T C Ayi

Nanyang Technological University, Singapore, Singapore

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Publications (14)20.14 Total impact

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    ABSTRACT: In this paper, for the first time, an on-chip optofluidic imaging system is innovated to measure the biophysical signature of single waterborne bacterium, including both the refractive index and morphology (size and shape), based on immersion refractometry. The key features of the proposed optofluidic imaging platform include (1) multiple sites for single bacterium trapping, which enable parallel measurements to achieve higher throughput, and (2) chaotic micromixer, which enable efficient refractive index variation of the surrounding medium. In the experiments, the distinctive refractive index of Echerichia coli, Shigella flexneri and Vibrio cholera are measured with a high precision of 5×10-3 RIU. The developed optofluidic imaging system has high potential not only for building up a database of waterborne bacterium biophysical signature, but also developing single bacterium detection in treated water that is real-time, label-free and low cost.
    Lab on a Chip 08/2014; · 5.70 Impact Factor
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    ABSTRACT: Bacteriophages are considered as attractive indicators for determining drinking water quality since its concentration is strongly correlated with virus concentrations in water samples. Previously, bacteriophage detection was based on a plague assay that required a complicated labelling technique and a time-consuming culture assay. Here, for the first time, a label-free bacteriophage detection is reported by using droplet optofluidic imaging, which uses host-cell-containing microdroplets as reaction carriers for bacteriophage infection due to a higher contact ratio. The optofluidic imaging is based on the effective refractive index changes in the microdroplet correlated with the growth rate of the infected host cells, which is highly sensitive, i.e. can detect one E. coli cell. The droplet optofluidic system is not only used in drinking water quality monitoring, but also has high potential applications for pathogenic bacteria detection in clinical diagnosis and food industry.
    Lab on a Chip 07/2014; · 5.70 Impact Factor
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    ABSTRACT: This paper presents an on-chip immersion refractometer for the measurement of size, shape and refractive index of protozoa in treated water. The key features of the on-chip immersion refractometer include (1) multiple single cyst trapping sites, which enable the measurement of multiple sample per test; and (2) zig-zag micromixer, which enables the refractive index variation of external medium as the key component of immersion refractometry. The results show that C. parvum oocysts have size of 3 to 7 μm, spherical with ovality lower than 0.3, and refractive index of 1.418. G. lamblia cysts have size of 8 to 12 μm, oval with ovality higher than 0.3, and refractive index of 1.433. The refractive indices of the samples are measured with high precision of <;10<sup>-3</sup>.
    Solid-State Sensors, Actuators and Microsystems Conference (TRANSDUCERS), 2011 16th International; 07/2011
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    ABSTRACT: This letter reports the development of an optofluidic Fabry-Pérot (FP) resonator, which consists of a microcavity and a pair of liquid microlenses. The microcavity forms part of the microchannel to facilitate sample injection. The liquid microlenses are used for efficient light coupling from the optical fiber to the microcavity. The liquid microlens collimates the diverging light from the optical fiber into the FP cavity, which provides real-time tuning to obtain the highest possible finesse up to 18.79. In volume refractive index measurement, a sensitivity of 960 nm per refractive index unit (RIU) and a detection range of 0.043 RIU are achieved.
    Biomicrofluidics 01/2010; 4(2). · 3.39 Impact Factor
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    ABSTRACT: A microfluidic cell sorting chip has been developed using micromachining technology, where electroosmotic flow (EOF) is exploited to drive and switch cells. For this electroosmotically driven system, it is found that the effect of induced hydrostatic pressure caused by unequal levels in solution reservoirs is not negligible. In this work, the numerical simulation of EOF and opposing pressure induced flow in microchannels is presented and the velocity profiles in the microchannels are measured experimentally using microparticle imaging velocimetry (PIV) system. The result shows that the final resulting velocity is the superposition of the two flows. A total volume of 0.305 μl is transported in the 50 μm microchannel and the back flow occurs after 240 s transportation. The task of sorting cells is realized at the switching structure by adjusting the electric fields in the microchannels. The performance of the cell sorting chip is optimized by investigating the effect of different switching structures. A Y-junction switching structure with 90° switching angle is highly recommended with simulated leakage distance of 53 μm and switching time of 8 ms.
    Sensors and Actuators A Physical 02/2007; · 1.84 Impact Factor
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    ABSTRACT: We report a novel method for measuring the effective refractive index (RI) of single living cell using a small integrated chip, which might be an efficient approach for diseases diagnosis. This microchip is able to determine the refractive index of single living cell in real time without any extra cell treatments such as fluorescence labelling, chemical modification and so forth, meanwhile, providing low cost, small size, easy operation and high accuracy. The measurement system integrates an external cavity laser, a microlens, and some microfluidic channels onto a monolithic chip. In the experiments, two standard polystyrene beads with nominal RI are utilized to calibrate the measurement system and five different types of cancerous cells are subsequently measured in the chip. The experimental results show that the refractive indices of the cancerous cells tested ranges from 1.392 to 1.401, which is larger than typical value of normal cell of 1.35–1.37. This integrated chip potentially has a serial of applications on biodefense, disease diagnosis, biomedical and biochemical analysis.
    Sensors and Actuators A: Physical. 01/2007;
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    ABSTRACT: This paper presents an interferometric method for measuring the dry/wet mass of a single living cell using an optofluidic chip. It consists of the fiber Mach-Zehnder interferometer and the fiber-optical trap, both of which are integrated onto a single chip. In experiment, a single living cell is captured by the fiber-optical trap, and then the cell's refractive index and diameter are simultaneously determined by the spectral shift in response to the buffer modulation. Hence, both cell dry and water masses can be calculated with a precision higher than 5%.
    Applied Physics Letters 01/2007; 91. · 3.52 Impact Factor
