Novel dual-sensitization electrochemiluminescence immunosensor using photopermeable Ru(bpy)3 2+ -doped chitosan/SiO2 nanoparticles as labels and chitosan-decorated Nafion/MWNTs composites as enhancer.

A novel dual-sensitization electrochemiluminescence (ECL) immunosensor for the detection of tumour protein prostate specific antigen (PSA) at trace level using Ru(bpy)3 2+ -doped chitosan/SiO2 nanoparticles (Ru(bpy)3 2+ /chitosan/SiO2 NPs) as the first signal enhancers was fabricated. Due to chitosan with excellent pore forming capacity, these nanoparticles possess porous structures and better photopermeability, and therefore have higher luminescence efficiencies compared with Ru(bpy)3 2+ /SiO2 NPs reported in previous publications. Conversely, chitosan with good biocompatibility and high hydrophilicity was electrochemically decorated onto a Nafion/multiwall carbon nanotubes (Nafion/MWNTs) modified electrode surface and used as the second sensitizing matrix to seize large amounts of prostate specific capture antibody (Ab1 ). The chitosan-decorated Nafion/MWNTs composites exhibited a 5.5-times higher ECL intensity than the unadorned Nafion/MWNTs films. Also, without additional reagents, such as (3-aminopropyl)triethoxysilane (APTS), the one-step functionalized Ru(bpy)3 2+ /chitosan/SiO2 NPs provided a large number of active arms to connect with PSA-detected antibodies (Ab2 ) through the amino groups in chitosan. After a sandwich immunoreaction, the PSA antigen and Ru(bpy)3 2+ /chitosan/SiO2 NPs-labelled Ab2 were sequentially captured onto the Ab1 /chitosan/Nafion/MWNTs-modified electrode surface. The ECL signal increases were linearly related to the PSA antigen concentrations and ranged from 0.01 pg·mLl-1 to 10.0 pg·mLl-1 . Under the optimized experimental conditions, the immunosensor displayed excellent sensitivity and selectivity. The detection limit was as low as 3.4 fg·mLl-1 , equivalent to, or better than, those of the reported ECL immunosensors for PSA.

An Electrochemiluminescence Immunosensor Based on Gold-Magnetic Nanoparticles and Phage Displayed Antibodies.

Using the multiple advantages of the ultra-highly sensitive electrochemiluminescence (ECL) technique, Staphylococcus protein A (SPA) functionalized gold-magnetic nanoparticles and phage displayed antibodies, and using gold-magnetic nanoparticles coated with SPA and coupled with a polyclonal antibody (pcAb) as magnetic capturing probes, and Ru(bpy)3(2+)-labeled phage displayed antibody as a specific luminescence probe, this study reports a new way to detect ricin with a highly sensitive and specific ECL immunosensor and amplify specific detection signals. The linear detection range of the sensor was 0.0001~200 µg/L, and the limit of detection (LOD) was 0.0001 µg/L, which is 2500-fold lower than that of the conventional ELISA technique. The gold-magnetic nanoparticles, SPA and Ru(bpy)3(2+)-labeled phage displayed antibody displayed different amplifying effects in the ECL immunosensor and can decrease LOD 3-fold, 3-fold and 20-fold, respectively, compared with the ECL immunosensors without one of the three effects. The integrated amplifying effect can decrease the LOD 180-fold. The immunosensor integrates the unique advantages of SPA-coated gold-magnetic nanoparticles that improve the activity of the functionalized capturing probe, and the amplifying effect of the Ru(bpy)3(2+)-labeled phage displayed antibodies, so it increases specificity, interference-resistance and decreases LOD. It is proven to be well suited for the analysis of trace amounts of ricin in various environmental samples with high recovery ratios and reproducibility.

Graphene-Ruthenium(II) complex composites for sensitive ECL immunosensors.

