Nako Nakatsuka

Fabrication of High-Performance Ultrathin In2O3 Film Field-Effect Transistors and Biosensors Using Chemical Lift-Off Lithography

We demonstrate straightforward fabrication of highly sensitive biosensor arrays based on field-effect transistors, using an efficient high-throughput, large-area patterning process. Chemical lift-off lithography is used to construct field-effect transistor arrays with high spatial precision suitable for the fabrication of both micrometer- and nanometer-scale devices. Sol-gel processing is used to deposit ultrathin (∼4 nm) In2O3 films as semiconducting channel layers. The aqueous sol-gel process produces uniform In2O3 coatings with thicknesses of a few nanometers over large areas through simple spin-coating, and only low-temperature thermal annealing of the coatings is required. The ultrathin In2O3 enables construction of highly sensitive and selective biosensors through immobilization of specific aptamers to the channel surface; the ability to detect subnanomolar concentrations of dopamine is demonstrated.

Controlled DNA Patterning by Chemical Lift-Off Lithography: Matrix Matters.

Nucleotide arrays require controlled surface densities and minimal nucleotide-substrate interactions to enable highly specific and efficient recognition by corresponding targets. We investigated chemical lift-off lithography with hydroxyl- and oligo(ethylene glycol)-terminated alkanethiol self-assembled monolayers as a means to produce substrates optimized for tethered DNA insertion into post-lift-off regions. Residual alkanethiols in the patterned regions after lift-off lithography enabled the formation of patterned DNA monolayers that favored hybridization with target DNA. Nucleotide densities were tunable by altering surface chemistries and alkanethiol ratios prior to lift-off. Lithography-induced conformational changes in oligo(ethylene glycol)-terminated monolayers hindered nucleotide insertion but could be used to advantage via mixed monolayers or double-lift-off lithography. Compared to thiolated DNA self-assembly alone or with alkanethiol backfilling, preparation of functional nucleotide arrays by chemical lift-off lithography enables superior hybridization efficiency and tunability.

Analyzing Spin Selectivity in DNA-Mediated Charge Transfer via Fluorescence Microscopy

Understanding spin-selective interactions between electrons and chiral molecules is critical to elucidating the significance of electron spin in biological processes and to assessing the potential of chiral assemblies for organic spintronics applications. Here, we use fluorescence microscopy to visualize the effects of spin-dependent charge transport in self-assembled monolayers of double-stranded DNA on ferromagnetic substrates. Patterned DNA arrays provide background regions for every measurement to enable quantification of substrate magnetization-dependent fluorescence due to the chiral-induced spin selectivity effect. Fluorescence quenching of photoexcited dye molecules bound within DNA duplexes is dependent upon the rate of charge separation/recombination upon photoexcitation and the efficiency of DNA-mediated charge transfer to the surface. The latter process is modulated using an external magnetic field to switch the magnetization orientation of the underlying ferromagnetic substrates. We discuss our results in the context of the current literature on the chiral-induced spin selectivity effect across various systems.

Self-assembling peptide assemblies bound to ZnS nanoparticles and their interactions with mammalian cells.

Self-assembling peptide sequences (both synthetic and natural) have emerged as a new group of building blocks for diverse applications. In this work we investigated the formation of assemblies of three diverse peptide sequences derived from the crustacean cardioactive peptide CCAP (1-9), a cardioaccelerator and neuropeptide transmitter in crustaceans, atrial natriuretic hormone ANP (1-28), a powerful vasodilator secreted by heart muscle cells of mammals, as well as adamstsostatin peptide ADS (1-17), which functions as an inhibitor of angiogenesis. The formation of assemblies was found to be dependent upon the sequences as well as the pH in which the assemblies were grown. The secondary structural transformation of the peptides was studied by circular dichroism as well as FTIR spectroscopy. In order to render the sequences luminescent, we conjugated the assemblies with ZnS nanoparticles. Finally the interactions of the peptide bound ZnS nanoparticles with mammalian normal rat kidney cells were explored. In some cases the nanoconjugates were found to adhere not only to the cellular membranes but also extend into the cytoplasm. Thus, such nanocomposites may be utilized for cell penetration and have the potential to serve as coercive multifunctional vectors for bioimaging and cellular delivery.

Biomimetic Formation of Pd and Au-Pd Nanocomposites and their Catalytic Applications

In this work, we probed the formation of gallic acid (GA) assemblies. It was observed that nanoassemblies of varying morphologies were formed depending upon the growth conditions. We then utilized the assemblies as templates for the growth of palladium (Pd) nanoparticles for developing catalytic systems biomimetically. Further, amide conjugates of GA were synthesized and self-assembled for the formation of uniformly coated assemblies of Pd nanoparticles and Au-Pd nanocomposites. Their catalytic abilities were explored by examining the degradation of para-nitrophenol. Thus, we have developed a new class of nanocomposites that were found to be effective catalytic nanomaterials via green synthesis.

