Volume holographic illuminator for Airy light-sheet microscopy.

Airy light sheets combined with the deconvolution approach can provide multiple benefits, including large field of view (FOV), thin optical sectioning, and high axial resolution. The efficient design of an Airy light-sheet fluorescence microscope requires a compact illumination system. Here, we show that an Airy light sheet can be conveniently implemented in microscopy using a volume holographic grating (VHG). To verify the FOV and the axial resolution of the proposed VHG-based Airy light-sheet fluorescence microscope, ex-vivo fluorescently labeled Caenorhabditis elegans (C. elegans) embryos were imaged, and the Richardson-Lucy deconvolution method was used to improve the image contrast. Optimized parameters for deconvolution were compared with different methods. The experimental results show that the FOV and the axial resolution were 196 µm and 3 µm, respectively. The proposed method of using a compact VHG to replace the common spatial light modulator provides a direct solution to construct a compact light-sheet fluorescence microscope.

Abrupt autofocusing beam from a phase-only mask.

Airy beams have become an important beam shape for structured light beams because of their interesting self-accelerating and parabolic propagation properties. Many variants of Airy beams have been proposed, among which the Airy beam with cylindrical symmetry [also known as the circular Airy beam or abrupt autofocusing (AAF) beam] is particularly peculiar and has attracted special attention due to its shape transformation during propagation. Much effort has been devoted to understanding the properties of the AAF beam. In this work, we present simulation results for generating the AAF beam using a phase-only mask. A cubic chirp-modulated axicon phase is used to create the mask. We found an optimal value for the axiconic phase, and the cubic phase is essential for controlling the AAF beam's shape. We demonstrate that a phase-only mask is an effective and simple method for generating high contrast between the initial and AAF plane. We present the results for beam formation and propagation dynamics of the AAF beam using the control parameters of the phase mask. We also discuss the design parameters and their influence on the AAF beam shapes. Our results pave the way for a deeper understanding of the beam formation and propagation dynamics of the AAF beam.

Multifocal confocal microscopy using a volume holographic lenslet array illuminator.

Multifocal illumination can improve image acquisition time compared to single point scanning in confocal microscopy. However, due to an increase in the system complexity, obtaining uniform multifocal illumination throughout the field of view with conventional methods is challenging. Here, we propose a volume holographic lenslet array illuminator (VHLAI) for multifocal confocal microscopy. To obtain uniform array illumination, a super Gaussian (SG) beam has been incorporated through VHLAI with an efficiency of 43%, and implemented in a confocal microscope. The design method for a photo-polymer based volume holographic beam shaper is presented and its advantages are thoroughly addressed. The proposed system can significantly improve image acquisition time without sacrificing the quality of the image. The performance of the proposed multifocal confocal microscopy was compared with wide-field images and also evaluated by measuring optically sectioned microscopic images of fluorescence beads, florescence pollen grains, and biological samples. The proposed multifocal confocal system generates images faster without any changes in scanning devices. The present method may find important applications in high-speed multifocal microscopy platforms.

Multi-plane confocal microscopy with multiplexed volume holographic gratings [Invited].

A volume holographic (VHG) grating-based multi-plane differential confocal microscopy (DCM) is proposed for axial scan-free imaging. Also, we briefly reviewed our previous works on volume holographic-based confocal imaging. We show that without degrading imaging performance, it is possible to simultaneously obtain two depth-resolved optically sectioned images with improved axial resolution using multi-plane DCM. The performance of our multi-plane DCM was evaluated by measuring the surface profile of a silicon micro-hole array with depths separation around 10 µm. The axial sensitivity of the system is around 25 nm. Our system has the advantages of multi-plane imaging with high axial sensitivity and high optical sectioning ability. Our method can be used for reflective surface profiling and multi-plane fluorescence imaging. The present methods may find important applications in surface metrology for label-free biological samples, as well as industrial applications.

Simultaneous multi-color optical sectioning fluorescence microscopy with wavelength-coded volume holographic gratings.

