Nae-Eung Lee

Sungkyunkwan University | SKKU · School of Advanced Materials Science and Engineering (AMSE)

In the era of artificial intelligence (AI), there is a growing interest in replicating human sensory perception. Selective and sensitive bio‐inspired sensory receptors with synaptic plasticity have recently gained significant attention in developing energy‐efficient AI perception. Various bio‐inspired sensory receptors and their applications in AI...

Nanomaterials like graphene and transition metal dichalcogenides are being explored for developing artificial photosensory synapses with low‐power optical plasticity and high retention time for practical nervous system implementation. However, few studies are conducted on Tellurium (Te)‐based nanomaterials due to their direct and small bandgaps. Th...

The development of wearable electronics with stretchable components that can conform seamlessly to human tissues and eventually disappear from the environment when disposed is of increasing interest. The challenge is to create materials that are pliable, tough, stretchable, biocompatible, and disintegrable. Biodegradable materials are promising for...

To create artificial visual perception systems, artificial retina structures that can imitate the behavior of the biological retina in human vision are of great interest. However, these devices have limited abilities to emulate the structure and working principles of human retinas and the fiber‐shaped structure of optic nerves. Here, a bio‐inspired...

Development of artificial mechanoreceptors capable of sensing and pre‐processing external mechanical stimuli is a crucial step toward constructing neuromorphic perception systems that can learn and store information. Here, bio‐inspired artificial fast‐adaptive (FA) and slow‐adaptive (SA) mechanoreceptors with synapse‐like functions are demonstrated...

Existing affinity-based fluorescence biosensing systems for monitoring of biomarkers often utilize a fixed solid substrate immobilized with capture probes limiting their use in continuous or intermittent biomarker detection. Furthermore, there have been challenges of integrating fluorescence biosensors with a microfluidic chip and low-cost fluoresc...

Hydrogel-based electrolytes for flexible solid-state supercapacitors (SSCs) have received significant attention due to their mechanical robustness and stable electrochemical performance over a wide temperature range. However, achieving flame retardancy in such SSCs at subzero temperatures to increase their practical utility remains challenging. Fur...

The human olfactory system comprises olfactory receptor neurons, projection neurons, and interneurons that perform remarkably sophisticated functions, including sensing, filtration, memorization, and forgetting of chemical stimuli for perception. Developing an artificial olfactory system that can mimic these functions has proved to be challenging....

Polydimethylsiloxane (PDMS) has been widely used for the rapid prototyping of microfluidic devices for biosensor cartridges. However, using PDMS to prototype capillary-driven microfluidic devices is often limited by the difficulty of maintaining the surface energy of surface-treated PDMS for an extended period in addition to the degradation of the...

Research on transient wearable electronics with stretchable components is of increasing interest because of their abilities to conform seamlessly to human tissues and, more interestingly, disappear from the environment when disposed. To wear them comfortably, their component materials must be pliable, tough, stretchable, biocompatible, and disinteg...

Accurate, onsite detection of pathogenic bacteria from food matrices is required to rapidly respond to pathogen outbreaks. However, accurately detecting whole-cell bacteria in large sample volumes without an enrichment step remains a challenge. Therefore, bacterial samples must be concentrated, identified, and quantified. We developed a tunable mag...

Wearable sensor patches for continuous or intermittent monitoring of biomolecules from body fluids are highly desired as a stretchable integrated platform conformable and attachable to the human body. However, realizing such integrated sensor patches is very challenging because of the difficulty of achieving full stretchability, controlling transpo...

Materials with a variety of required properties, including stretchability, toughness, optical transparency, biocompatibility, processability, and recyclability are in great demand for soft electronics. Creation of such materials, however, has been hampered due to the challenges of balancing these properties. Herein, we report intrinsically stretcha...

Current hydrogel strain sensors have met assorted essential requirements of wearing comfort, mechanical toughness, and strain sensitivity. However, an increment in the toughness of a hydrogel usually leads to an increase in elastic moduli that could be unfavorable for wearing comfort. In addition, traits of biofriendly and sustainability require sy...

