Sample preparation protocols for conventional high voltage transmission electron microscopy (TEM) heavily rely on the usage of staining agents containing various heavy metals, most commonly uranyl acetate and lead citrate. However high toxicity, rising legal regulations, and problematic waste disposal of uranyl acetate have increased calls for the reduction or even complete replacement of this staining agent. One of the strategies for uranyless imaging is the employment of low-voltage transmission electron microscopy. To investigate the influence of different imaging and staining strategies on the final image of cyanobacterial cells, samples stained by uranyl acetate with lead citrate, as well as unstained samples, were observed using TEM and accelerating voltages of 200 kV or 25 kV. Moreover, to examine the possibilities of reducing chromatic aberration, which often causes issues when imaging using electrons of lower energies, samples were also imaged using a scanning transmission electron microscopy at 15 kV accelerating voltages. The results of this study demonstrate that low-voltage electron microscopy offers great potential for uranyless electron microscopy.

Delong Instruments a s Palackeho Trida 3019 153 b 612 00 Brno Czech Republic

Department of Food Chemistry and Biotechnology Faculty of Chemistry Brno University of Technology Purkynova 118 612 00 Brno Czech Republic

Institute of Environmental Biotechnology Department of Agrobiotechnology IFA Tulln University of Natural Resources and Life Sciences Konrad Lorenz Strase 20 3430 Tulln an der Donau Austria

Institute of Scientific Instruments of the Czech Academy of Sciences v v i Kralovopolska 147 612 64 Brno Czech Republic

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