Search

Despite advances in numerous artificial synaptic devices, the search for a new functionalized synaptic device remains the subject of rigorous investigation for constructing neuromorphic systems. Op...

Electrochromic devices (ECDs) have been widely investigated for application in next-generation displays and smart windows thanks to their highly efficient optical transmittance modulation properties. However, several challenges such as chemical and environmental instabilities and leakage of electrolytes limit their practical applications. In this paper, we report a simple and efficient approach for synthesising ultraviolet (UV)-cured poly(methyl methacrylate) (PMMA) gels that can be used as safe electrolytes. The ECDs fabricated with the 10 min UV-cured PMMA gel electrolyte deliver remarkable device performances with a wide optical transmittance transition (ΔT) of 51.3% at a wavelength of 550 nm under −1.2–0 V bias range and fast switching times (Δt) of 1.5 s and 2.0 s for bleaching and colouration, respectively. In addition, excellent operational stability of 98.9% after 11 500 cycles and environmental stability at a wide temperature range of −20 to +70 °C are exhibited. Moreover, a smart electrochromic window system, including an ECD connected with an Arduino circuit, is developed. These smart windows can change colour by simultaneously monitoring the illumination and UV intensities of sunlight.

A new structure for a switchable mirror device based on reversible electrodeposition is proposed. This device does not contain Cu ions in the electrolyte and adapts a counter electrode. The feasibility of the device was evaluated with a WO3 film, which is a well-known electrochromic material, as a counter electrode. Even in the absence of Cu ions, the WO3 film facilitates a clean erase feature in the device. Furthermore, using a pre-deposited Ag film as a working electrode, Ag deposition can be driven at a substantially lower voltage than that in conventional devices. Moreover the deposition current decreases with the progress of Ag deposition, and stops after completion of the deposition process. The results clearly indicate that the tri-bromine ion, which makes the self-erasing circulation, is not generated during Ag deposition process. The new switchable mirror shows excellent bistability and size scale-up is possible because it does not consume continuous current in the mirror state. By appling the proposed technology, a switchable mirror device with a 7 cm × 9 cm active area was successfully fabricated.

Light-adaptable (LA) displays combining the advantages of reflective and emissive displays, are considered as the future of display technology. Electrochromic devices are potentially strong candidates for reflective-mode LA displays because of their high transmittance in the transparent state and low power consumption. However, the narrow viewing angle of these displays in relation to a hybrid structure of the LA display, is a technical barrier that must be overcome for the successful application of electrochromic devices to light-adaptable displays. In the present study, an electrochromic device with a self-diffusing function was developed for application to light-adaptable displays. Si3N4 scattering particles were incorporated in the TiO2 nanostructure-based electrochromic device. Efficient forward diffuse scatterings were obtained without deteriorating the total transmittance of the device. The contrast ratio and color gamut of the electrochromic device were dramatically improved because of the addition of the scattering particles.

Wearable strain sensors based on Au–Ag core–shell nanoparticle decorated yarns were fabricated by a solution-based approach. Smart wearable systems with our strain sensors that can monitor various human motions, including finger motion, marching and squatting, and transmit the information of human motion in real time to an LED light was demonstrated.

Long-lived electrochromic devices (ECDs) with multilevel bistability based on a portable film-type polymer electrolyte (PFPE) were fabricated and their optical and electrical properties were characterized. WO3 and NiOx, deposited via a vacuum method, were used as electrochromic materials, and PFPEs were assembled in ECDs by a transfer method. The PFPEs were fabricated by inserting a polyvinyl acetal (PVA) based gel electrolyte between a light and a tight release films. The PFPE-based ECD operated reliably for at least 109,000 cycles and showed excellent bistability in multilevel open circuits. For 30 min after removing the applied operating voltage, the ECD maintained 90% and 99% of the original coloration and decoloration transmittance at 550 nm, respectively. The average coloration and decoloration consumed charge and efficiency over 109,000 operation cycles were 4.2 and −4.5 mC/cm2 and 81.4 and −74.8 cm2/C, respectively.

