Ms Exposure Time Research Articles

Snapshot computed tomographic microscopic imaging spectrometer and its video-level tracking of poisonous Microcystis aeruginosa cells in mixed algae

Conventional microscopic spectral imaging suffers from extended scanning times across wavelength or spatial dimension. To improve capabilities of dynamic microscopic spectral imaging, we developed a snapshot computed tomographic microscopic imaging spectrometer (CTMIS) based on the zeroth and first orders dispersive diffraction of a two-dimensional grating. Utilizing the CTMIS-UNET reconstruction algorithm, we can reconstruct a spectral cube (541x541x26) for each frame of micro spectral imaging video. Experimental results demonstrate a sub-4 μm spatial resolution achievable through a 20x objective lens and a spectral resolution better than 10 nm among 450–700 nm, while maintaining spectral cosine similarities exceeding 0.9989 when comparing reconstructed spectra with ground truth data. Spectral imaging videos of four species of algae and mixed algae were captured under 10 ms exposure time using the CTMIS system. Leveraging the self-developed UNET-SI26 algae recognition network, precise identification and tracking of four types of algae and poisonous microcysts aeruginosa in mixed algae were conducted. The pixel-level recognition accuracy exceeds 95 %, while the accuracy for counting the numbers of different types of cells surpasses 85 %, offering an efficient and accurate spectral imaging method for real-time monitoring and early warning of harmful algae at the cellular level.

Developing a robust sensor for infrared imaging bolometers.

A new type of large area sensor for infrared imaging bolometers has been developed. It replaces the thin and fragile free-standing metal foils, which typically have been used, with a multi-layer coated sapphire (or diamond) substrate. Sapphire is transparent to mid-infrared wavelengths, is robust against transients, and can be thick enough to even be the vacuum window. The primary radiation absorber is still a thin deposited metal layer, but now it is partially insulated from the supporting sapphire substrate by a black (carbon-based) layer, which also acts as a blackbody remitter. Test results indicate 6× more noise equivalent power density (estimated NEPD = 23 W/m2 at 5ms camera exposure time, foil temperature decay time 60ms) for a 2μm gold-coated sapphire disk compared to estimated NEP = 4 W/m2 at 1.8ms exposure time, with foil decay time 420ms, for a nominal 2.5μm thick platinum-free-standing foil.

Toward a Wireless Image Sensor for Real-Time Fluorescence Microscopy in Cancer Therapy.

We present a mm-sized, ultrasonically powered lensless CMOS image sensor as a progress towards wireless fluorescence microscopy. Access to biological information within the tissue has the potential to provide insights guiding diagnosis and treatment across numerous medical conditions including cancer therapy. This information, in conjunction with current clinical imaging techniques that have limitations in obtaining images continuously and lack wireless compatibility, can improve continual detection of multicell clusters deep within tissue. The proposed platform incorporates a 2.4 × 4.7 mm2 integrated circuit (IC) fabricated in TSMC 0.18 µm, a micro laser diode (µLD), a single piezoceramic and off-chip storage capacitors. The IC consists of a 36 × 40 array of capacitive trans-impedance amplifier-based pixels, wireless power management and communication via ultrasound and a laser driver all controlled by a Finite State Machine. The piezoceramic harvests energy from the acoustic waves at a depth of 2 cm to power up the IC and transfer 11.5 kbits/frame via backscattering. During Charge-Up, the off-chip capacitor stores charge to later supply a high-power 78 mW µLD during Imaging. Proof of concept of the imaging front end is shown by imaging distributions of CD8 T-cells, an indicator of the immune response to cancer, ex vivo, in the lymph nodes of a functional immune system (BL6 mice) against colorectal cancer consistent with the results of a fluorescence microscope. The overall system performance is verified by detecting 140 µm features on a USAF resolution target with 32 ms exposure time and 389 ms ultrasound backscattering.

