Integrated Optics (“IO”) are the combination of different components to a photonic circuit in a chip. Waveguides are the main structures which guide and manipulate the light signal. With vast applications within the fields of communications and sensors, IO with its different optical components (e.g. frequency shifters, filters, interferometers or resonators) offers many advantages in term of speed and energy consumption, being among the most promising technologies for the future.
Our group develops IO systems for super-resolution microscopy applications. E.g. waveguide multiplexing over different inputs and frequencies or phase and intensity modulators allow for very compact systems which otherwise require large microscopes to produce the same complex illumination patterns. Our chips are produced through standard semiconductor technology, and being biocompatible they act as the substrate of the biological analyte. The possibility of retrofitting conventional microscopes to multimodal super-resolution capabilities offers the potential to a paradigm shift within the field.
Fluorescence microscopy is an essential technique within life sciences. The ability to visualize intracellular structures using fluorescent probes allows for imaging with high specificity and excellent contrast. However, the spatial resolution of optical microscopy is physically bound by the diffraction of light, which effectively limits the possible resolution to around 200-300 nm laterally, and 500-600 nm axially. This might seem very small, but many intra-cellular structures are far below this size limit. By the early 2000s a new range of imaging techniques emerged, where the aim was to generate images with spatial resolution below that of the diffraction limit. This field is known as super-resolution optical microscopy, or popularly called nanoscopy. Nanoscopic imaging techniques relies on different “tricks” to surpass the diffraction limit, e.g. by manipulating the photon emission of the fluorescent molecules, or by using advanced algorithms in combination with patterned excitation light.
In Tromsø, state-of-the-art optical nanoscopes are used to find new answers to central topics within the life sciences. At the same time we develop new instruments to improve already existing techniques, as well as create new imaging methods altogether.
We work on different computational nanoscopy techniques for fluorescent imaging, including structured illumination microscopy, localization microscopy, and fluorescence fluctuations based nanoscopy. Our research activities span from theoretical foundations in inverse problems to development to application of these techniques and finding innovative way for the computational nanoscopy and optical microscopy to achieve the best out of each other. We house the expertise of MUSICAL, a recent fluorescence fluctuations-based nanoscopy technique, which promises a good trade-off between phototoxicity, temporal resolution, and spatial resolution. We have shown its utility in imaging dynamics of cell organelles in diverse live cell systems. We have also adapted MUSICAL for high-throughput imaging and for chip-based high-throughput, high-speed nanoscopy. Watch out for publications on these topics. Check out this 5 minute video on MUSICAL here. MUSICAL is available as Matlab source code with a GUI and as an ImageJ plugin.
Krishna also has a dedicated website for her research here.
Quantitative phase microscopy (QPM) plays a vital role especially in the field of biomedical imaging as it is a non-contact, non-invasive and label-free technique. It has the capability to measure quantitative changes in various parameters such as refractive index, thickness and dry mass density (i.e., non-aqueous content) of cells/tissues during disease progression. The high spatial phase sensitivity and temporal phase stability is a primary requirement of any QPM system for their broad range industrial and biological applications. The high spatial phase sensitivity (≤ 10 mrad) provides accurate and precise phase/height measurement of the biological and industrial specimens. Whereas, high temporal stability of the interferometer is required where minute membrane fluctuations (~ 5 mrad) of the live biological cells are needed to be quantified.
We investigated various factors/components like coherence properties of light sources, calibration of piezoelectric transducer (PZT) and detector’s noise to improve the spatial phase sensitivity of QPM. While, high temporal stability is acquired through the development of a novel common-path QPM. A highly stable and sensitive QPM system is developed and subsequently successfully implemented for various biological and industrial applications. In addition, we integrated QPM and waveguide trapping techniques to study changes in RBC morphology during planar trapping and transportation. The Multi-modal chip-based fluorescence and QPM is also developed to study inflammation caused by lipopolysaccharide (LPS) on rat macrophages. QPM is also implemented for the quantitative analysis of human spermatozoa under oxidative stress condition.
Resolution in normal microscopic imaging is dictated by two parameters, the wavelength of the light in use and the performance of the objective lens, which is quantified as numerical aperture. The ratio of these values is the resolution limit (times a factor dependent on the specific definition of resolution used). Clearly, a shorter wavelength in the ultraviolet (UV) range thus provides better resolution! Counterintuitively, this approach has not been employed much in biomedical imaging. Why? The main two reasons for the limited use of UV light in the life sciences are (1) the high energy of UV photons, which can be damaging to cells, and (2) the lack of suitable optical materials that transmit UV light. Especially the latter reason has hindered the use of UV light for resolution improvements – the beneficial effect of shorter wavelengths is simply more than negated by the decrease in numerical aperture.
At UiT, we develop new optical systems that allow us to artificially increase the usable numerical aperture in UV microscopy, thus restoring a resolving power in the 100nm range – far below the diffraction limit of conventional microscopy. As this type of nanoscopic imaging does not rely on fluorescent markers, it is furthermore considered label-free and can thus reveal biological structures like mitochondria and their dynamics in undisturbed samples.