Differentiating Siblings: The Case of Dopamine and Norepinephrine

Monitoring dopamine and norepinephrine (or other structurally similar neurotransmitters) in the same brain region necessitates selective sensing. In this Viewpoint, we highlight electrochemical and optical strategies for advancing simultaneous real-time measurements of dopamine and norepinephrine transmission. The potential for DNA aptamers as recognition elements in the context of field-effect transistor sensing for selective and simultaneous neurotransmitter monitoring in vivo is also discussed.

Neurochips Enable Nanoscale Devices for High-Resolution In Vivo Neurotransmitter Sensing.

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Formation of hyaluronic acid–ellagic acid microfiber hybrid hydrogels and their applications

Microfiber assemblies prepared from ellagic acid (EA) were functionalized with histidine (His) and dispersed in hyaluronic acid (HA) hydrogel microstructures. Swelling studies indicated that the hybrids had a relatively lower water uptake compared to HA and was pH dependent. The percentage swelling ratio for EA–His–HA hybrids was 48xa0% when 0.04xa0mg/mL of HA was incorporated and increased to 70xa0% when 1.2xa0mg/mL HA was integrated. Release studies using the dye crystal violet (CV) as a model drug showed that the rates were concentration-dependent. Further the hybrids were found to be thermally stable compared to HA. Cellular toxicity assays performed with normal rat kidney (NRK) cells indicated biocompatibility and adherence of the hybrids to the cells. Thus, we have developed a new family of hybrid hydrogels which readily formed on the EA–His functionalized microfibers and may have potential applications in drug delivery or tissue regeneration applications.

Fabrication of Collagen–Elastin-Bound Peptide Microtubes for Mammalian Cell Attachment

Abstract In this work we have designed self-assembled peptide-based microconstructs and examined their interactions with elastin and collagen for potential application as scaffolds for chondrocyte cell attachment. Being biological in nature, peptide-based nano- and microstructures have intrinsic molecular recognition properties which allow extensive chemical, conformational and functional diversity. We have synthesized a new peptide bolaamphiphile, bis(N-α-amido-val)-1,5-pentane dicarboxylate, and examined its self-assembly at varying pH values. The formation of high-density networks of nano- and microtubular structures was found to be in the range of pH 4–6. The formed microtubes were then covalently bound to varying concentrations of the extracellular matrix protein elastin, a versatile protein that allows for an extensive array of physical and chemical modifications to attune properties towards diverse necessities of biomedical applications. We found that binding to microtubes was concentration dependent. The morphological and chemical changes complementing the processes of self-assembly and binding to elastin were examined by electron microscopic and spectroscopic methods. Furthermore, we also incorporated the extracellular matrix protein type-I collagen, a critical constituent for designing biocompatible scaffolds, into the elastin functionalized micro-tubes. Since the main goal is to develop highly biocompatible protein functionalized microstructures that support cellular interactions, we examined the interactions of the microcomposites with chondrocyte cell line, in order to assess the biocompatibility and interaction between the microconstructs and the cells. The designed elastin and collagen-bound peptide microtubes may potentially serve as a new class of biomaterials by promoting cell growth and proliferation.

Small-Molecule Patterning via Prefunctionalized Alkanethiols

Interactions between small molecules and biomolecules are important physiologically and for biosensing, diagnostic, and therapeutic applications. To investigate these interactions, small molecules can be tethered to substrates through standard coupling chemistries. While convenient, these approaches co-opt one or more of the few small-molecule functional groups needed for biorecognition. Moreover, for multiplexing, individual probes require different surface functionalization chemistries, conditions, and/or protection/deprotection strategies. Thus, when placing multiple small-molecules on surfaces, orthogonal chemistries are needed that preserve all functional groups and are sequentially compatible. Here, we approach high-fidelity small-molecule patterning by coupling small-molecule neurotransmitter precursors, as examples, to monodisperse asymmetric oligo(ethylene glycol)alkanethiols during synthesis and prior to self-assembly on Au substrates. We use chemical lift-off lithography to singly and doubly pattern substrates. Selective antibody recognition of pre-functionalized thiols was comparable to or better than recognition of small molecules functionalized to alkanethiols after surface assembly. These findings demonstrate that synthesis and patterning approaches that circumvent sequential surface conjugation chemistries enable biomolecule recognition and afford gateways to multiplexed small-molecule functionalized substrates.