Optical sectioning fluorescence microscopy provides high contrast images of volumetric samples and has been widely used for many biological applications. However, simultaneously acquiring multi-color fluorescence images require additional optical elements and devices, which are bulky, wavelength specific, and not cost-effective. In this paper, wavelength-coded volume holographic gratings (WC-VHGs) based optical sectioning fluorescence microscopy is proposed to simultaneously offer multi-color fluorescence images with fine out-of-focus background rejection. Due to wavelength degeneracy, multiplexed WC-VHGs are capable of acquiring multi-wavelength fluorescence images in a single shot, and displaying the laterally separated multi-wavelength images onto CCD. In our system optical sectioning capability is achieved through speckle illumination and HiLo imaging method. To demonstrate imaging characteristics of our system, dual-wavelength fluorescence images of both standard fluorescent microspheres and ex vivo mT/mG mice cardiac tissue are presented. Current results may find important applications in hyperspectral imaging for biomedical research.

Multi-wavelength quantitative differential phase contrast imaging by radially asymmetric illumination.

A new approach for achieving isotropic differential phase contrast imaging by applying multi-wavelength asymmetric illumination is demonstrated. Multi-wavelength isotropic differential phase contrast scheme (MW-iDPC) can be implemented using an add-on module in any commercial inverted microscope. Isotropy of intensity transfer function is achieved using three axis measurements. The expression for MW-iDPC imaging is presented, and detailed mathematical analysis is performed for transfer function. By applying color leakage correction, image sensor responses can be calibrated. Asymmetric illumination masks are designed, and simulation studies for intensity of the transfer function are performed. We utilize the MW-iDPC system to reconstruct quantitative phase images of standard microspheres and live breast cancer cells. The optical thickness of cells can be measured with high accuracy and image acquisition time is reduced significantly.

Multiplexed holographic non-axial-scanning slit confocal fluorescence microscopy.

A non-axial-scanning multi-plane microscopic system incorporating multiplexed volume holographic gratings and slit array detection to simultaneously acquire optically sectioned images from different depths is presented. The proposed microscopic system is configured such that multiplexed volume holographic gratings are utilized to selectively produce axial focal points in two or more planes inside the sample, and then to use confocal slit apertures to simultaneously image these multiple planes onto corresponding detection areas of a CCD. We describe the design, implementation, and experimental data demonstrating this microscopic system's ability to obtain optically sectioned multi-plane images of fluorescently labeled standard micro-spheres and tissue samples without scanning in axial directions.

Indium Nitrite (InN)-Based Ultrasensitive and Selective Ammonia Sensor Using an External Silicone Oil Filter for Medical Application.

Ammonia is an essential biomarker for noninvasive diagnosis of liver malfunction. Therefore, selective detection of ammonia is essential for medical application. Here, we demonstrate a portable device to selectively detect sub-ppm ammonia gas. The presented gas sensor is composed of a Pt coating on top of an ultrathin Indium nitrite (InN) epilayer with a lower detection limit of 0.2 ppm, at operating temperature of 200 °C, and detection time of 1 min. The sensor connected with the external filter of nonpolar 500 CS silicone oil to diagnose liver malfunction. The absorption of 0.7 ppm acetone and 0.4 ppm ammonia gas in 10 cc silicone oil is 80% (0.56 ppm) and 21.11% (0.084 ppm), respectively, with a flow rate of 10 cc/min at 25 °C. The absorption of acetone gas is 6.66-fold higher as compared to ammonia gas. The percentage variation in response for 0.7 ppm ammonia and 0.7 ppm acetone with and without silicone oil on InN sensor is 17.5% and 4%, and 22.5%, and 14% respectively. Furthermore, the percentage variation in response for 0.7 ppm ammonia gas with silicone oil on InN sensor is 4.3-fold higher than that of 0.7 ppm acetone. The results show that the InN sensor is suitable for diagnosis of liver malfunction.

Mechanical Strength and Broadband Transparency Improvement of Glass Wafers via Surface Nanostructures.

