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A photoelectrochemical (PEC) biosensor capable of detecting cytokeratin 19 fragment 21-1 (CYFRA21-1) was optimized by taking advantage of the powerful conjugate repeats of horseradish peroxidase and tyramine (HRP-tyramine)-triggered enzymatic biocatalytic precipitation (BCP) on high-performance BiVO 4 /Ag 3 VO 4 /SnS 2 photoelectrodes. Compared with the ubiquitous BCP strategy, we identified a design supporting conjugate repeats generated by HRP and tyramine-triggered immeasurable insoluble precipitates in the presence of hydrogen peroxide and 4-chloro-1-phenol (4-CN), and the steric hindrance improved sensitivity. Moreover, by virtue of BiVO 4 , Ag 3 VO 4 , SnS 2 excellent level matching structure and chemical stability, a heterojunction (BiVO 4 /Ag 3 VO 4 /SnS 2 ) with high light absorption efficiency has been successfully prepared. The novel heterostructure system of BiVO 4 /Ag 3 VO 4 /SnS 2 with high detection current and low background signal exhibited high-performance PEC determination. Generally, the hitherto untapped biosensor resource realized the sensitive detection of CYFRA21-1 with a wide linear range from 50 fg/mL to 200 ng/mL, and a detection limit of 15 fg/mL, which illustrated the potential for biotechnological applications., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

This research put forward a novel split-type electrochemical (EC) immunosensor which integrated the controlled-release strategy with EC detection for application in the field of biosensing. Concretely, ascorbic acid (AA) was packaged in a cadmium sulfide (CdS)-capped spherical mesoporous bioactive glass (SBG) nanocarrier (SBG CdS ) on account of encapsulation technology. To reduce the complexity of the bioanalysis, the detection antibody-labeled SBG CdS -AA bioconjugate was applied in a 96-well microplate for the immunoreaction process, which is independent of the EC determination procedure. Thus, the immune interference and steric hindrance caused by the accumulation of nanomaterials on the electrode could be minimized. Subsequently, AA was released efficiently via the destruction effect of dithiothreitol on the disulfide bond. In addition, for the as-prepared FcAI/l-Cys/gold nanoparticles (GNPs)/porous BiVO 4 (p-BVO)/ITO EC sensing platform in the detection solution, the synergetic catalysis of Fc and GNPs/p-BVO toward the oxidation of the released AA could be realized, which triggered AA-mediated significant signal magnification throughout this study. In particular, p-BVO with an ordered nanoarray structure could accelerate the electron transfer to assist in sensitivity improvement of this system. This novel biosensor was capable of assaying the neuron-specific enolase (NSE) biomarker sensitively, from which a linear range of 0.001-100 ng/mL was derived along with a low detection limit of 1.08 pg/mL. An innovative way could be paved in the bioanalysis of NSE and other biomarkers.

The accurate and rapid fungaltoxin detection at early stage can prevent people from getting cancer to a great extent. Here, an ultrasensitive electrochemical immunosensor for the detection of ochratoxin A was reported. Octahedral gold nanoparticles (Oct Au NPs) with edge and sharp corners as substrate materials can connect more primary antibodies and Au octahedron plasmonic colloidosomes (Au Oct PCs) were formed by the natural settlement of the Oct Au NPs in the inverse emulsion system. Au Oct PCs with high specific surface area and good electron transfer ability can hybridize with electron mediator toluidine blue to act as labels to amplify the output signal and ameliorate the stability of the immunosensor. The immunoassay was performed via the square wave voltammetry and showed a strong current response. The proposed immunosensor obtained a wide linear range from 0.1 pg mL -1 to 10 ng mL -1 and a low detection limit of 39 fg mL -1 . This new strategy achieved favorable stability, reproducibility and selectivity, which had potential application in real sample analysis., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The accurate and rapid ochratoxin A (OTA) detection at early stage can prevent people from getting cancer to a great extent due to its strong liver toxicity and renal toxicity. The development of an efficient strategy to detect OTA without sophisticated instruments is highly desired, but still remains a severe challenge. In this communication, a sandwich type point-of-care testing (POCT) immunoassay is developed for OTA detection. The 3-aminopropyltrimethoxysilane-glutaraldehyde (APTMS-GA) is used as color matrix and Au-N-TiO 2 as labels for loading more captured antibodies and glucose oxidases (GOD). When glucose is added, GOD can be catalyzed to produce H 2 O 2 which can weaken the color strength to quantify OTA concentrations. The mean gray values of reacted ITO-based immunosensors can be calculated by the software of Image J. The linear range of OTA is 0.0001-1 ng mL -1 with a low detection limit of 28 fg mL -1 at a signal-to-noise ratio of 3 s. This strategy can achieve the excellent performance without sophisticated instruments. This POCT method may has a potential application in the undeveloped countries with only a camera-equipped cellphone., (Copyright © 2018 Elsevier B.V. All rights reserved.)

