Here, we report a catalytic beacon sensor for uranyl (UO 2 2؉ ) based on an in vitro-selected UO 2 2؉ -specific DNAzyme. The sensor consists of a DNA enzyme strand with a 3 quencher and a DNA substrate with a ribonucleotide adenosine (rA) in the middle and a fluorophore and a quencher at the 5 and 3 ends, respectively. The presence of UO 2 2؉ causes catalytic cleavage of the DNA substrate strand at the rA position and release of the fluorophore and thus dramatic increase of fluorescence intensity. The sensor has a detection limit of 11 parts per trillion (45 pM), a dynamic range up to 400 nM, and selectivity of >1-million-fold over other metal ions. The most interfering metal ion, Th(IV), interacts with the fluorescein fluorophore, causing slightly enhanced fluorescence intensity, with an apparent dissociation constant of Ϸ230 M. This sensor rivals the most sensitive analytical instruments for uranium detection, and its application in detecting uranium in contaminated soil samples is also demonstrated. This work shows that simple, cost-effective, and portable metal sensors can be obtained with similar sensitivity and selectivity as much more expensive and sophisticated analytical instruments. Such a sensor will play an important role in environmental remediation of radionuclides such as uranium.DNA ͉ DNAzyme ͉ fluorescence ͉ deoxyribozyme ͉ catalytic DNA

Organized cellular alignment is critical to controlling tissue microarchitecture and biological function. Although a multitude of techniques have been described to control cellular alignment in 2D, recapitulating the cellular alignment of highly organized native tissues in 3D engineered tissues remains a challenge. While cellular alignment in engineered tissues can be induced through the use of external physical stimuli, there are few simple techniques for microscale control of cell behavior that are largely cell-driven. In this study we present a simple and direct method to control the alignment and elongation of fibroblasts, myoblasts, endothelial cells and cardiac stem cells encapsulated in microengineered 3D gelatin methacrylated (GelMA) hydrogels, demonstrating that cells with the intrinsic potential to form aligned tissues in vivo will self-organize into functional tissues in vitro if confined in the appropriate 3D microarchitecture. The presented system may be used as an in vitro model for investigating cell and tissue morphogenesis in 3D, as well as for creating tissue constructs with microscale control of 3D cellular alignment and elongation, that could have great potential for the engineering of functional tissues with aligned cells and anisotropic function.

We report on a novel type of triblock copolymer polymersomes with temperature-controlled permeability within the physiologically relevant temperature range of 37–42 °C for sustained delivery of anticancer drugs. These polymersomes combine characteristics of liposomes, such as biocompatibility, biodegradability, monodispersity, and stability at room temperature, with tunable size and thermal responsiveness provided by amphiphilic triblock copolymers. The temperature-sensitive poly­(N-vinylcaprolactam) n -poly­(dimethylsiloxane)65-poly­(N-vinylcaprolactam) n (PVCL n -PDMS65-PVCL n ) copolymers with n = 10, 15, 19, 29, and 50 and polydispersity indexes less than 1.17 are synthesized by controlled RAFT polymerization. The copolymers are assembled into stable vesicles at room temperature when the ratio of PVCL to the total polymer mass is 0.36 < f < 0.52 with the polymersome diameter decreasing from 530 to 40 nm as the length of PVCL is increased from 10 to 19 monomer units. Importantly, the permeability of polymersomes loaded with the anticancer drug doxorubicin can be precisely controlled by PVCL length in the temperature range of 37–42 °C. Increasing the temperature above the lower critical solution temperature of PVCL results in either gradual vesicle shrinkage (n = 10 and n = 15) or reversible formation of beadlike aggregates with no size change (n = 19), both leading to sustained drug release. All temperature-triggered morphological changes are reversible and do not compromise the structural stability of the vesicles. Finally, concentration- and time-dependent cytotoxicity of drug-loaded polymersomes to human alveolar adenocarcinoma cells is demonstrated. Considering the high loading capacity (∼40%) and temperature responsiveness in the physiological range, these polymer vesicles have considerable potential as novel types of stimuli-responsive drug nanocarriers.

