Enhancing the reliability of particulate matter sensing by multivariate Tobit model using weather and air quality data.

Low-cost particulate matter (PM) sensors have been widely used following recent sensor-technology advancements; however, inherent limitations of low-cost monitors (LCMs), which operate based on light scattering without an air-conditioning function, still restrict their applicability. We propose a regional calibration of LCMs using a multivariate Tobit model with historical weather and air quality data to improve the accuracy of ambient air monitoring, which is highly dependent on meteorological conditions, local climate, and regional PM properties. Weather observations and PM2.5 (fine inhalable particles with diameters ≤ 2.5 µm) concentrations from two regions in Korea, Incheon and Jeju, and one in Singapore were used as training data to build a visibility-based calibration model. To validate the model, field measurements were conducted by an LCM in Jeju and Singapore, where R2 and the error after applying the model in Jeju improved (from 0.85 to 0.88) and reduced by 44% (from 8.4 to 4.7 µg m-3), respectively. The results demonstrated that regional calibration involving air temperature, relative humidity, and other local climate parameters can efficiently correct the bias of the sensor. Our findings suggest that the proposed post-processing using the Tobit model with regional weather and air quality data enhances the applicability of LCMs.

Label-free quantitative measurement of cardiovascular dynamics in a zebrafish embryo using frequency-comb-referenced-quantitative phase imaging.

SIGNIFICANCE: Real-time monitoring of the heart rate and blood flow is crucial for studying cardiovascular dysfunction, which leads to cardiovascular diseases. AIM: This study aims at in-depth understanding of high-speed cardiovascular dynamics in a zebrafish embryo model for various biomedical applications via frequency-comb-referenced quantitative phase imaging (FCR-QPI). APPROACH: Quantitative phase imaging (QPI) has emerged as a powerful technique in the field of biomedicine but has not been actively applied to the monitoring of circulatory/cardiovascular parameters, due to dynamic speckles and low frame rates. We demonstrate FCR-QPI to measure heart rate and blood flow in a zebrafish embryo. FCR-QPI utilizes a high-speed photodetector instead of a conventional camera, so it enables real-time monitoring of individual red blood cell (RBC) flow. RESULTS: The average velocity of zebrafish's RBCs was measured from 192.5 to 608.8 µm / s at 24 to 28 hour-post-fertilization (hpf). In addition, the number of RBCs in a pulsatile blood flow was revealed to 16 cells/pulse at 48 hpf. The heart rates corresponded to 94 and 142 beats-per-minute at 24 and 48 hpf. CONCLUSIONS: This approach will newly enable in-depth understanding of the cardiovascular dynamics in the zebrafish model and possible usage for drug discovery applications in biomedicine.

Hygroscopic properties of particulate matter and effects of their interactions with weather on visibility.

The hygroscopic property of particulate matter (PM) influencing light scattering and absorption is vital for determining visibility and accurate sensing of PM using a low-cost sensor. In this study, we examined the hygroscopic properties of coarse PM (CPM) and fine PM (FPM; PM2.5) and the effects of their interactions with weather factors on visibility. A censored regression model was built to investigate the relationships between CPM and PM2.5 concentrations and weather observations. Based on the observed and modeled visibility, we computed the optical hygroscopic growth factor, [Formula: see text], and the hygroscopic mass growth, [Formula: see text], which were applied to PM2.5 field measurement using a low-cost PM sensor in two different regions. The results revealed that the CPM and PM2.5 concentrations negatively affect visibility according to the weather type, with substantial modulation of the interaction between the relative humidity (RH) and PM2.5. The modeled [Formula: see text] agreed well with the observed [Formula: see text] in the RH range of the haze and mist. Finally, the RH-adjusted PM2.5 concentrations based on the visibility-derived hygroscopic mass growth showed the accuracy of the low-cost PM sensor improved. These findings demonstrate that in addition to visibility prediction, relationships between PMs and meteorological variables influence light scattering PM sensing.

A rotationally focused flow (RFF) microfluidic biosensor by density difference for early-stage detectable diagnosis.

Label-free optical biosensors have received tremendous attention in point-of-care testing, especially in the emerging pandemic, COVID-19, since they advance toward early-detection, rapid, real-time, ease-of-use, and low-cost paradigms. Protein biomarkers testings require less sample modification process compared to nucleic-acid biomarkers'. However, challenges always are in detecting low-concentration for early-stage diagnosis. Here we present a Rotationally Focused Flow (RFF) method to enhance sensitivity(wavelength shift) of label-free optical sensors by increasing the detection probability of protein-based molecules. The RFF is structured by adding a less-dense fluid to focus the target-fluid in a T-shaped microchannel. It is integrated with label-free silicon microring resonators interacting with biotin-streptavidin. The suggested mechanism has demonstrated 0.19 fM concentration detection along with a significant magnitudes sensitivity enhancement compared to single flow methods. Verified by both CFD simulations and fluorescent flow-experiments, this study provides a promising proof-of-concept platform for next-generation lab-on-a-chip bioanalytics such as ultrafast and early-detection of COVID-19.