A novel and sensitive sandwich-type photoelectrochemical (PEC) sensor was fabricated using signal amplification strategy for the quantitative detection of the prostate specific antigen (PSA). CdSe nanoparticles (NPs) sensitized lanthanum-doped titanium dioxide (La-TiO 2 ) composites were used to bind the primary antibodies (Ab 1 ). The doping of lanthanum promoted the visible light absorption of TiO 2 and remarkably enhanced the photocurrent. Moreover, 0.3%La-TiO 2 displayed the highest photocurrent in the La-TiO 2 composites, which was twice as much as that of undoped TiO 2 . Carboxyl modified CdSe NPs were assembled onto La-TiO 2 composites via the dentate binding between -COOH and Ti atom in TiO 2 NPs, which dramatically promoted the photocurrent intensity by approximately 2.1 times. Carboxyl functionalized polystyrene (PS) microspheres were coated with the secondary antibodies (Ab 2 ). Owing to the better insulation property and steric hindrance of the prepared polystyrene@Ab 2 (PS@Ab 2 ) composites, the significant reduction of the photocurrent signal was achieved after the specific immune recognition. Under the optimum experimental conditions, the fabricated PEC sensor realized ultrasensitive detection of PSA in the range of 0.05-100pgmL -1 with a detection limit of 17fgmL -1 . Moreover, this well-designed PEC immunoassay exhibited ideal reproducibility, stability, and selectivity, which is a promising platform for the detection of other important tumor targets., (Copyright © 2016 Elsevier B.V. All rights reserved.)

