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Cholesterol Functionalization of Gold Nanoparticles Enhances Photoactivation of Neural Activity
journal contribution
posted on 2018-12-27, 00:00 authored by Joao L. Carvalho-de-Souza, Okhil K. Nag, Eunkeu Oh, Alan L. Huston, Igor Vurgaftman, David R. Pepperberg, Francisco Bezanilla, James B. DelehantyGold
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 light-responsiveness
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.
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Keywords
AP generationexcitable cell photosensitivityDRG neuronsGold Nanoparticles Enhances Photoactivationstably bind AuNP bioconjugateslight-induced AP generationDHLA-PEG-COOH532 nm lightPEGplasma membraneDorsal root gangliontransmembrane depolarizing capacitivesubthreshold depolarizing responsesDHLA-PEGplasmonic light absorptionNeural Activity Gold nanoparticles20 nm diameter