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A label-free aptasensor was developed for ultrasensitive detection of Pb2+ based on electrochemiluminescence resonance energy transfer (ECL-RET) from graphitic carbon nitride nanofibers (CNNFs) to Ru(phen)32+. The CNNFs synthesized via a facile two-step hydrolysis-electrolysis strategy showed intense and stable ECL signal by taking advantages of amplifying and stabilizing effect of carbon nanotubes and Au nanoparticles. After the specific hybridation between capture DNA and Pb2+ specific aptamer, Ru(phen)32+ could be captured onto CNNFs modified electrode by effectively intercalating into the grooves of double-strand DNA, thus triggering the ECL-RET and leading to highly enhanced ECL intensity. The presence of Pb2+ would result in the detachment of Ru(phen)32+ and then the inhibition of ECL-RET. Then Pb2+ concentration could be quantified based on ECL change before and after introduction of Pb2+. The target recycling based on exonuclease I (Exo I) mediated digestion of Pb2+-aptamer complex was implemented to further improve the sensitivity. These synergistic amplification strategies enabled the aptasensor to be ultrasensitive for Pb2+ determination with a detection limit of 0.04 pM. The proposed probe was utilized to analyze environmental samples with satisfactory results.

A feasible label-free electrochemiluminescence (ECL) aptasensor that uses an Au-nanoparticle-functionalized g-C3N4 nanohybrid (Au-g-C3N4 NH) as the luminophore was constructed for highly sensitive acetylcholinesterase (AChE) detection. The sensor was fabricated by successively modifying a glassy carbon electrode with Au-g-C3N4 NH and thiol-modified AChE-specific aptamers. In the presence of AChE, the ECL signal decreased significantly, because AChE could hydrolyze the substrate acetylthiocholine to generate acetic acid, which could react with the co-reactant triethylamine (Et3N), leading to evident consumption of the co-reactant. The ECL response of the aptasensor was linearly proportional to the concentration of AChE ranging from 0.1 pg/mL to 10 ng/mL, with a detection limit of 42.3 fg/mL (S/N=3). This novel ECL sensing strategy demonstrated a highly sensitive and selective method for AChE detection and was expected to possess potential applications in clinical diagnosis and biomedical technology.

A high-amylose starch was prepared from ginkgo by hydrolysis using isoamylase and its structures (morphology and crystallinity) and physicochemical properties (swelling factor, water solubility and gelatinization) were determined. The experiments used response surface methodology to determine the optimum parameters for enzymatic hydrolysis: pH 5.0 at 52 °C for 170 min, using an enzyme dose greater than 100 IU/ml. The experimentally observed maximum yield of ginkgo amylose under these conditions was 74.74% and the blue value was 0.756. The high-amylose ginkgo starch showed an irregular surface and porous inner structure while the native starch granules were oval with a smooth surface. X-ray showed that the high-amylose starch displayed a V-type structure. Because of its high amylose content and different structural characteristics, high-amylose starch exhibited a higher gelatinization peak temperature (109.25 °C) and water solubility, and a lower crystallinity (19.13%), gelatinization enthalpy (63.83 J/g), and swelling power. The present study has indicated that high-amylose starch prepared using isoamylase has unique functional properties, which lays the foundation for the wider application of ginkgo starch.

Ginkgo biloba seed starch was isolated and its morphological, compositional, physicochemical, and structural characteristics, and in-vitro enzymatic hydrolysis, were investigated. Ginkgo starch granules were oval or spherical (5–20 μm) with a smooth surface. Compared with normal maize and potato starches, ginkgo starch had a significantly higher amylose content of 33.26%, a C A -type crystal pattern and a significantly higher crystallinity degree (40.2%). Because of its different chemical composition and structural characteristics, ginkgo starch exhibited a higher pasting temperature (80.95 °C), setback viscosity (1463 cP), gelatinization temperature (69.23 °C), lower swelling factor and gelatinization enthalpy (4.34 J/g). Moreover, ginkgo starch showed the lowest hydrolysis degree of the three starches in vitro , indicating its higher resistance to α-amylase digestibility in the case of retrogradation. The present study demonstrated that ginkgo starch is a robust and potentially useful nutritional source of enzyme-resistant starch, and provides useful information for food industries using ginkgo seeds.