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Nowadays, the diagnosis of viral infections is receiving broad attention. We have developed a non-competitive fluorescence polarization immunoassay (NC-FPIA), which is a separation-free immunoassay, for a virus detection. H5 subtype avian influenza virus (H5-AIV) was used as a model virus for the proof of concept. The fluorescein-labeled Fab fragment that binds to H5 hemagglutinin was used for NC-FPIA. The purified H5-AIV which has H5 hemagglutinin was mixed with the fluorescein-labeled Fab fragment. After that, the degree of fluorescence polarization was measured with a portable FPIA analyzer. H5-AIV was successfully detected with an incubation time of 15 min. In addition, the portable FPIA analyzer enables performance of on-site NC-FPIA with a sample volume of 20 μL or less. This is the first research of detecting a virus particle by FPIA. This NC-FPIA can be applied to rapid on-site diagnosis of various viruses. Supplementary Information The online version contains supplementary material available at 10.1007/s00216-021-03193-y.

Fluorescent polarization immunoassay (FPIA) is a single-step immunoassay method that is applicable to point-of-care testing; however, its applicability to large biomolecules has been restricted because ordinary FPIA is a competitive assay. Here, we report a noncompetitive FPIA using the variable domain from the heavy chain of a camelid antibody (VHH antibody). FPIA with VHH was successfully used to quantitate rabbit immunoglobulin G (IgG) and demonstrated a wider response range than that observed with antibody-binding (Fab) fragment. Then, using a portable FPIA instrument, a VHH-based immunoassay of human IgG in a human serum certified reference material was demonstrated.

High-throughput fluorescence polarization immunoassays (FPIAs) for mycotoxin were conducted using a portable FP analyzer with a microdevice. Simultaneous FPIA measurements for 8 different deoxynivalenol (DON) concentrations in 12 chambers (total of 96 samples) and high-throughput FPIA measurements for single DON concentrations in more than 500 chambers were conducted. The results indicated that simultaneous FPIAs for 96 independent samples and for 500 samples were possible by FP imaging. The FP analyzer has a size of 65 cm (W 35 cm × D 15 cm × H 15 cm) and costs less than $5000. The sample volume was 1 nL. Furthermore, it is expected that sample reaction and FP detection can be automatically conducted with the analyzer by changing the microdevice and the software. Its features such as low cost and portability will contribute to on-site measurement and point-of-care testing. Additionally, the high-throughput feature will contribute to the study of molecular interactions based on FP measurements.

Antibody detection methods for viral infections have received broad attention due to the COVID-19 pandemic. In addition, there remains an ever-increasing need to quantitatively evaluate the immune response to develop vaccines and treatments for COVID-19. Here, we report an analytical method for the rapid and quantitative detection of SARS-CoV-2 antibody in human serum by fluorescence polarization immunoassay (FPIA). A recombinant SARS-CoV-2 receptor binding domain (RBD) protein labeled with HiLyte Fluor 647 (F-RBD) was prepared and used for FPIA. When the anti-RBD antibody in human serum binds to F-RBD, the degree of polarization (P) increases by suppressing the rotational diffusion of F-RBD. The measurement procedure required only mixing a reagent containing F-RBD with serum sample and measuring the P value with a portable fluorescence polarization analyzer after 15 min incubation. We evaluated analytical performance of the developed FPIA system using 30 samples: 20 COVID-19 positive sera and 10 negative sera. The receiver operating characteristic curve drawn with the obtained results showed that this FPIA system had high accuracy for discriminating COVID-19 positive or negative serum (AUC = 0.965). The total measurement time was about 20 min, and the serum volume required for measurement was 0.25 μL. Therefore, we successfully developed the FPIA system that enables rapid and easy quantification of SARS-CoV-2 antibody. It is believed that our FPIA system will facilitate rapid on-site identification of infected persons and deepen understanding of the immune response to COVID-19.

