The interactions of imidazolium ionic liquids (ILs), i.e., dibutylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, and 1-butyl-3-methylimidazolium nitrate, with bovine serum albumin (BSA) were studied by monitoring the spectral behaviors of IL-BSA aqueous systems. The intrinsic fluorescence of BSA at 340 nm excited at 230 nm is obviously quenched by these ILs due to complex dynamic collision and their quenching constants are at the order of 10(2) L mol(-1). However, no fluorescence quenching is observed within the same region when excited at 280 nm, which is widely used for probing protein conformations. Thermodynamic investigations reveal that the combination between ILs and BSA is entropy driven by predominantly hydrophobic and electrostatic interactions, leading to the unfolding of polypeptides within BSA. The influence of the ILs on the conformation of BSA follows a sequence of BmimNO(3) > BmimCl ≈ BbimCl. Molecular docking shows that cationic imidazolium moieties of ILs enter the subdomains of protein and interact with the hydrophobic residues of domain III. An agreement between fluorescence spectroscopic investigations and molecular docking is reached. It is found that the fluorescence of BSA at λ(ex) 230 nm arising from aromatic amino acids Trp and Tyr is almost as sensitive as that achieved at λ(ex) 280 nm for elucidating the protein conformational changes, which provides a valid and new probe for the investigation of binding kinetics between molecules/ions and proteins.

Ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6), as a green solvent, was successfully used for the direct extraction of dsDNA. The extraction efficiency and the distribution coefficient values indicated that trace amounts of DNA at the levels of <5 ng microL-1 facilitate quantitative fast extraction, while proteins and metal species do not interfere. A total of 30% of the DNA in ionic liquid at approximately 20 ng microL-1 was back extracted into aqueous phase in phosphate-citrate buffer with a single-stage extraction. The extraction is demonstrated to be endothermic with an enthalpy of 34.3 kJ moL-1. The extraction mechanisms were proposed and verified by 31P NMR and FT-IR spectra. Interactions between cationic 1-butyl-3-methylimidazolium (Bmim+) and P-O bonds of phosphate groups in the DNA strands take place both in the dissolved BmimPF6 in aqueous phase and at the interface of the two phases. This interaction consequently led to the transformation of DNA conformations, along with a reduction of ethidium resonance light scattering at 510 nm, and a procedure for DNA quantification in ionic liquid was developed based on this observation.

We report a facile green approach for in situ growth of silver nanoparticles (AgNPs) on the surface of graphene quantum dots (GQDs). GQDs serve as both reducing agent and stabilizer, and no additional reducing agent and stabilizer is necessary. The GQDs/AgNPs hybrid exhibits a superior absorbance fading response toward the reduction of H2O2. A simple colorimetric procedure is thus proposed for ultrasensitive detection of H2O2 without additional chromogenic agent. It provides a record detection limit of 33 nM for the detection of H2O2 by the AgNPs-based sensing system. This colorimetric sensing system is further extended to the detection of glucose in combination with the specific catalytic effect of glucose oxidase for the oxidation of glucose and formation of H2O2, giving rise to a detection limit of 170 nM. The favorable performances of the GQDs/AgNPs hybrid are due to the peroxidase-like activity of GQDs.

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We report a novel quantum-dot-conjugated graphene, i.e., hybrid SiO2-coated quantum dots (HQDs)-conjugated graphene, for targeted cancer fluorescent imaging, tracking, and monitoring drug delivery, as well as cancer therapy. The hybrid SiO2 shells on the surface of QDs not only mitigate its toxicity, but also protect its fluorescence from being quenched by graphene. By functionalizing the surface of HQDs-conjugated graphene (graphene-HQDs) with transferrin (Trf), we developed a targeted imaging system capable of differential uptake and imaging of cancer cells that express the Trf receptor. The widely used fluorescent antineoplastic anthracycline drug, doxorubicin (DOX), is adsorbed on the surface of graphene and results in a large loading capacity of 1.4 mg mg(-1). It is advantageous that the new delivery system exhibits different fluorescence color in between graphene-HQDs and DOX in the aqueous core upon excitation at a same wavelength for the purpose of tracking and monitoring drug delivery. This simple multifunctional nanoparticle system can deliver DOX to the targeted cancer cells and enable us to localize the graphene-HQDs and monitor intracellular DOX release. The specificity and safety of the nanoparticle conjugate for cancer imaging, monitoring, and therapy has been demonstrated in vitro.