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A novel imprinted material for glycoprotein detection was prepared based on metal-organic framework (MOF)/covalent-organic framework (COF) hybrid composite (MOF@COF-B(OH) 2) with fluorescent properties and boric component that facilitated glycoprotein imprinting. The MOF@COF-B(OH) 2 exhibited improved fluorescence emission from MOF due to efficient excited-state intramolecular proton transfer (ESIPT). Transferrin (TrF), an important transporting glycoprotein, was selected as the target. MOF@COF-B(OH) 2 effectively captured TrF through boronated affinity. The imprinted material (MOF@COF-B(OH) 2 @MIP) showed obvious fluorescence quenching after incubation with TrF at 430 nm via the photo-induced electron transfer (PET). A good linear relationship was demonstrated in the range of 0.1–40 µM with an associated limit of detection (LOD) of 57.6 nM under optimal conditions. An electrochemical platform for TrF detection was constructed by combining MOF@COF-B(OH) 2 @MIP with a disposable screen-printed carbon electrode (SPCE). The differential pulse voltammetry signal generated by MOF@COF-B(OH) 2 @MIP/SPCE served as a secondary signal to monitor TrF. The MOF@COF-B(OH) 2 @MIP/SPCE exhibited satisfactory linearity with a LOD of 2.7 nM. Moreover, the imprinted sensor showed good recovery rates for detection in actual samples using fluorescencent and electrochemical modes. This study offered a promising strategy for the application of boric acid-functionalized MOF@COF in glycoprotein sensing. [Display omitted] • A novel imprinted strategy based on MOF@COF-B(OH) 2 @MIP for glycoprotein was designed. • MOF@COF-B(OH) 2 was served as imprinted supporter and provided ideal imprinting environment. • Dual-mode sensing platform was constructed for sensitive and accurate detection of glycoprotein. • Boric acid-functionalized MOF@COF provided a new application in glycoprotein imprinting. [ABSTRACT FROM AUTHOR]

• A ternary ECL immunoassay based on ABEI is designed for amyloid-β protein detection. • Flower-like Co-MOFs with peroxidase-like activity is used as coreaction accelerator. • Co-MOFs not only act as nanocarriers of ABEI, but also catalyze H 2 O 2 decomposition. • The synergistic catalysis of Co-MOFs and Au NPs realize the ECL signal amplification. In this work, a "luminophore/coreactant/co-reaction accelerator" ternary electrochemiluminescence (ECL) system is proposed by using N -(aminobutyl)- N -(ethylisoluminol) (ABEI) functionalized cobalt-based MOFs (Co-MOFs/ABEI) with superior peroxidase-like activities as the luminophore. ABEI, the derivative of luminol, is used as the reductant and organic ligand to synthesize flower-like Co-MOFs/ABEI. The as-synthesized Co-MOFs/ABEI not only function as desirable nano-carriers for the enrichment of ABEI, but also act as co-reaction accelerators for the catalysis of H 2 O 2 decomposition. Furthermore, Au nanoparticles are decorated on Co-MOFs/ABEI via electrostatics attraction, endowing it with favorable biocompatibility and electrocatalytic property to bond with detection antibodies and generate more excited state ABEI*. Besides, with the advantages of large specific surface area and easy preparation, Au nanoparticles functionalized Fe 3 O 4 @polypyrrole is utilized to anchor the capture antibodies for immunoaction with target analyte. Amyloid-β protein (Aβ 42), a principal hallmark of Alzheimer's disease, is chosen as the target analyte. The proposed Aβ 42 immunosensor performs with a broad linear range from 10 fg mL−1 to 100 ng mL−1 and a detection limit down to 3 fg mL−1, opens up new prospects for clinical analysis of Aβ 42 and provides promising approaches to synthesize luminophore-functionalized MOFs with high luminous efficiency for ECL bioanalysis. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ultrasensitive electrochemical aptasensor was developed for detecting Pb2+. • Au@p-rGO was applied as support for immobilizing the aptamer. • Au NPs@GO as signal probe exhibited high electrocatalytic activity towards H 2 O 2. • The aptasensor displayed low detection limit of 1.67 pmol/L for Pb2+. Abstract A sensitive electrochemical aptasensor was designed based on gold modified graphene nanocomposite with different morphologies for the detection of lead ion (Pb2+). Specifically, a sulfydryl-labeled substrate strand (Apt1) and a sulfydryl-labeled catalytic strand (Apt2) were devised in fabricating the electrochemical aptasensor. Gold modified porous reduced graphene oxide (Au@p-rGO) was synthesized and applied as support for immobilizing the Apt1. And gold modified graphene oxide (Au NPs@GO) was employed as signal probe and connected with Apt2 to realize the immobilization of it on the electrode by means of the principle of complementary base pairing. The current signal can be obtained by recording the electrocatalytic conditions toward H 2 O 2. The Pb2+-dependent DNAzyme could play a role when Pb2+ existed. With the increase of the concentration of Pb2+, the current response revealed a diminishing signal, thus realizing the sensitive detection of Pb2+. Under the optimal conditions, the fabricated electrochemical aptasensor exhibited a linear response toward Pb2+ ranging from 5 pmol/L to 1 μmol/L, together with a low limit of detection of 1.67 pmol/L. Moreover, the prepared aptasensor displayed outstanding selectivity, acceptable stability and superior reproducibility for detecting Pb2+. This proposed tactics may provide reference and potential applications for detecting some other heavy metal ions. [ABSTRACT FROM AUTHOR]