We fabricated semitransparent and stretchable hybrid Ag-polytetrafluoroethylene (PTFE) conductors on a polyurethane (PU) substrate for use in high-performance wearable and self-cleaning sensors. The highly conductive Ag metal and stretchable PTFE polymer matrix were cosputtered, embedding the self-formed Ag in the PTFE matrix. Depending on the cosp...

The development of stretchable broadband photodetectors for applications in wearable optoelectronics and personal healthcare still has some limitations in obtaining materials, designing device structures, and developing reliable fabrication processes. Here, stretchable broadband plasmonic photodetectors (SBPPDs) by fabricating plasmonic photodetect...

Biodegradable stretchable electronics have demonstrated great potential for future applications in stretchable electronics and can be resorbed, dissolved, and disintegrated in the environment. Most biodegradable electronic devices have used flexible biodegradable materials, which have limited conformality in wearable and implantable devices. Here,...

Stretchable and highly sensitive gas sensors are currently receiving great attention due to their pertinence in wearable technology for detecting environmental conditions as well as for human safety. Herein, room-temperature operable, stretchable, highly selective, and stable gas sensors were engineered by decorating networked reduced graphene oxid...

Chemiresistive gas sensors with high-performance, stretchability, and low power consumption are of great interest to developers of wearable applications but sensing materials compatible with mechanical deformability and operability that do not require thermal heating have proven hard to find. Here, a high-performance and stretchable chemiresistive...

In the era of the Internet of Things, wearable technologies are expected to become an indispensable part of daily life. In recent times, highly sensitive, flexible, and stretchable electronic gas sensors are gaining tremendous interest due to their applicability in wearable electronics applications. The construction of wearable gas sensors are revi...

The on-body immunodetection of biomarkers in sweat would significantly augment the potential of wearable body-interfaced biosensors for self-testing but has been limited due to the difficulty of integrating liquid handling and immunobiosensing devices in a wearable platform. Herein, a stretchable microfluidic immunobiosensor (SMIB) patch with hollo...

Mimicking the skin's non‐linear self‐limiting mechanical characteristics is of great interest. Skin is soft at low strain but becomes stiff at high strain and thereby can protect human tissues and organs from high mechanical loads. Herein, the design of a skin‐inspired substrate is reported based on a spaghetti‐like multi‐nanofiber network (SMNN) o...

Challenges associated with local stress concentration on layers in stretchable devices under mechanical deformation by bodily motions, which causes strain‐induced signal interference and generates cracks, constitute one of the remaining issues for realization of skin‐attachable stretchable electronics. Herein, a new structural engineering approach...

Imbuing bio-inspired sensory devices with intelligent functions of human sensory organs has been limited by challenges in emulating the preprocessing abilities of sensory organs such as reception, filtering, adaptation, and sensory memory at the device level itself. Merkel cells, which is a part of tactile sensory organs, form synapse-like connecti...

Conformable, wearable biosensor-integrated systems are a promising approach to non-invasive and quantitative on-body detection of biomarkers in body fluids. However, realizing such a system has been slowed by the difficulty of fabricating a soft affinity-based biosensor patch capable of precise on-body fluid handling with minimal wearer interventio...

Stretchable organic light‐emitting diodes (OLEDs) are attractive for applications in wearable displays, conformal optical biomedical devices, and healthcare monitoring. Although many stretchable OLEDs have been demonstrated, their fabrication process still faces some limitations, including fabrication complexity, high cost and low yield, as well as...

Rapid, sensitive and accurate point-of-care-testing (POCT) of bacterial load from a variety of samples can help prevent human infections caused by pathogenic bacteria and mitigate their spreading. However, there is an unmet demand for a POCT device that can detect extremely low concentrations of bacteria in raw samples. Herein, we introduce the 'co...

