Nanolasers for in-vivo deep in tissue neuron activation and action potential sensing

Project Information

Neuralase

Grant agreement ID: 101023747

DOI

10.3030/101023747

Project terminated on 30 September 2022

EC signature date 12 April 2021

Start date 10 June 2021

End date 9 January 2024

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 174 806,40

EU contribution

€ 174 806,40

Coordinated by

UNIVERSITAT ZU KOLN
Germany

Periodic Reporting for period 1 - Neuralase (Nanolasers for in-vivo deep in tissue neuron activation and action potential sensing)

Reporting period: 2021-06-10 to 2023-06-09

Summary of the context and overall objectives of the project

The problem:
The operation of photonic devices deep inside tissues offers a great deal of information about internal physiological processes and small lasers are well-positioned to enable in vivo cell imaging, actuation, and sensing. There are severe issues with phototoxicity when devices operate in the visible part of the electromagnetic spectrum. Additionally, devices working at short wavelengths are limited to superficial layers of ≃ 100 um. This limits the more universal applicability of small lasers deeper into the tissues of living animals. Longer wavelengths, especially those falling in the high transmissive near-infrared NIR-I, and NIR-II windows present much higher penetration while preserving tissue integrity.

Important for society:
As we move towards hybrid and bionic models that can interface and help better understand animal and human models, optical innovations gain presence. Lasers are one of the quintessence discoveries of the 20th century, and it is currently ubiquitous in many technical areas of our society and has presented unique solutions never thought of before their invention. From displays to sensors, lasers offer a unique window to interface biological systems and society is investing resources to make better lasers to expand even further their applicability, and one of the most promising branches now is their integration into biological systems. Engineering issues with the fabrication of high-quality laser devices have shown to be of particular importance for laser discovery. An example of this is seen with the development of VCSELs, especially in the green. epitaxial growth precluded the extensive use of Vertical Cavity Surface Emitting Lasers (VCSELs) for illumination and displays. However, there are clever ways around epitaxy, and some lasers relying on plasmon hybrids or Whispering Gallery Modes (WGMs) seem to offer a way around the high power densities to pump microlasers. Effectively, WGMs can concentrate so much power that they have proved to work even with suboptimal Gain materials, and in more demanding systems relying on nonlinear optics to operate, examples of this can be found in my publication record.
Estimated to be $17B and it is projected to reach $25B The market for new laser systems is growing fast with a Compound annual growth rate (CAGR) of 8.9%, but it is also very challenging to evaluate the real impact they may have in future emergent technologies. Lasers have proven capabilities to disruptive technologies that range from optical communications to computing, and Brain-Computer Interfaces (BCIs).

The objectives are to produce bio-compatible lasers relying on nonlinear optics that can operate in the infrared (IR) at a fraction of the power they need in today’s technological landscape. Being able to tune the optical properties of laser cavities is of great interest to make lasers benign for biological tissue, but also keep them operating with Silicon-based detectors, a mature technology that offers great variability of cameras and sensors and an affordable price.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Cavity design:
Whispering gallery mode (WGM) cavities have a strong power concentration for laser pumping and made them highly efficient. Since the light concentrates around the rim of microspheres (0.7-10 um) laser modes are concentrated near the surface, their sensitivity to the environment makes them ideal sensors to operate in vivo.
Stand-alone cavities that can be pumped optically reduce the need for invasive electrodes and can be remotely pumped, but need to overcome transmission limitations of visible radiation through tissue. A solution to this problem is a robust operation in the infrared (IR). Here we present the first in vivo realization of upconverting microlasers operating in the near IR (NIR) inside freely behaving Drosophila larvae. We achieved lasing in stand-alone high-refractive index Barium Titanate (BaTiO3) whispering gallery modes (WGMs) cavities, at physiological temperatures, and under continuous wave (CW) excitation relying on the efficient coupling of Tm3+ based energy looping/photon avalanche nanoparticles (ELNPs, PANPs). These lasers present a significantly reduced footprint compared with previous designs with some devices presenting sub-micrometer radii, allowing the integration in living cells and Drosophila, while excited in the biologically transmissive second near-infrared (NIR-II) window. These lasers safely operated for over 39 hours in cells and several hours with Drosophila larvae.

Experiments with flies:
Drosophila melanogaster is a widespread animal model that in our case presents the perfect range of transparencies as the larvae undergo different stages of development, coming from almost transparent at instar 1 and 2 and increasing scattering and opacity as it transitions from instar 3 to pupa stages. Our experiments outlined a clear indication that infrared (IR) light has a much higher penetration even when the tissue is completely opaque, as it happens in the pupa phase where we can collect IR through the pupa. Laser emissions are clearly observed through instars 1, 2, and 3, being able to fully drive these lasers inside Drosophila and track development and function in larvae. This poses the first important step in driving microlasers inside tissues. The publication of these results is expected by the beginning of the next year 2023.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

There is no evidence of a fully integrated laser that can interface biological tissue to either investigate its properties or change its behavior in any way. Sensing and actuation are possible with microlasers but still remain the challenge of making autonomous laser devices. The main reason behind the complexity of integrating lasers in biological tissue, at almost any scale is the power delivery.
Delivering the power to excite lasers at short wavelengths can result in damaging or inefficient operation due to the intrinsic scattering and absorption of light by the tissue. It is well known that scattering in living tissues is a demanding challenge hard to get around. In the past, strategies to implement larger cavities with low power thresholds offered promising results to track contractility at the single cell level, for example, cardiomyocytes. Though, a major obstacle is that those lasers need pulsed excitation, increasing the instrument's complexity and constraining applicability to the laboratory environment. A more universal approach would require a continuous wave (CW) function at more benign wavelengths in the IR. A combination of near-infrared (NIR) wavelengths in the NIR-II window, excitation at 1064 nm with emission at 800 nm, significantly reduces scattering and presents higher tissue penetrations to excite lasers inside animals with increased collection efficiencies, which makes in vivo actuation of microlasers safer for biological tissue.
The stand-alone cavities in this work present a high refractive index (1.7-2.1) and high-power concentration that result in more efficient power usage. The gain material ELNPs using Tm3+ ions is capable of harnessing a photon-avalanche-like mechanism achieving in vivo lasing in sub-micron size cavities with volumes comparable to mitochondria, with dual emission/excitation in the near-infrared (NIR; 1064-800 nm), and continuous wave (CW) that can be implanted in tissue with minimal or no disruption.

Electron microscopy image of whispering gallery mode cavity made out of barium titanate