Carbon quantum dots/block copolymer ensembles for metal-ion sensing and bioimaging

Significance 

Nano-sized semiconducting inorganic Nano-crystals have bright photoluminescence reference to their quantum confinement effect. Therefore, these semiconducting Nanocrystals have become popular for fluorescent making necessary for sensing, cellular probes, and bioimaging. Unfortunately, their high toxicity continues to handicap their in vivo and in vitro applications. In quest to overcome this shortcoming, researchers have identified nano-sized fluorescent carbon quantum dots as suitable alternatives for multicolor patterning, bioimaging, and sensors.

Photoluminescence of carbon quantum dots has been assigned controversially to surface energy traps and quantum confinement effects that are majorly based on the varying fabrication processes. However, their tunable light absorption-emission properties, high solubility in physiological media and excellent biocompatibility, make them attractive as opposed to fluorophores for bioimaging. This has resulted in their implementation as fluorescent labels for cellular imaging, in vivo optical imaging, and real-time molecular tracking in live cells.

Unfortunately, bare carbon quantum dots suffer from inadequate cell specificity. Therefore, modification by incorporation of biomolecules has been identified to mitigate this problem. In addition, while looking for quantum dots, which can be effectively accumulated in cells, incorporating particular proteins with targeting capabilities is appropriate.

Although a good number of sensors based on carbon quantum dots for metal-ions detection lack adequate selectivity, making them susceptible to interference phenomena with other materials and hence demanding the integration of functional species to carbon quantum dots for improved selectivity. In spite of the huge potential demonstrated for carbon quantum dots, more research is still needed.

Researchers led by Dr Nikos Tagmatarchis at the Theoretical and Physical Chemistry Institute, at the National Hellenic Research Foundation in Greece successfully synthesized fluorescent carbon quantum dots with amine-rich surface. In collaboration with Dr Stergios Pispas within the same organization, they took a step beyond by incorporating the di-block copolymer (CSS-IEO-3) with aqueous carbon quantum dots in an acidic environment, by making use of the electrostatic interactions between the di-block copolymer and the carbon quantum dots, which led to the formation of carbon quantum dot-CSS-IEO-3. Their research work is published in Journal of Materials Chemistry B.

The authors objective was to employ the carbon quantum dots-CSS-IEO-3 ensemble first as a sensitive and selective sensor for metal-ions of biological interest. Secondly, they applied it for bioimaging probing. For the latter application, the authors incorporated a protein, bovine serum albumin (BSA), to increase biocombatibility and allow efficient cell permeability of the carbon quantum dot-based three-component hybrid Nano-system (Figure 1). In future studies BSA can be replaced by other therapeutic proteins/peptides.

The authors electrostatically interacted spherical carbon quantum dots with a periphery rich in free amine units with the di-block copolymer. The material formed, carbon quantum dots/block copolymer nanoensemble, was observed to be stable in high saline and neutral environments. This was in fact critical when aiming for biological applications. The photoluminescence of carbon quantum dots within the formed material, with emission at 420 nm, remained unchanged by pH as well as salinity changes. This denoted the absence of considerable aggregation and highlighted the potential of the material for bioimaging.

The researchers adopted the photoluminescence of the carbon quantum dots/block copolymer in the development of a selective and sensitive approach for metal-ion sensing, in this case Fe3+, in the presence of other heavy metal cations (Figure 2). To this end, the negative charges of CSS-IEO-3 block copolymer were utilized for Fe3+ complexation and due to the proximity of the carbon quantum dots the decrease of emission was employed for efficient detection.