A transparent stretchable (TS) capacitive sensor, which can detect pressure (force) and touch inputs distinguishably was fabricated by forming with a TS dielectric layer sandwiched between the upper piezoresistive electrode of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)–ionic liquid composite enabling to distinguish touch and pressure s...

Electronic skin (e-skin) is designed to mimic the comprehensive nature of human skin. Various advances in e-skin continue to drive the development of the multimodal tactile sensor technology on flexible and stretchable platforms. e-skin incorporates pressure, temperature, texture, photographic imaging, and other sensors as well as data acquisition...

Biosensor systems for wearable continuous monitoring are desired to be developed into conformal patch platforms. However, developing such patches is very challenging owing to the difficulty of imparting materials and components with both high stretchability and high performance. Herein we report a fully stretchable microfluidics-integrated glucose...

A key challenge for realizing mobile device-based on-the-spot environmental biodetection is that a biosensor integrated with fluid handling sensor cartridge must have acceptable accuracy comparable to that of conventional standard analytical methods. Furthermore, the user interface must be easy to operate, technologically plausible, and concise. He...

Creating stretchable and transparent conductive electrodes for stretchable and transparent electronics is very challenging due to difficulties in obtaining adequate optical and mechanical properties simultaneously. Here, we designed a stretchable and transparent nanofiber-networked electrode (STNNE) based on a networked structure of electrospun str...

Human skin is highly stretchable at low strain but becomes self-limiting when deformed at large strain due to stiffening caused by alignment of a network of stiff collagen nanofibers inside the tissue beneath the epidermis. To imitate this mechanical behavior and the sensory function of human skin, we fabricated a skin-like substrate with highly st...

Fiber‐based sensors integrated on textiles or clothing systems are required for the next generation of wearable electronic platforms. Fiber‐based physical sensors are developed, but the development of fiber‐based temperature sensors is still limited. Herein, a new approach to develop wearable temperature sensors that use freestanding single reducti...

A critical unmet need in the diagnosis of bacterial infections, which remain a major cause of human morbidity and mortality, is the detection of scarce bacterial pathogens in a variety of samples in a rapid and quantitative manner. Herein, we demonstrate smartphone-based detection of Staphylococcus aureus in a culture-free, rapid, quantitative mann...

Omnidirectionally stretchable photodetectors are limited by difficulties in designing material and fabrication processes that enable stretchability in multiaxial directions. Here, we propose a new approach involving an organic-inorganic p-n heterojunction photodetector comprised of free-standing ZnO nanorods (NRs) grown on a poly(3,4-ethylenedioxyt...

Stretchable piezoelectric nanogenerators (SPENGs) for human kinematics energy harvesting have limited use due to the low stretchability or mechanical robustness and the difficulty of structural design for omnidirectional stretchability. This study reports an efficient, omnidirectionally stretchable, and robust SPENG based on a stretchable graphite...

A Schottky diode based on a heterojunction of three-dimensional (3D) nanohybrid materials, formed by hybridizing reduced graphene oxide (RGO) with epitaxial vertical zinc oxide nanorods (ZnO NRs), and Al0.27GaN0.73(~25 nm)/GaN is presented as a new class of high-performance chemical sensor. The RGO nanosheet layer coated on the ZnO NRs enables the...

Our cost-effective approach for hybridizing methylammonium lead iodide and PbS nanoparticles at low temperature (≤100 °C) for photovoltaic devices is introduced. As employed into a perovskite based solar cell platform, effects of PbS on the device performance were investigated. Through experimental observations under simulated air-mass 1.5G illumin...

Stretchable and transparent touch sensors are essential input devices for future stretchable transparent electronics. Capacitive touch sensors with a simple structure of only two electrodes and one dielectric are an established technology in current rigid electronics. However, the development of stretchable and transparent capacitive touch sensors...

Abstracts Stretchable chemical sensors for detection of gases/vapours are of great interest for wearable applications in healthcare and environmental safety. Here, we demonstrate a simple but effective approach based on layering electro-spun elastomeric polyurethane (PU) nanofibres to produce stretchable chemically responsive nanohybrids of PU nano...

