83 research outputs found
Development of an Aptamer-Conjugated Polyrotaxane-Based Biodegradable Magnetic Resonance Contrast Agent for Tumor-Targeted Imaging
Gadolinium-based
magnetic resonance imaging (MRI) contrast agents
with biodegradability, biosafety, and high efficiency are highly desirable
for tumor diagnosis. Herein, a biodegradable, AS1411-conjugated, α-cyclodextrin
polyrotaxane-based MRI contrast agent (AS1411-G2Â(DTPA-Gd)-SS-PR) was
developed for targeted imaging of cancer. The polyrotaxane-based contrast
agent was achieved by the complexation of α-cyclodextrin (α-CD)
and a linear polyÂ(ethylene glycol) (PEG) chain containing disulfide
linkages at two terminals. The disulfides enable the dethreading of
the polyrotaxane into excretable small units due to cleavage of the
disulfide linkages by reducing agents such as intracellular glutathione
(GSH). Furthermore, the second-generation lysine dendron conjugated
with gadolinium chelates and AS1411, a G-quadruplex oligonucleotide
that has high binding affinity to nucleolin generally presenting a
high level on the surface of tumor cells, coupled to the α-CD
via click chemistry. The longitudinal relaxivity of AS1411-G2Â(DTPA-Gd)-SS-PR
(11.7 mMâ1 sâ1) was two times
higher than the clinically used Gd-DTPA (4.16 mMâ1 sâ1) at 0.5 T. The in vitro degradability was
confirmed by incubating with 10 mM 1,4-dithiothreitol (DTT). Additionally,
the cytotoxicity, histological assessment, and gadolinium retention
studies showed that the prepared polyrotaxane-based contrast agent
had a superior biocompatibility and was predominantly cleared renally
without long-term accumulation toxicity. Importantly, AS1411-G2Â(DTPA-Gd)-SS-PR
displayed the enhanced performance in MRI of breast cancer cells in
vitro as well as a subcutaneous breast tumor in vivo due to the targeting
ability of the AS1411 aptamer. The enhanced performance was due to
efficient multivalent interactions with tumor cells, producing faster
accumulation and longer contrast imaging time at the tumor site. This
work clearly confirms that the specially designed and fabricated α-CD-based
polyrotaxane is a promising contrast agent with an excellent contrast
imaging performance and biosafety for tumor MR imaging
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Integrated Microfluidic Isolation of Aptamers Using Electrophoretic Oligonucleotide Manipulation
We present a microfluidic approach to integrated isolation of DNA aptamers via systematic evolution of ligands by exponential enrichment (SELEX). The approach employs a microbead-based protocol for the processes of affinity selection and amplification of target-binding oligonucleotides, and an electrophoretic DNA manipulation scheme for the coupling of these processes, which are required to occur in different buffers. This achieves the full microfluidic integration of SELEX, thereby enabling highly efficient isolation of aptamers in drastically reduced times and with minimized consumption of biological material. The approach as such also offers broad target applicability by allowing selection of aptamers with respect to targets that are either surface-immobilized or solution-borne, potentially allowing aptamers to be developed as readily available affinity reagents for a wide range of targets. We demonstrate the utility of this approach on two different procedures, respectively for isolating aptamers against a surface-immobilized protein (immunoglobulin E) and a solution-phase small molecule (bisboronic acid in the presence of glucose). In both cases aptamer candidates were isolated in three rounds of SELEX within a total process time of approximately 10âhours
Molecular robots guided by prescriptive landscapes
Traditional robots rely for their function on computing, to store internal representations of their goals and environment and to coordinate sensing and any actuation of components required in response. Moving robotics to the single-molecule level is possible in principle, but requires facing the limited ability of individual molecules to store complex information and programs. One strategy to overcome this problem is to use systems that can obtain complex behaviour from the interaction of simple robots with their environment. A first step in this direction was the development of DNA walkers, which have developed from being non-autonomous, to being capable of directed but brief motion on one-dimensional tracks. Here we demonstrate that previously developed random walkersâso-called molecular spiders that comprise a streptavidin molecule as an inert âbodyâ and three deoxyribozymes as catalytic âlegsââshow elementary robotic behaviour when interacting with a precisely defined