Highlights • A new method for ricin detection was established based on TMR biosensor. • In this method, the magnetic immuno-chromatographic test strip and TMR magnetic sensitive sensor signal detection were combined effectively. • This method can overcome the interference of background color and light of complex environmental samples. • This method can realize the selective separation of complex samples and rapid quantitative detection. Abstract In this research, the magnetic immuno-chromatographic test strip and TMR magnetic sensitive sensor signal detection were combined effectively, which displayed the multiple advantages of magnetic nanoparticles (MNPs) label technique, immunochromatography (IC) and tunneling magnetoresistance (TMR) sensing technology. Through detecting magnetic field intensity generated by functionalized magnetic signal probe on immuno-chromatographic test strip, a new method for ricin detection was established based on TMR biosensor. Compared with traditional labeled biosensor based on optical signal detection, this method can overcome the interference of background color and light of complex environmental samples, and has advantages of easy operation, high sensitive, accurate quantification, good reproducibility, specificity and interference-resistance. With this method, the selective separation and rapid quantitative detection of complex samples can be achieved. The linear range of quantitative detection for ricin was 1 ng/mL–200 μg/mL, the regression equation was Y = 0.2125 X + 0.5675 (R = 0.9706, P < 0.0001, N = 12), the limit of detection (LOD) was 1 ng/mL. This method can overcome the influence of complex environmental interferents in the toxin detection, and can meet the analysis requirements for simulated samples such as water, soil, food, blood and so on. The method showed good recovery ratio and reproducibility, with the recovery ratio of 90.1%–94.2% and the RSD of 2.43%–3.35%. [ABSTRACT FROM AUTHOR]

Highlights • A label-free ECL immunosensor was designed based on Ti doped BiOBr for NT-proBNP detection. • BiOBr was employed as ECL substrate and emitter to simplify the construction process. • The ECL property was further improved by functionalizing BiOBr with Ti and Au NPs. • Sensitive detection of NT-proBNP was achieved with good selectivity and stability. Abstract Heart failure is a serious medical condition and has become one of the world's biggest killers. N-terminal pro-B-type natriuretic peptide (NT-proBNP) has been recommended as a new biomarker of excellent prognosis-predictive ability for heart failure. Herein, a label-free electrochemiluminescence (ECL) immunosensor based on gold nanopariticles (Au NPs) functionalized Ti doped BiOBr (Ti:BiOBr-Au) is fabricated for the detection of NT-proBNP. Firstly, three-dimensional flower-like Ti doped BiOBr (Ti:BiOBr), which is firstly proposed with ECL property, is employed as both the ECL substrate and emitter to simplify the construction procedure. In the presence of K 2 S 2 O 8 , the formed Ti:BiOBr can generate stronger ECL signal than pure BiOBr. Due to the large specific surface area, Ti:BiOBr is functionalized with large amounts of Au NPs to further improve ECL emission. Under optimal experimental conditions, a linear response range for NT-proBNP detection from 0.001 ng mL−1 to 50 ng mL−1 is obtained with a detection limit of 0.33 pg mL−1. Featuring high sensitivity and excellent reproducibility, the proposed ECL immunosensor blazes a novel trail for the sensitive determination of NT-proBNP and other biomarkers. It is worth noting that Ti:BiOBr with stable ECL emission displays tremendous potential in ECL bioanalysis as a novel type of emitter candidates. [ABSTRACT FROM AUTHOR]

