In a combined acoustic-gravitational field (CAG), a particle is levitated at a position that depends on its acoustic properties such as the density and compressibility but is independent of its size. Thus, the density and compressibility of the particle can be evaluated by measuring the levitation coordinate in the CAG field. We have developed several methods for highly sensitive detection and reaction evaluation based on the levitation coordinate measurements of a single particle. The acoustic property of a particle can be modified by reactions occurring on the surface or inside the particle. For example, the density change of a microparticle can be induced by the binding of gold nanoparticles (AuNP) through a reaction. Proteins, coenzymes, DNA, and RNA can be detected at a zepto mole level by appropriately designing the reaction-mediated microparticle-AuNP binding. The dynamic evaluation of the ion-exchange reaction is also feasible by monitoring the temporal change in the levitation coordinate of a resin bead because an ion exchange reaction modifies the density and compressibility of the ion-exchange resin. In this account, we discuss the designs of the scheme and results for highly sensitive detection and the dynamic evaluation of ion-exchange reactions, mainly focusing on the results of our work.

In this report, analytical method using ultra-small droplets of pico∼nano liter generated by a piezo-type inkjet, while focusing on our recent reports. At first, the generation of droplets by an inkjet and the analytical characteristics of the use of inkjet were described. Then, an enzyme-linked immune sorbent assay (ELISA) by the use of an inkjet as a nano-pipette. The fabrication method of a three-dimensional ordered micro bead structure and its application to ELISA was described in detail. The third topic is the application of the inkjet to electrophoresis-mediated micro analysis by drop-by-drop introduction for an antigen and a fluorescence-labeled antibody, followed by the immune reaction and separation by electrophoresis and detection. The forth topic is the development of the new concept of digital PCR, which enabled the on-line PCR amplification of single-target DNA without any transfer of the droplets. Finally, the use of the inkjet to generate micro polymer particles with a novel dipped injection method and its application to the controlled release of drug was described.

We report a rapid and simple method to detect endotoxin using a nanopore sensor based on the Coulter principle. An ion current momentary decreases when an endotoxin micelle translocates through the nanopore at a tip of the glass capillary with the voltage biased across the pore. Quantitative detection is available by counting pulsed currents appear within a limited period. First, we characterized the nanopores of fabricated glass capillaries using a scanning electron microscope. The size of the pore at the tip of the glass capillary was 260 nm. Next, endotoxin assays using a nanopipette were performed. An Ag/AgCl wire inserted into a glass capillary filled with phosphate buffer saline (PBS) containing endotoxin was biased at 1 V versus another Ag/AgCl wire inserted in a bulk solution containing endotoxin-free PBS. No pulsed current was observed during 4 min of monitoring when the endotoxin concentrations in the glass capillary were below 100 Endotoxin Unit (EU) L⁻¹. When 500-10000 EU L⁻¹ was in the glass capillary, pulsed currents were observed with an increase of the pulse height and pulse frequency with increasing of the endotoxin concentration. This is because the size of the endotoxin micelles as well as the micelle concentration were increased with the increase of the endotoxin concentration. The fact that pulses appeared far less frequently than expected indicates that only large micelles associated with each other were observed as a pulsed current. Although the current detection limit is 500 EU L⁻¹, optimization of the pore diameter will make it possible to detect even smaller micelles, resulting in an increased the sensitivity. This method is expected to be applied to use as a rapid and simple sensor to detect endotoxin, especially in the continuous monitoring of dialysis solution.

High hydrophilic compounds are difficult to separate by conventional reversed-phase chromatography. When they lack chromophores, they are also difficult to detect by ordinary UV detection. However, the complexation of hydrophilic compounds with metal ions can greatly change their steric and electrostatic properties, which would facilitate their separation by reversed-phase chromatography or ion-exchange chromatography. Complexation can also shift their absorptions to longer wavelengths and increase their extinction coefficients, which would facilitate their detection in UV. Here, we show that hydrophilic compounds can be separated by reversed-phase chromatography or ion-exchange chromatography by on-column complexation with metal ions added to the mobile phase, and can be detected by UV detection. Thus, the coordination ability of hydrophilic compounds provides new ways to separate them. We also apply the methods to measure hydrophilic compounds (e.g. sequestering agents, carboxylic acids, alcohols and sugar alcohols) in environmental water samples, common commodities and foods.

Electrochemical characterizations of chromatography paper-based electrochemical sensors are presented by means of chronoamperometory (CA), cyclicvoltammetry (CV), and impedance (IMP) measurement. Samples with co-planar electrodes with dropped solution, height-limited solution, and solution within a sheet of chromatography paper, were tested. It was found that the height limitation, reduction of diffusion coefficient, and thin solution layer between paper and chip substrate can impact the shapes of CA and CV, which was confirmed by computer simulations. It was also found that solution resistance due to ion conduction in paper sensor will be reduced because of ion conductivity reduction.

Quantitative analysis was performed by X-ray diffraction/Rietveld refinement with the Reference Intensity Ratio (RIR) method serving as the basis for determining the halo (background) intensity characteristic of the amorphous content. Although quantification by Rietveld analysis based on RIR is a standard-less method, there are few examples of this application in the literature. Since no RIR value exists for the amorphous phase, it was necessary to empirically determine the amorphous RIR value by gravimetrically preparing a set of simulated samples from blast-furnace slag and other reagents. The RIR value of the amorphous phase was determined to be 3.60, as calculated from the minimum root-mean-square error (RMSE) between known and analyzed values of crystalline and amorphous phases by a Rietveld refinement with various RIR values. Subsequently, this RIR value was applied to analyze the contents of amorphous phases in two commercial cement sample analytical results of the amorphous and crystalline phases in the cement samples by the RIR method were in good agreement with analytical results by the internal standard method (using silicon). It was thus demonstrated that Rietveld refinement, using the RIR value as the basis for the halo intensity, was an effective method for the quantitative analysis of the amorphous phase in cement.

A thorough molecular characterization is crucial for the quality control of polycarbonates (PCs), since their physical properties are dictated by the chemical nature of end-groups and/or repeating units. The high-molecular-weight of PCs prevents their direct characterization by MALDI-TOF mass spectrometry (MS). Instead, an “on-plate degradation” sample pretreatment developed for polyesters is proposed for the analysis of PCs. In a two-step method, a methanolic solution of sodium hydroxide is first added to high-molecular-weight samples deposited on a MALDI target plate. Polymer chains are rapidly and selectively cleaved at the carbonate ester bonds, producing short oligomers of under m/z 3000, readily observed by high-resolution MS. The characterization of chain-ends of a PC homopolymer and of the repeating units of a PC copolymer exemplify the capabilities of the procedure for a fine evaluation of molecular features. A low amount of 4-cumylphenyl terminus at a relative abundance of ∼4 %, compared to the t-butylphenyl terminus, is indeed successfully detected. It is also demonstrated that tetrabromobisphenol A, together with bisphenol A, are the two main components forming a copolymeric backbone, rather than a blend of homopolymers. For this second example, a Kendrick mass defect (KMD) analysis greatly facilitates the extraction and assignment of peaks from brominated species having complex isotope patterns in the mass spectrum.

The determination method of olive polyphenol hydroxytyrosol in a soft capsule was improved. The determination was carried out by HPLC with UV spectrophotometric detection. The capsule shell was included in the sample preparation. The samples were diluted with acetonitrile and water in an ultrasonic water bath for 60 min. After this, this solution was diluted with methanol again. The recovery was over 95 % and the relative standard deviation was within 3 %. This method allowed for the simultaneous determination of hydroxytyrosol and oleuropein.