Dual functional molecule aided background-free SERS sensor for intracellular pH dynamic monitoring based on foldable DNA transition

The microenvironment of lysosomes plays an important role in various functions within cells. Abnormal pH changes in lysosomes account for multiple diseases including tumors. Acid-responsive nanomaterials with reconfigurable structures and properties have garnered significant interests. Owing to the potential in biosensing, controlled release and nanomachinery, DNA based pH-responsiveness has been widely pursued. Herein, we designed an AuNPs-i-motifs based SERS probe to monitor the pH dynamics of lysosomal maturation in different cells. Taking advantages of biocompatibility and structural flexibility of DNA, unique optical and plasmonic properties of gold nanoparticles, excellent stability and enhanced sensitivity of background-free Raman reporter, the designed SERS probe could indicate the pH variation dynamically in lysosomes. What is more valuable is that 4-mercaptobenzonitrile is not only used as a Raman reporter to provide sensitive Raman signal for pH sensing, but also used as a sealing agent allowing for controllable aggregation, to improve the stability and accuracy of the sensor. With this versatile design, the sensor was prepared simply and feasibly and a tedious trial was avoided. It provides a feasible tool for understanding the relationship of lysosomal pH with fundamental cellular functions and mechanism of diseases. •A new i-motif based SERS biosensor was developed for pH monitoring dynamically in cells.•Biocompatible ssDNA modified AuNPs exhibits unique pH transition range especially suitable for endosomal tracing.•Background-free Raman reporter provides specific Raman signal in cellular Raman-silent region.•Second-generation hotspots generated by pH stimulation results in significantly enhanced Raman signal.•The proper pH responsive range, enhanced sensitivity and stability enable the biosensor to distinguish cancer cells.