Jinsik Kim

Enhancing surface functionality of reduced graphene oxide biosensors by oxygen plasma treatment for Alzheimer's disease diagnosis

We performed oxygen plasma treatment on reduced graphene oxide (rGO) to improve its surface reactivity with respect to biomolecular interactions. Oxygen-plasma-treated rGO surfaces were employed as reactive interfaces for the detection of amyloid-beta (Aβ) peptides, the pathological hallmarks of Alzheimers disease (AD), as the target analytes. By measuring the changes in electrical characteristics and confirmation through topographic analysis, the oxygen-plasma-treated rGO sensors had enhanced surface functionality for better antibody immobilization and sensing performance, with a 3.33-fold steeper slope for the electrical responses versus analyte concentration curve (logarithmic scale) compared to the untreated. The elicited biomolecular reactivity of the rGO surfaces with the oxygen plasma treatment remained at 46-51% of the initial value even after aging for 6h in ambient conditions. This phenomenon was also confirmed by pretreating the rGO surfaces with a blocking agent and subsequently subjecting them to antibody immobilization. Finally, the feasibility of the oxygen-plasma-treated rGO sensors as a diagnostic tool was evaluated with clinical samples of neural-derived exosomal Aβ peptides extracted from apparent AD patients and normal controls (NC). In contrast to the untreated sensors (p=0.0460), the oxygen-plasma-treated rGO sensors showed a significant p-value in the identification of clinical samples of AD and NC subjects (p<0.001). These results suggest that oxygen plasma treatment improves sensor performance without complicated fabrication procedures and should aid in the development of novel diagnostic tools based on carbon nanomaterials.

Piezoelectric layer embedded-microdiaphragm sensors for the determination of blood viscosity and density

We introduce a lead zirconate titanate [PZT; Pb(Zr0.52Ti0.48)O3] microdiaphragm resonating sensor packaged in a polydimethylsiloxane chip. The proposed sensor can measure the density and viscosity of a liquid that is within the density and viscosity regime of blood (1.060 × 103 kg/m3, 3–4 cP). To verify the basic characteristics of the sensor, viscous solutions were prepared from glycerol and deionized water with a density in the range from 0.998 to 1.263 × 103 kg/m3 and a viscosity in the range from 1 to 1414 cP. We measured the frequency responses of the sensor before and after injecting the viscosity- and density-controlled liquid under the bottom of the microdiaphragm. The resonant frequencies in the (1,1) and (2,2) modes decreased linearly as a function of the liquid density in the range from 0.998 to 1.146 × 103 kg/m3 with a sensitivity of 28.03 Hz/kg·m−3 and 81.85 Hz/kg·m−3, respectively. The full width at half maximum had a logarithmic relationship with the liquid viscosity in the viscosity range ...

Wafer-scale high-resolution patterning of reduced graphene oxide films for detection of low concentration biomarkers in plasma

Given that reduced graphene oxide (rGO)-based biosensors allow disposable and repeatable biomarker detection at the point of care, we developed a wafer-scale rGO patterning method with mass productivity, uniformity, and high resolution by conventional micro-electro-mechanical systems (MEMS) techniques. Various rGO patterns were demonstrated with dimensions ranging from 5 μm up to several hundred μm. Manufacture of these patterns was accomplished through the optimization of dry etching conditions. The axis-homogeneity and uniformity were also measured to verify the uniform patternability in 4-inch wafer with dry etching. Over 66.2% of uniform rGO patterns, which have deviation of resistance within range of ±10%, formed the entire wafer. We selected amyloid beta (Aβ) peptides in the plasma of APP/PS1 transgenic mice as a study model and measured the peptide level by resistance changes of highly uniform rGO biosensor arrays. Aβ is a pathological hallmark of Alzheimer’s disease and its plasma concentration is in the pg mL−1 range. The sensor detected the Aβ peptides with ultra-high sensitivity; the LOD was at levels as low as 100 fg mL−1. Our results provide biological evidences that this wafer-scale high-resolution patterning method can be used in rGO-based electrical diagnostic devices for detection of low-level protein biomarkers in biofluids.

