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We explore the use of magnetic relaxation sensors as an in vitroassay platform. Functionalized magnetic nanoparticles that exhibit transverse relaxation time (T2) changes with the introduction of an analyte have previously been used to detect proteins, antibodies, receptor ligands, peptides, nucleic acids, oligonucleotides, and other small molecules. The standard procedure for sensitizing particles towards specific targets is, however, time-consuming and cumbersome. We report here a new approach that exploits primary–secondary antibody binding for easily derivatizing particles against specific targets. The assay is shown to be quantitative and a multiplexed assay against three target analytes is demonstrated. [ABSTRACT FROM AUTHOR]

The encapsulation of mammalian cells within the bulk material of microfluidic channels may be beneficial for applications ranging from tissue engineering to cell-based diagnostic assays. In this work, we present a technique for fabricating microfluidic channels from cell-laden agarose hydrogels. Using standard soft lithographic techniques, molten agarose was molded against a SU-8 patterned silicon wafer. To generate sealed and water-tight microfluidic channels, the surface of the molded agarose was heated at 71 degrees C for 3 s and sealed to another surface-heated slab of agarose. Channels of different dimensions were generated and it was shown that agarose, though highly porous, is a suitable material for performing microfluidics. Cells embedded within the microfluidic molds were well distributed and media pumped through the channels allowed the exchange of nutrients and waste products. While most cells were found to be viable upon initial device fabrication, only those cells near the microfluidic channels remained viable after 3 days, demonstrating the importance of a perfused network of microchannels for delivering nutrients and oxygen to maintain cell viability in large hydrogels. Further development of this technique may lead to the generation of biomimetic synthetic vasculature for tissue engineering, diagnostics, and drug screening applications.