Show all abstracts
View Session
- Optical Monitoring of Glucose
- Optical Assessment of Blood Components, Whole Blood, and Blood Flow Parameters
- Diagnostic and Sensing Systems Based on Absorption, Scattering, and Fluorescence Detection
- Poster Session
Optical Monitoring of Glucose
Dendrimer-based fluorescent glucose sensor for diabetic monitoring
Show abstract
Fluorescent glucose assays based on the affinity reaction between Concanavalin A and dextran have been extensively studied. However, advancements in polymer science have allowed for new macromolecules capable of replacing dextran which may improve the performance of this well-known assay. Dendrimer macromolecules, being highly
ordered and spherical, allow for the binding of specific residues to the terminal (peripheral) binding sites, enabling researchers to customize the molecule. In this research, glycosylated dendrimers have been engineered to replace dextran to allow for more controlled chemical and fluorescent responses (eliminate multivalent binding and improve reversibility). This new assay has been shown to form small aggregate particles containing many Con A and glycosylated dendrimers resulting in a substantial loss in fluorescent intensity. Overall, this assay shows promise for use as part of an implantable glucose monitoring device, but more research needs to be done to increase sensor stability and optimize the sensor response to glucose.
Hydrogel microarray for monitoring of pH and dissolved oxygen in cell culture media
Show abstract
A combined dissolved oxygen and pH sensitive poly(ethylene glycol) hydrogel microarray was fabricated for use in monitoring cell culture media. The sensor was prepared by filling micro-channels with a hydrogel precursor solution containing pH or oxygen sensitive fluorophores. This solution was then cured by passing UV light through a mask placed to the channels, creating array with 100 μm elements. An imaging system with a monochrome CCD camera and
appropriate interference filters was used to capture the fluorescence image induced by excitation of microstructure in transmission mode. The sensor performance was characterized in buffer solution (PBS) and cell culture media (MEM) across the biological range of pH (6-8) and dissolved oxygen (3-21%).
Optical microsensor for continuous glucose measurements in interstitial fluid
Show abstract
Tight control of blood glucose levels has been shown to dramatically reduce the long-term complications of diabetes. Current invasive technology for monitoring glucose levels is effective but underutilized by people with diabetes because of the pain of repeated finger-sticks, the inconvenience of handling samples of blood, and the cost of reagent strips. A continuous glucose sensor coupled with an insulin delivery system could provide closed-loop glucose control without the need for discrete sampling or user intervention. We describe an optical glucose microsensor based on absorption spectroscopy in interstitial fluid that can potentially be implanted to provide continuous glucose readings. Light from a GaInAsSb LED in the 2.2-2.4 μm wavelength range is passed through a sample of interstitial fluid and a linear variable filter before being detected by an uncooled, 32-element GaInAsSb detector array. Spectral resolution is provided by the linear variable filter, which has a 10 nm band pass and a center wavelength that varies from 2.18-2.38 μm (4600-4200 cm-1) over the length of the detector array. The sensor assembly is a monolithic design requiring no coupling optics. In the present system, the LED running with 100 mA of drive current delivers 20 nW of power to each of the detector pixels, which have a noise-equivalent-power of 3 pW/Hz1/2. This is sufficient to provide a signal-to-noise ratio of 4500 Hz1/2 under detector-noise limited conditions. This signal-to-noise ratio corresponds to a spectral noise level less than 10 μAU for a five minute integration, which should be sufficient for sub-millimolar glucose detection.