We have developed a two-way multi-view 2-D/3-D display combining a liquid crystal lens and horizontally and vertically x times-density pixels (HVxDP) arrangement. The two-way multi-view display features the same display resolution in 2-D and 3-D modes and a quite small color moire for landscape and portrait, respectively, when using the HVxDP arrangement. In this paper, we realized suitable 3-D properties for achieving a good balance between 3-D moire and 3-D crosstalk for landscape and portrait by a two-way liquid crystal lens with two kinds of focal lengths for the edge part and the center part of the lens.

Graphical abstract, Highlights • FPIA for detection of anti-H5 subtype avian influenza virus (AIV) antibody was achieved. • Anti-H5 AIV serum was selectively detected in anti-H1–H16 AIV sera. • The Portable FP analyzer on the microfluidic device realized rapid and facile FPIA., A rapid, facile and selective detection of anti-H5 subtype avian influenza virus (AIV) antibody in serum by fluorescence polarization immunoassay (FPIA) was achieved. A fragment of recombinant H5 subtype AIV hemagglutinin was produced and labeled with fluorescein to use it as a labeled antigen in FPIA. This labeled antigen was mixed with anti-AIV sera (H1–H16 subtypes) and FP of the mixture was measured using a portable FP analyzer on a microdevice. It was found that FP increased in proportion to the concentration of anti-H5 AIV antibody (serum) and was significantly higher than FP obtained with the other sera. The selective detection of anti-H5 subtype AIV antibody was confirmed. The required volume of original sample was 2 μL and analysis time was within 20 min. This detection system realizes an efficient on-site diagnosis and surveillance of AIV.

We propose an autostereoscopic display system which optimizes a parallax value of arbitrary viewpoint images to reduce the influence of 3D-crosstalk space and to display motion parallax. The system monitors the observer's eye positions, and varies binocular parallax based on the viewing angle.

We propose an optimized parallax control method to reduce the influence of high-3D-crosstalk space and pseudoscopic space on autostereoscopic displays regardless of the observer's eye position. This method optimizes the parallax values of 3D images by using the 3D-crosstalk value of autostereoscopic displays and the observer's eye position.

For autostereoscopic displays with plastic optical films such as lenticular lenses, the 3D viewing space varies with the temperature. Through theoretical analysis and experiments, we find that their changes behave differently for the near objects and far objects. Taking this result into consideration, a novel temperature compensation system is proposed and is also verified.

We have developed a multi-view 2D/3D Display with the HxDP (Horizontally x times-Density Pixels) arrangement. The multi-view display features the same display resolution in 2D and 3D modes and simultaneously displays 2D and 3D images on the same screen. It has excellent optical characteristics: a low 3D crosstalk of less than 2%, a large QSVS (Qualified Stereoscopic Viewing Space), and a smooth motion parallax.

Fluorescence polarization (FP) offers easy operation and rapid processing, making it implementable in molecular interaction analysis. Previously we have developed a unique FP measurement system using a liquid crystal (LC) layer and an image sensor. The system is based on a principle of synchronized detection between the switching rate of the LC layer and the sampling rate of the CCD. The FP system realized simultaneous multiple sample detection; however, the measurement precision was lower than that of the conventional FP apparatus. The main drawbacks were low light transmittance of the LC layer and insufficient synchronization between the LC layer and CCD. In this paper, we developed a new FP analyzer based on LC-CCD synchronization detection. By using a newly designed LC with high transmittance and improving synchronization, the performance of the system has been dramatically improved. Additionally, we reduced the cost by using an inexpensive CCD and an LED as the excitation source. Simultaneous FP immunoassay of multiple samples of prostaglandin E2 was performed. The error rate of the FP system is reduced from 16.9% to 3.9%, as comparable to the commercial conventional FP system. Published by AIP Publishing.

A novel color electrophoretic E-Paper using independently movable colored particles with different threshold fields was proposed for the first time. An a-Si TFT driven two primary colors prototype with red and cyan particles was successfully demonstrated. A full color feasibility was also proved using three primary colored particles (yellow, magenta and cyan), which showed a gamut as wide as that of newsprint.