Sonophoric nanoprobe aided pH measurement in vivo using photoacoustic spectroscopy.

Presented here is a novel method of in vivo pH sensing utilizing a hybrid optical imaging technique, photoacoustic imaging (PAI), and pH sensitive polymeric nanoprobes. Nanoprobes with hydrophobic core containing a pH sensitive dye were synthesized and used to measure the pH level ex vivo first and then in vivo by performing experiments on a rat joint model, with an achieved precision of less than 0.1 pH units. The ability of the hydrophobic functional groups in the polyacrylamide matrix to shield the molecular dye from being affected by the proteins in the plasma, and prevent the dye from leaching out, is also demonstrated.

Fluorophore and dye-assisted dispersion of carbon nanotubes in aqueous solution.

DNA short oligo, surfactant, peptides, and polymer-assisted dispersion of single-walled carbon nanotube (SWCNTs) in aqueous solution have been intensively studied. It has been suggested that van der Waals interaction, π-π stacking, and hydrophobic interaction are major factors that account for the SWCNTs dispersion. Fluorophore and dye molecules such as Rhodamine B and fluorescein have both hydrophilic and hydrophobic moieties. These molecules also contain π-conjugated systems that can potentially interact with SWCNTs to induce its dispersion. Through a systematic study, here we show that SWCNTs can be dispersed in aqueous solution in the presence of various fluorophore or dye molecules. However, the ability of a fluorophore or dye molecule to disperse SWCNTs is not correlated with the stability of the fluorophore/dye-SWCNT complex, suggesting that the on-rate of fluorophore/dye binding to SWCNTs may dominate the efficiency of this process. We also examined the uptake of fluorophore molecules by mammalian cells when these molecules formed complexes with SWCNTs. The results can have potential applications in the delivery of poor cell-penetrating fluorophore molecules.

Cell-selective arrhythmia ablation for photomodulation of heart rhythm.

Heart disease, a leading cause of death in the developed world, is overwhelmingly correlated with arrhythmias, where heart muscle cells, myocytes, beat abnormally. Cardiac arrhythmias are usually managed by electric shock intervention, antiarrhythmic drugs, surgery, and/or catheter ablation. Despite recent improvements in techniques, ablation procedures are still limited by the risk of complications from unwanted cellular damage, caused by the nonspecific delivery of ablative energy to all heart cell types. We describe an engineered nanoparticle containing a cardiac-targeting peptide (CTP) and a photosensitizer, chlorin e6 (Ce6), for specific delivery to myocytes. Specificity was confirmed in vitro using adult rat heart cell and human stem cell-derived cardiomyocyte and fibroblast cocultures. In vivo, the CTP-Ce6 nanoparticles were injected intravenously into rats and, upon laser illumination of the heart, induced localized, myocyte-specific ablation with 85% efficiency, restoring sinus rhythm without collateral damage to other cell types in the heart, such as fibroblasts. In both sheep and rat hearts ex vivo, upon perfusion of CTP-Ce6 particles, laser illumination led to the formation of a complete electrical block at the ablated region and restored the physiological rhythm of the heart. This nano-based, cell-targeted approach could improve ablative technologies for patients with arrhythmias by reducing currently encountered complications.

A high-throughput photodynamic therapy screening platform with on-chip control of multiple microenvironmental factors.

We present a novel high-throughput microfluidic platform that enables the evaluation of the anticancer efficacy of photodynamic therapy (PDT) drugs over multiple microenvironmental factors. PDT is uniquely complex, originating from its dependence on three separate but essential elements: drug (also called photosensitizer), oxygen, and light. Thus, obtaining a reliable evaluation of PDT efficacy is highly challenging, requiring considerable effort and time to evaluate all three interdependent parameters. In this paper, we report a high-throughput efficacy screening platform that we implemented by developing microfluidic components that individually control basic PDT elements (photosensitizer concentrations, oxygen levels, and light fluence) and then integrating them into a single triple-layer device. The integrated microfluidic chip consists of an array of small compartments, each corresponding to a specific combination of these three variables. This allows for more than 1000 different conditions being tested in parallel. Cancer cells are cultured within the device, exposed to different PDT conditions, and then monitored for their viability using live/dead fluorescence staining. The entire screening assay takes only 1 hour, and the collected PDT outcomes (cell viability) for combinatorial screening are analysed and reported as traditional dose-response curves or 3D bubble charts using custom software. As a proof of concept, methylene blue is adopted as a photosensitizer and its drug efficacy on C6 glioma cells has been successfully evaluated for a total of 324 PDT conditions using the fabricated chip. This platform can facilitate not only the development of new photosensitizers but also the optimization of current PDT protocols.

