Oleksiy Krupin

Biosensing using straight long-range surface plasmon waveguides

Straight long-range surface plasmon waveguides are demonstrated as biosensors for the detection of cells, proteins and changes in the bulk refractive index of solutions. The sensors consist of 5 μm wide 22 nm thick Au stripes embedded in polymer (CYTOP™) with microfluidic channels etched into the top cladding. Bulk sensing is demonstrated by sequentially injecting six solutions of different refractive indices in 2 × 10(-3) RIU increments; such index steps were detected with a signal-to-noise ratio of ~1000. Selective capture of cells is demonstrated using Au waveguides functionalized with antibodies against blood group A, and red blood cells of group A and O in buffer as positive and negative analyte. Bovine serum albumin in buffer was used to demonstrate protein sensing. A monolayer of bovine serum albumin physisorbed on a carboxyl-terminated self-assembled monolayer on Au was detected with a signal-to-noise ratio of ~300. Overall, the biosensor demonstrated a good capability for detecting bulk changes in solution and for sensing analyte over a very wide range of mass (from cells to proteins). The biosensors are compact, inexpensive to fabricate, and may find use over a wide range of cost-sensitive sensing and detection applications.

Serological Diagnosis of Dengue Infection in Blood Plasma Using Long-Range Surface Plasmon Waveguides

We present a compact, cost-effective, label-free, real-time biosensor based on long-range surface plasmon polariton (LRSPP) gold (Au) waveguides for the detection of dengue-specific immunoglobulin M (IgM) antibody, and we demonstrate detection in actual patient blood plasma samples. Two surface functionalization approaches are proposed and demonstrated: a dengue virus serotype 2 (DENV-2) functionalized surface to capture dengue-specific IgM antibody in blood plasma and the reverse, a blood plasma functionalized surface to capture DENV-2. The results obtained via these two surface functionalization approaches are comparable to, or of greater quality, than those collected by conventional IgM antibody capture enzyme linked immunosorbent assay (MAC-ELISA). Our second functionalization approach was found to minimize nonspecific binding, thus improving the sensitivity and accuracy of the test. We also demonstrate reuse of the biosensors by regenerating the sensing surface down to the virus (or antibody) level or down to the bare Au.

Selective capture of human red blood cells based on blood group using long-range surface plasmon waveguides

An optical biosensor based on long-range surface plasmon-polariton waveguides is applied to the detection of blood group antigen A on whole erythrocytes. The biosensor consists of straight gold waveguides embedded in CYTOP with an etched fluidic channel. The gold waveguides were functionalized with immunoglobulin G against blood group A (anti-A IgG) by forming a self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid (16-MHA) and then conjugating the anti-A IgG through carbodiimide chemistry. In order to demonstrate anti-A surface selectivity, solutions of O-type, B-type, A-type and AB-type red blood cells (RBCs) were sequentially injected over an anti-A functionalized waveguide. Surfaces were regenerated by lysing attached cells with distilled/deionized water (DDI H2O). The efficiency of surface regeneration with DDI H2O was very high as determined by performing six sequential binding/regeneration cycles of A RBC capture on the same anti-A surface. Also, five solutions of different A RBC concentrations, ranging from 1.14 × 10(5)cells/ml to 1.83 × 10(6)cells/ml, were injected over an anti-A surface to determine the limit of detection (LOD), which was found to be less than 3 × 10(5)cells/ml. Finally, the response produced by a single cell bound to a waveguide was determined by relating the number of bound cells to the response produced, from which the signal-to-noise ratio for single cell detection was determined to be ~95. The waveguides are promising as simple, low-cost and compact transducers, functionalized using standard thiol-based chemistries, for the selective detection of cells.

Mach-Zehnder refractometric sensor using long-range surface plasmon waveguides

We demonstrate refractometric sensing using long-range surface plasmons on a compact integrated Mach-Zehnder interferometer (MZI) formed from thin Au stripes in Cytop with an etched microfluidic channel defining the sensing arm. The transfer characteristics of MZIs were obtained by sequentially injecting solutions of increasing refractive index in the sensing arm. A detection limit of 9 × 10−7 RIU was achieved at λ0 = 1310 nm, limited by unbalanced losses in the sensing and reference arms. A model is proposed for the MZIs, taking into account all loss mechanisms, and may be applied to MZI sensors in other technologies.