Using optimized particle imaging of micro-Raman to characterize microplastics in water samples

Characterizing the chemical properties, morphologies, size, and quantities of microplastics (MPs) in water samples with high precision is critically important for understanding the environmental behaviors of MPs. Traditional detection methods, such as Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy point-by-point detection, provide worthy reference techniques but are time- and labor-consuming. We established a super time-saving and high-precision technique to characterize MPs using micro-Raman automatic particle identification (MR-API). Based on the identification of PS spheres, screen magnification, exposure time, and the number of scans are selected as crucial detection parameters for MR-API analysis, which highly affect the precision of the results. Detecting particles down to 1 μm requires magnification of the mosaic until the scale showed 200 μm. The recommended setting parameters were 83.33 or 100 ms exposure time, 20 scans, 7 mW laser power, and 1 μm image pixel size, suitable for polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET), polyethylene (PE), polyvinyl chloride (PVC), and polyamide (PA) particles detection. With the complete procedure of MR-API measurements, the recovery of MPs was 61.67–90.00 %. To validate the feasibility of the MR-API, the method was used to detect samples of known plastic types (mask leachates) and unknown plastic types (urban lake). A total of 4540 particles in the sample of mask leachates consuming 35 h 50 min 43 s, and 0.92 ± 0.49 % of particles were identified as MPs. The urban river sample efficiently identified PP, PET, PE, PVC, PS, EVA, and VC/VAC MPs using this method. The detected MPs size ranged from 8.3 to 5000 μm, saving 75.03 % and 58.38 % of the time compared to the conventional micro-FTIR and micro-Raman point-by-point methods, respectively. Therefore, this method is effective for detecting MPs in the environmental samples and has excellent prospects.

Enhanced flotation of high density polyethylene and polyvinyl chloride mixtures based on clean corona modification

The dramatic increase in waste plastics has caused harm to both human health and the environment. Due to the variety of plastic products and their complex components, it is a technical challenge to effectively separate them. High density polyethylene (HDPE) and polyvinyl chloride (PVC) both have a high detection frequency in the common solid waste streams like automobile shredder residue (ASR), and due to the similar properties of different plastics, their mixtures lack reliable separation methods. Specifically for this kind of mixtures, this work provided a novel separation strategy with prepositive corona modification and postpositive flotation units. To obtain the optimal separation parameters, flotation performance of HDPE and PVC were investigated under different modification conditions controlled by the corona polarity, discharge power and exposure time. Besides, the modification mechanism was revealed through multi-characterization tests on surface morphology, molecular weight, contact angle, and spectrums. The results showed that corona discharge can generate non-thermal plasma to activate the surfaces of HDPE and PVC, thereby increasing their floatability difference. Under the optimal conditions of 300 W positive discharge power and 8000 ms exposure time, HDPE turned into the sinking tail while PVC still accumulated in the floating product, leading to the maximum separation recovery and purity of 96.36% and 97.01%, respectively. Amorphous low-molecular weight oxidic substances emerged on the upper layer of polymers was verified by the multi-characterization, representing in varying degrees of oxidation and chain scission (HDPE > PVC). Since the corona modification is reagent-free-addition and rapid in-line process, this work showed great advantages in the total cost of separation (only 450.03 USD/t) and potential environmental benefits, which also paves a clean way for the recycling of HDPE and PVC.

Correlation between X-ray tube current exposure time and X-ray photon number in GATE.

X-ray image quality relies heavily on the emitted X-ray photon number which depends on X-ray tube current and exposure time. To accurately estimate the absorbed dose in an imaging protocol, it is better to simulate the X-ray imaging with a Monte Carlo platform such as GATE (Geant4 Application for Tomographic Emission). Although input of GATE is the X-ray photon number of the simulated X-ray tube, it lacks a good way to setup the photon number for a desired X-ray tube current setting. To provide a method to correlate the experimental X-ray tube current exposure time and the X-ray photon number in GATE. The accumulated radiation dose of a micro-computed tomography (CT) X-ray tube was recorded at different current exposure times with a general-purpose ion chamber. GATE was used to model the experimental microCT imaging system and calculate the total absorbed dose (cGy) in the sensitive volume of the ion chamber with different X-ray photon numbers. Linear regression models are used to establish a correlation between the estimated X-ray photon number and the X-ray tube settings. At first, one model establishes the relationship between the experimentally measured dose and the X-ray tube setting. Then, another model establishes a relationship between the simulated dose and the X-ray number in GATE. At last, by correlating these two models, a regression model to estimate the X-ray output number from an experimental X-ray tube setting (mAs) is obtained. For a typical micro-CT scan, the X-ray tube is operated at 50 kVp and 0.5 mA for a 500 ms exposure time per projection (0.25 mAs). For these X-ray imaging parameters, the X-ray number per projection is estimated to be 3.613×106 with 1.0 mm Al filter. The findings of this work provide an approach to correlate the experimental X-ray tube current exposure time to the X-ray photon number in the GATE simulation of the X-ray tube to more accurately determine radiation dose for an imaging protocol.

