Gold Nanoparticle Synthesis for Surface Enhanced Raman Spectroscopically Active Substrate

Abstract

Large and small nanospheres, large and small nanoplates, nanorods and nanostars have been synthesized and fabricated into SERS substrates consisting of sandwiched and aggregated structure. Using 633 nm laser as excitation, individual SERS spectra of each labeling molecules, benzenethiol, 4-nitrobenzenethiol and 4-quinolinethiol, have been successfully obtained and the combination of these three molecules have the least amount of overlapping and can all be identified from the reference multiplexed spectra. Among all the substrates that have analyzed, the substrate made from nanospheres with sandwiched structure is able to produce multiplexed SERS spectra with more details and higher reproducibility. Although multiplexed SERS spectra can also be observed from substrates made from small nanoplates, nanostars and nanorods substrates with sandwiched structures, the unique peaks representing the labeling molecules are less consistent in their intensity. In addition, substrates with micro sized plates in sandwiched configuration are found to exhibit much lower SERS activities and this can be due to the size of the plate being much greater than the light source, restraining the surface plasmon resonance effect. Most of the substrates fabricated with aggregated nanoparticles have very low reproducibilities and saturated signals with 633 nm excitation. The spectra peaks are much easier to identify and are much more reproducible when 785 nm excitation have been adopted. This can be due to the size of the aggregated nanoparticles are much bulkier which a deeper penetrating light source is required to induce more molecules labels to exhibit SERS activities. A novel SERS substrate has been fabricated with nanoparticle-thiol-microplate sandwiched configuration by using a double ended thiol molecules, benzenedithiol, to strongly connect nanospheres and the plates together. However, the measurement of the SERS activity is limited by the overpowering of the light source, which has frequently melted and evaporated the plate samples once they have been exposed to the excitation radiation. In addition, instead of spreading evenly on the microplate surfaces, the nanoparticles have appeared to be aggregated which may have increased the difficulty in obtaining SERS activity.