Room-Temperature Fabrication of p-Type SnO Semiconductors Using Ion-Beam-Assisted Deposition.

Over the past decade, SnO has been considered a promising p-type oxide semiconductor. However, achieving high mobility in the fabrication of p-type SnO films is still highly dependent on the post-annealing procedure, which is often used to make SnO, due to its metastable nature, readily convertible to SnO2 and/or intermediate phases. This paper demonstrates a fully room-temperature fabrication of p-type SnOx thin films using ion-beam-assisted deposition. This technique offers independent control between ion density, via the ion-gun anode current and oxygen flow rate, and ion energy, via the ion-gun anode voltage, thus being able to optimize the optical band gap and the hole mobility of the SnO films to reach 2.70 eV and 7.89 cm2 V-1 s-1, respectively, without the need for annealing. Remarkably, this is the highest mobility reported for p-type SnO films whose fabrication was carried out entirely at room temperature. Using first-principles calculations, we rationalize that the high mobility is associated with the fine-tuning of the Sn-rich-related defects and lattice densification, obtained by controlling the density and energy of the oxygen ions, both of which optimize the spatial overlap of the valence bands to form a continuous conduction path for the holes. Moreover, due to the absence of the annealing process, the Raman spectra reveal no significant signatures of microcrystal formation in the films. This behavior contrasts with the case involving the air-annealing procedure, where a complex interaction occurs between the formation of SnO microcrystals and the formation of SnOx intermediate phases. This interplay results in variations in grain texture within the film, leading to a lower optimum Hall mobility of only 5.17 cm2 V-1 s-1. Finally, we demonstrate the rectification characteristics of all-fabricated-at-room-temperature SnOx-based p-n devices to confirm the viability of the p-type SnOx films.

Assessing Plasma Levels of α-Synuclein and Neurofilament Light Chain by Different Blood Preparation Methods.

The potential biomarkers of Parkinson's disease are α-synuclein and neurofilament light chain (NFL). However, inconsistent preanalytical preparation of plasma could lead to variations in levels of these biomarkers. Different types of potassium salts of EDTA and different centrifugation temperatures during plasma preparation may affect the results of α-synuclein and NFL measurements. In this study, we prepared plasma from eight patients with Parkinson's disease (PD) and seven healthy controls (HCs) by using di- and tri-potassium (K2- and K3-) EDTA tubes and recruited a separated cohort with 42 PD patients and 40 HCs for plasma samples prepared from whole blood by centrifugation at room temperature and 4°C, respectively, in K2-EDTA tubes. The plasma levels of α-synuclein and NFL in K2- and K3-EDTA were similar. However, the levels of α-synuclein in the plasma prepared at 4°C (101.57 ± 43.43 fg/ml) were significantly lower compared with those at room temperature (181.23 ± 196.31 fg/ml, P < 0.001). Room temperature preparation demonstrated elevated plasma levels of α-synuclein in PD patients (256.6 ± 50.2 fg/ml) compared with the HCs (102.1 ± 0.66 fg/ml, P < 0.001), whereas this increase in PD was not present by preparation at 4°C. Both plasma preparations at room temperature and 4°C demonstrated consistent results of NFL, which are increased in PD patients compared with HCs. Our findings confirmed that K2- and K3-EDTA tubes were interchangeable for analyzing plasma levels of α-synuclein and NFL. Centrifugation at 4°C during plasma preparation generates considerable reduction and variation of α-synuclein level that might hinder the detection of α-synuclein level changes in PD.

Enhanced Plasmonic Biosensor Utilizing Paired Antibody and Label-Free Fe3O4 Nanoparticles for Highly Sensitive and Selective Detection of Parkinson's α-Synuclein in Serum.

Parkinson's disease (PD) is an acute and progressive neurodegenerative disorder, and diagnosis of the disease at its earliest stage is of paramount importance to improve the life expectancy of patients. α-Synuclein (α-syn) is a potential biomarker for the early diagnosis of PD, and there is a great need to develop a biosensing platform that precisely detects α-syn in human body fluids. Herein, we developed a surface plasmon resonance (SPR) biosensor based on the label-free iron oxide nanoparticles (Fe3O4 NPs) and paired antibody for the highly sensitive and selective detection of α-syn in serum samples. The sensitivity of the SPR platform is enhanced significantly by directly depositing Fe3O4 NPs on the Au surface at a high density to increase the decay length of the evanescent field on the Au film. Moreover, the utilization of rabbit-type monoclonal antibody (α-syn-RmAb) immobilized on Au films allows the SPR platform to have a high affinity-selectivity binding performance compared to mouse-type monoclonal antibodies as a common bioreceptor for capturing α-syn molecules. As a result, the current platform has a detection limit of 5.6 fg/mL, which is 20,000-fold lower than that of commercial ELISA. The improved sensor chip can also be easily regenerated to repeat the α-syn measurement with the same sensitivity. Furthermore, the SPR sensor was applied to the direct analysis of α-syn in serum samples. By using a format of paired α-syn-RmAb, the SPR sensor provides a recovery rate in the range from 94.5% to 104.3% to detect the α-syn in diluted serum samples precisely. This work demonstrates a highly sensitive and selective quantification approach to detect α-syn in human biofluids and paves the way for the future development in the early diagnosis of PD.

