Development of spectroscopic chemical sensors for continuous and noninvasive monitoring of selected analytes in complex matrixes of biological and environmental origin.

Research

A. Solid-State Near Infrared Spectroscopy

  1. Solid-State Near Infrared Spectroscopy for Non-Laboratory Analytical Measurments
    The feasibility of noninvasive clinical glucose measurements has been established by using high-performance Fourier transform instrumentation. Translation of such measurements from the academic laboratory to clinical practice (so-called bench-to-bedside or B2B) requires the creation of novel solid-state optoelectronic elements that can be incorporated in to spectroscopy instrumentation designed for robust operation under non-laboratory conditions. Jon Olesberg is developing a set of novel emitters and detectors specifically for spectroscopic glucose measurements in clinical samples.

B. Noninvasive Near infrared Spectroscopy

  1. Skin Heterogeneity and Its Impact on Noninvasive Spectroscopic Sensing

    something right h\nowThe ability to measure glucose in people with diabetes noninvasively has been an objective of the ARG for many years.  The concept is to pass a band of harmless near infrared radiation across a section of skin and extracting the concentration of glucose from a multivariate analysis of the resulting spectrum.  Such noninvasive analyses have been demonstrated in an animal model by transmitted the near infrared light across a fold of skin by using a fiber-optic probe. These experiments illustrate that such measurements are highly sensitive to the placement of this probe on the skin surface.  In order to understand this sensitivity, near infrared microscopy is used to map the concentrations of the major chemical components of skin samples of animal and human origin.  These skin maps illustrate domains of the primary skin components (water, fat, keratin protein, collagen protein, and scattering bodies) on the order of several hundred square microns. Simulations indicate that chemical heterogeneity of this nature in the epidermis and dermis layers of skin is an important factor in the experimental variations observed during noninvasive glucose measurements.

     

  2. Hypoglycemic Nocturnal Alarm

    Diabetes is a condition where the ability to regulate the concentration of glucose in a person’s blood is diminished.  Chronic hyperglycemia, high blood glucose concentrations, is known to cause the medical complications associated with diabetes, including amputation, heart disease, and renal failure.  Hypoglycemia, low blood glucose concentrations, can be life threating.  People with Type I diabetes are prone to hypoglycemia, particularly while sleeping.  For this reason, a nocturnal hypoglycemic alarm is desired in order to waken the user before his/her blood glucose concentration reaches a critically low level.  We are exploring the use of noninvasive near infrared spectroscopy as a means to track blood glucose levels and alarm when a set hypoglycemic threshold is reached, thereby enabling the user to avoid an impending dangerous situation.

C. Time-Domain Terahertz Analytical Spectroscopy

  1. Terahertz Spectroscopy for Selective Measurements in Gaseous Mixture

    Terahertz (THz) spectroscopy corresponds to molecular transitions associated with absorptions of electromagnetic (EM) radiation over the THz frequencies of 0.3-4 THz or 10-133 cm-1.  These transitions correspond to rotations for gases and intermolecular interactions for solids.  We are interested in establishing the analytical utility of time-domain THz spectroscopy for the selective quantification of selected gaseous species in complex mixtures.  Ryan Smith’s dissertation details the ability to measure a series of environmentally relevant gases, including acetaldehyde, acetonitrile, ammonia, ethanol, methanol, propioaldehyde, propionitrile, and water at concentrations below the permissible exposure limits set by the Occupational Safety and Health Administration.  Selectivity of the THz spectral range is determined to be superior to that affording by gaseous measurements over mid-infrared frequencies.

     

  2. Understanding Analytical Terahertz Spectroscopic Measurements of Solid Samples
    Time-domain terahertz (THz) spectroscopy is under investigation by many research groups as a means to identify and quantify components within solid samples, especially associated with explosives, pharmaceutical preparations, biological samples, and polymers.  In many cases, the quantitative relationship between THz spectral features and sample composition is not well defined and the corresponding Beer-Lambert plots are highly scattered.  Following the pioneering work by Hankyu Namkung and Jaejin Kim, Madhuri Gundameedi is exploring the impact of sample parameters on THz spectral variations as a way to improve analytical precision.  Parameters of interest include compressed density and particle size of the sample components.
     

  3. Analysis of Single Crystal Photochemical Reactions with Noninvasive Terahertz Spectroscope
    THz analytical spectroscopy offers a unique method for studying single crystal single crystal (SCSC) reactions.  In collaboration with the MacGillivray research group, we are developing methods based on THz spectroscopy to follow such reactions in real time.  Bimali Bandaranayake is pursuing this approach by following the photodimerization reaction of 2(5-CN-Res)∙2(4,4’-bpe) to form 2(5-CN-Res)∙2(4,4’-tpcb) according to the following reaction:

                           Where:   (5-CN-Res) = 5-cyano-1, 3–dihydroxybenzene
                                           (4, 4-bpe) = trans–1, 2–bis(4–pyridyl)ethylene
                                           (4, 4’-tpcb) = tetrakis(4-pyridyl)cyclobutane

                                                                                                                                                                                                                                                                                                                           Differences in the absorption spectra the monomer and dimer over 20-110 cm-1 provide the means to follow the reaction in real-time.  A variety of spectral processing methods are being used to enhance the quantitative nature of these measurements.  In addition, systematic variations in the chemical structure of crystalline and co-crystal samples are being used to better understand the chemical processes and intermolecular interactions responsible for absorption bands of solids over the THz region of the electromagnetic spectrum.