A label-free immunosensor based on PtPd NCs@MoS2 nanoenzymes for hepatitis B surface antigen detection

Poly(ionic liquid)-regulated green one-pot synthesis of Au@Pt porous nanospheres for the smart detection of acid phosphatase and organophosphorus inhibitor

Here, a green poly(ionic liquid)-regulated one-pot method is developed for the synthesis of Au@Pt core-shell nanospheres (PNSs) under mild reaction conditions in water. It is found that the poly(ionic liquid) poly[1-methyl-3-butyl (3-hydroxy) imidazole] chloride (PIL-Cl) is very vital to guide the construction of Au@Pt PNSs. The as-obtained Au@Pt-1 PNSs have perfect spherical outlines, porous core-shell structures and large specific surface area by which they exhibit excellent peroxidase-like activity in acidic media and can be used to develop a simple and reliable colorimetric sensing platform. It is shown that the colorimetric sensing platform constructed with Au@Pt-1 PNSs nanozyme can effectively evaluate ACP activity, achieving a wide linear detection range of 0.1-3.0 U/L and having a low limit of detection (LOD) of 0.047 U/L (S/N = 3). Based on the cascade reaction, the Au@Pt-1 PNSs nanozyme and ACP are integrated to develop a biosensor, which can detect organophosphate inhibitor of malathion with a wide linear detection range of 5-80 nM and low LOD of 1.96 nM (S/N = 3). More importantly, this detection method is also practically applied to detect both ACP activity in fetal bovine serum and malathion concentration in cucumber juice with satisfied results. This work presents a simple and green feature for the synthesis of nanozyme with high performance and establishes a biosensing platform based on Au@Pt-1 PNSs nanozyme to effectively monitor the ACP activity and the concentration of its organophosphate inhibitor malathion with high sensitivity, anti-interference capability and good recovery capability.

A review on Pd-M bimetallic electrochemical sensors: Techniques, performance, and applications

Environmental pollution, food safety, and medical diagnostics pose severe threats to human health, making the development of effective detection technologies crucial. Electrochemical sensors, as an efficient detection method, are extensively employed in detecting environmental pollutants, food additives, and biomolecules. Pd-M bimetallic materials, known for their excellent electrocatalytic performance, are extensively utilized as electrode modification materials. Although earlier reviews have covered the sensing applications of bimetallic materials, they have not targeted discussed Pd-based bimetallic materials. This paper systematically summarizes the preparation methods of Pd-M bimetallic materials, explores their structural and morphological regulation, and elaborates on their recent applications in pesticide detection, environmental pollutant detection, food additive detection, drug detection, and biosensing. It enumerates the detection performance of various Pd-M bimetallic material-modified electrochemical sensors for the aforementioned analytes in detail, including specific modification materials, linear range, detection limits, and sensitivity parameters.

Gold nanoclusters stabilized with dopa-containing ligands: Catalyst-indicator integrated probe for tumor cell screening

Elevated hydrogen peroxide (H2O2) levels not only inflict cellular damage but also serve as a harbinger for various diseases. Tumor cells, in particular, often exhibit an abundance of H2O2. Hence, the detection of this pivotal molecule assumes paramount importance in monitoring physiological states and expediting cancer diagnosis. To this end, we have ingeniously devised an enzyme-free and monomeric system for intracellular H2O2 detection. Our astute selection of dopa-containing peptidomimetics, replete with ortho-bisphenol and amino acid moieties, has engendered the synthesis of distinctive fluorescent gold nanoclusters (AuNCs). These nanoclusters not only function as a peroxidase-like catalyst, catalyzing the decomposition of H2O2 into hydroxyl radicals (·OH), but also serve as an indicator, with their fluorescence quenched in response to varying H2O2 concentrations. Experimental results evince that our GDpE-AuNCs exhibit remarkable sensitivity, boasting a detection limit of 0.49 μM and a linear range of 5-1000 μM. Moreover, the amalgamation of catalyst and indicator within a single structure, facilitating efficient cellular uptake, engenders intracellular H2O2 detection and discernment of tumor cells. This pioneering approach bequeaths a valuable assay probe for monitoring physiological states and ushering in early disease diagnosis.

Multimodal biosensing systems based on metal nanoparticles

Biosensors are currently among the most commonly used devices for analysing biomarkers and play an important role in environmental detection, food safety, and disease diagnosis. Researchers have developed multimodal biosensors instead of single-modal biosensors to meet increasing sensitivity, accuracy, and stability requirements. Metal nanoparticles (MNPs) are beneficial for preparing core probes for multimodal biosensors because of their excellent physical and chemical properties, such as easy regulation and modification, and because they can integrate diverse sensing strategies. This review mainly summarizes the excellent physicochemical properties of MNPs applied as biosensing probes and the principles of commonly used MNP-based multimodal sensing strategies. Recent applications and possible improvements of multimodal biosensors based on MNPs are also described, among which on-site inspection and sensitive detection are particularly important. The current challenges and prospects for multimodal biosensors based on MNPs may provide readers with a new perspective on this field.

Tunable Structured 2D Nanobiocatalysts: Synthesis, Catalytic Properties and New Horizons in Biomedical Applications

2D materials have offered essential contributions to boosting biocatalytic efficiency in diverse biomedical applications due to the intrinsic enzyme-mimetic activity and massive specific surface area for loading metal catalytic centers. Since the difficulty of high-quality synthesis, the varied structure, and the tough choice of efficient surface loading sites with catalytic properties, the artificial building of 2D nanobiocatalysts still faces great challenges. Here, in this review, a timely and comprehensive summarization of the latest progress and future trends in the design and biotherapeutic applications of 2D nanobiocatalysts is provided, which is essential for their development. First, an overview of the synthesis-structure-fundamentals and structure-property relationships of 2D nanobiocatalysts, both metal-free and metal-based is provided. After that, the effective design of the active sites of nanobiocatalysts is discussed. Then, the progress of their applied research in recent years, including biomedical analysis, biomedical therapeutics, pharmacokinetics, and toxicology is systematically highlighted. Finally, future research directions of 2D nanobiocatalysts are prospected. Overall, this review to provide cutting-edge and multidisciplinary guidance for accelerating future developments and biomedical applications of 2D nanobiocatalysts is expected.

