Abstract
Cellular temperature and pH govern many cellular physiologies, especially of cancer cells. Besides, attaining higher cellular temperature plays key role in therapeutic efficacy of hyperthermia treatment of cancer. This requires bio-compatible, non-toxic and sensitive probe with dual sensing ability to detect temperature and pH variations. In this regard, fluorescence based nano-sensors for cancer studies play an important role. Therefore, a facile green synthesis of orange carbon nano-dots (CND) with high quantum yield of 90% was achieved and its application as dual nano-sensor for imaging intracellular temperature and pH was explored. CND was synthesized from readily available, bio-compatible citric acid and rhodamine 6G hydrazide using solvent-free and simple heating technique requiring purification by dialysis. Although the particle size of 19 nm (which is quite large for CND) was observed yet CND exhibits no surface defects leading to decrease in photoluminescence (PL). On the contrary, very high fluorescence was observed along with good photo-stability. Temperature and pH dependent fluorescence studies show linearity in fluorescence intensity which was replicated in breast cancer cells. In addition, molecular nature of PL of CND was established using pH dependent fluorescence study. Together, the current investigation showed synthesis of highly fluorescent orange CND, which acts as a sensitive bio-imaging probe: an optical nano-thermal or nano-pH sensor for cancer-related studies.
Highlights
Cellular temperature and pH govern many cellular physiologies, especially of cancer cells
Assessment of cellular pH and temperature are essential in cancer metastasis and hyperthermia treatment studies and this is possible if temperature and pH fluctuations in cancer cells are evaluated with sensitive probes such as non-invasive or non-destructive optical nano-sensors
The electron diffraction pattern for crystalline structure was not observed in Transmission Electron Microscopy (TEM) inferring that carbon nano-dots (CND) is amorphous in nature (Fig. S9A)
Summary
Cellular temperature and pH govern many cellular physiologies, especially of cancer cells. Attaining higher cellular temperature plays key role in therapeutic efficacy of hyperthermia treatment of cancer This requires bio-compatible, non-toxic and sensitive probe with dual sensing ability to detect temperature and pH variations. In this regard, fluorescence based nano-sensors for cancer studies play an important role. The current investigation showed synthesis of highly fluorescent orange CND, which acts as a sensitive bio-imaging probe: an optical nano-thermal or nano-pH sensor for cancer-related studies. Rh6G hydrazide and citric acid based CND fulfils the conditions required for a dual nano-sensor to detect intracellular temperature and/or pH for cancer studies owing to its high QY of 90%. The CND developed in the current investigation is helpful in measuring variation in pH in cancer cells under fixed temperature and in measuring fluctuations in temperature in cancer cells at constant pH
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