Functionalized HgTe nanoparticles promote laser-induced solid phase ionization/dissociation for comprehensive glycan sequencing.

Glycoconjugates are ubiquitously present and play a critical role in various biological processes. Due to their low stability and incredibly high degree of structural diversity, the structural characterization of glycan generally requires chemical derivatization and sophisticated instrumentation. Herein, we report a method for complicated glycan characterization in a single assay by employing 2,5-dihydroxybenzoic acid functionalized mercury telluride nanoparticles (HgTe@DHB NPs) as a dual ionization-dissociation element in matrix-assisted laser desorption/ionization mass spectrometry. Using a linear glycan, HgTe@DHB NPs promote laser-induced extensive and intense dissociation of the glycan, superior to HgTe microparticles and other inorganic nanoparticles (TiO2, ZnO, and Mn2O3 NPs). Abundant generation of diagnostic glycosidic (Y-, and B-type ions) and cross-ring cleavage (A-type ions) ions permits unambiguous determination of the composition, sequence, branching, and linkage of labile sialylated glycans. The general utility of this approach was demonstrated by the characterization of labile sialylated glycans and two sets of complicated isomeric glycans. This phenomenon was delineated further by investigating the NP's physico-chemical characteristics, revealing that their nanoscale-dependent thermodynamic properties, including UV absorption, photoelectron release dynamics and thermal energy, were the key to levitate temperature synergistically, thus inducing spontaneous glycan decomposition during the nanoparticle-assisted laser desorption-ionization process. Our results show that this "pseudo-MS/MS" obtained by HgTe@DHB can be beneficial for the analysis of biologically relevant and more complicated carbohydrates, without the need for chemical pre-derivatization and conventional tandem mass spectrometry.

High-directional light source using photon recycling with a retro-reflective Dome incorporated with a textured LED die surface.

This paper demonstrates a novel retro-reflective dome that enhances the directionality of a light emitting diode (LED) by recycling photons reflected by a textured LED die surface. A simulation model is developed to describe both the photon recycling process within the dome and the role of specific pyramid patterns on the top surface of the LED die. Advanced simulations showed that a perfectly polished surface with 100% reflectivity potentially enhances the directionality of the dome by 340%, 250%, and 240% using reflective domes with 10°, 20°, and 30° light cones, respectively. In the experiment, the directionality of the domes exhibiting surface imperfections is enhanced by approximately 160%, 150%, and 130% using 10°, 20°, and 30° light cones, respectively. By incorporating a textured top surface on the LED die, the proposed dome effectively increases the directionality of the LED light source.

Perceptions towards the COVID-19 Pandemic during Different Lockdown Levels among International Students in Taiwan.

International students face many impediments under the COVID-19 pandemic. The objectives of this study are to assess the association between the perceptions of international students and the lockdown policy for COVID-19. In 2021, three different levels of lockdown policy were enforced, including level I from January to April, level III from May to July, and level II from August to December. We conducted three surveys for international graduate students using a validated questionnaire during the different lockdown levels. We collected 185, 119, and 83 valid questionnaires in level I, II, and III, respectively. There were linear trends in the correlations of lockdown policy with the knowledge (p = 0.052), attitudes (p = 0.002), and practices (p < 0.001) of COVID-19. In brief, the stricter the lockdown policy, the better the students adhered to sufficient knowledge, positive attitudes, and healthy practices. Furthermore, there were significant linear correlations of lockdown policy with the transportation, school study, leisure, family life, and diet behavior. In conclusion, lockdown policy had important impacts on the knowledge, attitudes, practices, and daily lives of international students. The findings indicated that the lockdown system and its corresponding measures appear to affect perceptions in a positive way.

Site-specific immobilization of enzymes on magnetic nanoparticles and their use in organic synthesis.

Magnetic nanoparticles (MNPs) are attractive materials that serve as a support for enzyme immobilization and facilitate separations by applying an external magnetic field; this could facilitate the recycling of enzymes and broaden their applications in organic synthesis. Herein, we report the methods for the immobilization of water-soluble and membrane-bound enzymes, and the activity difference between free and immobilized enzymes is discussed. Sialyltransferase (PmST1, from Pasteurella multocida ) and cytidine monophosphate (CMP)-sialic acid synthetase (CSS, from Neisseria meningitides ) were chosen as water-soluble enzymes and expressed using an intein expression system. The enzymes were site-specifically and covalently immobilized on PEGylated-N-terminal cysteine MNPs through native chemical ligation (NCL). Increasing the length of the PEG linker between the enzyme and the MNP surface increased the activity of the immobilized enzymes relative to the free parent enzymes. In addition, the use of a fluorescent acceptor tag for PmST1 affected enzyme kinetics. In contrast, sialyltransferase from Neisseria gonorrheae (NgST, a membrane-bound enzyme) was modified with a biotin-labeled cysteine at the C-terminus using NCL, and the enzyme was then assembled on streptavidin-functionalized MNPs. Using a streptavidin-biotin interaction, it was possible to immobilize NgST on a solid support under mild ligation conditions, which prevented the enzyme from high-temperature decomposition and provided an approximately 2-fold increase in activity compared to other immobilization methods on MNPs. Finally, the ganglioside GM3-derivative (sialyl-lactose derivative) was synthesized in a one-pot system by combining the use of immobilized PmST1 and CSS. The enzymes retained 50% activity after being reused ten times. Furthermore, the results obtained using the one-pot two-immobilized-enzyme system demonstrated that it can be applied to large-scale reactions with acceptable yields and purity. These features make enzyme-immobilized MNPs applicable to organic synthesis.

