There are several applications of noninvasive spectroscopy in biological systems on which I presently working. One of those is the attempt to measure blood glucose (blood sugar) concentrations without having to draw blood. People who suffer from diabetes need to regularly monitor their blood glucose levels to avoid both acute and chronic complications. Unfortunately, the pain and cost involved in drawing even small quantities of blood multiple times a day deters many diabetics from monitoring their glucose levels as often as they should. Researchers have known for quite a while that it should, in principle, be possible to measure glucose in the body using near-infrared spectroscopy.
The idea is that a band of infrared light is passed through some part of the body and glucose concentrations are inferred from the the spectrum of light that emerges. However, no one has been able to demonstrate an instrument that is capable of measuring glucose to the satisfaction of the FDA. And that is not for lack of trying. Several proposed instruments have been studied by the FDA and been found wanting. It turns out that measuring glucose concentrations in the body is a very difficult spectroscopic task. Absorption spectra of skin must be recorded with extremely high signal-to-noise ratios that push the limits of present device technology. In addition, the "unique" glucose absorption signature must be disentangled from the signature of several other skin components.
Most of the work we do involves conventional FTIR instrumentation. We are also investigating alternative spectroscopic systems including those based on acousto-optic tunable filters and infrared laser diodes.
Recently, I and my colleages Mark Arnold and Gary Small have created ASL Analytical, a startup company to further commercialize some of the chmical sensing applications being developed in our research laboratories. ASL now has two full-time employees and has received on STTR grant from the NIH to explore the developement of a nocturnal alarm for hypoglycemia.
Slides from a presentation describing the basics of noninvasive glucose monitoring can be found here.
A recent paper describing the identification of the unique absorption signature for glucose can be found here.
Another application of near-infrared sensing is the monitoring of urea removal from patients undergoing hemodialysis. People with kidney failure need to undergo a 3-4 hour hemodialysis session typically three times per week. In the treatment, the patient's blood is circulated through an eternal device that removes small molecular weight toxins from the blood that would normally be removed by the kidneys. The goal of our work is to be able to monitor the removal of these toxins during the treatment in order to ensure that each patient receives the optimal dose of dialysis at each visit. Currently, the dose of delivered of dialysis is checked once a month using blood samples drawn before and after a dialysis treatment.
A paper describing some of our initial work can be found here.
We are developing a small optical sensor that we hope can eventually be implanted in order to provide continuous measurements of blood glucose. If successful, the sensor can be coupled to an insulin delivery system to provide closed-loop control of glucose levels. Such a unit would effectively become an artificial pancreas.
A proceedings from a talk delivered at Photonics West 2006 describing this technology can be found here.
Many of the chemical sensing applications we are working on would benefit from better optical sources and detectors in the 2.0-2.5 mm and 3-12 mm wavelength ranges. I work in collaboration with Thomas Boggess, John Prineas and Michael Flatte of the University of Iowa to design, grow, and fabricate LEDs, diode lasers, and detectors at these wavelengths using antimonide-based materials.
An example of some of our recent work can be found here and here.
I have designed and constructed a dual-trap optical tweezers apparatus for measuring the adhesion force between cells. The system is based on a pair of 830nm diodes that are injected into an optical microscope. The beams from the diodes are brought to a focus in the sample plane of the microscope, and can be used to move cell-sized objects. Because the system has two independently-movable traps, we can study the forces required to pull two cells apart under different environmental and cell-growth conditions. We are particularly interested in studying the cell-to-cell adhesion forces of cancer cells in order to learn more about the conditions leading to the metastasis phase of cancer growth, where cell-to-cell adhesion decreases dramatically.
Modern electronics relies upon the principle of controlling electronic charge in semiconductors for information processing. Recently, however, there has been intense interest in applying another fundamental electronic property, the intrinsic angular momentum or spin, to spin-sensitive electronic devices and circuits ("spintronics"). The successful controlled electrical injection of spin packets into semiconductors could lead to a variety of important new devices, including semiconductor-based magnetic memories and spin-sensitive transistors and diodes. Spin dynamics have also drawn much recent attention due to the broad proposal that physical realizations of quantum computer bits (or qbits) might be achieved in semiconductors using coherent superpositions of carrier spin. Such potential applications have generated considerable research activity focused on the injection of spin-polarized currents from ferromagnetic metals or spin filters into semiconductors. I have performed fundamental studies of spin dynamics in narrow-band semiconductor systems using a mid-infrared, ultrafast optical optical parametric oscillator based on a KTiOAsO[4] crystal. I have performed measurements of the lifetime of optically-generated spin populations in bulk InAs and various InAs/GaInSb structures. In addition, I have collaborated with Michael Flatté and Wayne Lau in performing some of the first accurate theoretical calculations of spin-lifetimes in antimonide-based quantum systems.
As part of the development of mid-infrared semiconductor materials for optical sources and detectors, I have developed a code-base for calculation of the optical and electronic properties of semiconductors quantum structures. The core of the computations are based on an implementation of 14-band K.p formalism. The physics on which the code is based are described in a book chapter authored by myself and Michael Flatte titled "Theory of mid-wavelength infrared laser active regions: intrinsic properties and design strategies" in Mid-infrared Semiconductor Optoelectronics, edited by Anthony Krier.
Most of the compuation work I do involves working with multidimensional arrays of numbers. I have developed a C++ library to facilitate hanling of these arrays, called the ArrayToolkit. The library is released under a BSD-style license and can be downloaded from hg.physics.uiowa.edu.
Last updated: January 7, 2009