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Apr 2012

Volume 83, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 83, 041101 (2012); http://dx.doi.org/10.1063/1.3697599 (19 pages)

Michael A. Duncan

The laser vaporization cluster source in the "cutaway" configuration. The sample rod is mounted from above with a flexible nylon screw in a holding block. The pulsed gas valve is mounted in the stainless steel can (left) and the skimmer is mounted on the opposite wall.

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back to top Biology and Medicine

A new device for performing reference point indentation without a reference probe

Daniel Bridges, Connor Randall, and Paul K. Hansma

Rev. Sci. Instrum. 83, 044301 (2012); http://dx.doi.org/10.1063/1.3693085 (8 pages)

Online Publication Date: 4 April 2012

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Here we describe a novel, hand-held reference point indentation (RPI), instrument that is designed for clinical measurements of bone material properties in living patients. This instrument differs from previous RPI instruments in that it requires neither a reference probe nor removal of the periosteum that covers the bone, thus significantly simplifying its use in patient testing. After describing the instrument, we discuss five guidelines for optimal and reproducible results. These are: (1) the angle between the normal to the surface and the axis of the instrument should be less than 10°, (2) the compression of the main spring to trigger the device must be performed slowly (>1 s), (3) the probe tip should be sharper than 10 μm; however, a normalized parameter with a calibration phantom can correct for dull tips up to a 100 μm radius, (4) the ambient room temperature should be between 4 °C and 37 °C, and (5) the effective mass of the bone or material under test must exceed 1 kg, or if under 1 kg, the specimen should be securely anchored in a fixation device with sufficient mass (which is not a requirement of previous RPI instruments). Our experience is that a person can be trained with these guidelines in about 5 min and thereafter obtain accurate and reproducible results. The portability, ease of use, and minimal training make this instrument suitable to measure bone material properties in a clinical setting.
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87.85.gp Mechanical systems
87.19.R- Mechanical and electrical properties of tissues and organs

A thermal study of cellular motility by optical time-resolved correlation

F. J. Sierra-Valdez, A. J. Cisneros-Mejorado, D. P. Sánchez Herrera, and J. C. Ruiz-Suárez

Rev. Sci. Instrum. 83, 044302 (2012); http://dx.doi.org/10.1063/1.3700248 (4 pages)

Online Publication Date: 4 April 2012

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The study of motor properties of cells under appropriate physical-chemical conditions is a significant problem nowadays. The standard techniques presently used do not allow to evaluate neither large samples nor to control their thermodynamic conditions. In this work, we report a cell motility sensor based on an optical technique with a time-resolved correlation, adapted in a system able to study several samples simultaneously. Image correlation analysis is used to follow their temporal behavior. A wide variety of motile cells, such as archaea, bacteria, spermatozoa, and even contractile cells, can be studied using this technique. Here, we tested our technique with the study of sperm motility. In particular, both the sperm motility and its prevalence are studied under a temperature range from 0 to 37 °C. We found that incubation at 10 °C presents the lengthiest prevalence in motility and observed, for the first time, an interesting thermal reversibility behavior.
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87.17.Jj Cell locomotion, chemotaxis
87.18.Gh Cell-cell communication; collective behavior of motile cells

Continuous-waveform constant-current isolated physiological stimulator

Mark R. Holcomb, Jack M. Devine, Rene Harder, and Veniamin Y. Sidorov

Rev. Sci. Instrum. 83, 044303 (2012); http://dx.doi.org/10.1063/1.3700977 (6 pages)

Online Publication Date: 6 April 2012

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We have developed an isolated continuous-waveform constant-current physiological stimulator that is powered and controlled by universal serial bus (USB) interface. The stimulator is composed of a custom printed circuit board (PCB), 16-MHz MSP430F2618 microcontroller with two integrated 12-bit digital to analog converters (DAC0, DAC1), high-speed H-Bridge, voltage-controlled current source (VCCS), isolated USB communication and power circuitry, two isolated transistor-transistor logic (TTL) inputs, and a serial 16 × 2 character liquid crystal display. The stimulators are designed to produce current stimuli in the range of ±15 mA indefinitely using a 20V source and to be used in ex vivo cardiac experiments, but they are suitable for use in a wide variety of research or student experiments that require precision control of continuous waveforms or synchronization with external events. The device was designed with customization in mind and has features that allow it to be integrated into current and future experimental setups. Dual TTL inputs allow replacement by two or more traditional stimulators in common experimental configurations. The MSP430 software is written in C++ and compiled with IAR Embedded Workbench 5.20.2. A control program written in C++ runs on a Windows personal computer and has a graphical user interface that allows the user to control all aspects of the device.
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87.19.Hh Cardiac dynamics
87.19.R- Mechanical and electrical properties of tissues and organs
87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)

