We have developed an effective molecular engineering mechanism which senses the metal ion controlled DNAzyme catalytic reactions, thus generating a sensitive metal ion sensing probe. DNAzymes are DNA sequences that catalyze chemical reactions, such as cleaving ribonucleic acid targets. 1 Among the DNAzymes attracting most attention are those that are divalent metal ion cofactor-specific. Accordingly, DNAzyme-based sensors have been reported for such metal ions as Cu 2+,2 Zn 2+,3 Pb 2+,4 Hg 2+,5 UO 2 2+6 and Ca 2+ . 7 Focusing on the development of DNAzyme-based probes for metal ions, many different design principles have been advanced. One strategy utilizes a molecular beacon consisting of two oligos: DNAzyme and substrate. Upon target ion binding, the dye-labeled substrates quenched by a quenchermodified DNAzyme are irreversibly cleaved and released to produce a fluorescent signal. 2,4,6 Another probe design uses the conformation alteration that results from the cleavage of substrate by the DNAzyme. In this case, the horseradish peroxidase (HRP)-mimicking DNAzyme is activated by a cleavage process, thus generating colorimetric or chemiluminescence readout signals. The Willner group has made significant advancements in this field. For example, they employed Pb 2+ and L-histidine-dependent DNAzymes, yielding HRP-mimicking nucleic acids that enable the colorimetric detection of Pb 2+ and L-histidine, 8 or used catalytic nucleic acid as labels to detect DNA and investigate the telomerase activity. 9 They also designed an autonomous DNA-based machine to amplify the detection of M13 phage single-stranded DNA 10 (ssDNA) and used it to detect the Hg 2+ ion. 11 These approaches do offer a general means of DNAzyme-based probe design, but they mostly still involve complicated modifications to DNAzyme and the hybridization of two oligos: annealing of the DNAzyme and substrate strands. These, however, are limitations that prevent applications such as on-site detection with sensitivity and stability. To address these problems, Wang et al. recently proposed covalently linking the DNAzyme and leaving a substrate fragment with polythymine to create a unimolecular beacon with a strong intramolcular interaction for lead ion monitoring. 12 Herein, we report the development of a novel and versatile allosteric dualDNAzyme unimolecular probe with simple and label-free design. As illustrated in Scheme 1, this unimolecular probe is a combination of a DNA-cleaving DNAzyme (D-DNAzyme) and a HRP-mimicking DNAzyme (H-DNAzyme), including three main components. Domain I is the substrate of DNA-DNAzyme. Domain II includes the sequence of the H-DNAzyme, and Domain III represents the D-DNAzyme. In the absence of target metal ion, these three domains act cooperatively in DNA-cleaving active state due to strong intra-molecular interaction, and the resulting structure reveals higher stability than the G-quadruplex structure ( H-DNAzyme). Conversely, when the probe meets its target, the cleavage of substrate by DDNAzyme will disturb the intramolecu...
As one of the effective measures of intelligent traffic control, on-ramp metering is often used to improve the traffic efficiency of expressways. Existing on-ramp metering research mainly discusses expressways with right-side on-ramps. However, for underground expressway systems (UESs), left-side on-ramps are frequently adopted to reduce the ground space occupied by ramp construction. Since traffic entering from the left and right sides of the mainline may have different traffic characteristics, on-ramp metering for UESs with left-side on-ramps should be explored specifically. This study examines the impacts of left-side on-ramps on the traffic safety and efficiency of UESs and proposes an effective on-ramp metering strategy. Firstly, using field data, traffic flow fundamental diagrams and speed dispersion are discussed to explore the traffic flow characteristics of the “left-in” UES. The results show that the capacity and critical occupancy are both reduced in left-side on-ramp compared to right-side on-ramp expressways. Meanwhile, the speed dispersion is higher in left-side on-ramp UESs, which means a higher accident risk. Based on this, considering traffic safety and efficiency, a novel two-parameter left-side on-ramp metering strategy for UESs is proposed, in which occupancy and speed are used as the control indicators simultaneously. Additionally, the mechanism of the metering strategy is explained. Finally, the proposed on-ramp metering strategy is simulated on a real UES. The results demonstrate the advantages of the proposed two-parameter on-ramp metering strategy for improving the traffic safety and efficiency of UESs.
Passenger orientation (pathfinding) is an important factor in designing the layout of comprehensive transportation hubs, especially for static guidance sign systems. In essence, static guidance signs within the hub should be designed according to passengers’ pathfinding demand, that is, to provide passengers with accurate information at the appropriate location. Therefore, from the perspective of passenger information demand, this study aims to determine the appropriate location and density of static guidance information. Two types of passenger information demand in the pathfinding process are defined in this study: one is generated at the path decision point, where multiple path options exist; the other is at the points between decision points, where pathfinders need to confirm that they are still on the correct path. According to the interaction of pathfinding behavior and guidance information, the abstract relationship model is established between macro-behavioral characteristics and the micro-psychological state. Moreover, based on walking speed analysis, the judgment criterion of passenger psychology in pathfinding is proposed to determine the spatial location and density of guidance information. The analysis results of Shanghai Hongqiao International Airport show that, under the threshold of the speed drop section given in the study, 80% of passenger information demand is satisfied when guidance information spacing is 47 m, and 60% of information demand is satisfied when the spacing is 56 m. The findings presented in this paper can provide a reference for the optimal design of static guidance information in comprehensive transportation hubs.
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