A photoelectrochemical immunosensor based on magnetic all-solid-state Z-scheme heterojunction for SARS-CoV-2 nucleocapsid protein detection.

Rapid, convenient and accurate detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is urgently needed to timely diagnosis of coronavirus pandemic (COVID-19) and control of the epidemic. In this study, a signal-off photoelectrochemical (PEC) immunosensor was constructed for SARS-CoV-2 nucleocapsid (N) protein detection based on a magnetic all-solid-state Z-scheme heterojunction (Fe3O4@SiO2@TiO2@CdS/Au, FSTCA). Integrating the advantages of magnetic materials and all-solid-state Z-scheme heterostructures, FSTCA was implemented to ligate the capture antibody to form magnetic capture probe (FSTCA/Ab1). It can simplify the separation and washing process to improve reproducibility and stability, while allowing immune recognition to be performed in the liquid phase instead of the traditional solid-liquid interface to improve anti-interference. Besides, the heterojunction inhibited the recombination of photogenerated electron/hole (e-/h+) and promoted the light absorption to provide superior photoelectric substrate signal. The mechanism of photogenerated e-/h+ transfer of FSTCA were investigated by the electron spin resonance (ESR) spectroscopy. SiO2 spheres loaded with Au NPs utilized as an efficient signal quencher. The steric hindrance effect of SiO2@Au labeled detection antibodies (SiO2@Au-Ab2) conjugates significantly diminished light absorption and hindered the transfer of photogenerated electrons, further amplifying the signal change value. Based on the above merits, the elaborated immunosensor had a wide linear range of 10 pg mL-1-100 ng mL-1 and a low detection limit down to 2.9 pg mL-1 (S/N = 3). The fabricated PEC immunosensor demonstrated strong anti-interference, easy operation, and high sensitivity, showing enormous potential in clinical diagnosis of SARS-CoV-2.

A signal-off photoelectrochemical sandwich-type immunosensor based on WO3/TiO2 Z-scheme heterojunction.

A sandwich "signal-off" type photoelectrochemical (PEC) immunosensor was fabricated based on a composite heterojunction of tungsten oxide/titanium oxide microspheres (WO3/TiO2) acting as signal amplification platform and carbon microspheres loaded by gold nanoparticles (Cs@Au NPs) utilized as the label for detecting antibody. WO3/TiO2 had excellent photoelectric performance, and the results of Mott-Schottky plots, open-circuit voltage, and electron spin resonance spectroscopy indicated that it belonged to the Z-scheme heterojunction transfer mechanism of photogenerated carriers. To achieve the sensitization of PEC immunosensor, Cs@Au NP-labeled immunocomplex can effectively reduce the photocurrent signal. The PEC immunosensors were fabricated under the optimal conditions of 1:1 WO3/TiO2 (molar ratio), 2.0 mg mL-1 WO3/TiO2, and 1.5 mg mL-1 Cs@Au NPs. Through comparison of the detection results of label-free and sandwich-type PEC immunosensors for nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), we found that the sensitivity of the sandwich type was 2.53 times the label-free type, and the limit of detection was 0.006 ng mL-1, i.e., 3.17 times lower than the label-free type. This demonstrates that the developed sandwich-type PEC immunosensor will have a brighter application prospect.

Surface Plasmon Resonance Sensor Based on Core-Shell Fe3O4@SiO2@Au Nanoparticles Amplification Effect for Detection of T-2 Toxin.

In this paper, a core-shell based on the Fe3O4@SiO2@Au nanoparticle amplification technique for a surface plasmon resonance (SPR) sensor is proposed. Fe3O4@SiO2@AuNPs were used not only to amplify SPR signals, but also to rapidly separate and enrich T-2 toxin via an external magnetic field. We detected T-2 toxin using the direct competition method in order to evaluate the amplification effect of Fe3O4@SiO2@AuNPs. A T-2 toxin-protein conjugate (T2-OVA) immobilized on the surface of 3-mercaptopropionic acid-modified sensing film competed with T-2 toxin to combine with the T-2 toxin antibody-Fe3O4@SiO2@AuNPs conjugates (mAb-Fe3O4@SiO2@AuNPs) as signal amplification elements. With the decrease in T-2 toxin concentration, the SPR signal gradually increased. In other words, the SPR response was inversely proportional to T-2 toxin. The results showed that there was a good linear relationship in the range of 1 ng/mL~100 ng/mL, and the limit of detection was 0.57 ng/mL. This work also provides a new possibility to improve the sensitivity of SPR biosensors in the detection of small molecules and in disease diagnosis.

