Optical properties of biomimetic probes engineered from erythrocytes

Abstract

Light-activated theranostic materials offer a potential platform for optical imaging and phototherapeutic applications. We have engineered constructs derived from erythrocytes, which can be doped with the FDA-approved near infrared (NIR) chromophore, indocyanine green (ICG). We refer to these constructs as NIR erythrocyte-mimicking transducers (NETs). Herein, we investigated the effects of changing the NETs mean diameter from micron- (≈ 4 μm) to nano- (≈ 90 nm) scale, and the ICG concentration utilized in the fabrication of NETs from 5 to 20 μM on the resulting absorption and scattering characteristics of the NETs. Our approach consisted of integrating sphere-based measurements of light transmittance and reflectance, and subsequent utilization of these measurements in an inverse adding-doubling algorithm to estimate the absorption (μa) and reduced scattering (μs′) coefficients of these NETs. For a given NETs diameter, values of μa increased over the approximate spectral band of 630 – 860 nm with increasing ICG concentration. Micron-sized NETs produced the highest peak value of μa when using ICG concentrations of 10 and 20 μM, and showed increased values of μs′ as compared to nano-sized NETs. Spectral profiles of μs′ for these NETs showed a trend consistent with Mie scattering behavior for spherical objects. For all NETs investigated, changing the ICG concentration minimally affected the scattering characteristics. A Monte Carlo-based model of light distribution showed that the presence of these NETs enhanced the fluence levels within simulated blood vessels. These results provide important data towards determining the appropriate light dosimetry parameters for an intended light-based biomedical application of NETs.

Near-Infrared-Fluorescent Erythrocyte-Mimicking Particles: Physical and Optical Characteristics

“…3(c)]. In a previous study, we showed that the reduced scattering coefficient of nNETs was less than half (≈45%) of that of NETs [54], which is consistent with the lower attenuation in the 250-500 nm spectral band for nNETs formed by sonication. nNETs formed by extrusion had even lower attenuation in this spectral band, due to loss of EG material during the extrusion process, resulting in fewer relative number of light-scattering particles.…”

“…3). These spectral peaks are attributed to the monomer form of ICG, as indicated in previous studies [54][55][56], and were bathochromically shifted with respect to the absorption peak of free ICG (780 nm) by approximately 20 nm. This shift is consistent with the behavior of ICG in emulsions and micellar formulations [52,84], and can be attributed to the intercalation of ICG into the lipid bilayer of NETs and binding to the phospholipids and membrane proteins therein [43,55,84], leading to changes in the conformation of ICG and its electronic states.…”

“…The absorption shoulder in the spectral range of 720-760 nm corresponds to the H-like aggregate form of ICG [54,74].…”

“…Recently, we have encapsulated ICG using hemoglobindepleted red blood cells (RBCs), also known as erythrocyte ghosts (EGs) [54][55][56][57]. We refer to these ICG loaded particles as NIR erythrocyte-mimicking transducers (NETs) since they can use NIR light to generate heat, fluorescence, and reactive oxygen species [58].…”

Functionalized erythrocyte-derived optical nanoparticles to target ephrin-B2 ligands

“…Absorption at ≈795 and ≈735 nm corresponds to the monomeric and H-like aggregate forms of ICG, respectively. 22,41,42 There was a near linear relationship between the absorbance values at 795 nm and N Ã . For example, when N Ã was increased to 2×, the absorbance value at 795 nm increased from ≈1.0 to ≈1.8 for both sets of nanoparticles.…”