Non-covalent modification method has been proven as an effective strategy for enhancing the chemical properties of graphene while the structure and electronic properties of graphene can be retained. This work describes a novel strategy to fabricate a solid-state electrochemiluminescent (ECL) immunosensor based on ruthenium(II) complex/3,4,9,10-perylenetetracarboxylic acid (PTCA)/graphene nanocomposites (Ru-PTCA/G) for sensitive detection of α-fetoprotein (AFP). It is found that immobilization of PTCA and reduction of GO can be simultaneously achieved in one-pot synthesis method under alkaline condition and moderate temperature, forming PTCA/G nanocomposites. Further covalent attachment of ruthenium(II) complex to the PTCA assembled on graphene sheets produces the functional Ru-PTCA/G nanocomposites which show good electrochemical activity and ca. 21 times higher luminescence quantum efficiency than the adsorbed derivative ruthenium(II) complex. The Ru-PTCA/G nanocomposites based solid-state ECL sensor exhibits high stability toward the determination of tripropylamine (TPA) coreactant. In addition, a new ECL immunosensor based on steric hindrance effect is fabricated by cross-linking α-fetoprotein antibody (anti-AFP) with chitosan covered on Ru-PTCA/G composites modified electrode for detection of cancer biomarker AFP. This ECL immunosensor shows an extremely sensitive response to AFP in a linear range of 5 pg·mL(-1) -10 ng·mL(-1) with a detection limit of 0.2 pg·mL(-1) . The present approach is effective for various molecules immobilization and may become a promising technique for biomolecular detection.

An electrochemiluminescence sensor based on lanthanide bimetallic MOFs with a "cascade sensitization mechanism" for the sensitive detection of CA242.

Lanthanide metal-organic frameworks (Ln-MOFs) broaden the optical sensing applications of lanthanide ions due to the antenna effect between organic ligands and metals. However, the sensitization ability of the ligand to metal ions is limited, and maximizing the sensitization of the electrochemiluminescence behavior of Eu3+ is still a challenge for the application of Ln-MOFs. Therefore, under the guidance of the "cascade sensitization mechanism" based on the antenna effect sensitizing the electrochemiluminescence of bimetallic Ln-MOFs, we proposed Eu/Tb-MOFs with high luminescence intensity as a signal probe. According to the antenna effect, the conjugated structure and high extinction coefficient of the benzene ring of 2-amino terephthalic acid (NH2-BDC) can enhance the ECL luminescence intensity of Eu/Tb-MOFs. Tb3+ can act as an energy bridge between NH2-BDC and Eu3+, buffering the energy gap. The bimetallic sensitization is formed between Tb3+ and Eu3+, which can inhibit the reverse internal flow of energy and ensure the high luminous efficiency of Eu3+. In addition, the nanosphere mixed valence Fe3O4 as a co-reactant accelerator promotes the formation of transient free radical SO4•- through the valence change of Fe2+/Fe3+. The ECL immunosensor constructed by luminophores Eu/Tb-MOFs and nanosphere Fe3O4 provided a new explanation for the ECL self-luminous of Eu/Tb-MOFs.

An electrochemiluminescence immunosensor based on Ag-Ti3C2 MXene and CNNVs with multiple signal amplification strategies.

In electrochemical immunoassays, great breakthroughs have been made in ultrasensitive detection of tumor markers by amplifying signals with coreaction accelerators. Herein, carbon nitrides with nitrogen vacancies (CNNVs) are proposed as emitter, due to the introduction of nitrogen vacancies this emitter has better ECL efficiency, the phenomena of interface electron transfer and electrode passivation are improved. At the same time, it can also promote the electrochemical reduction of coreactant, making it an attractive and potential emitter. The electrode was modified with Ag-Ti3C2 MXene. It not only accelerates electron transfer and increases the effective working area of the electrode, but also acts as a coreaction accelerator to promote the electrochemical reduction of the coreactant K2S2O8, resulting in a strong ECL signal. The immunosensor showed a good linear relationship in the range of 10-5-100 ng/mL with a detection limit of 0.36 fg/mL. In addition, the excellent properties of good specificity and ultra-high stability provide an effective method for ultra-sensitive immunoassays.

A double reaction system induced electrochemiluminescence enhancement based on SnS2 QDs@MIL-101 for ultrasensitive detection of CA242.

At present, the development of electrochemiluminescence (ECL) immunosensor with excellent performance is still the research focus of immunoassay and detection. Herein, SnS2 quantum dots (SnS2 QDs) and metal-organic framework (MIL-101 (Cr)) are effectively combined to achieve synergistic signal amplification based on K2S2O8 co-reactant, thereby constructing SnS2 QDs/SO4•- and SO4•-/O2 ECL double reaction luminous systems. SnS2 QDs and singlet oxygen (1(O2)2*) produced from the system as light-emitting devices jointly enhance the ECL response and significantly improve the sensitivity of the ECL immunosensor. Dissolved oxygen and SnS2 QDs respectively generate HOO• and SnS2 QDs•- under negative potential, and react with transient SO4•- to emit strong light respectively, so as to jointly enhance the ECL response. MIL-101 catalyzes the oxygen cathode reduction reaction to promote the conversion of dissolved oxygen into HOO•, which greatly improves the ECL response of 1(O2)2*. CuS with spherical nanoflower-like form as a co-reaction promoter of K2S2O8 generate more SO4•- active substances, which further enhance the ECL response of the immunosensor. The constructed ECL immunosensor has the advantages of low detection limit, high sensitivity and better stability. Under the optimal conditions, the detection range is 0.1 mU/mL∼100 U/mL, and the detection limit is 0.015 mU/mL. The results show that the constructed ECL immunosensor can detect human CA242 samples and have a broad application prospect in biological analysis and early diagnosis of diseases.

