Longitudinal Changes in Dual Decline in Memory and Gait Speed Association with Instrumental Activities of Daily Living: Findings from the National Social Life, Health, and Aging Project.

Objective: We investigated the association between dual decline (DD) (loss of memory and gait speed) and the instrumental activities of daily living (IADL) degeneration in older adults. Methods: Data were drawn from the National Social Life, Health, and Aging Project (NSHAP) reflecting changes over 5 years. This study used the NSHAP data set wave 2 (2010-2011, N = 3196) and wave 3 (2015-2016, N = 4377). Results: Data from 1640 participants were retrieved. There were 601 people with DD and 1039 people without-DD. The DD group had a 28.4% (95% CI = 1.013-1.626) greater risk of degrading in IADL than the without-DD group (odds ratio = 1.284, p < .05). Conclusion: Current research can be used when establishing intervention programs or policies that can prevent IADL degradation through simple memory training and walking activities for older adults living in the community.

An Organic/Inorganic Nanomaterial and Nanocrystal Quantum Dots-Based Multi-Level Resistive Memory Device.

A cadmium selenide/zinc sulfide (CdSe/ZnS) quantum dot (QD)-based multi-level memory device with the structure [ITO/PEDOT:PSS/QDs/ZnO/Al:Al2O3/QDs/Al] was fabricated via a spin-coating method used to deposit thin films. Two layers of QD thin films present in the device act as charge storage layers to form three distinct states. Zinc oxide (ZnO) and aluminum oxide (Al2O3) were added to prevent leakage. ZnO NPs provide orthogonality between the two QD layers, and a poly(3,4-ethylenedioxythio-phene): poly(styrenesulfonate) (PEDOT:PSS) thin film was formed for effective hole injection from the electrodes. The core/shell structure of the QDs provides the quantum well, which causes the trapping of injected charges. The resistance changes according to the charging and discharging of the QDs' trap site and, as a result, the current through the device also changes. There are two quantum wells, two current changes, and three stable states. The role of each thin film was confirmed through I-V curve analysis and the fabrication conditions of each thin film were optimized. The synthesized QDs and ZnO nanoparticles were evaluated via X-ray diffraction, transmission electron microscopy, and absorbance and photoluminescence spectroscopy. The measured write voltages of the fabricated device were at 1.8 and 2.4 V, and the erase voltages were -4.05 and -4.6 V. The on/off ratio at 0.5 V was 2.2 × 103. The proposed memory device showed retention characteristics of ≥100 h and maintained the initial write/erase voltage even after 200 iterative operations.

Air-stable and ultrasensitive solution-cast SWIR photodetectors utilizing modified core/shell colloidal quantum dots.

InGaAs-based photodetectors have been generally used for detection in the short-wave infrared (SWIR) region. However, the epitaxial process used to grow these materials is expensive; therefore, InGaAs-based photodetectors are limited to space exploration and military applications. Many researchers have expended considerable efforts to address the problem of SWIR photodetector development using lead sulfide (PbS) quantum dots (QDs). Along with their cost-efficient solution processability and flexible substrate compatibility, PbS QDs are highly interesting for the quantum-size-effect tunability of their bandgaps, spectral sensitivities, and wide absorption ranges. However, the performance of PbS QD-based SWIR photodetectors is limited owing to inefficient carrier transfer and low photo and thermal stabilities. In this study, a simple method is proposed to overcome these problems by incorporating CdS in PbS QD shells to provide efficient carrier transfer and enhance the long-term stability of SWIR photodetectors against oxidation. The SWIR photodetectors fabricated using thick-shell PbS/CdS QDs exhibited a high on/off (light/dark) ratio of 11.25 and a high detectivity of 4.0 × 1012 Jones, which represents a greater than 10 times improvement in these properties relative to those of PbS QDs. Moreover, the lifetimes of thick-shell PbS/CdS QD-based SWIR photodetectors were significantly improved owing to the self-passivation of QD surfaces.

Al atomistic surface modulation on colloidal gradient quantum dots for high-brightness and stable light-emitting devices.

Quantum-dot (QD) light-emitting devices (QLEDs) have been attracting considerable attention owing to the unique properties of process, which can control the emission wavelength by controlling the particle size, narrow emission bandwidth, and high brightness. Although there have been rapid advances in terms of luminance and efficiency improvements, the long-term device stability is limited by the low chemical stability and photostability of the QDs against moisture and air. In this study, we report a simple method, which can for enhance the long-term stability of QLEDs against oxidation by inserting Al into the shells of CdSe/ZnS QDs. The Al coated on the ZnS shell of QDs act as a protective layer with Al2O3 owing to photo-oxidation, which can prevents the photodegradation of QD with prolonged irradiation and stabilize the device during a long-term operation. The QLEDs fabricated using CdSe/ZnS/Al QDs exhibited a maximum luminance of 57,580 cd/m2 and current efficiency of 5.8 cd/A, which are significantly more than 1.6 times greater than that of CdSe/ZnS QDs. Moreover, the lifetimes of the CdSe/ZnS/Al-QD-based QLEDs were significantly improved owing to the self-passivation at the QD surfaces.

