Several polymeric membranes were evaluated for their potential to improve the sensitivity and impart chemical
selectivity to surface plasmon resonance (SPR)-based sensors. The membranes tested encompass a variety of deposition
methods, providing an insight of the contact requirements between polymers and the plasmon supporting metal. Among
the membranes evaluated, preliminary results utilizing polyelectrolyte multilayer membranes displayed reliable detection
of vapor-phase ammonia at ~40 ppm levels. Chemically synthesized polyaniline also presented encouraging results,
responding to ammonia gas at 48 ppm. This is in sharp contrast to the electropolymerized counterpart, which showed
minor wavelength shifts even at elevated ammonia levels (4 %).
SPR has been adopted by the bioanalytical community to probe biomolecular interactions and obtain information relating
to binding kinetics. Similarly, modifying plasmon-supporting surfaces with bioreceptors enables access to biosensing
applications. Gas-phase sensing with SPR has largely remained unexplored primarily due to the small changes in
refractive index from low molecular weight molecules. Coating SPR sensors with tailored polymers has been discussed
as a viable approach to amplifying refractive index changes related to low molecular weight analytes.
Ammonia is a low molecular weight analyte that is ubiquitously present in the gas phase. Industrial and medical interest
in ammonia at low ppm level yielded numerous scientific contributions describing diverse sensing approaches. Hence,
ammonia is a good candidate to provide a baseline for immediate comparison with other approaches for evaluation of the
polymers with regards to their susceptibility to undergo changes in dielectric properties and chemical affinity for the
A novel Surface Plasmon Resonance (SPR) sensor to detect glucose using molecularly imprinted polymer (MIP) will be presented in this paper. SPR has been traditionally used as a probe for surface interaction of large molecules but harder to measure small molecules since the effective change in the SPR condition becomes smaller. The accurate measurement of glucose in complex physiological fluids like urine is particularly challenging since the constituents of these fluids vary significantly from person to person and even throughout the day for a particular individual. The polymer was prepared by crosslinking polyallyamine in the presence of Glucose Phosphate, monobarium salt (GPS-Ba) and attached to a 50 nm thin film of gold which had been sputtered on top of a glass slide, via amide coupling. Upon removal of the template, this sensor was used to detect glucose in human urine in physiologically significant levels (1-20 mg/ml). Enhancement of the glucose sensor was made possible by incorporating gold nanoparticles which improved the signal. This study has demonstrated the specific detection of glucose in a complex physiological fluid using SPR spectroscopy. The association of glucose to the imprinted polymer results in the swelling of the polymer that can be tracked by the minima in SPR spectra. The sensitivity of this method, while lower than protein based detection schemes, is sufficient for quantitative measurement of glucose in urine at physiologically significant levels without extensive pre-treatment of the sample. Given the nature of the weak non-covalent binding of glucose to the amine functional groups, the scheme used here can be adapted to detect a number of different molecular species of sizes comparable to that of glucose without the need for extensive sample preparation or use of chemicals with limited shelf life.
Most applications of fiber optic SPR sensors are designed to measure refractive index (RI) of biological sample by single channel, also the sensitivity and stability of the sensor system is easily affected by the unexpected effects from instrumentation and external environment conditions. In this study, we presented two dual-channel fiber optic SPR sensors based on flat-tip or tetra-taper tip structure with two SPR spectrum located on separate wavelengths that can be used for self-compensating RI measurements of more than one biological samples. The prototyped sensors were fabricated and laboratory characterized. The preliminary experimental results demonstrate the characteristic responses of both SPR wavelengths from two channels are independently correspond to the RI changes of the detected samples or the temperature characters of external environment. Both of these two designs could be extend practicable highly sensitive multi-channel sensor systems that will have extensive applications for biological monitoring.
Surface Plasmon Resonance (SPR) spectroscopy offers many potential industrial applications. SPR sensors are suitable to monitor liquid and gas phase mixtures. The use of fiber-optic SPR sensors enables the possibility of remote sensing in real-time. The sensors can be made as small as 45mm long using 200um optical fibers. Measurement of organic vapors and salinity are demonstrated using the SPR sensors. The mixing dynamics are easily accessible using SPR sensors. The mixing of hexanes and isopropanol in static solution was monitored in real time. Another important application is the analysis of the excess dielectric properties for various binary mixtures using a SPR sensor. Binary mixtures with similar refractive index were measured. Strong deviations from ideality are seen using SPR to monitor the dielectric properties. SPR sensors can be integrated to production lines to monitor the extend of products or compounds inline.