Label-free electrochemical aptasensor for ultrasensitive lead ion detection based on flower-like AuNPs@MoS2 and core-shell Pt@Pd bimetallic nanoparticles

A signal-amplified platform was designed to construct a label-free electrochemical aptasensor for lead ions (Pb2+) assay. First, flower-like molybdenum disulfide-supported AuNPs (AuNPs@MoS2) nanocomposites were synthesized and used as substrates for modifying the electrode. The AuNPs@MoS2 material possessed large surface area and superior biocompatibility, which was beneficial to improve the loading amount of the complementary DNA (cDNA) and amplified the response signal. Importantly, the prepared core-shell Pt@Pd bimetallic nanoparticles (Pt@PdNPs) were used to conjugate with redox marker thionine (Thi) and aptamer (Apt) for further signal amplification; the obtained signal probes (Thi-Pt@PdNPs-Apt) were connected by the cDNA assembled on the electrode through DNA hybridization. Differential pulse voltammetry was performed to monitor the signal of Thi. After incubating of aptasensor with Pb2+, the specific recognition of Pb2+ and Apt resulted in the dissociation of aptamer-cDNA complex, thereby the Thi-Pt@PdNPs-Apt separated from the electrode surface and decreased current response was obtained. The prepared electrochemical sensor exhibited linear response to Pb2+ in the range 5.0 × 10-4-100 nM and a detection limit of 1.0 × 10-4 nM was achieved. The sensor was applied to the determination of Pb2+ in actual sample with high sensitivity and accuracy, demonstrating potential applications in heavy metal monitoring.

Electrochemical protein biosensors for disease marker detection: progress and opportunities

The development of artificial intelligence-enabled medical health care has created both opportunities and challenges for next-generation biosensor technology. Proteins are extensively used as biological macromolecular markers in disease diagnosis and the analysis of therapeutic effects. Electrochemical protein biosensors have achieved desirable specificity by using the specific antibody-antigen binding principle in immunology. However, the active centers of protein biomarkers are surrounded by a peptide matrix, which hinders charge transfer and results in insufficient sensor sensitivity. Therefore, electrode-modified materials and transducer devices have been designed to increase the sensitivity and improve the practical application prospects of electrochemical protein sensors. In this review, we summarize recent reports of electrochemical biosensors for protein biomarker detection. We highlight the latest research on electrochemical protein biosensors for the detection of cancer, viral infectious diseases, inflammation, and other diseases. The corresponding sensitive materials, transducer structures, and detection principles associated with such biosensors are also addressed generally. Finally, we present an outlook on the use of electrochemical protein biosensors for disease marker detection for the next few years.

Dual-Mode Lateral Flow Immunoassay Based on "Pompon Mum"-Like Fe3O4@MoS2@Pt Nanotags for Sensitive Detection of Viral Pathogens

Lateral flow immunoassay (LFIA) has been widely used for the early diagnosis of diseases. However, conventional colorimetric LFIA possesses limited sensitivity, and the single-mode readout signal is easily affected by the external environment, leading to insufficient accuracy. Herein, multifunctional Fe3O4@MoS2@Pt nanotags with a unique "pompon mum"-like structure were triumphantly prepared, exhibiting excellent peroxidase (POD)-like activity, photothermal properties, and magnetic separation capability. Furthermore, the Fe3O4@MoS2@Pt nanotags were used to establish dual-mode LFIA (dLFIA) for the first time, enabling the catalytic colorimetric and photothermal dual-mode detection of severe acute respiratory syndrome coronavirus 2 nucleocapsid protein (SARS-CoV-2 NP) and influenza A (H1N1). The calculated limits of detection (cLODs) of SARS-CoV-2 NP and H1N1 were 80 and 20 ng/mL in catalytic colorimetric mode and 10 and 8 ng/mL in photothermal mode, respectively, demonstrating about 100 times more sensitive than the commercial colloidal Au-LFIA strips (1 ng/mL for SARS-CoV-2 NP; 1 μg/mL for H1N1). The recovery rates of dLFIA in simulated nose swab samples were 95.2-103.8% with a coefficient of variance of 2.3-10.1%. These results indicated that the proposed dLFIA platform showed great potential for the rapid diagnosis of respiratory viruses.

Bifunctional Mo2N Nanoparticles with Nanozyme and SERS Activity: A Versatile Platform for Sensitive Detection of Biomarkers in Serum Samples

The combined application of nanozymes and surface-enhanced Raman scattering (SERS) provides a promising approach to obtain label-free detection. However, developing nanomaterials with both highly efficient enzyme-like activity and excellent SERS sensitivity remains a huge challenge. Herein, we proposed one-step synthesis of Mo2N nanoparticles (NPs) as a "two-in-one" substrate, which exhibits both excellent peroxidase (POD)-like activity and high SERS activity. Its mimetic POD activity can catalyze the 3,3',5,5'-tetramethylbenzidine (TMB) molecule to SERS-active oxidized TMB (ox-TMB) with high efficiency. Furthermore, combining experimental profiling with theory, the mechanism of POD-like activity and SERS enhancement of Mo2N NPs was explored in depth. Benefiting from the outstanding properties of Mo2N NPs, a versatile platform for indirect SERS detection of biomarkers was developed based on the Mo2N NPs-catalyzed product ox-TMB, which acts as the SERS signal readout. The feasibility of this platform was validated using glutathione (GSH) and target antigens alpha-fetoprotein antigen (AFP) and carcinoembryonic antigen (CEA) as representatives of small molecules with a hydroxyl radical (·OH) scavenging effect and proteins with a low Raman scattering cross-section, respectively. The limits of detection of GSH, AFP, and CEA were as low as 0.1 μmol/L, 89.1, and 74.6 pg/mL, respectively. Significantly, it also showed application in human serum samples with recoveries ranging from 96.0 to 101%. The acquired values based on this platform were compared with the standard electrochemiluminescence method, and the relative error was less than ±7.3. This work not only provides a strategy for developing highly active bifunctional nanomaterials but also manifests their widespread application for multiple biomarkers analysis.

Au/PANI@PtCu-based electrochemical immunosensor for ultrasensitive determination of pro-gastrin-releasing peptide

An ultrasensitive sandwich-type electrochemical immunosensor for pro-gastrin-releasing peptide (ProGRP) detection was constructed based on PtCu nanodendrites functionalized Au/polyaniline nanospheres (Au/PANI@PtCu). The prepared Au/PANI@PtCu nanocomposites not only possessed excellent electro-catalytic activity of H2O2 reduction due to the synergistic effect between the Au/PANI and PtCu NDs but also provided large specific surface area for detection of antibodies (Ab2) immobilization. In addition, Au nanoparticles encapsulated multi-wall carbon nanotubes (AuNPs@MWCNTs) were also applied to modify the glassy carbon electrode interface for loading numerous capture antibodies (Ab1). In the presence of target ProGRP, a sandwich-type electrochemical immunosensor showed a strong current response from the electro-catalysis of Au/PANI@PtCu toward H2O2 reduction. Benefiting from the exceptional electro-catalytic performance of Au/PANI@PtCu and the high conductivity of AuNPs@MWCNTs, the sandwich-type immunoassay exhibited remarkable sensitivity in detection. The linear range extended from 100 fg/mL to 10 ng/mL, while achieving an impressively low limit of detection of 77.62 fg/mL.

