Xin Huang,Limin He,Xiaoming Luo,Ke Xu,Yuling Lü,Donghai Yang
The dynamic behaviors of two droplets and droplet cluster under an alternating current (AC) electric field are investigated. Two droplets generally undergo transformation from complete coalescence to partial coalescence and finally to non-coalescence as the electric capillary number Ca p increases. The critical electric capillary number Ca pc for complete coalescence in the AC electric field remains unchanged and is twice as large as that in the direct current (DC) electric field when the frequency f ≥ 250 Hz. Charge transfer and reversal of electric field result in the reversal of the direction of electric force, which is the fundamental mechanism of non-coalescence of two droplets and chain formation in droplet cluster. The number of rebounds dramatically increases as f increases, promoting the stability of droplet chain. The droplet chains in the high-frequency AC electric field are longer and more stable than those in the low-frequency AC electric field.
DNA apurinic/apyrimidinic site (AP site) has received much attention due to its importance in disease evolution and development of selective genetic drugs. Fluorescence technique has been widely employed in identifying the AP sequence environment using fluorophores as the AP site-targeting probes. However, the sequence effect on the AP site binding of a ligand should be fully understood for illustrating the binding behavior. Triplex-forming oligonucleotide (TFO) can bind with its partner ds-DNA via specific hydrogen bonding interactions different from the canonical Watson-Crick pattern to form a triplex DNA structure . Due to its wide bioactivity, triplex has been recently investigated using small molecules as the structure identifiers and tuners. In this work, we spectroscopically characterized a novel fluorescent benz[ e ]indolium probe of BIFS and found that BIFS can selectively target the AP site and its fluorescence is significantly enhanced only when the TFO strand binds to the AP site-containing duplex DNA. The TFO binding restricts the non-radiative twist relaxation process of the excited state BIFS and results in the emissive BIFS. Because BIFS alone in aqueous solution is non-fluorescent, this selective lighting-up emission is advantageous for developing a practical sensor to target the triplex AP site with a weak fluorescence background. This selective recognition of the AP site by the lighting-up fluorescent probe would find wide applications including fluorescently evaluating the triplex-based small molecular binders.
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