In this study, a novel and ultrasensitive sandwich-type electrochemical immunosensor was designed for the quantitative detection of squamous cell carcinoma antigen (SCCA) based on the β-cyclodextrin functionalized graphene nanosheet (CD-GN) and the ternary hollow Pt/PdCu nanocube anchored on three-dimensional graphene framework (Pt/PdCu-3DGF). CD-GN exhibited high specific surface area and good dispersibility and stability in water, which were beneficial to fix captured antibodies (Ab1) through the supramolecular host-guest interaction between CD and Ab1. The abundant oxygen-containing functional groups on 3DGF provided binding sites for anchoring noble metal nanoparticles. Pt/PdCu-3DGF could capture detected antibodies via the interaction of Pd-NH2 and Pt-NH2. Furthermore, the ternary metal nanoparticles exhibited high electrocatalytic activity toward the reduction of hydrogen peroxide. Under optimal conditions, the fabricated immunosensor showed a sensitive response to SCCA with two linear ranges. The linear ranges are 0.0001-1 ng/mL and 1-30 ng/mL with a detection limit of 25 fg/mL. Additionally, the proposed immunosensor showed good reproducibility and stability., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A novel electrochemical immunosensor was developed for ultrasensitive detection of squamous cell carcinoma antigen (SCCA), which was based on the double-antibody single-channel amplification strategy. For the first time, human immunoglobulin antibody (anti-HIgG) was used as the supporting framework to amplify the loading quantity of SCCA antibody (anti-SCCA). In this strategy, SCCA can be detected without using mesoporous nanometers to amplify the signal. In addition, Pd icosahedrons were first used as the connecter to immobilize the antibodies and strengthen the sensitivity. Only one touch point exists under the limited condition between a sphere and another shape in geometry, thus the Pd icosahedron is an excellent candidate as the role of connecter. Gold nanoparticles (Au NPs) decorated with mercapto-functionalized graphene sheets (Au@GS) were synthesized as the transducing materials. The fabricated immunosensor exhibited an excellent detection limit of 2.8 pg/mL and wide linear range of 0.01-5 ng/mL. This kind of immunosensor would provide a potential application in clinical diagnosis., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A novel, sensitive electrochemical immunosensor for simultaneous determination of squamous cell carcinoma associated antigen (SCC-Ag) and carcinoembryonic antigen (CEA) for the combined diagnosis of cervical cancer was designed. The amplification strategy for electrochemical immunoassay was based on poly[3-(1,1'-dimethyl-4-piperidine-methylene) thiophene-2,5-diylchloride] (PDPMT-Cl) and functionalized mesoporous ferroferric oxide nanoparticles (Fe3O4 NPs). PDPMT-Cl dispersed in chitosan solution with enhanced electrical conductivity and solubility was used as matrices to immobilize the first antibodies. Different redox probes (thionine (Th) and ferrocenecarboxylic acid (Fca)) functionalized Fe3O4 NPs incubated with two kinds of secondary antibodies to fabricate the labels. Using an electrochemical analysis technique, two well-separated peaks were generated by Th and Fca, making the simultaneous detection of two analytes on the electrode possible. Under optimized conditions, this method showed wide linear ranges of three orders of magnitude with the detection limits of 4 pg mL(-1) and 5 pg mL(-1), respectively. The disposable immunosensor possessed excellent clinical value in cervical cancer screening as well as convenient point-of-care diagnostics., (Copyright © 2014 Elsevier B.V. All rights reserved.)

A new electrochemical dual amplification sandwich immunosensor (DASI) was designed for ultrasensitive and accurate detection of the breast cancer susceptibility gene based on the combination of N-doped graphene, hydroxypropyl chitosan and Co3O4 mesoporous nanosheets. N-doped graphene has better electroconductibility than traditional graphene. It is an ideal electrochemical material with a large specific surface area and low resistance. Hydroxypropyl chitosan replaces the pure chitosan in immobilization of the sensor to achieve the sensitivity increase. Co3O4 mesoporous nanosheets can enhance the effective area of the immunoreaction. This kind of dual amplification sandwich immunosensor was first used for the detection of the breast cancer susceptibility gene. It has a wide linear response range of 0.001-35 ng mL(-1) and a minimum detection limit of 0.33 pg mL(-1). It was demonstrated that the stability, selectivity and reproducibility of the sensor were acceptable. The fabricated immunosensor shows great potential applications in early disease diagnosis.

A photoelectrochemical (PEC) biosensor capable of detecting cytokeratin 19 fragment 21-1 (CYFRA21-1) was optimized by taking advantage of the powerful conjugate repeats of horseradish peroxidase and tyramine (HRP-tyramine)–triggered enzymatic biocatalytic precipitation (BCP) on high-performance BiVO4/Ag3VO4/SnS2 photoelectrodes. Compared with the ubiquitous BCP strategy, we identified a design supporting conjugate repeats generated by HRP and tyramine–triggered immeasurable insoluble precipitates in the presence of hydrogen peroxide and 4-chloro-1-phenol (4-CN), and the steric hindrance improved sensitivity. Moreover, by virtue of BiVO4, Ag3VO4, SnS2 excellent level matching structure and chemical stability, a heterojunction (BiVO4/Ag3VO4/SnS2) with high light absorption efficiency has been successfully prepared. The novel heterostructure system of BiVO4/Ag3VO4/SnS2 with high detection current and low background signal exhibited high-performance PEC determination. Generally, the hitherto untapped biosensor resource realized the sensitive detection of CYFRA21-1 with a wide linear range from 50 fg/mL to 200 ng/mL, and a detection limit of 15 fg/mL, which illustrated the potential for biotechnological applications. [ABSTRACT FROM AUTHOR]