A ratiometric fluorescence imprinted sensor based on N-CDs and metal-organic frameworks for visual smart detection of malathion.

Sensitive and rapid detection of pesticide residues in food is essential for human safety. A ratiometric imprinted fluorescence sensor N-CDs@Eu-MOF@MIP (BR@MIP) was constructed to sensitively detect malathion (Mal). Europium-based metal organic frameworks (Eu-MOF) were used as supporters to improve the sensitivity of the BR@MIP. N-doped carbon dots (N-CDs) were used as fluorescent source to produce fluorescent signal. A linear relationship between the concentration of Mal and the fluorescence response of the sensor was found in the Mal concentration range of 1-10 µM with a limit of detection (LOD) of 0.05 µM. Furthermore, the sensor was successfully applied for the detection of Mal in lettuce, tap water, and soil samples, with recoveries in the range of 93.0 % - 99.3 %. Additionally, smartphone-based sensors were used to detect Mal in simulated real samples. Thus, the construction of ratiometric imprinted fluorescence sensor has provided a good strategy for the detection of Mal.

CdTe QDs-sensitized TiO2 nanocomposite for magnetic-assisted photoelectrochemical immunoassay of SARS-CoV-2 nucleocapsid protein.

A sensitive, reliable, and cost-effective detection for SARS-CoV-2 was urgently needed due to the rapid spread of COVID-19. Here, a "signal-on" magnetic-assisted PEC immunosensor was constructed for the quantitative detection of SARS-CoV-2 nucleocapsid (N) protein based on Z-scheme heterojunction. Fe3O4@SiO2@Au was used to connect the capture antibody to act as a capture probe (Fe3O4@SiO2@Au/Ab1). It can extract target analytes selectively in complex samples and multiple electrode rinsing and assembly steps were avoided effectively. CdTe QDs sensitized TiO2 coated on the surface of SiO2 spheres to form Z-scheme heterojunction (SiO2@TiO2@CdTe QDs), which broadened the optical absorption range and inhibited the quick recombination of photogenerated electron/hole of the composite. With fascinating photoelectric conversion performance, SiO2@TiO2@CdTe QDs were utilized as a signal label, thus further realizing signal amplification. The migration mechanism of photogenerated electrons was further deduced by active material quenching experiment and electron spin resonance (ESR) measurement. The elaborated immunosensor can detect SARS-CoV-2 N protein in the linear range of 0.005-50 ng mL-1 with a low detection limit of 1.8 pg mL-1 (S/N = 3). The immunosensor displays extraordinary sensitivity, strong anti-interference, and high reproducibility in detecting SARS-CoV-2 N protein, which envisages its potential application in the clinical diagnosis of COVID-19.

A novel smartphone-integrated binary-emission molecularly imprinted fluorescence sensor embedded with MIL-101(Cr) for sensitive and real-time detection of protein.

