Achieving extraordinarily high sensitivity is a long-sought goal in the development of novel and more capable electromagnetic sensors. We present here how a coherent perfect absorber-laser (CPAL) enabled by parity-time (PT) symmetry breaking may be exploited to build ultrasensitive monochromatic electromagnetic sensors that use radio waves, microwaves, terahertz radiations, or light. We argue the possibility of using such CPAL sensors to detect extremely small-scale perturbations of admittance or refractive index caused by, for example, low-density gas molecules and microscopic properties, as they may drastically vary the system’s output intensity from very low (coherent absorption) to high (lasing). We derive the physical bounds on CPAL sensors, showing that their sensitivity and resolvability may go well beyond traditional electromagnetic sensors, such as sensors based on Fabry–Perot cavities.

We herein introduce a lightweight and zero-power smart face mask, capable of wirelessly monitoring coughs in real time and identifying proper mask wearing in public places during a pandemic. The smart face mask relies on the compact, battery-free radio frequency (RF) harmonic transponder, which is attached to the inner layer of the mask for detecting its separation from the face. Specifically, the RF transponder composed of miniature antennas and passive frequency multiplier is made of spray-printed silver nanowires (AgNWs) coated with a poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) passivation layer and the recently discovered multiscale porous polystyrene-block-poly­(ethylene-ran-butylene)-block-polystyrene (SEBS) substrate. Unlike conventional on-chip or on-board wireless sensors, the SEBS-AgNWs/PEDOT:PSS-based RF transponder is lightweight, stretchable, breathable, and comfortable. In addition, this wireless device has excellent resilience and robustness in long-term and repeated usages (i.e., repeated placement and removal of the soft transponder on the mask). We foresee that this wireless smart face mask, providing simultaneous cough and mask-wearing monitoring, may mitigate virus-transmissive events by tracking the potential contagious person and identifying mask-wearing conditions. Moreover, the ability to wirelessly assess cough frequencies may improve diagnosis accuracy for dealing with several diseases, such as chronic obstructive pulmonary disease.

ObjectiveThis study aimed to construct a biosensor using Au nanoparticles (Au NPs) and reduced graphene-polyamide-amine-ferrocene (rGO-PAMAM-Fc) nanomaterials designed for rapid and sensitive detection of cholesterol.Materials and methodsIn this study, a highly sensitive biosensor based on Au NPs/ rGO-PAMAM-Fc nanomaterials was manufactured for detection of cholesterol. The rGO-PAMAM-Fc and Au NPs were modified on the surface of the electrode and then coated with cholesterol oxidase (ChOx) and cholesterol esterase (ChEt) to develop the ChOx&ChEt/Au NPs/rGO-PAMAM-Fc biosensor.ResultsThe capability of rGO-PAMAM-Fc nanomaterials in fabricating a more efficient biosensor was validated through stability, selectivity and reproducibility checks. Under optimal conditions, the newly developed biosensor showed a linear relationship with logarithm of cholesterol concentration from 0.0004 to 15.36 mM (R2=0.9986), and a low detection limit of 2 nM was obtained at the signal/noise ratio of 3.ConclusionThe ChOx&ChEt/Au NPs/rGO-PAMAM-Fc biosensor was successfully applied for the measurement of cholesterol in human serum, which implies that the biosensor has a potential application in clinical diagnostics.

We propose and experimentally demonstrate a parity-time (PT)-symmetric electronic system exhibiting the self-dual emitter-absorber property with a remarkable modulation depth in the radio-frequency (RF) region. The dramatically different RF responses between the emitter and absorber modes may allow detection of ultrasmall conductive or reactive perturbations. Our measurement results show that even a perturbation of the 10 -2 order can greatly change the system's output intensity by more than 30 dB, consistent with the theoretical prediction. The measured sensitivity is far beyond traditional sensors based on a Fabry-Perot resonator, and may lead to monotonic RF sensors with high sensitivity and resolvability.

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