The effects of surface modification of nanocrystalline titanium dioxide (TiO 2 ) with specific chelating agents on photocatalytic degradation of nitrobenzene (NB) was investigated in order to design a selective and effective catalyst for removal of nitroaromatic compounds from contaminated waste streams. Mechanisms of NB adsorption and photodecomposition were investigated using infrared absorption and electron paramagnetic resonance spectroscopy. Liquid chromatography and gas chromatography/mass spectrometry were used for byproduct analyses. Arginine, lauryl sulfate, and salicylic acid were found to bind to TiO 2 via their oxygen-containing functional groups. Modification of the TiO 2 surface with arginine resulted in enhanced NB adsorption and photodecomposition, and compared to unmodified TiO 2 . The initial quantum yield for photodegradation of NB in this system was found to be Φ init ) 0.31 as compared to the one obtained for Degussa P25 of Φ init ) 0.18. NB degradation followed a reductive pathway over arginine-modified TiO 2 and was enhanced upon addition of methanol. No degradation of arginine was detected under the experimental conditions. Arginine improved the coupling between NB and TiO 2 and facilitated the transfer of photogenerated electrons from the TiO 2 conduction band to the adsorbed NB. These results indicate that surface modification of nanocrystalline TiO 2 with electron-donating chelating agents is an effective route to enhance photodecomposition of nitroaromatic compounds.

A Pb(II)-specific DNAzyme fluorescent sensor has been modified with a thiol moiety in order to immobilize it on a Au surface. Self-assembly of the DNAzyme is accomplished by first adsorbing the single-thiolated enzyme strand (HS-17E-Dy) followed by adsorption of mercaptohexanol, which serves to displace any Au-N interactions and ensure that DNA is bound only through the Sheadgroup. The preformed self-assembled monolayer is then hybridized with the complementary fluorophorecontaining substrate strand (17DS-Fl). Upon reaction with Pb(II), the substrate strand is cleaved, releasing a fluorescent fragment for detection. Fluorescence intensity may be correlated with original Pb(II) concentration, and a linear calibration was obtained over nearly four decades: 10 µM g [Pb(II)] g 1 nM. The immobilized DNAzyme is

The research areas of tissue engineering and drug development have displayed increased interest in organ-on-a-chip studies, in which physiologically or pathologically relevant tissues can be engineered to test pharmaceutical candidates. Microfluidic technologies enable the control of the cellular microenvironment for these applications through the topography, size, and elastic properties of the microscale cell culture environment, while delivering nutrients and chemical cues to the cells through continuous media perfusion. Traditional materials used in the fabrication of microfluidic devices, such as poly(dimethylsiloxane) (PDMS), offer high fidelity and high feature resolution, but do not facilitate cell attachment. To overcome this challenge, we have developed a method for coating microfluidic channels inside a closed PDMS device with a cell-compatible hydrogel layer. We have synthesized photocrosslinkable gelatin and tropoelastin-based hydrogel solutions that were used to coat the surfaces under continuous flow inside 50 μm wide, straight microfluidic channels to generate a hydrogel layer on the channel walls. Our observation of primary cardiomyocytes seeded on these hydrogel layers showed preferred attachment as well as higher spontaneous beating rates on tropoelastin coatings compared to gelatin. In addition, cellular attachment, alignment and beating were stronger on 5 % (w/v) hydrogel-coated devices than on 10 % (w/v) gel-coated channels. Our results demonstrate that cardiomyocytes respond favorably to the elastic, soft tropoelastin culture substrates, indicating that tropoelastin-based hydrogels may be a suitable coating choice for some organ-on-a-chip applications. We anticipate that the proposed hydrogel coating method and tropoelastin as a cell culture substrate may be useful for the generation of elastic tissues, e.g. blood vessels, using microfluidic approaches.

3D microfluidic networks are fabricated in a gelatin hydrogel using sacrificial melt-spun microfibers made from a material with pH-dependent solubility. The fibers, after being embedded within the gel, can be removed by changing the gel pH to induce dissolution. This process is performed in an entirely aqueous environment, avoiding extreme temperatures, low pressures, and toxic organic solvents.

Natural materials exhibit anisotropy with variations in soluble factors, cell distribution, and matrix properties. The ability to recreate the heterogeneity of the natural materials is a major challenge for investigating cell-material interactions and for developing biomimetic materials. Here we present a generic fluidic approach using convection and alternating flow to rapidly generate multi-centimeter gradients of biomolecules, polymers, beads and cells and cross-gradients of two species in a microchannel. Accompanying theoretical estimates and simulations of gradient growth provide design criteria over a range of material properties. A poly(ethyleneglycol) hydrogel gradient, a porous collagen gradient and a composite material with a hyaluronic acid/gelatin cross-gradient were generated with continuous variations in material properties and in their ability to regulate cellular response. This simple yet generic fluidic platform should prove useful for creating anisotropic biomimetic materials and high-throughput platforms for investigating cell-microenvironment interaction.