**6. A brief comparison between carbon-based QDs and BPQDs**

Carbon-based QDs and BPQDs both consist of only one type of element (carbon and phosphorus) and comparing their efficiency in cancer cell imaging can be very important. The results of various studies have shown that both types of quantum dots have a high ability in cancer cells imaging [73, 74]. However, concentrations of BPQDs used for cancer cell imaging are lower than carbon-based QDs [74, 75]. In this context, two hypothesis are raised: First, it is likely that BPQDs increase the intensity of the PL signal to a greater extent than carbon-based QDs. Second, the cytotoxicity of BPQDs is higher than that of carbon-based QDs, and they should be used in low concentrations. However, due to the few studies, especially on BPQDs, these two hypotheses cannot be decisive, and the need for more studies in this field will help to clarify the issue more.