Highlights • A novel signal-off ultrasensitive photoelectrochemical immunosensor was prepared for detection BNP. • The CeO 2 -CdS composites showed excellent visible-light activity benefited from the matched energy band. • SiO 2 /PDA-Ag NPs had dual-inhibition effect on the CeO 2 -CdS sensitivity structure. • The immunosensor showed a low detection limit of 0.05 pg mL−1. Abstract A novel sandwich photoelectrochemical (PEC) immunosensor was constructed for ultrasensitive brain natriuretic peptide (BNP) detection. In this work, CeO 2 -CdS was employed as excellent photoactive sensing platform, and SiO 2 /PDA-Ag nanocomposite was used as signal amplification element. CeO 2 -CdS, providing great photocurrent response due to the well matched energy band which effectively impeded the recombination of the electrons and holes. For SiO 2 , due to the poor electro-conductivity and easy modification, it could be well used as an excellent signal-off label. For the sake of improving sensitivity of the immunosensor, Ag nanoparticles (Ag NPs) was applied owing to the energy transfer between CdS, which could decrease the PEC response obviously for amplifying the change of signal value. Besides, Ag NPs could anchor plenty of the detection antibodies by the chemical bonding between Ag NPs and –NH 2 of antibodies. Using PDA to connected SiO 2 and Ag NPs because of it great biocompatibility and reducing capacity. The well-established PEC immunosensor exhibited a low detection limit of 0.05 pg mL−1 (S/N = 3) with a linear range from 0.1 pg mL−1−5 ng mL−1 for BNP detection. In addition, the immunosensor also exhibited good stability, satisfactory reproducibility and acceptable specificity, which could be applied to detect other biomarkers. [ABSTRACT FROM AUTHOR]

In this work, an ultrasensitive electrochemical immunosensor was developed for detecting carcinoembryonic antigen (CEA) based on Ag/MoS 2 @Fe 3 O 4 and an analogous enzyme linked immunosorbent assay (ELISA) method. The fabrication process was conducted by using 96-well microplate and the detection process was executed on magnetic glassy carbon electrode (MGCE), which was named analogous ELISA method. The technique of total internal reflection fluorescence (TIRF) was firstly employed to verify the feasibility of the proposed method. A sandwich-type strategy was applied for the fabrication of the immunosensor and Ag/MoS 2 @Fe 3 O 4 was used as label. Simultaneously, Ag nanoparticles (Ag NPs) were applied for modifying the MGCE as sensing platform due to its excellent electroconductivity. Ag/MoS 2 @Fe 3 O 4 could firmly attached on the surface of MGCE thanks to the magnetic property of Fe 3 O 4 . Differential pulse voltammetry (DPV) was applied for the detection of CEA and electrochemical impedance spectroscopy (EIS) confirmed the successful fabrication of the immunosensor. Under optimal experimental conditions, a linear response was achieved in the range of 0.0001–20 ng/mL with a low detection limit of 0.03 pg/mL. Furthermore, the proposed immunosensor exhibited good stability, excellent selectivity and fine reproducibility. This proposed strategy provides a new thought and a potential approach for clinical diagnosis of other tumor markers. [ABSTRACT FROM AUTHOR]

