Justin J. Palfreyman

Detection of Magnetically Labelled Microcarriers for Suspension Based Bioassay Technologies

Microarrays and suspension-based assay technologies have attracted significant interest over the past decade with applications ranging from medical diagnostics to high throughput molecular biology. The throughput and sensitivity of a microarray will always be limited by the array density and slow reaction kinetics. Suspension (or bead) based technologies offer a conceptually different approach, improving detection by substituting a fixed plane of operation with millions of microcarriers. However, these technologies are currently limited by the number of unique labels that can be generated in order to identify the molecular probes on the surface. We have proposed a novel suspension-based technology that utilizes patterned magnetic films for the purpose of generating a writable label. The microcarriers consist of an SU-8 substrate that can be functionalized with various chemical or biological probes and magnetic elements, which are individually addressable by a magnetic sensor. The magnetization of each element is aligned in one of two stable directions, thereby acting as a magnetic bit. In order to detect the stray field and identify the magnetic labels, we have developed a microfluidic device with an integrated tunneling magnetoresistive (TMR) sensor, sourced from Micro Magnetics Inc. We present the TMR embedding architecture as well as detection results demonstrating the feasibility of magnetic labeling for lab-on-a-chip applications.

Design and fabrication of SU8 encapsulated digital magnetic carriers for high throughput biological assays

A design of a biological molecule carrier is presented for the application of high throughput multiplexing biological assays. This carrier contains a bit addressable “magnetic barcode” made of either Permalloy or cobalt thin films, sandwiched between two planar SU8 protective layers. We describe how the design of the magnetic carriers is optimized by engineering the coercivity of each barcode element, allowing the number of available signatures to be increased. Fully encapsulated digital magnetic carriers which carry a 5 bit addressable barcode were also fabricated and are presented. Writing and reading of digital carriers were both performed after releasing in dried solution.

A composite element bit design for magnetically encoded microcarriers for future combinatorial chemistry applications

We present a new composite element (CE) bit design for the magnetic bit encoding of suspended microcarriers, which has significant implications for library generation applications based on microfluidic combinatorial chemistry. The CE bit design consists of high aspect ratio strips with appropriate dipolar interactions that enable a large coercivity range and the formation of up to 14 individually addressable bits (16 384 codes) with high encoding reliability. We investigate Ni80Fe20 and Co CEs, which produce coercivity ranges of 8–290 Oe and 75–172 Oe, respectively, showing significant improvements to previously proposed bit designs. By maintaining the total magnetic volume for each CE bit, the barcode design enables a consistent stray field for in-flow magnetic read-out. The CE bit design is characterised using magneto-optic Kerr effect (MOKE) measurements and the reliability of the design is demonstrated in a multi-bit encoding process capable of identifying each bit transition for every applied magnetic field pulse. By constraining each magnetic bit to have a unique switching field using the CE design, we enable sequential encoding of the barcode using external magnetic field pulses. We therefore discuss how the new CE barcode design makes magnetically encoded microcarriers more relevant for rapid and non-invasive detection, identification and sorting of compounds in biomolecular libraries, where each microcarrier is for example capable of recording its reaction history in daisy-chained microfluidic split-and-mix processes.

Magnetically labelled gold and epoxy bi-functional microcarriers for suspension based bioassay technologies.

Microarrays and suspension-based assay technologies have attracted significant interest over the past decade with applications ranging from medical diagnostics to high throughput molecular biology. The throughput and sensitivity of a microarray will always be limited by the array density and slow reaction kinetics. Suspension (or bead) based technologies offer a conceptually different approach, improving detection by substituting a fixed plane of operation with many individually distinguishable microcarriers. In addition to all the features of a suspension based assay technology, our technology offers a rewritable label. This has the potential to be truly revolutionary by opening up the possibility of generating, on chip, extensive labelled molecular libraries. We unveil our latest SU-8 microcarrier design with embedded magnetic films that can be utilized for both magnetic and optical labelling. The novel design significantly simplifies fabrication and additionally incorporates a gold cap to provide a dual surface, bi-functional architecture. The microcarriers are fabricated using deep-ultraviolet lithography techniques and metallic thin film growth by evaporation. The bi-functional properties of the microcarriers will allow us to use each microcarrier as its own positive control thereby increasing the reliability of our technology. Here we present details of the design, fabrication, magnetic detection and functionalization of these microcarriers.

Enabling suspension-based biochemical assays with digital magnetic microtags

Microarrays and suspension-based technologies have attracted significant interest over the past decade with applications in medical diagnostics and biochemical multiplexed assays. However, the throughput of microarrays will always be limited by the array density and the slow kinetics, while the suspension (or bead)-based technologies are currently limited by the number of distinct codes the beads can carry. A novel digital magnetic tagging technology based on magnetic tags that can be used as encoded microcarriers for biomolecular probes, is presented here. The highly disruptive platform technology can provide a very large number of unique codes, enabling a high degree of multiplexing. The design principles of a novel magnetic laboratory-on-a-chip device comprising microfluidic channels with embedded magnetic tunneling magnetoresistive sensors are also discussed.

Fabrication of Magnetic Barcoded Microcarriers for Biomolecular Labeling: SU‐8 Encapsulated Magnetic Tags

Rows of rectangular magnetic elements with different aspect ratio are encapsulated in polymer microcarriers to form a novel magnetic label, or tag, for multiplexed biological and chemical assays. We demonstrate that each tag can be encoded using an external magnetic field applied to the whole tag, which will allow for in‐flow writing, thanks to shape‐anisotropy controlled coercivity of the individual bits. This paper focuses on the fabrication of our 2nd generation tags, which facilitate optical trapping, do not require a sacrificial release layer, and the alignment procedure has been simplified to a single step. A new procedure is described for recovering a functional surface from fully cross‐linked SU‐8 via a cerium (IV) ammonium nitrate based chemical etch, and a novel method for releasing patterned photoresist from a bare Si wafer is discussed. In addition, a series of homobifunctional amine spacer compounds are compared as a method of increasing the binding efficiency of surface probe molecules.

Templated Growth and Selective Functionalization of Magnetic Nanowires

Magnetic nanowires are considered as an alternative to magnetic or coloured beads for the labeling of biological entities. Single metal and multisegment magnetic nanowires of lengths between 5–20 μm have been grown, magnetically characterized and released, and selective functionalization of the gold layer with fluorescently labeled DNA is demonstrated. The high magnetic moment of these nanowires, which is scaleable with their length, makes these nanowires a powerful alternative to bead‐based labeling techniques.

Digital magnetic tagging for multiplexed suspension-based biochemical assays

Microarrays and suspension (or bead)-based technologies have attracted significant interest for their broad applications in high throughput molecular biology. However, the throughput of microarrays will always be limited by the array density and the slow diffusion of molecules to their binding sites. Suspension-based technologies, in which all the reactions take place directly on the surface of microcarriers functionalized with molecular probes, could offer true multiplexing due to the possibility of extending their detection capability by a straightforward expansion of the size of the chemical library of probes. To fully exploit their potential, the microcarriers must be tagged, but the number of distinct codes available from spectrometric/graphical/physical encoding methods is currently fairly limited. A digital magnetic tagging method based on magnetic microtags, which have been anisotropy engineered to provide stable magnetization directions which correspond to digital codes, is reported. The tags can...