Dual-modality probe based on black phosphorous and NiFe2O4 NTs for electrochemiluminescence and photothermal detection of ovarian cancer marker.

An electrochemiluminescence and photothermal immunosensor based on a dual-modality integrated probe was proposed for sensitive and reliable detection of lipolysis stimulated lipoprotein receptor (LSR), a new biomarker of ovarian cancer. Black phosphorous quantum dots (BPQDs) possess fascinating electrochemical property and unique photothermal effect, which could not only enhance ECL signal of N-(4-aminobutyl)-N-ethylisoluminol (ABEI) through accelerating dissolved O2 evolution but also realize temperature signal output by converting laser energy into heat. Furthermore, NiFe2O4 nanotubes (NiFe2O4 NTs) have large specific surface area and favorable adsorption ability, which could increase the immobilized amount of ABEI and BPQDs, further strengthening ECL and temperature signal. As a result, a dual-mode immunosensor was constructed and realized ECL and temperature dual signal to detect LSR, making the results more reliable. This work provided a new thought for the development of sensitive and accurate sensors and was expected to employ for determination of other biomarkers.

An ultrasensitive ratiometric electrochemiluminescence immunosensor combining photothermal amplification for ovarian cancer marker detection.

Signal amplification strategies play important functions in the development of highly sensitive electrochemiluminescence (ECL) immunosensing system. Herein, a photothermal enhanced ratiometric ECL immunosensor was proposed for the detection of human epididymis protein 4 (HE4), an ovarian cancer biomarker. Mesoporous SiO2 (ms-SiO2) and carbon nanohorns (CNHs) was served as carrier of ECL emitter carbon nitride nanosheet (g-C3N4) and anodic ECL emitter polymer dots (Pdots), respectively. The large specific area of ms-SiO2 and CNHs improved the loading capacity of g-C3N4 and Pdots, enhancing ECL signals. Furthermore, CNHs was innovatively utilized as thermal convert unit to increase the electrode surface temperature, which benefited from its extraordinary photothermal property at 808 nm that can convert laser energy into heat for elevating the temperature, further amplified ECL signal. The delicately designed ECL immunosensor exhibited excellent sensitivity to HE4 detection with wide linear range from 1.0 × 10-5 to 10 ng/mL and low detection limit of 3.3 × 10-6 ng/mL. This work not only provided an effective way to develop highly sensitive ECL immunosensor but could attract more attention on the application of photothermal material in the ECL field.

Highly stable Ru-complex-grafted 2D metal-organic layer with superior electrochemiluminescent efficiency as a sensing platform for simple and ultrasensitive detection of mucin 1.

This work utilized ultrathin metal-organic layer (MOL) to immobilize luminophores for effectively shortening the ion/electron-transport distance and relieving the diffusional constraints of ion/electron, which greatly enhanced the ECL efficiency and intensity. Moreover, the MOL's immobilization amount of luminophores should be higher than these of bulk MOFs because MOLs possess more accessible postmodification sites for the luminophores with minimal diffusion barriers. As expected, our proof-of-concept experiment indicated that the Hf-MOL's loading number of Ru(bpy)2(mcpbpy)2+ was about 1.74 times that of a 3D mesoporous MOF (PCN-777), and the ECL efficiency and intensity of PEI@Ru-Hf-MOL were around 1.27 times and 14.5 times those of PEI@Ru-PCN-777, respectively. In view of these merits, this work utilized the prepared PEI@Ru-Hf-MOL as a highly efficient sensing platform for simple, rapid and sensitive detection of mucin 1, which exhibited a broad linearity from 1 fg/mL to 10 ng/mL and a low detection limit of 0.48 fg/mL. This work provided a practicable strategy to develop high-performance ECL materials, and therefore opened up a new avenue to design ultrasensitive ECL biosensors, which expanded the application potential of MOLs in ECL assays.

