Decagram-Scale Synthesis of Multicolor Carbon Nanodots: Self-Tracking Nanoheaters with Inherent and Selective Anticancer Properties.

Carbon nanodots (CDs) are a new class of carbon-based nanoparticles endowed with photoluminescence, high specific surface area, and good photothermal conversion, which have spearheaded many breakthroughs in medicine, especially in drug delivery and cancer theranostics. However, the tight control of their structural, optical, and biological properties and the synthesis scale-up have been very difficult so far. Here, we report for the first time an efficient protocol for the one-step synthesis of decagram-scale quantities of N,S-doped CDs with a narrow size distribution, along with a single nanostructure multicolor emission, high near-infrared (NIR) photothermal conversion efficiency, and selective reactive oxygen species (ROS) production in cancer cells. This allows achieving targeted and multimodal cytotoxic effects (i.e., photothermal and oxidative stresses) in cancer cells by applying biocompatible NIR laser sources that can be remotely controlled under the guidance of fluorescence imaging. Hence, our findings open up a range of possibilities for real-world biomedical applications, among which is cancer theranostics. In this work, indocyanine green is used as a bidentate SOx donor which has the ability to tune surface groups and emission bands of CDs obtained by solvothermal decomposition of citric acid and urea in N,N-dimethylformamide. The co-doping implies various surface states providing transitions in the visible region, thus eliciting a tunable multicolor emission from blue to red and excellent photothermal efficiency in the NIR region useful in bioimaging applications and image-guided anticancer phototherapy. The fluorescence self-tracking capability of SOx-CDs reveals that they can enter cancer cells more quickly than healthy cell lines and undergo a different intracellular fate after cell internalization. This could explain why sulfur doping entails pro-oxidative activities by triggering more ROS generation in cancer cells when compared to healthy cell lines. We also find that oxidative stress can be locally enhanced under the effects of a NIR laser at moderate power density (2.5 W cm-2). Overall, these findings suggest that SOx-CDs are endowed with inherent drug-independent cytotoxic effects toward cancer cells, which would be selectively enhanced by external NIR light irradiation and helpful in precision anticancer approaches. Also, this work opens a debate on the role of CD surface engineering in determining nanotoxicity as a function of cell metabolism, thus allowing a rational design of next-generation nanomaterials with targeted anticancer properties.

Luminescence mechanisms of defective ZnO nanoparticles.

ZnO nanoparticles (NPs) synthesized by pulsed laser ablation (PLAL) of a zinc plate in deionized water were investigated by time-resolved photoluminescence (PL) and complementary techniques (TEM, AFM, µRaman). HRTEM images show that PLAL produces crystalline ZnO NPs in wurtzite structure with a slightly distorted lattice parameter a. Consistently, optical spectra show the typical absorption edge of wurtzite ZnO (Eg = 3.38 eV) and the related excitonic PL peaked at 3.32 eV with a subnanosecond lifetime. ZnO NPs display a further PL peaking at 2.2 eV related to defects, which shows a power law decay kinetics. Thermal annealing in O2 and in a He atmosphere produces a reduction of the A1(LO) Raman mode at 565 cm(-1) associated with oxygen vacancies, accompanied by a decrease of defect-related emission at 2.2 eV. Based on our experimental results the emission at 2.2 eV is proposed to originate from a photo-generated hole in the valence band recombining with an electron deeply trapped in a singly ionized oxygen vacancy. This investigation clarifies important aspects of the photophysics of ZnO NPs and indicates that ZnO emission can be controlled by thermal annealing, which is important in view of optoelectronic applications.

Colloidally stable selenium@copper selenide core@shell nanoparticles as selenium source for manufacturing of copper-indium-selenide solar cells.

Selenium nanoparticles with diameters of 100-400nm are prepared via hydrazine-driven reduction of selenious acid. The as-prepared amorphous, red selenium (a-Se) particles were neither a stable phase nor were they colloidally stable. Due to phase transition to crystalline (trigonal), grey selenium (t-Se) at or even below room temperature, the particles merged rapidly and recrystallized as micronsized crystal needles. As a consequence, such Se particles were not suited for layer deposition and as a precursor to manufacture thin-film CIS (copper indium selenide/CuInSe2) solar cells. To overcome this restriction, Se@CuSe core@shell particles are presented here. For these Se@CuSe core@shell nanoparticles, the phase transition a-Se→t-Se is shifted to temperatures higher than 100°C. Moreover, a spherical shape of the particles is retained even after phase transition. Composition and structure of the Se@CuSe core@shell nanostructure are evidenced by electron microscopy (SEM/STEM), DLS, XRD, FT-IR and line-scan EDXS. As a conceptual study, the newly formed Se@CuSe core@shell nanostructures with CuSe acting as a protecting layer to increase the phase-transition temperature and to improve the colloidal stability were used as a selenium precursor for manufacturing of thin-film CIS solar cells and already lead to conversion efficiencies up to 3%.