ALB and neoplasm: Similarly, an alveolus‐epithelium CoC accurately recapitulated the acidic pH of the tumor microenvironment and demonstrated the efficacy of pH‐sensitive ZnO‐quantum dot (ZnO‐QD) loaded human serum albumin (HSA) NPs.[100] Non‐invasive optical pH sensors added further value to the CoC, as continuous pH monitoring and control were achieved.