Simultaneous Recognition and Detection of Adenosine Phosphates by Machine Learning Analysis for Surface-Enhanced Raman Scattering Spectral Data.

Adenosine phosphates (adenosine 5'-monophosphate (AMP), adenosine 5'-diphosphate (ADP), and adenosine 5'-triphosphate (ATP)) play important roles in energy storage and signal transduction in the human body. Thus, a measurement method that simultaneously recognizes and detects adenosine phosphates is necessary to gain insight into complex energy-relevant biological processes. Surface-enhanced Raman scattering (SERS) is a powerful technique for this purpose.

Selection of structure-induced aptamer targeting small molecule based on capillary sieving electrophoresis.

In this study, a structure-induced aptamer targeting small molecules was selected using capillary sieving electrophoresis (CSE). CSE was conducted using a capillary filled with a background solution containing hydroxypropyl cellulose as a sieving matrix to separate the aptamer candidates by changing their structures via complexation. Before aptamer selection, the original random-sequence DNA library was used to create structure-not-preorganized DNA sub-library containing straight-chain-like structures using CSE.

Fundamental investigation on fluorous nanoemulsion optodes: effect of matrix fluorination on selectivity.

As fundamental investigation on fluorous nanoemulsion (NE) optodes for highly selective perfluorooctanesulfonate (PFOS) sensing, the effect of matrix fluorination on selectivity was investigated. Due to the high hydrophobicity of PFOS itself, it responded in exhaustive mode regardless of the fluorination ratio of the matrix, and the lowest detectable PFOS concentration was on the order of 10 to 10 M. On the other hand, the response of non-fluorous interfering anions was suppressed as the fluorination ratio of the matrix increased.

Assessment of the structural change of DNA by binding with a small molecule based on capillary sieving electrophoresis.

In this study, capillary sieving electrophoresis (CSE) using polymer solutions was used to evaluate the structural changes in nucleic acids upon complexation with small molecules. As the model target and nucleic acids, L-tyrosinamide (Tyr-Am) and its aptamer, which is a type of DNA specifically binding to Tyr-Am, were selected. CSE was conducted using a capillary filled with background solution (BGS) containing hydroxypropyl cellulose (HPC) as a sieving matrix.

Water detection in organic solvents using a copolymer membrane immobilised with a fluorescent intramolecular charge transfer-type dye: effects of intramolecular hydrogen bonds.

Numerous fluorescent dye-based optical sensors have been developed to detect water in organic solvents. However, only a few such sensors can detect water in polar solvents such as methanol or dimethyl sulfoxide, and their detection range is generally narrow. Therefore, in this study, a copolymer membrane incorporated with a pyridinium betaine dye (denoted PB1), which exhibited intramolecular charge transfer (ICT) characteristics, was developed to realise simple water detection in organic solvents.

Dielectrophoretic trapping of nanosized biomolecules on plasmonic nanohole arrays for biosensor applications: simple fabrication and visible-region detection.

Surface plasmon resonance is an optical phenomenon that can be applied for label-free, real-time sensing to directly measure biomolecular interactions and detect biomarkers in solutions. Previous studies using plasmonic nanohole arrays have monitored and detected various biomolecules owing to the propagating surface plasmon polaritons (SPPs). Extraordinary optical transmission (EOT) that occurs in the near-infrared (NIR) and infrared (IR) regions is usually used for detection.

Nanoemulsion-based silver ion-selective optode based on colorimetrically silver ion-responsive ionic liquid-based dye.

In this study, we describe the fast-responsive nanoemulsion (NE)-based silver ion (Ag)-selective optode based on colorimetrically silver ion-responsive ionic liquid-based dye (ILD). The ILD comprises purely functional sensing molecules, a protonated cationic merocyanine dye (KD-M13-H) and an anionic Ag ionophore (BDM-SO), and thus, it can be used for highly sensitive silver ion (Ag) sensing due to the extremely high content of dye in the organic phase (ionic-liquid phase). However, during the Ag sensing, the cationic merocyanine dye is converted into electrically neutral form by deprotonation of the dye, which leads to the conversion of liquified dye into solid form in the organic phase, which makes the response time slower when ILD is used for poly(vinyl chloride) (PVC) membrane-based ion-selective optode, especially for sensing of high Ag concentration.

Aptamer Selection Based on Microscale Electrophoretic Filtration Using a Hydrogel-Plugged Capillary Device.

This study reports a novel aptamer selection method based on microscale electrophoretic filtration. Aptamers are versatile materials that recognize specific targets and are attractive for their applications in biosensors, diagnosis, and therapy. However, their practical applications remain scarce due to issues with conventional selection methods, such as complicated operations, low-efficiency separation, and expensive apparatus.