In this study, we mechanically strengthened a borosilicate glass wafer by doubling its bending strength and simultaneously enhancing its transparency using surface nanostructures for different applications including sensors, displays and panels. A fabrication method that combines dry and wet etching is used for surface nanostructure fabrication. Specifically, we improved the bending strength of plain borosilicate glass by 96% using these surface nanostructures on both sides. Besides bending strength improvement, a limited optical transmittance enhancement of 3% was also observed in the visible light wavelength region (400-800 nm). Both strength and transparency were improved by using surface nanostructures of 500 nm depth on both sides of the borosilicate glass without affecting its bulk properties or the glass manufacturing process. Moreover, we observed comparatively smaller fragments during the breaking of the nanostructured glass, which is indicative of strengthening. The range for the nanostructure depth is defined for different applications with which improvements of the strength and transparency of borosilicate glass substrate are obtained.

Investigation of C-terminal domain of SARS nucleocapsid protein-Duplex DNA interaction using transistors and binding-site models.

AlGaN/GaN high electron mobility transistors (HEMTs) were used to sense the binding between double stranded DNA (dsDNA) and the severe acute respiratory syndrome coronavirus (SARS-CoV) nucleocapsid protein (N protein). The sensing signals were the drain current change of the HEMTs induced by the protein-dsDNA binding. Binding-site models using surface coverage ratios were utilized to analyze the signals from the HEMT-based sensors to extract the dissociation constants and predict the number of binding sites. Two dissociation constants, K D1 = 0.0955 nM, K D2 = 51.23 nM, were obtained by fitting the experimental results into the two-binding-site model. The result shows that this technique is more competitive than isotope-labeling electrophoretic mobility shift assay (EMSA). We demonstrated that AlGaN/GaN HEMTs were highly potential in constructing a semiconductor-based-sensor binding assay to extract the dissociation constants of nucleotide-protein interaction.

Rapid ranging through evaluation of image distortion.

Distortion is an undesirable aberration found in optical imaging systems, necessitating numerical calibration. However, the fact that image distortion changes with observation distance can be used for ranging. This study developed a rapid, passive-ranging technique, which is simple, incurs low costs, results in minimal interference, and requires few parameters. After determining the location of reference points, the relationship between the normalized mean distortion of images and observation distance is described using two mathematical models, one of which is based on distortion theory and the other is derived from the curve fitting of the experimental results. Analyzing the instantaneous rate of image distortion can also assist in ranging. The proposed technique demonstrates high sensitivity at closer observation distances, but loses effectiveness as observation distances increase.

Probing cellular behaviors through nanopatterned chitosan membranes.

This paper describes a high-throughput method for developing physically modified chitosan membranes to probe the cellular behavior of MDCK epithelial cells and HIG-82 fibroblasts adhered onto these modified membranes. To prepare chitosan membranes with micro/nanoscaled features, we have demonstrated an easy-to-handle, facile approach that could be easily integrated with IC-based manufacturing processes with mass production potential. These physically modified chitosan membranes were observed by scanning electron microscopy to gain a better understanding of chitosan membrane surface morphology. After MDCK cells and HIG-82 fibroblasts were cultured on these modified chitosan membranes for various culture durations (i.e. 1, 2, 4, 12 and 24 h), they were investigated to decipher cellular behavior. We found that both cells preferred to adhere onto a flat surface rather than on a nanopatterned surface. However, most (> 80%) of the MDCK cells showed rounded morphology and would suspend in the cultured medium instead of adhering onto the planar surface of negatively nanopatterned chitosan membranes. This means different cell types (e.g. fibroblasts versus epithelia) showed distinct capabilities/preferences of adherence for materials of varying surface roughness. We also showed that chitosan membranes could be re-used at least nine times without significant contamination and would provide us consistency for probing cell-material interactions by permitting reuse of the same substrate. We believe these results would provide us better insight into cellular behavior, specifically, microscopic properties and characteristics of cells grown under unique, nanopatterned cell-interface conditions.

A comb-drive actuator driven by capacitively-coupled-power.