PCIe-based FPGA-GPU heterogeneous computation for real-time multi-emitter fitting in super-resolution localization microscopy.

Real-time multi-emitter fitting is a key technology for advancing super-resolution localization microscopy (SRLM), especially when it is necessary to achieve dynamic imaging quality control and/or optimization of experimental conditions. However, with the increase of activation densities, the requirements in the computing resources would increase rapidly due to the complexity of the fitting algorithms, making it difficult to realize real-time multi-emitter fitting for emitter density more than 0.6 mol/µm2 in large field of view (FOV), even after acceleration with the popular Graphics Processing Unit (GPU) computation. Here we adopt the task parallelism strategy in computer science to construct a Peripheral Component Interconnect Express (PCIe) based all-in-one heterogeneous computing platform (AIO-HCP), where the data between two major parallel computing hardware, Field Programmable Gate Array (FPGA) and GPU, are interacted directly and executed simultaneously. Using simulated and experimental data, we verify that AIO-HCP could achieve a data throughput of up to ∼ 1.561 GB/s between FPGA and GPU. With this new platform, we develop a multi-emitter fitting method, called AIO-STORM, under big data stream parallel scheduling. We show that AIO-STORM is capable of providing real-time image processing on raw images with 100 µm × 100 µm FOV, 10 ms exposure time and 5.5 mol/µm2 structure density, without scarifying image quality. This study overcomes the data throughput limitation of heterogeneous devices, demonstrates the power of the PCIe-based heterogeneous computation platform, and offers opportunities for multi-scale stitching of super-resolution images.

Synthetic exposure with a CMOS camera for multiple exposure speckle imaging of blood flow

Speckle contrast imaging is an established technique to obtain relative blood flow maps over wide fields of view. A major improvement of the method relies on the acquisition of raw speckle images at different exposure times but requires simultaneous modulation of a laser pulse in duration and intensity and precise synchronization with a camera. This complex instrumentation has limited the use of multiple exposure speckle imaging. We evaluate here the use of a CMOS camera for a simplified approach based on synthetic exposure images created from the sum of successive frames acquired at a 1 ms exposure time. Both methods have been applied to evaluate controlled flows in micro-channels. The contribution of noises to the speckle contrast have been quantified and compared. Dark, readout and shot noise contributions to the total contrast remain constant for modulated exposure, while all these contributions decrease with increasing exposure time for synthetic exposure. The relative contribution of noises to speckle contrast depends on the level of illumination and the exposure time. Guidelines for flow measurements and limitations of the use of a CMOS camera with a limited frame rate for synthetic exposure acquisition scheme are discussed. The synthetic exposure method is simple to implement and should facilitate the translation of multiple exposure speckle imaging to clinical set-ups.

Experimentally validated x-ray image simulations of 50 μm x-ray PIV tracer particles

We evaluate Beer–Lambert (BL) ray-tracing and Monte Carlo N-Particle (MCNP) photon tracking simulations for prediction and comparison of x-ray imaging system performance. These simulation tools can aid the methodical design of laboratory-scale x-ray particle image velocimetry (XPIV) experiments and tracer particles by predicting image quality. Particle image signal-to-noise ratio (SNR) is used as the metric of system performance. Simulated and experiment data of hollow, silver-coated, glass sphere tracer particles (AGSF-33) are compared. As predicted by the simulations, the AGSF-33 particles are visible with a SNR greater than unity in 100 ms exposure time images, demonstrating their potential as x-ray PIV or particle tracking velocimetry (XPTV) tracers. The BL approach predicts the image contrast, is computationally inexpensive, and enables the exploration of a vast parameter space for system design. MCNP simulations, on the other hand, predict experiment images slightly more accurately, but are more than an order of magnitude more computationally expensive than BL simulations. For most practical XPIV system design applications, the higher computational expense of MCNP is likely not justified by the modest accuracy improvement compared to BL.