Nanomaterials Connected to Bioreceptors to Introduce Efficient Biosensing Strategy for Diagnosis of the TORCH Infections: A Critical Review

TORCH infection is a significant risk factor for severe fetal damage, especially congenital malformations. Screening pregnant women for TORCH pathogens could reduce the incidence of adverse pregnancy outcomes and prevent birth defects. Hence, timely identification and inhibition of TORCH infections are effective ways to successfully prevent them in pregnant women. Recently, the superiority of biosensors in TORCH pathogen sensing has been emphasized due to their intrinsic benefits, such as rapid response time, portability, cost-effectiveness, much friendlier preparation and determination steps. With the introduction of advanced nanomaterials into biosensing, the diagnostic properties of biosensors have significantly improved. This study core presents and debates the current progress in biosensing systems for TORCH pathogens using various artificial and natural receptors. The incorporation of nanomaterials into various transduction systems can enhance diagnostic performance. The key performance characteristics of optical and electrochemical biosensors, such as response time, limit of detection (LOD), and linear detection range, are systematically discussed, along with the current TORCH pathogens used for constructing biosensors. Finally, the major problems that exist for converting scientific investigation into product development are also outlined.

Electrochemical immunosensor based on hollow Pt@Cu2O as a signal label for dual-mode detection of procalcitonin

As a reliable biomarker to evaluate the severity of sepsis, sensitive and accurate detection of procalcitonin (PCT) is essential. In this study, a dual-mode electrochemical immunosensor based on Au/ZIF-8 as substrate and Pt@Cu2O as signal label was constructed for the detection of PCT. By loading Au nanoparticles onto rhombic dodecahedral ZIF-8, the substrate (Au/ZIF-8) has large specific surface area and can immobilize antibody (Ab1) by Au-N bonds. Meanwhile, hollow Pt@Cu2O nanocomposite with excellent peroxidase-like activity and electrocatalytic activity were synthesized as signal label. In the process of electrochemical testing, Pt@Cu2O catalyzed the reduction of hydrogen peroxide (H2O2) and further promotes the oxidation of hydroquinone (HQ) to achieve the synergistic amplification of electrochemical signals. The proposed immunosensor detected PCT by amperometric i-t and differential pulse voltammetry (DPV) tests with a good linear response and low limit of detection (i-t: 0.70 fg/mL and DPV: 0.40 fg/mL) in the range of 10 fg/mL∼100 ng/mL. The immunosensor exhibited excellent sensitivity and accuracy, indicating the potential application of this method for PCT detection.

Differential identification of GSH for acute coronary syndrome using a colorimetric sensor based on nanoflower-like artificial nanozymes

The ability to detect glutathione (GSH) concentrations in human blood offered a simple and non-invasive method to monitor changes associated with cardiovascular diseases, cancers and diabetes. We showed the potential of employing catalytically active protein-directed nanoflower-like artificial nanozymes (apo-TF-MnOx NFs) by bio-mineralization method to produce simple and visible colorimetric sensor for GSH. The experiments proved that apo-TF-MnOx NFs exhibited peroxidase, catalase- and superoxide dismutase-like activities, but the most notable feature was the excellent peroxidase-like activity, which could efficiently catalyze the oxidation reaction of 3,3',5,5'- tetramethylbenzidine (TMB) in the existence of hydrogen peroxide (H2O2) to generate a blue product. Some outcomes also indicated that the apo-TF-MnOx NFs had stronger peroxidase-like activity, which was proved by the Michaelis-Menten constant (Km) and maximum initial velocity (Vmax). Hence, we used the peroxidase-like activity to develop a GSH colorimetric biosensor. Fortunately, the colorimetric platform exhibited a sensitive response to H2O2 and GSH in the range of 5 μМ to 300 μМ and 0.5 μМ to 35 μМ with a limit of detection of 3.29 μM and 0.15 μM (S/N = 3) under optimal conditions. The feasibility of the simple method was confirmed by qualitative detection of H2O2 and GSH in blood samples from acute coronary syndrome patients. A key outcome of our study was the ability to realized differential identification of GSH for acute coronary syndrome and healthy human without invasive treatment which was an advantage over other methods. This work not only proposed a new type of nanozymes, but also showed the multiple advantages of the apo-TF-MnOx NFs for the construction of biosensors. Thus, we believe that apo-TF-MnOx NFs with strong peroxidase-like activity can be employed as nanozymes and be widely applied in the fields of medicine and biological sensors.

Hydrangea-like AuPtRu/ZnO-rGO Nanocomposites with Enhanced Peroxidase Mimiking Activity for Senitive Colorimetric Determination of H2O2

In this study, a facile and cost-effective hydrothermal synthesis method was used to synthesize zinc oxide nanoflowers modified by reduced graphene oxide, and subsequently, trimetallic AuPtRu nanoparticles(AuPtRuNPs) were supported via the reduction method for high-sensitivity colorimetric detection of H2O2 in weakly acidic solutions. Compared to monometallic and bimetallic nanoparticles, trimetallic nanoparticles exhibit significant synergistic effects and enhanced catalytic activity. After providing a three-dimensional structure with multiple pores by zinc oxide and enhancing electron transfer ability by reduced graphene, the trimetallic nanocomposites (AuPtRu/ZnO-rGO) exhibited excellent peroxidase-mimicking activity, which can effectively catalyze 3,3',5,5'-tetramethylbenzidine (TMB) to produce a blue oxidation product (oxTMB) in the presence of H2O2. Compared to horseradish peroxidase (HRP), AuPtRu/ZnO-rGO demonstrated significantly enhanced catalytic velocity (Vmax = 6.16 × 10-8 M/s) and affinity (Km = 0.02) for H2O2. The study of the catalytic mechanism showed that trimetallic Au, Pt, and Ru could effectively catalyze H2O2 to produce hydroxyl radicals (•OH) to accelerate the oxidation of TMB and enhance the peroxidase-mimicking activity of the AuPtRu/ZnO-rGO nanocomposites. The results showed that the as-synthesized hydrangea-like AuPtRu/ZnO-rGO nanocomposites showed enhanced peroxidase-mimicking activity. It could be used for the colorimetric detection of H2O2 in the range 5-1000 μM with a LOD of 3.0 μM (S/N = 3), and the recoveries are 93.0-101.7%. In addition, the AuPtRu/ZnO-rGO nanocomposites have good applicability for sensitive colorimetric determination of H2O2 in milk, and it has broad application prospects as a multifunctional sensing platform in the food processing industry.

