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M L Myrick

Publications and source records attributed to M L Myrick.

14 recordsLinked to original sources
PubMed2006

Tuning D* with modified thermal detectors.

We report on the fabrication and characterization of a modified thermopile detector that has a spectral detectivity, D*, primarily determined by the absorbance of a polymer film. This was done by coating the detector with a metal mirror, followed by the polymer film, so that the film absorbances are responsible for most thermal conversion. The detector is designed to tailor the spectral response of optical systems more specifically to analytes in order to improve precision in methods such as multivariate optical computing and simple photometry. Interference effects in the thin-film response are eliminated by the textured surface of the silicon thermopile, which makes the spectral response relatively simple. The maximum detectivity due to a 1-micrometer-thick film is found to be 20% of the detectivity of the original wide-band detector at 10 Hz modulation frequency. We estimate the thermal diffusion length in the polymer at 10 Hz to be 40 micrometers. We also suggest that the detectivity of the modified detector can be approximated as the product of the D* of the underlying thermal detector and the absorbance of the modifying film, provided the modulation frequency is low and interference effects are defeated.

Journal Article↗
PubMed2005

Effects of metal coating on self-assembled monolayers on gold. 2. Copper on an oligo(phenylene-ethynylene) monolayer.

We report studies on the modifications induced by the evaporation of copper overlayers on a self-assembled monolayer (SAM) of the oligo(phenylene-ethynyl) dithiol, 1-thio-4-[4'-[(4'-thio)phenylethynyl]-1'-ethynyl]-benzene (TTPEB). These SAMs were characterized after deposition from a tetrahydrofuran solution on polycrystalline gold substrates and after copper evaporation and its subsequent removal by nitric acid. Monolayers were studied via cyclic voltammetry (CV), UV-vis multiwavelength ellipsometry, external reflectance infrared (IR) spectroscopy, and ion scattering spectroscopy (ISS). The results obtained indicate that TTPEB SAMs display the same packing characteristics before and after copper evaporation and removal. However, as shown by IR spectroscopy, the monolayers undergo a reorganization process that involves an increase in tilt angle accompanied by rotation of aromatic rings that results in a decrease in the average molecular twist angle. ISS data suggest that copper diffuses through the monolayer after copper evaporation, a result that is significant for applications of this molecule in molecular electronic devices.

Journal Article↗
PubMed2005

Fabricating optical fiber imaging sensors using ink jet printing technology: a pH sensor proof-of-concept.

We demonstrate the feasibility of using Drop-on-Demand microjet printing technology for fabricating imaging sensors by reproducibly printing an array of photo-polymerizable sensing elements, containing a pH sensitive indicator, on the surface of an optical fiber image guide. The reproducibility of the microjet printing process is excellent for microdot (i.e. micrometer-sized polymer) sensor diameter (92.2+/-2.2 microm), height (35.0+/-1.0 microm), and roundness (0.00072+/-0.00023). pH sensors were evaluated in terms of pH sensing ability (< or =2% sensor variation), response time, and hysteresis using a custom fluorescence imaging system. In addition, the microjet technique has distinct advantages over other fabrication methods, which are discussed in detail.

Biosensing Techniques↗
PubMed2005

Fourier transform infrared reflectance microspectroscopy study of Bacillus subtilis engineered without dipicolinic acid: the contribution of calcium dipicolinate to the mid-infrared absorbance of Bacillus subtilis endospores.

Mid-infrared spectra of spores of two strains of Bacillus subtilis, PS832 (wild-type) and FB122 (sleB spoVF), that are isogenic except for the two mutations in FB122 were obtained by Fourier transform infrared (FT-IR) reflectance microspectroscopy. The mutations in FB122 cause the spores of this strain to be devoid of dipicolinic acid (pyridine-2,6-dicarboxylic acid; DPA), a biomarker characteristic of bacterial spores. Analysis of these two strains by difference spectroscopy revealed a spectrum similar to that of calcium dipicolinate (CaDPA), a chelate salt of DPA. This difference spectrum was compared to mid-infrared spectra of both DPA and CaDPA, and was attributed to CaDPA only. This is the first report known to the authors of a genetically engineered organism being used to identify the spectral contribution of a particular cellular component.

