Nikodem Tomczak

Photostable fluorescent organic dots with aggregation-induced emission (AIE dots) for noninvasive long-term cell tracing

Long-term noninvasive cell tracing by fluorescent probes is of great importance to life science and biomedical engineering. For example, understanding genesis, development, invasion and metastasis of cancerous cells and monitoring tissue regeneration after stem cell transplantation require continual tracing of the biological processes by cytocompatible fluorescent probes over a long period of time. In this work, we successfully developed organic far-red/near-infrared dots with aggregation-induced emission (AIE dots) and demonstrated their utilities as long-term cell trackers. The high emission efficiency, large absorptivity, excellent biocompatibility, and strong photobleaching resistance of the AIE dots functionalized by cell penetrating peptides derived from transactivator of transcription proteins ensured outstanding long-term noninvasive in vitro and in vivo cell tracing. The organic AIE dots outperform their counterparts of inorganic quantum dots, opening a new avenue in the development of fluorescent probes for following biological processes such as carcinogenesis.

Ultrabright Organic Dots with Aggregation‐Induced Emission Characteristics for Real‐Time Two‐Photon Intravital Vasculature Imaging

Ultrabright organic dots with aggregation-induced emission characteristics (AIE dots) are prepared and shown to exhibit a high quantum yield, a, large two-photon absorption cross-section, and low in vivo toxicity. Real-time two-photon intravital blood vascular imaging in various tissues substantiates that the AIE dots are effective probes for in vivo vasculature imaging in a deep and high-contrast manner.

Reversible Phase Transfer of (CdSe/ZnS) Quantum Dots between Organic and Aqueous Solutions

Ttrioctylphosphine oxide (TOPO) stabilized CdSe/ZnS quantum dots (QD) were modified with 6-ferrocenyl-1-hexanethiol (FcHT) or 11-ferrocenyl-1-undecanethiol (FcUT) via ligand exchange. The presence of ferrocenyl thiol ligands on the surface of the QDs was proven by diffusion ordered NMR spectroscopy. Upon replacement of the initial TOPO ligand with ferrocene derivatives the emission of the QDs decreased. Phase transfer of ferrocene-modified QDs from organic solvents into water was achieved by complexation reactions with beta-cyclodextrin (beta-CD). The QDs coated with ferrocene thiols are soluble in nonpolar solvents and are transferred into the aqueous phase upon formation of host-guest complexes between the ferrocene units and the cavity of beta-CD. The reversibility of the phase transfer was probed by the addition of naphthalene and adamantane derivatives to the aqueous phase containing QD-[Fc-CD] adduct.

Precise and Long-Term Tracking of Adipose-Derived Stem Cells and Their Regenerative Capacity via Superb Bright and Stable Organic Nanodots

Monitoring and understanding long-term fate and regenerative therapy of administrated stem cells in vivo is of great importance. Herein we report organic nanodots with aggregation-induced emission characteristics (AIE dots) for long-term tracking of adipose-derived stem cells (ADSCs) and their regenerative capacity in living mice. The AIE dots possess high fluorescence (with a high quantum yield of 25±1%), excellent biological and photophysical stabilities, low in vivo toxicity, and superb retention in living ADSCs with negligible interference on their pluripotency and secretome. These AIE dots also exhibit superior in vitro cell tracking capability compared to the most popular commercial cell trackers, PKH26 and Qtracker 655. In vivo quantitative studies with bioluminescence and GFP labeling as the controls reveal that the AIE dots can precisely and quantitatively report the fate of ADSCs and their regenerative capacity for 42 days in an ischemic hind limb bearing mouse model.

Ultrabright organic dots with aggregation-induced emission characteristics for cell tracking.

Noninvasive fluorescence cell tracking provides critical information on the physiological displacement and translocation of actively migrating cells, which deepens our understanding of biomedical engineering, oncological research, stem cell transplantation and therapies. Non-viral fluorescent protein transfection based cell tracing has been widely used but with issues related to cell type-dependent expression, lagged readout, immunogenicity and mutagenesis. Alternative cell tracking methods are therefore desired to attain reliable, stable, and efficient labeling over a long time. In this work, we have successfully developed ultra-bright organic dots with aggregation-induced emission (AIE dots) and demonstrated their capabilities for cellular imaging and cell tracking. The AIE dots possess high fluorescence, super photostability, and excellent cellular retention and biocompatibility. As compared to commonly used pMAX-GFP plasmid labeling approach, the organic AIE dots showed excellent cell labeling on all tested human cell lines and superior tracing performance, which opens up new opportunities in the cell-based immunotherapies and other related biological researches.

