Metamaterials have attracted intensive research interest in recent years because their optical properties have a strong dependence on the geometry of metamaterial molecules rather than the material composition. [1][2][3] This feature has inspired the creation and tailoring of exotic properties, such as a negative refractive index, [ 4 , 5 ] perfect absorption, [ 6 ] and super lensing, [ 7 , 8 ] which are not readily available in nature. For many practical applications such as data storage [ 9 ] and optical switching, [ 10 ] switchable metamaterials that possess very different states are almost a necessity. [ 11 ] Most of the tunable metamaterials that have been demonstrated rely on tuning constituent materials or changing surrounding media by introducing natural materials with higher tunability, such as liquid crystals and phase changing materials. [12][13][14][15][16][17][18][19] However, this limits the choices of materials and becomes increasingly diffi cult to implement at higher frequencies. Moreover, the tuning range is usually too limited to achieve a switching effect between strikingly different states.A complementary approach is to mechanically reconfi gure the metamaterial molecules. [ 20 , 21 ] Micromachining technology has been developed for fabrication and actuation of micromechanical devices [22][23][24][25][26] with switching frequencies up to the GHz level. [ 27 ] An attempt was made to adjust the distance between several planar metamaterial layers in which effi cient transmission change was achieved but the tuning originated from a change in the layer structure rather than a change in metamaterial molecule. [ 22 ] Recently, another interesting work demonstrated the modifi cation of the optical properties of a metamaterial by reorienting the metamaterial molecules. [ 23 ] Inspired by these prior studies, we report the concept and design of switchable magnetic metamaterials by directly reshaping the metamaterial molecules using the micromachining technology and present working devices with switchable magnetic responses.The schematic diagram of the switchable magnetic metamaterial is shown in Figure 1 a. Each metamaterial molecule consists of two semi-square split rings. One is anchored on the substrate while the other can be moved by micromachined actuators. As a result, the gap between the split rings can be altered and thus the geometric shape of the metamaterial molecule can be changed. Figure 1 b-d illustrates the two semi-square spit rings in different states. In Figure 1 b, the two split rings are separated by a small gap, resulting in a geometric shape "[]". This is a typical split ring resonator. [ 28 ] For simple notation, this state is called the open-ring state. Figure 1 c,d show two extreme cases. In the former, the gap between the two split rings is closed and the actual metamaterial molecule becomes a closed ring in the "ٗ" shape. This is called the closed-ring state. In the latter, the movable ring is moved away until it touches the back side of the fi xed ring in the next metama...

A micromachined reconfigurable metamaterial is presented, whose unit cell consists of a pair of asymmetric split‐ring resonators (ASRRs); one is fixed to the substrate while the other is patterned on a movable frame. The reconfigurable metamaterial and the supporting structures (e.g., microactuators, anchors, supporting frames, etc.) are fabricated on a silicon‐on‐insulator wafer using deep reactive‐ion etching (DRIE). By adjusting the distance between the two ASRRs, the strength of dipole–dipole coupling can be tuned continuously using the micromachined actuators and this enables tailoring of the electromagnetic response. The reconfiguration of unit cells endows the micromachined reconfigurable metamaterials with unique merits such as electromagnetic response under normal incidence and wide tuning of resonant frequency (measured as 31% and 22% for transverse electric polarization and transverse magnetic polarization, respectively). The reconfiguration could also allow switching between the polarization‐dependent and polarization‐independent states. With these features, the micromachined reconfigurable metamaterials may find potential applications in transformation optics devices, sensors, intelligent detectors, tunable frequency‐selective surfaces, and spectral filters.

Direct monitoring of cell death (i.e., apoptosis and necrosis) during or shortly after treatment is desirable in all cancer therapies to determine the outcome. Further differentiation of apoptosis from necrosis is crucial to optimize apoptosis-favored treatment protocols. We investigated the potential modality of using tissue intrinsic fluorescence chromophore, reduced nicotinamide adenine dinucleotide (NADH), for cell death detection. We imaged the fluorescence lifetime changes of NADH before and after staurosporine (STS)-induced mitochondria-mediated apoptosis and hydrogen peroxide (H2O2)-induced necrosis, respectively, using two-photon fluorescence lifetime imaging in live HeLa cells and 143B osteosarcoma. Time-lapsed lifetime images were acquired at the same site of cells. In untreated cells, the average lifetime of NADH fluorescence was approximately 1.3 ns. The NADH average fluorescence lifetime increased to approximately 3.5 ns within 15 min after 1 microM STS treatment and gradually decreased thereafter. The NADH fluorescence intensity increased within 15 min. In contrast, no significant dynamic lifetime change was found in cells treated with 1 mM H2O2. Our findings suggest that monitoring the NADH fluorescence lifetime may be a valuable noninvasive tool to detect apoptosis and distinguish apoptosis from necrosis for the optimization of apoptosis-favored treatment protocols and other clinical applications.

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