low-Power USB Mesh-Type Piezoelectric Ultrasonic Transducer

A small, cheap, and low-power mesh-type piezoelectric ultrasonic transducer (MPUT) from a household USB humidifier has been developed as a sonochemiluminescence generator for the first time. The ultrasonication of an MPUT facilitates the generation of reactive oxygen species to trigger sonochemiluminescence. There is no light emission of luminol without sonication. In contrast, the luminescence becomes very intense by ultrasonication using the MPUT and can be readily observed by a smart phone, enabling the visual detection of luminol without adding any coreactants. Interestingly, ascorbic acid, a common chemiluminescence quencher in the literature, increases the sonochemiluminescence in this system. As a result, a sensitive sonochemiluminescence method has been developed for the visual detection of ascorbic acid with a linear range of 1-40 μM and a limit of detection (LOD) of 0.35 μM. Moreover, the visual detection of superoxide dismutase has been achieved on the basis of its quenching effect, which has a linear range of 0.05-2.0 μg/mL and a LOD of 0.018 μg/mL. Because of its advantages of low cost, small size, and low-power consumption, the USB MPUT holds great potential in sonochemiluminescence (SCL) for the development of portable and disposable analysis devices in point-of-care testing and field analysis as well as chemical education.

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.

Ultrasound-Enhanced Chemiluminescence for Bioimaging

Tissue imaging has emerged as an important aspect of theragnosis. It is essential not only to evaluate the degree of the disease and thus provide appropriate treatments, but also to monitor the delivery of administered drugs and the subsequent recovery of target tissues. Several techniques including magnetic resonance imaging (MRI), computational tomography (CT), acoustic tomography (AT), biofluorescence (BF) and chemiluminescence (CL), have been developed to reconstruct three-dimensional images of tissues. While imaging has been achieved with adequate spatial resolution for shallow depths, challenges still remain for imaging deep tissues. Energy loss is usually observed when using a magnetic field or traditional ultrasound (US), which leads to a need for more powerful energy input. This may subsequently result in tissue damage. CT requires exposure to radiation and a high dose of contrast agent to be administered for imaging. The BF technique, meanwhile, is affected by strong scattering of light and autofluorescence of tissues. The CL is a more selective and sensitive method as stable luminophores are produced from physiochemical reactions, e.g. with reactive oxygen species. Development of near infrared-emitting luminophores also bring potential for application of CL in deep tissues and whole animal studies. However, traditional CL imaging requires an enhancer to increase the intensity of low-level light emissions, while reducing the scattering of emitted light through turbid tissue environment. There has been interest in the use of focused ultrasound (FUS), which can allow acoustic waves to propagate within tissues and modulate chemiluminescence signals. While light scattering is decreased, the spatial resolution is increased with the assistance of US. In this review, chemiluminescence detection in deep tissues with assistance of FUS will be highlighted to discuss its potential in deep tissue imaging.

In situ amplified QCM immunoassay for carcinoembryonic antigen with colorectal cancer using horseradish peroxidase nanospheres and enzymatic biocatalytic precipitation

An innovative quartz crystal microbalance immunoassay was designed for detection of carcinoembryonic antigen using horseradish peroxidasenanoparticle as the enhancer, accompanying enzymatic biocatalytic precipitation toward 4-chloro-1-naphthol.

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.

DNA-Templated Fluorescent Nanoclusters for Metal Ions Detection

DNA-templated fluorescent nanoclusters (NCs) have attracted increasing research interest on account of their prominent features, such as DNA sequence-dependent fluorescence, easy functionalization, wide availability, water solubility, and excellent biocompatibility. Coupling DNA templates with complementary DNA, aptamers, G-quadruplex, and so on has generated a large number of sensors. Additionally, the preparation and applications of DNA-templated fluorescent NCs in these sensing have been widely studied. This review firstly focuses on the properties of DNA-templated fluorescent NCs, and the synthesis of DNA-templated fluorescent NCs with different metals is then discussed. In the third part, we mainly introduce the applications of DNA-templated fluorescent NCs for sensing metal ions. At last, we further discuss the future perspectives of DNA-templated fluorescent NCs in the synthesis and sensing metal ions in the environmental and biological fields.

Faraday-Cage-Type Electrochemiluminescence Immunoassay: A Rise of Advanced Biosensing Strategy

Electrochemiluminescence immunoassays are usually carried out through "on-electrode" strategy, i.e., sandwich-type immunoassay format, the sensitivity of which is restricted by two key bottlenecks: (1) the number of signal labels is limited and (2) only a part of signal labels could participate in the electrode reaction. In this Perspective, we discuss the development of an "in-electrode" Faraday-cage-type concept-based immunocomplex immobilization strategy. The biggest difference from the traditional sandwich-type one is that the designed "in-electrode" Faraday-cage-type immunoassay uses a conductive two-dimensional (2-D) nanomaterial simultaneously coated with signal labels and a recognition component as the detection unit, which could directly overlap on the electrode surface. In such a case, electrons could flow freely from the electrode to the detection unit, the outer Helmholtz plane (OHP) of the electrode is extended, and thousands of signal labels coated on the 2-D nanomaterial are all electrochemically "effective." Thus, then, the above-mentioned bottlenecks obstructing the improvement of the sensitivity in sandwich-type immunoassay are eliminated, and as a result a much higher sensitivity of the Faraday-cage-type immunoassay can be obtained. And, the applications of the proposed versatile "in-electrode" Faraday-cage-type immunoassay have been explored in the detection of target polypeptide, protein, pathogen, and microRNA, with the detection sensitivity improved tens to hundreds of times. Finally, the outlook and challenges in the field are summarized. The rise of Faraday-cage-type electrochemiluminescence immunoassay (FCT-ECLIA)-based biosensing strategies opens new horizons for a wide range of early clinical identification and diagnostic applications.