Utilization of kinetically enhanced monovalent binding affinity by immunoassays based on multivalent nanoparticle-antibody bioconjugates

Integrated nanoparticle-biomolecule hybrid systems: synthesis, properties, and applications

Nanomaterials, such as metal or semiconductor nanoparticles and nanorods, exhibit similar dimensions to those of biomolecules, such as proteins (enzymes, antigens, antibodies) or DNA. The integration of nanoparticles, which exhibit unique electronic, photonic, and catalytic properties, with biomaterials, which display unique recognition, catalytic, and inhibition properties, yields novel hybrid nanobiomaterials of synergetic properties and functions. This review describes recent advances in the synthesis of biomolecule-nanoparticle/nanorod hybrid systems and the application of such assemblies in the generation of 2D and 3D ordered structures in solutions and on surfaces. Particular emphasis is directed to the use of biomolecule-nanoparticle (metallic or semiconductive) assemblies for bioanalytical applications and for the fabrication of bioelectronic devices.

Recent advances in analytical chemistry--a material approach

Advancements of materials research have profound direct impacts on developments in analytical chemistry and may hold the key to improvement of existing or new techniques at present times and near future. Applications of materials in analytical chemistry are reviewed, with focus on sensors, separations and extraction techniques. This review aims to survey examples of interesting works carried out in the last five years over a broad spectrum of materials classified as hybrids, nanomaterials and biomolecular materials.

Magnetic nanoparticle-antibody conjugates for the separation of Escherichia coli O157:H7 in ground beef

The immunomagnetic separation with magnetic nanoparticle-antibody conjugates (MNCs) was investigated and evaluated for the detection of Escherichia coli O157:H7 in ground beef samples. MNCs were prepared by immobilizing biotin-labeled polyclonal goat anti-E. coli antibodies onto streptavidin-coated magnetic nanoparticles. For bacterial separation, MNCs were mixed with inoculated ground beef samples, then nanoparticle-antibody-E. coli O157:H7 complexes were separated from food matrix with a magnet, washed, and surface plated for microbial enumeration. The capture efficiency was determined by plating cells bound to nanoparticles and unbound cells in the supernatant onto sorbitol MacConkey agar. Key parameters, including the amount of nanoparticles and immunoreaction time, were optimized with different concentrations of E. coli O157:H7 in phosphate-buffered saline. MNCs presented a minimum capture efficiency of 94% for E. coli O157:H7 ranging from 1.6 x 10(1) to 7.2 x 10(7) CFU/ml with an immunoreaction time of 15 min without any enrichment. Capture of E. coli O157:H7 by MNCs did not interfere with other bacteria, including Salmonella enteritidis, Citrobacter freundii, and Listeria monocytogenes. The capture efficiency values of MNCs increased from 69 to 94.5% as E. coli O157:H7 decreased from 3.4 x 10(7) to 8.0 x 10(0) CFU/ml in the ground beef samples prepared with minimal steps (without filtration and centrifugation). An enrichment of 6 h was done for 8.0 x 10(0) and 8.0 x 10(1) CFU/ml of E. coli O157:H7 in ground beef to increase the number of cells in the sample to a detectable level. The results also indicated that capture efficiencies of MNCs for E. coli O157:H7 with and without mechanical mixing during immunoreaction were not significantly different (P > 0.05). Compared with microbeads based immunomagnetic separation, the magnetic nanoparticles showed their advantages in terms of higher capture efficiency, no need for mechanical mixing, and minimal sample preparation.

Synthesis of Ag/BSA composite nanospheres from water-in-oil microemulsion using compressed CO2 as antisolvent

In this work, a novel route to synthesize biomolecule/metal composite nanospheres is proposed. This method combines the advantages that the silver nanoparticles and bovine serum albumin (BSA) can be precipitated simultaneously from water-in-oil microemulsion by the easy control of CO2 pressure, which was revealed by our high-pressure UV-VIS spectra. The Ag/BSA nanocomposites were successfully prepared using this method. The transmission electronic microscopy (TEM) if the obtained nanocomposites shows that the small-sized Ag nanaoparticles are immobilized by the BSA nanospheres, and the phase structure was characterized by X-ray diffraction (XRD). The Ag/BSA nanocomposites show absorption properties at a wavelength around 435 nm.