Few-Photon Spectral Confocal Microscopy for Cell Imaging Using Superconducting Transition Edge Sensor.

A superconducting transition edge sensor (TES) is an energy-dispersive single-photon detector that distinguishes the wavelength of each incident photon from visible to near-infrared (NIR) without using spectral dispersive elements. Here, we introduce an application of the TES technique for confocal laser scanning microscopy (CLSM) as proof of our concept of ultra-sensitive and wide-band wavelength range color imaging for biological samples. As a reference sample for wide-band observation, a fixed fluorescence-labeled cell sample stained with three different color dyes was observed using our TES-based CLSM method. The three different dyes were simultaneously excited by irradiating 405 and 488 nm lasers, which were coupled using an optical fiber combiner. Even when irradiated at low powers of 80 and 120 nW with the 405 and 488 nm lasers respectively, emission signals were spectrally detected by the TES and categorized into four wavelength bands: up to 500 nm (blue), from 500 to 600 nm (green), from 600 to 800 nm (red), and from 800 to 1,200 nm (NIR). Using a single scan, an RGB color image and an NIR image of the fluorescent cell sample were successfully captured with tens of photon signals in a 40 ms exposure time for each pixel. This result demonstrates that TES is a useful wide-band spectral photon detector in the field of life sciences.

Theoretical and experimental investigations on speckle suppression of dual-wavelength imaging LiDAR by vibrating the multimode fiber

The multimode fiber (MMF) can be adopted to the fiber-coupling laser transmitting optics system of the array-imaging LiDAR for far-range detection due to the relatively high demand for laser energy which can melt the single-mode fiber. However, the modal noise within the multimode fiber (MMF) can result in severe speckle at the output face which seriously affects the staring imaging LiDAR detection performance. Based on the proposed dual-wavelength LiDAR prototype in which the ICCD detects the 532 nm signal and the array Gm-APD detects the 1064 nm signal, the micro vibrator which is beneficial to the system miniaturization is used for suppressing the speckle. For this application, it’s necessary to investigate the speckle suppression effect to evaluate whether the MMF could be suitable for the LiDAR system or not. To our best knowledge, the multimode speckle suppression for dual-wavelength LiDAR hasn’t been discussed ever, moreover, the Gm-APD speckle suppression research hasn’t been carried out, yet. In this paper, firstly, the principle of the speckle suppression by vibrating the MMF was investigated and the speckle suppression detection models of both detectors were first proposed and discussed. Then, the theoretical analysis was carried out, and it showed that the vibration amplitude of 9 mm and the vibration frequency of higher than 215 Hz could help to get a good suppression results. Finally, the vibrator’s parameters were chosen based on the theoretical results, and the experiments were carried out to investigate the effects of the vibrator’s voltage which affects the vibration frequency and the exposure time on the image contrast of the intensity and the contrast-to-noise ratio (CNR) for ICCD, besides, the Gm-APD’s contrast of triggering probability was also investigated. Experimental results indicated that the vibrator voltage for getting a good speckle suppression was at least 1.5 V, at which the ICCD’s CNR could be enhanced to 1.2 times within 40 ms exposure time and the contrast of intensity of ICCD could be lowered to 0.65 times; besides, the contrast of triggering probability of Gm-APD could be lowered to 0.58 times. Moreover, compared with the speckle suppression results within 5 ms, 40 ms exposure time could help to enhance the CNRs of ICCD to about 3.12 times, lower the contrast of intensity of ICCD and the contrast of the triggering probability of Gm-APD to 0.85 times and 0.84 times, respectively. This paper demonstrates the feasibility of using MMF coupling laser transmitting scheme in the dual-wavelength staring imaging LiDAR, and it provides the experimental and theoretical basis for the system miniaturization and flexible application of dual-wavelength LiDAR.