The optical and electrical properties of electrochromic devices (ECDs) have been studied as a function of the electrolyte concentration and the cell gap. During tests, the electrolyte concentration was adjusted from 0.01 to 1 M LiClO4, and the cell gaps between the positive and negative electrodes were set at 25, 60, and 100 µm. By varying the electrolyte concentrations and the cell gap, various parameters such as the transmittance, response time, charge consumption, coloration efficiency, and bistability of ECD were comparatively analyzed. Viologen (VO) was used as the reduction electrochromic material, and triarylamine (TAA) was used as the oxidation material.

Electrochromic mirrors (ECMs) that are used in automobile mirrors need to have high reflectance, a high contrast ratio, and a clear image. In particular, it is critical that distortions of clear images are minimized for safety. Therefore, an ECM is fabricated using viologen-anchored nanoparticles and a magnesium fluoride (MgF2) layer with an anti-reflection function. The ECM has approximately 30.42% in the reflectance dynamic range and 125 cm2/C high coloration efficiency.

Electrochromic devices (ECDs) having a high switching speed and a good durability were developed with viologen-anchored TiO 2 (VTO) nanoparticles and antimony-doped SnO 2 (ATO) nanoparticles. The fabricated ECDs showed a good stability after 30,000 cycles driving at 4 Hz speed. Also, the dynamic behavior of their devices was studied using 6×6 patterned array cells. The driving tests of 4 types were used to understand the exact driving mechanism and to prevent the rapid blur problem.

For environmental reason, buildings increasingly install smart windows, which can dim incoming daylight based on active electrochromic devices (ECDs). In this work, multi-layered graphene (MLG) was investigated as an ECD window electrode, to minimize carbon dioxide (CO2) emissions by decreasing the electricity consumption for building space cooling and heating and as an alternative to the transparent conductor tin-doped indium oxide (ITO) in order to decrease dependence on it. Various MLG electrodes with different numbers of graphene layers were prepared with environmentally friendly poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) to produce ECD cells. Tests demonstrated the reproducibility and uniformity in optical performance, as well as the flexibility of the ECD fabrication. With the optimized MLG electrode, the ECD cells exhibited a very fast switching response for optical changes from transparent to dark states of a few hundred msec.

Here, we fabricated high-performance gold/graphene yarns through a facile method by the electroless deposition of gold nanoparticles onto the surface of graphene yarns. The gold/graphene yarns are fabricated using a completely solution-based process that can be scaled up for practical applications. They possess high electrical conductivity (2.86 × 102 S cm-1) and good gravimetric specific conductivity (6.81 × 102 S cm2 g-1) as well as good reliability under 1000 bending tests with a maximum bending angle of 170° and 10 washing tests with laundry detergents. These stable conducting yarns could also be integrated into textiles and clothes in various forms to create smart fabrics and wearable devices. In addition, this facile approach is easily applicable to various graphene films and devices on soft substrates that are presently used in flexible/wearable electronics.

A novel silver (Ag) deposition-based electrochromic device was developed for the reversible electrodeposition (RED) system. The electrochromic device can switch between transparent and mirror states in response to a change in the applied voltage. The dynamic range of the transmittance percent (%) for the fabricated device was about 90% at the 550 nm wavelength. A large-area RED display system was also successfully fabricated using the parted electrochromic cells of the honeycomb structure. The interelectrode space and the extent of the large-area RED display system were 50 μm and 10×10 cm, respectively.

A novel and simple method for the colorimetric quantitative sensing of individual alkali metal ions (Li + , Na + , K + , and Rb + ) based on the reversible properties of self-assembled aggregates and individual gold nanoparticles (Au NPs) is described. This paper demonstrates reversible self-assembly processes where the degree of assembly and disassembly is dependent on the individual alkali metal ion concentration, nanoparticle size, and alkali metal ionic radii. The color changes of the colloidal Au NPs with metal ion concentrations in colloidal NP solutions occur reversibly. Below a certain concentration of alkali metal ions, the aggregates of Au NPs are redispersed. As the Au NP diameters and the alkali metal ionic radii increase, the critical concentration decreases.

