Human serum albumin interference on plasmon-based immunokinetic assay for antibody screening in model blood sera

Electrochemical biotool for the dual determination of epithelial mucins associated to prognosis and minimal residual disease in colorectal cancer

This work reports a dual immunoplatform for the simultaneous detection of two epithelial glycoproteins of the mucin family, mucin 1 (MUC1) and mucin 16 (MUC16), whose expression is related to adverse prognosis and minimal residual disease (MRD) in colorectal cancer (CRC). The developed immunoplatform involves functionalised magnetic microparticles (MBs), a set of specific antibody pairs (a capture antibody, cAb, and a biotinylated detector antibody b-dAb labelled with a streptavidin-horseradish peroxidase, Strep-HRP, polymer) for each target protein and amperometric detection at dual screen-printed carbon electrodes (SPdCEs) using the hydroquinone (HQ)/horseradish peroxidase (HRP)/H2O2 system. This dual immunoplatform allows, under the optimised experimental conditions, to achieve LOD values of 50 and 1.81 pg mL-1 (or mU mL-1) for MUC1 and MUC16, respectively, and adequate selectivity for the determination of the two targets in the clinic. The developed immunoplatform was employed to analyse CRC cell protein extracts (1.0 μg/determination) with different metastatic potential providing results in agreement with those obtained by blotting technologies but using affordable and applicable point-of-care instruments. This new biotool also emerges competitive in state-of-the-art electrochemical immunoplatforms seeking a compromise among simplicity, reduction of test time and analytical characteristics.

Accuracy and precision analysis for a biophotonic assay of C-reactive protein

A multiplexed biophotonic assay platform has been developed using the localised particle plasmon in gold nanoparticles assembled in an array and functionalised for two assays: total IgG and C-reactive protein (CRP). A protein A/G (PAG) assay, calibrated with a NIST reference material, shows a maximum surface coverage of θ_max = 7.13 ± 0.19 mRIU, equivalent to 1.5 ng mm^-2 of F(ab)-presenting antibody. The CRP capture antibody has an equivalent surface binding density of θ_max = 2.95 ± 0.41 mRIU indicating a 41% capture antibody availability. Free PAG binding to the functionalised anti-CRP surface shows that only 47 ± 3% of CRP capture antibodies are correctly presenting Fab regions for antigen capture. The accuracy and precision of the CRP sensor assay was assessed with 54 blood samples containing spiked CRP in the range 2-160 mg L^-1. The mean accuracy was 0.42 mg L^-1 with Confidence Interval (CI) at 95% from -14.7 to 13.8 mg L^-1 and the precision had a Coefficient of Variation (CV) of 10.6% with 95% CI 0.9%-20.2%. These biophotonic platform performance metrics indicate a CRP assay with 2-160 mg L^-1 dynamic range, performed in 8 minutes from 5 μL of whole blood without sample preparation.

Label-free Fab and Fc affinity/avidity profiling of the antibody complex half-life for polyclonal and monoclonal efficacy screening

A unified approach to affinity screening for Fab and Fc interactions of an antibody for its antigen and FcγR receptor has been developed. An antigen array is used for the Fab affinity and cross-reactivity screening and protein A/G proxy is the FcγR receptor. The affinities are derived using a simple 1:1 binding model with a consistent error analysis. The association and dissociation kinetics are measured over optimised times for accurate determination. The Fab/Fc affinities are derived for ten antibodies: mAb-actin (mouse), pAb-BSA (sheep), pAb-collagen V (rabbit), pAb-CRP (goat), mAb-F1 (mouse), mAbs (mouse) 7.3, 12.3, 29.3, 36.3 and 46.3 raised against LcrV in Yersinia pestis. The rate of the dissociation of antigen-antibody complexes relates directly to their immunological function as does the Fc-FcγR complex and a new half-life plot has been defined with a Fab/Fc half-life range of 17-470 min. The upper half-life value points to surface avidity. Two antibodies that are protective as an immunotherapy define a Fab half-life >250 min and an Fc half-life >50 min as characteristics of ideal interactions which can form the basis of an antibody screen for immunotherapy.

Glycosylation characterization of human and porcine fibrinogen proteins by lectin-binding biophotonic microarray imaging

Lectin binding has been studied using the particle plasmon light-scattering properties of gold nanoparticles printed into an array format. Performance of the kinetic assay is evaluated from a detailed analysis of the binding of concanavalin A (ConA) and wheat germ agglutinin (WGA) to their target monosaccharides indicating affinity constants in the order of KD ∼10 nM for the lectin-monosaccharide interaction. The detection limits for the lectins following a 200 s injection time were determined as 10 ng/mL or 0.23 nM and 100 ng/mL or 0.93 nM, respectively. Subsequently, a nine-lectin screen was performed on the porcine and human fibrinogen glycoproteins. The observed spectra of lectin-protein specific binding rates result in characteristic patterns that evidently correlate with the structure of the glycans and allow one to distinguish between glycosylation of the porcine and human fibrinogens. The array technology has the potential to perform a multilectin screen of large numbers of proteins providing information on protein glycosylation and their microheterogeneity.

Differential immuno-kinetic assays of allergen-specific binding for peanut allergy serum analysis

A label-free nanoparticle array platform has been used to detect total peanut allergen-specific binding from whole serum of patients suffering from peanut allergy. The serum from 10 patients was screened against a four-allergen panel of cat and dog dander, dust mite and peanut allergen protein Ara h1. The IgE and IgG contributions to the total specific-binding protein load to Ara h1 were identified using two secondary IgG- and IgE-specific antibodies and were found to contribute less than 50 % of the total specific protein load. The total mass of IgE, IgE and the unresolved specific-binding protein ΔsBP for Ara h1 provides a new serum profile for high-RAST-grade patients 5 and 6 with the IgG/IgE ratio of 4 ± 2 and ΔsBP/IgE ratio of 17 ± 11, neither of which is protective for the small patient cohort.

Whole blood screening of antibodies using label-free nanoparticle biophotonic array platform

A gold nanoparticle, localised plasmon array biosensor using light scattering has been employed in the detection of allergen-specific antibodies in whole blood and sera. The array sensor was functionalized with four different allergens, cat dander (Fel d1), dust mite (Der p1), peanut allergen (Ara h1) and dog dander (Can f1) and immuno-kinetic assay was performed to detect their respective anti-allergen IgG antibodies. Specific positive responses to antibodies at a concentration of 25 nM were observed for Fel d1, Der p1, and Ara h1 allergens, while the Can f1 channel served as a reference control. The sensitivity was further enhanced using a secondary anti-IgG detection antibodies to give a limit of detection of 2 nM. The results indicate the potential for nanoparticle scattering multiplexed arrays to screen unprepared blood samples at point-of-care for assays of complex samples such as the whole blood.