Feasibility of glucose sensing by time- and spatial-resolved detection: Monte Carlo simulations of diffuse reflection in a three-layer skin model
Show abstract
In this paper, we investigate possibilities of glucose level monitoring in skin
Optical Assessment of Blood Components, Whole Blood, and Blood Flow Parameters
Combined laser Doppler and laser speckle imaging for real-time blood flow measurements
Show abstract
Laser Doppler (LDI) and laser speckle imaging (LSI) are two optical non-invasive techniques that are used to obtain 2D maps of blood flow in biological tissues. Each of these techniques has some benefits and drawbacks for measuring the blood flow. LSI is a true real-time imaging technique, but less sensitive to changes of flow parameters such as speed and concentration. In contrast, LDI has superior measurement accuracy but it is not a real-time technique. Recently we have developed a blood-flow imaging system that combines both imaging modalities with a gain in speed and accuracy. Using a single integrating CMOS image sensor for measuring both the Doppler signal spectrum and the image speckle contrast flow-map images are produced. In LDI mode, the flow map refresh rate is 1.2 seconds per 256x256 pixels image. In LSI mode the frame rate is 10 flow-map images per second. We present the basic design and in-vivo performance of this new hybrid imaging system. Subsequently, we discuss the potential of the new instrument for future implementations into clinical research.
Effect of multiple scattering on the accuracy of velocity profile reconstruction from the Monte-Carlo simulated OCDT signal in a model of biological tissues
Show abstract
Using the Monte-Carlo method we simulated the Optical Coherence Doppler Tomography (OCDT) signals at the wavelength
of 1 = 822 nm from one and two plain flows of a non-aggregating particulate suspension mimicking blood embedded into a
stationary light scattering medium (2% Intralipid solution) with optical properties close to those of human skin. The
dependences of statistical characteristics such as mean value and standard deviation of the stochastic fluctuations of the
Doppler frequency behind the first flow (Doppler noise) on the angle between the direction of incident radiation and the
normal to the object surface (Doppler angle) were studied. It was shown that with the increase of Doppler angle the mean
value of Doppler Noise as well as its standard deviation decrease. It was shown that with an increase of embedding depth of
the flow the reconstructed velocity values become smaller than the predefined ones and the reconstructed profile is stretched
towards the rear border. In the case of two flows, it was shown that with an increase of the fist flow velocity the
reconstructed velocity values of the second flow increase too. The computer with multiprocessor architecture was used for
Monte-Carlo simulation.
Absolute flow velocity components in laser Doppler flowmetry
Show abstract
A method to separate a Doppler power spectrum into a number of flow velocity components, measured in absolute units (mm/s), is presented. A Monte Carlo software was developed to track each individual Doppler shift, to determine the probability, p(n), for a photon to undergo n Doppler shifts. Given this shift distribution, a mathematical relationship was developed and used to calculate a Doppler power spectrum originating from a certain combination of velocity components. The non linear Levenberg-Marquardt optimization method could thus be used to fit the calculated and measured Doppler power spectra, giving the true set of velocity components in the measured sample. The method was evaluated using a multi tube flow phantom perfused with either polystyrene microspheres or undiluted/diluted human blood (hct = 0.45). It estimated the velocity components in the flow phantom well, during both low and high concentrations of moving scatterers (microspheres or blood). Thus, further development of the method could prove to be a valuable clinical tool to differentiate capillary blood flow.
Diagnostic and Sensing Systems Based on Absorption, Scattering, and Fluorescence Detection
mTHPC pharmacokinetics following topical administration
Show abstract
Measurements of concentration of sensitizers for photodynamic therapy can provide important information in the dosimetry planning and can also give input to the optimal time for treatment. There has been skepticism towards fluorescence techniques for this purpose, as the signal depends on the fluorescence yield and optical properties of the
tissue. Absorption based techniques, lack on the other hand, often the sensitivity required for many sensitizers with relative weak absorption in a wavelength region where hemoglobin absorption is dominant. A direct comparison between absorption and fluorescence techniques for measuring mTHPC concentration after topical application on hairless SKH-1 mice bearing skin carcinomas has been performed. 20 μl/cm2 of m-THPC thermogel (0.5 mg m-THPC/ml) were applied on normal and tumor area and the concentration of mTHPC was measured at 4 and 6 hours after drug application by two methods: 1. A fluorescence imaging system capturing images at two wavelengths (500 and 650 nm) following 405 nm excitation. Signals from different regions of interest were averaged and the intensity ratio at 650 to 500 was calculated. 2. A diffuse reflectance spectroscopy system with a fiber separation of 2 mm, providing the absorbance at 652 nm. Both
systems provided consistent results related to the photosensitizer concentration. The methods show a remarkable difference in the concentration of photosensitizer in normal skin and tumor. No significant difference in mTHPC concentration in tumor could be observed between the 4 and 6h groups after drug application.