High sensitivity of biosensor is one of the most important factor to realize the accurate detection of biomarkers. To achieve this purpose, enhancing initial signal and amplifying the value of signal change are two main approaches. In this study, a novel signal-off photoelectrochemical (PEC) immunosensor for highly sensitive determination of insulin was developed upon dual inhibition effect of CuS-SiO 2 composites toward CdS sensitized carbon doped titanium dioxide (C-TiO 2 /CdS). Due to the doping of carbon and sensitization of CdS, C-TiO 2 /CdS sensitized structure was employed as ideal photoactive matrix, which provided stable and enhanced basal signal. To achieve the amplification of signal change value, CuS-SiO 2 composites were prepared and used as labels. On account of the competitively light harvesting and electron donors consuming by p-type semiconductor CuS, less light energy and electron donors arrived at the C-TiO 2 /CdS sensitized structure. Besides, the remarkable steric hindrance effect of CuS-SiO 2 labeled secondary antibodies (CuS-SiO 2 -Ab 2 ) conjugates obstructed the transfer of electrons and diffusion of the electron donors to the photoelectrode surface, leading to further decrease of photocurrent compared with the pure CuS nanoparticles. Greatly enhanced sensitivity is achieved due to the dual inhibition effect of CuS-SiO 2 composites on C-TiO 2 /CdS. Taking advantage of the synergy effect of C-TiO 2 /CdS sensitized structure and dual inhibition effect of CuS-SiO 2 -Ab 2 bioconjugates, the as-prepared immunosensor for insulin exhibited high sensitivity and good stability with a low detection limit of 0.03 pg mL −1 . Additionally, the strategy provided an efficient and simple approach for signal amplification and held great promise for other PEC immunoassay development. [ABSTRACT FROM AUTHOR]

Developing electrochemical biosensor, particularly for high sensitive recognizing and detecting tumor marker at low level under benign conditions, is highly desired, but still remains a severe challenge. In this communication, we report a dual-signaling ratiometric method for sensitive detection of carcinoembryonic antigen (CEA) based on gold nanoparticles (Au NPs) functionalized Cu 2 S-CuS/graphene composite (Au-Cu 2 S-CuS/graphene) as the matrix material and carboxyl-Au nanoparticles (Au-COOH) functionalized mesoporous CeO 2 nanoparticles (Au-CeO 2 ) supported toluidine blue (TB) complex as signal label. The oxidation peak current of Cu 2 S-CuS decreases with the increase of CEA concentration, while the oxidation peak current of TB increases. The change of dual signals “Δ I = Δ I TB + |Δ I Cu2S-CuS |” (Δ I TB and |Δ I Cu2S-CuS | are the change values of the oxidation peak currents of TB and Cu 2 S-CuS, respectively) is used as the response signal for quantitative determination of CEA. Notably, the linear range is 0.001 ∼ 100 ng/mL with a detection limit of 0.78 pg/mL (S/N = 3). The ratiometric electrochemical system provides an extremely simple strategy for detecting tumor markers in a reliable, facile, sensitive, and specific manner, which has a promising application for quantitative detection of other tumor markers in clinical diagnosis. [ABSTRACT FROM AUTHOR]