Easy-to-Fabricate and High-Sensitivity LSPR Type Specific Protein Detection Sensor Using AAO Nano-Pore Size Control.

In this study, we developed a pore size/pore area-controlled optical biosensor-based anodic aluminum oxide (AAO) nanostructure. As the pore size of AAO increases, the unit cell of AAO increases, which also increases the non-pore area to which the antibody binds. The increase in the number of antibodies immobilized on the surface of the AAO enables effective detection of trace amounts of antigen, because increased antigen-antibody bonding results in a larger surface refractive index change. High sensitivity was thus achieved through amplification of the interference wave of two vertically-incident reflected waves through the localized surface plasmon resonance phenomenon. The sensitivity of the fabricated sensor was evaluated by measuring the change in wavelength with the change in the refractive index of the device surface, and sensitivity was increased with increasing pore-size and non-pore area. The sensitivity of the fabricated sensor was improved and up to 11.8 ag/mL serum amyloid A1 antigen was detected. In addition, the selectivity of the fabricated sensor was confirmed through a reaction with a heterogeneous substance, C-reactive protein antigen. By using hard anodization during fabrication of the AAO, the fabrication time of the device was reduced and the AAO chip was fabricated quickly and easily.

Efficient exciton generation in atomic passivated CdSe/ZnS quantum dots light-emitting devices.

We demonstrate the first-ever surface modification of green CdSe/ZnS quantum dots (QDs) using bromide anions (Br-) in cetyl trimethylammonium bromide (CTAB). The Br- ions reduced the interparticle spacing between the QDs and induced an effective charge balance in QD light-emitting devices (QLEDs). The fabricated QLEDs exhibited efficient charge injection because of the reduced emission quenching effect and their enhanced thin film morphology. As a result, they exhibited a maximum luminance of 71,000 cd/m2 and an external current efficiency of 6.4 cd/A, both significantly better than those of their counterparts with oleic acid surface ligands. In addition, the lifetime of the Br- treated QD based QLEDs is significantly improved due to ionic passivation at the QDs surface.

Low Dark-Current, High Current-Gain of PVK/ZnO Nanoparticles Composite-Based UV Photodetector by PN-Heterojunction Control.

We propose a solution-processable ultraviolet (UV) photodetector with a pn-heterojunction hybrid photoactive layer (HPL) that is composed of poly-n-vinylcarbazole (PVK) as a p-type polymer and ZnO nanoparticles (NPs) as an n-type metal oxide. To observe the effective photo-inducing ability of the UV photodetector, we analyzed the optical and electrical properties of HPL which is controlled by the doping concentration of n-type ZnO NPs in PVK matrix. Additionally, we confirmed that the optical properties of HPL dominantly depend on the ZnO NPs from the UV-vis absorption and the photoluminescence (PL) spectral measurements. This HPL can induce efficient charge transfer in the localized narrow pn-heterojunction domain and increases the photocurrent gain. It is essential that proper doping concentration of n-type ZnO NPs in polymer matrix is obtained to improve the performance of the UV photodetector. When the ZnO NPs are doped with the optimized concentration of 3.4 wt.%, the electrical properties of the photocurrent are significantly increased. The ratio of the photocurrent was approximately 10³ higher than that of the dark current.

Enhanced Performance of Light-Emitting Diodes by Surface Ligand Modification on Quantum Dots.

The electrical characteristics of quantum dots (QDs) can vary depending on the surface modulation, which can change the luminance and efficiency of electroluminescent devices. Thus, understanding surface ligand is essential in improving the performance of QDs-based light-emitting diodes (LEDs). We analyzed the performance of QDs-based LEDs with respect to the QD surface volume. On the QD surfaces, the 1.1 nm-long tryoctylphosphine oxide (TOPO) ligand with three neck-type structure was replaced with a 1.7 nm-long oleic acid (OA) ligand with a one neck-type structure to evaluate the dependence of the LED properties on the ligand length. With all other conditions being identical, the luminance and efficiency of the QDs-based LEDs with an OA ligand were approximately 1,000 cd/m2 greater and 1.5 times higher, respectively, than those of the QDs-based LEDs with a TOPO ligand. These results show that if the physical length of the surface ligand is relatively long, decreasing the surface area would result in increased injection of electrons and holes into the QDs, increasing the luminance and efficiency.

