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Sensitivity amplification strategy by implementing click chemistry in the construction of biosensing interface can efficiently improve the performance of immunosensor. Herein, we developed a sandwich-type amperometric immunosensor for ultrasensitive detection of carbohydrate antigen 24-2 (CA 242) based on pH responsive label-assisted click chemistry triggered sensitivity amplification strategy. The sensitivity of amperometric immunosensor relies on the current response differences (ΔI) caused by per unit concentration target analyte. The pH responsive Cu 2+ -loaded polydopamine (CuPDA) particles conjugated with detection antibodies were employed as labels, which can release Cu(II) ions by regulating pH. In the presence of ascorbic acid (reductant), Cu(II) ions were reduced to Cu(I) ions. Azide-functionalized double-stranded DNA (dsDNA) as signal enhancer was immobilized on the substrate through Cu + -catalyzed azide/alkyne cycloaddition reaction. With the help of the click reaction, the ΔI caused by target was elevated prominently, resulting in sensitivity amplification of the immunosensor. Under optimal condition, the proposed immunosensor exhibited excellent performance with linear range from 0.0001 to 100 U mL −1 and ultralow detection limit of 20.74 μU mL −1 . This work successfully combines click chemistry with pH-responsive labels in sandwich-type amperometric immunosensor, providing a promising sensitivity amplification strategy to construct immunosensing platform for analysis of other tumor marker. [ABSTRACT FROM AUTHOR]

A new screen-printed carbon electrode (SPCE) with multiple working electrodes and one signal output channel without counter and reference electrodes was designed. The multiple working electrodes can be individually modified for each target of interest. The SPCE contained one signal output channel, making the immuniosensor be realized by common single-channel electrochemical workstation. The counter and reference electrodes were independent of disposable SPCE, reducing costs and eliminating precious metal pollution. Platinum network as counter electrode improved the reproducibility of the SPCE. Moreover, method of generating hydrogel on working electrode was used to enhance the conductivity of SPCE. Based on this, a multiplexed single channel label-free amperometric immuniosensor for four tumor markers, namely, squamous cell carcinoma antigen (SCCA), fragment antigen 21-1 (Cyfra21-1), carbohydrate antigen 125 (CA125), and neuron specific enolase (NSE) was developed, and the corresponding detection limits were 5.5 pg mL −1 , 4.8 pg mL −1 , 0.0054 U mL −1 and 2.3 pg mL −1 , respectively. The sensitivity of this immunosensor was 0.83 µA (lg(ng mL −1 )) −1 for SCCA, 1.92 µA (lg(ng mL −1 )) −1 for Cyfra21-1, 4.75 µA (lg(U mL −1 )) −1 for CA125 and 2.40 µA (lg(ng mL −1 )) −1 for NSE. Among them, the sensitivities of CA125 and NSE were four-fold higher than those of the previous works. [ABSTRACT FROM AUTHOR]

Sensitivity enhancement and proteins adsorption are the common challenges faced in protein immunoassays. In this work, an ultrasensitive and protein-resistant label-free amperometric immunosening platform for carcinoma antigen-125 (CA125) based on redox polyaniline-polythionine hydrogel (PANI-PThi gel) was developed. The as-prepared hydrogel, which was facilely synthesized by electropolymerization, exhibited good conductivity and strong hydrophilicity while the sensitivity and specificity of the immunosensor can be enhanced. Furthermore, the as-prepared AuNPs functionalized PANI-PThi gel exhibited strong current signal and H 2 O 2 electrocatalytic ability, which guaranteed a large current variable range. Based on these, the prepared immunosensor revealed a wide linear range from 0.0001 U mL −1 to 1 kU mL −1 , a limit of detection of 0.00125 U mL −1 and its sensitivity was at least three-fold higher than previous works. More importantly, the prepared immunosensor exhibited excellent specificity, making it capable of assaying CA125 in human serum. [ABSTRACT FROM AUTHOR]

In this work, a novel strategy for immunoprobe with triple signal amplification was developed, which bovine serum albumin-stabilized copper nanoclusters (BSA-CuNCs) and the labeled antibody were co-immobilized directly on platinum nanoparticles (PtNPs). The triple current signal amplification of the immunoprobe behaved: (1) BSA-CuNCs, realizing the enrichment of copper, served as redox species with current signal at 0.06 V. (2) PtNPs as carriers were employed to immobilize the labeled antibody and enrich BSA-CuNCs. (3) The current response was further enhanced by BSA-CuNCs to accelerate the catalytic oxidation of ascorbic acid. Prostate specific antigen (PSA) was used as a model analyte to study the performance of the immunoprobe and electrochemical immunosensor. The immunosensor was fabricated as follows: anti-PSA was immobilized directly on gold nanoparticles, which were electrochemically deposited on glass carbon electrode; after immune-adsorbing PSA, the as-prepared immunoprobes were immunoadsorbed. Under the optimal conditions, the proposed immunosensor performed a wide linear range from 0.5 pg mL −1 to 100 ng mL −1 and an ultralow limit of detection with 145.69 fg mL −1 (S/N = 3). In the assay of clinical serum samples, the results of the proposed immunosensor showed good consistent with those of enzyme-linked immunosorbent assay, indicating the immunosensor is promising in clinical diagnosis. This strategy will be of guiding significance to fabricating new immunoprobes with catalytic activity and signal amplification ability. [ABSTRACT FROM AUTHOR]