Abstract The accuracy of a bioassay based on smartphone-integrated fluorescent biosensors has been limited due to the occurrence of false signals from non-specific reactions as well as a high background and low signal-to-noise ratios for complementary metal oxide semiconductor image sensors. To overcome this problem, we demonstrate dual-wavelength...

Pressure sensing is one of the key functions for smart electronics. Considerably more effort is required to achieve the fabrication of pressure sensors that can imitate and overcome the sophisticated pressure sensing characteristics in nature and industry, especially in the innovation of materials and structures. Almost all of the pressure sensors...

Stretchable and conformal humidity sensors that can be attached to the human body for continuously monitoring the humidity of the environment around the human body or the moisture level of the human skin can play an important role in electronic skin and personal healthcare applications. However, most stretchable humidity sensors are based on the ge...

Organic gate dielectrics in thin film transistors (TFTs) for flexible display have advantages of high flexibility yet have the disadvantage of low dielectric constant (low-k). To supplement low-k characteristics of organic gate dielectrics, an organic/inorganic nanocomposite insulator loaded with high-k inorganic oxide nanoparticles (NPs) has been...

Stretchable electronic devices with intrinsically stretchable components have significant inherent advantages, including simple fabrication processes, a high integrity of the stacked layers, and low cost in comparison with stretchable electronic devices based on non-stretchable components. The research in this field has focused on developing new in...

High performance flexible thin film transistors (TFTs) for backplane technology in flexible displays require mechanically flexible, a high-dielectric constant (high-k), thermal stability and low-leakage gate dielectrics. Although insulating nanocomposite (NC) materials with high-k nanoparticles (NPs) dispersed in a low-k polymer matrix have been de...

Practical usage of piezoelectric nanogenerators (PENGs) under heavy loading environments for high power generation, such as smart shoes, has been limited due to the low mechanical endurance of many piezoelectric materials. Durability and performance under harsh environments are a stumbling block for the practical application of PENGs. Synthesis of...

Pressure sensing is one of the key function of smart electronics. The fabrication of pressure sensors that may imitate and overcome the sophisticated pressure sensing characteristics in nature and industry needs more much efforts, especially, in the innovation from new materials as well as structures. Almost reported pressure sensors have a high se...

In order to study the effects of bias pulsing on the etching characteristics of a silicon dioxide (SiO2) layer using multi-level hard mask (MLHM) structures of ArF photoresist/bottom anti-reflected coating/SiO2/amorphous carbon layer (ACL)/SiO2, the effects of bias pulsing conditions on the etch characteristics of a SiO2 layer with an ACL mask patt...

Flexible chemical sensors utilizing chemically sensitive nanomaterials are of great interest for wearable sensing applications. However, obtaining high performance flexible chemical sensors with high sensitivity, fast response, transparency, stability, and workability at ambient conditions is still challenging. Herein, a newly designed flexible and...

On page 3069, N.-E. Lee and co-workers propose a mogul-patterned stretchable substrate with bumps and valleys, which is inspired from mogul skiing, as a versatile platform for stretchable electronics with improved integrity, stability, and multi-directional stretchability compared to those with a wavy structure. On the rubber-like substrate with mo...

A new type of flexible ME organic field-effect transistor (ME-OFET) in which a magnetic-responsive stacked 2–2 horizontal heterostructure of alternating layers of a piezoelectric polymer and magnetostrictive was employed as the gate dielectric layer.

A new type of flexible ME organic field-effect transistor (ME-OFET) in which a magnetic-responsive stacked 2–2 horizontal heterostructure of alternating layers of a piezoelectric polymer and magnetostrictive was employed as the gate dielectric layer.

A new type of flexible ME organic field-effect transistor (ME-OFET) in which a magnetic-responsive stacked 2–2 horizontal heterostructure of alternating layers of a piezoelectric polymer and magnetostrictive was employed as the gate dielectric layer.