Optical spectroscopy of human blood serum albumin interaction with lead ions
A. Saha,
L. Manglass,
S. Lionel,
et al.
Show abstract
Lead ions in solution interact strongly with human blood serum albumin forming clusters and modifying electronic properties of albumin molecules. We experimentally demonstrate that this interaction can be detected at pM concentrations of lead in solution. The structural and electronic modifications of albumin were observed using Raman, light scattering, fluorescence, and circular dichroism absorption spectroscopies.
Bacteria-clay interactions investigated by light scattering and phase contrast microscopy
Show abstract
Light scattering experiments and phase contrast microscopy are used to evaluate the aggregate-forming characteristics of simple clay-bacteria mixtures. Colloidal suspensions of negatively charged Pseudomonas syringae (Ps) and Mg2+-, Li+ - or Ca2+ -exchanged smectite (and non-exchanged smectite) are flocculated in neutral (pH 7) aqueous media. Aggregate
formation is monitored using changes in optical transmission. Clustering is observed in all the clay-bacteria preparations. The Li+-substituted clay aggregates average 50-300 microns in diameter, in contrast to the Ca2+- substituted clay that
produces aggregates of 10-50 microns in diameter. Light scattering measurements indicate that aggregates begin forming 3 hours after mixing and that the (larger sized) aggregates exhibit less scattering than a mixture with an equivalent concentration of unattached Ps and clay particles.
Enhanced light-target interaction using a novel anti-resonant waveguide concept
Show abstract
In optical biosensors waveguides are a good choice to deliver light to the area used for sensing. In traditional optical waveguides the light is confined by total internal reflection inside of a high index layer surrounded by regions of low refractive index. Since many sensing applications are based on liquids, it is necessary to guide the light within the liquid. Liquids usually have a lower refractive index than their surroundings. Hence, conventional waveguides provide only a weak interaction between light and target molecules.
In order to improve the interaction we are using a novel anti-resonant waveguide concept, in which the core region has a lower refractive index than the cladding layers. With this concept the light can be guided within the target-containing medium, thereby enabling an extended interaction length. An anti-resonant waveguide is especially compatible with a fluidic biosensor because the fluidic channel itself can be used as the core of the anti-resonant waveguide.
The light propagation and coupling mechanism of an anti-resonant waveguide is reviewed and is demonstrated with large area fluorescence excitation. By coupling the excitation light into a liquid film between two glass slides we are able to excite fluorescence within a 5 cm long channel. The measured fluorescence intensity per unit area is equal to that obtained by focusing the total excitation power onto a small spot. From analyzing the angular intensity distribution at the end facet of the waveguide we gain a better understanding of the guiding mechanism.
Poster Session
Absorption spectra of sulfhemoglobin derivates of human blood
Show abstract
The spectrophotometric properties of sulfhemoglobin (SHb) were investigated. Some methods of determination the content of individual compounds in multi-component solutions were analyzed. The main principles of work of devices that allow to determine the hemoglobin derivates are described.
