Preparation and characterization of a magnetic and optical dual-modality molecular probe

Abstract

Multi-modality imaging probes combine the advantages of individual imaging techniques to yield highly detailed anatomic and molecular information in living organisms. Herein, we report the synthesis and characterization of a dual-modality nanoprobe that couples the magnetic properties of ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) with the near infrared fluorescence of Cy5.5. The fluorophore is encapsulated in a biocompatible shell of silica surrounding the iron oxide core for a final diameter of approximately 17 nm. This silica-coated iron oxide nanoparticle (SCION) has been analyzed by transmission electron microscopy, dynamic light scattering, and superconducting quantum interference device (SQUID). The particle demonstrates a strong negative surface charge and maintains colloidal stability in the physiological pH range. Magnetic hysteresis analysis confirms superparamagnetic properties that could be manipulated for thermotherapy. The viability of primary human monocytes, T cells, and B cells incubated with the particle has been examined in vitro. In vivo analysis of agent leakage into subcutaneous A431 tumors in mice was also conducted. This particle has been designed for diagnostic application with magnetic resonance and fluorescence imaging, and has future potential to serve as a heat-sensitive targeted drug delivery platform.

Figure 1

Emissions spectrum of Cy5.5 conjugated either directly to USPIO or to silica-coated USPIO

Figure 2

SCION particle synthesis.

Figure 3

Transmission electron microscopy of synthesized SCION particles.

Figure 4

SCION particles characterized across pH range for (a) number distribution hydrodynamic diameter and (b) zeta potential. At >pH 5, the absolute value of the zeta potential was less than 30 mV and flocculation was observed. Right of the dotted line, zeta potential was strong and the observed hydrodynamic diameter was ~18 nm.

Figure 5

SCION magnetic hysteresis results at 310K and (a) ±7 T and (b) ±0.01 T, demonstrating superparamagnetic behavior.

Figure 6

Particle fluorescence and T-cell, B-cell, and monocyte viability analysis. (a) Fluorescence spectrum of SCION and unlabeled USPIO with excitation at 635nm. Study 1: Evaluation post 1hr-incubation with SCION (b) the percentage of SCION-stained cells that are viable (normalized to control) and (c) the percentage of viable cells that are SCION-stained. Study 2: After various incubation times with SCION, (d) the total percentage of viable cells and (e) the percentage of viable cells that are SCION-stained.

Figure 7

In vivo application of SCION particle for EPR effect into leaky tumors. R₂ maps of a A431-tumor bearing mouse at (a) pre-injection, (b) 1 h, (c) 2 h, (d) 4 h, and (e) 22 h post-i.v. injection demonstrates peak particle retention at 2 h post-injection.