A Protein‐Nanocellulose Paper for Sensing Copper Ions at the Nano‐ to Micromolar Level

Tracing heavy metals is a crucial issue in both environmental and medical samples. In this work, a sensing biomolecule, the cyanobacterial C‐phycocyanin (CPC), is integrated into a nanocellulose matrix, and with this, a biosensor for copper ions is developed. The assembly of CPC‐functionalized nanocellulose into a red‐fluorescent, copper‐sensitive hybrid film “CySense”, enhances protein stability and facilitates the reuse and the regeneration of the sensor for several cycles over 7 days. CySense is suitable for the analysis of complex medical samples such as human serum filtrate. The reported biosensor reliably detects copper ion contents with a lower detection limit of 200 × 10⁻⁹m and an IC50 of 4.9 × 10⁻⁶m as changes in fluorescence emission intensity that can be measured with a fluorimeter or a microarray laser scanner.