Polydiacetylene/triblock copolymer nanoblend applied as a sensor for micellar casein: A thermodynamic approach

• Polydiacetylene (PDA) and triblock copolymer (TC) formed sensor nanoblends.
• Small amount of micellar casein was detected by PDA/TC nanosensors.
• Salt ions of micellar casein induce color transition in PDA/TC nanoblends.
• Hydrophylic/hydrophobic TC balance affected nanoblend color transition.
• PDA/TC nanoblend can be modulated to detect different targets based on TC molecule.

Polydiacetylene (PDA) and triblock copolymer nanoblends were synthesized to detect micellar casein (MC), the main milk protein and an indicator of milk quality. UV–Vis spectrum showed that MC induced blue-to-red transition in nanoblends. When nanoblends and MC were separated by dialysis membrane colorimetric response (CR) was similar, whereas a remarkable CR reduction was noticed after addition of dialyzed-MC, suggesting that small molecules present in MC (salts) caused PDA color change. Interaction enthalpy variation between nanoblends and MC showed an abrupt increase that coincided with MC concentration when colorimetric transition occurred. Copolymer hydrophobic/hydrophilic balance and presence of other molecules in the system affected nanoblends CR. MC salts were found to interact with nanoblends leading to color changes. MC concentration, MC salt release, copolymer hydrophobic/hydrophilic balance, and presence of other molecules in the system affected responses of the sensors. These results contribute to future applications of PDA/copolymer nanosensors to dairy models.