Self-calibrating dual-sensing electrochemical sensors for accurate detection of carbon dioxide in blood

A paper-based electrochemical dual-function biosensor capable of determining pH and TCO2 was synthesized for the first time using an iridium oxide pH electrode and an all-solid-state ion electrode (ASIE). In the study, to obtain highly reliable results, the biosensor was equipped with a real-time pH correction function before TCO2 measurements. Compared to traditional liquid-filling carbon dioxide detection sensors, the utilization of ferrocene endows our novel sensor with abundant positive sites, and thus greatly improves its performance. Conversely, the introduction of MXene with conductivity close to that of metals reduces electrode resistance, which is beneficial for accelerating the electrochemical reaction of the sensor and reducing LOD. After optimization, the detection range of TCO2 is 0.095 nM-0.66 M, with a detection limit of as low as 0.023 nM. In addition, the sensor was used in real serum sample-spiked recovery experiments and comparison experiments with existing clinical blood gas analyzers, which confirmed the effectiveness of its clinical application. This study provides a method for the rational design of paper-based electrochemical biosensors and a new approach for the clinical detection of blood carbon dioxide.

Signal Amplification Strategy Design in Nanozyme-Based Biosensors for Highly Sensitive Detection of Trace Biomarkers

Nanozymes show great promise in enhancing disease biomarker sensing by leveraging their physicochemical properties and enzymatic activities. These qualities facilitate signal amplification and matrix effects reduction, thus boosting biomarker sensing performance. In this review, recent studies from the last five years, concentrating on disease biomarker detection improvement through nanozyme-based biosensing are examined. This enhancement primarily involves the modulations of the size, morphology, doping, modification, electromagnetic mechanisms, electron conduction efficiency, and surface plasmon resonance effects of nanozymes for increased sensitivity. In addition, a comprehensive description of the synthesis and tuning strategies employed for nanozymes has been provided. This includes a detailed elucidation of their catalytic mechanisms in alignment with the fundamental principles of enhanced sensing technology, accompanied by the presentation of quantitatively analyzed results. Moreover, the diverse applications of nanozymes in strip sensing, colorimetric sensing, electrochemical sensing, and surface-enhanced Raman scattering have been outlined. Additionally, the limitations, challenges, and corresponding recommendations concerning the application of nanozymes in biosensing have been summarized. Furthermore, insights have been offered into the future development and outlook of nanozymes for biosensing. This review aims to serve not only as a reference for enhancing the sensitivity of nanozyme-based biosensors but also as a catalyst for exploring nanozyme properties and their broader applications in biosensing.

Bimetallic bionic taste sensor for perception of the synergistic effect of umami substances

Synergistic effect is one of the main properties of umami substances, elucidating the synergistic effect of umami is of great significance in the food industry. In this study, a bimetallic bionic taste sensor was developed to evaluate the synergistic effect of umami substances based on the perceptual mechanism of the human taste system. The Venus flytrap domain of T1R1 which is in charge of recognizing umami ligands was employed as the sensing element and self-assembled on the bimetallic nanomaterial (MoS₂-PtPd) by Au-S bonding, the binding of receptors and ligands is characterized by changes of electrical signals. The sensor had good linearity (R² > 0.99) and wide detection range in the detection of different kinds of umami substances (amino acids, nucleotides, organic acids, umami peptides) with detection limits as low as 0.03 pM. Comparing with electronic tongues, the sensor owned multiple characteristics of human taste system and could recognize the presence of synergistic effect of umami substances in a variety of real samples. Moreover, the differences in synergistic effect at different concentrations and ratios were also explored, the findings showed that the synergistic effect was more obvious at lower concentrations and balanced ratios of multiple umami substances added. The strategy would afford a promising platform for in-depth research on the mechanism of synergistic effect and multifunctional industrial applications.

An ultrasensitive electrochemical immunosensor for carcinoembryonic antigen detection based on two-dimensional PtPd/Cu-TCPP(Fe) nanocomposites

Establishing an effective signal amplification strategy is the key to achieving sensitive detection of analytes by electrochemical immunoassay. In this work, a novel sandwich-type electrochemical immunosensor with dual-signal amplification was successfully constructed using PtPd/Cu-TCPP(Fe) as the sensing platform and mesoporous silicon dioxide as the signal amplifier. Firstly, two-dimensional wrinkled Cu-TCPP(Fe) nanomaterials loaded with PtPd nanoparticles have strong affinity for the immobilization of capture antibodies and can generate excellent electrochemical signals. Meanwhile, the mesoporous silicon dioxide with large steric hindrance was used as signal label to further improve the sensitivity of the immunosensor by increasing the difference of the current response signal. Under optimal experimental conditions, the electrochemical immunosensor exhibited a wide linear detection range from 0.1 pg/mL to 1.0 μg/mL, with a detection limit as low as 0.166 fg/mL. The experimental results showed that the constructed immunosensor has a great application prospect in clinical biomarker detection.

Nanoenzyme Reactor-Based Oxidation-Induced Reaction for Quantitative SERS Analysis of Food Antiseptics

Nanoenzyme reactors based on shell-isolated colloidal plasmonic nanomaterials are well-established and widely applied in catalysis and surface-enhanced Raman scattering (SERS) sensing. In this study, a "double wing with one body" strategy was developed to establish a reduced food antiseptic sensing method using shell-isolated colloidal plasmonic nanomaterials. Gold nano particles (Au NPs) were used to synthesize the colloidal plasmonic nanomaterials, which was achieved by attaching ferrous ions (Fe²⁺), ferric ions (Fe³⁺), nitroso (NO^-) group, cyanogen (CN^-) group, and dopamine (DA) via coordinative interactions. The oxidation-induced reaction was utilized to generate •OH following the Fe²⁺-mediated Fenton reaction with the shell-isolated colloidal plasmonic nanomaterials. The •OH generated in the cascade reactor had a high oxidative capacity toward acid preservatives. Importantly, with the introduction of the signal molecule DA, the cascade reactor exhibited also induced a Raman signal change by reaction with the oxidation product (malondialdehyde) which improved the sensitivity of the analysis. In addition, the stable shell-isolated structure was effective in realizing a reproducible and quantitative SERS analysis method, which overcomes previous limitations and could extend the use of nanoenzymes to various complex sensing applications.

