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This letter presents the first quantitative, in vivo, transcutaneous glucose measurements using surface enhanced Raman spectroscopy (SERS). Silver film over nanosphere (AgFON) surfaces were functionalized with a mixed self-assembled monolayer (SAM) and implanted subcutaneously in a Sprague-Dawley rat. The glucose concentration was monitored in the interstitial fluid. SER spectra were collected from the sensor chip through the skin using spatially offset Raman spectroscopy (SORS). The combination of SERS and SORS is a powerful new approach to the challenging problem of in vivo metabolite and drug sensing. 10.1021/ac101951j

Lactate production under anaerobic conditions is indicative of human performance levels, fatigue, and hydration. Elevated lactate levels result from several medical conditions including congestive heart failure, hypoxia, and diabetic ketoacidosis. Real-time detection of lactate can therefore be useful for monitoring these medical conditions, posttrauma situations, and in evaluating the physical condition of a person engaged in strenuous activity. This paper represents a proof-of-concept demonstration of a lactate sensor based on surface-enhanced Raman spectroscopy (SERS). Furthermore, it points the direction toward a multianalyte sensing platform. A mixed decanethiol/mercaptohexanol partition layer is used herein to demonstrate SERS lactate sensing. The reversibility of the sensor surface is characterized by exposing it alternately to aqueous lactate solutions and buffer without lactate. The partitioning and departitioning time constants were both found to be ~30 s. In addition, physiological lactate levels (i.e., 6-240 mg/dL) were quantified in phosphate-buffered saline medium using multivariate analysis with a root-mean-square error of prediction of 39.6 mg/dL. Finally, reversibility was tested for sequential glucose and lactate exposures. Complete partitioning and departitioning of both analytes was demonstrated.

This paper presents the first in vivo application of surface-enhanced Raman scattering (SERS). SERS was used to obtain quantitative in vivo glucose measurements from an animal model. Silver film over nanosphere surfaces were functionalized with a two-component self-assembled monolayer, and subcutaneously implanted in a Sprague--Dawley rat such that the glucose concentration of the interstitial fluid could be measured by spectroscopically addressing the sensor through an optical window. The sensor had relatively low error (RMSEC = 7.46 mg/dL (0.41 mM) and RMSEP = 53.42 mg/dL (2.97 mM).

A new, mixed decanethiol (DT)/mercaptohexanol (MH) partition layer with dramatically improved properties has been developed for glucose sensing by surface-enhanced Raman spectroscopy. This work represents significant progress toward our long-term goal of a minimally invasive, continuous, reusable glucose sensor. The DT/MH-functionalized surface has greater temporal stability, demonstrates rapid, reversible partitioning and departitioning, and is simpler to control compared to the tri(ethylene glycol) monolayer used previously. The data herein show that this DT/MH-functionalized surface is stable for at least 10 days in bovine plasma. Reversibility is demonstrated by exposing the sensor alternately to 0 and 100 mM aqueous glucose solutions (pH ~7). The difference spectra show that complete partitioning and departitioning occur. Furthermore, physiological levels of glucose in two complex media were quantified using multivariate analysis. In the first system, the sensor is exposed to a solution consisting of water with 1 mM lactate and 2.5 mM urea. The root-mean-squared error of prediction (RMSEP) is 92.17 mg/dL (5.12 mM) with 87% of the validation points falling within the A and B range of the Clarke error grid. In the second, more complex system, glucose is measured in the presence of bovine plasma. The RMSEP is 83.16 mg/dL (4.62 mM) with 85% of the validation points falling within the A and B range of the Clarke error grid. Finally, to evaluate the real-time response of the sensor, the 1/e time constant for glucose partitioning and departitioning in the bovine plasma environment was calculated. The time constant is 28 s for partitioning and 25 s for departitioning, indicating the rapid interaction between the SAM and glucose that is essential for continuous sensing.

This research presents the achievement of significant milestones toward the development of a minimally invasive, continuously monitoring, glucose-sensing platform based on the optical quantitation of glucose in interstitial fluid. We expand our initial successes in the measurement of glucose by surface-enhanced Raman scattering (SERS), demonstrating substantial improvements not only in the quality and optical properties of the substrate system itself but also in the robusmess of the measurement methodology and the amenability of the technique to compact, diode laser-based instrumentation. Herein, we compare the long-term stability of gold to silver film over nanosphere (AuFON, AgFON) substrates functionalized with a partitioning self-assembled monolayer (SAM) using both electrochemical and SERS measurements. AuFONs were found to be stable for a period of at least 11 days. The switch to AuFONs not only provides a more stable surface for SAM formation but also yields better chemometric results, with improved calibration and validation over a range of 0.5-44 mM (10-800 mg/dL). Measured values for glucose concentrations in phosphate-buffered saline (pH ~7.4) based on 160 independent SERS measurements on AuFONs have a root-mean-square error of prediction of 2.7 mM (49.5 mg/dL), with 91% of the values falling within an extended A-B range on an expanded Clarke error grid. Furthermore, AuFONs exhibit surface plasmon resonances at longer wavelengths than similar AgFONs, which make them more efficient for SERS at near-infrared wavelengths, enabling the use of low-power diode lasers in future devices.