Collimating lamp with well color mixing of red/green/blue LEDs.

A novel light luminaire is proposed and experimentally analyzed, which efficiently mixes and projects the tunable light from red, green and blue (RGB) light-emitting diodes (LEDs). Simultaneous light collimation and color mixing is a challenging task because most collimators separate colors, and most color mixers spread the light beam. Our method is simple and compact; it only uses a short light pipe, a thin diffuser, and a total internal reflection lens. We performed an experimental study to find a balance between optical efficiency and color uniformity by changing light recycling and color mixing.

Calculating model of light transmission efficiency of diffusers attached to a lighting cavity.

A lighting cavity is a reflecting box with light sources inside. Its exit side is covered with a diffuser plate to mix and distribute light, which addresses a key issue of luminaires, display backlights, and other illumination systems. We derive a simple but precise formula for the optical efficiency of diffuser plates attached to a light cavity. We overcome the complexity of the scattering theory and the difficulty of the multiple calculations involved, by carrying out the calculation with a single ray of light that statistically represents all the scattered rays. We constructed and tested several optical cavities using light-emitting diodes, bulk-scattering diffusers, white scatter sheets, and silver coatings. All measurements are in good agreement with predictions from our optical model.

Analysis of the far-field region of LEDs.

Versatility in the design of optical systems is one of the key features of light-emitting diodes (LEDs) that has attracted considerable attention. In the analysis of systems using LEDs, it is useful to know if the distance is far enough from the LED to allow the radiation pattern to be simulated by the point source approach. We propose three far-zone conditions for LED light modeling: the far-field distance, and for practical purposes the quasi far-field and minimum far-field distances. Different types of LEDs have different far-field ranges. We analyze these differences by modulating key parameters like geometrical structure of encapsulating lens, chip size, chip shape, chip position, and package errors. We find that far-field region considerably depends more on the shape of both lens and chip than all other parameters.

Precise optical modeling for silicate-based white LEDs.

In this paper, as to our best knowledge, we propose and demonstrate the first precise phosphor modeling scheme to simulate the chromatic performance of white LEDs with silicate phosphors. The phosphor model is useful to accurately simulate the power ratio of the blue and yellow lights emitted by the white LEDs and is important in white LED package.

Precise optical model of multi-chip white LEDs.

A single-chip white light LED is commonly modeled by considering the phosphor coating as a homogeneous Lambertian light source. However, this approach leads to an incorrect optical simulation of phosphor-coated multi-chip LEDs due to the presence of a previously unreported spatial distribution of emission spots across the phosphor layer. We introduce "weighting" factors based on position-dependent light strength across the phosphor surface in order to improve the model accuracy. Following the modeling algorithm in the mid-field region, we have built up a precise and practical optical model by using Monte Carlo ray tracing and weighting factors. We measure the LED radiation distribution at several representative distances to test the model performance. In all cases, the accuracy is higher than 99.5% in normalized cross correlation between the simulated pattern and experimental measurement.

Light extraction analysis of GaN-based light-emitting diodes with surface texture and/or patterned substrate.

Light extraction analysis of GaN-based light-emitting diodes (LEDs) with Monte Carlo ray tracing is presented. To obtain high light extraction efficiency, periodic structures introduced on the top surface and/or on the substrate of various types of LED are simulated, including wire bonding, flip chip and Thin GaN. Micro pyramid array with an apex angle from 20o to 70o is shown to effectively improve the light extraction efficiency. In addition, for an LED encapsulated within an epoxy lens, the patterned substrate with pyramid array is found to be a more effective way to increase light extraction efficiency than the surface texture.

Sequential one-pot enzymatic synthesis of oligo-N-acetyllactosamine and its multi-sialylated extensions.

A simple and efficient protocol for the preparative-scale synthesis of various lengths of oligo-N-acetyllactosamine (oligo-LacNAc) and its multi-sialylated extensions is described. The strategy utilizes one thermophilic bacterial thymidylyltransferase (RmlA) coupled with corresponding sugar-1-phosphate kinases to generate two uridine diphosphate sugars, UDP-galactose and UDP-N-acetylglucosamine. By incorporating glycosyltransferases, oligo-LacNAcs and their sialylated analogs were synthesized.

Fabrication of carbohydrate microarrays through boronate formation.

A straightforward method for fabricating a stable and covalent carbohydrate microarray based on boronate formation between the hydroxyl groups of carbohydrate and boronic acid (BA) on the glass surface was used to identify carbohydrate-protein interactions.