Coupled Poly(ethylenimine) Coreactant to Enhance Electrochemiluminescence of Polymer Dots for Array Imaging of Protein Biomarkers.

Traditional electrochemiluminescent (ECL) bioanalysis suffers from the demand for excessive external coreactants and the damage of reaction intermediates. In this work, a poly(ethylenimine) (PEI)-coupled ECL emitter was proposed by covalently coupling tertiary amine-rich PEI to polymer dots (Pdots). The coupled PEI might act as a highly efficient coreactant to enhance the ECL emission of Pdots through intramolecular electron transfer, reducing the electron transfer distance between emitter and coreactant intermediates and avoiding the disadvantages of traditional ECL systems. Through modification of the PEI-Pdots with tDNA, a sequence partially complementary to cDNA that was complementary to the aptamer of target protein biomarker (aDNA), tDNA-PEI-Pdots were obtained. The biosensors were produced using Au/indium tin oxide (ITO) with an aDNA/cDNA hybrid, and an ECL imaging biosensor array was constructed for ultrasensitive detection of protein biomarkers. Using vascular endothelial growth factor 165 (VEGF165) as a protein model, the proposed ECL imaging method containing two simple incubations with target samples and then tDNA-PEI-Pdots showed a detectable range of 1 pg mL-1 to 100 ng mL-1 and a detection limit of 0.71 pg mL-1, as well as excellent performance such as low toxicity, high sensitivity, excellent selectivity, good accuracy, and acceptable fabrication reproducibility. The PEI-coupled Pdots provide a new avenue for the design of ECL emitters and the application of ECL imaging in disease biomarker detection.

Nanoconfined Cathodic Electrochemiluminescence for Self-Sensitized Bioimaging of Membrane Protein.

Self-enhanced electrochemiluminescence (ECL) can be achieved via the confinement of coreactants and ECL emitters in a single nanostructure. This strategy has been used for the design of anodic ECL systems with amine compounds as coreactants. In this work, a novel confinement system was proposed by codoping positively charged ECL emitter tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)32+) and negatively charged coreactant peroxydisulfate (S2O82-) in silica nanoparticles. The codoping process could be performed by introducing S2O82- in cationic poly(diallyldimethylammonium chloride) (PDDA) to form PDDA@S2O82- and then encapsulating it and Ru(bpy)32+ in the Triton X-100 vesicle followed by the hydrolysis of tetraethyl ortosilicate, surface modification, and demulsification. The obtained RuSSNs exhibited good homogeneity, excellent monodispersity, acceptable biocompatibility, and 2.9-fold stronger ECL emission than Ru(bpy)32+-doped silica nanoparticles at an equal amount of nanoparticles in the presence of 0.1 M K2S2O8. Thus, an in situ self-sensitized cathodic ECL imaging method was designed for the monitoring of glycoprotein on living cell membranes. This work provides a new way for the modification, enhancement, and application of nano-ECL emitters in biological analysis.

Electrochemiluminescence Imaging at a Single Nanoparticle Scale to Elucidate Diffusion-Accelerated Charge Transfer and Monitor Cell Permeability.

Accelerating the charge transfer between electroactive species and the electrode is always a hot topic. Here, we report a finding of Ru(bpy)33+ diffusion-induced acceleration of charge transfer from Ru(bpy)32+-doped silica nanoparticles (RDSNs) to the electrode via electrochemiluminescence (ECL) imaging at a single nanoparticle scale. Ru(bpy)32+ in the electrolyte can act as an enhancer of RDSN ECL emission in the presence of coreactant tripropylamine, which amplifies the RDSN ECL by 478 times at 10 µM free Ru(bpy)32+. According to percolation theory, the diffusion of electro-generated Ru(bpy)33+ near a single RDSN brings much quicker charge transfer to the electrode than electron hopping in RDSN, which is demonstrated by spatial and temporal interaction imaging of the RDSN and the Ru(III) diffusion layer. Taking advantage of this new mechanism, a real-time ECL imaging method has been constructed to monitor the rapid change of cell permeability during surfactant treatment.