Exploring facile strategy for developing highly efficient emitters using water-insoluble luminophores has become a vital topic in electrochemiluminescence (ECL) immunoassay. In this work, an ECL-active and water-dispersive iridium(III) complex-based polymer dots (IrPdots) was fabricated by encapsulating water-insoluble tris[1-phenylisoquinolinato-C2, N] iridium(III) complexes [Ir(piq) 3 ] into poly-(styrene-co-maleic anhydride) (PSMA) matrix by a controllable nanoprecipitation process. The obtained IrPdots generated strong ECL signals in the presence of tri- n -propylamine (TPrA) and were used to label detection antibody (Ab 2) to act as ECL probes to indicate the signal changes when analyzing target antigen. To construct a sandwich immunosensor, Pd nanoparticles (NPs) decorated MoS 2 /Ti 3 C 2 T x MXene nanocomposites (MoS 2 /Ti 3 C 2 T x MXene/Pd) were fabricated as substrates to bind capture antibody (Ab 1), which could further amplify ECL signals via a coreaction-accelerating pathway to improve the detection sensitivity. When the cytokeratin 19 fragment 21-1 (CYFRA 21-1) was chosen as model analyte, the developed immunosensor displayed a good linear relationship ranging from 0.1 pg/mL to 50 ng/mL with a low detection limit of 95 fg/mL (S / N = 3) was achieved as well. This research proposed a facile and effective method of fabricating IrPdots as ECL probes for immunoassay using water-insoluble iridium complexes, which expanded the application scope of those water-insoluble luminophores for aqueous bioanalysis. [Display omitted] • An ECL-active Ir(piq) 3 -based polymer dots (IrPdots) was fabricated through a controllable nanoprecipitation method. • The biocompatible IrPdots as ECL probe were used to construct a sandwich immunoassay. • Pd nanoparticles (NPs) decorated MoS 2 /Ti 3 C 2 T x MXene was fabricated to amplify ECL emission. • The IrPdots-based immunosensor performed high sensitivity and accuracy for CYFRA 21-1 detection. [ABSTRACT FROM AUTHOR]

Herein, a super-labeled immunoassay was fabricated for matrix metalloproteinases-2 detection. A self-corrosion ITO micro circuit board was designed in this sensing platform to reduce the random error in the same testing condition, and the self-constructed sensing platform is portable with a cheap price. The K-modified graphene (K-GS) was utilized as the matrix material, which was synthesized well by phenylate and phenanthrene through the polar bond of nonpolar molecule phenylate and the π-π interaction for the first time. An aptamer-based labels based on Au nanoparticles (AuNPs), thionine (Th) and horseradish peroxidase (HRP) were applied as the signal source for tri infinite amplification. This fabricated super-labeled immunoassay exhibit excellent performance for MMPs-2 detection. It displayed a broad linear range of 10 −4 −10 ng/mL with a low detection limit of 35 fg/mL, which may have a potential application in the clinical diagnose. [ABSTRACT FROM AUTHOR]

