Multiple functional strategies have shown great potential in ultrasensitive amperometric immunoassays for tumor markers, which promote conductivity and signal multiple amplification. The sensitivity ...of amperometric immunoassays is significantly affected by the conductivity and specific area of the sensing interface as well as the electrochemical activity of redox species. Thus, these strategies are generally based on integrating various materials together and endowing immunosensing systems with many advantages, such as large specific area, high electrochemical activity, good conductivity, biocompatibility, and catalytic performance. Owing to the rapid development of functional materials (such as conductive hybrids, catalytic hybrids, enzyme-like materials, highly electrochemical active species, redox nanocomposites, porous materials, hydrogels, and metal-organic framework) and new bioactive substances (including new blocking agents and receptors like peptides and oligonucleotide chains), the sensitivity of related biosensors is usually higher than that of traditional ones, indicating that multiple functional strategies are promising in amperometric immunoassays. Herein, we provide an overview of recent advances in multiple functional strategies that have proven to dramatically enhance the sensitivity of amperometric immunoassays, which incorporate the following materials: (1) conductive nanomaterials hybrids; (2) catalytic nanomaterials hybrids; (3) new redox materials; (4) three-dimensional porous materials; (5) new receptors and blocking agents.
•Multiple functional strategies for amplifying sensitivity of amperometric immunoassay are reviewed.•Effects of conductive nanomaterials, catalytic nanomaterials hybrids, new redox materials on the sensitivity were discussed.•Development of three-dimensional porous materials, new receptors, and blocking agents in immunoassay was summarized.
Efficient signal amplification strategies are crucial for ultrasensitive detection of tumor markers. Herein, a new signal amplification strategy by coupling cascade catalysis-initiated radical ...polymerization with impedimetric immunoassay was proposed for ultrasensitive detection of carbohydrate antigen 15–3 (CA15-3). Copper-based metal-organic framework nanoparticles (Cu-MOF), as peroxidase mimics, combined with CA15-3 antibody (Ab2) and glucose oxidase (GOx) were employed as immunoprobes to initiate radical polymerization by cascade catalysis. In this work, the oxidation of glucose was catalyzed by GOx to generate hydrogen peroxide (H2O2), which reacted with acetylacetone (ACAC) via Cu-MOF catalysis to yield ACAC radicals for the polymerization of N-isopropylacrylamide (NIPAM). The polymer, poly (N-isopropylacrylamide) (PNIPAM), was generated in situ from the radical polymerization. As resistance enhancer, PNIPAM was covered on electrode surface to amplify resistance value by its poor conductivity. With the help of polymerization-based amplification, the resistance differences caused by target were improved significantly. Under optimum conditions, the designed biosensor showed wide detection ranges from 10 μU/mL to 10 mU/mL and 10 mU/mL to 100 U/mL, with ultralow detection limit of 5.06 μU/mL for CA15-3. Such an approach opened a new avenue for signal amplification, thus offering an ultrasensitive detection platform for a broad range of tumor markers.
•Ultrasensitive impedimetric immunosensor was designed for CA15-3 detection.•A new immunoprobe composed of Cu-MOF, GOx and antibody was fabricated.•The immunoprobe triggered radical polymerization to amplify resistance.
Sensitivity amplification strategies in electrochemical immunoassays are mainly limited by redox signal leaking, degradation of catalytic activity caused by layers of decoration and the large ...hindrance effect caused by immunoprobes. Herein, we developed an innovative sensitivity amplification strategy based on the self-sacrificial label-assisted electroactivity conversion of a sensing interface, utilizing Fe3+-loaded polydopamine (Fe3+-PDA) nanoparticles as the self-sacrificial labels, which can be decomposed under acidic conditions and release Fe3+. When the assembled sensing interface was immersed in a prussian blue (PB) precursor solution (a mixed solution of 0.1 M KCl, 0.1M HCl and 1 mM K3Fe(CN)6), the as-formed sandwich-type structure was destroyed due to the decomposition of Fe3+-PDA caused by HCl in PB precursor solution, resulting in the reduce of interface resistance. The released Fe3+ reacted with the PB precursor solution and triggered the growth of electroactive PB nanoparticles (PB NPs) on the sensing interface. Assisted by self-sacrificial Fe3+-PDA, the sensing interface was converted from electrochemically inactive to electroactive with a strong redox signal, high catalytic activity, and decreased interface resistance. The PB NPs can catalyse H2O2 to amplify the redox signal, thus improving sensitivity. The redox signal and catalysts were generated in the final assembly step, which can avoid signal leaking and decreases of catalytic activity caused by layers of decoration. The decomposition of Fe3+-PDA can eliminate the large hindrance effect of the immunoprobe. Ultrasensitive quantification of carbohydrate antigen 125 (CA 125) was realized with a detection range from 0.00001 to 1000 U mL−1 and detection limit of 0.25 × 10−6 U mL−1.
