Robert J. Wilson

Matrix-insensitive protein assays push the limits of biosensors in medicine

Advances in biosensor technologies for in vitro diagnostics have the potential to transform the practice of medicine. Despite considerable work in the biosensor field, there is still no general sensing platform that can be ubiquitously applied to detect the constellation of biomolecules in diverse clinical samples (for example, serum, urine, cell lysates or saliva) with high sensitivity and large linear dynamic range. A major limitation confounding other technologies is signal distortion that occurs in various matrices due to heterogeneity in ionic strength, pH, temperature and autofluorescence. Here we present a magnetic nanosensor technology that is matrix insensitive yet still capable of rapid, multiplex protein detection with resolution down to attomolar concentrations and extensive linear dynamic range. The matrix insensitivity of our platform to various media demonstrates that our magnetic nanosensor technology can be directly applied to a variety of settings such as molecular biology, clinical diagnostics and biodefense.

Multiplex protein assays based on real-time magnetic nanotag sensing

Magnetic nanotags (MNTs) are a promising alternative to fluorescent labels in biomolecular detection assays, because minute quantities of MNTs can be detected with inexpensive giant magnetoresistive (GMR) sensors, such as spin valve (SV) sensors. However, translating this promise into easy to use and multilplexed protein assays, which are highly sought after in molecular diagnostics such as cancer diagnosis and treatment monitoring, has been challenging. Here, we demonstrate multiplex protein detection of potential cancer markers at subpicomolar concentration levels and with a dynamic range of more than four decades. With the addition of nanotag amplification, the analytic sensitivity extends into the low fM concentration range. The multianalyte ability, sensitivity, scalability, and ease of use of the MNT-based protein assay technology make it a strong contender for versatile and portable molecular diagnostics in both research and clinical settings.

Quantification of protein interactions and solution transport using high-density GMR sensor arrays

Monitoring the kinetics of protein interactions on a high density sensor array is vital to drug development and proteomic analysis. Label-free kinetic assays based on surface plasmon resonance are the current gold standard, but they have poor detection limits, suffer from non-specific binding, and are not amenable to high throughput analyses. Here we show that magnetically responsive nanosensors that have been scaled to over 100,000 sensors/cm2 can be used to measure the binding kinetics of various proteins with high spatial and temporal resolution. We present an analytical model that describes the binding of magnetically labeled antibodies to proteins that are immobilized on the sensor surface. This model is able to quantify the kinetics of antibody-antigen binding at sensitivities as low as 20 zeptomoles of solute.

Fluorescent Magnetic Nanoparticles for Magnetically Enhanced Cancer Imaging and Targeting in Living Subjects

Early detection and targeted therapy are two major challenges in the battle against cancer. Novel imaging contrast agents and targeting approaches are greatly needed to improve the sensitivity and specificity of cancer theranostic agents. Here, we implemented a novel approach using a magnetic micromesh and biocompatible fluorescent magnetic nanoparticles (FMN) to magnetically enhance cancer targeting in living subjects. This approach enables magnetic targeting of systemically administered individual FMN, containing a single 8 nm superparamagnetic iron oxide core. Using a human glioblastoma mouse model, we show that nanoparticles can be magnetically retained in both the tumor neovasculature and surrounding tumor tissues. Magnetic accumulation of nanoparticles within the neovasculature was observable by fluorescence intravital microscopy in real time. Finally, we demonstrate that such magnetically enhanced cancer targeting augments the biological functions of molecules linked to the nanoparticle surface.

