We demonstrate the potential use of silver nanorod (AgNR) array substrates for on-chip separation and detection of
chemical mixtures by ultra-thin layer chromatography (UTLC) and surface enhanced Raman spectroscopy (SERS). The
capability of the AgNR substrates to separate different compounds in a mixture was explored using a mixture of the food
colorant Brilliant Blue FCF and lactic acid, and the mixtures of Methylene Violet and BSA at various concentrations.
After the UTLC process, spatially-resolved SERS spectra were collected along the mobile phase development direction
and the intensities of specific SERS peaks from each component were used to generate chromatograms. The AgNR
substrates demonstrate the capability of separating Brilliant Blue from lactic acid, as well as revealing the SERS signal
of Methylene Violet from the massive BSA background after a simple UTLC step. This technique may have significant
practical implications in actual detection of small molecules from complex food or clinical backgrounds.
Analysis of bioimaging and biospectra data has received increasingly attention in recent years.
Here we will present two experimental results based on independent component analysis (ICA):
differentiation of superparamagnetic iron oxide (SPIO) nanoparticles used as contrast agents in magnetic
resonance imaging (MRI), and differentiation of mixed chemical analytes by surface-enhanced Raman
scattering (SERS). The SPIO nanoparticles have been applied extensively as contrast agent in MRI for
tracking of stem cells, targeted detection of cancer, due to its biocompatible and biodegradable features.
For differentiation of SPIO from the background signal (e.g. interface between air and tissues), the signal
voids from multiple sources makes the task very difficult. To solve this problem, we assume that the
number of sensors corresponds to the number of acquisitions with different combinations of MR
parameters, i.e., longitudinal and transverse relaxation times. For detection of chemical and biological
analytes, the SERS approach has drawn more interest because of its high sensitivity. SERS spectra of
mixed analytes were acquired at different locations of a silver nanorod array substrate. Due to the nonuniform
diffusion and adsorption of the analytes, these spectra have been successfully used to identify the
characteristic SERS spectrum of individual analytes. In both the MRI and SERS data, signal source separation (SPIO or mixed chemical analytes from background signal) was performed on a pixel by pixel basis. The ICA was performed by a spatial analysis using the fast ICA method.
SERS-active substrates are fabricated by oblique angle deposition and patterned by a polymer-molding technique to
provide a uniform array for high throughput biosensing and multiplexing. Using a conventional SERS-active molecule,
1,2-Bis(4-pyridyl)ethylene (BPE), we show that this device provides a uniform Raman signal enhancement from well to
well. The patterning technique employed in this study demonstrates a flexibility allowing for patterning control and
customization, and performance optimization of the substrate. Avian influenza is analyzed to demonstrate the ability of
this multi-well patterned SERS substrate for biosensing.