| Surface Plasmon Resonance (SPR) spectroscopy, a highly sensitive technique, has traditionally been used for the detection of large molecules such as proteins, peptides and DNA fragments. However, the same is not true for small molecules since the effective dielectric properties of the transduction layer do not undergo any significant change to produce a corresponding SPR shift. In order to address this problem, several polymeric substrates have been developed to detect small molecules indirectly, such that when they are absorbed by these polymers the induced change in dielectric constant of the polymer can be detected by SPR. This principle is shown by the use of (a) a molecularly imprinted polymer is shown to selectively bind glucose in human urine as well as (b) in the gas phase, by the use of a swellable polymer that absorbs dry ammonia. The response of these sensors was further enhanced by the addition of gold nanoparticles which have been shown to interact with the surface plasmon wave. The design of modified fiber-optic SPR sensors has also been described which, when combined with these polymers can enable the development of inexpensive, field-portable sensors for industrial, medical and environmental applications. |
