Lifting active matter into three dimensions using buoyancy control and external alignment

Sedimentation and gyrotaxis from metallic coatings in synthetic active matter confine particles to quasi-two-dimensional, wall-dominated states. To sustain a true three-dimensional distribution, both effects must be mitigated. Here, density matching in a glycerol/deionized water mixture (counteracting sedimentation) is combined with a uniform ac electric field that aligns and propels particles, minimizing gyrotaxis. Measurement of near-wall and bulk mobilities is now possible, revealing frequency-dependent particle-wall interactions consistent with theory. The method can be extended to other active systems to probe confinement effects and nonequilibrium behavior.