Long-range surface plasmon waveguides, and their application to various transducer architectures for amplitude- or
phase-sensitive biosensing, are discussed. Straight and Y-junction waveguides are used for direct intensity-based
detection, whereas Bragg gratings and single-, dual- and triple-output Mach Zehnder interferometers are used for phasebased
detection. In either case, multiple-output biosensors which provide means for referencing are very useful to
eliminate common perturbations and drift. Application of the biosensors to disease detection in complex fluids is
discussed. Application to biomolecular interaction analysis and kinetics extraction is also discussed.
The suitability and use of long-range surface plasmon-polaritons for leukemic biomarker detection is discussed. A novel optical biosensor comprised of gold straight waveguides embedded in CYTOP with an etched microfluidic channel was tested for detecting leukemia in patient serum. Gold surface functionalization involved the interaction of protein G (PG) with antibodies by first adsorbing PG on bare gold and then antibodies (Immunoglobulin G, IgG). Differentiation between healthy and leukemia patients was based on the difference in ratios of Ig kappa (Igκ) and Ig lambda (Igλ) light chains in both serums. The ratio for a normal patient is ~1.4 - 2, whereas for a leukemia patient this ratio is altered. As a receptor (primary antibodies), goat anti-human anti-IgGκ and anti-IgGλ were used to functionalize the surface. Diluted normal and leukemia patient serums were tested over the aforementioned surfaces. The ratios of mass surface densities of IgGκ:IgGλ for normal serum (NS) and patient serum (PS) were found to be 1.55 and 1.92 respectively.
A novel biosensing platform based on long-range surface plasmon waveguides is demonstrated for selective biosensing.
The sensor consists of gold waveguides embedded in CYTOP with a microfluidic channel. Gold surfaces were modified
by forming a self-assembled monolayer (SAM) and further they were functionalized by proper receptor (antibodies) with
carbodiimide chemistry. Investigation of biochemical interactions were performed with human immunoglobulin (Ig).
Human immunoglobulin M (IgM) kappa chain (IgM-κ) was tested on the waveguide, functionalized with anti-human
immunoglobulin-kappa specific chain (anti-Igκ). As a negative control, human IgM lambda chain (IgM-λ) was tested on
anti-Igκ surface. The response for IgM- sample was 0.173 dBm and that for IgM-λ was 0.033. The ratio of the
responses ΔS(IgM-κ)/ ΔS(IgM-λ) was found to be 5.3.
Biosensing using long-range surface plasmon-polariton waveguides is demonstrated. Current sensor consists of gold straight waveguides (SWGs) embedded in CYTOP with etched microfluidic channels. The sensing platform is capable of detecting analytes with a small mass as well as monitoring the change in refractive index of bulk solutions. Three solutions with different refractive indices were tested for bulk sensitivity: a mixture of Phosphate Buffered Saline (PBS) and Glycerol (7.25% w/w), Distilled/Deionized water and 2-Isopropanol. Protein Bovine Serum Albumin (BSA) was physisorbed on carboxyl-terminated self-assembled monolayer (SAM). A significant change in signal has been observed for these experiments.
Waveguides consisting of Au embedded in Cytop with micro-fluidic channels etched into the cladding are used for
sensing via the propagation of long-range surface plasmons. Initially, a range of water/glycerol solutions with varying
refractive indices were sequentially injected in a waveguide section in order to assess its bulk sensitivity and to find a
solution supporting a strong high quality mode. Au waveguide surfaces were then functionalized with antibodies against
Gram negative bacteria (Anti-Gneg) by first forming a self-assembled monolayer (SAM) of 16-mercaptohexadecanoic
acid (16-MHA) and subsequent conjugation with antibodies through carbodiimide chemistry. E.Coli XL-1 Blue was
used as an analyte in static incubations. Wavelength sweeps of 16-MHA covered waveguides were compared against
waveguides covered with E-coli. The results indicate that very few bacteria cells are required to obtain a measurable
change in output signal.