Nano-enabled SERS reporting photosensitizers

Abstract

To impart effective cellular damage via photodynamic therapy (PDT), it is vital to deliver the appropriate light dose and photosensitizer concentration, and to monitor the PDT dose delivered at the site of interest. In vivo monitoring of photosensitizers has in large part relied on their fluorescence emission. Palladium-containing photosensitizers have shown promising clinical results by demonstrating near full conversion of light to PDT activity at the cost of having undetectable fluorescence. We demonstrate that, through the coupling of plasmonic nanoparticles with palladium-photosensitizers, surface-enhanced Raman scattering (SERS) provides both reporting and monitoring capability to otherwise quiescent molecules. Nano-enabled SERS reporting of photosensitizers allows for the decoupling of the therapeutic and imaging mechanisms so that both phenomena can be optimized independently. Most importantly, the design enables the use of the same laser wavelength to stimulate both the PDT and imaging features, opening the potential for real-time dosimetry of photosensitizer concentration and PDT dose delivery by SERS monitoring.

Keywords: Dosimetry; Nanoparticles; PDT; Porphyrins; SERS; Theranostics.

Figure 1

A) Intrinsic SERS reporting theranostic nanoparticle that when excited with 638 nm light simultaneous produce PDT and SERS molecular imaging. B) Palladium metalation of free-base pyrolipid using acetate method. C) Fluorescence measurements of free-base pyrolipid, manganese-pyrolipid, and palladium-pyrolipid in methanol. D) Synthesis of PdPL theranostic nanoparticles using standard liposome techniques to form Pd-porphysomes that are subsequently sonicated onto AuNPs. E) Transmission electron micrograph of PdPL-NP using uranyl acetate lipid staining. F) Absorption and emission spectrum of the different components of PdPL-NPs.

Figure 2

A) Dose-dependent SERS intensity of PdPL-NP with a limit of detection of 500 fM. Inset better illustrates SERS intensity at low nanoparticle concentrations. B) Solution assay of PDT ROS photogeneration showing PdPL-NP concentration dependent ROS release relative to PDT quiescent MnPL-NPs and control. C) Photobleaching dependent SERS intensity correlates with increase in SOSG fluorescence for PDT dosimetry. Black squares correspond to left y-axis illustrating SOSG fluorescence assay and red circles correspond to right y-axis illustrating SERS intensity measurements. D) In vitro MTT assay using KB cells with PdPL-NPs treated with 0-250 pM nanoparticle concentration and 10 J/cm² light dose. Data for A and C acquired with laser fluence rate 250 mW/cm² while B and D were acquired with fluence rate of 50 mW/cm².

Figure 3

A) SERS molecular imaging of folate-receptor positive KB carcinoma cells with folate targeted PdPL- and MnPL-NPs. Pseudocolored Raman map overlay of background corrected area-under curve at 755 cm^-1 Raman shift for PdPL-NP and 753 cm^-1 Raman shift for MnPL-NP. SERS images obtained at laser fluence rate of 250 mW/cm². B) Representative SERS spectrum of PdPL-NPs from pre- and post-PDT Raman map overlay. Scale bars are 25 μm.

Figure 4

Cell viability (live/dead) assay during simultaneous PDT and SERS imaging. Green channel depicts live cells and red channel depicts compromised/dead cells. Field of view matched with SERS images above.