Sensitivity improvement of an electrical sensor achieved by control of biomolecules based on the negative dielectrophoretic force.

Effective control of nano-scale biomolecules can enhance the sensitivity and limit of detection of an interdigitated microelectrode (IME) sensor. Manipulation of the biomolecules by dielectrophoresis (DEP), especially the negative DEP (nDEP) force, so that they are trapped between electrodes (sensing regions) was predicted to increase the binding efficiency of the antibody and target molecules, leading to a more effective reaction. To prove this concept, amyloid beta 42 (Aβ42) and prostate specific antigen (PSA) protein were respectively trapped between the sensing region owing to the nDEP force under 5V and 0.05V, which was verified with COMSOL simulation. Using the simulation value, the resistance change (ΔR/Rb) of the IME sensor from the specific antibody-antigen reaction of the two biomolecules and the change in fluorescence intensity were compared in the reference (pDEP) and nDEP conditions. The ΔR/Rb value improved by about 2-fold and 1.66-fold with nDEP compared to the reference condition with various protein concentrations, and these increases were confirmed with fluorescence imaging. Overall, nDEP enhanced the detection sensitivity for Aβ42 and PSA by 128% and 258%, respectively, and the limit of detection improved by up to 2-orders of magnitude. These results prove that DEP can improve the biosensors performance.

Active control of dielectrophoretic force at nanowire electrode for ultrahigh single nanoparticle manipulation yield

We introduce ultrahigh-yield single nanoparticle control based on active control of the dielectrophoretic (DEP) force (ACDF). Attachment and detachment are accomplished reversibly using a combination of negative and positive DEP forces. A silicon-oxide (SiO2)-surrounded gold nanowire electrode was designed for ACDF. Nanoparticle motions were analyzed to confirm inducement of the negative DEP force, which is the most important for realizing ACDF. Polystyrene nanobeads and quantum dots were used. Ultrahigh-yield single nanoparticle manipulation was achieved at every designed position using ACDF.

Ultra-sensitive detection of brain-derived neurotrophic factor (BDNF) in the brain of freely moving mice using an interdigitated microelectrode (IME) biosensor

Brain-derived neurotrophic factor (BDNF) plays a critical role in cognitive processes including learning and memory. However, it has been difficult to detect BDNF in the brains of behaving animals because of its extremely low concentration, i.e., at the sub-nanogram/mL level. Here, we developed an interdigitated microelectrode (IME) biosensor coated with an anti-BDNF an anti-BDNF antibody in a polydimethylsiloxane (PDMS)-based microfluidic channel chip. This sensor could detect BDNF from microliter volumes of liquid samples even at femtogram/mL concentrations with high selectivity over other growth factors. Using this biosensor, we examined whether BDNF is detectable from periodical collection of cerebrospinal fluid microdialysate, sampled every 10 min from the hippocampus of mice during the context-dependent fear-conditioning test. We found that the IME biosensor could detect a significant increase in BDNF levels after the memory task. This increase in BDNF levels was prevented by gene silencing of BDNF, indicating that the IME biosensor reliably detected BDNF in vivo. We propose that the IME biosensor provides a general-purpose probe for ultrasensitive detection of biomolecules with low abundance in the brains of behaving animals.

A Micro-Preconcentrator Combined Olfactory Sensing System with a Micromechanical Cantilever Sensor for Detecting 2,4-Dinitrotoluene Gas Vapor