Noninvasive blood glucose monitoring with laser diode
Show abstract
The non-invasive measurement of blood sugar level was studied by use of near infrared laser diodes. The in vitro and in vivo experiments were carried out using six laser diodes having wavelengths range from 1550 nm to 1750nm. Several volunteers were tested for OGTT (Oral Glucose Tolerance Test) experiment. We took blood from a fingertip and measured its concentration with a glucose meter while taking signal voltage from laser diodes system. The data of signal voltage were processed to do calibration and prediction; in this paper PLS (Partial Least Square) method was used to do modeling. For in vitro experiment, good linear relationship between predicted glucose concentration and real glucose concentration was obtained. For in vivo experiments, we got the blood sugar level distributions in Clarke error grid that is a reference for doctors to do diagnosis and treatment. In the Clarke error grid, 75% of all data was in area A and 25 % was in area B. From the in vitro and in vivo results we know that multiple laser diodes are suitable for non-invasive blood glucose monitoring.
Dendrimer optimization for a glucose-sensitive fluorescent assay
Show abstract
A fluorescent assay based on the competitive binding between glycosylated PAMAM dendrimer and glucose with the sugar-binding lectin Concanavalin A has been developed. This assay, composed of the glycodendrimer and Alexa Fluor 647 labeled Concanavalin A, has shown a large dynamic response to physiological concentrations of glucose. The larger dynamic range is believed to be due to the spheriodal shape of the dendrimer molecule, which eliminates the multiple
binding of the same dextran chain to the Concanavalin A tetramer that plagued previous approaches. However, in order to further understand the operation of the assay and optimize the dynamic response, the dendrimer construction must be modified to determine the optimum degree of glycosylation. In this paper, a description of the assay function and the change in fluorescence response with various formulations of glycodendrimers are shown. Theories are also presented as means of understanding the various assay responses with different degrees of dendrimer functionalization.
The feasibility investigation of non-invasive blood glucose sensing based on near-infrared spectroscopy
Show abstract
We have performed transcutaneous measurement and vessel bypass measurement to obtain the skin spectra and the blood vessel spectra respectively over the 1100-1700nm in the animal trial. The aim of this study is to validate the feasibility of the near-infrared (NIR) spectroscopy as a non-invasive blood glucose monitoring method, in particular during clinically relevant fluctuation in blood glucose. Two steps are adopted to evaluate the correlation between the skin diffusion spectra and the blood vessel transmission spectra. First, the variation tendencies of the skin and the blood vessel spectra were evaluated, and the partial least square (PLS) regression was adopted to establish the calibration model between the skin spectra, the vessel spectra and the corresponding concentration respectively. Then, the correlation analysis method is used to describe the relationship between the two kinds of spectra mentioned above. The correlation between the skin and the vessel spectra will be a powerful proof to demonstrate the correlation between the skin spectra and the blood glucose concentration.
Discussion on floating-reference method for noninvasive measurement of blood glucose with near-infrared spectroscopy
Show abstract
Weak signal and great background variation have been the major challenges for noninvasive measurement of blood glucose. Two kinds of noise are analyzed, and it is found out that, when instruments achieve a high level of signal to noise ratio, physiological variation other than glucose concentration becomes the dominant over instrument noise. After analyzing the sensitivity of glucose concentration on diffuse reflectance spectroscopy at different source-detector separation, floating-reference method is proposed firstly. This method discusses how to extract signal relating to glucose and signal only relating to background variation respectively, by making use of two special points, reference point and measuring point. Experiments on phantom and Monte Carlo simulations have been performed to validate the feasibility of floating-reference method.
Analysis of leaching and stability of microporated PEG spheres for fluorescent analyte detection
Show abstract
Poly(ethylene glycol) (PEG) microspheres have been used to sense a variety of analytes by encapsulating fluorescently labeled molecules into a PEG hydrogel matrix. This matrix is designed to retain the sensing molecules while simultaneously allowing nearly unhindered analyte diffusion. Some sensing assays, however, depend on the
conformational rearrangement or binding of large macromolecular compounds which may be sterically prohibited in a dense polymer matrix. A new microporation process has been developed in order to create small cavities in the spheres containing aqueous solution and the assay components. This configuration insures a small mesh size for the supporting polymer, which limits leaching, while allowing the large assay components space to react within the aqueous cavities.
