Disclosed herein include methods, compositions, and kits suitable for use in sorting a population of cells. In some embodiments, the method comprises flowing a fluid sample comprising a population of cells through a microfluidic channel. The population of cells can be configured to express gas vesicles (GVs) in a context-dependent manner. The expression of GVs within a cell can increase the compressibility (β) and reduce the density (ρ) of said cell, thereby modulating the acoustic contrast (Φ) of said cell relative to the fluid in the microfluidic channel. The method can comprise applying ultrasound to the microfluidic channel. Applying ultrasound can generate acoustic standing wave(s) in the microfluidic channel, thereby positioning pressure antinode(s) in the microfluidic channel.