A novel sensitive electrochemical immunosensor was proposed for detection of CA125 based on ferrocenecarboxylic acid (FA), HCl-doped polyaniline (H-PANI) and chitosan hydrochloride (CS-HCl), which were used as substrate materials to generate signal and to enlarge specific surface area. The composite of these three materials (acid center compound, FA@H-PANI@CS-HCl) can be connected by hydrogen (H) in each molecule. Ag@Co 3 O 4 nanosheets were used in the immunosensor to amplify the antibody capacity and to enhance the sensitivity of the immunoassay. This kind of sensor was novel, concise and it is the first time to be used in the detection of CA125. The biosensor exhibited low detection limit (0.25 pg/mL) and wide linear range (0.001–25 ng/mL). The stability, selectivity and reproducibility were acceptable. Serum sample analysis proved that the proposed sensor owned well precision and it might be used in potential clinic testing application in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] Polycyclic aromatic hydrocarbons (PAHs) are excellent alternative luminophores for electrochemiluminescence (ECL) immunoassays. However, they are inevitably limited by the aggregation-caused quenching effect. In this study, aimed at eliminating the aggregation quenching of PAHs, luminescent metal–organic frameworks (MOFs) with 1,3,6,8-tetra(4-carboxybenzene)pyrene (H 4 TBAPy) as the ligand were exploited as a novel nano-emitter for the construction of ECL immunoassays. The luminophore exhibits efficient aggregation-induced emission enhancement, good acid-base resistance property and unusual ECL reactivity. In addition, the simultaneous use of potassium persulfate and hydrogen peroxide as dual co-reactants resulted in a synergistic enhancement of the cathodic ECL efficiency. The use of magnetic iron-nickel alloys as the multifunctional sensing platform can further enhance the ECL activity, and its enriched zero-valent iron as a co-reactant accelerator effectively drives ECL analytical performance. Profiting from the excellent characteristics, signal-on ECL immunoassays have been constructed. With carcinoembryonic antigen as the model analysis target, a detection limit of 0.63 pg/mL was obtained within the linear range of 1 pg/mL to 50 ng/mL, accompanied by excellent analytical performance. This report opens a new window for the rational design of efficient ECL illuminators, and the proposed ECL immunoassays may find promising applications in the detection of disease markers. [ABSTRACT FROM AUTHOR]

• A sandwich-type immunosensor for detection of PCT was designed. • CeO 2 -CuO-Au as platform can promote electron transfer. • Au@Ag-Th as signal labels can further effectually amplify the current signal. • The immunosensor presents prominent performance for PCT detection. Procalcitonin (PCT) is a kind of protein exists in the human blood. If the human bodies are infected with bacteria, fungi or parasites, the value of PCT in blood will be significantly raised. Thereby, we report an electrochemical immunosensor for measurement of PCT using gold nanoparticle (Au NP) decorated CeO 2 -CuO (CeO 2 -CuO-Au) as the platform and thionine modified Au@Ag heterojunction nanorods (Au@Ag-Th) as signal labels. Au NP decorated CeO 2 -CuO exhibits high surface area, high activity and good biocompatibility, which can immobilize more primary antibodies and promote electron transfer. The Au@Ag-Th provides good active sites to link secondary antibodies, further effectually amplify the current signal. This immunosensor exhibits a well-pleasing response with a limit detection of 0.17 pg mL−1 and linear detection between 0.5 pg mL−1 and 50 ng mL−1. Meanwhile, the high sensitivity, excellent specificity and acceptable human serum samples testing results of this method lead to potential applications in diagnosis of bacterial infections. [ABSTRACT FROM AUTHOR]

[Display omitted] • A split-type self-powered photoelectrochemical (PEC) and colorimetric dual-mode immunoassay platform was developed. • The work presented self-shedding of multifunctional biomolecular nanocarriers Fe 3 O 4 @Carbon@MnO 2. • Cu 2 ZnSnS 4 photocathode and BiVO 4 /FeOOH photoanode can effectively improve photoelectrochemical efficiency. • The biosensor for sensitive H-FABP detection exhibited highly effective physiological monitoring. To embrace the challenge of the limitations of traditional nano-solid materials, biomolecular layer-by-layer assembly and single detection mode, this work innovated a dual-mode immunoassay of split-type self-powered photoelectrochemical (PEC) and colorimetric detection based on self-shedding of biomolecular nanocarriers for physiological monitoring. The self-shedding process completed in 96 microplate is that the outer MnO 2 of MnO 2 -coated Fe 3 O 4 @Carbon nanosphere complex (Fe 3 O 4 @Carbon@MnO 2) is consumed by quantitative ascorbic acid. Fe 3 O 4 @Carbon as a peroxide-mimicking enzyme remaining with completely bare surface provides sufficient active sites and the seed solution affecting the photoanode are separated by magnetic forces. In this process, biometrics and dual-mode signal detection realize spatial isolation in mutual influence, and the sensitivity of immunoassay was further improved. The photoanode ITO/BiVO 4 was constructed by electrodeposition with the ad-vantages of high specific surface area and uniformity, and the hole consuming agent FeOOH was generated on electrode surface, which affects the signal of the PEC substrate to indirectly reflect the concentration of biomolecules. In addition, the self-powered biosensor constructed by assembling Cu 2 ZnSnS 4 (CZTS) with excellent interface-to-volume ratio on FTO using template method as working electrode. As a proof of principle, heart fatty acid binding protein (H-FABP) was analyzed and the obtained linear range of the dual mode biosensor was from 0.050 pg/mL to 100 ng/mL with a detection limit of 0.013 pg/mL (S/N = 3). [ABSTRACT FROM AUTHOR]

