Jin Wook Park

Polypyrrole Nanotube Embedded Reduced Graphene Oxide Transducer for Field-Effect Transistor-Type H2O2 Biosensor

We report a rapid-response and high-sensitivity sensor with specificity toward H2O2 based on a liquid-ion-gated field-effect transistor (FET) using graphene-polypyrrole (PPy) nanotube (NT) composites as the conductive channel. The rGO, PPy, NTs, and nanocomposite materials were characterized using Raman spectroscopy, Fourier transform-infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). On the basis of these results, a well-organized structure is successfully prepared owing to the specific interactions between the PPy NTs and the rGO sheet. Reliable electrical contacts were developed between the rGO/PPy NTs and the microelectrodes, which remained stable when exposed to the liquid-phase analyte. Liquid-ion-gated FETs composed of these graphene nanocomposites exhibited hole-transport behavior with conductivities higher than those of rGO sheets or PPy NTs. This implies an interaction between the PPy NTs and the rGO layers, which is explained in terms of the PPy NTs forming a bridge between the rGO layers. The FET sensor provided a rapid response in real time and high sensitivity toward H2O2 with a limit of detection of 100 pM. The FET-type biosensing geometry was also highly reproducible and stable in air. Furthermore, the liquid-gated FET-type sensor exhibited specificity toward H2O2 in a mixed solution containing compounds found in biological fluids.

An Ultrasensitive, Selective, Multiplexed Superbioelectronic Nose That Mimics the Human Sense of Smell

Human sensory-mimicking systems, such as electronic brains, tongues, skin, and ears, have been promoted for use in improving social welfare. However, no significant achievements have been made in mimicking the human nose due to the complexity of olfactory sensory neurons. Combinational coding of human olfactory receptors (hORs) is essential for odorant discrimination in mixtures, and the development of hOR-combined multiplexed systems has progressed slowly. Here, we report the first demonstration of an artificial multiplexed superbioelectronic nose (MSB-nose) that mimics the human olfactory sensory system, leading to high-performance odorant discriminatory ability in mixtures. Specifically, portable MSB-noses were constructed using highly uniform graphene micropatterns (GMs) that were conjugated with two different hORs, which were employed as transducers in a liquid-ion gated field-effect transistor (FET). Field-induced signals from the MSB-nose were monitored and provided high sensitivity and selectivity toward target odorants (minimum detectable level: 0.1 fM). More importantly, the potential of the MSB-nose as a tool to encode hOR combinations was demonstrated using principal component analysis.

Hierarchical core/shell Janus-type α-Fe2O3/PEDOT nanoparticles for high performance flexible energy storage devices

A new class of hierarchical α-Fe2O3/poly(3,4-ethylenedioxythiophene) (PEDOT) core/shell Janus-type hybrid nanoparticles (HNPs) was successfully synthesized using sonochemical, liquid–liquid diffusion-assisted crystallization, and vapor deposition polymerization methods. The synthesized α-Fe2O3/PEDOT HNPs exhibited several unique properties, including a large surface area, high conductivity, excellent electrochemical properties, and high chemical stability. In addition, the α-Fe2O3/PEDOT HNPs reduced the dynamic resistance of electrolyte ions, and enabled high charge–discharge rates and stable expansion of the cell voltage up to 2.0 V, thereby enabling high-performance supercapacitance. These results were attributed to synergetic effects between iron oxide (core structure with a negative working potential window) and PEDOT (shell structure with a positive working potential window), resulting in performance enhancements of specific capacitance (252.8 F g−1) and energy (136.3 W h kg−1) and power densities (10 526 W kg−1). The specific capacitance exhibited 92% retention after 1000 cycles. Additionally, a flexible supercapacitor based on the α-Fe2O3/PEDOT HNPs was successfully demonstrated using a hydrogel electrolyte. The fabricated all-solid-state symmetrical supercapacitor produced superior electrochemical and mechanical performance, even after several bending motions.

