Cationic Porphyrin-Based Ionic Nanomedicines for Improved Photodynamic Therapy

This study presents the synthesis and characterization of monosubstituted cationic porphyrin as a photodynamic therapeutic agent. Cationic porphyrin was converted into ionic materials by using a single-step ion exchange reaction. The small iodide counteranion was replaced with bulky BETI and IR783 anions to reduce aggregation and enhance the photodynamic effect of porphyrin. Carrier-free ionic nanomedicines were then prepared by using the reprecipitation method. The photophysical characterization of parent porphyrin, ionic materials, and ionic nanomaterials, including absorbance, fluorescence and phosphorescence emission, quantum yield, radiative and nonradiative rate, and lifetimes, was performed. The results revealed that the counteranion significantly affects the photophysical properties of porphyrin. The ionic nanomaterials exhibited an increase in the reactive oxygen yield and enhanced cytotoxicity toward the MCF-7 cancer cell line. Examination of results revealed that the ionic materials exhibited an enhanced photodynamic therapeutic activity with a low IC50 value (nanomolar) in cancerous cells. These nanomedicines were mainly localized in the mitochondria. The improved light cytotoxicity is attributed to the enhanced photophysical properties and positive surface charge of the ionic nanomedicines that facilitate efficient cellular uptake. These results demonstrate that ionic material-based nanodrugs are promising photosensitizers for photodynamic therapy.

Understanding of Förster Resonance Energy Transfer (FRET) in Ionic Materials

Herein, an ionic material (IM) with Förster Resonance Energy Transfer (FRET) characteristics is reported for the first time. The IM is designed by pairing a Nile Blue A cation (NBA⁺) with an anionic near-infrared (NIR) dye, IR820^-, using a facile ion exchange reaction. These two dyes absorb at different wavelength regions. In addition, NBA⁺ fluorescence emission spectrum overlaps with IR820^- absorption spectrum, which is one requirement for the occurrence of the FRET phenomenon. Therefore, the photophysical properties of the IM were studied in detail to investigate the FRET mechanism in IM for potential dye sensitized solar cell (DSSCs) application. Detailed examination of photophysical properties of parent compounds, a mixture of the parent compounds, and the IM revealed that the IM exhibits FRET characteristics, but not the mixture of two dyes. The presence of spectator counterion in the mixture hindered the FRET mechanism while in the IM, both dyes are in close proximity as an ion pair, thus exhibiting FRET. All FRET parameters such as spectral overlap integral, Förster distance, and FRET energy confirm the FRET characteristics of the IM. This article presents a simple synthesis of a compound with FRET properties which can be further used for a variety of applications.

Improved Photophysical Properties of Ionic Material-Based Combination Chemo/PDT Nanomedicine

Herein, a cost-effective and prompt approach to develop ionic material-based combination nanodrugs for cancer therapy is presented. A chemotherapeutic (phosphonium) cation and photodynamic therapeutic (porphyrin) anion are combined using a single step ion exchange reaction. Afterward, a nanomedicine is prepared from this ionic materials-based combination drug using a simplistic strategy of reprecipitation. Improved photophysical characteristics such as a slower nonradiative rate constant, an enhanced phosphorescence emission, a longer lifetime, and a bathochromic shift in absorbance spectra of porphyrin are observed in the presence of a chemotherapeutic countercation. The photodynamic therapeutic activity of nanomedicines is investigated by measuring the singlet oxygen quantum yield using two probes. As compared to the parent porphyrin compound, the synthesized combination material showed a 2-fold increase in the reactive oxygen species quantum yield, due to inhibition of face-to-face aggregation of porphyrin units in the presence of bulky chemotherapeutic ions. The dark cytotoxicity of combination therapy nanomedicines in the MCF-7 (cancerous breast) cell line is also increased as compared to their corresponding parent compounds in vitro. This is due to the high cellular uptake of the combination nanomedicines as compared to that of the free drug. Further, selective toxicity toward cancer cells was acquired by functionalizing nanomedicine with folic acid followed by incubation with MCF-7 and MCF-10A (noncancerous breast). Light toxicity experiments indicate that the synthesized ionic nanomedicine shows a greater cell death than either parent drug due to the improved photophysical properties and effective combination effect. This facile and economical strategy can easily be utilized in the future to develop many other combination ionic nanomedicines with improved photodynamics.

Photodegradable CuS SERS Probes for Intraoperative Residual Tumor Detection, Ablation, and Self-Clearance

Surface-enhanced Raman scattering (SERS) probes have exhibited great potential in biomedical applications. However, currently reported SERS probes are mainly fabricated by nondegradable Au or Ag nanostructures, which are not favorably cleared from the imaged tissues. This bottleneck hinders their in vivo applications. We herein explore a degradable SERS probe consisting of hollow CuS nanoparticles (NPs) to circumvent the current limitation. We identify, for the first time, the Raman enhancement effects of hollow CuS NPs as a SERS probe for Raman imaging of residual tumor lesions. Uniquely, CuS SERS probes are degradable, which stems from laser-induced photothermal effects of CuS NPs, leading to their disintegration from shell structures into individual crystals, thus facilitating their self-clearance from imaged tissues. This novel CuS SERS probe with photodegradation characteristics opens avenues for applying Raman imaging toward a myriad of biomedical applications.