Nano-photosensitizers Engineered to Generate a Tunable Mix of Reactive Oxygen Species, for Optimizing Photodynamic Therapy, Using a Microfluidic Device.

This work is aimed at engineering photosensitizer embedded nanoparticles (NPs) that produce optimal amount of reactive oxygen species (ROS) for photodynamic therapy (PDT). A revised synthetic approach, coupled with improved analytical tools, resulted in more efficient PDT. Specifically, methylene blue (MB) conjugated polyacrylamide nanoparticles (PAA NPs), with a polyethylene glycol dimethacrylate (PEGDMA, Mn 550) cross-linker, were synthesized so as to improve the efficacy of cancer PDT. The long cross-linker chain, PEGDMA, increases the distance between the conjugated MB molecules so as to avoid self-quenching of the excited states or species, and also enhances the oxygen permeability of the NP matrix, when compared to the previously used shorter cross-linker. The overall ROS production from the MB-PEGDMA PAA NPs was evaluated using the traditional way of monitoring the oxidation rate kinetics of anthracence-9,10-dipropionic acid (ADPA). We also applied singlet oxygen sensor green (SOSG) so as to selectively derive the singlet oxygen (1O2) production rate. This analysis enabled us to investigate the ROS composition mix based on varied MB loading. To effectively obtain the correlation between the ROS productivity and the cell killing efficacy, a microfluidic chip device was employed to provide homogeneous light illumination from an LED for rapid PDT efficacy tests, enabling simultaneous multiple measurements while using only small amounts of NPs sample. This provided multiplexed, comprehensive PDT efficacy assays, leading to the determination of a near optimal loading of MB in a PAA matrix for high PDT efficacy by measuring the light-dose-dependent cell killing effects of the various MB-PEGDMA PAA NPs using C6 glioma cancer cells.

Polymer-Protein Hydrogel Nanomatrix for Stabilization of Indocyanine Green towards Targeted Fluorescence and Photoacoustic Bio-imaging.

Indocyanine green (ICG) is an optical contrast agent commonly used for a variety of imaging applications. However, certain limitations of the free dye molecule, concerning its low stability, uncontrolled aggregation and lack of targeting ability, have limited its use. Presented here is a method of embedding ICG in a novel polymer/protein hybrid nanocarrier so as to overcome the above inherent drawbacks of the free molecule. The hybrid nanocarrier consists of a non-toxic and biocompatible polyacrylamide nanoparticle (PAA NP) matrix that incorporates human serum albumin (HSA). This nanocarrier was synthesized through pre-conjugation with HSA and amine functionalized monomer, followed by polymerization using biodegradable cross-linkers, in a water-in-oil emulsion. The ICG dye is loaded into the HSA conjugated PAA nanoparticles (HSA-PAA NPs) through post-loading. Compared to the PAA polymer matrix, the presence of hydrophobic pockets in the HSA-PAA NPs further increases the chemical and physical stability of ICG. This is manifested by lowering the chemical degradation rates under physiological conditions, as well as by improving the thermal- and photo-stability of the dye. A targeting moiety, F3-Cys peptide, was attached to the surface of the NPs, for selective delivery to specific cancer cell lines. The suitability of these NPs for optical imaging applications was demonstrated by performing fluorescence imaging on a rat gliosarcoma cell line (9L). We also present the photoacoustic response of the HSA-PAA NPs, used as imaging contrast agents, in the spectral window of 700 nm to 800 nm.