In this paper, we report a novel multiple amplification strategy for ultrasensitive near-infrared electrochemiluminescence (ECL) immunoassay in K 2 S 2 O 8 solution. The realization of this strategy is based on the antenna effect of Eu-MOF (EuBTC) and a high efficiency catalysis of CoS 2 hollow triple shelled nanoboxes (TSNBs). The H 3 BTC ligand in the antenna effect first undergoes π-π* absorption and a singlet-singlet electronic transition. Its energy passes through the intersystem to the triplet state, next transfers from the lowest excited triplet state to the vibrational energy level of the rare earth ion, finally realizing sensitizing center ion luminescence. Moreover, ionic reaction and structural advantages endow CoS 2 TSNBs a dual signal enhancement effect. This sandwich-type ECL biosensor has a near-infrared luminescence in 800–900 nm, thus avoiding damage to the sample in the meantime. In practical diagnosis, the normal critical value of procalcitonin (PCT) (<0.5 ng/mL) is much higher than the detection limit (3.65 fg/mL) and is in the detection range (10 fg/mL-100 ng/mL), which means that the ECL biosensor has a high sensitivity in the detection of PCT and meet the requirement for diagnosis of disease completely. Therefore, the strategy provides a feasible method for efficient and stable analysis of systemic inflammatory response such as fearful bacterial infection, hepatitis B, and peritonitis. • A novel near-infrared ECL biosensor was constructed to realize non-damage detection. • The EuBTC with special antenna effect as luminophore owned stronger and steadier property. • Complex hollow triple shelled nanoboxes structure catalyst containing only one component greatly boosted ECL intensity. [ABSTRACT FROM AUTHOR]

Nanostructured materials with elegant properties have promising potentials in chemiluminescence (CL) immunoassay. However, the robust preparation of such nanomaterials is still challenging. In this work, biocompatible and easily prepared gelatin/horseradish peroxidase (Gel/HRP) nanogels were exploited as signal labels for chemiluminescence immunoassays. The catalytic property of HRP was well retained and the stability was improved after the incorporation into nanogels. The prepared protein nanogels show enhanced and glow-type luminescence behaviors in luminol-H 2 O 2 CL system. Persistent and sensitive CL immunoassay for CEA were constructed using Gel/HRP nanogels as signal labels. A wide linear response range from 0.01 to 100 ng/mL was obtained with the limit of detection was 3.39 pg/mL (S/N = 3). [Display omitted] • Long-lasting chemiluminescence through nanogels with internal 3D network structure. • Green and simple to synthesize labeled probes with excellent biocompatibility. • High activity of horseradish peroxidase is retained • Immunoassay for accurate detection in an interference environment. [ABSTRACT FROM AUTHOR]