Quantum Dot Donor-Polymer Acceptor Architecture for a FRET-Enabled Solar Cell

Forster resonance energy-transfer (FRET)-based solution-processed solar cell is fabricated with cadmium sulfide (CdS) as the energy donor and poly[ N-9'-heptadecanyl-2,7-carbazole- alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) as the energy acceptor. Carbon dots (C-dots) deposited on carbon fabric are applied as a counter electrode. Although electron injection from CdS to PCDTBT is energetically disfavored, evidences for energy transfer between the two components of the cell are obtained in terms of FRET parameters with the relative quantum yield of donor CdS quantum dots (QDs) being ∼0.3, a Forster radius of ∼3.7 nm, and an energy-transfer efficiency of ∼55%. Power conversion efficiency (PCE) of the TiO₂/PCDTBT cell without the donor is 0.23% and when coupled with donor CdS QDs, the ensuing TiO₂/PCDTBT/CdS cell experiences a 23 time increment in PCE, reaching 5.3%. The complete FRET cell: TiO₂/PCDTBT/CdS/ZnS-S^2--C-dots/C-fabric produces a PCE of 7.42%, under 1 sun illumination. External quantum efficiency studies reveal an enhanced spectral response spanning from 300 to 670 nm, with 300 and 175% increases attained for the FRET-enabled TiO₂/PCDTBT/CdS/ZnS photoanode compared with the TiO₂/PCDTBT photoanode over the blue and green-red portions of the solar spectrum.

Heuristics from Modeling of Spectral Overlap in Förster Resonance Energy Transfer (FRET)

Among the photophysical parameters that underpin Förster resonance energy transfer (FRET), perhaps the least explored is the spectral overlap term ( J). While by definition J increases linearly with acceptor molar absorption coefficient (ε_(A) in M^-1 cm^-1), is proportional to wavelength (λ⁴), and depends on the degree of overlap of the donor fluorescence and acceptor absorption spectra, the question arose as to the value of J for the case of perfect spectral overlap versus that for representative fluorophores with incomplete spectral overlap. Here, Gaussian distributions of absorption and fluorescent spectra have been modeled that encompass varying degrees of overlap, full-width-at-half-maximum (fwhm), and Stokes shift. For ε_(A) = 10⁵ M^-1 cm^-1 and perfect overlap, the J value (in M^-1 cm^-1 nm⁴) ranges from 1.15 × 10¹⁴ (200 nm) to 7.07 × 10¹⁶ (1000 nm), is almost linear with λ⁴ (average of λ_abs and λ_flu), and is nearly independent of fwhm. For visible-region fluorophores with perfectly overlapped Gaussian spectra, the resulting value of J ( J_G-0) is ∼0.71 ε_(A)λ⁴ (M^-1 cm^-1 nm⁴). The experimental J values for homotransfer, as occurs in light-harvesting antennas, were calculated with spectra from a static database of 60 representative compounds (12 groups, 5 compounds each) and found to range from 4.2 × 10¹⁰ ( o-xylene) to 5.3 × 10¹⁶ M^-1 cm^-1 nm⁴ (a naphthalocyanine). The degree of overlap, defined by the ratio of the experimental J to the model J_G-0 for perfectly overlapped spectra, ranges from ∼0.5% (coumarin 151) to 77% (bacteriochlorophyll a). The results provide insights into how a variety of factors affect the resulting J values. The high degree of spectral overlap for (bacterio)chlorophylls prompts brief conjecture concerning the relevance of energy transfer to the question "why chlorophyll".

Increasing Photovoltaic Performance of an Organic Cationic Chromophore by Anion Exchange

A symmetrical cyanine dye chromophore is modified with different counteranions to study the effect on crystal packing, polarizability, thermal stability, optical properties, light absorbing layer morphology, and organic photovoltaic (OPV) device parameters. Four sulfonate-based anions and the bulky bistriflylimide anion are introduced to the 2-[5-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)-1,3-pentadien-1-yl]-1,3,3-trimethyl-3H-indolium chromophore using an Amberlyst A26 (OH^- form) anion exchanger. Anionic charge distribution clearly correlates with device performance, whereby an average efficiency of 2% was reached in a standard bilayer organic solar. Evidence is given that the negative charge of the anion distributed over a large number of atoms is significantly more important than the size of the organic moieties of the sulfonate charge carrying group. This provides a clear strategy for future design of more efficient cyanine dyes for OPV applications.