environment. Single-molecule microscopy observations confirm that such walkers achieve directional movement by sensing and modifying tracks of substrate molecules laid out on a two-dimensional DNA origami landscape. When using appropriately designed DNA origami, the molecular spiders autonomously carry out sequences of actions such as âstartâ, âfollowâ, âturnâ and âstopâ. We anticipate that this strategy will result in more complex robotic behaviour at the molecular level if additional control mechanisms are incorporated. One example might be interactions between multiple molecular robots leading to collective behaviour; another might be the ability to read and transform secondary cues on the DNA origami landscape as a means of implementing Turing-universal algorithmic behaviour
Light-up properties of complexes between thiazole orange-small molecule conjugates and aptamers
The full understanding of dynamics of cellular processes hinges on the development of efficient and non-invasive labels for intracellular RNA species. Light-up aptamers binding fluorogenic ligands show promise as specific labels for RNA species containing those aptamers. Herein, we took advantage of existing, non-light-up aptamers against small molecules and demonstrated a new class of light-up probes in vitro. We synthesized two conjugates of thiazole orange dye to small molecules (GMP and AMP) and characterized in vitro their interactions with corresponding RNA aptamers. The conjugates preserved specific binding to aptamers while showing several 100-fold increase in fluorescence of the dye (the âlight-upâ property). In the presence of free small molecules, conjugates can be displaced from aptamers serving also as fluorescent sensors. Our in vitro results provide the proof-of-concept that the small-molecule conjugates with light-up properties can serve as a general approach to label RNA sequences containing aptamers
Biomimicry of Limpet Teeth with Hybrid Colloidal Liquid Crystals: Mechanical Enhancement by Structural Orderliness from Self-Assembly
The teeth of limpets, consisting of orderly aligned hard goethite (iron oxyhydroxides) nanocrystals and flexible chitin microfibers, are one of the hardest and stiffest biomaterials found in nature. However, the replication of their composition and ordered microstructures to artificial biomimetic materials remains a challenge. Here, we fabricated large-sized limpet tooth analogues with hierarchically ordered structures by applying long-range orientational control to the short-scale self-assembly of hybrid colloidal liquid crystals formed by chitin nanocrystals and goethite nanorods. The obtained lightweight composite laminates exhibited excellent bending resistance compared with biomaterials, cements, and ceramics. These results suggest that the mass production of structurally ordered materials with high strength and toughness may be achieved using lyotropic liquid crystals
Guest Molecules with Amino and Sulfhydryl Groups Enhance Photoluminescence by Reducing the Intermolecular Ligand-to-Metal Charge Transfer Process of MetalâOrganic Frameworks
Micron-sized metalâorganic framework (MOF) sheets were prepared using organic molecules with aggregation-induced emission (AIE) properties as ligands. The intermolecular ligand-to-metal charge transfer (LMCT) process occurs in MOF structures, resulting in the disappearance of the matrix coordination-induced emission (MCIE) effect and emergence of the aggregation-caused quenching (ACQ) effect. Here, we demonstrate that molecules with electron donors can compete with the LMCT process in MOF structures, thereby changing the transfer path of the excitation energy and returning it to the ground state, mainly in the form of fluorescence. Organic molecules with amino or sulfhydryl groups can act as effective electron donors, reducing the LMCT process and causing the MCIE effect of the MOF sheet. The coexistence of amino and sulfhydryl groups will strongly inhibit the LMCT process of the MOF sheet, thereby greatly enhancing the MCIE effect. Therefore, these types of molecules can be used to regulate the photoluminescence intensity of AIE-based MOF materials. In addition, there are some organic molecules with multiple carboxyl or hydroxyl groups which can produce similar effects. Finally, it was confirmed that the intermolecular LMCT process is highly sensitive, and the MOF sheet showed distinguishable fluorescence results even with the addition of small molecules in the amount of 10â9 M. Thus, it is a feasible idea to use the fluorescence changes induced by the LMCT process as a sensitive sensing method for small molecules
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