In recent years there have been developed test cards, e.g. solid phase immunoassay test cards, for biomedical diagnostic purposes. Such test cards are normally provided with one or more test sites, normally only a few millimeters (eg. about 5 millimeters) wide, to which a liquid sample (e.g. blood or serum) is applied. The test sites are designed to change colour in response to the presence and concentration of a particular component (e.g. a certain protein) in the liquid sample.
This colour change can, at least to a certain extent, be detected and measured by eye, by for example comparing a treated test site with a reference colour chart. Such visual techniques are, however, clearly unsatisfactory when it is desired to produce an accurate reliable measurement. To obtain reliably highly accurate measurements, an instrumental system is sought.
Measurement of colour, colour spectra and colour intensity of an opaque surface is performed by analyzing the light reflected from the surface when exposed to a defined light. It is essential that the surface area to be measured and the detection system are not exposed to external light during measurements, and light shielding of the mechanism is therefore provided. This is particularly critical if weak light sources such as light emitting diodes (LEDs) are used rather than strong sources such as xenon arc lamps or the like. It is also important that the light emitter and the light detector have defined positions relative to the surface to be measured.
Conventional instruments for analyzing surface colours tend to be large and heavy, thus not readily transportable, or smaller but still inflexible in use. Attempts to develop more versatile, small transportable systems have been made, but to date no known system meets all the requirements to overcome the problems of the prior art.