Behavioral Biometrics Optical Tactile Sensors That Decouple Dynamic Touch Signals Using Human-skin Mimetic Luminescence Microarchitectures

School of Energy and Chemical Engineering (Chemical Engineering)clos

Full Color Tactile Sensor by Using Upconversion Nanoparticle Embedded Microarray

Rare-earth-doped upconversion nanoparticles (UCNP) release a visible ranged luminescence property under exposed near-infrared (NIR) light by multiphoton excitation. These particles are highly photochemical stability, absence of background autofluorescence, and showing various colors through one kind of light source. Therefore, UCNP have been studied extensively for applications such as a photodynamic therapy, bioimagings, and a luminescence display. In this work, we rationally utilized the unique properties of UCNP and report a new type of colorimetric tactile sensor using lanthanide doped upconverting nanoparticles. We fabricated full color array using lithography technique and applied this array into the NIR based sensor to recognize the direction and magnitude of applied pressure

Theoretical study on enhancement of heat transfer of nanofluids with functionalized graphene flakes in confined nanopipe system

In order to find a suitable type of nanoparticles to improve the heat transfer of nanofluids, the role of nanoparticles should be elucidated. The nanoparticles are known to affect the heat transfer, and here we investigated the role of nanoparticles using a nanopipe model system. Specifically, the heat transfer phenomena of nanofluids containing hydrophobic (i.e., hydrogenated) and hydrophilic (i.e., carboxylated) functionalized graphene flakes (GFs) were compared. Confined nanopipe (i.e., 325 K) with a diameter of 400 ?? system were adopted for the heat transfer and coarse-grained molecular dynamics (CGMD) simulations were performed. In the nanofluids, GF-concentrated layer was formed near the pipe wall, which induced the high HTC value of nanofluids. We found that after the thermal change of fluid became constant (i.e., thermally fully developed region), the thermal boundary layer was maintained for 100 ?? due the GF-concentrated layer. The thermal boundary layer and HTC was thicker and higher when using carboxylated GF, which was more soluble in the coolant

Facile Microfluidic Fabrication of 3D hydrogel SERS Substrate with High Reusability and Reproducibility via Programmable Maskless Flow Microlithography

In the field of surface???enhanced Raman scattering (SERS), advances in nanotechnology and surface chemistry have contributed to fabricating the metal substrates with highly sophisticated architectures and strong binding affinity to target molecules which enhanced the sensitivity to target molecules. However, the elaborate yet complicated steps for the synthesis, patterning, and surface modification of metal substrates have often resulted in compromising the reliability, reproducibility, and reusability as SERS substrates. Here, a fully programmable and automated digital maskless flow microlithography process that spatiotemporally controls the fluid flow, UV irradiation, and the shape and location of SERS polymer matrix is provided to fabricate a reliable, reproducible, and reusable hydrogel???based 3D SERS substrate. The SERS substrates are located inside the microfluidic device in the form of disk???shaped hydrogels. By rationally designing the functional group chemistry of the hydrogel microposts, Ag nanoparticles are homogeneously synthesized in situ, a target molecule is amplified by 25???fold inside the microposts, and an enhancement factor as high as 2.4 ?? 108 is observed. Furthermore, a highly reusable multitarget sensing capability is demonstrated by a sequential analysis of multiple analytes without the trace of former analytes via the intermittent washing step

Dynamic multimodal holograms of conjugated organogels via dithering mask lithography

Polymeric materials have been used to realize optical systems that, through periodic variations of their structural or optical properties, interact with light-generating holographic signals. Complex holographic systems can also be dynamically controlled through exposure to external stimuli, yet they usually contain only a single type of holographic mode. Here, we report a conjugated organogel that reversibly displays three modes of holograms in a single architecture. Using dithering mask lithography, we realized two-dimensional patterns with varying cross-linking densities on a conjugated polydiacetylene. In protic solvents, the organogel contracts anisotropically to develop optical and structural heterogeneities along the third dimension, displaying holograms in the form of three-dimensional full parallax signals, both in fluorescence and bright-field microscopy imaging. In aprotic solvents, these heterogeneities diminish as organogels expand, recovering the two-dimensional periodicity to display a third hologram mode based on iridescent structural colours. Our study presents a next-generation hologram manufacturing method for multilevel encryption technologies. Periodic patterns with varying cross-linking densities are realized in conjugated polydiacetylene films, creating multiple holographic images-all dynamically responsive to exposure to various solvents-simultaneously in the same polymeric structures