We have investigated the application of ultrasound modulated coherent light for quantitative determination of the ratio of dye concentrations and total concentration of absorbers in a blood vessel-mimicking sample. A 3-mm-diam tube containing the mixture of dyes inside an Intralipid-based gel with optical properties similar to tissue was interrogated by two different laser wavelengths in combination with intense microsecond ultrasound bursts. The use of calibration curves allowed us to extract quantitative information on the ratio of dye concentrations with the accuracy of better than 15%, as well as on the total concentration. Furthermore, we demonstrated the feasibility to obtain a quantitative 3-D map of the absorbing structure with a spatial resolution of better than 3 mm. These findings give an outlook to apply this technique for noninvasive 3-D mapping of oxygen saturation and total concentration of hemoglobin in tissue.
The light scattering and absorption properties of gold nanoparticles (GNPs) can be utilised for the detection of DNA.
Binding of molecules to the GNP influences the local refractive index. The increase in refractive index can be measured
as proportional red-shift of the GNPs extinction maximum; therefore GNPs are suitable for use as nanoparticle chemical
sensors. Utilizing this method it is possible to detect DNA in naturally occurring quantities.
In bulk measurements we have shown a red-shift of 7 nm of the absorption maximum (λmax) upon binding of thiolated
ssDNA. Subsequently, we were able to follow the interaction between two sets of GNPs functionalised with
complementary strands.
Randomly immobilised GNPs were visualised with an inverted darkfield microscope. The use of a colour camera enables
us to analyse the colour change of each individual particle in the field of view. A change of λmax of 1 nm can be detected
by the colour camera, which corresponds to ~100 20mer ssDNA molecules. For the detection of a single DNA binding
events we are developing an assay for DNA detection, utilizing a second set of GNPs. The interaction of two GNPs
within a range of 2.5 times the radius of each other results in a shift of ~7 nm in λmax for the presence of one DNA strand.
This increased shift makes the method not only more accurate but also easier to detect.
We have investigated the application of acousto-optic sensing for quantitative imaging of tissue-mimicking phantoms.
An Intralipid phantom, which contains a turbid absorber, confined in a silicone tube, was used. Scattered pulsed laser
light was modulated by ultrasonic bursts focused in a predefined volume in the medium. By varying the delay time
between ultrasound burst initiation and light pulse firing we could perform a scan in the ultrasound-propagation plane.
The use of calibration procedures allowed us to establish a quantitative correlation between local absorbances in the
phantom and the measured signal and to obtain information on the ratios of dye concentrations inside the tube.
Metal nanoparticles posses the property of changing their optical properties as a function of both internal
characteristics (size, shape, dielectric function) and refractive index of the local environment. A special class of
applications in the field of biosensing uses the dependency of the nanoparticle's plasmonic peak localization on the local
refractive index change. The response of this type of sensors is usually monitored by the change of the extinction
spectrum of an ensemble of nanoparticles where analytes interact with functionalized nanoparticles in solution or
immobilized at an interface; detection is done with a spectrophotometer. This type of sensors has a limited sensitivity.
This can be overcome by using single nanoparticle based biosensors. This type of sensors measures the changes of the
scatter spectrum of a collection of individually addressable functionalized nanoparticles in the presence of analytes.
Here we report on a new detection method of binding events of analytes to functionalized gold nanoparticle
using a standard colour camera attached to a darkfield microscopy setup. This setup is capable of parallel detection of
the spectral shifts of thousands of 60 nm antibody-functionalized gold spheres as a result of binding events of protein
analyte molecules. This setup can be the basis for multiplexing and quantification.
We have investigated the application of AO sensing for quantitative three-dimensional mapping of tissue-mimicking
phantoms. An Intralipid phantom, which contains a turbid absorber, confined in a silicone tube, was used. Multiply
scattered pulsed laser light was modulated by ultrasonic bursts focused in a predefined volume in the medium. By
varying the delay time between ultrasound burst initiation and light pulse firing we could perform a scan in the
ultrasound-propagation plane. By moving the ultrasound transducer, we could build up a volumetric map of modulation
depth values. We have experimentally determined the acousto-optical modulation depth as a function of the absorption
coefficient in phantom voxels of a few millimeters in size.
We have investigated if the application of microsecond length pulses of ultrasound and laser light for AO sensing
could result in an improvement of the detection of changes of local absorbances in tissue-mimicking phantoms.
An Intralipid-based phantom model, which mimics a blood vessel in human tissue, was used. The detection
technique was based on homodyne parallel speckle detection and subsequent image contrast processing. This
approach has proved that a spatial resolution of the system of a few millimeters can be obtained and thus, smaller
changes in the absorber concentration can be measured. Based on a comparison of experimental data and Monte-
Carlo simulations, the quantitative correlation between local absorbances of the phantom and the measured signal
has been shown.
KEYWORDS: Modulation, Photons, Signal to noise ratio, Acousto-optics, Absorbance, Speckle, Sensors, Monte Carlo methods, Spectroscopy, Systems modeling
We have made a comparison of various detection strategies for detection of acoustically modulated light in a scattering medium. Furthermore we have investigated the possibility to determine the local absorbance in a model system mimicking a blood vessel in tissue.
We investigate whether acousto-optic spectroscopy can be utilized for a non-invasive quantitative determination of chemical species in human blood or tissue. In a series of preliminary experiments in a model system consisting of a light absorbing structure buried in a light scattering environment we have found that it is possible to extract semi-quantitative information on the absorbance of this absorber. From these pilot experiments we conclude that our approach deserves further investigation.
A fiber optic polarimeter sensor is presented, which is capable of measuring low concentrations of biological macromolecules. Adsorption processes of two types of antibody- proteins have been measured so far, in a concentration of approximately equals 3X10-7Molar (MWequals150kD), resulting in phase changes of approximately equals 0.25X2(pi) .
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