In the realm of photoelectrochemical (PEC) analysis, it is customary to employ a lone photoanode or photocathode system for analyte detection. Nonetheless, such a single detection scheme inherently carries some deficiencies. While photoanode-based PEC immunoassay methods do exhibit conspicuous photocurrent responses and heightened sensitivity, they do suffer from inadequate resistance to interference when detecting in real sample detection. Photocathode-based analysis methods are capable of effectively surmounting the limitations of photoanode-based analysis methods, but their stability is poor. Based on the above reasons, this paper reports a novel immunosensing system combining ITO/WO 3 /Bi 2 S 3 photoanode and ITO/CuInS 2 photocathode. The system that incorporates both photoanode and photocathode exhibits a steady and discernible photocurrent, possesses robust resistance to external interference, and has effectively accomplished the quantification of NSE in the linear range from 5 pg/mL to 30 ng/mL. Remarkably, the detection limit has been determined to be 1.59 pg/mL. Besides the notable advantages of satisfactory stability, exceptional specificity, and outstanding reproducibility, the sensing system also introduces an innovative approach to fabricate PEC immunosensors. [Display omitted] • A photoelectrochemical sensing platform integrating photoanode and photocathode is constructed. • The WO 3 /Bi 2 S 3 nanomaterial electrode replaces the Pt electrode as the counter electrode. • Overcome the inherent shortcomings of single-photoanode mode and single-photocathode mode. • Satisfactory detection of NSE. [ABSTRACT FROM AUTHOR]

Abstract A sandwich-type electrochemical immunosensor for prostate-specific antigen (PSA) detection was constructed. In this sensing platform, palladium nanoparticles (Pd NPs) loaded electroactive amino-zeolitic imidazolate framework-67 (Pd/NH 2 -ZIF-67) nanocomposite is utilized as a novel redox mediator. Pd NPs, as the labeling signal molecule, owns good biocompatibility and excellent catalytic performance. Meanwhile, the electroactive ZIF-67 with lamellar structures serves not only as a carrier of Pd NPs but also as a synergistic catalyst of palladium to decompose H 2 O 2. Amperometric method is used to determine the current signal generated on the electrode surface, which is conducive to achieve the quantitative determination of PSA. Under optimum conditions, the proposed immunosensor shows a wide detection range from 100 fg mL–1 to 50 ng mL–1 with a low detection limit of 0.03 pg mL–1, featuring favorable selectivity, repeatability and stability. This proposed immunosensor is expected to be a powerful tool for realizing quantitative detection of PSA and other biomarkers in actural sample analysis. Highlights • Electrochemical immunoassay is proposed for detection of PSA based on Pd/NH 2 -ZIF-67. • The response signal is amplified by the synergetic effect between Pd and Co2+/3+. • The immunosensor exhibits a low detection limit of 0.03 pg mL-1 for PSA detection. [ABSTRACT FROM AUTHOR]

Generally, the photoanodic photoelectrochemical (PEC) immunoassay method has an outstanding photocurrent and low detection limit, but its poor anti-interference ability in the detection of real samples restricts its performance. The photocathode immunoassay method has an excellent ability to see interference in actual sample detection, but it has its own defect in that the photocurrent is not obvious. Here, a promising new cathodic PEC immunosensing platform is reported, which integrates a photocathode and photoanode. The photoanode and photocathode are WO 3 /Mn:CdS composite modified and reduced graphene oxide (RGO) modified indium tin oxide (ITO) electrodes, respectively. In addition to an excellent PEC response, the immunosensor constructed by the integrating the photoanode and photocathode also has good anti-interference ability in actual sample analysis. The constructed immunosensor achieves accurate detection of NSE with a range from 5.0 pg/mL to 20 ng/mL, and the limit of detection (LOD) is 1.2 pg/mL. The proposed immunoassay method has good stability, selectivity and reproducibility. Moreover, it introduces new ideas for the construction of PEC immunosensors. [ABSTRACT FROM AUTHOR]

