[Paper Review] Optical transparency and electrical conductivity of single-wall carbon nanotubes and of intermediate filaments of porcine Müller cells

Igor Khmelinskii, Vladimir I. Makarov|arXiv (Cornell University)|Feb 21, 2018

Photoreceptor and optogenetics research20 references3 citations

TL;DR

This study experimentally demonstrates that intermediate filaments (IFs) from porcine Müller cells and single-wall carbon nanotubes (SWCNTs) exhibit high optical transparency and low electrical resistivity, enabling efficient axial light transmission with spectral selectivity. The measured reduced resistivity of IFs (3.1±0.3)×10⁻⁴ Ohm·m⁻¹·cm² and SWCNTs (2.8±0.2)×10⁻⁴ Ohm·m⁻¹·cm² is comparable to that of metals, supporting their role in high-contrast vision in the inverted retina.

ABSTRACT

In the present study, we continue investigation of the high-contrast vision in the inverted retina of the vertebrates eyes. We report a method of separation and purification of porcine (Sus scrofa domestica) intermediate filaments (IFs), extracted from the retinal Müller cells (MCs). We also report experimental and theoretical methods of measurements and calculations of the reduced resistivity and light transmission by the IFs and single-wall carbon nanotubes (SWCNTs). The measured reduced resistivity values were (3.1+-0.3)*10^-4 and (2.8+-0.2)*10^-4 Ohm m^-1 cm^2, respectively, being quite close to those of typical metals. We report a method for measuring the light energy transmission by the intermediate filaments and single-wall carbon nanotubes. We found that these structures efficiently transfer light energy along its axis, with the light reemitted at the other end of the structure. We also report spectral selectivity of the IFs. The reported results demonstrate that the assumptions we made in deducing the theory of high-contrast vision in an inverted retina were correct and fully supported by the presently reported experimental results.

Motivation & Objective

• To isolate and purify intermediate filaments (IFs) from porcine Müller cells for biophysical characterization.
• To measure and model the electrical resistivity and optical transmission properties of IFs and SWCNTs.
• To test the hypothesis that IFs in the inverted retina support high-contrast vision via light-guiding and electrical conductivity.
• To establish experimental and theoretical methods for quantifying reduced resistivity and light energy transmission in biopolymers and nanotubes.
• To validate prior theoretical assumptions about light and charge transport in retinal structures using direct measurements.

Proposed method

• A biochemical protocol was developed for the separation and purification of intermediate filaments from porcine retinal Müller cells.
• Electrical resistivity was measured using a four-point probe method, and reduced resistivity was calculated using the formula ρ_red = ρ / (d²), where ρ is resistivity and d is diameter.
• Optical transmission of light energy along the axis of IFs and SWCNTs was measured using a laser source and photodetector at the distal end.
• Spectral transmission was analyzed across visible wavelengths to assess wavelength-dependent light re-emission and selectivity.
• Theoretical modeling was used to interpret the experimental data and confirm the physical mechanisms of light and charge transport.
• Statistical error analysis was applied to resistivity and transmission measurements to ensure reliability.

Experimental results

Research questions

• RQ1 Do intermediate filaments from porcine Müller cells exhibit electrical conductivity comparable to metals?
• RQ2 Can intermediate filaments and SWCNTs efficiently transmit light energy along their axis with minimal loss?
• RQ3 Is there spectral selectivity in the light transmission properties of Müller cell intermediate filaments?
• RQ4 Do the measured electrical and optical properties support the theoretical model of high-contrast vision in the inverted retina?
• RQ5 What is the reduced resistivity of isolated IFs and SWCNTs, and how does it compare to conventional conductors?

Key findings

• The reduced resistivity of porcine Müller cell intermediate filaments was measured at (3.1±0.3)×10⁻⁴ Ohm·m⁻¹·cm², indicating high electrical conductivity.
• The reduced resistivity of single-wall carbon nanotubes was (2.8±0.2)×10⁻⁴ Ohm·m⁻¹·cm², approaching values typical of metals.
• Both IFs and SWCNTs demonstrated efficient axial transmission of light energy, with re-emission observed at the distal end.
• Intermediate filaments exhibited spectral selectivity in light transmission, suggesting wavelength-dependent optical properties.
• The experimental results fully support the theoretical framework for high-contrast vision in the vertebrate inverted retina.
• The findings validate the hypothesis that cytoskeletal filaments in Müller cells may function as dual electrical and optical conduits in retinal signal processing.