Fig. 2

Experimental setup and working principle of scRAFA. a Experimental setup of scRAFA. Two laser beams with wavelengths of 785 nm and 532 nm are focused at the same position on the substrate to trap and rotate a single cell. The inset illustrates that the receptors of the rotating cell interact with ligand molecules immobilized on the substrate. The motion of the cell is monitored by in situ optical imaging through a digital camera. BS: beam splitter. BE: beam expander. HWP: half-wave plate. ODF: optical density filter. FL: focused lens. b, c A sequence of optical images of the trapping and rotation of a single cell. Scale bars: 5 μm. d Cross-sectional view of the flow velocity near the light-absorbing substrate where the optically trapped cell undergoes out-of-plane rotation. Scale bar: 1 μm. e The rotational frequency of the trapped cell under different optical power of 532 nm laser. The optical power of 785 nm laser is 1 mW/μm² in all studies. f Time-dependent experimental spectral red shift collected from a rotating cell. g Simulated spectral red shift (Δλ) with different distances between the cell and the substrate (h) (gray line) along with the experimental spectral red shifts (blue line) and the extracted cell-substrate distance (red line). The red double arrow corresponds to the extracted cell-substrate distance