"Spot and hop": internal referencing for surface plasmon resonance imaging using a three-dimensional microfluidic flow cell array.

We have developed a novel referencing technique for surface plasmon resonance imaging systems referred to as "spot and hop." The technique enables internal referencing for individual flow cells in a parallel processing microfluidic network. Internal referencing provides the ability to correct for nonspecific binding and instrument drift, significantly improving data quality at each region of interest. The performance of a 48-flow-cell device was demonstrated through a series of studies, including "rise and fall" time, ligand preconcentration, ligand immobilization, analyte binding, and regeneration tests. Interfacing parallel processing fluidics with imaging systems will significantly expand the throughput and applications of array-based optical biosensors while retaining high data quality.

Improved continuous-flow print head for micro-array deposition.

Limitations in depositing ligands using conventional micro-array pin spotting have hindered the application of surface plasmon resonance imaging (SPRi) technology. To address these challenges we introduce a modification to our continuous-flow micro-spotting technology that improves ligand deposition. Using Flexchip protein A/G and neutravidin capturing surfaces, we demonstrate that our new microfluidic spotter requires 1000 times less concentrated antibodies and biotinylated ligands than is required for pin spotting. By varying the deposition flow rate, we show that the design of our tip overlay flow cell is efficient at delivering sample to the substrate surface. Finally, contact time studies show that it is possible to capture antibodies and biotinylated ligands at concentrations of less than 0.1 ug/ml and 100 pM, respectively. These improvements in spotting technology will help to expand the applications of SPRi systems in areas such as antibody screening, carbohydrate arrays, and biomarker detection.

The submerged printing of cells onto a modified surface using a continuous flow microspotter.

The printing of cells for microarray applications possesses significant challenges including the problem of maintaining physiologically relevant cell phenotype after printing, poor organization and distribution of desired cells, and the inability to deliver drugs and/or nutrients to targeted areas in the array. Our 3D microfluidic printing technology is uniquely capable of sealing and printing arrays of cells onto submerged surfaces in an automated and multiplexed manner. The design of the microfluidic cell array (MFCA) 3D fluidics enables the printhead tip to be lowered into a liquid-filled well or dish and compressed against a surface to form a seal. The soft silicone tip of the printhead behaves like a gasket and is able to form a reversible seal by applying pressure or backing away. Other cells printing technologies such as pin or ink-jet printers are unable to print in submerged applications. Submerged surface printing is essential to maintain phenotypes of cells and to monitor these cells on a surface without disturbing the material surface characteristics. By printing onto submerged surfaces, cell microarrays are produced that allow for drug screening and cytotoxicity assessment in a multitude of areas including cancer, diabetes, inflammation, infections, and cardiovascular disease.