Aiming for precise, real-time, and on-site analysis of proteins, an innovative binary-emission fluorescence imprinted polymer was designed by sol-gel method after mixing MIL-101(Cr), green CdTe (g-CdTe) and red CdTe (r-CdTe) for detection of protein. In this proposal, MIL-101(Cr), as a favorable supporter, provided high surface area and porosity for imprinting sites, which ameliorated the transfer rate and the sensitivity of the nanosensor. And g-CdTe and r-CdTe were served as signal transduction for dual-emission response. Based on strengthened recognition reaction between high-affinity imprinting sites and protein, the fluorescence intensities of g-CdTe and r-CdTe yielded conspicuous two responses at 528 nm and 634 nm for protein under the excitation of 350 nm. The cytochrome c (Cyt c) and trypsin were served as model proteins to verify the generality of strategy. Given prominent merits of MIL-101(Cr), g-CdTe/r-CdTe@MIL-101(Cr)@MIP exhibited good linear range of 1-30 µM for Cyt c and 0.15-4 µM for trypsin, and the limit of detection were 0.13 µM and 0.014 µM, respectively. Significantly, an unsophisticated smartphone-based sensing device was developed by integrating g-CdTe/r-CdTe@MIL-101(Cr)@MIP with a 3D printing portable device to obtain precise on-site results. As expected, this portable platform was successfully applied for monitoring Cyt c and trypsin with a detection limit of 0.71 µM and 0.026 µM, respectively. These results indicated this dual-response molecularly imprinted fluorescence senor based on smartphone provided promising perspectives on futural on-site protein analysis.

A Novel SPR Immunosensor Based on Dual Signal Amplification Strategy for Detection of SARS-CoV-2 Nucleocapsid Protein.

Since the global outbreak of coronavirus disease 2019 (COVID-19), it has spread rapidly around the world. The nucleocapsid (N) protein is one of the most abundant SARS-CoV-2 proteins. Therefore, a sensitive and effective detection method for SARS-CoV-2 N protein is the focus of research. Here, we developed a surface plasmon resonance (SPR) biosensor based on the dual signal-amplification strategy of Au@Ag@Au nanoparticles (NPs) and graphene oxide (GO). Additionally, a sandwich immunoassay was utilized to sensitively and efficiently detect SARS-CoV-2 N protein. On the one hand, Au@Ag@Au NPs have a high refractive index and the capability to electromagnetically couple with the plasma waves propagating on the surface of gold film, which are harnessed for amplifying the SPR response signal. On the other hand, GO, which has the large specific surface area and the abundant oxygen-containing functional groups, could provide unique light absorption bands that can enhance plasmonic coupling to further amplify the SPR response signal. The proposed biosensor could efficiently detect SARS-CoV-2 N protein for 15 min and the detection limit for SARS-CoV-2 N protein was 0.083 ng/mL, with a linear range of 0.1 ng/mL~1000 ng/mL. This novel method can meet the analytical requirements of artificial saliva simulated samples, and the developed biosensor had a good anti-interference capability.

Enhanced degradation of chloramphenicol through peroxymonosulfate and visible light over Z-scheme Photocatalysts: Synergetic performance and mechanism insights.

Effective removal of antibiotics in the environment can be a demanding issue concerning the ecosystem and human health. Photocatalysis and peroxymonosulfate (PMS) oxidation have become important methods to effectively remove stubborn pollutants. In this work, by integrating these two technologies, an efficient system for degrading chloramphenicol (CAP) in water was proposed. The system was constructed by coupling strontium-doped lanthanum cobaltate (LSCO5) with chlorine-doped carbon nitride (CGCN). By doping, the increase of oxygen vacancy and the adjustment of bandgap were realized. Photoluminescence and electrochemical impedance experiments showed that the heterojunction can promote electron transfer and photogenerated carrier separation. Under the synergistic effect of PMS oxidation and photocatalysis, the prepared composite with an optimal loading of 40% LSCO5 can degrade 95.6% of CAP within 20 min. Degradation experiments on different pollutants proved the versatility of the catalytic system. The enhanced degradation mechanism of CAP was explored based on the assessment of the degradation efficiency of CAP, electron paramagnetic resonance (EPR), and quenching experiments. Through liquid chromatography-mass spectrometry (LC-MS) analysis, a possible route for CAP degradation was also proposed. This research provides some inspiration for the remediation of polluted water with perovskite-based catalyst under the synergistic effect of PMS and photocatalysis.

Construction of g-C3N4/Au/NH2-UiO-66 Z-scheme heterojunction for label-free photoelectrochemical recognition of D-penicillamine.