Carbon quantum dots/block copolymer ensembles for metal-ion sensing and bioimaging. Advances in Engineering

Figure 1

Carbon quantum dots/block copolymer ensembles for metal-ion sensing and bioimaging. Advances in Engineering

Figure 2

About the author

Nikos Tagmatarchis is Director of Research at the Theoretical and Physical Chemistry Institute (TPCI), National Hellenic Research Foundation (NHRF), in Athens, Greece. He is Deputy Director of TPCI/NHRF and member of the Scientific Council of TPCI/NHRF. Since 2014 is Member of the Editorial Board of Chemistry A European Journal. He has studied chemistry (BSc 1992) and holds a PhD (1997) from the Chemistry Department, University of Crete, Greece. His research interests focus on the chemistry of carbon-based nanostructured materials such as fullerenes, nanotubes and graphene, targeting applications in the fields of solar and photoelectrochemical cells, hydrogen production and photocatalysis.

His accomplishments in the area are reflected in over 210 scientific peer-reviewed research articles that he has published in prestigious scientific journals such as Angewandte Chemie International Edition, Journal of American Chemical Society, Advanced Materials, Advanced Functional Materials, ACS Nano, ACS Applied Materials & Interfaces, Chemical Communications and Chemistry-A European Journal, while his work has been cited more than 9200 times associated with an h-index of 39. He has given numerous invited oral presentations at significant international scientific conferences. He has been recipient of the European Young Investigator Award (2004), Visiting Professor at the Chinese Academy of Sciences (2011) and Invited Fellow for long-term research in Japan by the Japan Society for the Promotion of Science (2013 and 2018).

About the author

Stergios Pispas (born 1967) studied Chemistry at the University of Athens, Greece and obtained his PhD on Polymer Chemistry from the same university in 1994. During 1994 and 1995 he was a Postdoctoral Fellow at the Chemistry Department of the University of Alabama at Birmingham,USA. He then returned to Greece and joined again the Chemistry Department of the University of Athens as a Research Associate. In 2004 he became an Associate Researcher at the Theoretical and Physical Chemistry Institute at the National Hellenic Research Foundation, Athens, Greece, introducing the first Polymer Science oriented activities. Since 2014 he is Director of Research at TPCI-NHRF.

He serves as the chairman of the Scientific Council of TPCI-NHRF (2016) and an Advisory Board Member of the European Polymer Journal (2017). He has been awarded the American Institute of Chemists Foundation Award for Outstanding Post-doctoral Fellow (1995) and the A. K. Doolittle Award of the American Chemical Society (2003). He is a coauthor of more than 270 research articles in referred journals, several invited review articles and chapters in books and encyclopedias, as well as the co-author of two books. His research work has received more than 7000 citations (h-index=38). His current research focuses on the synthesis of functional block copolymers and polyelectrolytes by controlled polymerization methodologies, the study of their self-assembly properties, as well as the development of complex, hybrid, self-organized nanostructures based on designed synthetic polymers and inorganic nanomaterials and biomacromolecules.

About the author

Theodosis Skaltsas was born in Athens, Greece in 1986. He studied Materials Science at the University of Patras. He received his master degree on Polymer Science from the Chemistry department of the University of Athens and on 2016 he received his Ph.D. His research work both for master and PhD was performed in Theoretical and Physical chemistry institute, National Hellenic Research Foundation in Athens, working mainly in the synthesis and characterization of hybrid materials based on carbon nanostructures, polymers and quantum dots aiming to energy conversion applications. In 2017, he received the Talents3 fellowship and moved to Trieste, Italy at the Department of Chemical and Pharmaceutical Sciences of the University of Trieste, to work as a post-doctoral researcher.

Currently, his main scientific interests are focused on the synthesis of donor-acceptor hybrid materials based on inorganic quantum dots and carbon nanostructures with fine-tuned properties for photocatalytic applications, such as hydrogen production and organic pollutant degradation, as well as studying the photophysical properties of such materials.

Reference

T. Skaltsas, M. Goulielmaki, A. Pintzas, S. Pispas and N. Tagmatarchis. Carbon quantum dots/block copolymer ensembles for metal-ion sensing and bioimaging. Journal of Materials Chemistry B, volume 5 (2017), pages 5397—5402.

 

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