Injection-seeded high-repetition-rate short-pulse micro-laser based on upconversion nanoparticles.

We demonstrate a high repetition-rate upconversion green pulsed micro-laser, which is prepared by the fast thermal quenching of lanthanide-doped upconversion nanoparticles (UCNPs) via femtosecond-laser direct writing. The outer rim of the prepared upconversion hemi-ellipsoidal microstructure works as a whispering-gallery-mode (WGM) optical resonator for the coherent photon build-up of third-harmonic ultra-short seed pulses. When near-infrared (NIR) femtosecond laser pulses of wavelength 1545 nm are focused onto the upconversion WGM resonator, the optical third-harmonic is generated at 515 nm together with the upconversion luminescence. The weak third-harmonic (TH) seed pulses are coherently amplified in the hemi-ellipsoidal upconversion resonator as a result of the resonant interaction between the incident femtosecond laser field, the TH, the upconversion luminescence and the WGM. This upconversion lasing preserves the original repetition rate of the NIR pump laser and the output polarization state is also coherently aligned to the pump laser polarization. Because of the isotropic nature of the upconversion micro-ellipsoids, the upconversion lasing shows maximum intensity with a linearly polarized pump beam and minimum intensity with a circularly polarized pump beam. Our scheme devised for realizing high-repetition-rate lasing at higher photon energies in a compact micro platform will open up new ways for on-chip optical information processing, high-throughput microfluidic sensing, and localized micro light sources for optical memories.

Surface third-harmonic generation at a two-photon-polymerized micro-interferometer for real-time on-chip refractive index monitoring.

A micro-interferometer based on surface third-harmonic generation (THG) at two-photon-polymerized SU-8 cuboids for real-time monitoring of the refractive index changes of target fluids, which can be easily integrated into microfluidic photonic systems, is demonstrated. The third-harmonic (TH) interferogram is selectively generated only from the target volume by a simple vertical pumping, thereby eliminating the needs for complicated coupling and alignments. The dependence of the generated TH to the input pump polarization state is thoroughly investigated. The THG efficiency by linearly polarized excitation is found to be 2.6 × 10-7, which is the most efficient at the SU-8-air interface and independent of the input polarization direction. The THG efficiency from the SU-8-air interface is 12.17 times higher than that from the glass-air interface and 4.93 times higher than that from the SU-8-glass interface. Real-time monitoring of argon gas pressure is demonstrated using the micro- interferometer. The surface TH from two-photon-polymerized 3D structures offers novel design flexibility to the nonlinear optical light sources for microfluidic and microelectronic devices.

Inkjet-Printed Porous Silver Thin Film as a Cathode for a Low-Temperature Solid Oxide Fuel Cell.

In this work we report a porous silver thin film cathode that was fabricated by a simple inkjet printing process for low-temperature solid oxide fuel cell applications. The electrochemical performance of the inkjet-printed silver cathode was studied at 300-450 °C and was compared with that of silver cathodes that were fabricated by the typical sputtering method. Inkjet-printed silver cathodes showed lower electrochemical impedance due to their porous structure, which facilitated oxygen gaseous diffusion and oxygen surface adsorption-dissociation reactions. A typical sputtered nanoporous silver cathode became essentially dense after the operation and showed high impedance due to a lack of oxygen supply. The results of long-term fuel cell operation show that the cell with an inkjet-printed cathode had a more stable current output for more than 45 h at 400 °C. A porous silver cathode is required for high fuel cell performance, and the simple inkjet printing technique offers an alternative method of fabrication for such a desirable porous structure with the required thermal-morphological stability.

Proton-conducting Micro-solid Oxide Fuel Cells with Improved Cathode Reactions by a Nanoscale Thin Film Gadolinium-doped Ceria Interlayer.

An 8 nm-thick gadolinium-doped ceria (GDC) layer was inserted as a cathodic interlayer between the nanoscale proton-conducting yttrium-doped barium zirconate (BZY) electrolyte and the porous platinum cathode of a micro-solid oxide fuel cell (µ-SOFC), which has effectively improved the cathode reaction kinetics and rendered high cell power density. The addition of the GDC interlayer significantly reduced the cathodic activation loss and increased the peak power density of the µ-SOFC by 33% at 400 °C. The peak power density reached 445 mW/cm(2) at 425 °C, which is the highest among the reported µ-SOFCs using proton-conducting electrolytes. The impressive performance was attributed to the mixed protonic and oxygen ionic conducting properties of the nano-granular GDC, and also to the high densities of grain boundaries and lattice defects in GDC interlayer that favored the oxygen incorporation and transportation during the oxygen reduction reaction (ORR) and the water evolution reaction at cathode.

A Silicon-Based Nanothin Film Solid Oxide Fuel Cell Array with Edge Reinforced Support for Enhanced Thermal Mechanical Stability.

