Inspired by dual-wavelength fluorescence ratiometric method which could reduce the influence from the environmental change, here, we present a novel dual-potential electrochemiluminescence (ECL) ratiometric sensing approach. CdS nanocrystal (NC) and luminol as two different ECL emitters are employed. ECL from CdS NCs coated on glassy carbon electrode at -1.25 V (vs SCE) could be quenched by closely contacted Pt nanoparticles (NPs) via a biological binding event, while ECL from luminol at +0.45 V (vs SCE) could be enhanced by the same Pt NPs, in the presence of their common coreactant of H₂O₂. Thus, the quenching of ECL from CdS NCs and the enhancement of ECL from luminol could indicate the same biological binding event. With the mp53 oncogene as a model DNA molecule, a molecular beacon (MB) containing a 20-base loop, which is complementary with the mp53 oncogene, is immobilized on CdS NCs/GCE first; Pt NPs are then captured on CdS NCs surface by DNA hybridization between the MB and mp53 oncogene labeled on Pt NPs. By measuring the ratio of ECL intensities at two excitation potentials, this approach could sensitively detect the concentration of target DNA in a wide range from 5.0 fM to 1.0 pM. The sensing scheme is general and can be utilized for many other biological binding events.

Here, we report a novel type of signal-on dual-potential electrochemiluminescence (ECL) approach for telomerase detection based on bifunctionalized luminol-gold nanoparticles (L-Au NPs). In this approach, CdS nanocrystals (NCs) were first coated on glassy carbon electrode, and then thiol-modified telomerase primer was attached on CdS NCs via Cd-S bond. In the presence of telomerase and dNTPs, the primer could be extended. Telomerase primer would hybridize with its complementary DNA, and the extended part would hybridize with the capture DNA which was tagged with L-Au NPs. In the presence of coreactant H2O2, the L-Au NPs could not only enhance the ECL intensity of CdS NCs at -1.25 V (vs SCE) induced by the surface plasmon resonance (SPR) of Au NPs but also produce a new ECL signal at +0.45 V (vs SCE) that resulted from luminol in L-Au NPs. Both signals at two potentials increased with the increase of telomerase concentration. This method could be used to detect the telomerase from 100 to 9000 HL-60 cells and investigate the apoptosis of tumor cells. The ratio of the two signal increments (ΔECL(Luminol)/ΔECL(CdS NCs)), which showed a high consistency value for different numbers of cells, could be used to verify the reliability of tests. This dual-potential ECL strategy showed great promise in avoiding false positive or negative results in bioanalysis.

In this work, we developed a visual electrochemiluminescence (ECL) sensing platform based on a dual-bipolar electrode (D-BPE) array chip. The chip was composed of two arrays of BPEs and three separated arrays of reservoirs filled with buffer, Ru(bpy)3(2+)-TPrA and luminol solutions, respectively. Both BPEs served as ECL reporting platforms. By applying 6.0 V voltage, an array of orange electrochemiluminescence (ECL) signals belonging to Ru(bpy)3(2+) turned on. After adding DNAzyme and H2O2 in Ru(bpy)3(2+) and luminol reservoirs, the orange Ru(bpy)3(2+) signals decreased until vanished due to the quenching effect; meanwhile, a new array of blue ECL signals turned on because of the luminol-H2O2 ECL reaction. The designed D-BPE owns superior properties compared with the three-electrode system benefiting from the quantitative relation of bipolar systems, which greatly enhanced the ECL detection sensitivity. Meanwhile, the visual color-switch ECL and the ratiometric detecting principle made the results easier to evaluate and more accurate. Quantitative detection of HL-60 cancer cells from 320 cells/mL to 2.5 × 10(5) cells/mL with two linear ranges was achieved. The detection limit was down to 80 cells/mL. Finally, this D-BPE chip could distinguish the tumor cells from normal cells and provide a prospect for cancer diagnosis in a high-throughput, visual way.

Nanocrystals (NCs) usually suffer from weak electrogenerated chemiluminescence (ECL) emissions compared with conventional luminescent reagents like Ru(bpy)3(2+). In this work, we proposed a simple in situ activation approach by dipping CdS NCs film on glass carbon electrode (CdS NCs/GCE) in an activation solution containing H2O2 and citric acid, resulting in a ~58-fold enhancement of ECL intensity in the presence of coreactant H2O2. During activation, CdS NCs were oxidized by H2O2 to smaller ones which resulted in more surface S vacancies; meanwhile, citric acid played an important role in stabilizing NCs. The ECL enhancing mechanism was investigated in detail, and the coordination of H2O2 to surface excess Cd(2+) ions (S vacancies) on the CdS NCs surface formed in activation was the main factor which could stabilize the electrogenerated radicals, resulting in an enhanced ECL. ECL from the activated CdS NCs/GCE could be quenched in Na2S solution due to the bonding of S(II) to excess Cd(2+) ions on the surface of CdS NCs. On the basis of this, we then used the activated CdS NCs/GCE as an ECL probe for the detection of Na2S which showed good performance including a wide linear range of 5 nM to 20 μM and good anti-interference ability. Moreover, this ECL probe was successfully applied for hydrogen sulfide (H2S) detection in a biological system.