Selective detection of bacteria in urine with a long-range surface plasmon waveguide biosensor

Experimentation demonstrates long-range surface plasmon polariton waveguides as a useful biosensor to selectively detect gram negative or gram positive bacteria in human urine having a low concentration of constituents. The biosensor can detect bacteria at concentrations of 10(5) CFU/ml, the internationally recommended threshold for diagnostic of urinary tract infection. Using a negative control urine solution of bacterial concentration 1000☓ higher than the targeted bacteria, we obtain a ratio of 5.4 for the positive to negative signals.

Optimization of Long-Range Surface Plasmon Waveguides for Attenuation-Based Biosensing

The design and optimization of straight long-range surface plasmon waveguides to maximize attenuation surface sensitivity in biochemical sensing applications are discussed. The sensor consists of a Au stripe embedded in CYTOP, with a microfluidic channel etched into the top cladding to expose the surface of the Au stripe and define the sensing channel. The attenuation α_s of the structure changes as a biological adlayer grows on the Au surface. The dimensions of the stripe (thickness, width), the sensing length and the refractive index of the sensing buffer were varied in order to understand their impact on sensor performance. The attenuation sensitivity ∂α_s/∂a dominates over a wide range of waveguide designs, so we define a parameter K = (∂α_s/∂a)/αs where maximizing |K| and selecting the optimal sensing length as L_opt = 1/(2α_s) maximizes the overall sensitivity of the structure. Experimental results based on observing the physisorption of bovine serum albumin (BSA) on bare Au waveguides agree qualitatively and quantitatively with theory. Detection limits of ΔΓ_min <; 0.1 pg·mm^-2 are predicted for optimal designs, and a detection limit of ΔΓ_min = 4.1pg/mm² (SNR = 1) is demonstrated experimentally for a sub-optimal structure.

Long-Range Surface Plasmon-Polariton Waveguide Biosensors for Disease Detection

We review recent progress on the application of long-range surface plasmon-polariton waveguide biosensors for disease detection. The biosensors are constructed from metal stripe waveguides cladded in Cytop with etched microfluidic channels to expose the stripe surface to the sensing fluid. The waveguides support long-range surface plasmons in integrated optics geometries when excited in an end-fire manner. Application to the detection of leukemia, dengue fever, and urinary tract infection is discussed.

Detection of Small Molecules Using Long-Range Surface Plasmon Polariton Waveguides

An optical biosensor utilizing long-range surface plasmon-polariton waveguides is discussed. This paper first reviews the technology and its various applications such as protein sensing, cell detection, and disease diagnostics, and then presents results on the detection of small molecules using the biosensor. The surface was functionalized with 16-mercaptohexadecanoic acid and activated using carbodiimide chemistry. Covalent attachment of N-hydroxysulfosuccinimide ester (Sulfo-NHS) of molecular weight ~200 Da produced a significant response with a signal-to-noise ratio of ~81 as a result of molecular monolayer formation. Since carbodiimide chemistry is a protein coupling approach commonly used to functionalize biosensors, a calibration scheme for extracting the actual amount of attached protein based on biosensor responses to NHS is proposed.

Selective detection of bacteria in urine with a LRSPP waveguide biosensor

Laboratory experimentation demonstrates long range surface plasmon polaritons (LRSPP) waveguides as a useful biosensor to selectively detect gram negative bacteria in human urine. The biosensor can detect bacteria at concentrations of 10 CFU/ml, the internationally recommended threshold for diagnostic of urinary tract infection (UTI). Using a negative control solution at bacterial concentration 1000 X higher than the targeted bacteria in urine with a weak concentration of constituents, the power ratio between the negative control signal to the target bacteria signal is measured to be 6.7 on the first test and 2.5 for a lower bacterial concentration after regenerating the surface with SDS. Hence we report a conclusive demonstration of the LRSPP waveguide biosensor selectivity to the gram of bacteria in human urine.

Strategies for leukemic biomarker detection using long-range surface plasmon-polaritons

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.