A simple and selective technique which immobilizes protein onto a solid substrate by using UV illumination has been developed. In protein immobilization, a Bovine serum albumin (BSA) performed bifunctional role as a cross-linker between substrate and proteins and as a blocker inhibiting a nonspecific protein adsorption. A new photo-induced protein immobilization process has been investigated at each step by fluorescence microscopy, ellipsometry, and Fourier transform infrared (FT-IR) spectroscopy. A UV photomask has been used to induce selective protein immobilization on target regions of the surface of the SiO2 substrates under UV illumination with negligible nonspecific binding. The UV illumination also showed improved photostability than the conventional methods which employed bifunctional photo-crosslinker molecules of photo-reactive diazirine. This new UV illumination-based photo-addressable protein immobilization provides a new approach for developing novel protein microarrays for multiplexed sensing as well as other types of bio-immobilization in biomedical devices and biotechnologies.

A Fabry-Perot type integrated color reflector, with red/blue/green colors as subpixels, was designed and fabricated with Si substrate. Ag films were used as reflective mirror layers, SiO2 films were used as Fabry-Perot cavity layers and W films were used as partially reflective layers for the cavity. To minimize the effects of the thickness variation of the oxide cavity layers, the structure of the color reflector was optimized, and the differential deposition scheme was devised and applied in the fabrication process. The integrated color reflector was successfully fabricated with the proposed fabrication scheme. The measured white reflectance was > 45% in the visible spectrum range and -49% at 550 nm wavelength. The fabricated reflector had moderate color gamut of 17% of the National Television System Committee (NTSC) standard and it showed very high white reflectivity. The fabricated color reflector is expected to be applicable to reflective displays.

This paper describes a new technique for the detection of uncharged or feebly charged small molecules (

We demonstrate the application of ‘top-down’ fabricated Si nanochannel field effect transistor biosensors in measuring the configuration of charged proteins immobilized on the Si surface. We have immobilized monoclonal antibodies of PSA (anti-PSA) on the p-type Si channel surface, and monitored the channel conductance in response to the variation of ionic strength (salt concentration) and pH level of the buffer solution. The dependency of channel conductance on the salt concentration is consistent with the screening of protein charges by dissolved counterions, enabling quantitative estimation of the distance from the Si surface to anti-PSA molecules based on calculated Debye screening lengths (λD) for each salt concentration. The effect of salt concentration on the pH-dependency of channel conductance has also been studied, and explained in terms of the net charge of anti-PSA as a function of pH.

Cardiac markers in human serum with concentrations less than 0.1 ng/mL were analyzed by use of a guided-mode resonance (GMR) biosensor. Cardiac troponin I (cTnI), creatine kinase MB (CK-MB), and myoglobin (MYO) were monitored in the serum of both patients and healthy controls. Dose-response curves ranging from 0.05 to 10 ng/mL for cTnI, from 0.1 to 10 ng/mL for CK-MB, and from 0.03 to 1.7 μg/mL for MYO were obtained. The limits of detection (LOD) for cTnI, CK-MB, and MYO were less than 0.05, 0.1, and 35 ng/mL, respectively. Analysis time was 30 min, which is short enough to meet clinical requirements. Antibody immobilization and the hydrophilic properties of the guided-mode resonance filter (GMRF) surface were investigated by X-ray photoelectron spectroscopy (XPS) and by monitoring the peak wavelength shift and water contact angle (CA). Both assays used to evaluate the surface density of the immobilized antibodies, a sandwich enzyme-linked immunosorbent assay (ELISA) and a sandwich immunogold assay, showed that the antibodies were successfully immobilized and sufficiently aligned to detect the low concentration of biomarkers. Our results show that the GMR biosensor will be very useful in developing low-cost portable biosensors that can screen for cardiac diseases.

