In vivo optical interferometric imaging of human skin utilizing monochromatic light source.

We have demonstrated tomographic imaging of in vivo human skin with an optical interferometric imaging technique using a monochromatic light source. The axial resolution of this method is determined by the center wavelength and the NA of the objective and is irrelevant to the bandwidth of the light source in contrast to optical coherence tomography. Our imaging system is constructed with low-priced and small-sized compact disk optical pickup components, a laser diode, a high NA objective, and a voice coil actuator. In spite of its low cost and small size, our imaging system can visualize the structure of human skin as clearly as a commercial reflectance confocal microscope.

Three-Dimensional Homodyne Light Detection (3D-HLD) for High-Throughput Submicron Particle Analysis in (Highly Concentrated) Protein Biopharmaceuticals, Viral Vectors, and LNPs.

During biopharmaceutical development, particle monitoring and characterization are crucial. Notably, particles can be impurities considered as critical quality attribute, or active pharmaceutical ingredient (e.g., viral vectors) or drug delivery system (e.g., lipid nanoparticles) itself. Three-dimensional homodyne light detection (3D-HLD) is a novel technique that can characterize particles in the ∼0.2 µm to 2.0 µm size range. We evaluated 3D-HLD for the analysis of high concentration protein formulations (up to 200 mg/mL), where formulation refractive index and background noise became limiting factors with increasing protein concentration. Sample viscosity however did not impact 3D-HLD results, in contrast to comparative analyses with NTA and MRPS. We also applied 3D-HLD in high-throughput screenings at high protein concentration or of lipid nanoparticle and viral vector formulations, where impurities were analyzed in the presence of a small (<0.2 µm) particulate active pharmaceutical ingredient. 3D-HLD turned out to be in good agreement with or a good complement to other state-of-the-art particle characterization techniques, including BMI, MRPS, and DLS. The main application of 3D-HLD is high-throughput particle analysis at low sample volume. Follow-up investigation of the optimized particle sizing approach and of detection settings could further improve the understanding of the method and potentially increase ease of operation.

Plate Reader-Based Analytical Method for the Size Distribution of Submicron-Sized Protein Aggregates Using Three-Dimensional Homodyne Light Detection.

The assessment of aggregates is essential in biopharmaceutical development. Although submicron-sized aggregates are considered to have a potential immunogenicity risk, analytical techniques are limited. In this study, we present a new analytical technique using three-dimensional homodyne light detection (3D-HLD). In this system, submicron-sized particles are quantified by combining the reflected light detection of each particle by high-speed 3D scan and then enhancing the amplitude of the reflected light using HLD. The particle concentrations and size distributions of human tetanus immune globulin (TIG) aggregates generated by stirring were measured using 3D-HLD. Both concentrations and distributions were comparable to those obtained via resonant mass measurement (RMM), a technique commonly used for submicron-sized particle measurement. Aiming at feasibility assessment of 3D-HLD for the high-through-put formulation development, 30 formulations of TIG and rituximab under agitation stress were analyzed by 3D-HLD. The results showed that 3D-HLD can automatically and simultaneously assess the aggregate concentrations and size distributions of at least 90 samples. This study demonstrates that 3D-HLD can be used for submicron-sized aggregate analysis as an orthogonal method to RMM and also as a screening tool during formulation development.

Interlayer crosstalk reduction of a multilayer Blu-ray Disc using a grating in a three beam optical system.

In multilayer optical discs, light reflected by out-of-focus layers, which we call interlayer crosstalk, causes the tracking error signal to fluctuate, making the readout signal unstable. We previously proposed a novel method to use a grating along the optical axis in the return path of a pickup to suppress the fluctuation of a differential push-pull (DPP) signal. We develop a pickup and evaluate its performance to stabilize the DPP signal experimentally. DPP signal fluctuation is suppressed to one-third (6% to 2%), and also satisfactory readout jitters (about 8%) are obtained for a triple-layer Blu-ray Disc (BD), which demonstrate the validity of this method to reduce interlayer crosstalk of multilayer optical discs.