Functionalization of 2D MoS2 Nanosheets with Various Metal and Metal Oxide Nanostructures: Their Properties and Application in Electrochemical Sensors

Two-dimensional transition metal dichalcogenides (2D TMDs) have gained considerable attention due to their distinctive properties and broad range of possible applications. One of the most widely studied transition metal dichalcogenides is molybdenum disulfide (MoS₂). The 2D MoS₂ nanosheets have unique and complementary properties to those of graphene, rendering them ideal electrode materials that could potentially lead to significant benefits in many electrochemical applications. These properties include tunable bandgaps, large surface areas, relatively high electron mobilities, and good optical and catalytic characteristics. Although the use of 2D MoS₂ nanosheets offers several advantages and excellent properties, surface functionalization of 2D MoS₂ is a potential route for further enhancing their properties and adding extra functionalities to the surface of the fabricated sensor. The functionalization of the material with various metal and metal oxide nanostructures has a significant impact on its overall electrochemical performance, improving various sensing parameters, such as selectivity, sensitivity, and stability. In this review, different methods of preparing 2D-layered MoS₂ nanomaterials, followed by different surface functionalization methods of these nanomaterials, are explored and discussed. Finally, the structure-properties relationship and electrochemical sensor applications over the last ten years are discussed. Emphasis is placed on the performance of 2D MoS₂ with respect to the performance of electrochemical sensors, thereby giving new insights into this unique material and providing a foundation for researchers of different disciplines who are interested in advancing the development of MoS₂-based sensors.

Heterometallic nanomaterials: activity modulation, sensing, imaging and therapy

Heterometallic nanomaterials (HMNMs) display superior physicochemical properties and stability to monometallic counterparts, accompanied by wider applications in the fields of catalysis, sensing, imaging, and therapy due to synergistic effects between multi-metals in HMNMs. So far, most reviews have mainly concentrated on introduction of their preparation approaches, morphology control and applications in catalysis, assay of heavy metal ions, and antimicrobial activity. Therefore, it is very important to summarize the latest investigations of activity modulation of HMNMs and their recent applications in sensing, imaging and therapy. Taking the above into consideration, we briefly underline appealing chemical/physical properties of HMNMs chiefly tailored through the sizes, shapes, compositions, structures and surface modification. Then, we particularly emphasize their widespread applications in sensing of targets (e.g. metal ions, small molecules, proteins, nucleic acids, and cancer cells), imaging (frequently involving photoluminescence, fluorescence, Raman, electrochemiluminescence, magnetic resonance, X-ray computed tomography, photoacoustic imaging, etc.), and therapy (e.g. radiotherapy, chemotherapy, photothermal therapy, photodynamic therapy, and chemodynamic therapy). Finally, we present an outlook on their forthcoming directions. This timely review would be of great significance for attracting researchers from different disciplines in developing novel HMNMs.

Genosensors as an alternative diagnostic sensing approaches for specific detection of various certain viruses: a review of common techniques and outcomes

Viral infections are responsible for the deaths of millions of people throughout the world. Since outbreak of highly contagious and mutant viruses such as contemporary sars-cov-2 pandemic, has challenged the conventional diagnostic methods, the entity of a thoroughly sensitive, specific, rapid and inexpensive detecting technique with minimum level of false-positivity or -negativity, is desperately needed more than any time in the past decades. Biosensors as minimized devices could detect viruses in simple formats. So far, various nucleic acid, immune- and protein-based biosensors were designed and tested for recognizing the genome, antigen, or protein level of viruses, respectively; however, nucleic acid-based sensing techniques, which is the foundation of constructing genosensors, are preferred not only because of their ultra-sensitivity and applicability in the early stages of infections but also for their ability to differentiate various strains of the same virus. To date, the review articles related to genosensors are just confined to particular pathogenic diseases; In this regard, the present review covers comprehensive information of the research progress of the electrochemical, optical, and surface plasmon resonance (SPR) genosensors that applied for human viruses' diseases detection and also provides a well description of viruses' clinical importance, the conventional diagnosis approaches of viruses and their disadvantages. This review would address the limitations in the current developments as well as the future challenges involved in the successful construction of sensing approaches with the functionalized nanomaterials and also allow exploring into core-research works regarding this area.

A label-free amperometric immunosensor with improved electrocatalytic 3D braided AuPtCu-SWCNTs@MoS2-rGO for human growth differentiation factor-15 detection

Growth differentiation factor-15 (GDF-15) is a member of the transforming growth factor-β family. GDF-15 is overexpressed in cardiovascular diseases and has become a novel biomarker for these diseases. In this study, we fabricated a label-free electrochemical immunosensor for sensitive detection of GDF-15. Briefly, a three-dimensional braided composite of AuPtCu-SWCNTs@MoS₂-rGO (denoted A@M), which served as a label-free immunosensor platform, was obtained by wrapping single-walled carbon nanotubes (SWCNTs) with trimetallic nanoflowers (AuPtCu NFs) woven on a three-dimensional network nanostructure composed of Molybdenum disulfide (MoS₂) and reduced graphene oxide (rGO) nanosheets. This optimization improved the ability of the platform to immobilize antibodies, accelerated the reduction of hydrogen peroxide, and promoted the migration rate of electrons on the electrode surface, thereby further amplifying the electrical signal and improving the sensitivity. The constructed sensor exhibited high sensitivity over a wide linear range from 1 pg mL^-1 to 50 ng mL^-1, with a low detection limit of 0.825 pg mL^-1 for GDF-15. The fabricated label-free immunosensor exhibits satisfactory reproducibility, selectivity, and stability. The detection of actual samples was successful, enabling a broad scope of application in the early diagnosis, prognosis, and treatment of cardiovascular diseases.

3D V2O5-MoS2/rGO nanocomposites with enhanced peroxidase mimicking activity for sensitive colorimetric determination of H2O2 and glucose

In this work, we reported a novel nanozyme (3D V₂O₅-MoS₂/rGO) by decorating MoS₂ nano-flowers and V₂O₅ nanoparticles on reduced graphene oxide (rGO). The 3D V₂O₅-MoS₂/rGO nanocomposites exhibited intrinsic peroxidase mimicking activity and catalyzed the oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB) to produce a blue colored product in the presence of H₂O₂. Compared with horseradish peroxidase (HRP), 3D V₂O₅-MoS₂/rGO nanocomposites displayed high catalytic velocity (V_max) and affinity (K_m) for substrates (H₂O₂ and TMB). The study of the catalytic mechanism showed that the reduction of V⁵⁺ and the oxidation of S^2- in the 3D V₂O₅-MoS₂/rGO nanocomposites accelerate electron transfer between H₂O₂ and TMB, which enhanced the peroxidase mimicking activity of 3D V₂O₅-MoS₂/rGO nanocomposites. The as-synthetized 3D V₂O₅-MoS₂/rGO could be used for the colorimetric detection of H₂O₂ in the range of 20.00-800.00 μM with the LOD of 12.40 μM (3σ/S). Moreover, the 3D V₂O₅-MoS₂/rGO could also be used for the detection of glucose in the range of 4.00-300.00 μM with the LOD of 3.99 μM (3σ/S). In addition, the as-synthetized novel peroxidase mimics has good applicability for sensitive colorimetric determination of glucose in human blood samples and artificial urine samples, and has broad application prospects as a multi-functional sensing platform in clinical diagnosis.