In this study, we have developed a new detection method using Si field effect transistor (FET)-type biosensors, which enables the direct monitoring of antigen-antibody binding within very high-ionic-strength solutions such as 1×PBS and human serum. In the new method, as no additional dilution or desalting processes are required, the FET-type biosensors can be more suitable for ultrasensitive and real-time analysis of raw sample solutions. The new detection scheme is based on the observation that the strength of antigen-antibody-specific binding is significantly influenced by the ionic strength of the reaction solutions. For a prostate specific antigen (PSA), in some conditions, the binding reaction between PSA and anti-PSA in a low-ionic strength reaction solution such as 10 µM phosphate buffer is weak (reversible), while that in high-ionic strength reaction solutions such as 1×PBS or human serum is strong.

Anionic sulfate (SO(4)(-))-functionalized polystyrene (PS) nanoparticles were prepared by the thermal decomposition of potassium persulfate (KPS) in the presence of sodium tetraborate via emulsion polymerization. The presence of a SO(4)(-) group at a solid/liquid interface of a particle surface was confirmed by a zeta potential value of -40.6 mV as well as the shifting of S 2p spectra toward a lower-binding-energy region around 162.7 eV (2p(3/2)) and 164.4 eV (2p(1/2)) in X-ray photoelectron spectroscopy (XPS) analysis. The electrostatic attraction between positively charged antibodies of human immunoglobulin G (hIgG) and cardiac troponin I (cTnI) and negatively charged particle surfaces was accomplished. The atomic force microscopy (AFM) measurement and bicinchoninic acid (BCA) assay results show binding structure between hIgG and antibodies of hIgG (anti-hIgG) with a gradual increase in particle diameter to 152.6 nm (bare), 170.2 nm (hIgG), and 178.9 nm (hIgG/anti-hIgG). Surface coverage densities of 331.4 ng/cm(2) (hIgG) and 320.3 ng/cm(2) (cTnI) and the binding capacity of hIgG to HyLite-750-labeled Fab-specific anti-hIgG (approximately 81.2%) indicate that the majority of hIgG was immobilized with a Y-shaped orientation. The sandwich immunoassay results provide the evidence that the immunological activity of cTnI on the PS nanoparticle surface was retained because the binding activity of the cTnI-PS nanoparticle/cTnI (antigen)/detection cTnI-antibody reaction showed a 5-fold higher activity than that of the cTnI-PS nanoparticle/human serum albumin (HSA)/detection cTnI antibody used as a negative control.

In order to identify changes in the levels of key proteins in response to the onset or development of a disease, the research fields of proteomics and genomics seek to develop new biomarkers. Specifically, simple and fast biomarker screens have a central role in many areas of healthcare, including disease diagnosis and drug discovery. Biologically modified field-effect transistor (BioFET) is one of the most attractive approaches because of the on-chip integration of the sensor array, fast response, high reliability and low-cost mass production. However, the BioFETs used to detect macromolecules have been operated only in buffer solution with low salt concentrations because of the Debye screening length of blood or serum. Here we report a novel detection technique for direct label-free immunodetection of cancer markers in human serum using a Si-FET that was fabricated by conventional photolithographic processes. The proposed sensing method shows no dissociation of antigen-antibody binding as in general immunoassays, unlike the previous reports on Si-FET sensors. This method therefore overcomes the Debye length problem of immunodetection in human fluids, such as serum, that are generally encountered by FET-based biosensors. Our results demonstrate specific label-free and real-time immunodetection of a cancer marker at a concentration of 0.2 ng/mL in human serum, quantitative detection of the marker from 0.2 to 114 ng/mL, and successful multiplexed sensing of three different cancer markers. We believe that connecting our simple electrical detection method, which does not require pretreatment of serum, with well-established whole blood filter technology will contribute to the development of new point-of-care testing (POCT) sensors.

We present a simple semiconductor process to fabricate nanogap arrays for application in molecular electronics and nano-bio electronics using a combination of freestanding silicon nanowires and angle evaporation. The gap distance is modulated using the height of the silicon dioxide, the width of the Si nanowires, and the evaporation angle. In addition, we fabricate and apply the nanogap arrays in single-electron transistors using DNA-linked Au nanoparticles for the detection of DNA hybridization.

