Microsphere sedimentation arrays for multiplexed bioanalytics

Acoustic Sensing Based on Density Shift of Microspheres by Surface Binding of Gold Nanoparticles

Herein, we propose a concept for sensing based on density changes of microparticles (MPs) caused by a biochemical reaction. The MPs are levitated by a combined acoustic-gravitational force at a position determined by the density and compressibility. Importantly, the levitation is independent of the MPs sizes. When gold nanoparticles (AuNPs) are bound on the surface of polymer MPs through a reaction, the density of the MPs dramatically increases, and their levitation position in the acoustic-gravitational field is lowered. Because the shift of the levitation position is proportional to the number of AuNPs bound on one MP, we can determine the number of molecules involved in the reaction. The avidin-biotin reaction is used to demonstrate the effectiveness of this concept. The number of molecules involved in the reaction is very small because the reaction space is small for an MP; thus, the method has potential for highly sensitive detection.

Sensitive, quantitative, and high-throughput detection of angiogenic markers using shape-coded hydrogel microparticles

Demonstration of the application of shape coded hydrogel microparticles for multiplexed detection of angiogenic molecules. Utilization of single fluorophore eliminates the spectral overlap associated with microparticle based multiplexed analysis.

Towards a spectrum-based bar code for identification of weakly fluorescent microparticles

Spectrally resolved detection of fluorescent probes can be used to identify multiple labeled target molecules in an unknown mixture. We study how the spectral shape, the experimental noise, and the number of spectral detection channels affect the success of identification of weakly fluorescent beads on basis of their emission spectra. The proposed formalism allows to estimate the performance of the spectral identification procedure with a given set of spectral codes on the basis of the reference spectra only. We constructed a simple prism-based setup for spectral detection and demonstrate that seven distinct but overlapping spectral codes realized by combining up to three fluorescent dyes bound to a single bead in a barcode-based manner can be reliably identified. The procedure allows correct identification even in the presence of known autofluorescence background stronger than the actual signal.

Magnetic optical sensor particles: a flexible analytical tool for microfluidic devices

Magnetic optical sensor particles are used to generate in situ sensor spots within microfluidic channels and serve as flexible analytical tools.

Performance of fluorescent labels in sedimentation bead arrays--a comparison study

An extensive study is described to identify the most suitable fluorescent label in magnetic microsphere sedimentation arrays. The investigated fluorescent labels, commonly used in multiplex analysis, include organic dyes, (fluorescein, Alexa488, Cy5) fluorescent proteins (R-Phycoerythrin, Allophycocyanine, PBXL-3) polymer nanoparticles (FluoSpheres, PD-Pt) and semiconductor nanocrystals (Quantum dots). DNA hybridization assays on magnetic microspheres were applied as model systems to reveal label performance. The fluorescent labels were characterized under optimized conditions regarding signal intensity, non-specific binding and photo-stability. The advantages and drawbacks of individual labels are discussed. The limit of detection and dynamic ranges are determined to compare the performance of selected labels. Detection limits of 2 x 10(-10) mol/L are found for the determination of oligonucleotides using PBXl-3 as label, which is comparable with typical flow cytometer systems. The results and protocols are highly valuable for any type of bead based assays and can be easily transferred.

Mathematical model for mixing reactants in a capillary microreactor by transverse diffusion of laminar flow profiles

Transverse diffusion of laminar flow profiles (TDLFP) was recently suggested as a generic approach for mixing reactants inside a capillary microreactor. Conceptually, solutions of reactants are injected inside the capillary by high pressure as a series of consecutive plugs. Because of the laminar nature of the flow inside the capillary, the nondiffused plugs have parabolic profiles with predominantly longitudinal interfaces between the plugs. After the injection, the reactants are mixed by transverse diffusion across the longitudinal interfaces. TDLFP-based mixing is still in its infancy as only the principle was proved. Here, we develop the theory of TDLFP and introduce a dimensionless parameter, York number, which can be used in predicting the quality of TDLFP-based mixing. The theory uses a single simplifying assumption that the longitudinal diffusion is negligible; this assumption is readily satisfied. We then develop a numerical model of TDLFP and use it to simulate the concentration profiles of three reactants mixed by TDLFP in the capillary. The correlation between the York number and quality of mixing is analyzed. Two ways of improving the quality of TDLFP-based mixing are suggested and studied: (i) increasing the longitudinal interface between the plugs by a long last plug of a solvent and (ii) "shaking" the injected reactants by a series of alternating negative and positive pressure pulses. The developed theory and computational simulation of TDLFP will stimulate the practical use of capillary microreactors.

Multiplexed immunoassays for proteins using magnetic luminescent nanoparticles for internal calibration

Suspension arrays present a promising tool for multiplexed assays in large-scale screening applications. A simple and robust platform for quantitative multiprotein immunoanalysis has been developed with the use of magnetic Co:Nd:Fe(2)O(3)/luminescent Eu:Gd(2)O(3) core/shell nanoparticles (MLNPs) as a carrier. The magnetic properties of the MLNPs allow their manipulation by an external magnetic field in the separation and washing steps in the immunoassay. Their optical properties enable the internal calibration of the detection system. The multiplexed sandwich immunoassay involves dual binding events on the surface of the MLNPs functionalized with the capture antibodies. Secondary antibodies labeled with conventional organic dyes (Alexa Fluor) are used as reporters. The amount of the bound secondary antibody is directly proportional to the concentration of the analyte in the sample. In our approach, the fluorescence intensity of the reporter dye is related to the luminescence signal of the MLNPs. In this way, the intrinsic luminescence of the MLNPs serves as an internal standard in the quantitative immunoassay. The concept is demonstrated for a simultaneous immunoassay for three model proteins (human, rabbit, and mouse IgGs). The method uses a standard bench plate reader. It can be applied to disease diagnostics and to the detection of biological threats.

Luminescence decay time encoding of magnetic micro spheres for multiplexed analysis

Magnetic microspheres are optically encoded by doping with three luminescent dyes. The combination of a fluorophore with a nanosecond decay profile and two phosphorescent Ruthenium metal ligand complexes with a microsecond decay profile generates a characteristic signature described by three features: bead brightness, luminescent decay time and dual lifetime referencing (DLR). The beads are identified by time resolved imaging in the microsecond range. A series of fluorophores is tested and the interference of the resulting luminescent code in the red and green label detection channels is investigated. A detailed staining procedure is worked out to increase the staining efficiency of the dyes with hydrophilic character into the lipophilic polystyrene microspheres. A mathematical model is established to calculate the dye amounts that are needed for staining a bead family with a specific feature set. Nineteen bead families were prepared representing the grid points in the three planes of a cube referring to the three features. The coefficient of variation over all bead families is 7%, 1.4% and 1.6% for bead brightness, luminescence decay time and DLR, respectively. The combination of these features and the bead size as additional feature enables the creation of 840 distinguishable bead families.

Filter cubes with built-in ultrabright light-emitting diodes as exchangeable excitation light sources in fluorescence microscopy

The use of ultrabright light-emitting diodes as a potential substitute for conventional excitation light sources in fluorescence microscopy is demonstrated. We integrated ultrabright light-emitting diodes in the filter block of a conventional fluorescence microscope together with a collimating Fresnel lens, a holographic diffuser and emission filters. This setup enabled convenient changes between different excitation light sources and resulted in high excitation efficiencies. Quantitative comparison of image intensities of test samples revealed that light-emitting diodes yielded intensities in the range of a mercury arc lamp depending on the wavelength. The use of ultrabright light-emitting diodes also enabled luminescence lifetime imaging without the need for image intensification.