A functional DNA-modified dual-response gold nanoprobe for simultaneously imaging the acidic microenvironment and membrane proteins of tumor cells.

Tumor progression is a complicated process influenced by multiple factors, in which the acidic tumor microenvironment (TME) and altered tumor-associated membrane proteins (TA-MPs) are closely involved. Monitoring the status of these factors is of significance for tumor progression research. Here, we develop a novel probe for simultaneously imaging the acidic TME and TA-MPs in situ. In this probe, i-motif-forming sequences (strand I) are conjugated to a gold nanoparticle (AuNP) via gold-sulfur bonds for acid-response. Extended aptamers (strand A) for protein recognition are labeled with Cy3 and Cy5 respectively at two ends. The extended part of strand A hybridizes with strand I to quench Cy3 by the proximal AuNP, and the protein recognition part hybridizes with a strand labeled with BHQ2 (strand Q) to quench Cy5. When the integrated probe encounters an acidic TME, the strand I fold into i-motif quadruplexes and release the AQ duplexes from the AuNP, enabling Cy3 to be lit to indicate the acidic TME. The aptamers in AQ duplexes bind to target proteins, removing the hybridization between strand A and Q thus leading to the fluorescence recovery of Cy5 for in-situ imaging of the proteins. Fluorescence measurement and confocal microscopy imaging showed that the probe could sensitively respond to the alteration in acidity from pH 7.4 into pH 6.5, which is coincide with the acidity gap of extracellular microenvironment between normal and tumor cells. Besides, it enabled the in-situ imaging of MUC1 proteins on living cell surface, revealing their expression level and distribution. This probe demonstrates a new approach for simultaneously imaging the acidic TME and TA-MPs, providing a useful tool for multifactor research of tumor progression.