This work reports a highly efficient electrogenerated chemiluminescence (ECL) quenching on lipid-coated multifunctional magnetic nanoparticles (MMNP) for the determination of proteases incorporating membrane-confined quenching with a specific cleavage reaction for the first time. A new ruthenium complex [Ru(bpy) 2 (ddcbpy)](PF 6 ) 2 (bpy = 2,2′-bipyridine, ddcbpy = 4,4′-didodecyl-carbonyl-2,2′-bipyridine with two hydrophobic long alkyl chains) was synthesized as a signal probe, while [cholesterol-(CH 2 ) 6 -HSSKLQK(peptide)-ferrocene (quencher)] was designed as a specific peptide-quencher probe. The MMNP were prepared by inserting both the signal probe and the peptidequencher probe into the cholesterol−phospholipid-coated Fe 3 O 4 magnetic nanoparticles (Fe 3 O 4 NP, ∼200 nm). When prostate specific antigen (PSA) taken as a model analyte was introduced into the suspension of MMNP, PSA cleaved the amide bond of SK in cholesterol-(CH 2 ) 6 -HSSKLQK-Fc, and then the cleaved peptidemotif-Fc-quencher was deviated from the MMNP, resulting in the increase in the ECL intensity. It was found that the ECL quenching constant of [Ru(bpy) 2 (ddcbpy)] 2+ on MMNP (K SV, NP/lip ECL =2.68 × 10 7 M −1 ) is 137-folds higher than that on the lipidcoated electrode (K SV, lip ECL =1.95 × 10 5 M −1 ) and 391-folds higher than that in the solution (K SV, aq ECL =6.86 × 10 4 M −1 ). The ECL emission of Ru(bpy) 3 2+ derivative-attached Fe 3 O 4 NP was observed at ∼1.2 V, involving the tunnel-electron transfer pathway (TPA • + Ru(bpy) 3 3+ = Ru(bpy) 3 2+ *). Based on the highly efficient ECL quenching of the ruthenium complex by ferrocene on the MMNP, a new ECL method was developed for PSA with a linear range from 0.01 to 1.0 ng/mL and a limit of detection of 3.0 pg/mL. This work demonstrates that the approach of ECL quenching by ferrocene on lipid-coated Fe 3 O 4 NP is promising and could be easily extended to determine other proteases.

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This Feature Article simply introduces principles and mechanisms of electrochemiluminescence (ECL) biosensors for the determination of biomarkers, highlights recent advances of the ECL biosensors on key aspects including new ECL...

This work reports a gold nanoelectrode ensembles (Au-NEE) platform taken as a disposable electrogenerated chemiluminescence (ECL) platform with immunomagnetic microbeads for ECL immunoassays for the first time. The peak-shaped voltammograms were obtained at the Au-NEE, attributed to the total diffusional overlap. The ECL intensity at Au-NEE was 12.9 folds in the Ru(bpy) 3 2+ -tri-n-propylamine (TPA) ECL system and 19.6 folds in the luminol-H 2 O 2 system, compared with that at the Au macroelectrode using the normalized active area of the electrodes, mainly attributed to the diffusion overlap of the Au-NEE and the edge effect of the individual gold nanodisks of the Au-NEE. The ECL immunoassay on the Au-NEE platform with magnetic microbeads for the determination of cancer biomarkers was developed. Carbohydrate antigen 19-9 (CA 19-9) was chosen as a model analyte while CA 19-9 antibody on the magnetic microbeads was taken as the capture probe, and ruthenium complex-labeled CA 19-9 antibody was used as the signal probe. A "sandwich" bioconjugates on the magnetic beads were transferred onto the ECL platform, and then the ECL measurements were performed in TPA solution. The developed method showed that the ECL peak intensity was directly in proportion to the concentration of CA 19-9 in the range from 0.5 to 20 U/mL with a limit of detection of 0.4 U/mL. This work demonstrates that the Au-NEE can be employed as a useful disposable ECL platform with the merits of cheapness, low nonspecific adsorption and practical application. The proposed approach will open a new avenue in the point-of-care test for the determination of protein biomarkers.