Carbon based nanodots and microspheres for bioimaging and biosensing

Abstract

With the development of nanomaterials and fluorescence detection techniques, carbon-based fluorescent nano- and micro- materials are arousing tremendous interests because of their great application potential in biomolecules detection and bioimaging. Compared to other fluorescent materials such as organic dyes, fluorescent proteins, semiconductor quantum dots, metal nanoparticles etc., fluorescent carbon-based nano- and micro- materials show advantages of easy preparation, simple functionalization, stable fluorescence, tunable fluorescence characteristics, low biotoxicity, and minimal environmental hazards. The research in this dissertation is aimed at developing simple preparation methods of fluorescent carbon dots (CDs) and carbon microspheres and applying the synthesized nano- and micro- structures in small biomolecules detection, cell imaging, and specific cell targeting. The first part of this thesis is focused on nitrogen-doped carbon dots (N-CDs), including synthesis, characterization and application in studying cellular uptake behaviors on different stiffness substrates. N-CDs with bright blue fluorescence are prepared from a one-step hydrothermal method. Cells are cultured on poly(acrylamide) (PAA) gels substrates with variable stiffness, which are synthesized via photopolymerization. We find that substrate stiffness influence cellular uptake of N-CDs, which is regulated by the interaction between cell and matrix. In the second part, a heparin sensing platform based on branched polyethylenimine carbon dots (BPEI-CDs) is developed. The positively charged BPEI-CDs are prepared from citric acid (CA) and BPEI using a one-step hydrothermal route. The electrostatic interaction between heparin and BPEI-CD, which induce aggregation formation, is the basis of the sensing mechanism. Using this method, we achieve a linear detection range of 2-20 μg/mL with a detection limit of 0.46 μg/mL. This heparin sensing method shows distinct strong response to heparin even in presence of heparin-analogue interferents. The capability of detecting heparin in real sample is also verified by standard addition method. In the third part, gadolinium-doped carbon microspheres (GdCMS) are studied. The formation and morphology of GdCMS are largely dependent on the starting material proportion and reaction conditions. We optimize the parameters to obtain GdCMS with uniform size and rough surface. The GdCMS not only possess fluorescence properties, but also show unique magnetic properties due to Gd doping. GdCMS functionalized with epithelial cell adhesion molecule (EpCAM) antibody preliminarily show potential in targeting specific cancer cells and magnetic separation.