Recycling of used capsules for coffee machines and 3D printing of sensors detecting caffeine

Nowadays, the recycling of materials and the sustainable use of resources is becoming more and more important. Recent scientific research reports an interesting use of industrial PLA waste from coffee machine capsules, which can be turned into electroanalytical sensors for detecting caffeine in tea and coffee samples.

In research conducted by researchers from Brazil and the UK, non-conductive and conductive filaments were used to produce complete electroanalytical cells, including 3D printed electrodes. The electroanalytical cell is designed with separate printouts for the cell body and electrodes, increasing the recyclability of the system. The cell body made of non-conductive filament could be processed three times before the print failed due to contamination.

The researchers developed three specialized formulations of the conductive filament, of which PLA (61.62 wt%), black carbon (CB, 29.60 wt%) and poly(ethylene succinate) (PES, 8.78 wt%) were found to be most suitable due to equivalent electrochemical properties, lower material cost and better thermal stability compared to higher PES charge filaments.

This system allows the detection of caffeine with a sensitivity of 0.055 ± 0.001 μA μM–1, a detection limit of 0.23 μM, a quantitative limit of 0.76 μM and a relative standard deviation of 3.14% after activation. Interestingly, non-activated electrodes with 8.78% PES showed significantly better results than activated commercial filaments for detecting caffeine.

Studies show that an activated electrode with 8.78% PES can detect the caffeine content of Earl Gray tea and Arabica coffee samples, both pure and caffeinated, with excellent recovery results (96.7-102%). This work demonstrates a paradigm shift in how 3D printing, electrochemical research and sustainability can interact and impact part of the circular economy, which can be compared to electrochemistry based on a circular economy.

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