Preventing unexpected explosive attacks and tracing explosion-related molecules require the development of highly sensitive gas-vapor detection systems. For that purpose, a micromechanical cantilever-based olfactory sensing system including a sample preconcentrator was developed to detect 2,4-dinitrotoluene (2,4-DNT), which is a well-known by-product of the explosive molecule trinitrotoluene (TNT) and exists in concentrations on the order of parts per billion in the atmosphere at room temperature. A peptide receptor (His-Pro-Asn-Phe-Ser-Lys-Tyr-Ile-Leu-His-Gln-Arg) that has high binding affinity for 2,4-DNT was immobilized on the surface of the cantilever sensors to detect 2,4-DNT vapor for highly selective detection. A micro-preconcentrator (µPC) was developed using Tenax-TA adsorbent to produce higher concentrations of 2,4-DNT molecules. The preconcentration was achieved via adsorption and thermal desorption phenomena occurring between target molecules and the adsorbent. The µPC directly integrated with a cantilever sensor and enhanced the sensitivity of the cantilever sensor as a pretreatment tool for the target vapor. The response was rapidly saturated within 5 min and sustained for more than 10 min when the concentrated vapor was introduced. By calculating preconcentration factor values, we verified that the cantilever sensor provides up to an eightfold improvement in sensing performance.

A highly sensitive plasma-based amyloid-β detection system through medium-changing and noise cancellation system for early diagnosis of the Alzheimer's disease

We developed an interdigitated microelectrode (IME) sensor system for blood-based Alzheimer’s disease (AD) diagnosis based on impedimetric detection of amyloid-β (Aβ) protein, which is a representative candidate biomarker for AD. The IME sensing device was fabricated using a surface micromachining process. For highly sensitive detection of several tens to hundreds of picogram/mL of Aβ in blood, medium change from plasma to PBS buffer was utilized with signal cancellation and amplification processing (SCAP) system. The system demonstrated approximately 100-folds higher sensitivity according to the concentrations. A robust antibody-immobilization process was used for stability during medium change. Selectivity of the reaction due to the affinity of Aβ to the antibody and the sensitivity according to the concentration of Aβ were also demonstrated. Considering these basic characteristics of the IME sensor system, the medium change was optimized in relation to the absolute value of impedance change and differentiated impedance changes for real plasma based Aβ detection. Finally, the detection of Aβ levels in transgenic and wild-type mouse plasma samples was accomplished with the designed sensor system and the medium-changing method. The results confirmed the potential of this system to discriminate between patients and healthy controls, which would enable blood-based AD diagnosis.

Study of Alzheimer’s Disease-Related Biophysical Kinetics with a Microslit-Embedded Cantilever Sensor in a Liquid Environment

A microsized slit-embedded cantilever sensor (slit cantilever) was fabricated and evaluated as a biosensing platform in a liquid environment. In order to minimize the degradation caused by viscous damping, a 300 × 100 µm2 (length × width) sized cantilever was released by a 5 µm gap-surrounding and vibrated by an internal piezoelectric-driven self-actuator. Owing to the structure, when the single side of the slit cantilever was exposed to liquid a significant quality factor (Q = 35) could be achieved. To assess the sensing performance, the slit cantilever was exploited to study the biophysical kinetics related to Aβ peptide. First, the quantification of Aβ peptide with a concentration of 10 pg/mL to 1 μg/mL was performed. The resonant responses exhibited a dynamic range from 100 pg/mL to 100 ng/mL (−56.5 to −774 ΔHz) and a dissociation constant (KD) of binding affinity was calculated as 1.75 nM. Finally, the Aβ self-aggregation associated with AD pathogenesis was monitored by adding monomeric Aβ peptides. As the concentration of added analyte increased from 100 ng/mL to 10 µg/mL, both the frequency shift values (−813 to −1804 ΔHz) and associate time constant increased. These results showed the excellent sensing performance of the slit cantilever overcoming a major drawback in liquid environments to become a promising diagnostic tool candidate.

Structural defects in LiCoO2 studied by L7i nuclear magnetic relaxation

Microscopic environments and dynamics in LiCoO2 systems were probed by L7i nuclear magnetic relaxation measurements with regard to the structural defects as revealed by x-ray diffraction and electron spin resonance measurements. Thus, the structural defects of differing degrees, associated with Li vacancies, were well accounted for in the temperature-dependent spin-lattice relaxation rate analysis, and in the structural and dynamical inhomogeneity as derived from the relaxation patterns.