Solution Processable CdSe/ZnS Quantum Dots Light-Emitting Diodes Using ZnO Nanocrystal as Electron Transport Layer.

In this paper, we propose interface engineering between cadmium selenide/zinc sulfide (CdSe/ZnS) quantum dots (QDs) as the emissive layer (EML) and ZnO nanocrystals (NCs) as the electron transport layer (ETL) for reducing the potential barrier in QDs based light-emitting diode (QLED). The n-type ZnO NCs were effective in confining charge to the QDs EML because of their wide band gap. The ZnO NCs were synthesized using a modified sol-gel process and were applied as the ETL in QLED. For comparison, a standard QLED with Tris(8-hydroxyquinolinato)aluminium as the ETL was also fabricated. The standard QLED was shown to have a luminance of 11,240 cd/m2 and current efficiency of 2.3 cd/A. However, QLED with ZnO NCs showed a higher luminance of 28,760 cd/m2 and current efficiency of 4.9 cd/A than the reference structure, and so has more efficient charge transport. Thus, QLED with ZnO NCs not only simplified the process, but also enhanced the luminance and current efficiency by factor of two.

Au-Polypyrrole Framework Nanostructures for Improved Localized Surface Plasmon Resonance Volatile Organic Compounds Gas Sensing.

In this paper, we propose an Au-polypyrrole (Ppy) nanorod gas sensor for the detection of volatile organic compound (VOC) gases. This gas sensor operates on the principle of localized surface plasmon resonance (LSPR). The Au-Ppy nanorods used in this experiment were synthesized using an anodic aluminum oxide template by the electrochemical deposition method. Using field emission scanning electron microscopy, we confirmed that the Au-Ppy nanorod arrays were successfully fabricated with a uniform size. By depositing gold, the Au-Ppy nanorods exhibited both optical and LSPR interference. The gas sensing properties of the fabricated nanorods were tested for VOCs such as acetic acid, benzene, and toluene with a short response time (~1 min). Moreover, the proposed VOC gas sensing system was tested with three types of VOC gases over a wide concentration range from 10 to 100 ppm. Highest sensitivity was observed for acetic acid gas, which had a linear relation with the gas concentration, indicating that the system can be used as a gas sensor.

Response characterization of a fiber optic sensor array with dye-coated planar waveguide for detection of volatile organic compounds.

We have developed a multi-array side-polished optical-fiber gas sensor for the detection of volatile organic compound (VOC) gases. The side-polished optical-fiber coupled with a polymer planar waveguide (PWG) provides high sensitivity to alterations in refractive index. The PWG was fabricated by coating a solvatochromic dye with poly(vinylpyrrolidone). To confirm the effectiveness of the sensor, five different sensing membranes were fabricated by coating the side-polished optical-fiber using the solvatochromic dyes Reinhardt's dye, Nile red, 4-aminophthalimide, 4-amino-N-methylphthalimide, and 4-(dimethylamino)cinnamaldehyde, which have different polarities that cause changes in the effective refractive index of the sensing membrane owing to evanescent field coupling. The fabricated gas detection system was tested with five types of VOC gases, namely acetic acid, benzene, dimethylamine, ethanol, and toluene at concentrations of 1, 2,…,10 ppb. Second-regression and principal component analyses showed that the response properties of the proposed VOC gas sensor were linearly shifted bathochromically, and each gas showed different response characteristics.

Fiber-optic multi-sensor array for detection of low concentration volatile organic compounds.

In this paper, we proposed a new type high sensitive volatile organic compounds (VOCs) gas sensor array that is based on the pulse width modulation technique. Four different types of solvatochromic dyes and two different types of polymers, were used to make the five different types of sensing membranes. These were deposited on the five side-polished optical fibers by a spin coater to make the five different sensing elements of the array. In order to ascertain the effectiveness of the sensors, five VOC gases were tested. Finally, principal component analysis (PCA) has been used to discriminates different types of VOCs.

Highly sensitive nano-porous lattice biosensor based on localized surface plasmon resonance and interference.

