Precision transducer for Fluorescence-Based Immunoassays

This paper outlines a new sensing method for a competitive fluorescence immunoassay; without the need for the expensive optical components of filter, dichroic mirror and photo-multiplier, typically employed in fluorescence spectroscopy. This work is directed towards the measurement of progesterone in dairy milk; however the approach is applicable to other biomolecules, and could be employed as a general purpose biosensor. The sensor benefits from a novel geometrical design that reduces the effect of background LED light on the photo-detectors. It also incorporates a set of photodiodes with different frequency responses, in order to provide an adaptive dynamic offset cancellation, allowing for a high amplification level while mitigating the adverse effects of ambient and operational conditions. The transducer can measure down to 1 nM fluorescein concentration level in milk, a higher level of accuracy than what is required for identifying a cow´s oestrus cycle.