Biomedical subjects

Linda Z Shi

Publications and source records attributed to Linda Z Shi.

4 recordsLinked to original sources

PubMed2007

High-throughput sorting and analysis of human sperm with a ring-shaped laser trap.

Sperm motility is an important concept in fertility research. To this end, single spot laser tweezers have been used to quantitatively analyze the motility of individual sperm. However, this method is limited with throughput (single sperm per spot), lacks the ability of in-situ sorting based on motility and chemotaxis, requires high laser power (hundreds of milliWatts) and can not be used to dynamically monitor changes in sperm swimming behavior under the influence of a laser beam. Here, we report a continuous 3-D ring-shaped laser trap which could be used for multi-level and high-throughput (tens to hundred sperm per ring) sperm sorting based on their motility and chemotaxis. Under a laser power of only tens of milliWatts, human sperm with low to medium velocity are slowed down, stopped, or forced to change their trajectories to swim along the ring due to the optical gradient force in the radial direction. This is the first demonstration of parallel sperm sorting based on motility with optical trapping technology. In addition, by making the sperm swimming along the circumference of the ring, the effect of laser radiation, optical force and external obstacles on sperm energetics are investigated in a more gentle and quantitative way. The application of this method could be extended to motility and bio-tropism studies of other self-propelled cells, such as algae and bacteria.

Cell Separation↗

PubMed2006

Real-time automated tracking and trapping system for sperm.

We have developed a microscope system for real-time single sperm tracking with an automated laser tweezers escape power assay. Phase contrast images of swimming sperm are digitized to the computer at video rate. The custom algorithm creates a region of interest centered about a sperm in response to a mouse click and performs all subsequent tasks autonomously. Microscope stage movement responds to feedback from video analysis of swimming sperm to center the sperm with respect to the field of view. For escape power assays, sperm are automatically relocated to the laser trap focus where they are held for a user-defined duration at fixed power, or held as laser power is gradually reduced. The sperm's position is automatically monitored to measure the laser power at which the sperm escapes the trap. Sperm are tracked for extended durations before and after laser trap experiments. Motility measurements including the curvilinear velocity and the absolute position of the sperm relative to the cell chamber are calculated and written to the hard drive at video rate. Experimental throughput is increased over 30 times compared to off-line data analysis. The efficacy of the "track and trap" algorithm is validated through examples and comparisons with the manually collected data.

Animals↗

PubMedDate not supplied

Analysis of sperm motility using optical tweezers.

This study examines the use of optical trapping as a quantitative measure of sperm motility. The effects of laser trap duration and laser trapping power on sperm motility are described between sperm swimming force, swimmimg speed, and speed of progression (SOP) score. Sperm (SOP scores of 2-4) were trapped by a continuous-wave 1064 nm single-point gradient laser trap. Trap duration effects were quantified for 15, 10, and 5 seconds at 420 mW laser power. Laser power effects were quantified at powers of 420 mW, 350 mW, 300 mW, and 250 mW for five seconds. Swimming force, swimming speed, and SOP score relationships were examined at a trap duration and trapping power shown to minimally affect sperm motility. Swimming forces were measured by trapping sperm and subsequently decreasing laser power until the sperm escaped the trap. Swimming trajectories were calculated by custom-built software, and SOP scores were assigned by three qualified sperm scoring experts. A ubiquitous class of sperm were identified that swim with relatively high forces that are uncorrelated to swimming speed. It is concluded that sperm swimming forces measured by optical trapping provide new and valuable quantitative information to assess sperm motility.

Animals↗

PubMedDate not supplied

Computer-based tracking of single sperm.

This paper describes a robust single sperm tracking algorithm (SSTA) that can be used in laser optical trapping and sperm motility studies. The algorithm creates a region of interest (ROI) centered about a sperm selected by the user. SSTA contrast enhances the ROI image and implements a modified four-class thresholding method to extract the tracked sperm as it transitions in and out of focus. The nearest neighbor method is complemented with a speed-check feature to aid tracking in the presence of additional sperm or other particles. SSTA has a collision-detection feature for real or perceived collision or near-miss cases between two sperm. Subsequent postcollision analysis employs three criteria to distinguish the tracked sperm in the image. The efficacy of SSTA is validated through examples and comparisons to commercially available computer-aided sperm tracking systems.

Algorithms↗