PBA-MoS2 nanoboxes with enhanced peroxidase activity for constructing a colorimetric sensor array for reducing substances containing the catechol structure

A fast colorimetric sensor array is constructed based on the enhanced peroxidase-like activity of nickel cobalt Prussian blue analogue-MoS2 nanoboxes (PBA-MoS2) for the detection of reducing substances containing the catechol structure.

Sandwich-type electrochemical aptasensor based on hollow mesoporous carbon spheres loaded with porous dendritic Pd@Pt nanoparticles as signal amplifier for ultrasensitive detection of cardiac troponin I

Signal amplification is crucial to improve the sensitivity for the electrochemical detection of cardiac troponin I (cTnI), one of the ideal biomarkers for early acute myocardial infarction (AMI) diagnosis. Herein, we developed a novel signal amplification strategy to construct a sandwich-type electrochemical aptasensor for the detection of cTnI. Core-shell Pd@Pt dendritic bimetallic nanoparticles loaded on melamine modified hollow mesoporous carbon spheres (Pd@Pt DNs/NH₂-HMCS) was prepared as labels to conjugate with thiol-modification DNA aptamers probe for signal amplification. While introducing numerous amino groups, the melamine functionalized hollow mesoporous carbon spheres (NH₂-HMCS) retained the edge-plane-like defective sites for the adhesion and electrocatalytic reduction of H₂O₂. With the unique characteristics of NH₂-HMCS, it not only enhanced the dispersity and loading capacity of core-shell Pd@Pt dendritic bimetallic nanoparticles (Pd@Pt DNs), but also improved the stability of bonding by the affinity interaction between Pd@Pt DNs and amino groups of melamine. Meanwhile, the synergistic catalysis effect between Pd@Pt DNs and NH₂-HMCS significantly enhanced the electrocatalytic reduction of H₂O₂ and further amplified the signal. Under optimal conditions, this recommended aptasensor for cTnI detection displayed a wide dynamic range from 0.1 pg/mL to 100.0 ng/mL and a low detection limit of 15.4 fg/mL (S/N = 3). The sensor also successfully realized the analysis of cTnI-spiked human serum samples, meaning potential applications in AMI diagnosis.

Attomolar analyte sensing techniques (AttoSens): a review on a decade of progress on chemical and biosensing nanoplatforms

Detecting the ultra-low abundance of analytes in real-life samples, such as biological fluids, water, soil, and food, requires the design and development of high-performance biosensing modalities. The breakthrough efforts from the scientific community have led to the realization of sensing technologies that measure the analyte's ultra-trace level, with relevant sensitivity, selectivity, response time, and sampling efficiency, referred to as Attomolar Analyte Sensing Techniques (AttoSens) in this review. In an AttoSens platform, 1 aM detection corresponds to the quantification of 60 target analyte molecules in 100 μL of sample volume. Herein, we review the approaches listed for various sensor probe design, and their sensing strategies that paved the way for the detection of attomolar (aM: 10^-18 M) concentration of analytes. A summary of the technological advances made by the diverse AttoSens trends from the past decade is presented.

Au@Zr-based metal-organic framework composite as an immunosensing platform for determination of hepatitis B virus surface antigen

An ultrasensitive electrochemical immunosensor has been prepared using an immunofunctionalized zirconium (Zr)-based metal-organic framework (MOF) with gold (Au) decoration Au@UiO-66(NH2) composite-coated glassy carbon electrode (GCE) for the determination of infectious hepatitis B surface antigen (HBsAg). We fabricated GCE with specific composite via immune-functionalization using anti-HBsAg with Au nanoparticles embedded in UiO-66(NH2). The electrochemical sensing performance of the immunofunctionalized Au@UiO-66(NH2)/GCE with HBsAg was characterized by cyclic voltammetry and differential pulse voltammetry. Under optimized conditions, there was a linear dynamic relationship in the buffer system between the electrical signal and HBsAg levels over the range 1.13 fg mL-1-100 ng mL-1 (R2 = 0.999) with a detection limit of 1.13 fg mL-1. The total analysis time was 15 min per sample. Further validations were performed with HBsAg-spiked human serum samples, and similar detection limits as in the buffer system were observed with reduced signal intensities at lower concentrations of HBsAg (1, 10, and 100 fg mL-1) and minimal interference. The HBsAg electrochemical immunosensing assay had good selectivity and excellent reproducibility, thereby indicating its significant potential in the super-fast diagnosis of hepatitis B.

Noble metal-molybdenum disulfide nanohybrids as dual fluorometric and colorimetric sensor for hepatitis B virus DNA detection

Hepatitis B virus (HBV) infection is one of the global healthcare burdens, and its early diagnosis is crucial for the prevention of HBV-induced chronic hepatitis, liver fibrosis, cirrhosis, and hepatocellular carcinoma. Although different detection approaches have been reported, most of these methods either rely on sophisticated machines or procedures, which limit their use particularly in the high endemic, developing countries. In this work, we report a dual-sensing nanoplatform built on noble metal-molybdenum disulfide (MoS₂) nanohybrids, and this platform can detect the HBV DNA target through either fluorometric or colorimetric readouts. The design with the silver nanocluster (AgNC)-MoS₂ nanohybrid enables multiplex fluorescent detection, while the HBV DNA-regulated growth of platinum nanoparticles (PtNPs) on the MoS₂ nanosheets offers signal-on colorimetric detection. Both AgNC-MoS₂ and PtNP-MoS₂ nanohybrids show high sensitivity with pico-molar detection limit and single nucleotide specificity, even with the spiked human serum. Collectively, the proposed nanohybrids possess their potential in the use of early HBV diagnosis, particularly suitable for the high endemic areas with limited medical and instrumental supports.

A novel signal amplification label based on AuPt alloy nanoparticles supported by high-active carbon for the electrochemical detection of circulating tumor DNA

The detection of circulating tumor DNA (ctDNA) has increasingly received a great deal of attention considering its significance in cancer diagnosis. And the signal amplification plays an important role in the development of sensitive ctDNA biosensors. Herein, the nanocomposites (denoted as HAC-AuPt), integrating from high-active carbon (HAC) and AuPt alloy nanoparticles, were synthesized and subsequently used as a signal amplification label to fabricate a sandwich-type ctDNA electrochemical biosensor. Characterizations demonstrated that HAC presents uniform size distribution and AuPt alloy nanoparticles were successfully loaded on HAC. The current response could be amplified to a great extent by the resultant HAC-AuPt due to its excellent electrochemical property. The nanocomposites were further bounded with DNA signal probes (SPs) via Au-S or Pt-S assembly to form SPs-label. After the capture probes (CPs) were immobilized on the electrode surface, the target DNA (tDNA) and SPs-label were stepwise incubated on the CPs-modified electrode, thus forming a sandwich-type structure. By monitoring the catalytic signal of HAC-AuPt towards the reduction process of H₂O₂, this biosensor provided a wide linear range of 10^-8 mol/L - 10^-16 mol/L with a low detection limit of 3.6 × 10^-17 mol/L (S/N = 3) for the detection of the tDNA. Furthermore, obvious differences in response signals among different DNAs were observed benefitting from the excellent selectivity of the biosensor. Besides, the long-term stability, reproducibility, and recovery rate were proved to be outstanding. These results indicate that the established biosensor holds a potential application in the clinical diagnosis of ctDNA.

