Microalgae living sensor for metal ion detection with nanocavity-enhanced photoelectrochemistry.

Metal ions are known to play various roles in living organisms; therefore, the detection of metal ions in water resources is essential for monitoring health and environmental conditions. In contrast to artificially fabricated materials and devices, biological-friendly materials such as microalgae have been explored for detecting toxic chemicals by employing fluorescence emissions and biophotovoltaic fuel cells. However, complicated fabrication, long measurement time, and low sensitivity remain the greatest challenge due to the minimal amount of bioelectricity generated from whole-cell microalgae. Herein we report the novel concept of a microalgae living biosensor by enhancing photocurrent through nanocavities formed between copper (Cu) nanoparticles and the Cu-electrode beneath. The strong energy coupling between plasmon cavity modes and excited photosynthetic fluorescence from Chlorella demonstrated that photoelectrical efficiency could be significantly amplified by more than two orders of magnitude through nanocavity confinement. Simulation results reveal that substantial near-field enhancements could help confine the electric field to the electrodes. Finally, the microalgae sensor was exploited to detect various light and heavy metal ions with a breakthrough detection limit of 50 nM. This study is envisioned to provide inspirational insights on nanocavity-enhanced electrochemistry, opening new routes for biochemical detection, water monitoring, and sustainable optoelectronics.

Plasmonic Spherical Heterodimers: Reversal of Optical Binding Force Based on the Forced Breaking of Symmetry.

The stimulating connection between the reversal of near-field plasmonic binding force and the role of symmetry-breaking has not been investigated comprehensively in the literature. In this work, the symmetry of spherical plasmonic heterodimer-setup is broken forcefully by shining the light from a specific side of the set-up instead of impinging it from the top. We demonstrate that for the forced symmetry-broken spherical heterodimer-configurations: reversal of lateral and longitudinal near-field binding force follow completely distinct mechanisms. Interestingly, the reversal of longitudinal binding force can be easily controlled either by changing the direction of light propagation or by varying their relative orientation. This simple process of controlling binding force may open a novel generic way of optical manipulation even with the heterodimers of other shapes. Though it is commonly believed that the reversal of near-field plasmonic binding force should naturally occur for the presence of bonding and anti-bonding modes or at least for the Fano resonance (and plasmonic forces mostly arise from the surface force), our study based on Lorentz-force dynamics suggests notably opposite proposals for the aforementioned cases. Observations in this article can be very useful for improved sensors, particle clustering and aggregation.