The inability to have children can cause great heartache for many couples, with infertility affecting at least one-in-six couples in Britain and one-in-eight in the United States. The most common cause is male infertility, usually characterised by sperm with little or no mobility. One treatment commonly used in these cases is in vitro fertilisation (IVF). This involves injecting sperm into the egg in a laboratory.
The fertilised egg, or zygote, is then transferred to the mother's uterus with the intent of establishing a successful pregnancy. However, the DNA in sperm with limited mobility is often damaged, which can affect the success rate of IVF treatment and has led to concerns amongst the medical community of increased rates of disorder in children conceived by this method. What is needed is a method of non-destructively testing the DNA of sperm and then selecting the best sperm for IVF. Unfortunately most tests that can spot DNA damage are destructive.
Joint research by the University of Edinburgh and the University of California—performed using a Renishaw inVia Raman microscope—could one day lead to a new technique that solves this problem. The researchers are using laser light both to trap individual sperm (optical trapping) and analyse the DNA (by Raman spectroscopy). The optical trapping uses a tightly focused laser beam to create enough force to hold the sperm stationary for analysis. Once the wriggling sperm has been trapped, the DNA within it is analysed using Raman spectroscopy. The researchers are developing a statistical model that can predict the healthiness of the sperm from the Raman results, by analysing sperm of varying degrees of natural healthiness.
It is essential that the IVF sperm are not damaged by the lasers. The researchers will determine laser damage thresholds by performing tests where they compare Raman data from chemically damaged sperm with that from sperm that have been exposed to varying laser powers. If successful, the final result will be a system that can rapidly give a health report for individual sperm. Of course, the quality of the sperm is only half the story in the making of an embryo; a healthy egg is needed too. In theory, Raman spectroscopy could also be used to assess the egg cells, thereby maximising the chances of successful fertilisation. The research continues ...
Dr Alistair Elfick and Ruby Raheem at The Centre for Biomedical Engineering, School of Engineering and Electronics, University of Edinburgh, UK. Dr Rod Balhorn, Dr Stuart Myers and Dr James Chan at NSF Center for Biophotonics Science and Technology, University of California, USA.