Fabrication of Gold Nanostructures on Quartz Crystal Microbalance Surface Using Nanoimprint Lithography for Sensing Applications.

A quartz crystal microbalance (QCM) is a sensor that uses the piezoelectric properties of quartz crystals sandwiched between conductive electrodes. Localized surface plasmon resonance (LSPR) is an analytical technique that uses the collective vibration of free electrons on metal surfaces. These measurements are known as analysis techniques that use metal surfaces and have been applied as biosensors because they allow for the label-free monitoring of biomolecular binding reactions.

Gold Nanocone Array with Extensive Electromagnetic Fields for Highly Reproducible Surface-Enhanced Raman Scattering Measurements.

Surface-enhanced Raman scattering (SERS) is a technique used to distinguish the constitution of disease-related biomarkers in liquid biopsies, such as exosomes and circulating tumor cells, without any recognition elements. Previous studies using metal nanoparticle aggregates and angular nanostructures have achieved the detection of various biomarkers owing to strong hot spots and electromagnetic (EM) fields by localized surface plasmon resonance (LSPR). Although these SERS platforms enable significant enhancement of Raman signals, they still have some problems with the fabrication reproducibility of platforms in obtaining reproducible SERS signals.

Imprinted Photonic Crystal-Film-Based Smartphone-Compatible Label-Free Optical Sensor for SARS-CoV-2 Testing.

The coronavirus disease (COVID-19) caused by SARS-CoV-2 has caused a global pandemic. To manage and control the spread of the infection, it is crucial to develop and implement technologies for the early identification of infected individuals and rapid informatization in communities. For the realization of such a technology, a widely available and highly usable sensor for sensitive and specific assay of the virus plays a fundamental role.

Evaluation of the interactions between oligonucleotides and small molecules by partial filling-nonequilibrium affinity capillary electrophoresis.

Recently, high-throughput analysis with minimal reagent consumption has been desired to assess interactions between drug candidates and disease-related oligonucleotides. To realize an ideal assay for drug screening, a rapid assay based on affinity capillary electrophoresis was generated to reduce the consumption of samples/reagents by a partial-filling technique under nonequilibrium conditions. In the proposed method, the first sample, oligonucleotide as a ligand, and second sample zones were injected into a capillary with spacers of background solution between the samples and oligonucleotide zones.

Chloride ion-selective dye liquid nanoemulsion: improved sensor performance due to intermolecular interactions between dye and ionophore.

Ionophore-based dye liquid nanoemulsion sensors exhibiting rapid response, high selectivity, and high sensitivity to chloride were developed. Since nanoemulsions contain extremely high concentrations of dyes and have large surface areas, rapid and highly sensitive measurements were possible. H-NMR measurements revealed intermolecular interactions between the dye and the ionophore, which contributed to the suppression of the background signal.

Fabrication of Metal-Insulator-Metal Nanostructures Composed of Au-MgF-Au and Its Potential in Responding to Two Different Factors in Sample Solutions Using Individual Plasmon Modes.

In this paper, metal-insulator-metal (MIM) nanostructures, which were designed to exhibit two absorption peaks within 500-1100 nm wavelength range, were fabricated using magnesium difluoride (MgF) as the insulator layer. Since the MIM nanostructures have two plasmon modes corresponding to the absorption peaks, they independently responded to the changes in two phases: the surrounding medium and the inside insulator layer, the structure is expected to obtain multiple information from sample solution: refractive index (RI) and molecular interaction between solution components and the insulator layer. The fabricated MIM nanostructure had a diameter of 139.

Modulating Optical Characteristics of Nanoimprinted Plasmonic Device by Re-Shaping Process of Polymer Mold.

Metal nanostructures exhibit specific optical characteristics owing to their localized surface plasmon resonance (LSPR) and have been studied for applications in various optical devices. The LSPR property strongly depends on the size and shape of metal nanostructures; thus, plasmonic devices must be designed and fabricated according to their uses. Nanoimprint lithography (NIL) is an effective process for repeatedly fabricating metal nanostructures with controlled sizes and shapes and require optical properties.

Enzyme-responsive fluorescent nanoemulsion based on lipophilic dye liquid.

An enzyme-responsive fluorescent nanoemulsion (NE) based on lipophilic dye liquid (LDL) was developed for alkaline phosphatase (ALP). The response mechanism of the NE involved enzymatic reactions and simultaneous extraction of anions. The LDL-based NE exhibited 3.

Single-step Trypsin Inhibitor Assay on a Microchannel Array Device Immobilizing Enzymes and Fluorescent Substrates by Inkjet Printing.