Cathode temperature measurement of a hydrogen self-field MPD thruster during 1 ms quasi-steady operation

In this study, a 2D two-color pyrometer was developed to measure the cathode surface temperature distribution of a high-power hydrogen magnetoplasmadynamic thruster. The developed measurement system consists of an object lens, a beam splitter, bandpass filters, and two cameras. Wavelengths of 950 and 980 nm were selected to achieve a high signal-to-noise ratio by reducing the effects of plasma radiation. The cathode temperature distribution was measured in a discharge current range of 6–13 kA during approximately 1 ms quasi-steady operation. A spot-like high-temperature region over 3000 K and an overall low temperature were observed at low discharge currents. The overall cathode tip region was heated to approximately 2800 K at high discharge currents. The temperature distribution with high temperature only near the cathode tip was measured during quasi-steady operation, the duration of which is shorter than the duration of thermal conduction. These results show that the discharge current distribution near the cathode is stable during the time scale of sub-milliseconds. We confirmed that this temperature distribution remains constant during a 1 ms duty cycle through cathode temperature measurements at each operation time with a 0.2 ms exposure time. The measurement error was approximately 10% of the calculated temperature; a cross-check was performed utilizing near-infrared spectrum measurements.

Accelerating multi-emitter localization in super-resolution localization microscopy with FPGA-GPU cooperative computation.

The real-time multi-emitter localization method is essential for advancing high-throughput super-resolution localization microscopy (HT-SRLM). In the past decade, the graphics processing unit (GPU) computation has been dominantly used to accelerate the execution speed of the multi-emitter localization method. However, if HT-SRLM is combined with a scientific complementary metal-oxide-semiconductor (sCMOS) camera working at full frame rate, real-time image processing is still difficult to achieve using this acceleration approach, thus resulting in a massive data storage challenge and even system crash. Here we take advantage of the cooperative acceleration power of field programming gate array (FPGA) computation and GPU computation, and propose a method called HCP-STORM to enable real-time multi-emitter localization. Using simulated images, we verified that HCP-STORM is capable of providing real-time image processing for raw images from a representative Hamamatsu Flash 4 V3 sCMOS camera working at full frame rate (that is, 2048×2048 pixels @ 10 ms exposure time). Using experimental images, we prove that HCP-STORM is 25 times faster than QC-STORM and 295 times faster than ThunderSTORM, with a small but acceptable degradation in image quality. This study shows the potential of FPGA-GPU cooperative computation in accelerating multi-emitter localization, and pushes a significant step toward the maturity of HT-SRLM technology.

Micromirror Total Internal Reflection Microscopy for High-Performance Single Particle Tracking at Interfaces.

Single particle tracking has found broad applications in the life and physical sciences, enabling the observation and characterization of nano- and microscopic motion. Fluorescence-based approaches are ideally suited for high-background environments, such as tracking lipids or proteins in or on cells, due to superior background rejection. Scattering-based detection is preferable when localization precision and imaging speed are paramount due to the in principle infinite photon budget. Here, we show that micromirror-based total internal reflection dark field microscopy enables background suppression previously only reported for interferometric scattering microscopy, resulting in nanometer localization precision at 6 μs exposure time for 20 nm gold nanoparticles with a 25 × 25 μm2 field of view. We demonstrate the capabilities of our implementation by characterizing sub-nanometer deterministic flows of 20 nm gold nanoparticles at liquid–liquid interfaces. Our results approach the optimal combination of background suppression, localization precision, and temporal resolution achievable with pure scattering-based imaging and tracking of nanoparticles at interfaces.

Laser–induced nanopillar structures around particles

In biomedical engineering, laser-induced periodic surface structures (LIPSSs) have been extensively applied where laser irradiation of selective laser-melted (SLMed) samples to generate LIPSS-covered free-form samples is a promising technique. Using this technique, nanopillars around a spheroidal particle that was not molten during the SLM process have been formed, indicating that nanopillars can be induced around spheroidal particles on a material surface. This study investigates the mechanism of LIPSS and nanopillar formation on SLMed and uneven surfaces experimentally and through finite-difference time-domain simulation. A 50 Hz picosecond laser with 1064 nm fixed wavelengt, 20 ps pulse duration, 0.5 J/cm2 laser fluence, and 400 μm/s scanning speed was employed to irradiate Ti6Al4V alloy samples with 100 μs exposure time. The results show that induced nanopillars form a concentric area around a single particle with curvature radius approximately twice the particle radius. The simulated electric field intensity is ripple-like distributed for particle size beyond 5 μm, with approximately 1 μm periodic length and is close to the laser wavelength. This matches the experimental results from scanning electron microscopy for 800–00 nm LIPSS periodic length, indicating that desired nanostructures can be generated by appropriately designing the surface topography before laser irradiation.

