Light interacts with biological materials in several different ways. This field of research is known as biophotonics.

Associate Professor Rainer Künnemeyer, from the University of Waikato, is investigating how these light interactions can be used in the agricultural/horticultural and medical fields.

Most aspects of Rainer’s work involve shining low-energy laser light onto or through biological materials. Depending on the type of material being investigated, the light can be reflected, absorbed, scattered or transmitted, or a combination of these.

By carefully assessing the degree to which the beam has been altered, Rainer can gather information about the structure and composition of the material. The method is non-invasive and does not damage the biological material.

Ripeness of fruit

Before leaving New Zealand’s shores, it is critical that the quality and ripeness of fruit exports are determined. Scientists like Rainer have developed biophotonic methods to do this.

By shining a beam of light onto the surface of a piece of fruit, like kiwifruit, some of the light is reflected and some enters the fruit where it is scattered by the cells and other structures within the fruit pulp. Some of this scattered light can exit through the skin close to where the incident light entered. Analysis of this exiting light provides information about the ripeness of the fruit.

Although this method of fruit analysis is in its early stages of development, it has the potential to be developed further.

Temperature of blood

In major medical operations involving the cardiovascular system, such as a heart transplant, the patient’s core body temperature is often reduced for the duration of the operation. By linking the patient up to a heart-lung machine, not only can the patient’s blood circulation be maintained but also the blood can be oxygenated and cooled. At the conclusion of the operation, the core temperature needs to be raised. If this is done too quickly, brain damage can result. A more accurate method of determining the blood temperature needs to be found.

Part of Rainer’s research work in biophotonics has focused on this problem. It involves the production of a pure white light beam such that all wavelengths present have the same amplitude. This beam is then passed through a thin layer of the patient’s blood as it travels through the heart-lung machine. The transmitted light is then analysed using a spectrometer, and from this, an accurate measure of the blood temperature can be made.

Recent trials of this proposed non-invasive method have been encouraging, but further development is needed.

Eggshell crack detection

The estimated production of hens’ eggs in New Zealand is in the region of 970 million eggs, and of these, it has been estimated that about 4% have been cracked prior to processing. Egg quality prior to sorting and packing is controlled using a process called candling. This is a relatively slow process in which the eggs are illuminated with a bright light and visually inspected.

Rainer’s previous experience with modal testing, which is used to check mechanical structures for flaws and cracks, led him to devise a mechanical method of eggshell-crack detection. The eggshell is vibrated by high energy ‘white noise’, which is a type of noise that is produced by combining sounds of all different frequencies together. The response of the shell is detected using a phase-locked self-mixing diode laser interferometer. Cracks present in the shell give a different response to the vibration than an intact shell.

This is the first time a fully non-contact modal testing method has been applied to the assessment of chicken eggshells.

Further work is planned to develop and refine this innovative eggshell-crack detection method.

This type of scientific research that Rainer is involved with is of great importance to the agricultural/horticultural and medical fields. The advantage of using light to probe the structure, composition and properties of biological materials is that the materials under investigation do not need to be destroyed to analyse them.

    Published 19 March 2012