Joseph D. Kimball

Physicochemical properties of potential porphyrin photosensitizers for photodynamic therapy

This research evaluated the suitability of synthetic photosensitizers for their use as potential photosensitizers in photodynamic therapy using steady state and time-resolved spectroscopic techniques. Four tetraphenylporphyrin derivatives were studied in ethanol and dimethyl sulfoxide. The spectroscopic properties namely electronic absorption and emission spectra, ability to generate singlet oxygen, lifetimes of the triplet state, as well as their fluorescence quantum yield were determined. Also time-correlated single photon counting method was used to precisely determine fluorescence lifetimes for all four compounds. Tested compounds exhibit high generation of singlet oxygen, low generation of fluorescence and they are chemical stable during irradiation. The studies show that the tested porphyrins satisfy the conditions of a potential drug in terms of physicochemical properties.

Effect of ionic liquids on the conformation of a porphyrin -based viscometer

Structure of the cationic and anionic counterparts of ionic liquids has a significant impact on the conformational bias of the porphyrin rotor; an apparent correlation between the conformation and the viscosity of ionic liquids was noted, albeit it was found to be distinct and more complex from that found in molecular solvents.

Photophysical characterization of anticancer drug valrubicin in rHDL nanoparticles and its use as an imaging agent.

Nanoparticles are target-specific drug delivery agents that are increasingly used in cancer therapy to enhance bioavailability and to reduce off target toxicity of anti-cancer agents. Valrubicin is an anti-cancer drug, currently approved only for vesicular bladder cancer treatment because of its poor water solubility. On the other hand, valrubicin carrying reconstituted high density lipoprotein (rHDL) nanoparticles appear ideally suited for extended applications, including systemic cancer chemotherapy. We determined selected fluorescence properties of the free (unencapsulated) drug vs. valrubicin incorporated into rHDL nanoparticles. We have found that upon encapsulation into rHDL nanoparticles the quantum yield of valrubicin fluorescence increased six fold while its fluorescence lifetime increased about 2 fold. Accordingly, these and potassium iodide (KI) quenching data suggest that upon incorporation, valrubicin is localized deep in the interior of the nanoparticle, inside the lipid matrix. Fluorescence anisotropy of the rHDL valrubicin nanoparticles was also found to be high along with extended rotational correlation time. The fluorescence of valrubicin could also be utilized to assess its distribution upon delivery to prostate cancer (PC3) cells. Overall the fluorescence properties of the rHDL: valrubicin complex reveal valuable novel characteristics of this drug delivery vehicle that may be particularly applicable when used in systemic (intravenous) therapy.

BSA Au Clusters as a Probe for Enhanced Fluorescence Detection Using Multipulse Excitation Scheme

Although BSA Au clusters fluoresce in red region (λmax: 650 nm), they are of limited use due to low fluorescence quantum yield (~6%). Here we report an enhanced fluorescence imaging application of fluorescent bio-nano probe BSA Au clusters using multipulse excitation scheme. Multipulse excitation takes advantage of long fluorescence lifetime (> 1 µs) of BSA Au clusters and enhances its fluorescence intensity 15 times over short lived cellular auto-fluorescence. Moreover we have also shown that by using time gated detection strategy signal (fluorescence of BSA Au clusters) to noise (auto-fluorescence) ratio can be increased by 30 fold. Thereby with multipulse excitation long lifetime probes can be used to develop biochemical assays and perform optical imaging with zero background.

Simple multipulse excitation for enhanced detection of long-lived fluorophores

Typically the signal-to-background ratio is the limiting aspect of fluorescence-based detecting and imaging. The background signal can be composed of a variety of sources-excitation scattering, contaminants, and autofluorescence from cellular constituents. Most of these sources have a short-lived lifetime (ps to ns range). In order to increase the signal-to-background ratio, fluorophores with high brightness or in large concentrations are typically used along with time-gated detection. This unfortunately sacrifices the probe’s signal unless it has a very long lifetime. Herein we are presenting a simple method to enhance the detection of widely available and well-known mid-range lifetime (~20 ns) fluorophores’ signal against short-lived backgrounds. This requires a repetition rate of ~300 MHz to pump a 20 ns probe sufficiently. Typical laser sources today are not equipped with repetition rates above 80 MHz. However, this multipulse method allows these rates to be attainable for nearly any pulsed laser source. Multiple pulses of excitation are separated by a variable temporal length, which is short compared to the lifetime of the long-lived fluorophore, to increase the excited state population of a long-lived fluorophore, while the short-lived background decays almost completely between pulses. This is accomplished by simply redirecting the pulsed excitation beam through glass and then a delay length any number of times and lengths as desired to control the number of pulses and separation times.

Fluorescent nanodiamonds for ultrasensitive detection

Fluorescent nanodiamonds (NDs) are new and emerging nanomaterials that have potential to be used as fluorescence imaging agents and also as a highly versatile platform for the controlled functionalization and delivery of a wide spectrum of therapeutic agents. We will utilize two experimental methods, TIRF, a relatively simple method based on total internal reflection fluorescence and SPRF, fluorescence enhanced by resonance coupling with surface plasmons. We estimate that the SPRF method will be 100 times sensitive than currently available similar detectors based on detectors. The ultimate goal of this research is to develop microarray platforms that could be used for sensitive, fast and inexpensive gene sequencing and protein detection.