This paper presents a new actuation mechanism to drive comb-drive actuators. An asymmetric configuration of the finger overlap was used to generate capacitive coupling for the actuation mechanism. When the driving voltages were applied on the stators, a voltage would be induced at the rotor due to the capacitive coupling. Then, an electrostatic force would be exerted onto the rotor due to the voltage differences between the stators and the rotor. The actuator's static displacement and resonant frequency were theoretically analyzed. To verify the design, a comb-drive actuator with different initial finger overlaps, i.e., 159.3 µm and 48.9 µm on each side, was fabricated and tested. The results show that the actuator worked well using the proposed actuation mechanism. A static displacement of 41.7 µm and a resonant frequency of 577 Hz were achieved. Using the actuation mechanism, no electrical connection is required between the rotor and the outside power supply. This makes some comb-drive actuators containing heterogeneous structures easy to design and actuate.

A sub-ppm acetone gas sensor for diabetes detection using 10 nm thick ultrathin InN FETs.

An indium nitride (InN) gas sensor of 10 nm in thickness has achieved detection limit of 0.4 ppm acetone. The sensor has a size of 1 mm by 2.5 mm, while its sensing area is 0.25 mm by 2 mm. Detection of such a low acetone concentration in exhaled breath could enable early diagnosis of diabetes for portable physiological applications. The ultrathin InN epilayer extensively enhances sensing sensitivity due to its strong electron accumulation on roughly 5-10 nm deep layers from the surface. Platinum as catalyst can increase output current signals by 2.5-fold (94 vs. 37.5 µA) as well as reduce response time by 8.4-fold (150 vs. 1,260 s) in comparison with bare InN. More, the effect of 3% oxygen consumption due to breath inhalation and exhalation on 2.4 ppm acetone gas detection was investigated, indicating that such an acetone concentration can be analyzed in air.

A pilot study for the prediction of liver function related scores using breath biomarkers and machine learning.

Volatile organic compounds (VOCs) present in exhaled breath can help in analysing biochemical processes in the human body. Liver diseases can be traced using VOCs as biomarkers for physiological and pathophysiological conditions. In this work, we propose non-invasive and quick breath monitoring approach for early detection and progress monitoring of liver diseases using Isoprene, Limonene, and Dimethyl sulphide (DMS) as potential biomarkers. A pilot study is performed to design a dataset that includes the biomarkers concentration analysed from the breath sample before and after study subjects performed an exercise. A machine learning approach is applied for the prediction of scores for liver function diagnosis. Four regression methods are performed to predict the clinical scores using breath biomarkers data as features set by the machine learning techniques. A significant difference was observed for isoprene concentration (p < 0.01) and for DMS concentration (p < 0.0001) between liver patients and healthy subject's breath sample. The R-square value between actual clinical score and predicted clinical score is found to be 0.78, 0.82, and 0.85 for CTP score, APRI score, and MELD score, respectively. Our results have shown a promising result with significant different breath profiles between liver patients and healthy volunteers. The use of machine learning for the prediction of scores is found very promising for use of breath biomarkers for liver function diagnosis.

Powerless tunable photonic crystal with bistable color and millisecond switching.

This study demonstrated a tunable photonic crystal (PhC) with 70 nm-wide spectral tuning (535 nm to 605 nm) and 3 ms of response time. The tunable PhC is based on reciprocal capillary action of liquid in the nanoscale PhC voids. By wetting the porous silicon PhC with ethanol and water, the PhC can be bistably switched respectively between liquid-filled state (orange color) and vapor-filled state (yellow color). Owing to the energy barrier between the two wetting states, the tunable PhC can remain at either of the two states with no external power consumption.

Three-dimensional illumination system using dielectric liquid lenses.

A 25-pixel illumination system composed of a 5 × 5 dielectric liquid-lens (DLL) zoom module array, 25 light-emission diodes (LEDs), and a secondary optical lens demonstrates 3D light field manipulation. LEDs function as 2D illumination pixels while the DLL module array performs longitudinal illuminance adjustability by zooming each illumination pixel. A test on the similarity of two illuminance patterns between experiments and simulations shows a normalized cross correlation (NCC) higher than 0.8, indicating the feasibility of the system design. Also, the illumination system is further applied to correct a distorted light pattern on a 45° tilt screen as well as to perform light compensation on distance-differential objects.

