Target-catalyzed hairpin assembly and intramolecular/intermolecular co-reaction for signal amplified electrochemiluminescent detection of microRNA.

Herein, a new electrochemiluminescence (ECL) strategy for enzyme-free microRNA-21 (miR-21) amplified detection was designed based on target-catalyzed hairpin assembly by combining the signal-amplification capability of both intramolecular and intermolecular ECL co-reaction. In this strategy, two hairpin DNA probes of H1 and H2 were designed as capture probes and detection probes, respectively. To be specific, the capture probes of H1 were immobilized on the multilayer interface of AuNPs and thiosemicarbazide (TSC) assembly on the single-walled carbon nanohorns decorated electrode, while the detection probes of H2 was anchored on the nanocarriers of gold nanoparticals functionalized reduced graphene oxide (Au-rGO) which were tagged with the self-enhanced ruthenium complex (PEI-Ru(ΙΙ)) in advance. Based on the target-catalyzed hairpin assembly, target miR-21 could trigger the hybridization of H1 and H2 to further be released for initiating the next hybridization process to capture a large number of H2 bioconjugates on the sensing surface. Herein, the TSC was used not only as a coupling reagent to attach the AuNPs via Au-S and Au-N bonds but also as a novel intermolecular coreactant to enhance the ECL intensity, and the PEI-Ru(ΙΙ) as emitters exhibited enhanced ECL efficiency. Therefore, a strong ECL signal was achieved by the dual amplification strategies of target recycle and the intramolecular/intermolecular co-reaction of PEI-Ru(ΙΙ) and TSC. The designed protocol provided an ultrasensitive ECL detection of miR-21 down to the sub-femtomolar level with a linear response about 6 orders of magnitude (from 1.0 × 10(-16)M to 1.0 × 10(-11)M) with a relatively low detection limit of 0.03 fM (S/N=3).

Electrochemiluminescence-based detection method of lead(II) ion via dual enhancement of intermolecular and intramolecular co-reaction.

A novel analytical method to design a highly selective and sensitive detection technique for lead(II) ions (Pb(2+)) detection was developed based on an electrochemiluminescence (ECL) sensor, taking advantage of the high specificity of the aptamer for Pb(2+) and the use of both intermolecular and intramolecular co-reaction to achieve signal enhancement. For sensing interface construction, L-cysteine (Cys) and gold nanostructured layers were electrodeposited on the electrode surface successively, which afforded a large surface area to anchor massive thiol-terminated auxiliary probes (APs) via a thiol-Au interaction. Then, a DNA duplex was generated based on the hybridization of the APs with capture probes (CPs, Pb(2+) specific aptamers). In the presence of Pb(2+), Pb(2+)-induced aptamers were released from the DNA duplex via the formation of a Pb(2+)-stabilized G-quadruplex, accompanied by leaving the single CPs on the sensing interface. Herein, the ruthenium(ii) complexes with functional groups of -COOH (Ru-COOH) were covalently bonded on the polyamidoamine dendrimers with amine end groups (PAMAM), which were capped by the high-index-faceted Au nanoparticles (HIFAuNPs) to obtain the ECL signal labels of Ru-PAMAM-HIFAuNPs. Then, the detection probes (DPs) of amino-terminated Pb(2+) specific aptamers were tagged with the Ru-PAMAM-HIFAuNPs. It was demonstrated that the covalent bonding of PAMAM and Ru-COOH could generate a self-enhanced ECL luminophore by an intramolecular co-reaction and the use of a Cys layer modified electrode could enhance the ECL by the intermolecular co-reaction of Cys and Ru-COOH, which lead to a significant enhancement of the ECL response. Based on this analytical method, the ECL signal increased with Pb(2+) concentration which presented a linear relationship in the range 1.0 × 10(-13)-1.0 × 10(-7) M with the detection limit of 4.0 × 10(-14) M. The proposed approach was also successfully utilized for the determination of Pb(2+) in soil samples.

Highly efficient electrogenerated chemiluminescence quenching of PEI enhanced Ru(bpy)3²âº nanocomposite by hemin and Au@CeO2 nanoparticles.

In this work, a new signal amplified strategy based on the quenching effect of hemin and Au nanoparticles decorated CeO2 nanoparticles (Au@CeO2 NPs) for ultrasensitive detection of thrombin (TB) is reported for the first time. Herein, the poly(ethylenimine) (PEI) enhanced Ru(bpy)3(2+) nanocomposite was implemented by direct chemical polymerization, which could provide the desirable enhanced initial ECL signal. Furthermore, the detection aptamer of thrombin (TBA 2) was immobilized on Au@CeO2 NPs to form TBA 2/Au@CeO2 conjugates. Then, the G-rich DNA of TBA 2 sequence could fold into a G-quadruplex structure to embed hemin to obtain the quenching probe of hemin/TBA 2/Au@CeO2 conjugates. In the presence of target TB, the sandwiched structure could be formed between capture aptamer (TBA 1), TB and hemin/TBA 2/Au@CeO2 conjugates, thereby resulting in a proportional quenching in ECL response with TB, due to the quenching of both hemin and Au@CeO2 NPs. As a result, the signal-off aptasensor showed a wider linear range response from 10(-13) to 10(-8) M with lower detection limit of 0.03 pM.