A new type of flexible ME organic field-effect transistor (ME-OFET) in which a magnetic-responsive stacked 2–2 horizontal heterostructure of alternating layers of a piezoelectric polymer and magnetostrictive was employed as the gate dielectric layer.

A new type of flexible ME organic field-effect transistor (ME-OFET) in which a magnetic-responsive stacked 2–2 horizontal heterostructure of alternating layers of a piezoelectric polymer and magnetostrictive was employed as the gate dielectric layer.

Flexible and stretchable physical sensors that can measure and quantify electrical signals generated by human activities are attracting a great deal of attention as they have unique characteristics, such as ultrathinness, low modulus, light weight, high flexibility, and stretchability. These flexible and stretchable physical sensors conformally att...

A transparent stretchable (TS) gated sensor array with high optical transparency, conformality, and high stretchability of up to 70% is demonstrated. The TS-gated sensor array has high responsivity to temperature changes in objects and human skin. This unprecedented TS-gated sensor array, as well as the integrated platform of the TS-gated sensor wi...

Although real-time label-free fluorescent aptasensors based on nanomaterials are increasingly recognized as a useful strategy for the detection of target biomolecules with high fidelity, the lack of an imaging-based quantitative measurement platform limits their implementation with biological samples. Here we introduce an ensemble strategy for a re...

Monitoring of human activities can provide clinically relevant information pertaining to disease diagnostics, preventive medicine, care for patients with chronic diseases, rehabilitation, and prosthetics. The recognition of strains on human skin, induced by subtle movements of muscles in the internal organs, such as the oesophagus and trachea, and...

Growth of ZnO nanorods (NRs) on single-layer graphene (SLG) is of great interest for various applications including energy harvesting devices, sensors, and transistors. SLG synthesized by means of chemical vapor deposition was transferred onto the desired substrate by using a thin Au layer as a supporting layer to keep the SLG surface clean, and Zn...

A simple, scalable, clean and fast transfer process of graphene (Gr) grown on Cu by chemical vapor deposition onto an arbitrary substrate is desirable for practical applications of Gr. The conventional transfer method using poly(methyl methacrylate) (PMMA) as a supporting layer leaves residues on the Gr surface after transfer and takes a long time...

Organic gate dielectric layers in thin film transistors (TFTs) for the backplane in flexible displays have the advantage of superior flexibility but several disadvantages including low thermal and chemical resistivities, a low dielectric constant, and a high leakage current at a small thickness. To overcome the issues of flexible organic gate diele...

Mechanically adaptive electronic skins (e-skins) emulate tactition and thermoception by cutaneous mechanoreceptors and thermoreceptors in human skin, respectively. When exposed to multiple stimuli including mechanical and thermal stimuli, discerning and quantifying precise sensing signals from sensors embedded in e-skins are critical. In addition,...

For realization of wearable and smart electronics, developments of physical, chemical and biological sensors and sensor-integrated platforms are essentially required. For various applications such as smart health, cars, buildings or environments in the future, highly sensitive and reliable sensors with new functionalities such as flexibility, stret...

Flexible magnetoelectric (ME) materials have been studied for new applications such as memory, energy harvesters, and magnetic field sensors. Herein, with the widely studied and progressive advantages of ME phenomena in the multiferroic field, we demonstrate a new approach for utilizing flexible ME materials as gate dielectric layers in ME organic...

The realization of a high-throughput biosensor platform with ultrarapid detection of biomolecular interactions and an ultralow limit of detection in the femtomolar (fM) range or below has been retarded due to sluggish binding kinetics caused by the scarcity of probe molecules on the nanostructures and/or limited mass transport. Here, as a new metho...

A newly designed 3D core-shell microcapsule structure composed of a cell-containing liquid core and an alginate hydrogel shell is fabricated using a coaxial dual-nozzle electrospinning system. Spherical alginate microcapsules are successfully generated with a core-shell structure and less than 300 μm in average diameter using this system. The thick...