A label-free photoelectrochemical (PEC) immunosensor for carcinoembryonic antigen (CEA) detection was developed using two-dimensional (2D) ultrathin graphitic carbon nitride (g-C 3 N 4 ) nanosheets hybridized with Zn 0.1 Cd 0.9 S nanocrystals as the photoactive matrix. The g-C 3 N 4 ultrathin nanosheets, which are 2D conjugated polymers, were synthesized through a thermal polymerization-exfoliation method that can generate a high specific surface area. Next, the Zn 0.1 Cd 0.9 S nanocrystals was successfully grown on the g-C 3 N 4 ultrathin nanosheets (Zn 0.1 Cd 0.9 S/g-C 3 N 4 ), forming a well-matched band structure where the presence of Zn 0.1 Cd 0.9 S/g-C 3 N 4 accelerated the separation and transfer of photogenerated electron-hole pairs. The as-synthesized Zn 0.1 Cd 0.9 S/g-C 3 N 4 composites showed excellent photoelectrochemical activity, considerably higher than that of pure Zn 0.1 Cd 0.9 S and g-C 3 N 4 . It was worth noting that the heterojunction with strong interfacial interaction formed between Zn 0.1 Cd 0.9 S and g-C 3 N 4 was adopted in the construction of an immunosensor for the first time. CEA antibody (anti-CEA) was immobilized on the surface of a modified electrode using a chemical bonding effect, with mercaptoacetic acid (MPA) and EDC/NHS being used as bridging media. The highly specific introduction of CEA resulted in increased steric hindrance via the antigen-antibody specific immunoreaction; Thus, the concentrations of CEA could be detected by observing the decrease in photocurrent. Under optimal conditions, the linear range for the immunosensor was from 0.005 ng mL −1 to 20 ng mL −1 . The detection limit was 1.4 pg mL −1 . [ABSTRACT FROM AUTHOR]

In this work, a label-free electrochemical immunosensor was developed for the quantitative detection of carcinoembryonic antigen (CEA). Flower-like Ag/MoS 2 /rGO nanocomposites were employed as the signal amplification platform of the designed immunosensor for the first time. Due to the synergistic effect between molybdenum disulfide (MoS 2 ), reduced graphene oxide (rGO) and Ag nanoparticles (NPs), Ag/MoS 2 /rGO nanocomposites could provide a high sensitivity for the label-free electrochemical immunosensor. The detection mechanism was based on the monitoring of the electrocatalytic current response change towards the reduction of hydrogen peroxide (H 2 O 2 ) when immunoreaction occurred on the surface of the electrode modified with Ag/MoS 2 /rGO nanocomposites. Using amperometric i-t curve to record the electrocatalytic process, the proposed immunosensor achieved an ultrasensitive and specific detection of CEA with a low detection limit of 1.6 fg/mL. Under optimal conditions, the fabricated immunosensor exhibited acceptable reproducibility, selectivity and excellent stability. This designed immunosensor could provide an effective method in the clinical diagnosis of other tumor markers. [ABSTRACT FROM AUTHOR]

In this work, silver nanoparticles functionalized cuprous oxide nanowires (Ag@Cu 2 O) nanocomposites were synthesized by a simple method. The nanostructure of it could be well confirmed by a scanning electron microscope (SEM) image. Due to the good synergistic effect between silver nanoparticles (Ag NPs) and cuprous oxide nanowires (Cu 2 O NWs), Ag@Cu 2 O nanocomposites displayed a good electrocatalytic performance towards the reduction of hydrogen peroxide (H 2 O 2 ). Cyclic voltammograms (CVs) were employed to investigate electrocatalytic mechanism of it. Using Ag@Cu 2 O nanocomposites as the labels, a novel and ultrasensitive sandwich-type electrochemical immunosensor was developed for the quantitative detection of carcinoembryonic antigen (CEA). Due to the special electrochemical performance of Ag@Cu 2 O nanocomposites, the facile and sensitive fabrication of the designed immunosensor was achieved. Under optimal conditions, the designed immunosensor exhibited a wide linear range with a low detection limit. It also displayed an electrochemical performance with good reproducibility, selectivity and stability, which would provide potential applications in the clinical diagnosis of other tumor markers. [ABSTRACT FROM AUTHOR]

Detection of tissue polypeptide antigen (TPA) in human serum plays an important role in monitoring the occurrence of cancers. In this work, a sandwich-type electrochemical immunosensor based on a novel dual signal amplification strategy was employed for quantitative detection of TPA. Multifunctional graphene nanocomposites (Au@MGN) were designed as labels to achieve a high sensitivity and low limit of detection (LOD), which dominated the dual signal amplification strategy. On one hand, introduction of graphene could accelerate the electron transfer capability of magnetic graphene nanocomposites (MGN) than single ferriferrous oxide nanoparticles (Fe 3 O 4 NPs). On the other hand, introduction of gold nanoparticles (Au NPs) could build a synergetic effect between Fe 3 O 4 NPs and Au NPs, which resulted in the increasing of electrocatalytic properties of Au@MGN. In short, due to the excellent electrochemical property of Au@MGN, high electrocatalytic current responses toward the reduction of hydrogen peroxide (H 2 O 2 ) were achieved. Under optimum conditions, the proposed sandwich-type electrochemical immunosensor exhibited a wide linear range from 10 −5 ng/mL to 10 2 ng/mL with a low LOD of 7.5 fg/mL for TPA. The designed immunosensor displayed an excellent analytical performance with good reproducibility, high selectivity and stability, indicating potential application promising in clinical monitoring of tumor markers. [ABSTRACT FROM AUTHOR]