We present a method for spatially selective immobilization of functional materials, such as proteins and nanoparticles, onto pre-activated silicon surfaces by electrochemical reaction. Carboxymethylbenzendiazonium (CMBD) cations, being adsorbable on silicon surfaces through electrochemically reductive deposition, is used as an anchor molecule to prepare the pre-activated silicon surfaces. It is demonstrated that the use of BD reaction is very efficient for the selective immobilization because the functional materials are immobilized exclusively onto the pre-adsorbed CMBD region. The method is applied to immobilize gold nanoparticles on the selected nanowire of the nanowire array.

Gold nanoparticles exhibited strong surface plasmon absorption and couplings between neighboring particles within bioactivated self-assembly modified their optical properties. Colorimetric analysis on the optical modification of surface plasmon resoanance (SPR) shift and flocculation parameter functionalized bioinspired gold assembly for biophotonic application. The physical origin of bioinspired gold aggregation-induced shifting, decreasing, or broadening of the plasmon absorption spectra could be explained in terms of dynamic depolarization, collisional damping, and shadowing effects.

The sizes, shapes, and growth rates of gold and silver nanoparticles stabilized with polyvinylpyrrolidone in water can be controlled by using picosecond laser pulses. The nucleation of small metal clusters formed with NaBH4 addition to produce nanoparticles takes two months with aging but 30 min with laser irradiation. Laser pulses can also induce nanoparticles to have narrow size and shape distribution or to undergo aggregation into much larger particles. The latter process is more likely found when the metal is silver or the irradiation wavelength is short. Laser-induced growth and shape transformation processes are explained in terms of BH4− depletion, metal fusion, and electron ejection followed by disintegration.

The laser-induced sintering of TiO2 nanoparticles into larger nanospheres is accelerated by adsorbed silver particles. For the same weight fraction of silver, silver nanoparticles of 5 nm in diameter modify TiO2 nanoparticles more effectively than those of 1.5 nm do, suggesting that the photocatalysis of TiO2 nanoparticles as well as their stability is highly dependent on the sizes, the shapes, and the distribution of adsorbed metal nanoparticles. The photoexcited electrons of TiO2 nanoparticles are quenched at trap sites and surface states by transfer to the conduction band of silver, implying that the presence of adsorbed silver nanoparticles enhances the photocatalytic effect of TiO2.

Aspect ratio of gold nanorods can be controlled by simply adjusting the reaction temperature in the seed-mediated synthesis of the nanorods. The gold nanorods were synthesized by the injection of gold nanoparticle seeds of around 4nm in diameter into a reaction mixture containing hydrogen tetrachloroaurate, hexadecyltrimethylammonium bromide, and ascorbic acid. Average aspect ratio of the resulting nanorod increases from 1 to about 40 with decreasing the reaction temperature from 315to276K, which can be attributed to the temperature-induced change in the shape of the micellar templates. For further understanding of the growth mechanism, silver nanoparticles were also used as seeds in the preparation of the gold nanorod.

Monodispersive size-controlled gold nanoplates were synthesized with high purity from the reduction of hydrogen tetrachloroaurate by reduced amount of sodium citrate, which kinetically controls the reaction pathway, in the presence of poly(vinyl pyrrolidone) (PVP). With the insufficient addition of the reductant, the molar ratio of sodium citrate and PVP relative to hydrogen tetrachloroaurate played an important role in determining the geometric shape and size of the product. These nanoplates were single crystals with planar width of 80−500 nm and thickness of 10−40 nm, exhibiting strong surface plasmon absorption in the near-infrared (NIR) region of 700−2000 nm. The gold nanoplates were used as the synthetically provided nanoblocks to fabricate single-crystalline nanocomponents, such as a nanoscaled gear or a nanoscaled letter.

The excited-state tautomerization dynamics of 7-hydroxyquinoline encapsulated in beta-cyclodextrin is compared with that in pure water by measuring isotope-dependent fluorescence kinetics as well as absorption and emission spectra. The normal species tautomerizes stepwise via forming anionic intermediate species in both systems. However, the enol-deprotonation time (40 ps in water) becomes as large as 170 ps whereas the imine-protonation time of the anionic intermediate (160 ps in water) becomes as short as 85 ps in beta-cyclodextrin. The slow formation and the fast decay of the anionic species are attributed to the unstability of the charged species in hydrophobic cages. Encapsulation can be utilized to enhance fluorescence enormously and to accelerate selective reactions by retarding other processes.