•Fe3+-PDA acted as self-sacrificial label to trigger the electroactivity conversion of sensing interface.•Sensing interface exhibited strong redox signal, high catalytic activity and decreased interface resistance.•Self-sacrificial label assisted electroactivity conversion was used to amplify sensitivity.
Abstract Developing a biocompatible and efficient photothermal coupling agent with appropriate size is a prerequisite for the development of near-infrared (NIR) light-induced photothermal therapy ...(PTT). In the present study, polyaniline nanoparticles (PANPs) with a size of 48.5 ± 1.5 nm were fabricated and exhibited excellent dispersibility in water by a hydrothermal method and further surface functionalization by capping with F127. The developed F127-modified PANPs (F-PANPs) had a high molar extinction coefficient of 8.95 × 108 m−1 cm−1 , and high NIR photothermal conversion efficiency of 48.5%. Furthermore, combined with NIR irradiation at 808 nm and injection of F-PANP samples, in vivo photothermal ablation of tumor with excellent treatment efficacy was achieved. In vitro transmission electron microscopy (TEM) images of cells, methyl thiazolyl tetrazolium (MTT) assay, histology, and hematology studies revealed that the F-PANPs exhibit low toxicity to living systems. Therefore, F-PANPs could be used as PTT agents for ablating cancer, and the concept of developing polyaniline-based nanoparticles can serve as a platform technology for the next generation of in vivo PTT agents.
In general, current difference (ΔI) due to immunoreactions is significant in determining biosensor sensitivity. In this work, a new strategy of triple sensitivity amplification for ultrasensitive ...electrochemical detection of prostate specific antigen (PSA) was developed. Au-poly(methylene blue) (Au-PMB) was implemented as a redox species with strong current signal at −0.144V and used to fabricate the substrate of the biosensor. Conductive reduced graphene oxide-Au nanocomposites (Au-rGO) were coated on the Au-PMB modified glassy carbon electrode (GCE) to amplify current signal. After peptides (CEHSSKLQLAK-NH2) were fixed on the Au-rGO/Au-PMB/GCE, the fixed peptides reacted with glutaraldehyde to immobilize polydopamine-Au-horse radish peroxidase nanocomposites (PDA-Au-HRP). The electrochemical sensing interface for PSA was realized. Due to smaller resistance compared to antibodies, the peptides which can be cleaved specifically by PSA were employed. After the incubation of PSA, a large ΔI was obtained and behaved as the decrease of current signal. Then the remaining PDA-Au-HRP accelerated an enzyme-catalyzed precipitation reaction between 4-chloro-1-naphthol and H2O2. A further decrease in current signal (namely the increase in ΔI) resulted from the poorly conductive precipitation adhering onto the biosensor. The designed biosensor presented a wide linear range from 1.0fgmL−1 to 100ngmL−1 with an ultralow detection limit of 0.11fgmL−1.
•A new peptide-based biosensor was fabricated for the ultrasensitive detection of prostate specific antigen.•Au-poly(methylene blue) as a novel redox species were synthesized by oxidative polymerization.•Polydopamine-Au-horse radish peroxidase nanocomposites were used to accelerate an enzyme-catalyzed precipitation reaction to enhance sensitivity.
A conducting long-chain polythiols (poly (2-aminothiophenol), PATP) was synthesized by a chemical polymerization process and combined with Au nanoparticles (AuNPs) to prepare a novel, sensitive and ...label-free electrochemical biosensor by adsorption of carcinoembryonic antibody (anti-CEA) on the PATP–AuNPs modified gold electrode. Differential pulse voltammetry (DPV) was used to characterize the recognition of carcinoembryonic antigen (CEA). Under the optimized conditions, the proposed immunosensor displayed a good amperometric response to CEA with linear range from 1fgmL−1 to 10ngmL−1 and a detection limit of 0.015fgmL−1 (signal/noise=3). The results demonstrated that the immunosensor has advantages of high sensitivity, wide linear range, good repeatability, and good selectivity. Importantly, the results of the detection of clinical serum specimens with the proposed sensor were well consistent with the data determined by micropartical enzyme immunoassay (MPEI), showing that the present work provides a promising ultrasensitive immunoassay strategy for clinical applications.
