Spectrally tailored hyperpixel filter arrays for efficient imaging of chemical compositions

Taylor-Williams, Michaela; Cousins, Richard; Williams, Calum; Bohndiek, Sarah E.; Mellor, Christopher J.; Gordon, George S. D.

Abstract

We present a method for designing and fabricating 'HyperPixels': pixel filter arrays with custom spectral transmission properties that enable efficient imaging of specific chromophores or fluorophores. Multispectral imaging typically targets particular spectral bands to uncover the spectral properties of tissue in combination with spatial resolution. Unmixing spectral properties can uncover the type and quantity of chromophores or fluorophores due to their unique spectral absorption or emission. Pixelated filter arrays atop imaging sensors are low-cost techniques used to achieve multispectral imaging. Typically, the filter pixels exhibit bandpass spectral behaviour, allowing only a fraction of the incident light to reach the sensor. As a result, narrowband filter pixels trade off high spectral resolution with optical power loss. A way to avoid this issue and improve the signal to noise ratio (SNR) for individual targets is to use a filter array where individual pixels are matched to a target chemical compound's reflectance or emission spectrum. Simulations show a > 5-fold improvement in SNR under realistic noise conditions. These matched optical filters can also reduce the complexity of software or hardware spectral unmixing algorithms, offering the potential for real-time imaging of target compounds. We present a method for tailoring spectral transmission of individual pixels by building HyperPixels comprising multiple Fabry-Perot resonator subpixels with varying bandpass properties (FWHM = approximately 50-60 nm, thicknesses 75-150 nm) that collectively have the desired transmission spectrum. We used a numerical optimization process to design filter arrays for simultaneous detection of methylene blue and indocyanine green, commonly used in cancer diagnostics by clinicians. We then fabricated filters for indocyanine green detection using grayscale lithography with pixel sizes down to 5 µm and individual subpixels down to 0.5 µm and characterized them for their spectral properties.

Citation

Taylor-Williams, M., Cousins, R., Williams, C., Bohndiek, S. E., Mellor, C. J., & Gordon, G. S. D. (2022). Spectrally tailored hyperpixel filter arrays for efficient imaging of chemical compositions. Proceedings of SPIE, 11954, https://doi.org/10.1117/12.2606917

• Presentation Conference Type: Conference Paper (published)
• Conference Name: SPIE Photonics West 2022
• Acceptance Date: Dec 31, 2021
• Online Publication Date: Mar 2, 2022
• Publication Date: Mar 2, 2022
• Deposit Date: Jan 4, 2022
• Publicly Available Date: Mar 2, 2022
• Journal: Progress in Biomedical Optics and Imaging - Proceedings of SPIE
• Print ISSN: 0277-786X
• Publisher: Society of Photo-optical Instrumentation Engineers
• Peer Reviewed: Peer Reviewed
• Volume: 11954
• ISBN: 9781510647794
• DOI: https://doi.org/10.1117/12.2606917
• Keywords: Multispectral imaging; filter arrays; fluorescence imaging; biomarker imaging; greyscale lithography; atomic force microscopy; spectral characterization
• Public URL: https://nottingham-repository.worktribe.com/output/7165015
• Publisher URL: https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11954/1195406/Spectrally-tailored-hyperpixel-filter-arrays-for-imaging-of-chemical-compositions/10.1117/12.2606917.short?SSO=1
• Related Public URLs: https://spie.org/conferences-and-exhibitions/photonics-west
• Additional Information: Copyright 2022 Society of Photo‑Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this publication for a fee or for commercial purposes, and modification of the contents of the publication are prohibited.