The Mn2+ impurity luminescence decay of Mn2+-doped ZnS nanoparticles has been clearly distinguished from ZnS host emission decay by measuring transient absorption and emission kinetic profiles in t...

Photochemical reaction of n-dodecanethiol-derivatized silver nanoclusters dispersed in cyclohexane has been studied in the picosecond−second time range and has been found to depend nonlinearly on the irradiance of photolysis light. The static absorption bleach by excitation at 532 and 355 nm increases with the irradiance raised to the powers of 1.9 and 1.4, respectively. Furthermore, transient absorption produced with a high-energy pulse rises further on a time scale of a few nanoseconds, whereas that with low-energy pulse decays. Transient absorption owing to the dielectric change of the immediately surrounding medium arises in 0.5 ns with the conduction of the thermalized photon energy. It decays in 1.4 ns as the heat spreads further. A fraction of excited nanoparticles experience a further absorption increase as hot alkanethiols dissociate for a period determined by the heat dissipation time (3.6 ns). The fraction increases with excitation-pulse energy. Within the recombination time (40 ns) of thiols, ...

Dodecanethiol-derivatized nanoparticles of Ag, Ag/Au, and Au with an average size of 5.5 nm have been prepared via a two-phase synthetic route in water/toluene and characterized with various methods. In particular, their photochemical dynamics and mechanisms have been studied with laser flash photolysis. The surface plasmon absorption peak varies linearly from 532 to 429 nm as the Ag fraction of Ag/Au alloy clusters, in which Ag atoms are more abundant at the outer part, increases. Excited silver nanoparticles dispersed in cyclohexane undergo dethiolation in 8 ns and then fragmentation in 40 ns. Thereafter, the fragments gradually aggregate owing to the presence of less soluble bare metal sides.

The photolysis dynamics of benzyl phenyl sulfide adsorbed on silver nanoparticles suspended in water has been studied by using time-resolved transient-absorption spectroscopy. The adsorbed molecule desorbs from the metallic surface with a photoejected electron within 2 ns after excitation. The anionic species dissociates into benzenethiolate and benzyl radical on the time scale of 8 ns. The benzenethiolate combines to the metallic surface of a silver nanoparticle in 30 ns while the benzyl radical abstracts atomic hydrogen from water in 130 ns to form toluene.

We present a novel blood filter unit that is designed to separate blood plasma from whole blood by simple magnetic actuation. A non-diluted blood sample is dropped into the filter unit and magnetic attraction is applied to squeeze out only blood plasma while blood particles are filtered by membranes stacked in the filter unit. The new filter device yields good filtering performance with nearly perfect filtering efficiency (∼99.999%), high plasma recovery (∼30%), low blood consumption (

We present a novel blood filter device which is actuated by simple magnetic squeezing to layered membranes. The filter gives a good performance in high plasma recovery yield (∼25%), nearly-perfect filtering efficiency (∼100%), low blood consumption (

We propose a new type of photosensitive biosensor with a CMOS compatible Si photodiode integrated circuit, for the high-sensitive detection of small mycotoxin molecules requiring competitive assay approach. In this work, a photodiode is connected to the gate of a field effect transistor (FET) so that the open circuit voltage ( V OC ) of the illuminated photodiode is transferred into the drain/source current ( I DS ) of the FET. The sensing scheme employs competitive binding of toxin molecules (within the sample solution) and toxin–BSA conjugates (immobilized on the photodiode surface) with Au-nanoparticle-labeled antibodies, followed by silver enhancement to generate opaque structures on the photodiode surface. By utilizing the non-linear dependence of the V OC on the light intensity, we can maintain a sufficiently high signal resolution at low toxin concentrations (with most of the incident light blocked) for the competitive assay. By monitoring the I DS of the FET whose gate is driven by the V OC , quantitative detection of Aflatoxin B1 has been achieved in the range of 0–15 ppb.