A field-effect transistor (FET) with two-dimensional (2D) few-layer MoS2 as a sensing-channel material was investigated for label-free electrical detection of the hybridization of deoxyribonucleic acid (DNA) molecules. The high-quality MoS2-channel pattern was selectively formedthrough the chemical reaction of the Mo layer with H2S gas. The MoS2 FE...

Flexible UV photodetector based on ZnO nanorods (NRs) as nanostructure sensing materials integrated into a graphene (Gr) field-effect transistor (FET) platform is investigated with high-performance. Based on the negative shift of the Dirac point (VDirac) in the transfer characteristics of a phototransistor, high photovoltage responsivity (RV) is ca...

Unlabelled: Interactivity between humans and smart systems, including wearable, body-attachable, or implantable platforms, can be enhanced by realization of multifunctional human-machine interfaces, where a variety of sensors collect information about the surrounding environment, intentions, or physiological conditions of the human to which they a...

Photodetectors using optically responsive graphene (Gr) or reduced graphene oxide (R-GO) on rigid substrates have showed promising results for detection of broad band light including infrared (IR). However, there have been only a few reports on Gr or R-GO photodetectors with new functionalities such as optical transparency and/or flexibility. Herei...

Ultraviolet (UV) photodetectors based on ZnO nanostructure/graphene (Gr) hybrid-channel field-effect transistors (FETs) are investigated under illumination at various incident photon intensities and wavelengths. The time-dependent behaviors of hybrid-channel FETs reveal a high sensitivity and selectivity toward the near-UV region at the wavelength...

C3F6 and C3F6 gases were investigated as replacement gases for SF6 used in display industry due to their low global warming potential and short lifetime. In the C3F6/O2 and C3F6/O2 capacitively coupled plasmas, Si3N4 etch conditions were varied by controlling process parameters. The global warming effects were quantified as million metric ton carbo...

The sensing performance of chemical sensors can be achieved not only by modification or hybridization of sensing materials but also through new design in device geometry. The performance of a chemical sensing device can be enhenced from a simple three-dimensional (3D) chemiresistor-based gas sensor platform with an increased surface area by forming...

Pulse-biased plasma etching of various dielectric layers is investigated for patterning nano-scale, multi-level resist (MLR) structures composed of multiple layers via dual-frequency, capacitivelycoupled plasmas (CCPs). We compare the effects of pulse and continuous-wave (CW) biasing on the etch characteristics of a Si3N4 layer in CF4/CH2F2/O2/Aret...

Piezoelectric coupling phenomena in a graphene field-effect transistor (GFET) with a nano-hybrid channel of chemical-vapor-deposited Gr (CVD Gr) and vertically aligned ZnO nanorods (NRs) under mechanical pressurization were investigated. Transfer characteristics of the hybrid channel GFET clearly indicated that the piezoelectric effect of ZnO NRs u...

To develop physically flexible electronics, high performance and mechanical stability of component materials and devices are required. For a flexible display, a backplane with flexible thin-film transistors (TFTs) must be developed. Gate insulating materials with excellent electrical and mechanical properties are highly important to the development...

The two-dimensional nanocarbon material graphene (Gr) has been extensively studied due to its many potential biomedical applications including regenerative medicine, drug delivery, bioimaging, and biosensing. The effects of nitrogen-functionalisation on chemically driven Gr (CDG) cellular responses were studied by investigating the generation of re...

Graphene (G) nanoflake toxicity was analyzed using cell-based electrochemical impedance biosensing with interdigitated indium tin oxide (ITO) electrodes installed in a custom-built mini- incubator positioned on an inverted optical microscope. Sensing with electrochemical measurements from interdigitated ITO electrodes was highly linear (R(2) = 0.93...

We investigated flexible amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) on a polyimide (PI) substrate by using organic/inorganic hybrid gate dielectrics of poly-4vinyl phenol (PVP) and ultrathin Al2O3. IGZO TFTs were fabricated with hybrid PVP/Al2O3 gate dielectrics having Al2O3 layers of different nanoscale thicknesses, which were deposit...