A Wireless, Multicolor Fluorescence Image Sensor Implant for Real-Time Monitoring in Cancer Therapy

Real-time monitoring of dynamic biological processes in the body is critical to understanding disease progression and treatment response. This data, for instance, can help address the lower than 50% response rates to cancer immunotherapy. However, current clinical imaging modalities lack the molecular contrast, resolution, and chronic usability for rapid and accurate response assessments. Here, we present a fully wireless image sensor featuring a 2.5$\times$5 mm$^2$ CMOS integrated circuit for multicolor fluorescence imaging deep in tissue. The sensor operates wirelessly via ultrasound (US) at 5 cm depth in oil, harvesting energy with 221 mW/cm$^{2}$ incident US power density (31% of FDA limits) and backscattering data at 13 kbps with a bit error rate <$10^{-6}$. In-situ fluorescence excitation is provided by micro-laser diodes controlled with a programmable on-chip driver. An optical frontend combining a multi-bandpass interference filter and a fiber optic plate provides >6 OD excitation blocking and enables three-color imaging for detecting multiple cell types. A 36$\times$40-pixel array captures images with <125 $μ$m resolution. We demonstrate wireless, dual-color fluorescence imaging of both effector and suppressor immune cells in ex vivo mouse tumor samples with and without immunotherapy. These results show promise for providing rapid insight into therapeutic response and resistance, guiding personalized medicine.

💡 Research Summary

This paper presents a fully wireless, miniaturized fluorescence imaging implant designed for real‑time monitoring of immune responses during cancer immunotherapy. The core of the system is a 2.5 × 5 mm² CMOS ASIC that integrates a 36 × 40 pixel array (≤125 µm resolution), three programmable micro‑laser diodes (λ = 455 nm, 650 nm, 785 nm), and a multi‑bandpass interference filter coupled to a fiber‑optic plate (FOP). Power and bidirectional communication are achieved via ultrasound (US) at 1 MHz. With an incident US intensity of 221 mW/cm²—only 31 % of the FDA limit—the implant harvests enough energy to operate at a depth of 5 cm in oil, while backscattering data at 13 kbps with a bit‑error rate below 10⁻⁶.

The optical front‑end provides >6 optical density (OD) attenuation of excitation light across all three laser wavelengths, thanks to the combination of a three‑passband interference filter (centered at ~500 nm, ~650 nm, and ~800 nm) and the angular filtering properties of the FOP. This design mitigates the angle‑dependent shift of interference filters, ensuring robust excitation rejection even in a lens‑less, contact‑imaging configuration. The programmable laser driver accommodates forward voltages ranging from 2 V to 4.5 V, enabling independent control of each µLD while maintaining high wall‑plug efficiency.

The ASIC’s power‑management circuitry includes a rectifier, voltage regulator, and storage capacitor, allowing continuous operation during the US power‑on window and efficient data transmission during the off‑window. The backscatter communication scheme modulates the acoustic impedance of the piezoelectric transducer, achieving reliable uplink without additional RF components.

In ex‑vivo experiments, mouse tumor sections were stained with fluorescein (FAM) to label effector immune cells and cyanine‑5 (Cy5) for suppressor cells. Dual‑color imaging captured spatial distributions of both populations before and after checkpoint‑inhibitor treatment. The system resolved distinct fluorescence signals, demonstrating the ability to assess therapeutic response at the cellular level within minutes, far faster than conventional histology or PET imaging.

Compared with prior wireless fluorescence sensors, this work reduces the implant volume to 0.09 cm³, eliminates the need for bulky batteries, expands from single‑color to three‑color imaging, and operates safely at clinically relevant depths and power levels. The authors discuss pathways toward chronic implantation, including long‑term biocompatibility testing, integration with FDA‑approved fluorophores, and scaling to higher pixel counts for finer spatial resolution. Overall, the study establishes a viable platform for continuous, multiplexed molecular imaging inside the body, offering a new tool for personalized oncology and potentially other biomedical applications.