• This report outlines a method to detect CYFRA21−1 by quenching electrochemiluminescence immunosensor. • Electron transfer and energy transfer occurs between TP−COOH NCs and Fe-HAP. • TP−COOH NCs was prepared with low impedance and good functionalization. • The cathode emission excited at -1.15 V to obtain better biocompatibility in K 2 S 2 O 8. • This electrochemiluminescence immunosensor obtains the detection limit of 0.01471 pg/mL. This report outlines a versatile novel quenching electrochemiluminescence immunosensor based on electrochemiluminescence (ECL) emission with aggregation induced emission (AIE) from TP−COOH NCs, which was utilized by poly-(styrene-co-maleicanhydride) to wrap on tetraphenylethylene nanocrystals. On the one hand, the cathode emission excited at -1.15 V could reduce emission produced by oxygen from high potential stimulation, on the other hand, such low potential can further protect the activity of immune molecules. Meanwhile, the coating can reduce interface impedance and completed functionalization. Herein, based on the synergistic effect of electron transfer and energy transfer between TP−COOH NCs and iron doped hydroxyapatite (Fe-HAP), the high efficiency of this ECL sensing platform can be achieved. The proposed ECL immunosensor for detection of trace Cytokeratin 19 fragment 21−1 (CYFRA21−1), exhibited a satisfied detection limit low to 0.01471 pg/mL (S/N = 3). As a result, this approach not only enriches the ECL strategies study to provide a feasible method for foundational clinical examination but also expands the potential application of ECL sensors in biological testing and clinical high-throughput diagnosis. [ABSTRACT FROM AUTHOR]

• Bifunctional peptides that biomineralize gold clusters and specifically recognize antibody Fc domains. • Flexible fragmented-antibody are used as sensing substrate instead of using traditional micro-nano carrier. • The sensing platform fabricated by these strategies exhibit ultralow detection limit of 1.8 fg/mL. Non-competitive immunoassay systems often are used for detecting biomarkers, and their sensitivity depends on the arrangement mode of substrate and the property of signal label. In this work, a novel electrochemiluminescence (ECL) sensing platform utilizing split antibody fragments (Fab') 2 as substrate and self-designed nonapeptide H 2 N-CCYHWRGWV-COOH (CCYTAR) biomineralized gold nanocluster (Au NCs) as label was fabricated. Fixated (Fab') 2 domains on gold-plated electrodes via Au-S bonds could form well-ordered microarray with higher immune affinity than random antibody fixation. Besides, The CCYTAR nonapeptide not only could function as reductant and capping agent for synthesizing Au NCs, but also act as specific antibody immobilizer for recognizing Fc domains specifically. Also, related experiments verified that CCY and TAR, two independent regions of bifunctional nonapeptide, acted independently. In the end, the Cyfra 21-1 is employed as target to test the feasibility of all strategies, and the results confirmed that the sensing platform could be promising candidate for ECL-based biosensor fabrication in the future. [ABSTRACT FROM AUTHOR]

• An enzyme-free colorimetric immunosensor was designed for detection PCT. • MgFe 2 O 4 @Cys was first used as the sacrificial probe of the immunosensor. • MgFe 2 O 4 @Cys released Fe3+ under acidic condition and reacted with [Fe(CN) 6 4− can generate soluble PB. • PCT determination was established by measuring absorbance of generated PB. • It achieved an excellent result in human serum sample analysis. An enzyme-free immunosorbent assay using MgFe 2 O 4 modified with cysteine (MgFe 2 O 4 @Cys) as sacrificial probe for the detection of procalcitonin (PCT) was developed. MgFe 2 O 4 @Cys was linked with second antibody of PCT (Ab 2) by cysteine amino group and released Fe3+ under acidic conditions. Taking advantage of Fe3+ and [Fe(CN) 6 4− generating soluble Prussian blue (PB), a novel method of PCT determination was established by measuring the absorbance of the generated PB. Different from the traditional immunosensor detection mode, the enzyme-free colorimetric immunosensor in this work can not only avoid the interference of nano-enzymes or enzymes, but also has the advantages of rapid detection, low cost, high selectivity and sensitivity. Therefore, the developed immunosensor for PCT detection exhibited a wide linear response (0.0001–50 ng/mL) and a low detection limit (44.9 fg/mL). Additionally, the immunosensor exhibits satisfactory performance in human serum testing, which indicated its good application value in clinical diagnoses. [ABSTRACT FROM AUTHOR]