All-Optical and Label-Free Stimulation of Action Potentials in Neurons and Cardiomyocytes by Plasmonic Porous Metamaterials

Abstract

Optical stimulation technologies are gaining great consideration in cardiology, neuroscience studies, and drug discovery pathways by providing control over cell activity with high spatio-temporal resolution. However, this high precision requires manipulation of biological processes at genetic level concealing its development from broad scale application. Therefore, translating these technologies into tools for medical or pharmacological applications remains a challenge. Here, an all-optical nongenetic method for the modulation of electrogenic cells is introduced. It is demonstrated that plasmonic metamaterials can be used to elicit action potentials by converting near infrared laser pulses into stimulatory currents. The suggested approach allows for the stimulation of cardiomyocytes and neurons directly on commercial complementary metal-oxide semiconductor microelectrode arrays coupled with ultrafast pulsed laser, providing both stimulation and network-level recordings on the same device.

Keywords: cardiomyocytes; complementary metal-oxide semiconductor multielectrode arrays; metamaterials; microelectrode arrays; neurons; plasmonic optical stimulation; plasmonics.

Figure 1

Optical stimulation of cells with plasmonic metamaterials. A) Principle of activity stimulation by single‐cell excitation with ultrafast pulsed laser. Inset: the concept of plasmonically driven stimulation. B) Bright field image of the HiPSC‐CMs cultured on a CMOS‐MEA device. The arrows show the typical configuration in which an electrode is used for optical stimulation and the surrounding electrodes are used for recording. Scale bar: 30 µm. C) Detail of the optical charge emission induced by metamaterials when irradiated by NIR laser. Inset: SEM image of the porous material. Scale bar: 400 nm.

Figure 2

Photo‐generation of hot charges in nanoporous gold. A) Absorption profile of 50 nm thick porous gold. B) Current recorded with different laser intensity and with 10 ms pulse train duration. C) Faradaic photocurrent behavior with respect to the laser power. D) Comparison of the photocurrent recorded in the case of flat and porous gold surface when stimulated with 6 ms laser pulses. E) Recorded current in case of different laser pulses length and constant laser intensity of 5 mW.

Figure 3

Optical stimulation of HL‐1 cells and hiPSC‐CMs. A) Instantaneous maps of spontaneous (highlighted in green) and stimulated activity (pink) propagation in HL‐1. The arrow indicates the propagation wave direction. B) Recording of the standard activity of HL‐1 before and after the stimulus application. In the inset, the stimulated field potential event compared with the physiological one. C) Magnification of the field potential generated in standard condition. D) Magnification of the stimulated field potential. E) Example of the persistent pattern induced by the optical stimulation. F) Instantaneous maps of stimulated activity propagation in hiPSC‐CMs. Please refer to the corresponding movies in the Supporting Information for further details and clarifications, as indicated in the main text.

Figure 4

Optical stimulation of rat primary neurons. A) Spontaneous bursting activity of rat primary neurons on CMOS‐MEA. B) Burst activity on the same electrode stimulated by periodic laser pulses (8 s repetition period). The red asterisks indicate the presence of stimulated activity after the laser pulse. The inset shows a magnified view of a laser stimulation and consequent stimulated burst activity. C) Recovered spontaneous bursting activity after stopping the laser stimulation. D) A second series of periodic stimulation with 10 s repetition period. E) Recovered spontaneous bursting activity after stopping the second series of laser stimulation.