The wide clinical application of d-penicillamine (D-PA) makes it inevitably accumulates in the environment, seriously threatening human health and the ecological environment. To better supervisory control D-PA, a highly sensitive and reliable photoelectrochemical (PEC) sensor based on gold nanoparticles (Au NPs) loaded on graphitic carbon nitride sheet and hexagonal NH2-UiO-66 composite (g-C3N4/Au/NH2-UiO-66) was synthesized. Tactfully using the strong bonding between D-PA and Au NPs and the effective carrier separation of Z-scheme heterojunction, the designed g-C3N4/Au/NH2-UiO-66 PEC sensor without an extra recognition unit exhibited a selective and sensitive photocurrent to D-PA. With the aid of UV diffuse reflectance spectra (UV-DRs), electron paramagnetic resonance (EPR) characterization, and free radical capture experiments, the electron transfer path of the PEC sensing system was deduced. The proposed g-C3N4/Au/NH2-UiO-66 PEC-based sensor achieved a low detection limit of 0.0046 µM (S/N = 3) with a wide linear response ranging from 10 nM to 400 µM. In addition, its good stability and selectivity also laid a good foundation for practical applications.

Trimetallic Au@Pd@Pt nanozyme-enhanced lateral flow immunoassay for the detection of SARS-CoV-2 nucleocapsid protein.

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seriously threatened global public health. Establishing a rapid and sensitive diagnostic test for early detection of the SARS-CoV-2 nucleocapsid protein is urgently required to defend against the pandemic. Herein, an enhanced lateral flow immunoassay (LFIA) was fabricated by trimetallic Au@Pd@Pt core-shell nanozymes for detection of the SARS-CoV-2 nucleocapsid protein. The Au@Pd@Pt nanozymes (Au@Pd@Pt NZs) synthesized via a one-pot method, with a dendrite morphology and uniform particle size, showed excellent peroxidase-like activity. Due to the perfect enzyme-like catalytic activity toward 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2), the catalytic signal could be generated even by a tiny amount of Au@Pd@Pt NZs accumulated on the test strip. Therefore, rapid detection with higher sensitivity was achieved. The Au@Pd@Pt NZs-based LFIA provided a quantitative range of 0.05-100 ng mL-1 with a limit of detection of 0.037 ng mL-1, which was 17-fold lower than the LFIA without enhancement. The average recoveries from spiked samples were in the range of 92.5-107.9% with relative standard deviations all less than 4%, indicating the reliability and repeatability of the proposed LFIA. Additionally, the proposed LFIA could report results within 30 min using a microplate reader. In conclusion, the Au@Pd@Pt NZs-LFIA is a rapid, simple, and sensitive method for detecting the SARS-CoV-2 nucleocapsid protein.

Magnetic/fluorescent dual-modal lateral flow immunoassay based on multifunctional nanobeads for rapid and accurate SARS-CoV-2 nucleocapsid protein detection.

The SARS-CoV-2 pandemic has posed a huge challenge to rapid and accurate diagnosis of SARS-CoV-2 in the early stage of infection. In this work, we developed a novel magnetic/fluorescent dual-modal lateral flow immunoassay (LFIA) based on multifunctional nanobeads for rapid and accurate determination of SARS-CoV-2 nucleocapsid protein (NP). The multifunctional nanobeads were fabricated by using polyethyleneimine (PEI) as a mediate shell to combine superparamagnetic Fe3O4 core with dual quantum dot shells (MagDQD). The core-shell structure of MagDQD label with high loading density of quantum dots (QDs) and superior magnetic content realized LFIA with dual quantitative analysis modal from the assemblies of individual single nanoparticles. The LFIA integrated the advantages of magnetic signal and fluorescent signal, resulting excellent accuracy for quantitative analysis and high elasticity of the overall detection. In addition, magnetic signal and fluorescent signal both had high sensitivity with the limit of detection (LOD) as 0.235 ng mL-1 and 0.012 ng mL-1, respectively. The recovery rates of the methods in simulated saliva samples were 91.36%-103.60% (magnetic signal) and 94.39%-104.38% (fluorescent signal). The results indicate the method has a considerable potential to be an effective tool for diagnose SARS-CoV-2 in the early stage of infection.