Development of a microbial high-throughput screening instrument based on elastic light scatter patterns

Euiwon Bae, Valery Patsekin, Bartek Rajwa, Arun K. Bhunia, Cheryl Holdman, V. Jo Davisson, E. Daniel Hirleman, and J. Paul Robinson

Rev. Sci. Instrum. 83, 044304 (2012); http://dx.doi.org/10.1063/1.3697853 (10 pages) | Cited 1 time

Online Publication Date: 12 April 2012

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A microbial high-throughput screening (HTS) system was developed that enabled high-speed combinatorial studies directly on bacterial colonies. The system consists of a forward scatterometer for elastic light scatter (ELS) detection, a plate transporter for sample handling, and a robotic incubator for automatic incubation. To minimize the ELS pattern-capturing time, a new calibration plate and correction algorithms were both designed, which dramatically reduced correction steps during acquisition of the circularly symmetric ELS patterns. Integration of three different control software programs was implemented, and the performance of the system was demonstrated with single-species detection for library generation and with time-resolved measurement for understanding ELS colony growth correlation, using Escherichia coli and Listeria. An in-house colony-tracking module enabled researchers to easily understand the time-dependent variation of the ELS from identical colony, which enabled further analysis in other biochemical experiments. The microbial HTS system provided an average scan time of 4.9 s per colony and the capability of automatically collecting more than 4000 ELS patterns within a 7-h time span.
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87.80.-y Biophysical techniques (research methods)
87.64.-t Spectroscopic and microscopic techniques in biophysics and medical physics

Spectral contaminant identifier for off-axis integrated cavity output spectroscopy measurements of liquid water isotopes

J. Brian Leen, Elena S. F. Berman, Lindsay Liebson, and Manish Gupta

Rev. Sci. Instrum. 83, 044305 (2012); http://dx.doi.org/10.1063/1.4704843 (5 pages) | Cited 2 times

Online Publication Date: 26 April 2012

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Developments in cavity-enhanced absorption spectrometry have made it possible to measure water isotopes using faster, more cost-effective field-deployable instrumentation. Several groups have attempted to extend this technology to measure water extracted from plants and found that other extracted organics absorb light at frequencies similar to that absorbed by the water isotopomers, leading to δ2H and δ18O measurement errors (Δδ2H and Δδ18O). In this note, the off-axis integrated cavity output spectroscopy (ICOS) spectra of stable isotopes in liquid water is analyzed to determine the presence of interfering absorbers that lead to erroneous isotope measurements. The baseline offset of the spectra is used to calculate a broadband spectral metric, mBB, and the mean subtracted fit residuals in two regions of interest are used to determine a narrowband metric, mNB. These metrics are used to correct for Δδ2H and Δδ18O. The method was tested on 14 instruments and Δδ18O was found to scale linearly with contaminant concentration for both narrowband (e.g., methanol) and broadband (e.g., ethanol) absorbers, while Δδ2H scaled linearly with narrowband and as a polynomial with broadband absorbers. Additionally, the isotope errors scaled logarithmically with mNB. Using the isotope error versus mNB and mBB curves, Δδ2H and Δδ18O resulting from methanol contamination were corrected to a maximum mean absolute error of 0.93 ‰ and 0.25 ‰ respectively, while Δδ2H and Δδ18O from ethanol contamination were corrected to a maximum mean absolute error of 1.22 ‰ and 0.22 ‰. Large variation between instruments indicates that the sensitivities must be calibrated for each individual isotope analyzer. These results suggest that the properly calibrated interference metrics can be used to correct for polluted samples and extend off-axis ICOS measurements of liquid water to include plant waters, soil extracts, wastewater, and alcoholic beverages. The general technique may also be extended to other laser-based analyzers including methane and carbon dioxide isotope sensors.
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92.40.Qk Surface water, water resources
06.20.Dk Measurement and error theory
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
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