Magnetically Responsive Inorganic/Polydiacetylene Nanohybrids

Colorimetric Detection of HER2-Overexpressing-Cancer-Derived Exosomes in Mouse Urine Using Magnetic-Polydiacetylene Nanoparticles

Breast cancer (BC) is a major global health problem, with ≈20-25% of patients overexpressing human epidermal growth factor receptor 2 (HER2), an aggressive marker, yet access to early detection and treatment varies across countries. A low-cost, equipment-free, and easy-to-use polydiacetylene (PDA)-based colorimetric sensor is developed for HER2-overexpressing cancer detection, designed for use in low- and middle-income countries (LMICs). PDA nanoparticles are first prepared through thin-film hydration. Subsequently, hydrophilic magnetic nanoparticles and HER2 antibodies are sequentially conjugated to them. The synthesized HER2-MPDA can be concentrated and separated by a magnetic field while inheriting the optical characteristics of PDA. The specific binding of HER2 antibody in HER2-MPDA to HER2 receptor in HER2-overexpressing exosomes causes a blue-to-red color change by altering the molecular structure of the PDA backbone. This colorimetric sensor can simultaneously separate and detect HER2-overexpressing exosomes. HER2-MPDA can detect HER2-overexpressing exosomes in the culture medium of HER2-overexpressing BC cells and in mouse urine samples from a HER2-overexpressing BC mouse model. It can selectively isolate and detect only HER2-overexpressing exosomes through magnetic separation, and its detection limit is found to be 8.5 × 108  particles mL-1 . This colorimetric sensor can be used for point-of-care diagnosis of HER2-overexpressing BC in LMICs.

Modifying Polydiacetylene Vesicle Compositions to Reduce Non-Specific Interactions

Polydiacetylene (PDA) vesicles provide useful stimuli-responsive behavior as well as by the modular structure afford a means for the design of sensing and delivery systems with tunable target specificity. To reduce inherent non-specific interaction with either anionic or cationic formulations of polydiacetylene vesicles, we explored the use of various lengths of poly(ethylene glycol) (PEG) amphiphiles for integration and polymerization within PDA vesicles. Our results established that as little as 1% of polyethylene glycol amphiphile integration into anionic vesicles was sufficient to significantly reduce non-specific association with mammalian cells. Similarly integrating a low percent of PEG amphiphile content within cationic vesicles could also significantly reduce non-specific cell association, and moreover reduced cytotoxicity. These results may be prove useful in augmenting PDA vesicles formulations for reduced non-specific interaction which is of particularly interest to enhancing selectivity in vesicles designed with integrated targeting moieties for sensing and drug delivery applications.

Tuning the Surface Charge of Self-Assembled Polydiacetylene Vesicles to Control Aggregation and Cell Binding

Polydiacetylene vesicles of various compositions were assembled using a two-part mixture of 10,12-pentacosadiynoic acid (PCDA) and ethylenedioxy-bis-ethylamine (EDEA)-labeled PCDA in order to control surface charge and stability within a desired pH range. Investigation of the interaction of the vesicles with mammalian cells as a function of surface charge was carried out and identified a clear correlation in cell–vesicle association and corresponding cell death for vesicles with positive surface charge. The binding behavior of the vesicles was found to be tunable by regulating the proportion of anionic PCDA relative to cationic PCDA–EDEA content within vesicles as to control the surface charge as a function of pH. Association of vesicles with cells thus depended on the corresponding charge of the vesicles and cell surface. The prospect of this work may serve as a step toward future vesicle designs to allow triggered uptake of vesicles locally within low pH tumor microenvironments.

