Applications of high-brightness 280nm light emitting diodes in biomedical optical imaging

McFarlane, Mollie

Thesis

Applications of high-brightness 280nm light emitting diodes in biomedical optical imaging

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Creator

McFarlane, Mollie

Rights statement

Strathclyde Thesis Copyright

Awarding institution

University of Strathclyde

Date of award

2023

Thesis identifier

T16547

Person Identifier (Local)

201855336

Qualification Level

Doctoral (Postgraduate)

Qualification Name

Doctor of Philosophy (PhD)

Department, School or Faculty

Department of Physics

Abstract

Light-emitting diodes (LEDs) have long been proven as excellent illumination sources for optical microscopy for reasons including their versatile spectral emission, reliability and fast switching times. Deep-ultraviolet (deep-UV) microscopy using LEDs has, however, historically been limited due to low optical power and poor transmission through glass. Recently, new developments in deep-UV LED technology have allowed high-brightness LEDs emitting at 280 nm with powers in the 100 mW range. In this thesis, I explore the applications of these 280 nm LEDs in biomedical optical imaging. I first characterise the optical properties of the LED important in microscopy, including electroluminescence spectrum and optical stability. Within this chapter, I also present the development of a novel technique for characterisation of the emission pattern of deep-UV LEDs without the need for UV-enhanced detectors. I next discuss the issue of transmission of this wavelength of light through glass and present a systematic comparison of existing methods to overcome this issue, including quartz objective lenses, reflective objective lenses and transmission fluorescence. I compare these methods based on properties such as transmission of 280 nm light, illumination homogeneity and image quality, and use this information to identify the most appropriate illumination method for applying this LED to image biological specimens. After choosing an illumination method, I then use this to excite quantum dotlabelled cells with 280 nm light and present the benefits of using this wavelength compared to the longer, more traditionally used wavelength of 365 nm, determining an up to 3.59-fold increase in fluorescence intensity associated with using 280 nn excitation. Finally, I develop a new method of generating a standing wave using 280 nm light and use this to carry out 280 nm standing wave microscopy of fluorescent lens specimens and fixed mammalian cells. I characterise the standing wave both in air and in a biologically-equivalent environment and quantify an achieved axial resolution of 48.9 nm - a near two-fold improvement on previous standing wave work with visible wavelengths.

Advisor / supervisor