Ruth Keir

Novel SERS-active optical fibers prepared by the immobilization of silver colloidal particles

A novel sensor based upon surface-enhanced Raman scattering (SERS) has been constructed by immobilizing colloidal silver particles onto the distal end of an optical fiber. This same single fiber was then used to both transport the exciting laser radiation and collect the Raman scattering from analytes sorbed onto the colloidal particles. The colloidal particles were immobilized by functionalization of the end of the optical fiber with (3-aminopropyl)trimethoxysilane prior to immersion of the fiber in silver colloid. Spectra were obtained from both 4-(5′-azobenzotriazol)3,5-dimethoxyphenylamine and crystal violet. The within-batch variation of a set of five fibers has been measured as approximately 10%. Raman imaging experiments demonstrated that the effects due to spatial variations in the intensity of the SERS recorded over the distal end of the fiber are removed by the use of a multimode fiber.

Comparison of surface-enhanced resonance raman scattering and fluorescence for detection of a labeled antibody

A comparison is made of the quantitative detection of a labeled antibody by surface-enhanced resonance Raman scattering (SERRS) and by fluorescence using the same instrument with the same laser excitation source. The area under the curve for the fluorescence band is greater than for any single peak in the SERRS spectrum, but the broad fluorescence band is more difficult to discriminate from the background at low concentrations. Using the peak height of one SERRS band and the peak height at the fluorescence maximum, the detection limit for SERRS was lower (1.19 x 10-11 mol.dm-3) than that obtained using fluorescence (3.46 x 10-10 mol.dm-3). The SERRS detection limit is calculated for the concentration of the sample added, but compared to fluorescence, there is an additional dilution step due to the addition of the colloid and the extent of this dilution is dependent on assay format. For comparison with the detection limits found earlier with labeled oligonucleotides, SERRS was remeasured with a 10 s accumulation time, and the final concentration in the cuvette after colloid addition and before any adsorption to the silver was used to calculate a detection limit of 2.79 x 10-13 mol.dm-3. This is comparable to the detection limit found using a similar SERRS procedure for an oligonucleotide labeled with the same dye. This experiment is dependent on many parameters that could affect this result, including the nature of the SERRS substrate, the excitation wavelength, and the dye chosen. However, the result indicates that SERRS can give assay sensitivities comparable or better than fluorescence for quantitative direct assay determination, suggesting that the much greater potential for multiple analyte detection could be exploited.

Preparation of Stable, Reproducible Silver Colloids for Use as Surface-Enhanced Resonance Raman Scattering Substrates

A flow system for the production of stable, reproducible batches of silver colloid for use as substrates for surface-enhanced resonance Raman spectroscopy (SERRS) is described. The colloids were prepared by borohydride reduction of silver nitrate and subsequent stabilization was achieved by adding trisodium citrate. The batches of colloid produced were analyzed using UV-visible spectroscopy and their suitability for use as SERRS substrates was assessed using 3,5-dimethoxy-4-(5′-azobenzotriazole)phenylamine as the analyte. SERRS analysis was carried out using a flowcell. Using the method described, batches of silver colloid were prepared that were stable for at least five months and when used as SERRS substrates resulted in a relative standard deviation in SERRS intensity of 3,5-dimethoxy-4-(5′-azobenzotriazole)phenylamine of 6.6% between colloid batches. The robustness of the system for production of stable, reproducible colloids was assessed using experimental design. The final method proposed enables reproducible, time-stable colloid to be made in a simple manner, thus eliminating one of the major problems associated with the use of SERRS detection in analytical procedures.

Selective functionalisation of TNT for sensitive detection by SERRS

Selective chemical functionalisation of 2,4,6-trinitrotoluene to a surface enhanced resonance Raman active species for sensitive detection.

SERRS multiplexing from labelled oligonucleotides in a microfluidics lab-on-a-chip

The growing need for accurate and fast methods of DNA detection in the post genomic era has generated the development of a number of new platforms for sample analysis. Two of the most popular approaches have been the use of microarrays of immobilized probes and microfluidics chips. Both approaches require a detection technique to be used with the platform which has a high enough sensitivity for such small analyte volumes. The techniques of choice tend to be mass spectrometry or fluorescence spectroscopy. Here we propose SERRS as an alternative spectroscopy for detection. SERRS and fluorescence have comparable sensitivities but one main advantage of SERRS is that the peaks in the spectra are much narrower and are more easily resolved. This, in principle, opens up the potential for the simultaneous detection of multiple labels to a degree not possible with fluorescence, thus providing an enabling technology for the more complex assays required since the completion of the human genome map. Also, when using SERRS both fluorophores and nonfluorophores are suitable so that a more extensive and simpler labelling chemistry can be employed.