Narrowband detection of mid-wave infrared is of great importance for many applications including thermal imaging and scientific research. Detection of narrowband signals is typically achieved by using broadband photodetectors combined with interference filters or interferometric optics, which inevitably increase the architectural complexity and transmission loss. Here, we report an uncooled and filterless narrowband photodetector for the detection of mid-wave infrared with an enhanced photoresponse by plasmon resonance. Colloidal HgSe quantum-dot films were employed as sensing materials with narrowband optical absorption due to the intraband 1S_e–1P_e transition. Furthermore, gold nanodisk arrays were designed, fabricated and integrated with the HgSe quantum-dot films. Based on the near-field resonance created by the nanodisk structure, the responsivity at the center wavelength of the HgSe quantum-dot film based narrowband photodetector can be increased. In our experiments, four narrowband photodetectors with tunable center wavelengths of 4.2 μm, 6.4 μm, 7.2 μm and 9.0 μm were fabricated. After the integration with the plasmonic nanodisk array, the responsivity at the center wavelength of the four fabricated narrowband photodetectors was enhanced by 517%@ 4.2 μm, 288%@ 6.4 μm, 257%@ 7.2 μm, and 208%@ 9.0 μm, reaching up to 145 mA W⁻¹, 92.3 mA W⁻¹, 88.6 mA W⁻¹, and 86 mA W⁻¹, respectively. The results demonstrated that the full-width at half-maxima of spectral responsivity was also decreased by 42.9% to 59.9% after the integration of the plasmonic nanodisk array. The full-width at half-maxima for four types of photodetectors were all below 2 μm (center wavelength- full-width at half-maxima: 4.2–1.05 μm, 6.4–1.15 μm, 7.2–1.25 μm, and 9.0–1.75 μm), indicating a very sharp spectral photoresponsivity.

Waterproof fiber-based strain sensors with a high gauge factor and outstanding stability are essential for smart textiles, wearable devices and biomedical electronics. In this work, we demonstrate a highly flexible, stretchable, sensitive, and waterproof core-sheath structure strain sensor with a relatively wide strain-sensing range fabricated by a simple approach. Such a core-sheath structure is composed of a superelastic core material polyurethane (PU) yarn; a highly conductive multilayer sheath material, namely, graphene nanosheets/thin gold film/graphene nanosheets (GNSs/Au/GNSs); and a thin polydimethylsiloxane (PDMS) wrapping layer. The combination of the PU yarn, multilayer GNSs/Au/GNSs, and PDMS wrapping layer enables the strain sensor to achieve high flexibility and stretchability, high sensitivity, broad strain-sensing range, and good waterproof property simultaneously due to the infiltration of PDMS into the multilayer during stretching. Particularly, the yarn strain sensor exhibits a high gauge factor (GF: 661.59), outstanding stability with an applied strain of 50% for approximately 10 000 stretch/release cycles, and superior water resistance. Moreover, it can be readily integrated into textiles, including medical textile bandages and textile gloves, for monitoring various human motions (e.g., phonation, pulse, finger bending, and walking) and effectively control a hand robot. Therefore, strain sensors show considerable potential in textile, wearable, and biomedical electronics for healthcare-related applications, such as disease diagnosis, preventive healthcare, and rehabilitation care, and robot controlling-related applications (e.g., controlling a hand robot to catch some objects).

Conventional MEMS actuators are not suitable for underwater applications such as cell grasping due to two main reasons: 1) their required actuation voltage are typically higher than 2 V, which would cause electrolysis in water and 2) they have small displacement/deflection due to their inherent driving principles. In this paper, three-different types of novel polymer-based MEMS underwater actuators developed in our laboratory are discussed: 1) ionic conducting polymer films (ICPF) actuator, which actuates by stress gradient induced by ionic movement due to electric field; 2) parylene thermal actuator, which actuates due to the induced stress gradient across a structure made of different layers of materials with different thermal expansion coefficients; and 3) polyaniline (PANI) actuator, which actuates due to its volumetric change caused by a reversible electrochemical oxidation-reduction (redox) reaction. All these polymer micro actuators can be actuated underwater with large deflections and require less power input than conventional MEMS actuators. The experimental results from characterizing these prototype actuators are presented in this paper.