The Image Processing and Biometry Laboratory focus is the use of optical microelements and fiber optics in biological and medical applications. The research includes both numerical research and fabrication of optical elements, their characterization, and the final application. Examples of elements that the research team investigates with are microprobe for the electroporation of single cells, imaging bundles with very high spatial resolution, refractive and diffraction microlenses, and imaging systems. The team also deals with image processing, in particular related to medical research.

Research area

The research team's goal is to use the available technology related to the fabrication of optical fibers, fiber structures, and nano-structured optical elements in biological applications.

A microprobe for the electroporation of single cells

Electroporation is a technique that consists of the reversible change of the permeability of a cell membrane by applying an electrical voltage. Standard electroporation systems are macroscopic. The electrodes, from a few to several dozen centimeters in size, are placed outside the body. When a voltage of a few hundred or several thousand volts of low intensity is applied, the cell membranes between the electrodes unseal, allowing more efficient ion-exchange into and from inside the cell. This allows, for example, better absorption of drugs. A similar technique can also be used in in vitro tests. The research team has developed one of the smallest systems that allow electroporation of a selected single cell. The main element of the system is fiberglass with two metal electrodes. The fiber is the thickness of a human hair and the distance between the electrodes is less than 50 µm. At such short distances, a voltage of a few volts is enough to unseal the cell membrane. As shown, it is possible in this way to modify the ion exchange in a single cell or a group of several cells.

Fig. 1 Electroporation microprobe: a) appearance of the probe in the housing, b) distribution of the electric field near the ends of the electrodes, c) electrode and a single cell stained with a blue dye due to the unsealing of the cell membrane as a result of electroporation

Optical bundles with a very high spatial resolution

Optical imaging is a diagnostic tool that is often used in biology and medicine. It became especially important when traditional surgery was replaced by the so-called pinhole surgery. Progress in this area would not be possible without progress in the field of optical endoscopy. Modern endoscopes are mainly available in two types. The first group is based on the direct use of a CCD camera. However, due to the size of the available cameras, ranging from a few to several millimeters, these systems are used to penetrate only parts of the organs. The second group of endoscopes includes all kinds of optical fiber systems. Techniques based on single-core fibers and techniques based on multi-core fibers, i.e. imaging bundles, can be distinguished here. The imaging bundles consist of several thousand cores placed in one thin flexible element. The imaging bundles ensures direct image transmission, where every single core is a separate pixel of the image being created. The limitation is the optical coupling between adjacent cores. Due to their advantages, endoscopic systems based on images have found more and more applications in recent years, such as deep imaging of the brains of live animals and in vivo imaging in the sub-cell resolution of tumor tissues. In the best currently available images, the size of a single-pixel is not less than 3 μm. Such a relatively large pixel size causes 'pixelization' of the image, which may be inconvenient in practical application, and the crosstalk reduces the contrast of the resulting image.

The way to increase the spatial resolution of imaging devices is the use of new materials characterized by a very large difference in refractive index, modification of the imaging bundle structure itself, and control of the fabrication process. All these issues are the subject of research conducted at the Image Processing and Biometry Laboratory.

Fig. 2 Imaging bundles: a) Imaging bundles with a high spatial resolution (~ 16000 pixels, pixel size 3 μm), b) Imaging bundles with limited diffusion (~ 850 pixels, pixel size 2 μm), c) imaging example.

Publications

J. Kulbacka, R. Kasztelanic, M. Kotulska, D. Pysz, G. Stepniewski, R. Stępień, J. Saczko, D. Miklavčič, R. Buczyński, Ultrathin glass fiber microprobe for arbitrary selective single-cell electroporation, Bioelectrochem., 135, 107545 (2020).

R. Kasztelanic, I. Kujawa, R. Stepien, A. J. Waddie, M. R. Taghizadeh, R. Buczynski, Development of diffraction binary grating using hot embossing processing with electroformed nickel mold for broadband IR optics, Infrared Phys. Techn., 107, 103293 (2020).

A. Gierej, A. Filipkowski, D. Pysz, R. Buczynski, M. Vagenede, T. Geernaert, P. Dubruel, H. Thienpont, F. Berghmans, On the Characterization of Novel Step-Index Biocompatible and Biodegradable poly(D, L- lactic acid) Based Optical Fiber, Jour. Light. Technol., 38(7), 1905 - 1914 (2020).

R. Kasztelanic, D. Pysz, R. Stepien, R. Buczynski, Light field camera based on a hexagonal array of flat-surface nanostructured GRIN lenses, Opt. Express. 27(24), 34985-34996 (2019)

A. Gierej, M. Vagenede, A. Filipkowski, B. Siwicki, R. Buczynski, H. Thienpont, S. Van Vlierberghe, T. Geernaert, P. Dubruel F. Berghmans, Poly(D, L-lactic acid) (PDLLA) allows for the fabrication of biodegradable and biocompatible polymer optical fiber, Jour. Light. Technol. 37(9), 1916-1923 (2019).

B. Moreover, N. Bavili, Ö. Yaman, B. Yigit, M. Zeybel, M. Aydin, B. Dogan, R. Kasztelanic, D. Pysz, R. Buczynski, and A. Kiraz, Design and fabrication of large numerical aperture, high-resolution optical fiber bundles based on novel high-contrast pairs of soft glasses for fluorescence imaging, Opt. Express 27(7), 9502-9515 (2019).

V.T. Hoang, G. Stepniewski, K. Czarnecka, R. Kasztelanic, V.C. Long, K.D. Xuan, L. Shao, M. Smietana, R. Buczynski, Optical properties of buffers and cell culture media for optofluidic and sensing applications, Appl. Sci., 9, 1145 (2019).

R. Buczynski, T. Szoplik, I.P. Veretennicoff, H. Thienpont, Photonic morphological image processing, Critical Review Collection, 2017, Proc. SPIE 10302, 103020F-103020F-25, 2017.

R. Kasztelanic, I. Kujawa, R. Sepien, P. Kluczynski, A. Kozlowska, R. Buczynski, Low-cost soft-glass diffractive and refractive lenses for efficient mid-IR fiber coupling systems, Infrared Phys.Techn., 71, 307-312 (2015).

R. Kasztelanic, I. Kujawa, H. Ottevaere, D. Pysz, R. Stepien, H. Thienpont, R. Buczynski, Optical quality study of refractive lenses made out of oxide glass using hot embossing, Infrared Phys. Techn., 73, 212-218 (2015).