Fig. 9: Label-free measurement of onion epidermal cells.

a Surface morphology of onion monolayer epidermal cell wall covered on the gold-film SPR chip observed by the dark-field microscope. b Spectral SPR image of the same onion cell area as in Fig. 9a. c Single-pixel SPR spectrum of the exposed gold film (without coverage) and the SPR spectrum at the pixel marked A in the cell wall covered area in Fig. 9b. d Measured PWR spectrum at the pixel marked B in the cell wall covered area in Fig. 9b. The simulated spectrum is also shown for quantifying the cell wall thickness and RI. e 2D thickness distribution of the cell walls attached to the substrate. f 2D effective RI distribution of the cell walls attached to the substrate. The similar results were obtained with two independent measurements.