Antibody-conjugated gold nanoparticles as nanotransducers for second near-infrared photo-stimulation of neurons in rats

Abstract

Infrared neural stimulation with the assistance of photothermal transducers holds great promise as a mini-invasive neural modulation modality. Optical nanoparticles with the absorption in the near-infrared (NIR) window have emerged as excellent photothermal transducers due to their good biocompatibility, surface modifiability, and tunable optical absorption. However, poor activation efficiency and limited stimulation depth are main predicaments encountered in the neural stimulation mediated by these nanoparticles. In this study, we prepared a targeted polydopamine (PDA)-coated gold (Au) nanoparticles with specific binding to thermo-sensitive ion channel as nanotransducers for second near-infrared (NIR-II) photo-stimulation of neurons in rats. The targeted Au nanoparticles were constructed via conjugation of anti-TRPV1 antibody with PEGylated PDA-coated Au nanoparticles and thus exhibited potent photothermal performance property in the second NIR (NIR-II) window and converted NIR-II light to heat to rapidly activate Ca²⁺ influx of neurons in vitro. Furthermore, wireless photothermal stimulation of neurons in living rat successfully evoke excitation in neurons in the targeted brain region as deep as 5 mm beneath cortex. This study thus demonstrates a remote-controlled strategy for neuromodulation using photothermal nanotransducers.

Keywords: Gold nanoparticles; Near-infrared; Neural stimulation; Photothermal transducers; Polydopamine.

Fig. 1

Scheme of NIR-II neural stimulation via targeted Au nanoparticles. a Preparation of antibody-conjugated gold nanoparticles. b Mechanisms of nanoparticle-mediated NIR-II neural stimulation

Fig. 2

Characterization of Au nanoparticles. a Size distributions of Au@PDA, Au@PDA-PEG, and Au@PDA-PEG-Ab. b Hydrodynamic sizes of Au nanoparticles (n = 3). c Zeta potentials of Au nanoparticles (n = 3). d The UV–vis absorbance spectrum of TRPV1 antibody, Au@PDA-PEG, and Au@PDA-PEG-Ab. e TEM images of Au@PDA-PEG-Ab nanoparticles. Inset: SAED pattern of nanoparticles. f Enlarged view of Au@PDA-PEG-Ab nanoparticles

Fig. 3

Photothermal performance of Au nanoparticles. a Temperature curve of Au@PDA-PEG-Ab solution (50 μg/mL, 2 mL) irradiated with a 1064-nm laser at a power density of 1.5 W/cm². The laser was shut off after 30 min of irradiation. b Temperature curves of aqueous dispersion (100 μL) of Au@PDA-PEG-Ab at different concentrations from 10, 25, and 50 to 100 μg/mL under NIR-II laser irradiation (1.0 W/cm²). c Temperature curves of Au@PDA-PEG-Ab solution (50 μg/mL) under NIR-II laser irradiation at different power densities (0.5, 1.0, and 1.5 W/cm²). d Infrared thermal images of aqueous dispersion of Au@PDA, Au@PDA-PEG, and Au@PDA-PEG-Ab (50 μg/mL) upon NIR-II irradiation for 4 min. e Temperature curves of solutions in d. f Photothermal stability of Au@PDA, Au@PDA-PEG, and Au@PDA-PEG-Ab after 5 on/off cycles of laser irradiation (1.0 W/cm²). The concentration of nanoparticle dispersion was 50 μg/mL

Fig. 4

Cellular uptake and cytotoxicity of Au nanoparticles. a UV–vis spectra of FITC modified and unmodified Au nanoparticles. b Fluorescence spectra of FITC modified and unmodified Au nanoparticles. c Western blotting for TRPV1 from SH-SY5Y and HT-22 cells. d Cellular uptake of FITC modified Au nanoparticles. e Cell viability of HT-22 treated with different concentrations of Au@PDA-PEG-Ab for 24 h. f Cell viability of HT-22 treated with NIR-II laser irradiation of different power intensities and laser duration

Fig. 5

NIR-II photothermal activation of TRPV1 in HT-22 and SH-SY5Y neurons. a Fluorescent images of HT-22 or SH-SY5Y cells treated with Au@PDA-PEG or Au@PDA-PEG-Ab before and after laser irradiation at 1064 nm (0.5 W/cm²) for 1 s. b Changes in the Fluo-4 fluorescence intensity with the 1064 nm laser switching on and off at 1 s intervals. c The fluorescence intensity of Fluo-4 as a function of laser irradiation time

Fig. 6

In vivo NIR neural stimulation. a Procedures for in vivo neural stimulation. b H&E and c TUNEL staining of hippocampal slices after treated with Au@PDA-PEG-Ab and NIR-II laser irradiation. d C-fos staining of hippocampal slices after Au nanoparticles and NIR-II laser irradiation (1.0 W/cm²)