Bacillus subtilis↗
PubMed2005

Improved dispersion of bacterial endospores for quantitative infrared sampling on gold coated porous alumina membranes.

An improved method for qualitative and quantitative sampling of bacterial endospores using Fourier transform infrared (FT-IR) microscopy on gold-coated porous alumina membranes is presented. Bacillus subtilis endospores were filtered onto gold-coated alumina membranes serving as substrates. Studies in the mid-infrared (MIR) region revealed the characteristic bacterial absorption spectrum at low surface concentration, while scanning electron microscopy (SEM) images of the same samples provided precise calculation of the surface concentration of the bacterial endospores. Under the conditions of study, the average concentration of endospores was determined to be 1356 +/- 35 spores in a 100 x 100 mum(2) area, with a relative standard deviation of 0.0260. Examination of ten random spots on multiple substrates with FT-IR microscopy apertured to the same area gave an average relative standard deviation of 0.0482 in the signal strength of the amide A band at 3278 cm(-1). An extinction cross-section in reflection of sigma(ext) = (7.8 +/- 0.6) x 10(-9) cm(2)/endospore was calculated for the amide A band at the frequency of its peak absorbance, 3278 cm(-1). The absorption cross-section of the amide A band in reflection is estimated to be sigma(abs) approximately (2.10 +/- 0.12) x 10(-9) cm(2)/endospore.

Aluminum Oxide↗
PubMed2003

Multi-wavelength raman imaging using a small-diameter image guide with a dimension-reduction imaging array.

A commercially available fiber-optic Raman probe was modified for high-resolution spectral Raman imaging using a 350 microm diameter optical fiber image guide coupled to a dimension-reduction imaging array (DRIA). The DRIA comprised 672 optical fibers, arranged as a square array (21 x 32 fibers) on one end and a linear array (672 x 1 fibers) on the other. An imaging spectrograph was used with the DRIA to acquire multi-wavelength Raman images from -250 to 1800 cm(-1) at a spectral resolution of approximately 5 cm(-1). The utility of this technique for in situ and remote Raman imaging is demonstrated by monitoring the polymerization of a model polymer, dibromostyrene (DBS), while simultaneously measuring the Raman Stokes/ anti-Stokes ratio as a function of sample heating time, over a sample area of approximately 4 x 1.6 mm.

Fiber Optic Technology↗
PubMed2001

Identification of nucleotides with identical fluorescent labels based on fluorescence polarization in surfactant solutions.

A solution-phase steady-state polarization-based method for discriminating among the four DNA nucleotides labeled identically with tetramethylrhodamine is described and demonstrated. Labeled nucleotides were dissolved in buffered surfactant solutions. In room temperature 4.5 mM Triton X-100 solutions at neutral pH, the measured steady-state polarizations of tetramethylrhodamine-labeled dATP, dCTP, dGTP and dUTP were 0.261 +/- 0.003, 0.112 +/- 0.003, 0.288 +/- 0.003, and 0.147 +/- 0.003, respectively. A blind test of 40 samples showed no errors in classification based on polarization. The reproducibility obtained during this study demonstrates that the four dye-labeled nucleotides can be discriminated with more than 99.8% confidence.

Deoxyadenine Nucleotides↗
PubMed2001

Field-deployable sniffer for 2,4-dinitrotoluene detection.

A field-deployable instrument has been developed to detect low-level 2,4-dinitrotoluene (2,4-DNT) vapors. The system is based on previously developed artificial nose technology and employs an array of sensory materials attached to the distal tips of an optical fiber bundle. Both semiselective and nonspecific, cross-reactive sensors were employed. Each sensor within the array responds differentially to vapor exposure so the array's fluorescence response patterns are unique for each analyte. The instrument is computationally "trained" to discriminate target response patterns from nontarget and background environments. This detection system has been applied to detect 2,4-DNT, an analyte commonly detected on the soil surface above buried 2,4,6-trinitrotoluene (TNT) land mines, in spiked soil and aqueous and ground samples. The system has been characterized and demonstrated the ability to detect 120 ppb 2,4-DNT vapor in blind (unknown) humidified samples during a supervised field test.