Radiometric and design model for the tunable light-guide image processing snapshot spectrometer (TuLIPSS)

The tunable light-guide image processing snapshot spectrometer (TuLIPSS) is a novel remote sensing instrument that can capture a spectral image cube in a single snapshot. The optical modelling application for the absolute signal intensity on a single pixel of the sensor in TuLIPSS has been developed through a numerical simulation of the integral performance of each optical element in the TuLIPSS system. The absolute spectral intensity of TuLIPSS can be determined either from the absolute irradiance of the observed surface or from the tabulated spectral reflectance of various land covers and by the application of a global irradiance approach. The model is validated through direct comparison of the simulated results with observations. Based on tabulated spectral reflectance, the deviation between the simulated results and the measured observations is less than 5% of the spectral light flux across most of the detection bandwidth for a Lambertian-like surface such as concrete. Additionally, the deviation between the simulated results and the measured observations using global irradiance information is less than 10% of the spectral light flux across most of the detection bandwidth for all surfaces tested. This optical modelling application of TuLIPSS can be used to assist the optimal design of the instrument and explore potential applications. The influence of the optical components on the light throughput is discussed with the optimal design being a compromise among the light throughput, spectral resolution, and cube size required by the specific application under consideration. The TuLIPSS modelling predicts that, for the current optimal low-cost configuration, the signal to noise ratio can exceed 10 at 10 ms exposure time, even for land covers with weak reflectance such as asphalt and water. Overall, this paper describes the process by which the optimal design is achieved for particular applications and directly connects the parameters of the optical components to the TuLIPSS performance.

High-resolution fast-tomography brain-imaging beamline at the Taiwan Photon Source.

The new Brain Imaging Beamline (BIB) of the Taiwan Photon Source (TPS) has been commissioned and opened to users. The BIB and in particular its endstation are designed to take advantage of bright unmonochromatized synchrotron X-rays and target fast 3D imaging, ∼1 ms exposure time plus veryhigh ∼0.3 µm spatial resolution. A critical step in achieving the planned performances was the solution to the X-ray induced damaging problems of the detection system. High-energy photons were identified as their principal cause and were solved by combining tailored filters/attenuators and a high-energy cut-off mirror. This enabled the tomography acquisition throughput to reach >1 mm3 min-1, a critical performance for large-animal brain mapping and a vital mission of the beamline.

Insights on Space‐Leader Characteristics and Evolution in Natural Negative Cloud‐to‐Ground Lightning

AbstractWe present sub‐microsecond‐scale, high‐speed video camera observations of three negative stepped leaders in cloud‐to‐ground flashes with return‐stroke peak currents (estimated by the U.S. National Lightning Detection Network) of −17, −104, and −228 kA. The camera frame exposure times for these observations were 1.8, 1.0, and 0.74 µs, respectively. The 0.74 µs exposure time is the shortest reported to date. We observed the temporal and spatial evolution of space leaders from their inception to their attachment to the pre‐existing leader channel (PELC). For stepped leaders that led to return strokes having higher peak currents, the space leaders appear to have incepted at farther median two‐dimensional distances from their respective PELC‐attachment points. These median distances were 6.1, 16.6, and 17.6 m, respectively, for the three strokes. Our observations indicate that space leader characteristics are likely influenced by stepped‐leader line‐charge‐density, which is expected to be higher in strokes with higher return‐stroke peak currents.

