Fig. 2: Characterization of subcellular-sized electronics with optical remote control.

a, Schematic energy diagram illustrating the working principle of the photovoltaic devices (three-layered device based on organic polymers) and the final device structure developed. OSC, organic semiconductor. b, SEM images of the SWEDs fabricated at wafer scale. SWED structure, PEDOT:PSS|P3HT:PCBM|Ti. Scale bar, 10 µm (inset, 1 µm), n = 5. c, Schematic diagram of the setup used for in-air and ex vivo measurements. The devices were illuminated from the bottom with a laser. For ex vivo measurements, brain tissue or whole brain with the skull was placed on a no. 1.5 cover slip (while keeping the tissue wet in PBS) and in close contact with the devices. The microscope was used to assist with alignment while probing the devices from the top using the three-stage micromanipulators. The probes were connected to a potentiostat and the laser was operated in continuous-wave mode to obtain the current–voltage (I–V) curves. In-air measurements were as follows: d, Representative plot showing the power generated by different-sized devices as a function of applied voltage. Device structure, PEDOT:PSS|P3HT:PCBM|Ti, Intensity 10 mW mm⁻² incident on the devices, n > 5 devices. Legend, device diameter. e, Representative I–V characteristics of a SWED (10 µm in diameter) for varied light intensities incident on the SWED. SWED structure, PEDOT:PSS|P3HT:PCBM|Ti, n > 5 devices. A 520-nm wavelength laser was used as the light source for d and e. Ex vivo measurements: f, Representative I–V plot for the SWEDs (10 µm in diameter) with light passing through different thicknesses of brain slices or whole brain (6.1 ± 0.3 mm) or whole brain with skull (6.5 ± 0.3 mm). The transmittance of NIR penetration through the brain tissue was measured and is presented in Supplementary Fig. 9 (Methods section ‘NIR light transmittance measurements’). SWED structure, PEDOT:PSS|PCPDTBT:PCBM|Ti, n = 3 devices. Laser, 792 nm; intensity, 24.6 mW mm⁻² incident on the bottom surface of the brain. g, Maximum power generated by the SWEDs (10 µm in diameter) with light passing through the whole brain without the skull (and the whole brain with an intact skull) at different light intensities (792 nm) incident on the bottom surface of the brain. SWED structure, PEDOT:PSS|PCPDTBT:PCBM|Ti, values represent median ± standard deviation (s.d.) (n = 5 devices). h, Box plot showing the multiplexing effect using the two SWED structures (10 µm in diameter) we have developed: PEDOT:PSS|PCPDTBT:PCBM|Ti and PEDOT:PSS|P3HT:PCBM|Ti. The plot shows the mean (circle within the box), median (horizontal line within the box), lower and upper quartile (delineated by the box), whiskers extending to the most extreme data points within 1.5× IQR from the quartiles, with minima and maxima beyond this range shown as individual outlier points (n = 3 devices per condition). The inset shows the absorption coefficients for the two SWED structures indicating their orthogonal absorption coefficients at the operating wavelengths. Labels, α (absorption coefficient, ×10⁵ cm⁻¹) and λ (wavelength, nm). The measurements were done with light passing through a 0.5-mm-thick brain tissue slice. Intensities used for this measurement were 10 mW mm⁻² (520 nm) and 2 mW mm⁻² (785 nm) incident on the bottom surface of the brain slice.

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