Photochemical Characterization of Up-Converting Inorganic Lanthanide Phosphors as Potential Labels

We have characterized commercially available up-converting inorganic lanthanide phosphors for their rare earth composition and photoluminescence properties under infrared laser diode excitation. These up-converting phosphors, in contrast to proprietary materials reported earlier, are readily available to be utilized as particulate reporters in various ligand binding assays after grinding to submicron particle size. The laser power density required at 980 nm to generate anti-Stokes photoluminescence from these particulate reporters is significantly lower than required for two-photon excitation. The narrow photoluminescence emission bands at 520-550 nm and at 650-670 nm are at shorter wavelengths and thus totally discriminated from autofluorescence and scattered excitation light even without temporal resolution. Transparent solution of colloidal bead-milled up-converting phosphor nanoparticles provides intense green emission visible to the human eye under illumination by an infrared laser pointer. In this article, we show that the unique photoluminescence properties of the up-converting phosphors and the inexpensive measurement configuration, which is adequate for their sensitive detection, render the up-conversion an attractive alternative to the ultraviolet-excited time-resolved fluorescence of down-converting lanthanide compounds widely employed in biomedical research and diagnostics.

Immunoassay of total prostate-specific antigen using europium(III) nanoparticle labels and streptavidin-biotin technology

Nanoparticle labels conjugated with biomolecules are used in a variety of different assay applications. We investigated the possibility of using europium(III)-labeled 68-nm nanoparticles coated with monoclonal antibodies or streptavidin (SA) to detect prostate-specific antigen (PSA) in serum. The selection of a suitable antibody pair and interference caused by the combination of nanoparticle label and structurally complex analyte were of special interest. A set of antibodies recognizing different epitope areas of PSA was mapped to find the optimal antibody pair for the immunometric nanoparticle-based assay. Different assay configurations were tested to obtain a good correlation with a conventional method based on biotinylated detection antibodies and europium(III) chelate-labeled streptavidin. Monoclonal capture antibody 5E4 was covalently coated on a microtitration well surface; biotinylated 5H6 monoclonal antibody (Mab) was used for detection, and europium(III)-labeled streptavidin-coated nanoparticles were utilized for signal generation. Total PSA concentrations were determined from a panel of male serum samples to test the developed assay. The correlation of the nanoparticle-based and reference assays was good; y=0.9844x-0.1252, R2=0.98, n=27; and the lowest limit of detection of the assay (LLD=0.83 ng/l) was 35-fold lower than for the reference method. The assay application presented here, where a structurally complex analyte is detected, combines the exceptionally high affinity of streptavidin-biotin technology and the high specific activity of long lifetime fluorescence nanoparticle labels. The general characteristics of this combination should permit the development of various immunoassay applications featuring high sensitivity, rapidity, and low consumption of reagents.

Fluorescent nanoparticles as labels for immunometric assay of C-reactive protein using two-photon excitation assay technology

We describe the use of fluorophore-doped nanoparticles as reporters in a recently developed ArcDia TPX bioaffinity assay technique. The ArcDia TPX technique is based on the use of polymer microspheres as solid-phase reaction carrier, fluorescent bioaffinity reagents, and detection of two-photon excited fluorescence. This new assay technique enables multiplexed, separation-free bioaffinity assays from microvolumes with high sensitivity. As a model analyte we chose C-reactive protein (CRP). The assay of CRP was optimized for assessment of CRP baseline levels using a nanoparticulate fluorescent reporter, 75 nm in diameter, and the assay performance was compared to that of CRP assay based on a molecular reporter of the same fluorophore core. The results show that using fluorescent nanoparticles as the reporter provides two orders of magnitude better sensitivity (87 fM) than using the molecular label, while no difference between precision profiles of the different assay types was found. The new assay method was applied for assessment of baseline levels of CRP in sera of apparently healthy individuals.