Microfabrication of Custom Collagen Structures Capable of Guiding Cell Morphology and Alignment

The patterning of biological components into structural analogues of native tissues to simulate an environment for directing cell growth is one important strategy in biomaterials fabrication. It is widely accepted that chemical, mechanical, and topological cues from the extracellular matrix (ECM) provide important signals for guiding cells to exhibit characteristic polarity, orientation, and morphology. To fully understand the delicate relationship between cell behavior and ECM features, biomaterials fabrication requires improved techniques for tailoring nano/microstructured patterns from relevant biological building blocks rather than using nonbiological materials. Here we reveal a unique approach for the nano/microfabrication of custom patterned biomaterials using collagen as the sole building material. With this new fabrication technique, we further revealed that custom collagen patterns could direct the orientation and morphology of fibroblast growth as a function of vertex density and pattern spacing. Our findings suggest that this technique may be readily adopted for the free form fabrication of custom cell scaffolds purely from natural biological molecules including collagen, among other relevant ECM components.

A polymerizable supramolecular approach for the fabrication of patterned magnetic nanoparticles

A straightforward method for the preparation of patterned magnetite nanoparticles (MNPs) was developed. The polymerizable supramolecular approach afforded finely patterned MNPs on a solid substrate after a sequential UV-irradiation-wet etching-calcination process with an MNP-embedded diacetylene film.

Janus-compartmental alginate microbeads having polydiacetylene liposomes and magnetic nanoparticles for visual lead(II) detection

Janus-compartmental alginate microbeads having two divided phases of sensory polydiacetylene (PDA) liposomes and magnetic nanoparticles were fabricated for facile sensory applications. The sensory liposomes are composed of PDA for label-free signal generation and 1,2-dipalmitoyl-sn-glycero-3-galloyl (DPGG) lipids whose galloyl headgroup has specific interactions with lead(II). The second phase having magnetic nanoparticles is designed for convenient handling of the microbeads, such as washing, solvent exchange, stirring, and detection, by applying magnetic field. Selective and convenient colorimetric detection of lead(II) and efficient removal of lead(II) by alginate matrix at the same time are demonstrated.

A portable and chromogenic enzyme-based sensor for detection of abrin poisoning

A first of its kind portable, colorimetric detection system has been developed for the rapid diagnosis of abrin poisoning. Abrin, a natural biotoxin that is homologous to ricin yet more lethal, has high potential for becoming a weapon of bioterrorism given its ease of production. Using an immobilization strategy that implements non-natural amino acids for site-specific conjugation, we have created a reusable N-methyltryptophan oxidase based magnetic bead system that is capable of detecting L-abrine, a marker for abrin poisoning, at concentrations as low as 4 μM in mock urine. Furthermore, we propose that this detection strategy may be readily adaptable for sensing other targets of interest. This unique diagnostic test for abrin poisoning has demonstrated key benefits of portability and simple visual readout. These significant advantages can thus provide the potential for more rapid assessment and corresponding poison management if dedicated toxicology laboratories are not an option.

Controlling and assessing the surface display of cell-binding domains on magnetite conjugated fluorescent liposomes

Biological systems provide us with a diverse source of peptide-based ligands for cellular adhesion. Controlling and assessing the ligand surface density as well as tailoring the surface chemistry to have specific cellular adhesion properties are important in biomaterials design. In the following work, we provide a means for displaying peptide-based ligands on magnetic liposomes in which the surface density and chemistry may be controlled. Simultaneously, the conjugated vesicles provide a fluorescent signal for examining steric hindrance among surface ligands. In addition, the inherent magnetic and fluorescence features of this system revealed potential for magnet-based cell isolation and fluorescent labeling of adhered cells, respectively. Adhered cells were found to remain viable and proliferative, thereby allowing them to be used for subsequent evaluation. In a specific demonstration, we control the density of fibronectin-mimetic ligands on the polydiacetylene liposome surfaces. We find that steric limitation occurring at over 20% surface density result in decreased cell adhesion, in accord with related techniques. The magnetic-liposome system offers the means for not only separating cells adhered to the biomaterial, but also providing the ability to control and assess the biomaterial surface. This may prove particularly useful for examining combinations of peptide-based ligands or for evaluating the molecular-level ligand accessibility and its effect on cell attachment to a biomaterial surface.