Telecentric design for digital-scanning-based HiLo optical sectioning endomicroscopy with an electrically tunable lens.

Confocal endoscopy has been widely used to obtain fine optically sectioned images. However, confocal endomicroscopic images are formed by point-by-point scanning in both lateral and axial directions, which results in long image acquisition time. Here, an endomicroscope with telecentric configuration is presented to achieve nonmechanical and rapid axial scanning for volumetric fluorescence imaging. In our system, optical sectioning in wide-field fashion is obtained through HiLo imaging with a digital micromirror device. Axial scanning, without mechanical moving parts, is conducted by digital focus adjustment using an electrically tunable lens, offering constant magnification and contrast. We demonstrate imaging performance of our system with optically sectioned images using fluorescently labeled beads, as well as ex vivo mice cardiac tissue samples. Our system provides multiple advantages, in terms of improved scanning range, and reduced image acquisition time, which shows great potentials for three-dimensional biopsies of volumetric biological samples.

Surface Wettability and Electrical Resistance Analysis of Droplets on Indium-Tin-Oxide Glass Fabricated Using an Ultraviolet Laser System.

Indium tin oxide (ITO) is widely used as a substrate for fabricating chips because of its optical transparency, favorable chemical stability, and high electrical conductivity. However, the wettability of ITO surface is neutral (the contact angle was approximately 90°) or hydrophilic. For reagent transporting and manipulation in biochip application, the surface wettability of ITO-based chips was modified to the hydrophobic or nearly hydrophobic surface to enable their use with droplets. Due to the above demand, this study used a 355-nm ultraviolet laser to fabricate a comb microstructure on ITO glass to modify the surface wettability characteristics. All of the fabrication patterns with various line width and pitch, depth, and surface roughness were employed. Subsequently, the contact angle (CA) of droplets on the ITO glass was analyzed to examine wettability and electrical performance by using the different voltages applied to the electrode. The proposed approach can succeed in the fabrication of a biochip with suitable comb-microstructure by using the optimal operating voltage and time functions for the catch droplets on ITO glass for precision medicine application. The experiment results indicated that the CA of droplets under a volume of 20 µL on flat ITO substrate was approximately 92° ± 2°; furthermore, due to its lowest surface roughness, the pattern line width and pitch of 110 µm exhibited a smaller CA variation and more favorable spherical droplet morphology, with a side and front view CA of 83° ± 1° and 78.5° ± 2.5°, respectively, while a laser scanning speed of 750 mm/s was employed. Other line width and pitch, as well as scanning speed parameters, increased the surface roughness and resulted in the surface becoming hydrophilic. In addition, to prevent droplet morphology collapse, the droplet's electric operation voltage and driving time did not exceed 5 V and 20 s, respectively. With this method, the surface modification process can be employed to control the droplet's CA by adjusting the line width and pitch and the laser scanning speed, especially in the neutral or nearly hydrophobic surface for droplet transporting. This enables the production of a microfluidic chip with a surface that is both light transmittance and has favorable electrical conductivity. In addition, the shape of the microfluidic chip can be directly designed and fabricated using a laser direct writing system on ITO glass, obviating the use of a mask and complicated production processes in biosensing and biomanipulation applications.

Tunable photonic crystal based on capillary attraction and repulsion.

A tunable photonic crystal (PhC) based on the capillary action of liquid is demonstrated in this work. The porous silicon-based photonic crystal (PSiPhC) features periodic porosity and is fabricated by electrochemical etching on 6" silicon wafer followed by hydrophobic modification on the silicon surface. The capillary action is achieved by varying the mixture ratio of liquids with high and low surface tension, yielding either capillary attraction or capillary repulsion in the nanoscale voids of the PSiPhC. By delivering the liquid mixture into and out of the voids of the PSiPhC, the reflective color of the PSiPhC can be dynamically tuned.