Feasibility of using bimetallic Au-Ag nanoparticles for organic light-emitting devices.

Matching the resonant wavelength of plasmonic nanoparticles (NPs) and the emission band of organic materials is critical for achieving optimal plasmon-enhanced luminescence in organic light-emitting devices (OLEDs). However, the spectral matching is often unsatisfactory because the interior architecture of OLEDs limits the dimensions of the NPs to support the desired wavelength adjustment. In this article, we proposed a design strategy via AuxAg1-x alloy NPs to enable resonance tuning while preserving the size of the NP to suit the OLED design requirements. The bimetallic NPs, especially for x < 0.6, not only add one more degree of freedom to vary the plasmon wavelength but also provide the benefits of higher scattering and more intense and outspread electric fields over a broader spectrum compared to Au monometallic NPs. These features allow smaller NPs, which are more compatible with OLED interiors, to scatter electric fields more efficiently and increase the density of molecules interacting with the NP plasmons. In the presence of a nearby dipole emitter, the bimetallic NPs can simultaneously increase radiative enhancement and suppress non-radiative losses, which are advantageous for increasing the quantum yield and luminescence efficiency of the emitter. These improvements are associated with lower intraband and interband activities resulting from the higher molar fraction of Ag in the alloy NPs. We provided composition mappings to achieve enhanced luminescence for specified wavelengths at fixed NP sizes. Finally, we theoretically demonstrated that the bimetallic NPs could improve the light-extraction efficiency of OLEDs better than Au monometallic NPs. This work provides essential guidance to enable versatile plasmon-enhanced applications with predefined nanostructural geometries and wavelengths to match the device requirements.

Gold nanoparticle-assisted plasmonic enhancement for DNA detection on a graphene-based portable surface plasmon resonance sensor.

The impact of different gold nanoparticle (GNP) structures on plasmonic enhancement for DNA detection is investigated on a few-layer graphene (FLG) surface plasmon resonance (SPR) sensor. Two distinct structures of gold nano-urchins (GNu) and gold nanorods (GNr) were used to bind the uniquely designed single-stranded probe DNA (ssDNA) of Mycobacterium tuberculosis complex DNA. The two types of GNP-ssDNA mixture were adsorbed onto the FLG-coated SPR sensor through the π-π stacking force between the ssDNA and the graphene layer. In the presence of complementary single-stranded DNA, the hybridization process took place and gradually removed the probes from the graphene surface. From SPR sensor preparation, the annealing process of the Au layer of the SPR sensor effectively enhanced the FLG coverage leading to a higher load of the probe DNA onto the sensing interface. The FLG was shown to be effective in providing a larger surface area for biomolecular capture due to its roughness. Carried out in the DNA hybridization study with the SPR sensor, GNu, with its rough and spiky structures, significantly reinforced the overall DNA hybridization signal compared with GNr with smooth superficies, especially in capturing the probe DNA. The DNA hybridization detection assisted by GNu reached the femtomolar range limit of detection. An optical simulation validated the extreme plasmonic field enhancement at the tip of the GNu spicules. The overall integrated approach of the graphene-based SPR sensor and GNu-assisted DNA detection provided the proof-of-concept for the possibility of tuberculosis disease screening using a low-cost and portable system to be potentially applied in remote or third-world countries.

Surface plasmon-enhanced solution-processed phosphorescent organic light-emitting diodes by incorporating gold nanoparticles.

