Rod‐Shaped Nanocrystals Elicit Neuronal Activity In Vivo

Abstract

The development of novel nanomaterials has raised great interest in efforts to evaluate their effect on biological systems, ranging from single cells to whole animals. In particular, there exists an open question regarding whether nanoparticles per se can elicit biological responses, which could interfere with the phenomena they are intended to measure. Here it is reported that challenging the small cnidaria Hydra vulgaris in vivo with rod-shaped semiconductor nanoparticles, also known as quantum rods (QRs), results in an unexpected tentacle-writhing behavior, which is Ca(2+) dependent and relies on the presence of tentacle neurons. Due to the absence of surface functionalization of the QRs with specific ligands, and considering that spherical nanoparticles with same composition as the QRs fail to induce any in vivo behavior on the same experimental model, it is suggested that unique shape-tunable electrical properties of the QRs may account for the neuronal stimulation. This model system may represent a widely applicable tool for screening neuronal response to nanoparticles in vivo.

Hydra, a model system for environmental studies

“…Hydra were also seemingly sensitive to single-wall carbon nanotubes with an EC 50 in the 1-10 mg/L range. Interestingly rod-shaped nanocrystals proved excitatory to cnidarians (Malvindi et al, 2008). Exposure of Hydra to rod-shaped semiconductor quantum dots resulted in an unexpected tentacle-writhing behaviour suggesting the involvement of tentacle neurons and depends on Ca 2+ ions.…”

An Ancient Model Organism to Test In Vivo Novel Functional Nanocrystals

“…b) Within seconds of addition of QRs to the culture medium the polyp's tentacle begin to writhe, bending toward the mouth. Contractions are not synchronous for all tentacles and lasted for an average of ten minutes (Malvindi et al, 2008). The elicitation of this behaviour over an average period of ten minutes was dependent on the presence of calcium ions into Hydra medium, as shown by the inhibition of such activity by the calcium chelator EGTA.…”

“…Noteworthy attention should be paid to the chemical composition of surfactant-polymer-coated nanoparticles not only in determining their stability in aqueous media but also in investigating their interaction with cells and intracellular localization. With the aim to test the impact of a new kind of semiconductor nanocrystal on Hydra vulgaris, we demonstrated that specific behaviours might be induced by exposure of whole animals to unfunctionalized nanocrystals and that a careful investigation of the impact of the new material on living cells must be carried out before designing any nanodevice for biomedical purposes (Malvindi et al, 2008). The nanocrystals under investigation were fluorescent CdSe/CdS quantum rods (from here named QRs).…”

“…We suggested that CdSe/CdS QRs, regardless of surface chemical functionalization, may generate local electric fields associated with their permanent dipole moments that are intense enough to stimulate voltage dependent ion channels, thus eliciting an action potential resulting in motor activity. Results from a geometrical approximation (Malvindi et al, 2008) showed that a QR voltage potential of sufficient intensity to stimulate a voltage gated ion channel can be produced at nanometric separation distances, i.e. those lying between cell membranes and medium suspended QR, regardless of its orientation at the cell surface, thus it is theoretically possible for QRs to elicit neuronal activity.…”

“…In this scenario, the emerging nanomaterials, variable in size (from 2 to 100 nm), chemical composition (gold, cadmium telluride, cadmium selenide, iron oxide) and physical properties (charge, spectral profile, colloidal stability, magnetism) represent a new class of compounds interacting with biological systems, which underlying mechanisms need to be carefully investigated. When studying the impact of CdSe/CdS QRs on Hydra (Malvindi et al, 2008), beside the detection of a specific behavioural response, an accurate microscopy analysis was performed in order to assess the putative internalization of the QRs into Hydra cells. At neutral pH, QR uptake was never detectable at the concentrations (7nM) eliciting biological activity.…”