Fluorescence spectroscopy in probing spontaneous and induced aggregation amongst size-selective gold nanoclusters

Foliar uptake and leaf-to-root translocation of nanoplastics with different coating charge in maize plants

Foliar uptake of nanoplastics could represent a pathway responsible for pollutant loads in crop plants, thereby posing risks to human health. To evaluate the foliar uptake, leaf-to-root translocation of nanoplastics, as well as the influences of surface charge on the above processes and physiological effects to plants, maize (Zea mays L.) seedlings were foliar exposed to carboxyl-modified polystyrene nanoplastics (PS-COOH) and amino-modified polystyrene nanoplastics (PS-NH₂), respectively. Both PS nanoplastics could effectively accumulate on the maize leaves, accompanied by observable particle aggregation. Due to electrostatic attraction to the negatively charged cell wall, positively charged PS-NH₂ association with the leaf surfaces was significantly more than negatively charged PS-COOH. The fraction of PS nanoplastics entry into the leaves could efficiently transfer to the vasculature mainly through stomatal opening and move down to the roots through vascular bundle. Meanwhile, the occurrence of aggregation limited the nanoplastic translocation to the roots, especially for PS-NH₂ with larger aggregate sizes relative to PS-COOH. Compared with negatively charged PS-COOH, positively charged PS-NH₂ treatment had a higher inhibitory effect on photosynthesis and a stronger stimulation to the activity of antioxidant systems. Overall, our findings give a scientific basis for the risk assessment of nanoplastic exposure in air-plant systems.

Surface curvature-dependent adsorption and aggregation of fluorescein isothiocyanate on gold nanoparticles

The interaction between metallic nanoparticles and fluorescent molecules and its influence on the optical properties of the particles/molecules have been intensively investigated because of their biology and sensing applications. Here, we studied the adsorption and aggregation of a commonly used dye, fluorescein isothiocyanate (FITC), on gold nanoparticles of various diameters. It was observed that the adsorption of FITC on relatively large gold nanoparticles (≥15 nm in diameter) induced quenching in the two-photon fluorescence (TPF) emission from the FITC molecules, while smaller-sized gold nanoparticles (1.6 nm) had no such effect. This difference was interpreted by the fluorescence resonance energy transfer (FRET) between the FITC molecules and the larger gold nanoparticles. At the same time, it was observed that the ratio of TPF quenching was notably higher than the ratio of the FITC molecules chemically adsorbed on the large gold particles. This unexpected observation revealed that the aggregation-induced fluorescence quenching also contributed significantly to the attenuation of the TPF emission. Time-dependent TPF attenuation during the interaction of FITC and the larger gold nanoparticles was recorded and used to confirm this interpretation. With this experimental evidence, a clear picture of the interaction of the FITC molecules on the gold surface was presented: FITC molecules chemically adsorbed on the small gold nanoparticles. However, the relatively larger surface curvature hindered the aggregation of the FITC molecules on the small gold nanoparticles. On the surface of the larger gold nanoparticles, both adsorption and aggregation occured. The influence of the surface curvature on the interfacial structure of the adsorbed molecules on nanoparticles was discussed.

Noble metal nanoparticle-induced oxidative stress modulates tumor associated macrophages (TAMs) from an M2 to M1 phenotype: An in vitro approach

Diagnosis of cancer and photothermal therapy using optoelectronic properties of noble metal nanoparticles (NPs) has established a new therapeutic approach for treating cancer. Here we address the intrinsic properties of noble metal NPs (gold and silver) as well as the mechanism of their potential antitumor activity. For this, the study addresses the functional characterization of tumor associated macrophages (TAMs) isolated from murine fibrosarcoma induced by a chemical carcinogen, 3-methylcholanthrene (MCA). We have previously shown antitumor activity of both gold nanoparticles (AuNPs) and silver nanoparticle (AgNPs) in vivo in a murine fibrosarcoma model. In the present study, it has been seen that AuNPs and AgNPs modulate the reactive oxygen species (ROS) and reactive nitrogen species (RNS) production, suppressing the antioxidant system of cells (TAMs). Moreover, the antioxidant-mimetic action of these NPs maintain the ROS and RNS levels in TAMs which act as second messengers to activate the proinflammatory signaling cascades. Thus, while there is a downregulation of tumor necrosis factor-α (TNF-α) and Interleukin-10 (IL-10) in the TAMs, the proinflammatory cytokine Interleukin-12 (IL-12) is upregulated resulting in a polarization of TAMs from M2 (anti-inflammatory) to M1 (pro-inflammatory) nature.