Rapid Screening for COVID-19 Using Field Effect Transistor Biosensors

In this study, we have developed a platform for the rapid screening of the SARS-CoV-2 virus in saliva. Electrical double layer (EDL) gated field-effect transistors (FET) biosensor is applied in this research to detect the electrical signals in the sample. Nucleocapsid protein is used as the target protein since it is expressed abundantly during infection. The sensor illustrates a lower detection limit compared to recent methods, which shows the potential of our sensor to make a diagnosis in the early stages of the disease. Besides, additional pre-pretreatment is not needed. The sensor is a robust diagnostic tool for rapid screening of COVID-19. Introduction The coronavirus pandemic, also known as COVID-19, is caused by SARS-CoV-2 virus. COVID-19 causes severe acute respiratory syndrome and poses a significant threat to health internationally. The World Health Organization (WHO) declared this as a global pandemic. Symptom-based screening cannot be an effective strategy to identify individuals. The symptoms of mild patients are similar to influenza, which may easily lead to false negative confirmation of disease. Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) is the most well-known method employed for the clinical diagnosis of COVID-19. But, this method is costly and needs a long time to get the result. Hence, a rapid and low-cost diagnosis method is urgently required. Experimental Sensor array fabrication The disposable sensor array chip consists of two gold electrodes. One electrode is connected to the gate voltage supply, defined as the reference electrode. The other one is connected to the gate metal, and considered as the sensing electrode. Functionalization of sensor surface Antibody against SARS-CoV-2 nucleocapsid protein is used as receptor in this study, which is immobilized on the gold gate electrode. Traut’s Reagent (Thermo Scientific, (26101)) introduces sulfhydryl (-SH) groups to the primary amines of antibody. The modified antibody can then covalently bind to Au gate electrode by Au-S Bond. The antibody(1.5mg/mL) and Traut’s reagent (14 mM) are mixed and incubated at room temperature for 1 hour. The mixture is then dropped on the sensor surface and incubated in 4 °C refrigerator for 12 hours. Electrical measurement The sensor array chip is inserted into a portable prototype device with FET LND150. 2V DC bias as the drain-source voltage and a short duration gate pulse are steadily provided. The difference between the two current drains is defined as current gain, which is used as the index in data analysis. Fluorescence experiment After the electrical measurement, the secondary antibody, anti-mouse IgG (DyLight® 594), is added to the sensor to conjugate with the primary antibody. The sensor array chip is incubated for 1 hour at room temperature, and the unbound molecule is washed away by 1X PBS. Fluorescence microscope, (LEICA DM2500 LED) is used to capture the fluorescence image with 100 ms exposure time and quantitative analysis is performed using imageJ software. Result and conclusion When infected with SARS-CoV-2, the body produces antibodies that bind specific to nucleocapsid proteins and other surface antigens to help eliminate the virus. SARS-CoV-2 virus nucleocapsid protein is abundantly expressed during infection and is one of the highly immunogenic proteins. Hence, nucleocapsid protein is used as the target protein in this study. We immobilized antibody for nucleocapsid protein on the sensor. Electrical signal changed as the concentration of nucleocapsid protein increased from 0 to 400 ng/mL. The limit of detection for N protein was established at 0.4ng/mL. Tests that can distinguish between IgM and IgG can provide information about the stage of infection, indicating how long the person has been infected with SARS-CoV-2. In this study, we developed a platform that can help to confirm the infection in patients quickly in saliva. N-protein testing can potentially help us track the spread of the disease and accurately detect the infected individuals so as to control further spreading of the disease. Figure 1

VECSEL-based virtually imaged phased array spectrometer for rapid gas phase detection in the mid-infrared.

We present a novel, to the best of our knowledge, system for high-resolution, time-resolved spectroscopy in the mid-wave infrared based on a modelocked vertical external cavity surface emitting laser (VECSEL) frequency comb coupled to a virtually imaged phased array (VIPA) spectrometer. The GHz level repetition rate of VECSEL-based systems coupled to VIPA spectrometers enables comb tooth resolved spectra without the use of additional filter cavities often required to increase comb tooth spacing. We demonstrate absorption spectroscopy on a methane (CH4) gas mixture at 2900cm-1 (3.4 µm) with over 35cm-1 spectral bandwidth in a single image. Rapid time-resolved measurements were made using a 300 µs exposure time with an acquisition rate limited to 125 Hz by the available camera. High-resolution absolute frequency measurements were performed by scanning the repetition rate of the VECSEL frequency comb.