Hetero-Coated Magnetic Microcarriers for Point-Of-Care Diagnostics

Abstract

SU8 microcarriers containing magnetic thin film (40 nm cobalt) elements were fabricated by photolithography and thermal evaporation, and included a gold coating on the base. The microcarriers, which can be encoded with a magnetic barcode for later identification in a multiplexed suspension assay, now possess two distinct surfaces for further chemical derivitization. This allows us to attach different bio-molecules to each side, which we suggest, could be used to add a positive control to typical hybridization assays as a test for binding conditions, thus giving confidence against false negative events. As a proof-of-concept we developed a chemical pathway to attach <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$5^{\prime},6^{\prime}$</tex></formula> -tetramethyl rhodamine onto the gold coated side via the growth of a mixed self-assembled monolayer (characterized by Electrochemical Quartz Crystal Microbalance measurements), while also attaching fluorescein to the SU8 side after first adding a homo-bifunctional spacer to the native surface epoxide groups. Fluorescence microscopy was used to verify the success of this strategy and the feasibility of using PicoGreen as a post-hybridization reporter was studied.