We propose a design for a highly sensitive biosensor based on nanostructured anodized aluminum oxide (AAO) substrates. A gold-deposited AAO substrate exhibits both optical interference and localized surface plasmon resonance (LSPR). In our sensor, application of these disparate optical properties overcomes problems of limited sensitivity, selectivity, and dynamic range seen in similar biosensors. We fabricated uniform periodic nanopore lattice AAO templates by two-step anodizing and assessed their suitability for application in biosensors by characterizing the change in optical response on addition of biomolecules to the AAO template. To determine the suitability of such structures for biosensing applications, we immobilized a layer of C-reactive protein (CRP) antibody on a gold coating atop an AAO template. We then applied a CRP antigen (Ag) atop the immobilized antibody (Ab) layer. The shift in reflectance is interpreted as being caused by the change in refractive index with membrane thickness. Our results confirm that our proposed AAO-based biosensor is highly selective toward detection of CRP antigen, and can measure a change in CRP antigen concentration of 1 fg/ml. This method can provide a simple, fast, and sensitive analysis for protein detection in real-time.

Improved performance of nanocrystal quantum dots-based LEDs by modifying hole transport layer.

Reported herein are the effects of the fabrication variables and surface capping of nanocrystal quantum dots (NQDs) on the characteristics of NQDs-based light-emitting diodes (LEDs). The molecular weight of the hole transport layer (HTL) material and the annealing conditions of the NQDs layer were chosen as fabrication process variables. Their effects on the layer characteristics and device efficiency were characterized. The maximum brightness varied over 50% according to the molecular weight of the HTL material. The optimized annealing temperature was shown to improve the maximum brightness by 20%. The surface-capping molecules of the NQDs were changed from conventional trioctyl phosphine/trioctyl phosphine oxide (TOPO/TOP) to pyridine and were incorporated into LEDs, and its effects on the device characteristics were discussed.

Nanostructures in biosensor--a review.

In the 21(st) century, it is widely recognized that along with information technology (IT) and biotechnology (BT), nanotechnology (NT) will be a key field of science that will drive future developments. NT is expected to allow innovations in industrial fields such as electrical and electronics, biochemistry, environment, energy, as well as materials science by enabling the control and operation of materials at the atomic and molecular levels. In particular, the application of NT in the field of biochemistry is now enabling the realization of previously unachievable objectives.This review discusses the growth, synthesis, and biocompatible functionalization of each materials, with an emphasis on 1D nanomaterials such as CNTs, inorganic nanowires (made of Si, metals, etc.), and conducting polymer nanowires, along with 0D nanomaterials such as nanoparticles. This review also investigates the sensing principle and features of nanobiosensors made using the abovementioned materials and introduce various types of biosensors with nanostructure 0-D and 1-D. Finally, the review discusses future research objectives and research directions in the field of nanotechnology.

Highly efficient hybrid light-emitting device using complex of CdSe/ZnS quantum dots embedded in co-polymer as an active layer.

We propose a highly efficient hybrid light-emitting device (LED) with a single active layer where CdSe/ZnS quantum dots (QDs) are dispersed as a guest material in a conjugated polymer (co-polymer) matrix used for a host material. In our structure, the QDs act on light-emitting chromophores by trapping the migrating excitons in the co-polymer matrix via Förster energy transfer, and improve the charge balance within the co-polymer by trapping the injected electron carriers. Experimental results show that the electroluminescent properties highly depend on the doping density of the QDs within the co-polymer matrix, where the luminance as well as the external current efficiency are initially enhanced with increasing the concentration of the dispersed QDs in the co-polymer solution, and then such properties are degraded due to aggregation of the QDs. We can get the maximum brightness of 9,088 cd/m(2) and the maximum external current efficiency of 7.5 cd/A in mixing ratio of the QDs by 1.0 wt%. The external current efficiency is enhanced by over 15 times and the turn-on voltage is reduced in comparison with the corresponding values for a reference device that uses only a co-polymer as an active layer.

Variable wavelength surface plasmon resonance (SPR) in biosensing.

In this study, we fabricated a novel variable wavelength surface plasmon resonance (SPR) sensor, which detects resonance conditions such as a maximum attenuation wavelength, measuring change of microscopic refractive index. Such a change was measured to detect a salmonella antigen-antibody reaction and a penicillinase-penicillin reaction. Our experiments were performed after immobilizing a salmonella antibody on the sensor chip. We measured the shift in resonant wavelength during the antigen-antibody reaction for 30 min by injecting 5 x 10(7) cells/ml concentration of salmonella antigen solution into the sample chamber. Also, after immobilizing penicillinase on the sensor chip, we measured the shift in resonant wavelength during the reaction. Penicillin solution at 10mM was injected into the sample chamber. The shift of resonant wavelength for each experiment was measured using a white light source, multimode optical fiber, a part of sensor chip and an optical spectrum analyzer. As a result, the resonant wavelength shifted about 0.26 nm/min owing to the salmonella antibody-antigen reaction. Thus, we could detect the change in wavelength (0.8 nm/min) through the interaction of penicillin and penicillinase for 15 min using variable wavelength SPR sensor.