Hyukjin Jung

Silver nanoislands on cellulose fibers for chromatographic separation and ultrasensitive detection of small molecules

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.

Plasmonic Schirmer Strip for Human Tear-Based Gouty Arthritis Diagnosis Using Surface-Enhanced Raman Scattering

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.

Monolithic polymer microlens arrays with antireflective nanostructures

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.

Monolithic Polymer Microlens Arrays with High Numerical Aperture and High Packing Density

This work reports a novel method for monolithic fabrication of high numerical aperture polymer microlens arrays (high-NA MLAs) with high packing density (PD) at wafer level. The close-packed high-NA MLAs were fabricated by incorporating conformal deposition of ultrathin fluorocarbon nanofilm and melting the cylindrical polymer islands. The NA and PD of hemispherical MLAs with a hexagonal arrangement increase up to 0.6 and 89%, respectively. The increase of NA enhances the lens transmission securing the beam width down to 1.1 μm. The close-packed high-NA MLAs enable high photon collection efficiency with signal-to-noise ratio greater than 50:1.

Microfabricated ommatidia using a laser induced self-writing process for high resolution artificial compound eye optical systems

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.

Planar Emulation of Natural Compound Eyes

Natural compound eyes comprise an array of integrated optical units called ommatidia whose individual component includes a facet lens, a crystalline cone, a light-guiding rhabdom, and photoreceptor cells. The unique schemes exhibit distinguished benefi ts in wide fi eld-of-view, fast motion, or polarization detection. [ 1–3 ] The compound eyes have attracted extensive research interest in photonics because the physiological features and the principles of visual information processing can provide technical solutions for cutting-edge optical systems in medical, industrial, and military fi elds. [ 4–11 ] The vision has been emulated with multiapertures on an image sensor arrays by stitching multiple sets of angular images. [ 4–8 ] The physiological structures were mimicked by spherically arranging artifi cial ommatidia on a hemispherical dome. [ 9 ] The previous works, however, still have some technical limitations in mining smartness from diverse natural compound eyes. Nature provides ten different optical schemes of compound eyes. The distinctive features include seven apposition and three superposition types. The apposition types cover simple apposition, open rhabdom apposition, neural superposition, afocal apposition, transparent apposition lightguide, transparent apposition axial gradient, and transparent apposition radial gradient types. [ 12–16 ] The superposition types can also be classifi ed into refracting, refl ecting, and parabolic types. [ 12 , 17–19 ] The individual scheme was not well researched for engineering applications even though it has some attractive fi gures-of-merit for sustainable life style in visual acuity, photon collection effi ciency, and spectral or polarization sensitivity. In particular, the cross-sectional anatomical structures of ten different types provide a clear indication to understand their functions and even to utilize the optical schemes for advanced photonic sensors. The diverse optical schemes can be predetermined on a planar substrate as illustrated in Figure 1 . A natural ommatidium can be emulated by a cylindrical microlens, a conical structure, a waveguide, and a photodetector. Like the natural one, the ommatidia of the apposition type are optically isolated so that each waveguide

Micropatterned complex optical surface for wide angle illumination

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.

Monolithic polymer microlens arrays with anti-reflective structures using a metal annealed mask

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.

Laser induced self-aligned microlens and waveguide arrays using a self-writing process in a photosensitive polymer resin

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.

Biologically inspired optical structures for wide field-of-view imaging and wide angle illumination

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.