Efficient detection for Nitrofurazone based on novel Ag2S QDs/g-C3N4 fluorescent probe.

In the paper, a novel fluorescent probe based on Ag2S QDs/g-C3N4 composite was synthesized by loading Ag2S quantum dots (Ag2S QDs) on the surface of g-C3N4 through in-situ synthesis method and developed to detect Nitrofurazone (NFZ) sensitively. The results showed that the linear detection range of Ag2S QDs/g-C3N4 to NFZ was 0-30 µM, with a low detection limit of 0.054 µM. The results of time-fluorescence-resolved spectroscopy and UV-vis absorption spectroscopy exhibited that the possible detection mechanism of Ag2S QDs/g-C3N4 to NFZ was proposed to be Internal Filtration Effect (IFE). Moreover, Multiwfn wavefunction analysis was employed to uncover the possible interaction between the Ag2S QDs/g-C3N4 and NFZ, thereby further revealing the fluorescence detection mechanism from the scale of atoms. Combining experiments and theoretical calculations, we proposed the sensing mechanism of the formation of non-fluorescent ground state complex linked by hydrogen bonds. This work indicated that the Ag2S QDs/g-C3N4 composite processed the ability to detect NFZ efficiently and sensitively.

A Highly Sensitive Fluorescence and Screen-Printed Electrodes-Electrochemiluminescence Immunosensor for Ricin Detection Based on CdSe/ZnS QDs with Dual Signal.

A sensitive dual-readout immunosensor for fluorescence and electrochemiluminescence (ECL) detection of ricin was established, which was combined with a streptavidin-biotin signal amplification system. CdSe/ZnS quantum dots with fine fluorescence and ECL properties were used as the dual-signal function probes of the sandwich immunocomplex. Under the optimum experimental conditions, the dual signal intensity increased significantly with the rise in ricin concentration. The fluorescence intensity of the senor exhibited a good liner relationship toward the ricin concentrations with 0.1~100 ng/mL and the limit of detection (LOD) was 81.7 pg/mL; taking ECL as the detection signal, the sensor showed a linear relationship with the ricin concentrations ranging from 0.01 ng/mL to 100 ng/mL and the LOD was 5.5 pg/mL. The constructed sensor with high sensitivity had been successfully applied to the detection of ricin in complex matrices with satisfactory recoveries. The proposed immunosensor model can be extended to the analysis and detection of others target proteins.

A photoelectrochemical immunosensor based on Z-scheme CdS composite heterojunction for aflatoxin B1.

Aflatoxin B1 (AFB1) is a highly toxic fungal contaminant widely found in agricultural products. It causes serious harm to human health and the environment. Thus, a fast and sensitive detection approach is urgently needed to prevent AFB1-contaminated products from entering the market effectively. A photoelectrochemical (PEC) immunosensor was developed based on tungsten trioxide/cadmium sulfide core/shell coated with a composite layer consisting of polydopamine and loaded gold nanoparticles (WO3/CdS@PDA/Au) for AFB1 detection. CdS formed a heterojunction with WO3, which improved the photoelectric performance. The coated PDA reducing CdS toxicity was demonstrated by biological experiment of Bacillus subtilis. PDA and Au NPs promoted electron transfer between the semiconductors, being beneficial promoting the photoelectron transfer. Additionally, the antibodies were immobilized on WO3/CdS@PDA/Au via the reactive quinones on the surface of the PDA and electrostatic adsorption from Au NPs. The WO3/CdS@PDA/Au composite as a Z-scheme heterojunction possessed high performance of photocurrent response, and the photoproduced electron/hole transfer path was speculated by electrons spin-resonance spectroscopy technique. Under the optimum experimental conditions, the PEC immunosensor showed a wide linear detection range from 0.05 to 100 ng mL-1 for AFB1, indicating that the immunosensor has a bright application prospect.