Three hydrogel compositions (100% PEG, 50% PEG hydrogels, and microporated 100% PEG) were studied by embedding traditional pH (FITC) and oxygen sensitive fluorophores (Ru(Phen)). These hydrogels were analyzed for leaching and dynamic response to evaluate the functionality of the new microporated hydrogel.
Sensitivity of different light scattering techniques to variations of optical parameters of a blood layer in vitro studied by Monte Carlo simulations
Show abstract
In various publications, the values of blood optical parameters reported or used by different authors dffer dramatically.
The aim of the present work is to estimate by means of Monte Carlo simulation the effect of variations of some of these
parameters on the signals measured by different light scattering techniques. The following techniques are considered.
optical coherence tomography, time-of-flight measurements, goniophotometry, and spectrophotometry implementing
the integrating spheres measurements. The base wavelength of 820 mn within the diagnostic window, which is
frequently used when implementing the mentioned techniques was chosen for the simulations. It was shown that both
scattering coefficient and anisotropy factor affect the output signals. which vary significantly in the considered ranges
of the parameters values. The strongest variations are due to varying the anisotropy factor, while varying the scattering
coefficient influences primarily the level of the signal, but preserves its shape.
Interpretation of interference signals in label free integrated interferometric biosensors
Show abstract
In the future fast, simple and reliable biosensors will be needed to detect various analytes from different biosamples. This is due to fact that the needs of traditional health care are changing. In the future homecare of patients and peoples' responsibility for their own health will increase. Also, different wellness applications need new parameters to be analysed, reducing costs of traditional health care, which are increasing rapidly.
One fascinating and promising sensor type for these applications is an integrated optical interferometric immunosensor, which is manufactured using organic materials. The use of organic materials opens up enormous possibilities to develop different biochemical functions. In label free biosensors the measurement is based on detecting changes in refractive index, which typically are in the range of 10-6-10-8 [1].
In this research, theoretically generated interferograms are used to compare various signal processing methods. The goal is to develop an efficient method to analyse the interferogram. Different time domain signal processing methods are studied to determine the measuring resolution and efficiency of these methods. A low cost CCD -element is used in detecting the interferogram dynamics.
It was found that in most of the signal processing methods the measuring resolution was mainly limited by pixel size. With calculation of Pearson's correlation coefficient, subpixel resolution was achieved which means that nanometer range optical path differences can be measured. This results in the refractive index resolution of the order of 10-7.
Synthesis of CdSe/CdS core/shell quantum dots for biological sensing applications
Show abstract
A simple, room temperature, one-pot method to produce biocompatible CdSe/CdS quantum dots (QDs) in aqueous solution is presented. CdCl2 and NaSeSO3 are the precursors for the CdSe core where gelatin is used as an inhibitor. A CdS shell is grown by injecting H2S gas, generated by a reaction between sulfuric and sodium sulfide, into the solution. This fast, low cost synthesis approach is simple for scale-up production of QDs. Transmission electron microscopy shows that the bare CdSe quantum dots were 2-3 nm in diameter. The emission peak from the CdSe can be tuned over most of the visible wavelength (from 520nm to 600 nm) as the diameter of the QDs is allowed to increase before growth of the CdS shell. The core/shell structure was confirmed via UV-Vis absorption spectroscopy, PL studies, and structural characterization (XRD). The higher band gap CdS coatings significantly enhanced the photoluminescence (PL) of CdSe quantum dots by a factor of 2-3. However, the large lattice mismatch between the CdS coating and the CdSe core results in eventually quenched luminescence from CdSe with thicker CdS coatings. To increase the photochemical stability and biocompatibility of the CdSe/CdS QDs, a silica coating is grown directly on the QDs. Preliminary data indicates that the PL from CdSe/CdS QDs post-growth is affected as the applied electric field is altered. Efforts to functionalize the QDs with DNA and antibodies have begun. Studies have been initiated to demonstrate the feasibility of microinjecting the QDs into Xenopus embryo with minimal post-synthesis processing.