Abstract
Herein, we demonstrate the fabrication of innovative pH-activable carbon nanoparticles (CNPs) based on urea and citric acid by microwave-assisted green synthesis for application in cell imaging. These CNP-based nanoprobes offer significant advantages of pH responsiveness and excellent biocompatibility. The pH responsiveness ranges from 1.0 to 4.6 and the slightly pH responsiveness ranges from 4.6 to 9.0. In addition, the pH-dependent modification of charge as well as the final diameter of the designed CNPs not only provide support as stable sensors for cell imaging under pH values from 4.6 to 9.0, but can also observe the pH change in cells from 1.0 to 4.6. Importantly, this significantly enhances the cellular internalization process resulting in tumor cell death. Together, we believe that these superior photoluminescence properties of our designed nanomaterials potentially allow for biological labeling, bioimaging, and drug delivery applications.
Highlights
Most of the available cellular imaging probes are based on small molecules due to their low target-to-background ratios and excellent light-induced activation [1,2]
The surface morphology of carbon nanoparticles (CNPs) from transmission electron microscope (TEM) images (Figure 1A) depicted that the average diameter of CNPs was in the range of 12 to 18 nm
It was observed that the CNPs resulted in altered absorption peaks at around 233 and 337 nm, due to the π-π* transition of the C=C bond, and the n-π* transition of the C=O bond (Figure 1B), respectively, which confirms that the sp2 clusters were contained in CNPs
Summary
Most of the available cellular imaging probes are based on small molecules due to their low target-to-background ratios and excellent light-induced activation [1,2]. Owing to their advantageous features of biocompatibility, environmental friendliness, and simple preparation methods, carbon-based photoluminescent nanomaterials have garnered enormous interest for application in biological labeling, bioimaging, and bioanalytical analysis [15,16,17] These excellent properties of the carbon nanoparticles (CNPs) allow them to be considered as a useful alternative for a cell imaging application. In an attempt to demonstrate this fact, Liu and colleagues fabricated charge-switching nanoparticles that switch to positively charged under slightly acidic conditions and significantly facilitated their interactions with the negatively charged cell membranes to enhance their cellular uptake [21] They extended the design by using 2,3-dimethylmaleic anhydride (DMMA) to obtain a pH-dependent, charge-switchable polymer as an anticancer drug carrier. Utilizing the intrinsic optical properties of CNPs, our CNPs could be used as pH-responsive sensors that would allow for cell imaging
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