Carcinogens↗
PubMed2001

Spectral tolerance determination for multivariate optical element design.

Recent reports from our laboratory have described a method for all-optical multivariate chemometric prediction from optical spectroscopy. The concept behind this optical approach is that a spectral pattern (a regression vector) can be encoded into the spectrum of an optical filter. The key element of these measurement schemes is the multivariate optical element (MOE), a multiwavelength interference-based spectral discriminator that is tied to the regression vector of a particular measurement. The fabrication of these MOEs is a complex operation that requires precise techniques. However, to date, no quantitative means of determining the allowable design/ manufacturing errors for MOEs has existed. The purpose of the present report is to show how the spectroscopy of a sample is used to define the accuracy with which MOEs must be designed and manufactured. We conclude this report with a general treatment of spectral tolerance and a worked example. The worked example is based on actual experimental measurements. We show how the spectral bandpass is defined operationally in a real problem, and how the statistics of the theoretical regression vector influence both the bandpass and the minimum tolerances. In the experimental example, we demonstrate that tolerances range continuously between 1 (totally tolerant) to approximately 10(-3) (0.1% T) in this problem.

Journal Article↗
PubMed2001

Identification of major water-soluble fluorescent components of some petrochemicals.

The chemical identities of several organic compounds that dominate the ultraviolet (UV) fluorescence of water after exposure to gasoline, diesel fuel and crude oil are presented. A combination of high-performance liquid chromatography with UV-fluorescence detection, fluorescence spectroscopy and gas chromatography-mass spectrometry (GC-MS) is used to show that naphthalene, methylnaphthalene and methylstyrene are the major fluorescent species in water following exposure to gasoline. These compounds are not dominant in water exposed to other petrochemicals we studied.

Chromatography, High Pressure Liquid↗
PubMed2001

Spectroelectrochemical study of the oxidative doping of polydialkylphenyleneethynylene using iterative target transformation factor analysis.

Iterative target transformation factor analysis (ITTFA) was used to determine the spectra of the individual species generated during the oxidative p-doping of films of poly(para-phenyleneethynylene) (PPE). UV-visible spectra of PPE films on transparent electrodes were obtained in-situ during an anodic sweep. ITTFA identified 4 species present during the oxidation, which we assign as neutral polymer, polaron species, bipolaron species, and a species formed by further bipolaron reaction. The region of electrochemical stability for each of these species was identified and their potential-dependent profiles were obtained. This work is the first deconvolution of conjugated polymer spectroelectrochemistry.

Electrochemistry↗
PubMed1999

Simultaneous enantiomeric determination of dansyl-D,L-phenylalanine by fluorescence spectroscopy in the presence of alpha-acid glycoprotein.

Few techniques are amenable to real-time analysis of enantiomers. In this paper, total complexation by alpha-acid glycoprotein (AGP) is shown to discriminate between enantiomers of dansyl-D,L-phenylalanine (DPs) by changing the local environment of the D and L enantiomers (DDP and DLP, respectively) from hydrophilic to hydrophobic. DDP and DLP show the same native fluorescence at lambda ex/lambda em = 200/544 nm in the absence of AGP, but show shifted emissions with a component at lambda ex/lambda em = 220/497 nm in the presence of AGP and in lipophilic solutions. The conditions for an analytical determination have been optimized, and the method has been used to measure the enantiomeric composition of DDP/DLP mixtures with concentration ratios varying over 2 orders of magnitude. The mechanism of chiral recognition for DDP and DLP by AGP is discussed and should be equally applicable to other dansyl-derivative amino acid enantiomers. The association constants for AGP with DDP and with DLP have been determined to be 1.33 x 10(2) L g-1 and 2.29 x 10(2) L g-1, respectively.

Animals↗