Carbon dots have demonstrated great potential as luminescent nanoparticles in bioapplications. Although such nanoparticles appear to exhibit low toxicity compared to other metal luminescent nanomaterials, today we know that the toxicity of carbon dots (C-dots) strongly depends on the protocol of fabrication. In this work, aqueous fluorescent C-dots have been synthesized from cinnamon, red chilli, turmeric and black pepper, by a one-pot green hydrothermal method. The synthesized C-dots were firstly characterized by means of UV–vis, fluorescence, Fourier transform infrared and Raman spectroscopy, dynamic light scattering and transmission electron microscopy. The optical performance showed an outstanding ability for imaging purposes, with quantum yields up to 43.6%. Thus, the cytotoxicity of the above mentioned spice-derived C-dots was evaluated in vitro in human glioblastoma cells (LN-229 cancer cell line) and in human kidney cells (HK-2 non-cancerous cell line). Bioimaging and viability studies were performed with different C-dot concentrations from 0.1 to 2 mg·mL−1, exhibiting a higher uptake of C-dots in the cancer cultures compared to the non-cancerous cells. Results showed that the spice-derived C-dots inhibited cell viability dose-dependently after a 24 h incubation period, displaying a higher toxicity in LN-229, than in HK-2 cells. As a control, C-dots synthesized from citric acid did not show any significant toxicity in either cancerous or non-cancerous cells, implying that the tumour cell growth inhibition properties observed in the spice-derived C-dots can be attributed to the starting material employed for their fabrication. These results evidence that functional groups in the surface of the C-dots might be responsible for the selective cytotoxicity, as suggested by the presence of piperine in the surface of black pepper C-dots analysed by ESI-QTOF-MS.

Photo-luminescent carbon dots (CD) have become promising nanomaterials and their synthesis from natural products has attracted attention by the possibility of making the most of affordable, sustainable and, readily-available carbon sources. Here, we report on the synthesis, characterization and bioimaging potential of CDs produced from diverse extensively produced fruits: kiwi, avocado and pear. The in vitro cytotoxicity and anticancer potential of those CDs were assessed by comparing human epithelial cells from normal adult kidney and colorectal adenocarcinoma cells. In vivo toxicity was evaluated using zebrafish embryos given their peculiar embryogenesis, with transparent embryos developing ex-utero, allowing a real-time analysis. In vitro and in vivo experiments revealed that the synthesized CD presented toxicity only at concentrations of ≥1.5 mg mL−1. Kiwi CD exhibited the highest toxicity to both cells lines and zebrafish embryos, presenting lower LD50 values. Interestingly, despite inducing lower cytotoxicity in normal cells than the other CDs, black pepper CDs resulted in higher toxicity in vivo. The bio-distribution of CD in zebrafish embryos upon uptake was investigated using fluorescence microscopy. We observed a higher accumulation of CD in the eye and yolk sac, avocado CD being the ones more retained, indicating their potential usefulness in bio-imaging applications. This study shows the action of fruit-based CDs from kiwi, avocado and pear. However the compounds present in these fruit-based CDs and their mechanism of action as a bioimaging agent need to be further explored.

The present work describes the determination of picogram Hg(II) using 2,5-dimercapto-1,3,4-thiadiazole stabilized gold nanoparticles (DMT-AuNPs) by a spectrofluorimetry method. DMT-AuNPs show emission maximum at 773 nm with excitation at 514 nm. They show a large stock shift (259 nm), narrow emission profile and good photostability. While adding 10 μM Hg(II) the red color solution of DMT-AuNPs changes to purple and the UV-visible spectrum of DMT-AuNPs band at 514 nm was decreased. This is due to aggregation of DMT-AuNPs and it was confirmed by high resolution transmission electron microscopy (HR-TEM). UV-visible spectra of DMT-AuNPs in the presence of nanomolar concentrations of Hg(II) do not show any significant changes at 514 nm. However, the emission intensity of DMT-AuNPs was enhanced during adding even at picomolar concentration of Hg(II) due to photoinduced electron transfer and metal binding-induced conformational restriction upon complexation. Based on the enhancement of emission intensity the concentration of Hg(II) was determined. The binding constant (K(A) = 2.6514 × 10(4) mol(-1) L) value suggested that there is a strong binding force between Hg(II) and DMT-AuNPs. The present fluorophore showed an extreme selectivity towards Hg(II). The emission intensity was increased linearly against a wide range of Hg(II) concentration from 1 × 10(-12) to 1 × 10(-7) M and a detection limit of 0.64 pg L(-1) Hg(II) (S/N = 3) was achieved for the first time using DMT-AuNPs by spectrofluorimetry method. The proposed method was successfully applied for the determination of Hg(II) in environmental samples. The obtained results were validated by ICP-AES.

No abstract