Dynamic bioprocessing and microfluidic transport control with smart magnetic nanoparticles in laminar-flow devices.

In the absence of applied forces, the transport of molecules and particulate reagents across laminar flowstreams in microfluidic devices is dominated by the diffusivities of the transported species. While the differential diffusional properties between smaller and larger diagnostic targets and reagents have been exploited for bioseparation and assay applications, there are limitations to methods that depend on these intrinsic size differences. Here a new strategy is described for exploiting the sharply reversible change in size and magnetophoretic mobility of "smart" magnetic nanoparticles (mNPs) to perform bioseparation and target isolation under continuous flow processing conditions.

Modeling of a competitive microfluidic heterogeneous immunoassay: sensitivity of the assay response to varying system parameters.

We present a fractional sensitivity analysis of a competitive microfluidic heterogeneous immunoassay for a small molecule analyte. A simple two-dimensional finite element model is used to determine the fractional sensitivity of the assay signal with respect to analyte concentration, flow rate, initial surface density of binding sites, and antibody concentration. The fractional sensitivity analysis can be used to identify (1) the system parameters for which it is most crucial to control or quantify the variability between assays and (2) operating ranges for these parameters that improve assay sensitivity (within the constraints of the experimental system).

Conditioning saliva for use in a microfluidic biosensor.

This report details an approach to saliva conditioning for compatibility of raw patient samples with microfluidic immunoassay components, principally biosensor surfaces susceptible to fouling. Stimulated whole human saliva spiked with a small molecule analyte (phenytoin, 252 Da) was first depleted of cells, debris and high molecular weight glycoproteins (mucins) using membrane filtration. This process significantly reduced but did not eliminate fouling of biosensor surfaces exposed to the sample.

Concentration gradient immunoassay. 2. Computational modeling for analysis and optimization.

A novel microfluidic surface-based competition immunoassay, termed the concentration gradient immunoassay (described in detail in a companion paper (Nelson, K.; Foley, J.; Yager, P.

Concentration gradient immunoassay. 1. An immunoassay based on interdiffusion and surface binding in a microchannel.

We describe a novel microfluidic immunoassay method based on the diffusion of a small-molecule analyte into a parallel-flowing stream containing a cognate antibody. This interdiffusion results in a steady-state gradient of antibody binding site occupancy transverse to convective flow. In contrast to the diffusion immunoassay (Hatch, A.

SPR imaging-based salivary diagnostics system for the detection of small molecule analytes.

Saliva is an underused fluid with considerable promise for biomedical testing. Its potential is particularly great for monitoring small-molecule analytes since these are often present in saliva at concentrations that correlate well with their free levels in blood. We describe the development of a prototype diagnostic device for the rapid detection of the antiepileptic drug (AED) phenytoin in saliva.

Compact, high performance surface plasmon resonance imaging system.

We report the construction and characterization of a new compact surface plasmon resonance imaging instrument. Surface plasmon resonance imaging is a versatile technique for detection, quantification and visualization of biomolecular binding events which have spatial structure. The imager uses a folded light path, wide-field optics and a tilted detector to implement a high performance optical system in a volume 7 in.

Microfluidic diagnostic technologies for global public health.

The developing world does not have access to many of the best medical diagnostic technologies; they were designed for air-conditioned laboratories, refrigerated storage of chemicals, a constant supply of calibrators and reagents, stable electrical power, highly trained personnel and rapid transportation of samples. Microfluidic systems allow miniaturization and integration of complex functions, which could move sophisticated diagnostic tools out of the developed-world laboratory. These systems must be inexpensive, but also accurate, reliable, rugged and well suited to the medical and social contexts of the developing world.

Structural characterization and comparison of RGD cell-adhesion recognition sites engineered into streptavidin.

The RGD (arginine-glycine-aspartic acid) sequence is found in several important extracellular matrix proteins and serves as an adhesion ligand for members of the integrin family of cell-surface receptors. This sequence and flanking residues from fibronectin or osteopontin have been engineered into an accessible surface loop of streptavidin to create two new streptavidin variants (FN-SA or OPN-SA, respectively) that bind cells through the alpha(v)beta(3) and/or alpha(5)beta(1) integrin receptors. Their crystal structures confirm the design and construction of the mutants and provide evidence about the conformational dynamics of the RGD loops.