AppliedPhys

Rapid evaluation of water toxicity requires biological methods capable of detecting sub-lethal physiological changes without depending on chemical identification. Conventional microscopy-based bioassays are limited by low throughput and difficulties in observing small, transparent and fast-moving microorganisms. This study applies a laser-biospeckle, non-imaging microbioassay to assess the motility responses of Paramecium caudatum and Euglena gracilis exposed to two organic pollutants, trichloroacetic acid (TCAA) and acephate. Dynamic speckle patterns were recorded using a 638 nm laser diode (Thorlabs Inc., Tokyo, Japan) and a CCD camera (Gazo Co., Ltd., Tokyo, Japan) at 60 fps for 120 s. Correlation time, derived from temporal cross-correlation analysis, served as a quantitative indicator of motility. Exposure to TCAA (0.1–50 mg/L) produced strong concentration-dependent inhibition, with correlation time increasing up to 16-fold at 500× PL in P. caudatum (p < 0.01), whereas E. gracilis showed a delayed response, with significant inhibition only above 250× PL. In contrast, acephate exposure (0.036–3.6 mg/L) induced motility enhancement in both species, reflected by decreases in correlation time of up to 57% in P. caudatum and 40% in E. gracilis at 100× PL. Acute trends diminished after 24–48 h, indicating time-dependent physiological adaptation. These results demonstrate that biospeckled-derived correlation time sensitively captures both inhibitory and stimulatory behavioral responses, enabling real-time, high-throughput water toxicity screening without microscopic imaging. The method shows strong potential for integration into automated water-quality monitoring systems.

In this paper, we explore the magnetization dynamics in a long ferromagnetic nanostripe with finite width in the presence of antisymmetric Dzyaloshinskii–Moriya exchange interactions (DMIs). It is known that DMIs, which are currently of great interest because they give rise to chiral and nonreciprocal properties and influence surface topologies, can be enhanced by interfacing the nanostripe with a heavy metal. Our theoretical approach employs a microscopic (or Hamiltonian-based) analysis that includes symmetric bilinear exchange, antisymmetric DMI, long-range dipole–dipole interactions, and Zeeman energy due to an external magnetic field applied out of the plane of the nanostripe. In this geometry, we calculate the frequencies and amplitudes of the discrete spin-wave modes that have a standing-wave character across the finite width of the stripe and a propagating character (with wavenumber k) along the stripe length. The individual spin-wave modes display nonreciprocal propagation in their dispersion relations due to DMI. We also find that there may be localized edge spin waves with amplitudes that undergo spatial decay near the stripe edges.

AppliedPhys (ISSN 3042-6553) is a new Open Access journal launched under the leadership of Prof [...]