CMOS Integrated DNA Microarray Based on GMR Sensors

A high density GMR sensor array was integrated with a standard CMOS chip for DNA hybridization detection. Absorption of magnetic nanoparticles by the hybridized DNA alters the sensor resistance, and generated electrical signals are directly measured with the on-die circuitry. The proposed biochip can be applied to other bio-reaction detection, e.g. protein assay, through different surface modifications

Protein‐Functionalized Synthetic Antiferromagnetic Nanoparticles for Biomolecule Detection and Magnetic Manipulation

Direct protein functionalization provides synthetic antiferromagnetic nanoparticles with high chemical specificity and multifunctionality. These nanoparticle-protein conjugates function as improved magnetic labels for biological detection experiments, and exhibit tunable responses to a small external magnetic field gradient, thus allowing the observation of distinctive single nanoparticle motion.

The influence of Fermi level pinning/depinning on the Schottky barrier height and contact resistance in Ge/CoFeB and Ge/MgO/CoFeB structures

We demonstrated that an ultrathin MgO layer between CoFeB and Ge modulated the Schottky barrier heights and contact resistances of spin diodes. We confirmed that, surprisingly, an insulating MgO layer significantly decreased the Schottky barrier heights and contact resistances of spin diodes on N+Ge, opposite to the increase observed for P+Ge. A 0.5 nm thick MgO layer on N+Ge decreases the Schottky barrier height from 0.47 to 0.05 eV and lowers the minimum contact resistance 100-fold to 1.5×10−6u2002Ωu2009m2. These results open a pathway for high efficient spin injection from ferromagnetic materials and semiconductors.

Sombrero-Shaped Plasmonic Nanoparticles with Molecular-Level Sensitivity and Multifunctionality

We demonstrate top-down synthesis of monodisperse plasmonic nanoparticles designed to contain internal Raman hot spots. Our Raman-active nanoparticles are fabricated using nanoimprint lithography and thin-film deposition and are composed of novel internal structures with sublithographic dimensions: a disk-shaped Ag core, a Petri-dish-shaped SiO2 base whose inner surface is coated with Ag film, and a sub-10 nm scale circular gap between the core and the base. Confocal Raman measurements and electromagnetic simulations show that Raman hot spots appear at the inside perimeter of individual nanoparticles and serve as the source of a 1000-fold improvement of minimum molecular detection level that enables detection of signals from a few molecules near hot spots. A multimodality version of these nanoparticles, which includes the functionality offered by magnetic multilayers, is also demonstrated. These results illustrate the potential of direct fabrication for creating exotic monodisperse nanoparticles, which combine engineered internal nanostructures and multilayer composite materials, for use in nanoparticle-based molecular imaging and detection.

A Novel Zero-Drift Detection Method for Highly Sensitive GMR Biochips

In this paper, we present a novel drift compensation mechanism for highly sensitive biodetection based on giant magnetoresistive (GMR) sensors and magnetic nanoparticles. Micromagnetic simulations showed the quantitative detection ability of this new method. The proposed detection scheme uses both ac current sources and ac magnetic fields along with two dc bias states. Experiments were carried out to detect Miltenyi Biotec (MACS) magnetic nanoparticles on the spin-valve sensor (0.2 mumtimes4 mum). The experimental results show that sub-microvolt drifts can be achieved by this dual bias-double modulation (DBDM) method

Nanosensor dosimetry of mouse blood proteins after exposure to ionizing radiation

Giant magnetoresistive (GMR) nanosensors provide a novel approach for measuring protein concentrations in blood for medical diagnosis. Using an in vivo mouse radiation model, we developed protocols for measuring Flt3 ligand (Flt3lg) and serum amyloid A1 (Saa1) in small amounts of blood collected during the first week after X-ray exposures of sham, 0.1, 1, 2, 3, or 6u2005Gy. Flt3lg concentrations showed excellent dose discrimination at ≥ 1u2005Gy in the time window of 1 to 7 days after exposure except 1u2005Gy at day 7. Saa1 dose response was limited to the first two days after exposure. A multiplex assay with both proteins showed improved dose classification accuracy. Our magneto-nanosensor assay demonstrates the dose and time responses, low-dose sensitivity, small volume requirements, and rapid speed that have important advantages in radiation triage biodosimetry.