Ultrasensitive and easily reproducible biosensor based on novel doped MoS2 nanowires field-effect transistor in label-free approach for detection of hepatitis B virus in blood serum

An ultrasensitive field-effect transistor (FET) for hepatitis B virus deoxyribonucleic acid (HBV DNA) detection in label free approach and easily reproducible setup was reported. The fabricated FET biosensor was materialized by ZnO doped MoS₂ nanowires (NWs). This report introduced a novel structure of the MoS₂ in bio-sensing approach. Because of unique electrical and structural properties of MoS₂, HBV biosensor could demonstrate the high sensitivity and showed the detection limit of 1 fM. The MoS₂ NWs fabrication was materialized through ZnO based vapor-liquid-solid (VLS) technique. The fabricated device could measure the DNA targets in a linear concentration range from 0.5 pM to 50 μM. The dynamic response time of FET biosensor was 25 s. The functionality of the NWs biosensor for label-free measurements could be repeated for several times without any significant malfunction and biosensor could retain 96% of its initial response after eight weeks maintenance. The HBV biosensor showed high selectivity by discrimination the complementary DNA oligonucleotides from non-complementary and the mismatch (1, 2 and 3 bases) oligonucleotides. The materialized platform was desirably reproduced for HBV concentrations in human serum. The specificity of the biosensor was evaluated against several different types of DNAs and the fabricated device showed the outstanding performance. In order to optimize the device functionality, the biosensor was checked for two different human samples and device could distinguish the samples from each other in the same manner.

A Bifunctional Nanosilver-Reduced Graphene Oxide Nanocomposite for Label-Free Electrochemical Immunosensing

A bi-functional material based on silver nanoparticles (AgNPs)-reduced graphene oxide (rGO) composite for both electrode modification and signal generation is successfully synthesized for use in the construction of a label-free electrochemical immunosensor. An AgNPs/rGO nanocomposite is prepared by a one-pot wet chemical process. The AgNPs/rGO composite dispersion is simply cast on a screen-printed carbon electrode (SPCE) to fabricate the electrochemical immunosensor. It possesses a sufficient conductivity/electroreactivity and improves the electrode reactivity of SPCE. Moreover, the material can generate an analytical response due to the formation of immunocomplexes for detection of human immunoglobulin G (IgG), a model biomarker. Based on electrochemical stripping of AgNPs, the material reveals signal amplification without external redox molecules/probes. Under optimized conditions, the square wave voltammetric peak current is responded to the logarithm of IgG concentration in two wide linear ranges from 1 to 50 pg.ml-1 and 0.05 to 50 ng.ml-1, and the limit of detection (LOD) is estimated to be 0.86 pg.ml-1. The proposed immunosensor displays satisfactory sensitivity and selectivity. Importantly, detection of IgG in human serum using the immunosensor shows satisfactory accuracy, suggesting that the immunosensor possesses a huge potential for further development in clinical diagnosis.

Development of Highly Sensitive Immunosensor for Detection of Staphylococcus aureus Based on AuPdPt Trimetallic Nanoparticles Functionalized Nanocomposite

The rapid and sensitive detection of Staphylococcus aureus (S. aureus) is essential to ensure food safety and protect humans from foodborne diseases. In this study, a sensitive and facile electrochemical immunosensor using AuPdPt trimetallic nanoparticles functionalized multi-walled carbon nanotubes (MWCNTs-AuPdPt) as the signal amplification platform was designed for the label-free detection of S. aureus. The nanocomposite of MWCNTs-AuPdPt was prepared by an in situ growth method of loading AuPdPt trimetallic nanoparticles on the surface of MWCNTs. The synthesized MWCNTs-AuPdPt featured good conductivity and superior catalytic performance for hydrogen peroxide. The nanocomposite of MWCNTs-AuPdPt with good biocompatibility and high specific surface area was further functionalized by anti-S. aureus antibodies. The immobilized antibodies could efficiently capture S. aureus to the modified electrode by an immune reaction, which resulted in the change of catalytic current intensity to realize the sensitive detection of S. aureus. The designed immunosensor could detect S. aureus in a linear range from 1.1 × 102 to 1.1 × 107 CFU mL-1 with a low detection limit of 39 CFU mL-1. Additionally, the proposed immunosensor was successfully applied to determine S. aureus in actual samples with acceptable results. This strategy provided a promising platform for highly sensitive determination of S. aureus and other pathogens in food products.

Recent Advances of Hepatitis B Detection towards Paper-Based Analytical Devices

Hepatitis B virus (HBV) still remains a major global public health problem. One-half to one-third of the total HBV infected people died due to late detection of HBV. Serological antigen and viral HBV detections can help in the diagnosis, referral, and treatment of HBV. Available methods for HBV detection mostly used bulky instruments. Miniaturization of devices for HBV detection has been started by narrowing down the size of the devices. Several methods have also been proposed to increase the selectivity and sensitivity of the miniaturized methods, such as sandwich recognition of the biomarkers and the use of nano- to micro-sized materials. This review presents recent HBV detections in the last two decades from laboratory-based instruments towards microfluidic paper-based analytical devices (µPADs) for point-of-care testing (POCT) purposes. Early and routine analysis to detect HBV as early as possible could be achieved by POCT, especially for areas with limited access to a central laboratory and/or medical facilities.

Electrochemical immunosensor based on Au/Co-BDC/MoS2 and DPCN/MoS2 for the detection of cardiac troponin I

The content of cardiac troponin I (CTnI) in human blood is the key factor in judging acute myocardial infarction (AMI). In order to detect the content of CTnI, we constructed a sandwich-type electrochemical immunosensor based on hydrogen peroxide (H2O2) as a signal source. Dendritic platinum-copper alloy nanoparticles (DPCN) loaded on molybdenum disulfide (MoS2) nanosheets (DPCN/MoS2) as secondary antibodies (Ab2) label provided signal amplification. The hollow three-dimensional (3D) pyramid-shaped structure of DPCN exposed abundant active sites and exhibited excellent catalytic properties. MoS2 nanosheets with flower-like structure and a larger specific surface area can effectively load more DPCN. The combination of MoS2 and DPCN enhanced the catalytic performance of DPCN/MoS2 towards H2O2 reduction and realized signal amplification. For the substrate material, the two-dimensional (2D) metal-organic framework (Co-BDC, 1,4-benzenedicarboxylate is abbreviated as BDC) was hybridized with MoS2 nanosheets to load gold nanoparticles (Au NPs). The obtained Au/Co-BDC/MoS2 had low catalytic activity and excellent electrical conductivity, which was used to load primary antibodies (Ab1) to effectively enhance the sensitivity. Under the best conditions, we constructed the immunosensor with the detection range of 10 fg/mL to 100 ng/mL and the limit of detection (LOD) of 3.02 fg/mL. At the same time, the content of CTnI in human serum was tested with satisfactory results. Therefore, the constructed immunosensor has important significance in the sensitive and accurate detection of CTnI and early diagnosis of AMI.

