The detection of acoustic signals is of relevance for a range of practical applications, for example in medical diagnostics. However, whereas rectification of electric current and other energy forms such as thermal flux has been demonstrated, acoustic rectification has not yet been achieved. Here, on the basis of the earlier theoretical proposal of an 'acoustic diode', we present the first experimental demonstration of a rectified energy flux of acoustic waves. A one-dimensional acoustic rectifier is fabricated by coupling a superlattice with a layer of ultrasound contrast agent microbubble suspension. A significant rectifying effect is observed within two frequency bands at locations that agree well with theoretical predictions. Following optimization of the concentration of the microbubble suspension, rectifying ratios can be as high as ~10(4). This realization of an acoustic rectifier should have substantial practical significance, for example in the focusing of ultrasound in medical applications.

Sonodynamic therapy (SDT) activated by ultrasound is attractive as a potential alternative to conventional phototriggered therapies owing to the deeper penetration depth and the absence of phototoxicity. Nevertheless, the low quantum yield of nano‐sonosensitizer and the tumor hypoxia remain significant challenges for SDT. Herein, a novel TiO2‐based nano‐sonosensitizer is reported to bilaterally enhance the quantum yield by simultaneous integration of precious metal Pt nanoparticles (NPs) and an oxygen‐deficient layer. Furthermore, the hollow cavity of TiO2 serves as a reservoir to load doxorubicin, an anticancer drug for chemotherapy as well as a molecular sonosensitizer for SDT. The decorated Pt NPs act as nanozymes to catalyze the decomposition of endogenous hydrogen peroxide for the generation of oxygen to alleviate tumor hypoxia, reduce resistance to chemotherapy, and provide sufficient oxygen source for subsequently facilitating SDT‐induced reactive oxygen species production. The high chemo‐sonodynamic synergistic efficacy is systematically demonstrated both in vitro and in vivo. More importantly, it is believed that the novel design and the new finding in the synthesis of Pt–TiO2 heterostructures can be popularized for the preparation and application of the semiconductor‐based nanoplatforms in many fields.

Focusing and enriching submicrometer and nanometer scale objects is of great importance for many applications in biology, chemistry, engineering, and medicine. Here, we present an acoustofluidic chip that can generate single vortex acoustic streaming inside a glass capillary through using low-power acoustic waves (only 5 V is required). The single vortex acoustic streaming that is generated, in conjunction with the acoustic radiation force, is able to enrich submicrometer- and nanometersized particles in a small volume. Numerical simulations were used to elucidate the mechanism of the single vortex formation and were verified experimentally, demonstrating the focusing of silica and polystyrene particles ranging in diameter from 80 to 500 nm. Moreover, the acoustofluidic chip was used to conduct an immunoassay in which nanoparticles that captured fluorescently labeled biomarkers were concentrated to enhance the emitted signal. With its advantages in simplicity, functionality, and power consumption, the acoustofluidic chip we present here is promising for many point-of-care applications.