A low-cost handheld device for monitoring cutaneous photosensitivity

Photodynamic therapy (PDT) has been shown to be clinically effective for multiple cancers with low side effects and minimal off-target toxicity in comparison to traditional anticancer drugs. One of the only widely noted safety considerations for PDT is the potential for residual cutaneous photosensitivity after treatment, especially for protocols where the photosensitizer is administered systemically. The need to monitor cutaneous photosensitivity is particularly important for the implementation of PDT in resource-limited settings where overnight hospitalization is not available. Here, we report a compact, low-cost, cutaneous photosensitivity detection (CPD) device enabling real-time, contact-based fluorescence quantification that can be used as a home health solution for assessing cutaneous phototoxicity risk. The prototype device uses a 405 nm excitation LED, a long-pass emission filter (> 600 nm), and a photodiode to measure protoporphyrin IX (PpIX) fluorescence. Validation in tissue-mimicking phantoms, TR146 oral squamous carcinoma cell models, and murine in vivo studies demonstrates sensitivity within the clinically relevant submicromolar regime (R² > 0.9), accurate capture of aminolaevulinic acid-induced PpIX kinetics, and strong concordance with fluorescence spectroscopy measurements and imaging using a commercial in vivo imaging system. To model the effect of epidermal melanin, we also measure the fluorescence signal as a function of phantom pigmentation using coffee. To further investigate the role of epidermal melanin in attenuating blue excitation light used by this hardware, we ran a series of Monte Carlo simulations modeling light propagation in skin with varying percent melanin corresponding to a range of Fitzpatrick skin types. This study sets the stage for clinical validation of the CPD device as a tool for personalized photoprotection and data-driven discharge decisions following PDT, with relevance for point-of-care and resource-limited settings.