All Publications

  • Rapid switching and durable on-chip spark-cavitation-bubble cell sorter. Microsystems & nanoengineering Jiao, Z., Han, Y., Zhao, J., Chao, Z., Tarnok, A., You, Z. 2022; 8: 52


    Precise and high-speed sorting of individual target cells from heterogeneous populations plays an imperative role in cell research. Although the conventional fluorescence-activated cell sorter (FACS) is capable of rapid and accurate cell sorting, it occupies a large volume of the instrument and inherently brings in aerosol generation as well as cross-contamination among samples. The sorting completed in a fully enclosed and disposable microfluidic chip has the potential to eliminate the above concerns. However, current microfluidic cell sorters are hindered by the high complexities of the fabrication procedure and the off-chip setup. In this paper, a spark-cavitation-bubble-based fluorescence-activated cell sorter is developed to perform fast and accurate sorting in a microfluidic chip. It features a simple structure and an easy operation. This microfluidic sorter comprises a positive electrode of platinum and a negative electrode of tungsten, which are placed on the side of the main channel. By applying a high-voltage discharge on the pair of electrodes, a single spark cavitation bubble is created to deflect the target particle into the downstream collection channel. The sorter has a short switching time of 150mus and a long lifespan of more than 100 million workable actions. In addition, a novel control strategy is proposed to dynamically adjust the discharge time to stabilize the size of the cavitation bubble for continuous sorting. The dynamic control of continuously triggering the sorter, the optimal delay time between fluorescence detection and cell sorting, and a theoretical model to predict the ideal sorting recovery and purity are studied to improve and evaluate the sorter performance. The experiments demonstrate that the sorting rate of target particles achieves 1200 eps, the total analysis throughput is up to 10,000 eps, the particles sorted at 4000 eps exhibit a purity greater than 80% and a recovery rate greater than 90%, and the sorting effect on the viability of HeLa cells is negligible.

    View details for DOI 10.1038/s41378-022-00382-2

    View details for PubMedID 35600222

  • Flexible method for generating needle-shaped beams and its application in optical coherence tomography Optica Zhao, J., Winetraub, Y., Du, L., Vleck, A. V., Ichimura, K., Huang, C., Aasi, S. Z., Sarin, K. Y., de la Zerda, A. 2022; 9 (8): 859-867

    View details for DOI 10.1364/optica.456894

  • A simple approach to fabricate multi-layer glass microfluidic chips based on laser processing and thermocompression bonding MICROFLUIDICS AND NANOFLUIDICS Han, Y., Jiao, Z., Zhao, J., Chao, Z., You, Z. 2021; 25 (9)
  • Dynamics of spark cavitation bubbles in a microchamber MICROFLUIDICS AND NANOFLUIDICS Jiao, Z., Zhao, J., Han, Y., Chao, Z., You, Z. 2021; 25 (2)
  • Diffractive beam shaper for multi-wavelength lasers for flow cytometry. Cytometry. Part A : the journal of the International Society for Analytical Cytology Han, Y., Zhao, J., Jiao, Z., Chao, Z., Tarnok, A., You, Z. 2020


    Illumination spot in a flow cytometer is a crucial factor determining the measurement accuracy and stability. The traditional mechanism is to precisely calibrate multiple optical components to convert circular Gaussian beams into elliptical Gaussian beams, making it difficult to shape multi-wavelength lasers simultaneously. A diffractive beam shaper for multi-color lasers with high simplicity, only containing one diffractive optical element and one focusing lens is created in this work. It can produce rectangular spots, of which the number, the sizes, and the positions are accurately determined by the incident wavelengths. Demonstrated in the customized microflow cytometer, the coefficient of variations (CV) of the optical signals by the beam shaper are 3.6~6.5%, comparable to those derived from the commercial instrument with 3.3~6.3% CVs. Benefiting from the narrow rectangular spots and the flexibility of diffractively shaped lasers, the measurement of bead sizes with 4~15 mum diameters and the real-time detection of flow velocity from 0.79 to 9.50 m/s with the CV of <5% are achieved.