Label-free photoelectrochemical immunosensor for aflatoxin B1 detection based on the Z-scheme heterojunction of g-C3N4/Au/WO3.

Aflatoxin B1 (AFB1) is the most toxic mycotoxin, is widely found in foods and animal feeds, and can pose a serious threat to our lives. A label-free photoelectrochemical (PEC) immunosensor was fabricated for the sensitive detection of AFB1. A Z-scheme heterojunction of gold nanoparticles (Au NPs) loaded on graphitic carbon nitride sheet and tungsten trioxide sphere composite (g-C3N4/Au/WO3) acted as the highly sensitive platform. The g-C3N4/Au/WO3 is capable, not only of immobilizing antibodies via Au NPs, but also enhancing the separation of electron-hole pairs due to its good energy band matching efficiency. The mechanism of photo-generated electron/hole transfer on g-C3N4/Au/WO3 was explored using scavengers to eliminate active components. On this basis, an electron transfer pathway for the immunosensor was deduced. The PEC immunosensor displayed a linear concentration range from 1.0 pg mL-1 to 100 ng mL-1 and a low detection limit of 0.33 pg mL-1 (S/N = 3) for AFB1. Good reproducibility, stability, and specificity provide a solid foundation for the practical application of this immunosensor.

A ratiometric fluorescent sensor based on g-CNQDs@Zn-MOF for the sensitive detection of riboflavin via FRET.

A novel ratiometric fluorescent sensor based on Förster resonance energy transfer (FRET) platform was designed for riboflavin (RF) detection. The graphitic carbon nitrides quantum dots - Zn-MOF composite (g-CNQDs@Zn-MOF) was used as the fluorescent probe. In the FRET system, g-CNQDs@Zn-MOF and RF acted as donor and acceptor, respectively. The probe exhibited high sensitivity and good selectivity to RF, and had been successfully used for the detection of RF in milk and vitamin B2 tablets. The detection limit of the sensor was 15 nM. The strategy expanded the application of MOF in sensing filed and provided a new method for the detection of RF.

Electrochemical Immunosensors for Sensitive Detection of Neuron-Specific Enolase Based on Small-Size Trimetallic Au@Pd

Medically, neuron-specific enolase (NSE) as a specific tumor marker has become an important indicator to diagnose small-cell lung carcinoma. In this study, a sandwich-type electrochemical immunosensor was designed to determine NSE sensitively. Au nanoparticle (Au NP)-embedded zinc-based metal-organic frameworks (Au@MOFs) were prepared as the substrate materials to modify the electrode and immobilize the primary antibody (Ab1). The Au@MOFs with the free amino groups on the MOF surface could effectively increase the immobilization amount of Ab1 through covalent linkage. Simultaneously, the embedding of Au NPs improved the conductivity of MOFs and accelerated interface electron transfer. Sub-30 nm trimetallic Au@Pd^Pt nanocubes (Au@Pd^Pt NCs) loaded onto ultrathin MnO2 nanosheets (MnO2 UNs/Au@Pd^Pt NCs) acted as the labels of secondary antibodies. The small-size Au@Pd^Pt NCs enhanced atomic utilization efficiency and offered more catalytic active sites. The MnO2 UNs with high external surface areas could improve the dispersion of Au@Pd^Pt NCs. The MnO2 UNs/Au@Pd^Pt NCs could catalyze the H2O2 reduction and promote the oxidation of hydroquinone to quinone effectively because of their synergistic effect; thus, the generated quinone achieved amplification of the highly reductive peak current. Furthermore, under the optimal conditions, the immunosensor exhibited a low detection limit (4.17 fg/mL) and broad linear range (10 fg/mL to 100 ng/mL). The results were satisfactory for NSE detection in human serum samples, implying that the presented method had great application potential in clinical bioanalysis.

Fluorescent MoS2 QDs based on IFE for turn-off determination of FOX-7 in real water samples.

