Neuroactive Carbon Dots: Perspective Neurotheranostic Agents and Harmful Environmental Pollutant

T. Borisova, M. Dekaliuk, N. Pozdnyakova, A. Pastukhov, M. Dudarenko, M. Galkin, A. Borysov, S.G. Vari, A.P. Demchenko
Palladin Institiute of Biochemistry NAS of Ukraine,

Keywords: carbon dots, environmental pollutant, neurotoxicity risk assessment, neurotheranostics


1 Palladin Institute of Biochemistry, NAS of Ukraine – RECOOP CRRC 2 International Research and Innovation in Medicine Program, Cedars-Sinai Medical Center, LA, CA, USA Carbon dots (C-dots) are a newly discovered class of fluorescent carbon nanosized particles. C-dots are strongly fluorescent, non-blinking, and their emission color can be tuned by varying the excitation wavelength. C-dots are used as fluorescent nanoparticles since easily synthesized at low cost ("green chemistry"). Beside their use in nanomedicine and nanotechnology C-dots are a component of ash from incompletely combusted carbohydrate products (black carbon), therefore from environmental point of view C-dots are major contributors of air pollution. Carbon particles of outdoor air pollution may have a significant impact on the central nervous system of mammals and translocation of inhaled ultrafine particles to the brain was also shown. This was underlined by the National Institute of Environmental Health Sciences/NIH panel of research scientists (Block et al., 2012). Recently, we revealed neuroactive properties of C-dots synthesized from β-alanine, and it is unclear whether this effect is inherent to these C-dots only. Being synthesized from different types of carbon-containing precursors, C-dots expose different atoms at their surface. Our study focused on synthesis of C-dots from sulfur-, nitrogen-, hydrogen- containing carbohydrate precursors and displaying the nitrogen sulfur and hydrogen atoms in the nanoparticle structure and compared their neuroactive properties. It was found that C-dots synthesized from thiourea, cystein, urea, glutamate, gamma-aminobutryic acid (GABA), glycine, and natural leafs possessed unique stable spectroscopic properties at the size less than 10 nm. Assessment of neuroactivity was conducted based on the C-dots’ effects on glutamatergic and GABAergic neurotransmission in brain nerve terminals as recommended US EPA 1998 in the Guidelines for Neurotoxicity Risk Assessment. It was observed that all synthesized C-dots at concentration range from 0.5 to 1.0 mg/ml attenuated the initial rate of transporter-mediated uptake and accumulation of L-[14C]glutamate and [3H]GABA by nerve terminals in a dose-dependent manner and increased the ambient level of these neurotransmitters. Starting from concentration of 0.2 mg/ml, C-dots evoked gradual dose-dependent depolarization of the plasma membrane of nerve terminals measured with cationic potentiometric dye rhodamine 6G. With this study we demonstrated C-dots have activities on cell membranes and they are changing the membrane permeability. Within the concentration range of 0.1-0.5 mg/ml, C-dots caused an “unphysiological” effect since increased the рН-sensitive acridine orange dye’s fluorescence intensity that accumulated by synaptic vesicles. Also it was observed despite the different surface properties and fluorescent features of C-dots made from different materials, their neuroactive effects are analogous however displayed on a different level of efficiency. On one side the uncontrolled presence of carbon-containing substances in the air and in the food chain poses a toxicity risk for central nervous system. These effects enhanced during natural disasters with increased concentration of C-dots in the air. On the other side, combination of fluorescent and neuroactive features of C-dots (and their nanocomposites) make them useful for visualization of key transport mechanisms and pathways in nerve terminals in neurotheranostics also.