There is a need for highly sensitive, multi-parallel protein sensors within diagnostics and proteomic research. Conjugated polymers (CPs) have been demonstrated as highly sensitive optical probes for protein biosensing. Compared to small molecules, the polymeric probe has the possibility of multiple interactions and a collective response, which enhances the sensor signal. The optical output is colorimetric or, more sensitive, fluorescence based, including Förster energy transfer and changes in the emission wavelengths and/or intensity. Using CPs, many interesting protein detection events have been demonstrated, e.g., protein interactions, enzymatic activity, amyloid fibril formation, and detection by aptamers. CPs have also been successfully used to stain bacterial, cellular, and tissue samples.