title: Detection of leukemia markers using long-range surface plasmon waveguides functionalized with Protein G.
abstract: A novel optical biosensor based on long-range surface plasmon-polariton (LRSPP) waveguides is demonstrated for the detection of leukemia markers in patient serum using a functionalization strategy based on Protein G. The sensor consists of thin straight Au waveguides (5 μm × 35 nm × 3.2 mm) embedded in fluoropolymer CYTOP™ with a fluidic channel etched into the top cladding. B-cell leukemia is characterized by a high B-cell count and abnormal distribution of immunoglobulin G kappa (IgGκ) and lambda (IgGλ) light chains in serum. The detection of leukemic abnormalities in serum was performed based on determining IgGκ-to-IgGλ ratios (κ : λ). Three patient sera were tested: high kappa (HKS, κ : λ ~12.7 : 1), high lambda (HLS, λ : κ ~6.9 : 1) and normal (control) sera (NS, κ : λ ~1.7 : 1). Au waveguides were functionalized with Protein G and two complementary immobilization approaches were investigated: a) the reverse approach, where the Protein G surface is functionalized with patient serum and then tested against goat anti-human IgG light chains in buffer, and b) the direct approach, where the Protein G surface is functionalized with goat anti-human IgGs first and then tested against patient serum. The reverse approach was found to be more effective and robust because Protein G-functionalized surface performs as an "immunological filter" by capturing primarily IgGs out of the pool of serum proteins. For the reverse approach, the ratios measured were 3.7 : 1(κ : λ), 9.7 : 1(λ : κ) and 1.9 : 1(κ : λ) for HKS, HLS and NS, respectively, which compare favorably with corresponding protein densitometry measurements. The respective ratios for the direct approach were 2.6 : 1(κ : λ), 2.6 : 1(λ : κ) and 1.7 : 1(κ : λ). The binding strength and cross-reactivity of goat anti-human IgGs light chains were also determined using pure solutions. The LRSPP biosensor along with the innovative "reverse approach" can provide a low-cost and compact solution to B-cell leukemia screening.
authors.affiliation: Department of Biological and Chemical Engineering, University of Ottawa, 161 Louis Pasteur, Ottawa, Ontario K1N 6N5, Canada. a_kupin@hotmail.com.
authors.forename: O
authors.initials: O
authors.lastname: Krupin
authors.forename: C
authors.initials: C
authors.lastname: Wang
authors.forename: P
authors.initials: P
authors.lastname: Berini
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry*; D014408:Biomarkers, Tumor / Q000097:blood*; D001774:Blood Chemical Analysis / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D055767:Immobilized Proteins / Q000737:chemistry; D007074:Immunoglobulin G / Q000097:blood*; D015448:Leukemia, B-Cell / Q000097:blood*; D020349:Surface Plasmon Resonance / Q000295:instrumentation / Q000379:methods*
chemical_list: D001426:Bacterial Proteins; D014408:Biomarkers, Tumor; C034284:IgG Fc-binding protein, Streptococcus; D055767:Immobilized Proteins; D007074:Immunoglobulin G