Fish scales repurposed for spectroscopy

Chemists commonly use ultraviolet-visible (UV-vis) spectroscopy to study molecules and materials. To hold their analytes during UV-vis analysis, chemists use cuvettes or microplates made of either quartz, which is expensive, or disposable plastic, which accumulates in the environment. These sample holders typically require a minimum volume of 200 µL. Seeking a way to study smaller volumes inexpensively and with less environmental impact, researchers led by Anil K. Suresh of SRM University, Andhra Pradesh turned to an unlikely source—fish scales. Suresh’s team used discarded scales from Rohu labeo, a type of carp, from a local market, cleaned them, and removed the surface layer. Suresh says this process whittled the thickness of the scales from 0.4 mm to 0.23 mm and made them about 80% transparent in the 350–900 nm spectral window, which is comparable to plastic cuvettes (Green Chem. 2021, DOI: 10.1039/D1GC02569D). The researchers cut the fish-scale films into squares (shown) which can slot into a 3D-printed holder designed to fit into a UV-vis spectrometer. Drops of analyte stay suspended vertically on the film, allowing the researchers to analyze samples 0.25–10 µL in volume. After analysis, the researchers could recover the samples. What’s more, they report that it costs less than $1.50 to make 3,000 of the fish-scale films.