Taihu Wu

Compact 405-nm random-modulation continuous wave lidar for standoff biological warfare detection

Abstract. A compact bioaerosol standoff system was developed and tested for bio warfare agent stimulant aerosol detection. It used a continuous-wave semiconductor laser diode with an output power of 100 mW and a wavelength of 405 nm. It was modulated with a pseudorandom code at 100 MHz to provide the 1.5 m range resolution for both scattering and fluorescence detection. A 200-mm-diameter Cassegrain telescope and four photon-counting detection channels centered at 405 nm (two polarization detection channels), 450 nm, and 530 nm constituted the optical receiver. A field-programmable gate array chip was controlled to generate the laser driver signal and record four synchronized channel signals. Field tests were performed with stimulant aerosols of Bacillus subtilis, Staphylococcus aureus, and yeast. The detected biological warfare stimulant aerosol lidar was released at ranges of several hundred meters. The preliminary result showed that the fluorescence channel detected the stimulants at ranges up to 90 m and the elastic scattering channel up to 200 m.

AUTOMATED GATING OF PORTABLE CYTOMETER DATA BASED ON SKEW t MIXTURE MODELS

A major component of flow cytometry (FCM) data analysis involves gating, which is the process of identifying homogeneous groups of cells. With the rapid development of the portable flow cytometer, manual gating techniques have been unable to meet the demand for accurate and rapid analysis of samples. To provide a practical application for portable devices, we propose a flexible, statistical model-based clustering approach for identifying cell populations in FCM data. This approach, which mimics the manual gating process, employs a finite mixture model with a density function of skew t distribution and estimates parameters via an expectation maximization algorithm. Data analysis from an experiment on a patient’s peripheral blood samples have proven that the proposed methodology yields better results in terms of robustness against outliers than current state-of-the-art automated gating methods, has more flexibility in clustering symmetric data and leads to lower misclassification rates (misclassification rates of skew t method is 0.06442) when handling highly asymmetric data. The method we proposed will improve data analysis of portable flow cytometers, especially when the users have no professional training.

Detection of bacteria based on quantum dots by using a laboratory-made system

This study investigated a method that simultaneously detects three bacteria, Salmonella typhimurium, Escherichia coli, and Staphylococcus aureus via an approach that use antibody-conjugated quantum dots (QDs) as fluorescence markers, by using a laboratory-made system. QDs with different emission wavelenghs were immobilized with antibody. Antibody conjugated QDs capture the bacteria selectively and specifically so that ”sandwich” complex were formed. The suspension of the labeled bacteria was trickled onto a microporous membrane. A 450nm semiconductor laser was used as a part of the laboratory-made system to excite the QDs. Three PMT detectors were utilized to detect the fluorescence intensity. This method, of which the detection procedures are completed within 1 h, can be applied to the cost-effective and rapid detecting of bacterial contamination.