When a lensless fluorometer outperforms a lensed system

Asim  Maharjan; Prashant  Waiba; Shreya  Shrestha; Rijan  Maharjan; Kezheng Li; Augusto Martinez Alves; Thomas Fraser Krauss; Ashim  Dhakal

doi:10.1364/OPTICA.527289

When a lensless fluorometer outperforms a lensed system

Asim Maharjan, Prashant Waiba, Shreya Shrestha, Rijan Maharjan, Kezheng Li, Augusto Martinez Alves, Thomas Fraser Krauss, Ashim Dhakal^*

^*Corresponding author for this work

Physics

Research output: Contribution to journal › Article › peer-review

Abstract

The excitation and collection of optical signals using lenses form the basis for many applications in imaging, nephelometry, fluorometry, and spectroscopy. While lenses are needed for imaging systems, their use is not so obvious for volume sensing applications. Here, we study the excitation and collection of fluorescence signals to show that lensless systems generally provide a stronger signal compared to lensed systems for the case of extended Lambertian-like sources, such as LEDs. To elucidate this result, we provide a foundational framework to analyze the signal collection efficiency from an arbitrary detection volume with and without lenses when extended sources and detectors are used. A combination of factors, including the limited numerical aperture, the use of extended sources/detectors, and the requirement of a finite imaging distance between the source/detector, lenses, and the sample, limits the performance of the lensed system compared to the lensless system. Our theoretical and experimental results indicate that conventional wisdom based on the assumption of point-like sources and detectors should not always be followed. We provide a systematic approach for analyzing and simplifying the design of low-cost, lensless fluorometers and nephelometers without sacrificing their performance, reporting a sub-ppb level detection limit for measuring tryptophan-like-fluorescence in drinking water.

Original language	English
Pages (from-to)	1124-1128
Number of pages	5
Journal	Optica
Volume	11
Issue number	8
DOIs	https://doi.org/10.1364/OPTICA.527289
Publication status	Published - 8 Aug 2024

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10.1364/OPTICA.527289Licence: CC BY

When a lensless fluorometer outperforms a lensed system
© 2024 Optica Publishing Group
Final published version, 856 KBLicence: CC BY

Cite this

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title = "When a lensless fluorometer outperforms a lensed system",

abstract = "The excitation and collection of optical signals using lenses form the basis for many applications in imaging, nephelometry, fluorometry, and spectroscopy. While lenses are needed for imaging systems, their use is not so obvious for volume sensing applications. Here, we study the excitation and collection of fluorescence signals to show that lensless systems generally provide a stronger signal compared to lensed systems for the case of extended Lambertian-like sources, such as LEDs. To elucidate this result, we provide a foundational framework to analyze the signal collection efficiency from an arbitrary detection volume with and without lenses when extended sources and detectors are used. A combination of factors, including the limited numerical aperture, the use of extended sources/detectors, and the requirement of a finite imaging distance between the source/detector, lenses, and the sample, limits the performance of the lensed system compared to the lensless system. Our theoretical and experimental results indicate that conventional wisdom based on the assumption of point-like sources and detectors should not always be followed. We provide a systematic approach for analyzing and simplifying the design of low-cost, lensless fluorometers and nephelometers without sacrificing their performance, reporting a sub-ppb level detection limit for measuring tryptophan-like-fluorescence in drinking water.",

author = "Asim Maharjan and Prashant Waiba and Shreya Shrestha and Rijan Maharjan and Kezheng Li and {Martinez Alves}, Augusto and Krauss, {Thomas Fraser} and Ashim Dhakal",

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AU - Maharjan, Asim

AU - Waiba, Prashant

AU - Shrestha, Shreya

AU - Maharjan, Rijan

AU - Li, Kezheng

AU - Martinez Alves, Augusto

AU - Krauss, Thomas Fraser

AU - Dhakal, Ashim

PY - 2024/8/8

Y1 - 2024/8/8

N2 - The excitation and collection of optical signals using lenses form the basis for many applications in imaging, nephelometry, fluorometry, and spectroscopy. While lenses are needed for imaging systems, their use is not so obvious for volume sensing applications. Here, we study the excitation and collection of fluorescence signals to show that lensless systems generally provide a stronger signal compared to lensed systems for the case of extended Lambertian-like sources, such as LEDs. To elucidate this result, we provide a foundational framework to analyze the signal collection efficiency from an arbitrary detection volume with and without lenses when extended sources and detectors are used. A combination of factors, including the limited numerical aperture, the use of extended sources/detectors, and the requirement of a finite imaging distance between the source/detector, lenses, and the sample, limits the performance of the lensed system compared to the lensless system. Our theoretical and experimental results indicate that conventional wisdom based on the assumption of point-like sources and detectors should not always be followed. We provide a systematic approach for analyzing and simplifying the design of low-cost, lensless fluorometers and nephelometers without sacrificing their performance, reporting a sub-ppb level detection limit for measuring tryptophan-like-fluorescence in drinking water.

AB - The excitation and collection of optical signals using lenses form the basis for many applications in imaging, nephelometry, fluorometry, and spectroscopy. While lenses are needed for imaging systems, their use is not so obvious for volume sensing applications. Here, we study the excitation and collection of fluorescence signals to show that lensless systems generally provide a stronger signal compared to lensed systems for the case of extended Lambertian-like sources, such as LEDs. To elucidate this result, we provide a foundational framework to analyze the signal collection efficiency from an arbitrary detection volume with and without lenses when extended sources and detectors are used. A combination of factors, including the limited numerical aperture, the use of extended sources/detectors, and the requirement of a finite imaging distance between the source/detector, lenses, and the sample, limits the performance of the lensed system compared to the lensless system. Our theoretical and experimental results indicate that conventional wisdom based on the assumption of point-like sources and detectors should not always be followed. We provide a systematic approach for analyzing and simplifying the design of low-cost, lensless fluorometers and nephelometers without sacrificing their performance, reporting a sub-ppb level detection limit for measuring tryptophan-like-fluorescence in drinking water.

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DO - 10.1364/OPTICA.527289

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