OIST-KEIO SHOWCASE TALK Series 4

With recent advances in nanofluidic applications such as single-molecule analysis, enhanced ion conduction and high-efficiency separation, understanding fluid flows in nanospaces with dominant surface effects becomes important. We have developed a measurement method exploiting defocused nanoparticle images to determine the flow profile in nanochannels with spatial resolution overcoming the optical diffraction limit. Combining with the design of measurement system by statistical mechanical analysis for the nanoparticle behavior, we drastically reduced artifacts specific to nanoscale particle tracking and enabled to reveal the nanochannel flows for the first time. The developed method will accelerate researches in nanofluidics and other related fields.

Biofunctional hydrogel microparticles have played a central role in biomedical fields involving drug delivery systems, scaffold materials for in vitro tissue culture and implantable biochemical sensors. Here I introduce recent progress on simple centrifuge-based techniques for synthesizing microparticles (typical diameter: ~100 µm) composed of functional hydrogels. The feature of this particle synthesizing technique is simple, easy-to-use and cost-effective and is applicable to encapsulation of tiny amounts of precious samples in the microparticles. The variations of the functional hydrogel microparticles were demonstrated such as structural-color-based biochemical sensors and drug delivery carriers for gene therapy.

There is a strong demand for point-of-care testing without sophisticated laboratory equipment. In this context, (microfluidic) paper-based analytical devices (µ)PADs have gained significant attention. Using porous substrates with spontaneous capillarity driven liquid transport, we have demonstrated that analytical assays conventionally depending on benchtop instruments can be implemented into paper or thread platforms not requiring any reagent handling. Examples include the quantification of antibodies from whole blood based on bioluminescent probes and digital cameras as detector. Going further in terms of simplicity, we will present devices for naked eye “calibration-free” semiquantitative analysis of various clinical parameters applicable by untrained users.

Scanning probe microscopy (SPM) is one of the powerful techniques to investigate structures of material surfaces at the atomic and single molecular scale. Among various examples, I will discuss two topics. The first is isomerization reactions and monolayer formation of diarylethene molecules, which are prepared by vacuum evaporation of molecular powder on metal substrates. The other is hydrogen-bonded organic framework thin films fabricated at the air-water interface. In both cases, comparison of SPM images with theoretical calculations clarifies the subtle balance between intermolecular and interfacial interactions, which is a key to the self-assembly of functional molecules on surfaces and interfaces.

N-type organic semiconductors have been widely investigated toward promising various device application, while some instability issues in their electronic properties remain to be solved. So far, our group has intensively studied carrier doping effects in organic thin-film transistors (OTFTs) with experimental and simulation approach. In this talk, I will introduce characteristic control in n-channel OTFTs by n-type (electron) doping with newly synthesized solution-processable air stable dopants, and the n-type doping mechanisms therein will be discussed. In addition, our recent results on photoenergy conversion such as photocatalytic hydrogen production using n-type polymeric carbon nitrides will be presented.

Microfluidics and lab-on-a-chip devices have emerged as powerful platforms to advance our knowledge and open up new possibilities in biotechnology research. In this talk, I will showcase two examples. (1) A microfluidic device with controlled microenvironment is developed to study population genetics and understand the diversity of a microbial population. (2) An optomicrofluidic sensing platform is developed to rapidly detect antibodies against the SARS-CoV-2 spike protein in diluted human plasma within 30 minutes, at the limit of detection of ~0.5 pM (0.08 ng/mL). 

Glow-in-the-dark materials are widely used as emergency lights and clock faces. These materials can store the absorbed photon energy and exhibit photoluminescence for several hours. Currently, most glow-in-the-dark materials are based on inorganic systems of metal oxide doped with rare metals. Although the inorganic system has high durability, it requires rare metals and high fabrication temperatures. In contrast, we realized glow-in-the-dark emission from an organic system that is free from rare elements and easy to fabricate. I will present the detailed emission process of the organic afterglow.

Carbon nanostructures such as graphene quantum dots (GQDs) and graphene nanoribbons (GNRs) are attracting attentions for their intriguing optical, electronic, and magnetic properties that are dependent on their precise chemical structures. With the sizable energy gaps opened by the quantum confinement effect, these nanomaterials are of high potential for nanoelectronics as well as photonics. In this talk, I will introduce our bottom-up molecular approach to chemically synthesize atomically precise GQDs and demonstrate their intriguing properties and potentials, for example as highly stable fluorophores for super-resolution imaging applications.