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

a b s t r a c t 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. Ó 2008 Elsevier Inc. All rights reserved. Whereas standard surface plasmon resonance (SPR) 1 biosensors have become widely adapted for molecular interaction analysis, imaging systems such as those available from Biacore (Flexchip), Genoptics, GWC, IBIS, and Maven have had less of an impact to date. Imaging systems typically involve patterning spots of ligands within a large flow cell and then testing the binding of a single analyte at a time, the so-called ''one on many" approach [1]. Two issues limit the widespread application of imaging systems. The first challenge is how to pattern protein ligands onto the sensor surface. The majority of imaging instruments rely on pin spotting, inkjet printing, and stamping methods that do not work well for many real-world applications To address this first problem, we have developed a threedimensional microfluidic flow cell array (MFCA) [6-8] (see The second issue limiting the widespread adoption of imaging systems is the limited number of applications for the one on many assay approach. Most users, in fact, want to run the reverse assay; they have many analytes to test against one ligand or a few ligands. Drug discovery is a good example. In these cases, the problem is not with the imaging technology but rather with sample delivery. In this article, we demonstrate how our MFCA devices can be used to create independent yet parallel processing flow cells when interfaced with imaging systems. We also introduce the concept of ''spot and hop" as a simple yet novel method of creating both a reaction and a reference surface within each flow cell. The current device incorporates 48 isolated flow cells that can be used to deliver different analytes to the sensor surface. Using protein A/immunoglobulin G (IgG) as a model system, we demonstrate the effectiveness of the MFCA system as well as the benefits of internal referencing. Interfacing parallel processing microfluidics with imaging technology will expand the use of array biosensor technology in drug discovery, diagnostics, and biomarker detection. 0003-2697/$ -see front matter

Tiger Woods and the New Racial Order

There is no more serviceable celebrity than Tiger Woods. He is a colour- free emblem of a new America in which racism is dead and there are no barriers to progress for any member of its citizenry – a new racial order. His success obscures the grimmer reality of contemporary America. This article examines Woods, less as a person, more as a commodity of immense utility: something that effectively advertises a society that has long struggled with the issue of racism, but has finally won. Woods functions as ambulant publicity: he studiously avoids engaging with any political or remotely sensitive issue and refuses to align him- self with any particular ethnic group. In a sense, he is what one writer has called ‘a new kind of white person’. On the evidence presented here, Woods effectively invites consumers not to challenge racism directly, but to buy commodities that externalize success and in this way avoid confronting the racism that continues to bedevil most of America’s black population