Aptamer conformations are susceptible to environmental conditions, which makes it difficult to achieve stable targets detection in complex environments with aptasensors. Imprinting strategy was proposed to immobilize the specific conformation of aptamers, aiming to enhance their recognition anti-interference. However, it is mechanistically unclear how the imprinted polymers affect aptamers' recognition, which limits application of the strategy. Herein, MD simulation was applied to explore the structural reason why nanogel imprinting improves binding affinity and selectivity of T30695 aptamer to Pb 2+ observed experimentally. Results show the imprinted polymers stabilize the domain-limited T30695 by noncovalent interactions. The coating process undergoes three evolution stages, finally achieving a polymer-aptamer-polymer sandwich-shaped conformation. Notably, it was found the polymers provide additional non-specific binding of Pb 2+ at acylamine group of acrylamide monomers, which accounts for the improved binding affinity with association constant K a 2.5 times larger. More importantly, imprinting enhances selectivity of aptamer to Pb 2+ by changing coordination mode of interfering ions (Ca 2+ , K + , Mg 2+ , NH 4 + and Cu 2+ ), which significantly destroys G-quadruplex conformation and thus its binding ability. This work revealed mechanistic effects of imprinting strategy on aptamers recognition at molecular level, which can guide rational design of high-performance aptamer-based biosensors applied in various detection areas.
A novel electrochemiluminescence (ECL) biosensor based on CdSe@CdS quantum dots (QDs) functionalized MoS2 modified electrode was developed for sensitive detection of Pb(II) using HRP-mimicking DNAzyme biocatalytic precipitation (BCP) for ECL signal quenching. Polycationic poly(diallyldimethylammonium chloride) (PDDA) and negatively charged QDs were adsorbed on the surface of MoS2, in sequence, to form the MoS2–QDs composites, which were employed as a matrix for the immobilization of the G-rich DNA strand, i.e., T30695. The MoS2–QDs were characterized by UV-vis absorption spectroscopy, fluorescence spectroscopy, energy dispersive spectrometry, transmission electron microscopy, and field emission scanning electron microscopy. CdSe@CdS QDs can produce an ECL signal using 0.1 M K2S2O8 as a co-reactant. T30695 can combine with Pb(II) ions to form a stable parallel G-quadruplex. The G-quadruplex can further combine with hemin to form DNAzyme, which can catalyze H2O2 and oxidize 4-chloro-1-naphthol (4-CN) to produce an insoluble precipitation of benzo-4-chlorohexadienone on the surface of the sensor. When the concentration of Pb(II) in the solution was increased, more of DNAzyme was generated and subsequently more 4-CN molecules were oxidized catalytically, leading to a decrease of the ECL signal. Using this quenching strategy, the ECL signal of the biosensor was linearly dependent on the logarithm of the Pb(II) concentration ranging from 1.0 × 10−15 to 1.0 × 10−11 M with a detection limit of 0.98 f M. The stability and selectivity of the sensor were also investigated. The sensor was applied in the determination of Pb(II) in the real water samples and satisfactory results were obtained.
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