Duplex Bioelectronic Tongue for Sensing Umami and Sweet Tastes Based on Human Taste Receptor Nanovesicles

For several decades, significant efforts have been made in developing artificial taste sensors to recognize the five basic tastes. So far, the well-established taste sensor is an E-tongue, which is constructed with polymer and lipid membranes. However, the previous artificial taste sensors have limitations in various food, beverage, and cosmetic industries because of their failure to mimic human taste reception. There are many interactions between tastants. Therefore, detecting the interactions in a multiplexing system is required. Herein, we developed a duplex bioelectronic tongue (DBT) based on graphene field-effect transistors that were functionalized with heterodimeric human umami taste and sweet taste receptor nanovesicles. Two types of nanovesicles, which have human T1R1/T1R3 for the umami taste and human T1R2/T1R3 for the sweet taste on their membranes, immobilized on micropatterned graphene surfaces were used for the simultaneous detection of the umami and sweet tastants. The DBT platform led to highly sensitive and selective recognition of target tastants at low concentrations (ca. 100 nM). Moreover, our DBT was able to detect the enhancing effect of taste enhancers as in a human taste sensory system. This technique can be a useful tool for the detection of tastes instead of sensory evaluation and development of new artificial tastants in the food and beverage industry.

One-pot synthesis of multidimensional conducting polymer nanotubes for superior performance field-effect transistor-type carcinoembryonic antigen biosensors

Carcinoembryonic antigen (CEA), a glycoprotein, is a crucially important tumor marker due to its relation to carcinomas. An abnormal level of CEA in the serum is connected to a diagnosis of cancer. In this work, highly sensitive and selective field-effect transistor (FET) biosensors were fabricated to detect CEA, using aptamer-functionalized multidimensional conducting-polymer (3-carboxylate polypyrrole) nanotubes (Apt–C-PPy MNTs). The multidimensional system, C-PPy MNTs, is firstly produced by a solution based temperature controlled self-degradation method. The C-PPy MNTs are integrated with the CEA-binding aptamer immobilized on an interdigitated array electrode substrate by covalent bonding with amide groups (–CONH) to produce a FET-type biosensor transducer. The resulting C-PPy MNT-based FET sensors exhibit a rapid response in real time (<1 s) and ultrasensitivity toward CEA with a limit of detection of 1 fg mL−1. This limit of detection is 2–3 orders of magnitude more sensitive than previous reports. The liquid-gated FET-type sensor showed specificity toward CEA in a mixed solution containing compounds found in similar proteins and biological signals. Additionally, a superior lifetime is demonstrated for the FET sensor, owing to the covalent bonding involved in the immobilization processes.

Size-controllable ultrathin carboxylated polypyrrole nanotube transducer for extremely sensitive 17β-estradiol FET-type biosensors

17β-Estradiol is known as a steroid hormone in the human body but it is also known as a disruptor that can cause disequilibrium and dysfunction of the human immune system. Recently, there has been much interest in developing biosensors to detect low concentrations of 17β-estradiol. In this work, size-controllable aptamer conjugated ultrathin carboxylated polypyrrole nanotubes (A-UCPPyNTs) were fabricated as transducers in 17β-estradiol field-effect transistor (FET)-type biosensors. They were manufactured via a self-degradation method under several different conditions to control the diameter of the nanotubes. For targeting 17β-estradiol, the binding aptamers were immobilized through covalent bonding on its surface. The resulting A-UCPNT FET-type biosensor demonstrated p-type behavior with outstanding electrical conductivity, and exhibited Ohmic contacts between the samples and electrodes. The smaller diameter (40 nm) of ultrathin carboxylated polypyrrole nanotubes (UCPPyNTs) contributed to the biosensors enhanced performance by generating a larger surface area, thereby increasing the number of conjugated binding aptamers. In conclusion, the A-UCPPyNT FET-type biosensor showed extremely high sensitivity (∼1 fM) toward 17β-estradiol, approximately 103 times more sensitive than the results found in other reports. Moreover, the A-UCPPyNT FET-type biosensor showed unique selectivity to the 17β-estradiol molecule, in addition to outstanding reusability and long-term storage stability (4 weeks of duration achieved in this work). These performances concerned with reusability and stability were achieved by the formation of covalent bonding in the anchorage to the substrate electrode. Thus this study can be effectively applied in biological and environmental fields.