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    ABSTRACT: This paper reports a novel method for measuring the effective refractive index (RI) of single living cell with a small integrated chip. This microchip is able to determine the RI of living cell in real time without extra requirements of fluorescence labeling and chemical treatments, offering low cost and high accuracy meanwhile. It might provide an efficient approach for diseases or cancer diagnosis. The measurement system integrates laser diode, microlenses, and microfluidic channels onto a monolithic chip. In the experiments, two standard polystyrene beads with nominal RIs are, employed to calibrate the system and five types of cancerous cells are subsequently measured. The results indicate that the RI of the tested cells ranges from 1.392 to 1.401, which is larger than typical value 1.35-1.37 for normal cells.
    Solid-State Sensors, Actuators and Microsystems, 2005. Digest of Technical Papers. TRANSDUCERS '05. The 13th International Conference on; 07/2005
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    Y. Sun, A.Q. Liu, P.H. Yap, T.C. Ayi
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    ABSTRACT: This paper described a self-contained microfluidic system that is capable of monitoring the progression of the HIV infection by counting and sorting CD4 cells. The system can handle raw blood sample without off-chip sample preparation step and by using laser diode as the light source, the need for big and expensive laser is eliminated. Blood analysis is currently being performed in central labs on expensive, high-maintenance equipment and can be time consuming, whereas our system is portable, low-cost and could be used in each doctor's office, as a point-of-care instrument at home or in places with high risk of exposure to biowarfare agents.
    Solid-State Sensors, Actuators and Microsystems, 2005. Digest of Technical Papers. TRANSDUCERS '05. The 13th International Conference on; 07/2005
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    ABSTRACT: Figure 1: (a) Schematic of molecule mass transfer across the two immiscible phase boundary. (b) Schematic of the solute extracting (concentration varying) process indicated by droplets at different reaction times. ABSTRACT This paper demonstrated a fluorescence-indicated mass transfer liquid-liquid extraction process based on a droplet microfluidic system. Analysis of the droplet-based liquid-liquid extraction process based on the description of mass transfer into or out of droplets is conducted. The relationship between the extraction efficiency and the droplet size is measured and the mass transfer coefficient for fluorescein from octanol to PBS buffer is determined as 3.07 × 10 -5 m/s. This work has wide potential applications in extraction system design and other chemical-biological areas.
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    ABSTRACT: This UROP project aims to do a feasibility study on electronic properties of DNA especially on Metallic DNA (M-DNA). We are trying to prove the conductivity of M-DNA. This document begins with a general introduction of electronic properties of DNA and M-DNA. The experiment set up and results will also be covered in later part. Finally, a short discussion based on the experiment results with respect to the results.
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    Y Sun, A Q Liu, P H Yap, T C Ayi
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    ABSTRACT: This paper presents an integrated and self-contained microfluidic system for monitoring the progression of the HIV infection by counting and sorting CD4 cells. The system can handle raw blood samples without the need of off-chip sample preparation. In addition, the system has integrated a laser diode onto the microchip as the light source, making it more compact and portable. Compared with the current blood analysis method performed in central laboratories, our system is low cost, portable and low requirement for maintenance, and thus could be used for point-of-care diagnosis. 1. INTRODUCTION Progression from clinical latency to AIDS in persons with HIV infection is suggested by CD4 lymphocyte counts of less than 500 cells per ml. Blood analysis is currently being performed in central labs on expensive, high-maintenance equipment and can be time consuming. Therefore there is a need for portable, fast and easy-to-operate cytometer system for small clinics or ever household use. Kruger et al. demonstrated a miniaturized flow cytometer which can perform the key functions of detection, enumeration and sorting of fluorescent species [1]. Dittrich et al. reported a microfluidic device for reaction, high-sensitivity detection and sorting of fluorescent cells and particles [2]. But for all these miniaturized flow cytometers, blood samples need to be pre-processed before they can be put into the chip. And another problem is that external laser has to be used as the light source for optical detection, which results in the difficulty of integration. We proposed a self-contained microfluidic system fabricated in poly (dimethyl siloxane) (PDMS) to monitor the progression of the HIV infection. Reagents will be preloaded in the respective reservoirs such that the system can handle the raw blood sample without any off-chip sample preparation step. Laser diode will be integrated in the chip as the light source, which eliminates the need for bulky and expensive laser system and makes the optical system more compact.
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    ABSTRACT: This paper proposes a novel, non-invasive and reliable method for cell identification based on MEMS laser spectroscopy and microfluidic chip. This system integrates micro flow and micro-optics into one chip to realize cell identification and manipulation. An argon laser at 488 nm passing through a microlens array was used to excite a fluorescence-labeled cells suspended in solution. The microlens array serves the function to focus the laser to the desired spot size and also to reduce the scattering in the channel sidewall. A spectrometer is used for detecting the fluorescence spectrum and identifying the cells. The device was calibrated by use of polystyrene micro beads and tested on HeLa cells. As expected, different cells are identified according to their specific fluorescence spectra. This identification system might provide a valuable tool for cell studying and cancer diagnosis such as leukemia, AIDS and so on.
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    ABSTRACT: Isolation and purification of cell subpopulations are of great importance to cell biology and molecular genetics. This paper presents an integrated microfluidic device for fluorescence activated cell sorting based on the indirect manipulation of cells by precisely steering the liquid flow. Unlike conventional pressure-driven system, this microfluidic device exploits electroosmotic flow for sample transportation, focusing and switching. Electroosmotic manipulation on-chip eliminates the need for external syringe pump and provides faster and accurate switching and consequently, higher throughput.