This Small Business Innovation Research (SBIR) Phase I project will develop a compact, widely-tunable, high-brightness laser diode spectrometer that will be the core of an automated point-of-care (POC) monitor capable of tracking key blood metabolites for patients in intensive care units. The tunable laser is based on a 2.4 micron wavelength laser diode that utilizes antimonide III-V semiconductor materials and is coupled to an external cavity. A high-brightness source will be a great aid for spectroscopy in turbid solutions with low optical throughput like whole blood. The tunable laser spectrometer will have significantly higher brightness than is available with conventional broad-band sources. The wide tunability required to differentiate the spectral signatures of the target analytes from those of other biomolecules will be achieved first by broadening the gain spectrum through a series of quantum wells with staggered emission wavelengths, and second, by fabricating laser devices using a curved-waveguide geometry to suppress optical feedback from the laser diode facets. An intracavity, temperature-controlled acousto-optic tunable filter will provide the necessary wavelength stability and tuning range, giving the instrument a rugged, compact, all-solid state design with no moving parts. The tunable laser diode will enable direct spectroscopic measurements in small volumes of whole blood. The broader impact/commercial potential of this project is to significantly enhance patient care. The point-of-care monitor based on this tunable laser spectrometer will provide automated measurement of key blood metabolites at the bedside and semi-continuous monitoring of metabolic status. The monitor will periodically collect absorption spectra of a small blood sample, and reinfuse the blood into the patient through an arterial catheter, allowing regular monitoring of glucose, urea, creatinine and lactate. Regular monitoring of glucose enables the use of intensive insulin therapy, which has been shown to improve the outcome of intensive care unit patients. Tracking urea and creatinine concentrations provides a measure of renal function that can be used for early identification of acute kidney failure. Detection of elevated lactate concentrations can be used as an indicator of metabolic distress for unstable patients. The tunable laser-based point-of-care monitor can provide more information than is available now without increasing costs. Unlike standard blood chemistry assays, optical measurements do not require reagents, so there is no incremental cost to limit the frequency of monitoring. Since the measurement results in no blood loss, it is safe to use in patients who would be intolerant of frequent blood draws
