With increasing peak voltage applied to a plasma jet, surface discharge patterns are formed on the dielectric target, which include diffuse spot, single ring, and concentric triple rings. During the evolvement of these patterns, the number of positive current pulses increases and there is only one negative pulse per voltage cycle. Fast photography reveals that all of these patterns originate from temporal superposition of negative and positive surface discharges. The negative surface discharge is always diffused for each pattern. However, the positive surface discharges in a streamer regime are more complicated. The first positive streamer per voltage cycle is short, which propagates along radial spokes that are distributed symmetrically, resulting in a central spot of each pattern. The last positive streamer per voltage cycle is long, which propagates along a straight line at a lower peak voltage and bifurcates randomly at a higher peak voltage, resulting in diffuse background of each pattern. Other positive streamers also bifurcate after traveling certain distance from the center, and then propagate along an arc, leading to the formation of ring in patterns. The propagation behaviors of these positive streamers are discussed qualitatively by analyzing the influence of applied electric field, residual charges, and air diffusion.
Efficient drug delivery into tumor cells while bypassing many biological barriers is still a challenge for cancer therapy. By taking advantage of the palladium (Pd)-mediated in situ activation of a prodrug and the glucose oxidase (GOD)-based β-Dglucose oxidation reaction, we developed a multisynergistic cancer therapeutic platform that combined doxorubicin (DOX)-induced chemotherapy with GOD-mediated cancer-orchestrated oxidation therapy and cancer starvation therapy. In the present work, we first synthesized DOX prodrugs (pDOXs) and temporarily assembled them with β-cyclodextrins to reduce their toxic side effects. Then, a nanoreactor was constructed by synthesizing Pd 0 nanoparticles in situ within the pores of mesoporous silica nanoparticles for the conversion of pDOX into the active anticancer drug. Furthermore, GOD was introduced to decrease the pH of the tumor microenvironment and induce cancer-orchestrated oxidation/starvation therapy by catalyzing β-D-glucose oxidation to form hydrogen peroxide (H 2 O 2 ) and gluconic acid. Our study provides a new strategy that employs a cascade chemical reaction to achieve combined orchestrated oxidation/starvation/chemotherapy for the synergistic killing of cancer cells and the suppression of tumor growth.
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