Absorption of microwaves by metallic conductors is typically inefficient, albeit naturally broadband, due to the huge impedance mismatch between metal and free space. Reducing metal to ultrathin profile may improve absorption efficiency, but a maximal 50% absorption limit induced by the field continuity exists. Here, we experimentally show that broadband, perfect (100%) absorption of microwaves can be realized in a single layer of ultrathin conductive film when illuminated coherently by two oppositely directed incident beams. Our experiments keep the field continuity and simultaneously break the 50% limit. Inheriting the intrinsic broadband feature of metals, complete absorption is observed to be frequency independent in microwave experiments from 6 to 18 GHz. Remarkably, this occurs in films with thicknesses that are at the extreme subwavelength scales, ∼λ/10 000 or less. Our work proposes a way to achieve total electromagnetic wave absorption in an ultrawide spectrum of radio waves and microwaves with a simple conductive film.

We present the optical diagnosis of dengue virus infection in human blood serum using Raman spectroscopy. Raman spectra were acquired from 18 blood serum samples using a laser at 532 nm as the excitation source. A multivariate regression model based on partial least-squares regression is developed that uses Raman spectra to predict dengue infection with leave-one-sample-out cross validation. The prediction of dengue infection by our model yields correlation coefficient r2 values of 0.9998 between the predicted and reference clinical results. The model was tested for six unknown human blood sera and found to be 100% accurate in accordance with the clinical results.

We have experimentally and numerically demonstrated that the coherent perfect absorption (CPA) can equivalently be accomplished under single beam illumination. Instead of using the counter-propagating coherent dual beams, we introduce a perfect magnetic conductor (PMC) surface as a mirror boundary to the CPA configuration. Such a PMC surface can practically be embodied, utilizing high impedance surfaces, i.e., mushroom structures. By covering them with an ultrathin conductive film of sheet resistance 377 Ω, the perfect (100%) microwave absorption is achieved when the film is illuminated by a single beam from one side. Employing the PMC boundary reduces the coherence requirement in the original CPA setup, though the present implementation is limited to the single frequency or narrow band operation. Our work proposes an equivalent way to realize the CPA under the single beam illumination, and might have applications in engineering absorbent materials.

Protamine proteins dramatically condense DNA in sperm to almost crystalline packing levels. Here, we measure the first step in the in vitro pathway, the folding of DNA into a single loop. Current models for DNA loop formation are one-step, all-or-nothing models with a looped state and an unlooped state. However, when we use a Tethered Particle Motion (TPM) assay to measure the dynamic, real-time looping of DNA by protamine, we observe the presence of multiple folded states that are long-lived (∼100 s) and reversible. In addition, we measure folding on DNA molecules that are too short to form loops. This suggests that protamine is using a multi-step process to loop the DNA rather than a one-step process. To visualize the DNA structures, we used an Atomic Force Microscopy (AFM) assay. We see that some folded DNA molecules are loops with a ∼10-nm radius and some of the folded molecules are partial loops—c-shapes or s-shapes—that have a radius of curvature of ∼10 nm. Further analysis of these structures suggest that protamine is bending the DNA to achieve this curvature rather than increasing the flexibility of the DNA. We therefore conclude that protamine loops DNA in multiple steps, bending it into a loop.

Surface plasmon resonance (SPR) has become an important optical biosensing technology due to its real-time, label-free, and noninvasive nature. These techniques allow for rapid and ultra-sensitive detection of biological analytes, with applications in medical diagnostics, environmental monitoring, and agriculture. SPR is widely used in the detection of biomolecular interactions, and improvements are required for both sensitivity and in vivo uses for practical applications. In this study, we developed an SPR biosensor to provide a highly sensitive and specific approach to early-stage detection of viral and malignant diseases, such as cancer tumors, for which biomarker detection is very important. A cancer cell line (HeLa cells) with biomarker Rodamine 6G was experimentally analyzed in vitro with our constructed SPR biosensor. It was observed that the biosensor can offer a potentially powerful solution for tumor screening with dominant angular shift. The angular shift for both regents is dominant with a time curve at a wavelength of 632.8 nm of a He–Ne laser. We have successfully captured and detected a biomarker in vitro for cancer diagnostics using the developed instrument.