Dr. Daniel B. Hall Profile

Dr. Daniel B. Hall

Staff Scientist at Radiation Monitoring Devices Inc

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Proceedings Article | 8 February 2011 Paper

Application of field-modulated birefringence and light scattering to biosensing

Louis Strong, Daniel Hall, Clark Edson, Hiep-hoa Nguyen, Michael Whitt, Gyula Varadi

Proceedings Volume 7888, 78880P (2011) https://doi.org/10.1117/12.875342

KEYWORDS: Birefringence, Light scattering, Nanoparticles, Scattering, Receptors, Proteins, Particles, Magnetism, Lamps, Modulation

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Superparamagnetic nanoparticles (NPs) coated with surface ligands are shown to be an effective means to impart magnetic field modulation to optical signals from targeted receptor complexes. The modulated signals they produce can be used for a number of important high throughput applications in bio-sensing including: detecting (weaponized) viruses, screening recombinant libraries of proteins, identifying pathogenic conversions of microbes, and monitoring gene amplification. We compare the results of two dynamic methods of measuring target binding to NPs: birefringence and field modulated light scattering (FMLS). These measurements reflect complementary manifestations of NP alignment (orientation) and de-alignment (relaxation) dynamics. Birefringence originates from the specific crystalline properties of a small subset of paramagnetic NPs (for example, maghemite) when oriented in a magnetic field. Upon quenching the field, it decays at a rate exhibiting the Debye-Stokes-Einstein rotational relaxation constant of target-NP complexes. Birefringence relaxation reflects the particle dynamics of the mixed suspension of NPs, with signal components weighted in proportion to the free and complexed NP size distributions. FMLS relaxation signals, on the other hand, originate predominately from the inherent optical anisotropy of the target complexes, show little contribution from non-complexed NPs when the targets are more optically anisotropic than the NPs, and provide a more direct and accurate method for determining target receptor concentrations. Several illustrations of the broad range of applications possible using these dynamic measurements and the kind of information to be derived from each detection modality will be discussed.

Proceedings Article | 3 March 2009 Paper

Improved molecular barcodes by lifetime discrimination

Daniel Hall, William Lawrence

Proceedings Volume 7189, 71890R (2009) https://doi.org/10.1117/12.809400

KEYWORDS: Luminescence, Quantum dots, Molecules, Pulsed laser operation, Time metrology, Absorption, Silica, Oscilloscopes, Multiplexing, Fluorescence resonance energy transfer

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Individual microspheres labeled with a unique barcode and a surface-bound probe are able to provide multiplexed biological assays in a convenient and high-throughput format. Typically, barcodes are created by impregnating microspheres with several colors of fluorophores mixed at different intensity levels. The number of barcodes is limited to hundreds primarily due to variability in fluorophore loading and difficulties in compensating for signal crosstalk. We constructed a molecular barcode based on differences in lifetimes rather than intensities. Lifetime-based measurements have an advantage in that signal from neighboring channels is reduced (because signal intensities are equal) and may be mathematically deconvoluted. The excited state lifetime of quantum dots (QDs) was systematically altered by attaching a variable number of quencher molecules to the surface. We have synthesized a series of ten QDs with distinguishable lifetimes all emitting at the same wavelength. The QDs were loaded into microspheres to determine the expected signal intensities. The uncertainty in lifetimes as a function of the interrogation time was determined. An acceptable standard deviation (3%) was obtained with a measurement time of approximately 10-30 μsec. Currently, we are expanding these studies to include multiple wavelengths and determining the maximal number of barcodes for a given spectral window.

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