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A label-free electrogenerated chemiluminescence (ECL) aptasensing method for highly sensitive determination of dopamine (DA) was developed based on target-induced DNA conformational change. After anti-DA specific aptamer, as molecular recognition element, was hybridized with a capture ss-DNA (complementary with the aptamer), the formed double-strand DNA (ds-DNA) was self-assembled onto the surface of a gold electrode, and then Ru(phen) 3 2+ , as ECL reagent, was intercalated into ds-DNA to form an ECL biosensing platform. In the presence of DA, DA bound with its aptamer and target-induced DNA conformational change occurred, resulting in the dissociation of ds-DNA, the release of intercalated Ru(phen) 3 2+ from the electrode surface, and the decrease of ECL intensity. For comparison, an ECL aptamer-based biosensing method using an ECL reagent-labeled aptamer was also developed for DA assay based on target-induced DNA conformational change. Because of the increase in the amount of ECL reagent into ds-DNA over that of the single-site ECL reagent-labeled aptamer, an obvious increase of ECL intensity was found at the ds-DNA modified electrode over the aptamer modified electrode. DA can be sensitively detected with a lower detection limit of 0.05 nM in the range from 0.1 to 100 nM. With the recognition of the aptamer for DA, DA can be selectively and sensitively detected in artificial cerebrospinal fluid and serum samples without interference from common small molecules. This work demonstrates that the combination of the direct transduction of specific recognition of DA and its aptamer into an ECL signal with Ru(phen) 3 2+ intercalated ds-DNA amplification provides a promising strategy for the development of a simple, sensitive, and selective method for DA assay, which is of great importance in neurochemical assays and clinical diagnosis.

Developing water-stable and adaptive supramolecular materials is of great importance in various research fields. Here, we demonstrate a new kind of water-stable, adaptive, and electroactive supramolecular ionic materials (SIM) that is formed from the aqueous solutions of imidazolium-based dication and dianionic dye (i.e., 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), ABTS) through ionic self-assembly. The formed SIM not only shows good thermostability and unique optical and electrochemical properties that are raised from precursors of the SIM, but also exhibits good water-stability, salt-stability, and adaptive encapsulation properties toward some heterocyclic cationic dye molecules. UV-vis and FT-IR results demonstrate that this encapsulation property is essentially based on the electrostatic interactions between the guest dye molecules and ABTS in the SIM. The application of the SIM prepared here is illustrated by the development of a new electrochemical sensor for NADH sensing at a low potential. This study not only opens a new avenue to the preparation of the supramolecular materials, but also provides a versatile platform for electrochemical (bio)sensing.

This study demonstrates a facile yet effective strategy for amperometric assay of electrochemically inactive heparin based on an anion-exchange mechanism with polyimidazolium (Pim) as the synthetic receptor. The rationale for the amperometric heparin assay is essentially based on the different binding affinity of the synthetic Pim receptor toward electrochemically active ferricyanide (Fe(CN)6(3-)) and electrochemically inactive heparin. To accomplish the amperometric assay, Pim is first synthesized and used as the artificial receptor to recognize the anions (i.e., Fe(CN)6(3-) and heparin). The stronger binding affinity of the synthetic Pim receptor toward heparin than toward Fe(CN)6(3-) essentially validates the amperometric heparin assay through an anion-exchange mechanism with the decrease in the redox peak current of Fe(CN)6(3-) adsorbed onto the Pim film as the signal readout. The anion exchange between Fe(CN)6(3-) and heparin on the Pim receptor is verified by cyclic voltammetry and Fourier transform IR and UV-visible spectroscopies. The ratio of the current decrease shows a linear relationship with heparin concentration with a concentration range from 0.5 to 10 μM. With animal experiments by dosing intraperitoneally and collecting the serum sample, the method is demonstrated to be potentially useful for investigating heparin metabolism in the biological system. This study not only provides a simple yet effective route to a heparin assay but also opens a new way to developing amperometric methods for electrochemically inert species by fully utilizing the supramolecular principles.