Fig. 2. Designing duty-cycled NIR-emitting devices for remotely-controlled triggering of nanoparticles photothermal effect in the brain over a long-term (15 days) treatment cycle.

(A) Schematics showing the backside and frontside views of the device, and circuit design and components used for their fabrication. Flexibility of the device enables its curvilinear fitting on the mouse skull. (B and C) Representative photograph of a device (scale bar: 3 mm) and scanning electron microscopy at a selected point on the surface of the device showing a 2-μm thick parylene polymer coating (scale bar: 10 μm; also see Supplementary Fig. 15). (D) Thermal image of a device with received power of 19 dBm at the RX coil (λ = 810 nm emission, resulting in ~3 °C temperature difference in a droplet of nanoparticles) (scale bar: 1 mm). (E and F) Conventional approach for wireless powering of the LEDs integrating a matching network, a rectifier, and an optional energy storage capacitor along with a circuit which programs the duty-cycle of the LED. The duty-cycle can be adjusted by employing a switch which allows for a programmable duty-cycle generation (red box) using a continuous input or by modulating the incoming RF signal (red and blue waveforms in (E)). The definition and values of the device power efficiencies are provided in Supplementary Text. (G) Single and (H) back-to-back LED circuit designs used for wireless activation of nanoparticles’ photothermal effect. In single LED design, the LED was only ON for half the cycle, achieving a maximum duty cycle of 31.8%. However, in the back-to-back LED topology, each LED was turned on for half the cycle, and therefore at least one LED was ON during each half-cycle. This effectively doubles the duty-cycle. (I) Evaluation of nanoparticles’ heating effect during irradiations with 810-nm and 940-nm devices. Graph shows variations of nanoparticles’ ΔT with voltage amplitude (peak voltage, V_p) with a sinusoidal input. A peak voltage of around 4 V (~ 80 mW input power) resulted in ~3 °C temperature difference in a droplet of nanoparticles deposited on top of a coverslip, due to their photothermal response. TEM analysis of the nanostars (Supplementary Fig. 8) shows their morphological stability after 15 min photothermal activation for 15 consecutive days, verifying that duty-cycled irradiation of the nanoparticles with our back-to-back LED design helped to maintain the morphology of the nanoparticles and is suitable for long-term and consistent photothermal heating in the brain.