In this paper, we report a single-step trypsin inhibitor assay on a microchannel array device immobilizing enzymes and substrates by inkjet printing. The microdevice is composed of a poly(dimethylsiloxane) (PDMS) microchannel array that immobilizes trypsin and fluorescent substrates as reactive reagents at the two bottom corners of a microchannel. Inkjet printers allow simple, accurate, and position-selective immobilization of reagents as nanoliter spots.

Fractionation of Single-stranded DNAs with/without Stable Preorganized Structures Using Capillary Sieving Electrophoresis for Aptamer Selection.

Aptamers, single-stranded DNAs/RNAs with a strong and specific interaction towards a target molecule, have wide applications in the fields of medicine and biosensors. In conventional aptamer selection methods, it is difficult to obtain "preorganized" and/or "induced-fit" type of aptamers selectively. In this study, separation and fractionation of single-stranded DNAs with/without stable preorganized structures were carried out using capillary sieving electrophoresis.

Direct Measurement of Initial Rate of Enzyme Reaction by Electrokinetic Filtration Using a Hydrogel-plugged Capillary Device.

A novel electrokinetic filtration device using a plugged hydrogel was developed to directly measure the initial rate of enzyme reactions. In the proposed method, the enzyme reaction proceeded only for a short time when the substrate was passed through a thin layer of enzyme trapped by the hydrogel without any lag times for mixing and detection. In experimental conditions, alkaline phosphatase (enzyme) was filtrated at a cathodic-side interface of the plugged hydrogel by molecular sieving effect, providing the thin enzyme zone whose thickness was approximately 100 μm.

Simple Approach for Fluorescence Signal Amplification Utilizing a Poly(vinyl alcohol)-Based Polymer Structure in a Microchannel.

Analytical methods with fluorescence detection are in widespread use for detecting low abundance analytes. Here, we report a simple method for fluorescence signal amplification utilizing a structure of an azide-unit pendant water-soluble photopolymer (AWP) in a microchannel. The AWP is a poly(vinyl alcohol)-based photocross-linkable polymer, which is often used in biosensors.

Lipophilic Fluorescent Dye Liquids: Förster Resonance Energy Transfer-Based Fluorescence Amplification for Ion Selective Optical Sensors Based on a Solvent Polymeric Membrane.

Optical sensors based on solvent polymeric membranes have the potential to measure analytes present in an aqueous solution through the development of a tailored method for a specific target. However, limits in the concentrations of the component dyes have prevented improvements in sensitivity. We propose a Förster resonance energy transfer (FRET)-based fluorescence amplification system for ion-selective optical sensors using a highly fluorescent liquid material composed of a lipophilic phosphonium cation and a pyrene modifying sulfonate anion ([P][HP-SO]), as both the plasticizer and donor, in addition to a combination of the lipophilic phosphonium cation and the fluorescein dodecyl ester anion ([P][12-FL]) as the fluorescent sensing dye acceptor.

Inkjet Printing-Based Immobilization Method for a Single-Step and Homogeneous Competitive Immunoassay in Microchannel Arrays.

In this study, we report an inkjet printing-based method for the immobilization of different reactive analytical reagents on a single microchannel for a single-step and homogeneous solution-based competitive immunoassay. The immunoassay microdevice is composed of a poly(dimethylsiloxane) microchannel that is patterned using inkjet printing by two types of reactive reagents as dissolvable spots, namely, antibody-immobilized graphene oxide and a fluorescently labeled antigen. Since nanoliter-sized droplets of the reagents could be accurately and position-selectively spotted on the microchannel, different reactive reagents were simultaneously immobilized onto the same microchannel, which was difficult to achieve in previously reported capillary-based single-step bioassay 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.

A lipophilic ionic liquid-based dye for anion optodes: importance of dye lipophilicity and application to heparin measurement.

Herein, a fully lipophilic ionic liquid (IL) comprising a lipophilic fluorescein anion and a trihexyltetradecylphosphonium cation was synthesized and used as the plasticizer for a plasticized poly(vinyl chloride) (PVC) membrane optode. Systematic investigation of the alkyl chain length of the fluorescein anion proved the significance of lipophilicity for obtaining the reversible absorbance measurements. A PVC membrane fabricated with the synthesized lipophilic IL was observed to comprise an unusually high dye concentration (915 mmol kg) and exhibited good sensitivity as well as response time in its sensor performance.

Size Sorting of Exosomes by Tuning the Thicknesses of the Electric Double Layers on a Micro-Nanofluidic Device.

Exosomes, a type of extracellular vesicle with a diameter of 30-150 nm, perform key biological functions such as intercellular communication. Recently, size sorting of exosomes has received increasing attention in order to clarify the correlation between their size and components. However, such sorting remains extremely difficult.