Regioselective Immobilization of a PVC Membrane Composed of an Ionic Liquid-based Dye on Convex-shaped PDMS Surface for Multiplexed Microanalytical Devices

Highly sensitive optical ion sensor with ionic liquid-based colorimetric membrane/photonic crystal hybrid structure

An ionic liquid-based thin (~ 1 µm) colorimetric membrane (CM) is a key nano-tool for optical ion sensing, and a two-dimensional photonic crystal slab (PCS) is an important nano-platform for ultimate light control. For highly sensitive optical ion sensing, this report proposes a hybrid of these two optical nano-elements, namely, a CM/PCS hybrid. This structure was successfully fabricated by a simple and rapid process using nanoimprinting and spin-coating, which enabled control of the CM thickness. Optical characterization of the hybrid structure was conducted by optical measurement and simulation of the reflection spectrum, indicating that the light confined in the holes of the PCS was drastically absorbed by the CM when the spectrum overlapped with the absorption spectrum of the CM. This optical property obtained by the hybridization of CM and PCS enabled drastic improvement in the absorption sensitivity in Ca ion sensing, by ca. 78 times compared to that without PCS. Experimental and simulated investigation of the relation between the CM thickness and absorption sensitivity enhancement suggested that the controlled light in the PCS enhanced the absorption cross-section of the dye molecules within the CM based on the enhanced local density of states. This highly sensitive optical ion sensor is expected to be applied for micro-scale bio-analysis like cell-dynamics based on reflectometric Ca ion detection.

Enzyme-responsive Fluorescent Ionic Liquid

Herein, we describe the development of a novel material, "enzyme-responsive fluorescent ionic liquid", which enabled a highly sensitive detection of alkaline phosphatase (ALP). We prepared a plasticized poly(vinyl chloride) (PVC) membrane using this new material as a plasticizer and quantified ALP in aqueous solutions. Preliminary results suggested that the PVC membrane responded to ALP at an interface between the membrane and the sample solution with anion extraction to maintain electroneutrality in the membrane phase. The developed PVC membrane showed an approximately six-times higher sensitivity than the conventional membrane, thereby demonstrating highly sensitive ALP detection. These results suggested the potential applicability of the proposed membrane for highly sensitive protein detection by using ALP-labeled antibodies.

An ionic liquid composed of purely functional sensing molecules: a colorimetrically calcium responsive ionic liquid

A highly lipophilic ionic liquid (IL) consisting of stoichiometrically equal amounts of two purely functional chemical sensing molecules, an anionic calcium ionophore and a cationic dye, was synthesized for the first time, and used as a component for a poly(vinyl chloride)-based or neat liquid membrane optical sensor. This is the first report of an IL consisting of purely functional chemical sensing molecules, which is completely different from the previously reported ionic liquids typically consisting of imidazolium or other lipophilic cations. Since the present IL contained an extremely high concentration of dyes, the IL-based sensor showed dramatically enhanced sensitivity (13 times higher compared to that of a conventional sensor), and fully reversible and selective response to Ca2+. Preliminary investigation on the unique response characteristics of the present liquid membrane IL-based sensor was performed with the responses to Ca2+ and Na+.

Fabrication of a Polydimethylsiloxane Fluidic Chip Using a Sacrificial Template Made by Fused Deposition Modeling 3D Printing and Application for Flow-injection Analysis

Fluidic chip fabrication technologies using three-dimensional (3D) printing have received broad attention recently. Herein, we describe a new method for fabricating polydimethylsiloxane (PDMS) fluidic chips using a 3D-printed polyvinyl alcohol (PVA) or acrylonitrile butadiene styrene (ABS) template and polymer coating. In this method, polyethylene glycol (PEG) was coated on the 3D-printed template. This coated template was immersed in liquid PDMS, and subsequently the PDMS was cured. Space can be created between the template and PDMS by removing this liquid PEG from the channel. This space renders template removal easier. A flow path is formed by dissolving the template with a solvent. These PDMS chips are used for flow injection measurement.

An Ionic Liquid-based Microextraction Method for Ultra-High Preconcentration of Paraquat Traces in Water Samples Prior to HPLC Determination

An ionic liquid (IL)-based microextraction method was developed for the preconcentration of paraquat traces in water samples prior to HPLC determination. On the basis of the relationship between the aqueous solubility and the extractability of known ILs, 1-ethyl-3-methylimidazolium bis(nonafluorobutanesulfonyl)amide ([EMIm][NNf₂]) was selected as the extractant for paraquat. The distribution ratio of paraquat dication in the [EMIm][NNf₂]/water biphasic system was theoretically estimated to be nearly 10⁸ at its maximum level, indicating that [EMIm][NNf₂] was suitable for the ultra-high preconcentration (a maximum of 10⁶-fold concentration) of paraquat with a quantitative recovery (more than 99%). The extraction procedure could be performed easily and quickly following the in situ solvent formation microextraction technique, and the paraquat traces in the IL phase could be determined by hydrophilic interaction chromatography with good detection limits and linearity ranges (0.16 and 1 - 50 ng mL^-1 for paraquat, respectively). The combined method was successfully applied to four real environmental water samples spiked with paraquat and its analog, diquat at 5.0 ng mL^-1.