► The poly (2-aminothiophenol) was synthesized as a conducting long-chain polythiols. ► Au electrode was modified with PATP and AuNPs to fabricate electrochemical immunosensor. ► The detection limit for CEA reached 0.015fgmL−1. ► This method performed very well on the detection of clinical serum specimens.
In this work, a novel and sensitive multiplexed immunoassay protocol for simultaneous electrochemical determination of alpha-fetoprotein (AFP) and carcinoembryonic antigen (CEA) was designed using ...functionalized chitosan composites. The immunosensing platform was prepared via immobilizing capture anti-AFP and anti-CEA on chitosan-Au nanoparticles (AuNPs) through EDC/NHS linking. The signal tags were fabricated by immobilizing electroactive redox probes – Prussian blue (PB) and ferrocenecarboxylic acid (Fc) on chitosan (CHIT), following by absorbing AuNPs to immobilize labeled anti-AFP and anti-CEA, respectively. A sandwich-type immunoassay format was employed for the simutaneous detection of AFP and CEA. The assay was based on the electrochemical oxidation/reduction of the redox species in signal tags, which has a relationship with the concentration of analytes. Experimental results revealed that the multiplexed electrochemical immunoassay enabled the simutaneous monitoring of AFP and CEA with a wide range of 0.05–100ngmL−1 for both AFP and CEA. The detection limits (LOD) was 0.03ngmL−1 for AFP and 0.02ngmL−1 for CEA (S/N=3). The assay results of serum samples with the proposed method were in a good agreement with the reference values from standard ELISA method. And the negligible cross-reactivity between the two analytes makes it possesses potential promise in clinical diagnosis.
•Electrochemical simultaneous detection of AFP and CEA was successfully performed.•CHIT-PB-AuNPs-Ab2,1 and CHIT-Fc-AuNPs-Ab2,2 were used as signal tags.•The detection limit was 0.03ngmL−1 for AFP and 0.02ngmL−1 for CEA.•This method performed very well on the detection of clinical serum specimens.
•Fenton and Fenton-like catalysts in electrochemical immunosensor were summarized.•Challenge and future prospect of Fenton and Fenton-like catalysts were discussed.•Advantages of Fenton and ...Fenton-like catalysts were elaborated in detail.
With the rapid development of electrochemical immunoassay, various catalysts have been applied for initiating catalytic reaction to improve the sensitivity of electrochemical immunosensor. Sensitivity, the change in electrochemical signal caused by antigen per unit concentration, is a crucial indictor to evaluate the performance of electrochemical immunosensor for detecting tumor markers. As a traditional inorganic reaction, Fenton and Fenton-like reaction has been widely used in amplifying sensitivity, owing to their fast reaction, mild reaction conditions, low cost and environmental friendliness. By virtue of these advantages, increasingly Fenton and Fenton-like catalysts with high catalytic efficiency have been exploited in conceiving immunosensor. Herein, recent progresses in Fenton and Fenton-like catalysts including Fe3O4, iron-based metal organic frameworks, iron-based hydrogel, hemin, ferrous reagent and iron-free catalysts like metallic peroxide and noble metal particles are summarized. The remaining challenges and prospects for future directions for the rational application of Fenton and Fenton-like catalysts are also discussed.
In this work, polyamidoamine dendrimers capped-carbon dots (PAMAM-CDs) were fabricated by one-step microwave assisted pyrolysis of citric acid (CA) and PAMAM, where the formation of CDs and the ...surface passivation were accomplished simultaneously. The obtained graphitic PAMAM-CDs, with abundant amine groups, were employed as reducing and capping agents for the formation of PAMAM-CDs/Au nanocrystal nanocomposites. The resulting nanocomposites exhibited excellent conductivity, stability and biocompatibility on the surface of electrode and were designed as an immobilized matrix for sensitive immunosensing of alpha-fetoprotein (AFP). The proposed immunosensor showed a wide linear detection range from 100fgmL−1 to 100ngmL−1. The detection limit for AFP was 0.025pgmL−1. Importantly, the immunosensor was evaluated for the analysis of clinical serum samples, obtaining a good correlation with enzyme-linked immunosorbent assay (ELISA). The results indicated that the immunosensor provided a possible application for the detection of AFP in clinical diagnosis.
•PAMAM-CDs/Au nanocrystal nanocomposites were prepared.•PAMAM-CDs/Au was used to fabricate electrochemical immunosensor.•The detection limit for AFP reached 0.025pgmL−1.•This method performed very well on the detection of clinical serum specimens.
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