Organic light-emitting diodes (OLEDs) have attracted increasing attention due to their superiority as high quality displays and energy-saving lighting. However, improving the efficiency of solution-processed devices especially based on blue emitter remains a challenge. Excitation of surface plasmons on metallic nanoparticles has potential for increasing the absorption and emission from optoelectronic devices. We demonstrate here that the incorporation of gold nano particles (GNPs) in the hole injection layer of poly(3,4-ethylene dioxythiophene):polystyrene sulfonic acid with an appropriate size and doping concentration can greatly enhance the efficiency OLED device especially at higher voltage. Apparently, the spectral of the multiple plasmon resonances of the GNPs and the luminescence of the emitting materials significantly overlap with each other. At 1000 cd m-2 for example, the power efficiency of a studied green device is increased from 29.0 to 36.2 lm W-1, an increment of 24.8%, and the maximum brightness improved from 21 550 to 27 810  cd m-2, an increment of 29.1%, as 2 wt% of a 12 nm GNP is incorporated. Remarkably, designed blue OLED also exhibited an increment of 50% and 35% in power efficacy at 100 and 1000 cd m-2, respectively, for same device structure. The reason why the enhancement is marked may be attributed to a strong absorption of the short-wavelength emission from the device by the gold nano particles, which in turn initiates a strong surface plasmon resonance effect, leading to a high device efficiency.

Surface Plasmon Resonance Optical Sensor: A Review on Light Source Technology.

The notion of surface plasmon resonance (SPR) sensor research emerged more than eight decades ago from the first observed phenomena in 1902 until the first introduced principles for gas sensing and biosensing in 1983. The sensing platform has been hand-in-hand with the plethora of sensing technology advancement including nanostructuring, optical technology, fluidic technology, and light source technology, which contribute to substantial progress in SPR sensor evolution. Nevertheless, the commercial products of SPR sensors in the market still require high-cost investment, component, and operation, leading to unaffordability for their implementation in a low-cost point of care (PoC) or laboratories. In this article, we present a comprehensive review of SPR sensor development including the state of the art from a perspective of light source technology trends. Based on our review, the trend of SPR sensor configurations, as well as its methodology and optical designs are strongly influenced by the development of light source technology as a critical component. These simultaneously offer new underlying principles of SPR sensor towards miniaturization, portability, and disposability features. The low-cost solid-state light source technology, such as laser diode, light-emitting diode (LED), organic light emitting diode (OLED) and smartphone display have been reported as proof of concept for the future of low-cost SPR sensor platforms. Finally, this review provides a comprehensive overview, particularly for SPR sensor designers, including emerging engineers or experts in this field.

Rapid detection and quantification of Enterovirus 71 by a portable surface plasmon resonance biosensor.

This study presents the first report on a label-free detection and rapid quantification method for human enterovirus 71 (EV71) using a portable surface plasmon resonance (SPR) system. The SPR sensor instrument was configured to run on low power in a miniaturized platform to improve the device portability for a wider application both in laboratories and in the field. A color tunable organic light emitting diode in red spectrum was attached on a trapezoidal prism for the disposable light source module. The SPR signal processing using integration area under the reflectivity curve is applied for optimum signal to noise ratio (SNR) enhancement. The major capsid protein VP1 of EV71 was selected as the biomarker target in the detection study. The experimental time required for the EV71 quantification was reduced from 6 days using the conventional viral plaque assay to several minutes using the proposed method. The study results establish a detection limit of approximately 67 virus particles per milliliter (vp/ml) of EV71 in a Dulbecco's modified Eagle's medium. The VP1 detection in the portable SPR biosensor had a detection limit of approximately 4.8pg/ml in the PBS buffer. Therefore, the proposed direct EV71 viral particle quantification method can be rapidly performed in real time, with high sensitivity and less labor and without assays or fluorescence.

Graphene oxide-based SPR biosensor chip for immunoassay applications.

This work develops a highly sensitive immunoassay sensor for use in graphene oxide sheet (GOS)-based surface plasmon resonance (SPR) chips. This sensing film, which is formed by chemically modifying a GOS surface, has covalent bonds that strongly interact with the bovine serum albumin (BSA), explaining why it has a higher sensitivity. This GOS film-based SPR chip has a BSA concentration detection limit that is 100 times higher than that of the conventional Au-film-based sensor. The affinity constants (K A) on the GOS film-based SPR chip and the conventional SPR chip for 100 µg/ml BSA are 80.82 × 10(6) M(-1) and 15.67 × 10(6) M(-1), respectively. Therefore, the affinity constant of the GOS film-based SPR chip is 5.2 times higher than that of the conventional chip. With respect to the protein-protein interaction, the SPR sensor capability to detect angle changes at a low concentration anti-BSA of 75.75 nM on the GOS film-based SPR chip and the conventional SPR chip is 36.1867 and 26.1759 mdeg, respectively. At a high concentration, anti-BSA of 378.78 nM on the GOS film-based SPR chip and the conventional SPR chip reveals two times increases in the SPR angle shift. Above results demonstrate that the GOS film is promising for highly sensitive clinical diagnostic applications.