A novel method for turn-off sensing 1,1-diamino-2,2-dinitroethylene (FOX-7) in aqueous medium was first proposed based on the inner filter effect (IFE) of FOX-7 on the fluorescence of molybdenum disulfide quantum dots (MoS2 QDs). Water-soluble MoS2 QDs as the fluorophore were prepared by the simple hydrothermal method. The morphology, structure, composition and optical properties of the prepared MoS2 QDs were characterized by Transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), UV-vis absorption and photoluminescence spectra. The results showed that the MoS2 QDs had good water dispersibility and emitted strong photoluminescence with a particle size of 2 nm. Under the optimal experimental conditions, the fluorescence signal of MoS2 QDs was quenched in the concentrations range of FOX-7 (0.5-100 µM) and the limit of detection (LOD) of the sensor was 0.19 µM. The method had been applied to analyze the real water samples with good selectivity and stability. Moreover, the quenching mechanism was studied systematically by the Fourier transform infrared (FT-IR), UV-vis absorption spectra, fluorescence lifetime, and Stern-Volmer equation, which had been proved to be static quenching. The fluorescence quenching mechanism is mainly IFE and electron transfer.

The preparation of hollow AgPt@Pt core-shell nanoparticles loaded on polypyrrole nanosheet modified electrode and its application in immunosensor.

The designed synthesis of efficient materials can significantly enhance the performance of electrochemical immunoassay in the detection of diseases, pesticide residues and environmental pollutants. The hollow AgPt@Pt core-shell nanoparticles (AgPt@Pt HNs) have exhibited high catalytic efficiency to the hydrogen peroxide (H2O2) reduction for its high mass activity from their hollow structure. Their limitation of instability can be overcome by loading on polypyrrole nanosheet (PPy NS). Besides, PPy NS exhibits good conductivity, and there exists environmentally-friendly method for its synthetic. Thus, AgPt@Pt HNs loaded on PPy NS (AgPt@Pt HNs/PPy NS) exhibits high catalytic efficiency to the reduction of H2O2 and good stability. Furthermore, the quick electron transfer of AgPt@Pt HNs/PPy NS modified glassy carbon electrode has been evidenced by the finding that the large constant of apparent electron transfer rate has also enlarged the current signal when the amount of electron is invariant. The modified electrode has fabricated a label-free amperometric immunosensor to detect sensitively prostate-specific antigen (PSA) with H2O2 as the electroactive material. The immunosensor in hollow core-shell nanosheet structure exhibiting good detection performance of PSA shows its promising applications in the clinical diagnosis.

Electrochemical immunosensor based on MoS2 NFs/Au@AgPt YNCs as signal amplification label for sensitive detection of CEA.

Medically, the dynamic change of carcinoembryonic antigen (CEA) concentration has been an important indicator for monitoring and diagnosing tumors. The sensitive and early detection of CEA plays a momentous role in the prevention and diagnosis of cancer and the evaluation of treatment efficiency. In this work, a sensitive sandwich-type electrochemical immunosensor was fabricated for the quantitative detection of CEA. The trimetallic yolk-shell Au@AgPt nanocubes (Au@AgPt YNCs) loaded on amino-functionalized MoS2 nanoflowers (MoS2 NFs/Au@AgPt YNCs) were used as the labels to conjugate with secondary antibodies. The Au@AgPt YNCs with internal space and permeable shell improved catalytic active surface area. The nanosheet-based MoS2 NFs with good catalytic activity were used as carriers to load Au@AgPt YNCs effectively. Due to the biphasic synergistic catalysis, MoS2 NFs/Au@AgPt YNCs catalyzed the reduction of H2O2 effectually to amplify the current signal. Besides, Au triangular nanoprisms (Au TNPs) were used as substrate material to increase the effective contact areas with the surface of electrode and accelerate the interface electron transfer. Under the optimal conditions, a broad linear range from 10 fg mL-1 to 100 ng mL-1 with low detection limit of 3.09 fg mL-1 (S/N = 3) for detecting CEA was obtained. Moreover, the detection results of the human serum samples were satisfactory, indicating the fabricated immunosensor had potential application values in the early clinical analysis.