We demonstrate the ability to overcome the slow data transmission of a phosphor-coated white light emitting diode (LED) by replacing a conventional Si photodiode with a narrowband, green InGaN LED as receiver. By relying on the wavelength selectivity of an InGaN LED, we are able to detect the fast blue light components and reject the slow phosphor components from white light illumination, thereby increasing the modulation speed significantly from 5 MHz to 20 MHz. V-pit texturing is used to improve the peak responsivity of InGaN LEDs to 0.23 A/W at 380 nm, which is comparable with the highest values reported in InGaN detectors. Such V-pit structures also help to shield nonradiative recombination at threading dislocations, so that a high breakdown voltage of −40 V with a high bandwidth of 275 MHz can be obtained. This demonstrates the suitability of V-pit textured InGaN LEDs to function not only as a bright emitter but also as a highly responsive, fast photodetector. This dual functionality enables high-speed LED-to-LED communications, without the need for an extra photodetector.

Dark mode in metamaterials has become a vital component in determining the merit of the Fano type of interference in the system. Its strength dictates the enhancement and suppression in the amplitude and Q-factors of resulting resonance features. In this work, we experimentally probe the effect of strong near-field coupling on the strength of the dark mode in a concentrically aligned bright resonator and a dark split ring resonator (SRR) system exhibiting the classical analog of the electromagnetically induced transparency effect. An enhanced strong magnetic field between the bright-dark resonators destructively interferes with the inherent magnetic field of the dark mode to completely annihilate its effect in the coupled system. Moreover, the observed annihilation effect in the dark mode has a direct consequence on the disappearance of the SRR effect in the proposed system, wherein under the strong magnetic interactions, the LC resonance feature of the split ring resonator becomes invisible to the incident terahertz wave.

A chiral meta-foil consisting of a self-supported square array of interconnected conjugated rosettes is demonstrated at terahertz frequencies. It exhibits strong optical activity and circular dichroism. Negative refractive index with a figure-of-merit as high as 4.2 is achieved, attributed to its free-standing nature. Experimental results are in good agreement with numerical simulation. Free-standing chiral meta-foils provide a unique approach to create a completely all-metal chiral metamaterial, which can be flexibly integrated into optical setups while eliminating dielectric insertion losses.

There is clinical need for a quantifiable point‐of‐care (PoC) SARS‐CoV‐2 neutralizing antibody (nAb) test that is adaptable with the pandemic's changing landscape. Here, we present a rapid and semi‐quantitative nAb test that uses finger stick or venous blood to assess the nAb response of vaccinated population against wild‐type (WT), alpha, beta, gamma, and delta variant RBDs. It captures a clinically relevant range of nAb levels, and effectively differentiates prevaccination, post first dose, and post second dose vaccination samples within 10 min. The data observed against alpha, beta, gamma, and delta variants agrees with published results evaluated in established serology tests. Finally, our test revealed a substantial reduction in nAb level for beta, gamma, and delta variants between early BNT162b2 vaccination group (within 3 months) and later vaccination group (post 3 months). This test is highly suited for PoC settings and provides an insightful nAb response in a postvaccinated population.

Monodispersed luminescent nanoparticles for ink-jet printing and bioimaging.