Interactions between carbon nanodots with human serum albumin and γ-globulins: The effects on the transportation function.

Carbon nanodots (C-dots) have attracted great attention as a new class of luminescent nanomaterials due to their superior physical and chemical properties. In order to better understand the basic behavior of C-dots in biological systems, a series of photophysical measurements were applied to study the interactions of C-dots with human serum albumin (HSA) and γ-globulins. The fluorescence of proteins was quenched by the dynamic mechanism rather than the formation of a protein/C-dots complex. The apparent dissociation constants of the C-dots bound to HSA and γ-globulins were of the same order of magnitude. Furthermore, it is proven that C-dots showed little influence on the conformation of HSA and γ-globulins. In addition, Fourier transform infrared and fluorescence spectroscopic studies demonstrated that the interaction between C-dots and two kinds of serum proteins was driven by hydrophobic and van der waals forces. Since the bioavailability of drugs can be modulated by their interactions with proteins, the variations of binding constants of three drugs with HSA and γ-globulins in the presence of different concentrations of C-dots (0-84 µmol L(-1)) have also been analyzed in this work, to reflect the effect of C-dots on the transportation function of HSA and γ-globulins.

Highly Photoluminescent Nitrogen-Doped Carbon Nanodots and Their Protective Effects against Oxidative Stress on Cells.

Highly photoluminescent (PL) (quantum yield = 54%) nitrogen doped carbon nanodots (C-dots) have been prepared through one-step carbonizing citric acid and tris(hydroxymethyl)aminomethane and using oleic acid as solvent. The synthesized C-dots are monodisperse with narrow size distribution (average 1.7 nm). The PL properties of C-dots are pH dependent, and hence, using C-dots as sophisticated pH sensor to detect pH values between 7 and 9 can be expected. In addition, the PL intensity of C-dots remains stable under high ionic strength. The C-dots can protect cells from oxidative stress, which shows potential to expand the biological application of C-dots, especially in medical treatment. The protective mechanism is associated with intracellular reactive oxygen species elimination and the intracellular superoxide dismutase production.

Mechanistic studies on the reversible photophysical properties of carbon nanodots at different pH.

The pH-dependent photoluminescence (PL) behavior of carbon nanodots (C-dots) and its mechanism has been exhaustively studied in this work. The PL and UV-vis absorption spectra are reversible in the pH between 3 and 13. We speculate that two kinds of reactions (fast and slow) occurring at the surface of C-dots may contribute to this pH-dependent PL behavior. When C-dots solutions are switched to acidic conditions, they will quickly self-assembled aggregate into larger particles and surface oxygen-related groups of C-dots would be slowly oxidized at room temperature. Moreover, it should be noted that this is the first direct observation of self-assembled aggregation of C-dots under acidic conditions. In addition, the optimal PL spectra of C-dots blue-shift while their sizes increase, so-called 'inverse PL shift' phenomenon is also observed. Meanwhile, as the solution is adjusted to alkaline conditions, a structural tautomerization of C-dots rapidly takes place and hydrogenation/deoxygenation reaction proceeds in a much slower rate. Furthermore, through distinct decay dynamics as well as the characterizations of C-dots at different pHs, the PL properties are proposed to be mainly related to the surface states of C-dots.