    View details for DOI 10.1002/cyto.a.24240

    View details for PubMedID 33078537

  • Angular compounding for speckle reduction in optical coherence tomography using geometric image registration algorithm and digital focusing. Scientific reports Zhao, J., Winetraub, Y., Yuan, E., Chan, W. H., Aasi, S. Z., Sarin, K. Y., Zohar, O., de la Zerda, A. 2020; 10 (1): 1893


    Optical coherence tomography (OCT) suffers from speckle noise due to the high spatial coherence of the utilized light source, leading to significant reductions in image quality and diagnostic capabilities. In the past, angular compounding techniques have been applied to suppress speckle noise. However, existing image registration methods usually guarantee pure angular compounding only within a relatively small field of view in the focal region, but produce spatial averaging in the other regions, resulting in resolution loss and image blur. This work develops an image registration model to correctly localize the real-space location of every pixel in an OCT image, for all depths. The registered images captured at different angles are fused into a speckle-reduced composite image. Digital focusing, based on the convolution of the complex OCT images and the conjugate of the point spread function (PSF), is studied to further enhance lateral resolution and contrast. As demonstrated by experiments, angular compounding with our improved image registration techniques and digital focusing, can effectively suppress speckle noise, enhance resolution and contrast, and reveal fine structures in ex-vivo imaged tissue.

    View details for DOI 10.1038/s41598-020-58454-0

    View details for PubMedID 32024946

  • An air-chamber-based microfluidic stabilizer for attenuating syringe-pump-induced fluctuations MICROFLUIDICS AND NANOFLUIDICS Jiao, Z., Zhao, J., Chao, Z., You, Z., Zhao, J. 2019; 23 (2)
  • Spark-generated microbubble cell sorter for microfluidic flow cytometry CYTOMETRY PART A Zhao, J., You, Z. 2018; 93A (2): 222-231


    High-speed and accurate cell sorting is of great significance for cell analysis regarding both bioresearch and clinical application. Different from the jet-in-air sorting of commercial flow cytometers, sorting in fully enclosed and disposal microfluidic chips can avoid aerosols and crosscontamination, thus contributing to the improvement of biosafety and test accuracy. However, current microfluidic sorters usually require complicated structures, or otherwise cannot attain high throughput. In this article, a sorting mechanism for microfluidics is proposed for the first time based on the jet flow induced by the spark-generated cavitation microbubble that can be easily realized by a pair of electrodes. The sorter was integrated into a microfluidic chip based on three-dimensional (3D) hydrodynamic focusing and a binary optical element (BOE) for laser illumination. Besides, several aspects of the sorting mechanism were studied to optimize the device. It achieved a switching time of 250 μs at the sample flow velocity of 5 m/s and performed the continuous operation at 200 Hz. Both the stability of fluorescence signals and the viability of cells were basically maintained. To conclude, this work explores a new on-chip sorting mechanism which possesses the merits of simple structure, easy control, and fast switching. © 2018 International Society for Advancement of Cytometry.

    View details for DOI 10.1002/cyto.a.23296

    View details for Web of Science ID 000426061500012

    View details for PubMedID 29346713

  • Using binary optical elements (BOEs) to generate rectangular spots for illumination in micro flow cytometer BIOMICROFLUIDICS Zhao, J., You, Z. 2016; 10 (5): 054111


    This work introduces three rectangular quasi-flat-top spots, which are provided by binary optical elements (BOEs) and utilized for the illumination in a microflow cytometer. The three spots contain, respectively, one, two, and three rectangles (R1, R2, and R3). To test the performance of this mechanism, a microflow cytometer is established by integrating the BOEs and a three-dimensional hydrodynamic focusing chip. Through the experiments of detecting fluorescence microbeads, the three spots present good fluorescence coefficients of variation in comparison with those derived from commercial instruments. Benefiting from a high spatial resolution, when using R1 spot, the micro flow cytometer can perform a throughput as high as 20 000 events per second (eps). Illuminated by R2 or R3 spot, one bead emits fluorescence twice or thrice, thus the velocity can be measured in real time. Besides, the R3 spot provides a long-time exposure, which is conducive to improving fluorescence intensity and the measurement stability. In brief, using the spots shaped and homogenized by BOEs for illumination can increase the performance and the functionality of a micro flow cytometer.

    View details for DOI 10.1063/1.4963010

    View details for Web of Science ID 000387577400011

    View details for PubMedID 27733892

    View details for PubMedCentralID PMC5045444

  • A Microflow Cytometer with a Rectangular Quasi-Flat-Top Laser Spot SENSORS Zhao, J., You, Z. 2016; 16 (9)


    This work develops a microflow cytometer, based on a microfluidic chip for three-dimensional (3D) hydrodynamic focusing and a binary optical element (BOE) for shaping and homogenizing a laser beam. The microfluidic chip utilizes sheath flows to confine the sample flow along the channel centerline with a narrow cross section. In addition to hydrodynamic focusing, secondary flows are generated to strengthen the focusing in the vertical direction. In experiments, the chip was able to focus the sample flow with cross sections of 15 μm high and 8-30 μm wide at 5 m/s, under the condition of the sample flow rates between 10 and 120 μL/min. Instead of using the conventional elliptical Gaussian spot for optical detection, we used a specially designed BOE and obtained a 50 μm × 10 μm rectangular quasi-flat-top spot. The microflow cytometer combining the chip and the BOE was tested to count 3, 5, and 7 μm fluorescence microbeads, and the experimental results were comparable to or better than those derived from two commercial instruments.