Highly Stable Mesoporous Luminescence-Functionalized MOF with Excellent Electrochemiluminescence Property for Ultrasensitive Immunosensor Construction.

In this work, a novel mesoporous luminescence-functionalized metal-organic framework (Ru-PCN-777) with high stability and excellent electrochemiluminescence (ECL) performance was synthesized by immobilizing Ru(bpy)2(mcpbpy)2+ on the Zr6 cluster of PCN-777 via a strong coordination bond between Zr4+ and -COO-. Consequently, the Ru(bpy)2(mcpbpy)2+ could not only cover the surface of PCN-777 but also graft into the interior of PCN-777, which greatly increased the loading amount of Ru(bpy)2(mcpbpy)2+ and effectively prevented the leaching of the Ru(bpy)2(mcpbpy)2+ resulting in a stable and high ECL response. Considering the above merits, we utilized the mesoporous Ru-PCN-777 to construct an ECL immunosensor to detect mucin 1 (MUC1) based on proximity-induced intramolecular DNA strand displacement (PiDSD). The ECL signal was further enhanced by the enzyme-assisted DNA recycling amplification strategy. As expected, the immunosensor had excellent sensitivity, specificity, and responded wide linearly to the concentration of MUC1 from 100 fg/mL to 100 ng/mL with a low detection limit of 33.3 fg/mL (S/N = 3). It is the first time that mesoporous Zr-MOF was introduced into ECL system to assay biomolecules, which might expand the application of mesoporous metal-organic frameworks (MOFs) in bioanalysis. This work indicates that the use of highly stable mesoporous luminescence-functionalized MOFs to enhance the ECL intensity and stability is a feasible strategy for designing and constructing high-performance ECL materials, and therefore may shed light on new ways to develop highly sensitive and selective ECL sensors.

Highly sensitive electrochemiluminescent immunosensor based on gold nanoparticles-functionalized zinc oxide nanorod and poly(amidoamine)-graphene for detecting brombuterol.

ß-adrenergic agonists (ß-agonists) recognized as a growth promoter will reflect the health of human. Sensitive detection of ß-agonists in foodstuff is valuable for the health of animals and human. A novel ultrasensitive competition-type electrochemiluminescent (ECL) immunosensor was developed for detecting brombuterol (Brom) based on CdTe Quantum dot (QDs) and polyamidoamine dendrimer (PAMAM, G2) modified graphene oxide (GO) (CdTe QDs-PAMAM-GO composite) as bioprobe for the first time. The surface of glassy carbon electrode (GCE) was coated with AuNPs-ZnO NRs composite film as the platform, which facilitated the electronic transmission rate to enhance the ECL intensity and provide enough active sites for capturing antibody. The resulting ECL immunosensor enabled the real samples detection of Brom with a lower detection limit of 0.3pgmL(-1) (S/N=3) and a wider linear range from 0.001 to 500ngmL(-1). The proposed immunosensor coupled with the excellent advantages of CdTe QDs-PAMAM-GO and AuNPs-ZnO NRs composite displayed high sensitivity and long-term stability, and provided an approach for determining other important biomarkers.

Sandwich-format electrochemiluminescence assays for tumor marker based on PAMAM dendrimer-L-cysteine-hollow gold nanosphere nanocomposites.

In this work, a novel polyamidoamine (PAMAM) dendrimer-L-cysteine-hollow gold nanospheres nanocomposite was fabricated and used as the promoter for the peroxydisulfate/O2 ECL system to detect the concentration of the tumor marker carcinoembryonic antigen (CEA). Herein, the carboxyl-terminated PAMAM dendrimers were decorated with L-cysteine (L-Cys) by EDC/NHS coupling chemistry. Then, the hollow gold nanospheres (HGNPs) were employed as effective nano-carriers for the assembly of PAMAM-L-Cys via thiols-Au bonding, which was used for further loading of detection antibody (Ab2) to form the PAMAM-L-Cys-HGNPs-Ab2 bioconjugates. In the presence of target CEA, the sandwiched immuno-structure can be formed between the capture anti-CEA antibodies (Ab1), which self-assembled on deposited gold modified electrode, and the Ab2 on the PAMAM-L-Cys-HGNPs, thereby resulting in a proportional increase in ECL response, due to the significant enhancement of PAMAM-L-Cys-HGNPs toward peroxydisulfate/O2 ECL system. As a result, a sandwich ECL assay for CEA detection was developed with excellent sensitivity of a large concentration variation from 20 fg/mL to 1.0 ng/mL and a detection limit of 6.7 fg mL(-1).