In this review we discuss conventional methods of performing biological assays and molecular identification and highlight their advantages and limitations. An alternative approach based on magnetic nanotechnology is then presented. Firstly, magnetic carriers are introduced and their biocompatibility and functionalisation discussed, with spotlights on functionalisation via self assembled monolayers and on methods of reducing nonspecific binding. In addition an introduction is provided to the basic physical concepts behind the various types of sensors used to detect magnetic labels. Finally, progress in the field of magnetic biosensors and the outlook for the future are discussed.

Prefluorescent radical probes, in which fluorescence is activated by radical trapping, and photoinitiators were used to detect radical generation in polymer films using fluorescence spectroscopy and microscopy. Prefluorescent radical probes are the foundation of a fluorescence imaging system for polymer films, that may serve both as a mechanistic tool in the study of photoinitiated radical processes in polymer films and in the preparation of functional fluorescent images.

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.

We describe proof-of-principle experiments and theory that demonstrate a new method of performing multiplexed biological assays by using microscopic tags which carry multi-bit magnetic codes to label probe biomolecules. It is demonstrated that these "micro-barcode tags" can be encoded, transported using micro-fluidics and are compatible with surface chemistry. We also present simulations and experimental results which suggest the feasibility of decoding the micro-barcode tags using magnetoresistive sensors. Together, these results demonstrate substantial progress towards meeting the critical requirements of a magnetically encoded, high-throughput and portable biological assay platform. We also show that an extension of our technology could be potentially used to label libraries consisting of~10 4 distinct probe molecules, and could therefore have a strong impact on mainstream medical diagnostics.

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.