A silicon-based micro-solid oxide fuel cell (µ-SOFC) with electrolyte membrane array embedded in a thin silicon supporting membrane, featuring a unique edge reinforcement structure, was demonstrated by utilizing simple silicon micromachining processes. The square silicon supporting membrane, fabricated by combining deep reactive ion etching and through-wafer wet etching processes, has thicker edges and corners than the center portion of the membrane, which effectively improved the mechanical stability of the entire fuel cell array during cell fabrication and cell operation. The 20 µm thick single crystalline silicon membrane supports a large number of 80 nm thick free-standing yttria-stabilized zirconia (YSZ) electrolytes. The fuel cell array was stably maintained at the open circuit voltage (OCV) of 1.04 V for more than 30 h of operation at 350 °C. A high peak power density of 317 mW/cm(2) was obtained at 400 °C. During a rigorous in situ thermal cycling between 150 and 400 °C at a fast cooling and heating rate of 25 °C/min, the OCV of the µ-SOFC recovered to its high value of 1.07 V without any drop caused by membrane failure, which justifies the superior thermal stability of this novel cell architecture.

Direct observation of nanoscale Pt electrode agglomeration at the triple phase boundary.

Nanoporous platinum electrode thin films were delaminated from yttria-stabilized zirconia (YSZ) substrates via double cantilever beam delamination to reveal the structure located at the interface between electrode and electrolyte. The thermally driven morphological evolution between the electrode top surface and the substrate contact interface of agglomerated nanoporous platinum thin films were compared. We found the temperature required for significant agglomeration to occur was approximately 100 °C higher at the electrolyte contact interface side than at the top surface side. Judging the reaction active site from the electrode top surface could be inaccurate because higher resistance of thermal agglomeration at the interface could retain the reaction active site during fuel cell operation.

Plasma-enhanced atomic layer deposition of nanoscale yttria-stabilized zirconia electrolyte for solid oxide fuel cells with porous substrate.

Nanoscale yttria-stabilized zirconia (YSZ) electrolyte film was deposited by plasma-enhanced atomic layer deposition (PEALD) on a porous anodic aluminum oxide supporting substrate for solid oxide fuel cells. The minimum thickness of PEALD-YSZ electrolyte required for a consistently high open circuit voltage of 1.17 V at 500 °C is 70 nm, which is much thinner than the reported thickness of 180 nm using nonplasmatic ALD and is also the thinnest attainable value reported in the literatures on a porous supporting substrate. By further reducing the electrolyte thickness, the grain size reduction resulted in high surface grain boundary density at the cathode/electrolyte interface.

Biotin-streptavidin binding interactions of dielectric filled silicon bulk acoustic resonators for smart label-free biochemical sensor applications.

Sensor performance of a dielectric filled silicon bulk acoustic resonator type label-free biosensor is verified with biotin-streptavidin binding interactions as a model system. The mass sensor is a micromachined silicon square plate with a dielectric filled capacitive excitation mechanism. The resonance frequency of the biotin modified resonator decreased 315 ppm when exposed to streptavidin solution for 15 min with a concentration of 10(-7) M, corresponding to an added mass of 3.43 ng on the resonator surface. An additional control is added by exposing a bovine serum albumin (BSA)-covered device to streptavidin in the absence of the attached biotin. No resonance frequency shift was observed in the control experiment, which confirms the specificity of the detection. The sensor-to-sensor variability is also measured to be 4.3%. Consequently, the developed sensor can be used to observe in biotin-streptavidin interaction without the use of labelling or molecular tags. In addition, biosensor can be used in a variety of different immunoassay tests.

Nano-patterned dual-layer ITO electrode of high brightness blue light emitting diodes using maskless wet etching.

We propose a dual-layer transparent Indium Tin Oxide (ITO) top electrode scheme and demonstrate the enhancement of the optical output power of GaN-based light emitting diodes (LEDs). The proposed dual-layer structure is composed of a layer with randomly distributed sphere-like nano-patterns obtained solely by a maskless wet etching process and a pre-annealed bottom layer to maintain current spreading of the electrode. It was observed that the surface morphologies and optoelectronic properties are dependent on etching duration. This electrode significantly improves the optical output power of GaN-based LEDs with an enhancement factor of 2.18 at 100 mA without degradation in electrical property when compared to a reference LED.

Solid oxide fuel cell with corrugated thin film electrolyte.

A low temperature micro solid oxide fuel cell with corrugated electrolyte membrane was developed and tested. To increase the electrochemically active surface area, yttria-stabilized zirconia membranes with thickness of 70 nm were deposited onto prepatterned silicon substrates. Fuel cell performance of the corrugated electrolyte membranes released from silicon substrate showed an increase of power density relative to membranes with planar electrolytes. Maximum power densities of the corrugated fuel cells of 677 mW/cm2 and 861 mW/cm2 were obtained at 400 and 450 degrees C, respectively.