    View details for DOI 10.3390/s16091474

    View details for Web of Science ID 000385527700135

    View details for PubMedID 27626428

    View details for PubMedCentralID PMC5038752

  • A Self-Powered Insole for Human Motion Recognition SENSORS Han, Y., Cao, Y., Zhao, J., Yin, Y., Ye, L., Wang, X., You, Z. 2016; 16 (9)


    Biomechanical energy harvesting is a feasible solution for powering wearable sensors by directly driving electronics or acting as wearable self-powered sensors. A wearable insole that not only can harvest energy from foot pressure during walking but also can serve as a self-powered human motion recognition sensor is reported. The insole is designed as a sandwich structure consisting of two wavy silica gel film separated by a flexible piezoelectric foil stave, which has higher performance compared with conventional piezoelectric harvesters with cantilever structure. The energy harvesting insole is capable of driving some common electronics by scavenging energy from human walking. Moreover, it can be used to recognize human motion as the waveforms it generates change when people are in different locomotion modes. It is demonstrated that different types of human motion such as walking and running are clearly classified by the insole without any external power source. This work not only expands the applications of piezoelectric energy harvesters for wearable power supplies and self-powered sensors, but also provides possible approaches for wearable self-powered human motion monitoring that is of great importance in many fields such as rehabilitation and sports science.

    View details for DOI 10.3390/s16091502

    View details for Web of Science ID 000385527700158

    View details for PubMedID 27649188

    View details for PubMedCentralID PMC5038775

  • Microfluidic hydrodynamic focusing for high-throughput applications JOURNAL OF MICROMECHANICS AND MICROENGINEERING Zhao, J., You, Z. 2015; 25 (12)
  • Miniaturized Air-Driven Planar Magnetic Generators ENERGIES Zhao, J., Shi, G., Du, L. 2015; 8 (10): 11755-11769

    View details for DOI 10.3390/en81011755

    View details for Web of Science ID 000364230500057

  • A Shoe-Embedded Piezoelectric Energy Harvester for Wearable Sensors SENSORS Zhao, J., You, Z. 2014; 14 (7): 12497-12510


    Harvesting mechanical energy from human motion is an attractive approach for obtaining clean and sustainable electric energy to power wearable sensors, which are widely used for health monitoring, activity recognition, gait analysis and so on. This paper studies a piezoelectric energy harvester for the parasitic mechanical energy in shoes originated from human motion. The harvester is based on a specially designed sandwich structure with a thin thickness, which makes it readily compatible with a shoe. Besides, consideration is given to both high performance and excellent durability. The harvester provides an average output power of 1 mW during a walk at a frequency of roughly 1 Hz. Furthermore, a direct current (DC) power supply is built through integrating the harvester with a power management circuit. The DC power supply is tested by driving a simulated wireless transmitter, which can be activated once every 2-3 steps with an active period lasting 5 ms and a mean power of 50 mW. This work demonstrates the feasibility of applying piezoelectric energy harvesters to power wearable sensors.

    View details for DOI 10.3390/s140712497

    View details for Web of Science ID 000340035700066

    View details for PubMedID 25019634

    View details for PubMedCentralID PMC4168512

  • Models for 31-Mode PVDF Energy Harvester for Wearable Applications SCIENTIFIC WORLD JOURNAL Zhao, J., You, Z. 2014: 893496


    Currently, wearable electronics are increasingly widely used, leading to an increasing need of portable power supply. As a clean and renewable power source, piezoelectric energy harvester can transfer mechanical energy into electric energy directly, and the energy harvester based on polyvinylidene difluoride (PVDF) operating in 31-mode is appropriate to harvest energy from human motion. This paper established a series of theoretical models to predict the performance of 31-mode PVDF energy harvester. Among them, the energy storage one can predict the collected energy accurately during the operation of the harvester. Based on theoretical study and experiments investigation, two approaches to improve the energy harvesting performance have been found. Furthermore, experiment results demonstrate the high accuracies of the models, which are better than 95%.

    View details for DOI 10.1155/2014/893496

    View details for Web of Science ID 000343551700001

    View details for PubMedID 25114981

    View details for PubMedCentralID PMC4119733