Cholesterol Functionalization of Gold Nanoparticles Enhances Photoactivation of Neural Activity

Abstract

Gold nanoparticles (AuNPs) attached to the extracellular leaflet of the plasma membrane of neurons can enable the generation of action potentials (APs) in response to brief pulses of light. Recently described techniques to stably bind AuNP bioconjugates directly to membrane proteins (ion channels) in neurons enable robust AP generation mediated by the photoexcited conjugate. However, a strategy that binds the AuNP to the plasma membrane in a non protein-specific manner could represent a simple, single-step means of establishing lightresponsiveness in multiple types of excitable neurons contained in the same tissue. On the basis of the ability of cholesterol to insert into the plasma membrane, here we test whether AuNP functionalization with linear dihydrolipoic acid-poly(ethylene) glycol (DHLA-PEG) chains that are distally terminated with cholesterol (AuNP–PEG–Chol) can enable light-induced AP generation in neurons. Dorsal root ganglion (DRG) neurons of rat were labeled with 20 nm diameter spherical AuNP–PEG–Chol conjugates wherein ~30% of the surface ligands (DHLA-PEG-COOH) were conjugated to PEG–Chol. Voltage recordings under current-clamp conditions showed that DRG neurons labeled in this manner exhibited a capacity for AP generation in response to microsecond and millisecond pulses of 532 nm light, a property attributable to the close tethering of AuNP–PEG–Chol conjugates to the plasma membrane facilitated by the cholesterol moiety. Light-induced AP and subthreshold depolarizing responses of the DRG neurons were similar to those previously described for AuNP conjugates targeted to channel proteins using large, multicomponent immunoconjugates. This likely reflected the AuNP–PEG–Chol’s ability, upon plasmonic light absorption and resultant slight and rapid heating of the plasma membrane, to induce a concomitant transmembrane depolarizing capacitive current. Notably, AuNP–PEG–Chol delivered to DRG neurons by inclusion in the buffer contained in the recording pipet/electrode enabled similar light-responsiveness, consistent with the activity of AuNP–PEG–Chol bound to the inner (cytofacial) leaflet of the plasma membrane. Our results demonstrate the ability of AuNP–PEG–Chol conjugates to confer timely stable and direct responsiveness to light in neurons. Further, this strategy represents a general approach for establishing excitable cell photosensitivity that could be of substantial advantage for exploring a given tissue’s suitability for AuNP-mediated photocontrol of neural activity.

In Situ Self‐Assembly of Quantum Dots at the Plasma Membrane Mediates Energy Transfer‐Based Activation of Channelrhodopsin

“…This is consistent with observations from other studies that have confirmed the long-term membrane residence (in some cases as long as 48 h) of QDs and other NPs when they are interfaced with the plasma membrane using membrane-insertion peptides [29,30] and PEGylated cholesterol moieties. [9] This result also agrees well with the known membrane turnover and recycling of ChR-expressing cells. [31] It was also evident that the binding of the QDs to the plasma membrane was specific for the presence of the His 6 tract on His 6 -ChR-C1V1-iRFP as cells that were not transfected with the fusion protein showed negligible QD binding/labeling (Figure S4, Supporting Information).…”

“…For example, several reports have now detailed the use of the plasmonic heating of plasma membrane-tethered, photoexcited gold NPs for the controlled stimulation of action potentials via the activation of voltage-gated sodium channels. [6][7][8][9][10] Semiconductor nanocrystals or quantum dots (QDs) have emerged as another class of NP for neural imaging and activation. QDs interfaced with the plasma membrane have been used in energy and charge transfer [6,11] configurations to optically report realtime changes in membrane potential.…”

Neural Stimulation in vitro and in vivo by Photoacoustic Nanotransducers

“…The photothermal effect of nanoparticles has been reported to successfully modulate neurons mainly in vitro 9,[11][12][13]17,[36][37][38][39][40] . Two potential stimulation mechanisms were proposed, one through the increase of temperature, with highest temperature often found in the range of 50 °C to 70 °C 17,38 , and another through an optocapacitive stimulation determined by the rate of temperature change [13][14][15] .…”

“…Nanostructures target neuron membrane locally, convert and amplify the external excitation to local stimuli, offering new interfaces as promising alternative neural stimulation approaches. Gold nanoparticles and nanorods were studied for photothermal neural stimulation in vitro [9][10][11][12] . Gold nanoparticles and carbon nanotubes were also used for photothermal-driven optocapacitive stimulation in vitro [13][14][15] .…”

Plasmonic Nanofactors as Switchable Devices to Promote or Inhibit Neuronal Activity and Function

“…Utilizing PNFs is considered an innovative approach for modulating cellular activity based on cell-plasmon or cell-surface interaction [9,22,23,29,30,31,32,33,34,35,36]. Past in vitro experiments have exposed cells to a plasmonic nanomaterial dispersed in the cell culture medium or to a plasmonic nanomaterial deposited as 2D structures.…”