Self-assembled architectures with multiple aqueous compartments

A vital organizational feature of living cells is that of compartmentalization. This allows cells to run concurrently incompatible metabolic processes and to regulate these processes by selective trans-membrane transport. Although strategies that effectively mimic cell function in simple architectures have been researched extensively, soft matter systems with membranes that delineate distinct and multiple aqueous environments have only recently caught attention. We highlight a range of multi-compartmentalized soft matter systems including vesosomes, capsosomes, polymersomes, double emulsions, and their combinations, and demonstrate that the unique properties of the multi-compartmentalized architectures have the potential to add value to application areas such as drug-delivery and multi-enzyme biosynthesis.

A Multifunctional Probe with Aggregation-Induced Emission Characteristics for Selective Fluorescence Imaging and Photodynamic Killing of Bacteria Over Mammalian Cells

A multifunctional probe aggregation-induced emission-Zinc(II)-dipicolylamine (AIE-ZnDPA) is developed for selective targeting, fluorescence imaging, and photodynamic killing of both Gram-positive and Gram-negative bacteria over mammalian cells. The probe has significant advantages in simple probe design, enhanced fluorescence upon bacteria binding, excellent photostability, and broad-spectrum antibacterial activity with almost no harm to mammalian cells.

On the role of electromagnetic boundary conditions in single molecule fluorescence lifetime studies of dyes embedded in thin films

Single molecule fluorescence lifetime studies are generally performed in thin polymer films, where the influence of the interface on the behaviour of fluorescing molecules is not negligible. In order to describe this influence, we investigate annealed films of different thickness. We show that the distribution of fluorescence lifetimes of the embedded dyes is shifted to lower values as the thickness of the film increases. We explain this shift by simple electromagnetic arguments related to the boundary conditions at the interfaces of the polymer film with air and glass, respectively. The conclusion is that extreme care must be taken in order to interpret single molecule data with respect to the true chemical nature of the phenomena.

An intercompartmental enzymatic cascade reaction in channel-equipped polymersome-in-polymersome architectures

Compartmentalization, as a design principle, is a prerequisite for the functioning of eukaryotic cells. Although cell mimics in the form of single vesicular compartments such as liposomes or polymersomes have been tremendously successful, investigations of the corresponding higher-order architectures, in particular bilayer-based multicompartment vesicles, have only recently gained attention. We hereby demonstrate a multicompartment cell-mimetic nanocontainer, built-up from fully synthetic membranes, which features an inner compartment equipped with a channel protein and a semi-permeable outer compartment that allows passive diffusion of small molecules. The functionality of this multicompartment architecture is demonstrated by a cascade reaction between enzymes that are segregated in separate compartments. The unique architecture of polymersomes, which combines stability with a cell-membrane-mimetic environment, and their assembly into higher-order architectures could serve as a design principle for new generation drug-delivery vehicles, biosensors, and protocell models.

Highly emissive PEG-encapsulated conjugated polymer nanoparticles

A novel bioimaging probe based on a conjugated polymer, poly(9,9-dihexylfluorene-alt-2,1,3-benzoxadiazole) (PFBD), is demonstrated. Transfer of the hydrophobic polymer into water using a short chain poly(ethylene glycol) (PEG) resulted in conjugated polymer nanoparticles (PEG-PFBD) with a fluorescence quantum yield of 46%. The PEG-PFBD nanoparticles possessed several desirable structural and photophysical properties, such as colloidal stability in a broad range of pH values, sub-20 nm particle size, the presence of surface chemical functionality, as well as desirable excitation and emission spectra, for bioimaging applications. PEG-PFBD nanoparticles were conjugated with cyclic RGDfK targeting peptide for labeling of membrane α(V)β(3) integrin receptors on live HT-29 adenocarcinoma cells. Single nanoparticle microscopy revealed that the PEG-capped PFBD nanoparticles exhibit at least ten times higher emitted photon counts than single quantum dots (QD655) of comparable size. In addition, Fluorescence Lifetime Imaging Microscopy (FLIM) of single PEG-PFBD nanoparticles revealed that the nanoparticles display a clearly resolvable single nanoparticle fluorescence lifetime.