Molybdenum disulfide-based materials with enzyme-like characteristics for biological applications

Nanozyme, a kind of nanomaterials with enzymatic activity, has been developing vigorously over the past years owing to its advantages such as low-cost, easy storage, ease of use in harsh environments and so on, compared with natural enzymes. At present, as a typical two-dimensional nanomaterial, molybdenum disulfide (MoS₂) and their hybrids with unexpected enzyme-like activities have caused wide attention. In this review, we mainly investigated the enzyme-like activities of MoS₂ based nanomaterials, including peroxidase-like activity, catalase-like activity and superoxide dismutase-like activity. Furthermore, we systematically introduce recent research progress of MoS₂ based nanomaterials in the fields of biological applications such as radiation protection, cancer therapy, antibacterial, and wound healing. Finally, the current challenges and perspectives of MoS₂ based nanomaterials in the future are also discussed and proposed. We expect this review may be significant to understand the properties of MoS₂ based nanomaterials and the development of two-dimensional nanomaterials with enzyme mimicking activities.

Pathogen detection with electrochemical biosensors: Advantages, challenges and future perspectives

Detection of pathogens, e.g., bacteria and viruses, is still a big challenge in analytical medicine due to their vast number and variety. Developing strategies for rapid, inexpensive, specific, and sensitive detection of the pathogens using nanomaterials, integrating with microfluidics devices, amplification methods, or even combining these strategies have received significant attention. Especially, after the health-threatening COVID-19 outbreak, rapid and sensitive detection of pathogens became very critical. Detection of pathogens could be realized with electrochemical, optical, mass sensitive, or thermal methods. Among them, electrochemical methods are very promising by bringing different advantages, i.e., they exhibit more versatile detection schemes and real-time quantification as well as label-free measurements, which provides a broader application perspective. In this review, we discuss the recent advances for the detection of bacteria and viruses using electrochemical biosensors. Moreover, electrochemical biosensors for pathogen detection were broadly reviewed in terms of analyte, bio-recognition and transduction elements. Different fabrication techniques, detection principles, and applications of various pathogens with the electrochemical biosensors were also discussed.

A novel electrochemical immunosensor for hepatitis B surface antigen based on Fe3O4 nanoflowers and heterogeneous chain reaction signal amplification strategy

Herein, a novel sandwich-type electrochemical immunosensor was fabricated based on Fe₃O₄ nanoflowers (Fe₃O₄ NFs) and heterogeneous chain reaction (HCR) signal amplification strategy for the sensitive detection of hepatitis B surface antigen (HBsAg). The aldehyde-functionalized Fe₃O₄ NFs are used as a supporting matrix to immobilize the hepatitis B surface antibody 1 (HBsAb1). The biotin-modified single-strand DNA (biotin-S0) was connected onto the biotin-HBsAb2 via linkage of streptavidin (SA), followed by addition of methylene blue (MB) modified single strand DNA1 (MB-S1) and DNA2 (MB-S2) for HCR signal amplification. The designed immunosensor exhibited a detection linear range of 0.5 pg mL^-1-0.25 ng mL^-1 and a low detection limit of 0.16 pg mL^-1, with excellent stability, selectivity and reproducibility. Furthermore, HBsAg is detected in the serum samples with a stable and fast response, indicating that the proposed immunosensor has a promising potential application in clinical analysis.

"Gold-plated" IRMOF-3 and sea cucumber-like Pd@PtRh SNRs based sandwich-type immunosensor for dual-mode detection of PCT

Electrochemical immunoassays are often used in the detection of biomarkers, and their sensitivity depends on the nature of the substrate and the catalytic activity of the signal amplification platform. In this work, a novel sandwich-type signal amplification strategy with a "gold-plated" organometallic frame (Au/IRMOF-3) as the substrate and the sea cucumber-like Pd@PtRh trimetallic nanomaterial (Pd@PtRh SNRs) as label was fabricated. For the substrate, gold nanoparticles (Au NPs) are stably connected to the free amino groups on the surface of organometallic frame (IRMOF-3), which not only prevent the agglomeration of Au NPs, but also greatly enhance the conductivity of the nanocomposites. The synergy between the two nanomaterials further shows a stronger affinity for the fixation of capture antibodies (Ab1). For the label, the effective high catalytic activity comes from the Pd@PtRh SNRs with a sea cucumber-like morphology. The nano-scale spherical PtRh crystals epitaxially grown on smooth Pd nanorods (Pd NRs) have more catalytically active sites because of the abundant edge and corner atoms, resulting in high catalytic activity and durability towards H2O2 reduction. Choosing calcitonin (PCT) as the target, differential pulse voltammetry (DPV) and amperometric i-t dual-mode detection was used to demonstrate the feasibility of the immunosensor. The results confirmed that the immunosensor exhibits excellent analytical capabilities and is satisfied in the analysis of human serum samples. Therefore, this strategy has great potential in the clinical application of electrochemical immunosensors.

Chemiluminescent Optical Fiber Immunosensor Combining Surface Modification and Signal Amplification for Ultrasensitive Determination of Hepatitis B Antigen

Optical fiber based immunosensors are very attractive for biomarker detection. In order to improve the sensor response, we propose a promising strategy which combines porous-layer modification of the fiber surface and streptavidin-biotin-peroxidase nano-complex signal amplification in chemiluminescent detection. Two hepatitis B antigens, hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg), are used as the targets for analysis using the proposed sensor. Comparing to immunoassays using normal optical fiber sensors, the response of the present sensor is enhanced by a factor of 4.8 and 6.7 for detection of HBsAg and HBeAg, respectively. The limit-of-quantitation of the proposed method is as low as 0.3 fg/mL (0.01 fg/mL) with a wide linear response range of 3 fg/mL–150 ng/mL (0.1 fg/mL–160 ng/mL) for sensing HBsAg (HBeAg). Quantitative determination of HBsAg and HBeAg in human serum samples is performed, showing the applicability of the proposed method for biomarker detection.