Sustainable development of pellucid bio-slides from discarded fish scales for microscopy imaging

Abstract

Microscopy is an indispensable scientific imaging tool that is used for the magnified visualization of diverse kinds of cells, cellular structures and post-labelled molecules for various microbiological, diagnostic and biomedical applications. Conventionally, for microscopic imaging, specimens are often mounted or fixed onto glass slides with or without covering them with glass coverslips. However, both these components are brittle, chemically inert, involve expensive and sophisticated manufacturing, and possess razor-sharp edges that pose safety hazards, causing blood borne disease transmission via accidental cuts under clinical scenarios. In response to the growing need for sustainable and safe laboratory materials, we developed a transparent, biodegradable bio-slide processed from pristine fish-scale bio-wastes. This is an extension of our previous study, where we utilized the transparency of the scale for UV-vis spectroscopy. Rich in collagen and hydroxyapatite, the scales were subjected to controlled demineralization and bio-casting to yield slide-comparable optically clear bio-slides with a mechanical strength of ∼40 ± 4 mPa. The bio-slides demonstrated consistent (n = 10) light transmittance (over 82%), acceptable autofluorescence, solvent compatibility and enhanced sample adherence with a contact angle of 81°, supporting imaging of a broad range of specimen (plant parts and tissue sections, bacteria, and cells). As conventional microscopes are designed to stage “slides”, a customized reusable 3D-printed slide-mimicking adapter was developed to position our bio-slide on the microscope. The bio-slide could withstand laser excitation, permitting imaging using confocal microscopy, and showed high-compatibility towards dyes (SynaptoRed C2, DAPI, crystal violet, and safranin) and antibody-labels (anti-NeuN antibody and Alexa 555-conjugated secondary antibody (goat anti-mouse IgG1)) enabling microbial and cell staining and immunohistochemistry of mice spinal cord neuronal sections (20 µm and 30 µm). Finally, the renewable and biodegradable nature of the bio-slide supports circular bio-economy goals through effective bio-waste valorisation. This study introduces an eco-friendly class of bio-slides for imaging using microscopy with promising applications in green diagnostics, sustainable laboratory practices, and biomedical research.