Yongkai Zhao

Rapid quantitative detection of Yersinia pestis by lateral-flow immunoassay and up-converting phosphor technology-based biosensor

Abstract Up-converting phosphor technology (UPT)-based lateral-flow immunoassay has been developed for quantitative detection of Yersinia pestis rapidly and specifically. In this assay, 400nm up-converting phosphor particles were used as the reporter. A sandwich immumoassay was employed by using a polyclonal antibody against F1 antigen of Y. pestis immobilized on the nitrocellulose membrane and the same antibody conjugated to the UPT particles. The signal detection of the strips was performed by the UPT-based biosensor that could provide a 980nm IR laser to excite the phosphor particles, then collect the visible luminescence emitted by the UPT particles and finally convert it to the voltage as a signal. V T and V C stand for the multiplied voltage units for the test and the control line, respectively, and the ratio V T/V C is directly proportional to the number of Y. pestis in a sample. We observed a good linearity between the ratio and logCFU/ml of Y. pestis above the detection limit, which was approximately 104 CFU/ml. The precision of the intra- and inter-assay was below 15% (coefficient of variation, CV). Cross-reactivity with related Gram-negative enteric bacteria was not found. The UPT-LF immunoassay system presented here takes less than 30min to perform from the sample treatment to the data analysis. The current paper includes only preliminary data concerning the biomedical aspects of the assay, but is more concentrated on the technical details of establishing a rapid manual assay using a state-of-the-art label chemistry.

Design and application of fiber optic evanescent wave biosensor

A fiber-optic biosensor is developed based on the principle of evanescent wave while light propagates in optical fiber. The biosensor uses a red laser diode at 636.85 nm for exciting Cy5 fluorescent dye. Sensitivity limit of 0.01 nnmol/l is obtained from the detection of serial Cy5 solutions with various concentrations. In log-to-log plot, excellent linear response characteristic is seen in the Cy5 concentrations ranging from 0.01 nmlo/l to 100 nmol/l. And a good result of signal-to-noise ratio of 4.61 is obtained when the biosensor is used to measure Legionella pneumophila solution of 0.01 μmol/l. All the results are comparable with those that are obtained by a commercial biochip scanner GeneTAC 1000.

Theoretical studies on bioaerosol particle size and shape measurement from spatial scattering prof iles

A method of clarifying bioaerosol particles is proposed based on T-matrix. Size and shape characterizations are simultaneously acquired for individual bioaerosol particles by analyzing the spatial distribution of scattered light. The particle size can be determined according to the scattering intensity, while shape information can be obtained through asymmetry factor (AF). The azimuthal distribution of the scattered light for spherical particles is symmetrical, whereas it is asymmetrical for non-spherical ones, and the asymmetry becomes intense with increasing asphericity. The calculated results denote that the 5o-10o scattering angle is an effective range to classify the bioaerosol particles that we are concerned of. The method is very useful in real-time environmental monitoring of particle sizes and shapes.

A miniaturized laser-diode-based optical sensor for laser particle counter

A miniature optical sensor for laser particle counter is described, and some calculated and test results are reported in this paper. A reflective spherical mirror coated with highly reflective optical film is applied as collecting element for scattered light, and a PIN photodiode with high performance is used as the photo-detector. A band-pass preamplifier is used to eliminate lower-frequency electromagnetic interference from external environment, as well as to filter high-frequency components from electronic noise. An air sampling system can provide a very constant flow rate. The smallest particle diameter of the optical sensor is 0.3 microns with a signal-to-noise ratio exceeding 2:1.

Single-particle size measurement by light-scattering method

We have designed and constructed a white light optical sensor for optical particle counter (OPC). The optical system of the sensor is a right-angle scattering type optics. It consists of an illumination system and a collection system for scattered light. A large illuminating aperture angle of 24 degrees is obtained by applying an aplanatic singlet in the illumination system, and a large collecting aperture angle of +/- 44 degrees is achieved by a spherical mirror. With the two large apertures, high signal-to-noise ratio and good monotonic light scattering response have been gained.

Light scattering modeling of bacteria using spheroids and cylinders

Numerical simulations of light scattering by irregularly shaped bacteria are carried out using the T-matrix method. A previously developed T-matrix code for the study of light scattering by randomly oriented non-spherical particles is used for the current purpose and it is validated against Mie-theory using coccus. Simplified particle shapes of spheroids and cylinders for simulating scattering by irregularly shaped bacteria are studied. The results for the angular distributions of the scattering matrix elements of B.Subtilis at wavelength 0.6328μm are presented. Their dependence on shape and model are discussed. Analysis suggests that spheroids perform better than cylinders for B.Subtilis. Calculations of the scatter matrix elements to determine bacteria sizes as well as shapes may be an accurate method and may be used to determine what the bacteria are.

UPT-based biosensor and its application

An up-converting phosphor technology-based biosensor (UPT-based biosensor) has been developed for immunoassay using Up-converting phosphor (UCP) as the biological marker. The UPT system has realized quantitative detection and has good ability to meet the need of some emergencies. High sensitivity (nanogram/ml), good linear response characteristics and an excellent correlation (R2greater than or equal to 0.95) have been verified by quantitative detection results. The sensitivity of the UPT-based biosensor is better than that of the indirect hemagglutination test in the practical application. All the results are comparable with that obtained by Western Blot detection.

Performance test of focusing optics based on the Hartmann principle

The performance inspection of focusing optics, such as focusing lens and focusing assemblies, is of great importance in the machining of optical elements, alignment and regular maintenance of optical facilities. Currently, however the interferometric method and the knife-edge method used normally for the measurement of the large-aperture surface have limitations for the test in the large optical equipment. To solve the problems, a scanning Hartmann inspection apparatus based on the Hartmann principle for focusing optics performance test has been developed. In this paper, the experimental setup and test principle are described, experimental results and analysis are given, and the improvement plan further to obtain better test capability is briefly presented in the end.

Displacement measurement based on moire technique and polarization modulation

A method to measure displacements based on Moire technique and polarization modulation is presented and analyzed with Fourier transform and Jones matrix in this paper. A collimated laser beam illuminates a scale grating moved in the direction perpendicular to its groove. The scale grating is imaged on a two-phase index grating through a 4f system with an aperture in its frequency plane to form Moire fringes. The scale grating and the index grating have same grating period and their line and space ratio is 1:1. Two sections of the index grating are imaged on two parts of a bi-cell detector through a telecentric system, thereby the displacement of the scale grating can be obtained by detecting the Miore signals on the detector. Before the index grating, a polarizer and a Savart plate are placed. In the telecentric system, a photoelastic modulator between two quarter-wave plates and an analyzer are arranged. Thus the polarization modulation of the Moire signals is realized. The polarization modulation improves the measurement accuracy of the displacement. The analysis shows the displacement measuring method is of nanometer accuracy. In experiments, we verified the feasibility of the method. The repeatability of the method was less than 12nm.

Laser-diode-based optical sensor for laser particle counter

A laser-diode based optical sensor for laser particle counter is described,nd some calculated and test results are reported in this paper. A low-powered 650 nm laser diode is used as the light source. The optical system of the sensor is a right- angle scattering optics, which consists of an illumination system and a wide-angle collection system for scattered light. The sensor features high counting efficiency and high signal- to-noise ratio for smaller particles.