A sensitive adenovirus immunoassay as a model for using nanoparticle label technology in virus diagnostics

BACKGROUND

Currently, PCR-based hybridization assays are widely applied in adenovirus diagnostics. However, the technology requires tedious sample preparation, and the amplification phase is susceptible to various contaminants leading to inconvenient and time-consuming assay procedure. Methods relying on viral antigen detection, e.g. immunofluorometric assays (IFMAs) and enzyme immunoassays (EIAs), are less complicated to carry out, but they provide limited sensitivity.

OBJECTIVE

Our aim was to develop a simple and sensitive adenovirus assay based on direct antigen detection via sandwich-forming immunoreaction. The assay employed highly fluorescent europium(III)-chelate-doped nanoparticle labels and selection of high affinity monoclonal antibodies (anti-hexon) coated on label particles and microtitration wells.

RESULTS AND CONCLUSIONS

The extremely high specific activity of the nanoparticle labels enabled the detection limit over 5000 virus particles per millilitre with purified virus particles. The sensitivity was improved by three orders of magnitude (800-fold) compared to concurrent time-resolved IFMA. Furthermore, the nanoparticle assay showed reasonably low coefficients of variation (4.0-20%) and excellent linearity of more than four orders of magnitude (from below 10(5) to 10(9) virus particles per millilitre). Analyzed nasopharyngeal patient specimens revealed a minor disturbance of matrix components, which could be avoided by dilution. The average signal difference between negative and positive samples was nearly four orders of magnitude. The developed assay was sensitive and more convenient approach to adenovirus screening compared to available assays. In addition, the study demonstrates the potential of nanoparticles in sensitive screening of viral analytes.

Bionanotechnology based on silica nanoparticles

We have developed uniform core/shell nanoparticles, consisting of a silica layer coating and pigments or magnetite core, using a water-in-oil microemulsion method. The nanoparticles are highly luminescent and photostable with the size ranging from 5 nm to 400 nm. Bioconjugation of these silica nanoparticles adds unique biofunctions with various molecules such as enzymes, antibodies, and DNA molecules. Significant advantages have been shown in using bioconjugated nanoparticles for biosensing and bioimaging, such as cell staining, DNA detection and separation, rapid single bacterium detection, and biotechnological application in DNA protection.

Highly sensitive immunoassay of free prostate-specific antigen in serum using europium(III) nanoparticle label technology

BACKGROUND

Recent proceedings in utilization of europium(III) chelate-dyed polystyrene nanoparticles as labels have combined the advantages of an enhanced monovalent binding affinity and a high specific activity of nanoparticle-antibody bioconjugate. Our objective was to evaluate the performance of the nanoparticle label technology with biological samples in an immunoassay of free prostate-specific antigen (PSA-F) using a standard microtitration well platform.

METHODS

Long-lifetime luminescent europium(III)-chelate nanoparticles, 107 nm in diameter, were coated with a PSA-F specific monoclonal antibody. The two-step noncompetitive immunoassay was performed in a microtitration well coated with a second monoclonal antibody. The signal of the surface-bound nanoparticle-antibody bioconjugates was measured directly from the bottom of the well using a standard time-resolved plate fluorometer.

RESULTS

The detection limit (mean + 2SD) of the nanoparticle-based PSA-F assay was 0.21 ng/l using a 20-microl sample volume. The assay response was linear up to 5 microg/l, and the functional sensitivity was approximately 0.5 ng/l. The within-run imprecision for spiked serum samples at concentrations 0.0005-0.5 microg/l was 6.4-21.8%, and the within-run and between-run imprecisions for serum samples at concentrations 0.2-2.5 microg/l were 3.4-7.2% and 4.4-7.6%, respectively. The concentrations obtained from serum samples correlated well with the reference immunoassay; slope = 1.018 +/- 0.018; intercept = 0.012 +/- 0.021 microg/l; S(y/x) = 0.112 microg/l; r = 0.993; n = 51.

CONCLUSIONS

The developed method demonstrated acceptable performance characteristics allowing clinical studies utilizing patient samples with extremely low concentrations of PSA-F. The present assay detected PSA-F in most of samples from prostatectomized men and in few samples from healthy women that were nondetectable according to the reference immunoassay.