A novel label-free electrochemiluminescence (ECL) immunosensor was developed for the detection of Nuclear Matrix Protein 22 (NMP 22) based on the graphite-like carbon nitride (g-C 3 N 4 ) and gold nanoparticles (AuNPs). Graphite-like carbon nitride was firstly combined with AuNPs, which promoted the electrons transfer and enhanced the ECL intensity of g-C 3 N 4 largely. Then, anti-NMP 22 was immobilized onto the electrode through Au–NH 2 without the usage of crosslinking agents. The connection between AuNPs and antibody influenced the conductive performance of AuNPs, leading to some decrease of ECL intensity. Then, bovine serum albumin (BSA) solution was dropped on the surface to block nonspecific binding sites. Finally, after the specific immunoreaction between NMP 22 and anti-NMP 22, the ECL intensity decreased further, because the protein on the electrode hindered the diffusion of luminescent reagents and electrons toward the electrode surface. Therefore, a linear relation between ECL intensity and the logarithm of NMP 22 concentration was obtained from 50.0 pg mL −1 to 2.0 ng/mL ( R 2 = 0.988) with the detection limit of 10.0 pg mL −1 . The proposed ECL immunosensor provides a rapid, simple, and sensitive immunoassay strategy for protein detection, which might be promising for clinical application. [ABSTRACT FROM AUTHOR]

• A novel photoelectrochemical aptasensor for the detection of Tc was designed. • MIL-68 (In) derived In 2 O 3 nanoparticles were employed as substrate to fabricate PEC aptasensor for the first time. • Au-In 2 O 3 @g-C 3 N 4 nanoarchitectures performed outstanding photoelectrochemical activity. • The aptasensor exhibited a low detection limit of 3.3 pM. A label-free photoelectrochemical (PEC) aptasensor for tetracycline (Tc) detection was successfully fabricated, and plasmon Au coupling with MOF-derived In 2 O 3 @g-C 3 N 4 nanoarchitectures (AuInCN) with excellent PEC performance was employed as matrix for the first time. The homogeneous In 2 O 3 nanoparticles (In 2 O 3 NPs) derived from MIL-68(In) precursor were synthesized via calcination in air. The g-C 3 N 4 nanosheets provided a favorable substrate for the fine distribution of In 2 O 3 NPs. The In 2 O 3 @g-C 3 N 4 (InCN) heterojunction with compact interface and matching band structure, facilitated the separation and transfer of electron-hole pairs. The surface plasmon resonance (SPR) of gold nanoparticles (Au NPs) could improve the light absorption and the photoelectron transfer of the modified electrode. Meanwhile, the decorated cysteamine stabilized Au NPs were also adequate to immobilize the SH-terminated aptamer as a biorecognition unit, and Tc molecules could be trapped through the specific interaction with the immobilized aptamer. An enhanced PEC photocurrent was realized under visible light illumination, due to the oxidation of captured Tc by photo-generated holes. Thereby, the concentration of Tc could be detected by observing the changes of photocurrent signals. Under optimized conditions, the PEC aptasensor exhibited the linear range from 0.01 nmol L−1 to 500 nmol L−1, with a detection limit (S/N = 3) of 3.3 pmol L−1. The prepared PEC aptasensor demonstrated acceptable stability, specificity and reproducibility, indicating the potential applications for the detection of Tc. [ABSTRACT FROM AUTHOR]