The use of laser-based diagnostics for the rapid identification of infectious agents in human blood.

AIMS: To investigate the use of a laser-based method of detection as a potential diagnostic test for the rapid identification of infectious agents in human blood. METHODS AND RESULTS: In this study, the successful differentiation of blood spiked with viruses, bacteria or protozoan parasites to clinically relevant levels is demonstrated using six blood types (O+, O-, AB+, A+, A-, B+) using blood from different individuals with blood samples prepared in two different laboratories. Experiments were performed using various compositions of filters, experimental set-ups and experimental parameters for spectral capture. CONCLUSIONS: The potential for developing a laser-based diagnostic instrument to detect the presence of parasites, bacteria and viruses in human blood capable of providing analysis results within minutes was demonstrated. SIGNIFICANCE AND IMPACT OF THE STUDY: There is an ongoing need for clinical diagnostics to adapt to newly emerging agents and to screen simultaneously for multiple infectious agents. A laser-based approach can achieve sensitive, multiplex detection with minimal sample preparation and provide rapid results (within minutes). These properties along with the flexibility to add new agent detection by simply adjusting the detection programming make it a promising tool for clinical diagnosis.

Measuring total soil carbon with laser-induced breakdown spectroscopy (LIBS).

Improving estimates of carbon inventories in soils is currently hindered by lack of a rapid analysis method for total soil carbon. A rapid, accurate, and precise method that could be used in the field would be a significant benefit to researchers investigating carbon cycling in soils and dynamics of soil carbon in global change processes. We tested a new analysis method for predicting total soil carbon using laser-induced breakdown spectroscopy (LIBS). We determined appropriate spectral signatures and calibrated the method using measurements from dry combustion of a Mollisol from a cultivated plot. From this calibration curve we predicted carbon concentrations in additional samples from the same soil and from an Alfisol collected in a semiarid woodland and compared these predictions with additional dry combustion measurements. Our initial tests suggest that the LIBS method rapidly and efficiently measures soil carbon with excellent detection limits (approximately 300 mg/kg), precision (4-5%), and accuracy (3-14%). Initial testing shows that LIBS measurements and dry combustion analyses are highly correlated (adjusted r2 = 0.96) for soils of distinct morphology, and that a sample can be analyzed by LIBS in less than one minute. The LIBS method is readily adaptable to a field-portable instrument, and this attribute--in combination with rapid and accurate sample analysis--suggests that this new method offers promise for improving measurement of total soil carbon. Additional testing of LIBS is required to understand the effects of soil properties such as texture, moisture content, and mineralogical composition (i.e., silicon content) on LIBS measurements.

Thermooptic-based differential measurements of weak solute absorptions with an interferometer.

An interferometric method of measuring small differences between weak optical absorptions of solutions has been developed using the thermooptic effect. To record the small changes in optical path length ~lambda/200 due to heating, it was necessary to stabilize the fringe pattern with respect to slow thermal drift using a galvanometer-driven compensator plate controlled by a closed feedback loop. Fringe shifts from background absorptions were nulled out to better than 1 part in 400, permitting the measurement of differences in absorptions between two solutions that were l/100th of background. Using laser powers of 100 mW, absorptions approximately 5 x 10(-6) cm(-1) (base e) could be measured with CC1(4) solutions.

Thermally induced laser pulsing to measure weak optical absorptions.

Intracavity thermal lensing has been used to convert a cw dye laser to pulsed operation. The pulse width is a measure of the absorptivity of the solution in the cell. Experimental data are presented to show how this technique can be used to measure the absorptivity of a pure solvent and the concentration of a solute. The absorptivities (base e) of water, CH(3)OH, CH(3)COCH(3), and CCl(4) were determined to be, respectively, (1.24 +/- 0.17) x 10(-3), (1.01 +/- 0.07) x 10(-3), (1.74 +/- 0.09) x 10(-4), and (3.95 +/- x(-6) cm(-1). For CCl(4) in a 10-cm sample cell, the minimum detectable absorptivity is ~4 x 10(-6) cm(-1).

Reliable, inexpensive microcomputer interface for the optical multichannel analyzer (OMA).

A microprocessor system and interface for the optical multichannel analyzer (OMA) is described. The interface hardware and software are very simple and easy to implement. The microcomputer is used in conjunction with the OMA in the 2-d (two-dimensional) mode as the data acquisition, analysis and storage system for a 8-ps-resolution transient absorption spectrometer. However, the microcomputer and interface hardware and software are of general use in any application where rapid transfer, processing and storage of spectroscopic information from the OMA are required.