Integrated Optics
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.
PI: Balpreet Singh Ahluwalia
Optical Nanoscopy
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.
Primary PI: Balpreet Singh Ahluwalia
Computational Nanoscopy
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, and you can check out this 5 minute video on MUSICAL here. MUSICAL is available as Matlab source code with a GUI and as an ImageJ plugin.
Additional information on computational nanoscopy projects is available here.
Primary PI: Krishna Agarwal
Label-free Microscopy
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.
PIs: Balpreet Singh Ahluwalia (QPM), Krishna Agarwal (tomography)
Ultraviolet Microscopy
Most cells are transparent at visible wavelengths, which means the imaginary component of their complex refractive index, also known as extinction coefficient, is close to zero. In the c-band of the ultra-violet region, however, the extinction coefficient is naturally much higher than at visible wavelengths. We develop novel UV-compatible microscopes and associated image processing, which offer excellently contrasted, high-resolution, label-free microscopy of conventionally invisible features of biological samples.
But that it not all the c-band has to offer. Virtually all samples become fluorescent at c-band UV wavelengths. This is due to the three intrinsically fluorescent amino-acids tryptophan, tyrosine, and phenylalanine, which can be excited at wavelengths below 280nm, and which are prevalent in most proteins. We can use this intrinsic fluorescence as contrast mechanism to gain insights into the nanoscopic structure of biological matter – both above and even below the diffraction limit with c-band structured illumination microscopy (SIM) and related computational approaches.
Click here to learn more about this UV microscopy research.
Primary PI: Florian Ströhl
Volumetric Microscopy
This type of microscope is best suited for fragile samples that would not tolerate too much light (especially UV). Light-sheet microscopes illuminate the sample only in the plane in which they also acquire an image, making them extremely light efficient. This way of sample illumination is also highly beneficial for 3D imaging. The mayor drawback of light-sheet microscopy is the complex optical setup with two objective lenses at placed at a right angle, which prohibits simple sample mounting. We strive to alleviate this caveat through single-objective light-sheet microscopy. A prime area of study is the role of mitochondria in engineered human heart tissue – our trusted experts on this type of high-tech sample are our locals Åsa Birgisdottir and Truls Myrmel.
Click here to know more about this volumetric microscopy research.
Primary PI: Florian Ströhl