Retraction Note: Fluorescence spectrum–based dual-parameter detection method for pH and DO in cancer cell metabolic fluid

Abnormal metabolism of cancer cells leads to changes in the concentration of various components in the cell metabolic fluid, which is obviously different from that in normal cells. The two most representative parameters used for the early diagnosis of cancer are acidity (pH) and dissolved oxygen (DO) in the external environment of cancer cells. This study aimed to propose a dual-parameter detection method to simultaneously determine the pH and DO of cancer cell metabolic fluid based on the fluorescence spectrum of coumarin-modified CdSe quantum dots. Quantum dot is an important low dimensional semiconductor material with nanometer level. The coumarin-modified CdSe quantum dots can be ultraviolet-excited with an excitation light of wavelength 365 nm. The realization of detecting pH and DO was demonstrated by characterizing the fluorescence intensity at 625 nm produced by CdSe quantum dots and at 485 nm induced by coumarin upon excitation. The results of the experiment with phosphate-buffered saline showed that the detection limit of pH was 0.05 and that of DO was 0.04 mg/L. Based on this, the pH and DO of the extracellular environment of cancer and normal cells were tested and compared to verify the accuracy of the measurement.The method proposed in this study could realize the dual-parameter detection of the cell metabolic fluid with high measurement accuracy, high speed, and less loss of raw liquid. The method could also be applied to other related detection fields.