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Biomarkers in tear fluid have attracted much interest in daily healthcare sensing and monitoring. Recently, surface-enhanced Raman scattering (SERS) has enabled highly sensitive label-free detection of small molecules. However, a highly stable straightforward tear assay with superior sensitivity is still under development in tear collection and analysis. Here we report a plasmonic Schirmer strip for on-demand, rapid, and simple identification of biomarkers in human tears. The diagnostic strip features gold nanoislands directly and evenly formed on the top surface of cellulose fibers, which maintain a hygroscopic nature for an efficient collection of tear production as well as provide plasmonic enhancement in SERS signals for identification of tear molecules. The uric acid in human tears was quantitatively detected at physiological levels (25-150 μM) by using SERS. The experimental results also clearly reveal a strong linear correlation between uric acid level in both human tears and blood for gouty arthritis diagnosis. This functional paper strip enables noninvasive diagnosis of disease-related biomarkers and healthcare monitoring using human tears.

We demonstrate the rheological percolation of carbon nanotubes (CNTs) in microstructured polymer matrices. Polymer/CNT composites are fabricated from polycarbonates with different molecular weights to diversify the microstructures, which vary with the polymer radius of gyration and entanglements. We propose a model for the dispersion of CNTs in polymer matrices, which explains the electrical and rheological properties. The percolation theory represented by a power–law relation cannot account for the rheological percolation of CNTs in this work. Therefore, we investigate the crossover points to provide a quantitative indication of the rheological percolation threshold of nanofillers in polymer matrices. For the first time, the rheological percolation threshold is determined experimentally with this definition. The effects of molecular weight and shear viscosity of the medium on the percolation of CNTs are demonstrated separately.

Mining smartness from vision organs found in nature becomes of much interest in optical applications such as imaging, display, or lighting. Unlike conventional bulk optics, miscellaneous hierarchical structures at micro- or nanoscale deliver highly efficient light management with a small form factor. For example, natural species have evolved their eyes to obtain all necessary visual information from surrounding environment. Natural imaging schemes can be chiefly classified by three different types of pinholes, camera, and compound eyes. Pinhole eyes found in clam are sensitive enough to allow the animals to protect themselves from dangerous environment but not so sensitive to collect all visual inputs. Unlike other types, the pinhole eye as one of natural eyes with the simplest and thinnest optical configurations is well known for infinite depth-of-field, i.e., no blurred imaging depending on object distance and thus these unique features have been implemented on early-stage simple camera imaging systems. Besides, advanced pinhole eyes are also found in viper snakes of Crotalinae and some python of Boidae, which combine both pinhole eye and ordinary camera eye in order to confer infrared (IR) as well as visible imaging for warm-blooded preys. Compound eyes found in arthropods exhibit many intriguing features for wide field-of-view (FOV), fast motion detection, polarization sensing, color imaging, or high-resolution imaging with compact optical configuration unlike other types. They comprise arrays of integrated optical units called ommatidia. The individual component consists of a facet lens, a crystalline cone, a light-guiding rhabdom, and photoreceptor cells. Furthermore, nature exhibits ten different optical schemes of compound eyes, which have some attractive figures-of-merits for sustainable life style in visual acuity, photon collection efficiency, and polarization or spectral sensitivity. Such biological inspiration recently and actively provides new opportunities for improving optical capability of conventional imaging systems by incorporating nano- and microfabrication methods and furthermore it delivers technical solutions for miniaturized optical systems in medical, industrial, and military fields. In this chapter, we will review engineering approach inspired from diverse biological organs, which can be utilized for miniaturized optical systems in diverse optical applications.

High-throughput small-molecule assays play essential roles in biomedical diagnosis, drug discovery, environmental analysis, and physiological function research. Nanoplasmonics holds a great potential for the label-free detection of small molecules at extremely low concentrations. Here, we report the development of nanoplasmonic paper (NP-paper) for the rapid separation and ultrasensitive detection of mixed small molecules. NP-paper employs nanogap-rich silver nanoislands on cellulose fibers, which were simply fabricated at the wafer level by using low-temperature solid-state dewetting of a thin silver film. The nanoplasmonic detection allows for the scalable quantification and identification of small molecules over broad concentration ranges. Moreover, the combination of chromatographic separation and nanoplasmonic detection allows both the highly sensitive fluorescence detection of mixed small molecules at the attogram level and the label-free detection at the sub-nanogram level based on surface-enhanced Raman scattering. This novel material provides a new diagnostic platform for the high-throughput, low-cost, and label-free screening of mixed small molecules as an alternative to conventional paper chromatography.

This work presents a simple method for a nanofabrication of antireflective structures (AR) over the surface of polymer microlens arrays by incorporating a metal annealed mask and isotropic etching. The reflection of AR microlens is 83% lower than that of conventional microlens.

A microfabricated compound eye lens, compatible to a natural compound eye shows a spherical arrangement of integrated optical units called artificial ommatidia. Each consists of a self-aligned microlens and waveguide. The increase of the waveguide length is an indispensible prerequisite for obtaining high resolution images through an artificial compound eye for wide field-of-view imaging as well as fast motion detection. This work presents an effective method for increasing the waveguide length of artificial ommatidium using a laser inducec self-writing process in a photosensitive polymer resin. The experimental results show the uniform formation of waveguides and the increment of waveguide length over 500µm.

Two optical schemes inspired by an insect are implemented to novel optical devices for wide field-of-view imaging and wide angular illumination in miniaturized optical systems, using polymer based microfabrication techniques.

A direct-type LED based back-light-unit (BLU) in LCD displays requires wide angle illumination with high uniformity. As a single lens surface, a micropatterned complex optical surface can provide wide angle LED illumination angle over 150deg by designing the micropattern arrays on the hemispherical surface.

This work reports a novel method for fabricating monolithic polymer microlens arrays with antireflective nanostructures (AR-MLAs) at wafer level. The antireflective nanostructures (ARS) were fabricated by etching the curved surface of polymer microlens with a metal annealed nanoisland mask. The effective refractive index of ARS was controlled with the etch profile of nanostructures to reduce the mismatch in refractive indices at air-lens interface. The reflectance of AR-MLAs decreases below 4% from 490 nm to 630 nm in wavelength. The lens transmission significantly increases by 67% across the visible spectrum by minimizing the reflection and absorption, compared to that of MLAs without ARS.

A microfabricated compound eye, comparable to a natural compound eye shows a spherical arrangement of integrated optical units called artificial ommatidia. Each consists of a self-aligned microlens and waveguide. The increase of waveguide length is imperative to obtain high resolution images through an artificial compound eye for wide field-of - view imaging as well as fast motion detection. This work presents an effective method for increasing the waveguide length of artificial ommatidium using a laser induced self-writing process in a photosensitive polymer resin. The numerical and experimental results show the uniform formation of waveguides and the increment of waveguide length over 850 microm.