We describe the colloidal hot-injection synthesis of phase-pure nanocrystals (NCs) of a highly abundant mineral, chalcopyrite (CuFeS2). Absorption bands centered at around 480 and 950 nm, spanning almost the entire visible and near-infrared regions, encompass their optical extinction characteristics. These peaks are ascribable to electronic transitions from the valence band (VB) to the empty intermediate band (IB), located in the fundamental gap and mainly composed of Fe 3d orbitals. Laser-irradiation (at 808 nm) of an aqueous suspension of CuFeS2 NCs exhibited significant heating, with a photothermal conversion efficiency of 49%. Such efficient heating is ascribable to the carrier relaxation within the broad IB band (owing to the indirect VB–IB gap), as corroborated by transient absorption measurements. The intense absorption and high photothermal transduction efficiency (PTE) of these NCs in the so-called biological window (650–900 nm) make them suitable for photothermal therapy as demonstrated by tumor cell annihilation upon laser irradiation. The otherwise harmless nature of these NCs in dark conditions was confirmed by in vitro toxicity tests on two different cell lines. The presence of the deep Fe levels constituting the IB is the origin of such enhanced PTE, which can be used to design other high performing NC photothermal agents.

Nanoparticles (NPs) are increasingly used in biomedical applications, but the factors that influence their interactions with living cells need to be elucidated. Here, we reveal the role of NP surface charge in determining their neuronal interactions and electrical responses. We discovered that negatively charged NPs administered at low concentration (10 nM) interact with the neuronal membrane and at the synaptic cleft, whereas positively and neutrally charged NPs never localize on neurons. This effect is shape and material independent. The presence of negatively charged NPs on neuronal cell membranes influences the excitability of neurons by causing an increase in the amplitude and frequency of spontaneous postsynaptic currents at the single cell level and an increase of both the spiking activity and synchronous firing at neural network level. The negatively charged NPs exclusively bind to excitable neuronal cells, and never to nonexcitable glial cells. This specific interaction was also confirmed by manipulating the electrophysiological activity of neuronal cells. Indeed, the interaction of negatively charged NPs with neurons is either promoted or hindered by pharmacological suppression or enhancement of the neuronal activity with tetrodotoxin or bicuculline, respectively. We further support our main experimental conclusions by using numerical simulations. This study demonstrates that negatively charged NPs modulate the excitability of neurons, revealing the potential use of NPs for controlling neuron activity.

We present the synthesis of colloidally stable ultrasmall (diameter of 1.5 ± 0.6 nm) and fluorescent copper clusters (Cu-clusters) exhibiting outstanding quantum efficiencies (up to 67% in THF and approximately 30% in water). For this purpose, an amphiphilic block copolymer poly(ethylene glycol)-block-poly(propylene sulfide) (MPEG-b-PPS) was synthesized by living anionic ring-opening polymerization. When CuBr is mixed with the living polymer chains in THF, the formation of Cu-clusters is detected by the appearance of the fluorescence. The cluster growth is quenched by the addition of water, followed by THF removal. The structural features of the MPEG-b-PPS copolymer control the cluster formation and the stabilization: the poly(propylene sulfide) segment acts as coordinating and reducing agent for the copper ions in THF, and imparts a hydrophobic character. This hydrophobic block protects the Cu-clusters from water exposure, thus allowing to obtain a stable emission in water. The PEG segment instead provides the hydrophilicity, rendering the Cu-clusters water-soluble. To obtain fluorescent and stable Cu-clusters exhibiting outstanding quantum efficiencies, the removal of the excess of free polymer and copper salt was crucial. The Cu-clusters are also colloidally and optically stable in physiological media and showed bright fluorescence even when taken up by HeLa cells, being noncytotoxic when administered at a Cu dose between 10 nM and 1.6 μM. Given the very small size of the Cu-clusters, localization and fluorescent staining of cell nucleus is achieved, as demonstrated by confocal cell imaging performed at different Cu-cluster doses and at different incubation temperatures.

No abstract

The ability of neurons to extend projections and to form physical connections among them (i.e., "connect-ability") is altered in several neuropathologies. The quantification of these alterations is an important read-out to investigate pathogenic mechanisms and for research and development of neuropharmacological therapies, however current morphological analysis methods are very time-intensive. Here, we present and characterize a novel on-chip approach that we propose as a rapid assay. Our approach is based on the definition on a neuronal cell culture substrate of discrete patterns of adhesion protein spots (poly-d-lysine, 23 ± 5 μm in diameter) characterized by controlled inter-spot separations of increasing distance (from 40 μm to 100 μm), locally adsorbed in an adhesion-repulsive agarose layer. Under these conditions, the connect-ability of wild type primary neurons from rodents is shown to be strictly dependent on the inter-spot distance, and can be rapidly documented by simple optical read-outs. Moreover, we applied our approach to identify connect-ability defects in neurons from a mouse model of 22q11.2 deletion syndrome/DiGeorge syndrome, by comparative trials with wild type preparations. The presented results demonstrate the sensitivity and reliability of this novel on-chip-based connect-ability approach and validate the use of this method for the rapid assessment of neuronal connect-ability defects in neuropathologies.