Caleb Behrend

Aspherical magnetically modulated optical nanoprobes (MagMOONs)

Aspherical magnetic particles orient in a magnetic field due to magnetic shape anisotropy. They also emit different fluxes of light from their different geometric faces due to self-absorption and total internal reflection within the particles. The particles rotate in response to rotating magnetic fields and appear to blink as they rotate. We have made pancake and chain shaped particles and magnetically modulated their fluorescent intensities. Demodulating the signal extracts the probe fluorescence from electronic and optical backgrounds dramatically increasing signal to noise ratios. The probes have applications in sensitive and rapid immunoassays, improved intracellular sensors, and inexpensive single molecule analysis.

Identification of Outliers in Hyperspectral Raman Image Data by Nearest Neighbor Comparison

A new algorithm for removal of cosmic spikes from hyperspectral Raman image data sets is presented. Spectra in a 3 × 3 pixel neighborhood are used to identify outlier-contaminated data points in the central pixel of that neighborhood. A preliminary despiking of the neighboring spectra is performed by median filtering. Correlations between the central pixel spectrum and its despiked neighbors are calculated, and the most highly correlated spectrum is used to identify outliers. Spike-contaminated data are replaced using results of polynomial interpolation. Because the neighborhood contains spectra obtained in three different frames, even large multi-pixel spikes are identified. Spatial, spectral, and temporal variation in signal is used to accurately identify outliers without the acquisition of any spectra other than those needed to generate the image itself. Sharp boundaries between regions of high chemical contrast do not interfere with outlier identification.

Photonic and magnetic nanoexplorers for biomedical use: from subcellular imaging to cancer diagnostics and therapy

A paradigm for brain cancer detection, treatment, and monitoring uses synergistic, multifunctional, biomedical nanoparticles for: (1) external delivery to cancer cells of singlet oxygen and reactive oxygen species (ROS), but no drugs, thus avoiding multi-drug resistance, (2) photodynamic generation of singlet oxygen and ROS by a conserved critical mass of photosensitizer, (3) enhancement of magnetic relaxivity providing for MRI contrast, (4) control of plasma residence time, (5) specific cell targeting, (6) minimized toxicity, (7) measurement of tumor kill with diffusion MRI. The 40 nm polyacrylamide nanoparticles contained Photofrin, iron-oxide (or Gd), polyethylene glycol and targeting moieties. In-vivo tumor growth was halted and even reversed.

Characterization and Applications of Modulated Optical Nanoprobes (MOONs)

Modulated optical nanoprobes (MOONs) are microscopic (spherical and aspherical) particles designed to emit different fluxes of light in a manner that depends on particle orientation. When particle orientation is controlled remotely using magnetic fields (MagMOONs) it allows modulation of fluorescence intensity in any selected pattern including square and sinusoidal waves. The broad range of sizes over which MOONs can be prepared allows them to be tailored to applications from intracellular sensors using submicron MOONs to immunoassays using larger MOONs (1-10µm). In the absence of external fields, or material that responds to external fields, the particles tumble erratically due to Brownian thermal forces. These erratic changes in orientation cause the MOONs to blink. The temporal pattern of blinking contains information about the local rheological environment and any forces and torques acting on the MOONs.

Fluorescent Pebble Nano-Sensors and Nanoexplorers for Real-Time Intracellular and Biomedical Applications

PEBBLEs (Probes Encapsulated By Biologically Localized Embedding) are sub-micron sized optical sensors specifically designed for minimally invasive analyte monitoring in viable, single cells with applications for real time analysis of drug, toxin, and environmental effects on cell function. PEBBLE nanosensor is a general term that describes a family of matrices and nano-fabrication techniques used to miniaturize many existing optical sensing technologies. The main classes of PEBBLE nanosensors are based on matrices of cross-linked polyacrylamide, cross-linked poly(decyl methacrylate), and sol-gel silica. These matrices have been used to fabricate sensors for H+, Ca2+, K+, Na+, Mg2+, Zn2+, Cu2+, Cl−, O2, NO, and glucose that range from 20 nm to 600 nm in diameter. A number of delivery techniques have been used successfully to deliver PEBBLE nanosensors into mouse oocytes, rat alveolar macrophages, rat C6-glioma, and human neuroblastoma cells. For majority of this chapter, we will focus on the fabrication, characterization and applications of all the different kinds of PEBBLE sensors developed up to date. In the remainder of the chapter, we will introduce a new family of PEBBLEs with several emerging directions in PEBBLE design and applications, from intracellular imaging to in-vivo actuating and targeting.