ABSTRACT
The development of COVID-19 detection strategies with high sensitivity and selectivity are urgent for early diagnosis. Herein, we constructed an electrochemical dual-aptamer biosensor based on the metal organic frameworks MIL-53(Al) decorated with Au@Pt nanoparticles and enzymes to determine SARSCoV-2 nucleocapsid protein (2019-nCoV-NP) via co-catalysis of the nanomaterials, horseradish peroxidase (HRP) and G-quadruplex DNAzyme. First, the two thiol-modified aptamers (N48 and N61), as recognition elements, were immobilized on the surface of gold electrode (GE) to capture the biomarker 2019nCoV-NP. Then, the nanomaterial composites Au@Pt/MIL-53 (Al) were decorated by HRP and hemin/Gquadruplex DNAzyme as signal nanoprobe. The designed nanoprobe was applied to amplifying the aptasensor signal via co-catalyzing the oxidation of hydroquinone in the presence of hydrogen peroxide. Finally, the aptamer-protein-nanoprobe sandwich electrochemical detection system was fabricated on the GE surface. The results demonstrated that this aptasensor had a wide linear range from 0.025 to 50 ng mL -1 and the detection limit was 8.33 pg mL -1 for 2019-nCoV-NP. This aptasensor has great potential in the early diagnosis of COVID-19 with high sensitivity, selectivity and reliability. (c) 2021 Elsevier Ltd. All rights reserved.
ABSTRACT
During the COVID-19 lockdown period (from January 23 to February 29, 2020), ambient PM2.5 concentrations in the Yangtze River Delta (YRD) region were observed to be much lower, while the maximum daily 8 h average (MDA8) O-3 concentrations became much higher compared to those before the lockdown (from January 1 to 22, 2020). Here, we show that emission reduction is the major driving force for the PM2.5 change, contributing to a PM2.5 decrease by 37% to 55% in the four YRD major cities (i.e., Shanghai, Hangzhou, Nanjing, and Hefei), but the MDA8 O-3 increase is driven by both emission reduction (29%-52%) and variation in meteorological conditions (17%-49%). Among all pollutants, reduction in emissions mainly of primary PM contributes to a PM2.5 decrease by 28% to 46%, and NOx emission reduction contributes 7% to 10%. Although NOx emission reduction dominates the MDA8 O-3 increase (38%-59%), volatile organic compounds (VOCs) emission reduction lead to a 5% to 9% MDA8 O-3 decrease. Increased O-3 promotes secondary aerosol formation and partially offsets the decrease of PM2.5 caused by the primary PM emission reductions. The results demonstrate that more coordinated air pollution control strategies are needed in YRD.