Choroidal perfusion measurements are complicated by the choroid's location posterior to the retina and its associated retinal blood vessels. Optical coherence tomography is a relatively new imaging technique with sufficient spatial resolution to isolate choroidal backscattering events from the posterior eye. We modified a speckle imaging algorithm to analyze sequential axial depth scans obtained from posterior rat eye to obtain an indicator of choroidal perfusion. This indicator is correlated with known changes in choroidal blood flow in response to increased intraocular pressure. OCIS codes: 170.4500, 110.4500, 170.1650, 170.0110, 170.6480.

The initial steps toward a miniature, field portable sensor based on surface-enhanced Raman spectroscopy (SERS) are presented. It is demonstrated that a low-cost miniaturized Raman system can be used in place of a larger, higher-cost conventional Raman system. This system was developed by sequentially replacing components of a laboratory scale Raman spectroscopy system with smaller, lower-cost, commercially available components. For example, a green laser pointer was used as the excitation source, a reflectance probe fiber-optic cable was used for laser delivery and collection, and a compact card-based spectrometer was used for dispersion and detection. Spectra, collected with the laser pointer Raman system, are presented of a resonant (Rhodamine 6G) and a non-resonant (trans-1,2-bis(4-pyridyl)ethylene) molecule as well as a self-assembled monolayer (1-decanethiol). Small, low-cost sensors are in demand for a variety of applications, and SERS is positioned to contribute significantly with its remarkable sensitivity and molecular specificity. Key words: Raman, SERS, fiber-optics, sensor.

We report a new method by which phase slope and group dispersion can be calculated with a simple optical low-coherence reflectometer to quantify physiological conditions. A discrete-time signal processing algorithm based on the first and second derivatives of the phase with respect to wave number was developed from discrete-time Fourier properties. The algorithm avoids the 2[pi] ambiguity associated with most phase unwrapping. Experimental data collected by use of well-characterized optical materials validated the algorithm, which was minimally sensitive to phase noise. The group dispersion of bovine cornea was measured at various hydrations and was significantly dependent on hydration. The results suggest that group dispersion is an indicator of corneal alterations. OCIS codes: 070.6020, 260.2030, 120.5050, 120.3180, 170.4500.

The use of surface-enhanced Raman spectroscopy for a systematic detection of glucose is described. Glucose is preconcentrated within the zone of electromagnetic field enhancement for this purpose.

The effects of fluid shear stress on the synthesis of platelet-derived growth factors (PDGF) peptides and endothelin-1 (ET-1) were analyzed in rat visceral pleura mesothelial (RVPM) cells. Exposure of cultured RVPM to cyclic strain stimulated the release of ET-1 and activated the mitogenic activity of pleural mesothelial cells. However, exposure of RVPM to shear stress or cyclic strain did not alter the secretion of PDGF.

Both theoretical and experimental studies of pleural fluid dynamics and lung buoyancy during steady-state, apneic conditions are presented. The theory shows that steady-state, top-to-bottom pleural-liquid flow creates a pressure distribution that opposes lung buoyancy. These two forces may balance, permitting dynamic lung floating, but when they do not, pleural--pleural contact is required. The animal experiments examine pleural-liquid pressure distributions in response to simulated reduced gravity, achieved by lung inflation with perfluorocarbon liquid as compared to air. The resulting decrease in lung buoyancy modifies the force balance in the pleural fluid, which is reflected in its vertical pressure gradient. The data and model show that the decrease in buoyancy with perfluorocarbon inflation causes the vertical pressure gradient to approach hydrostatic. In the microgravity analogue, the pleural pressures would be toward a more uniform distribution, consistent with ventilation studies during space flight. The pleural liquid turnover predicted by the model is computed and found to be comparable to experimental values from the literature. The model provides the flow field, which can be used to develop a full transport theory for molecular and cellular constituents that are found in pleural fluid. [DOI: 10.1115/1.1392317]

Changes in hydrostatic pressure, at levels as low as 10 mm Hg, have been reported in some studies to alter cell function in vitro; however, other studies have found no detectable changes using similar methodologies. We here investigate the hypothesis that the rate of depressurization, rather than elevated hydrostatic pressure itself, may be responsible for these reported changes. Hydrostatic pressure (100 mm Hg above atmospheric pressure) was applied to bovine aortic endothelial cells (BAECs) and PC12 neuronal cells using pressurized gas for periods ranging from 3 hours to 9 days, and then the system was either slowly (~30 minutes) or rapidly (~5 seconds) depressurized. Cell viability, apoptosis, proliferation, and F-actin distribution were then assayed. Our results did not show significant differences between rapidly and slowly depressurized cells that would explain differences previously reported in the literature. Moreover, we found no detectable effect of elevated hydrostatic pressure (with slow depressurization) on any measured variables. Our results do not confirm the findings of other groups that modest increases in hydrostatic pressure affect cell function, but we are not able to explain their findings. [ABSTRACT FROM AUTHOR]

The pulsating bubble surfactometer (PBS) is often used for in vitro characterization of exogenous lung surfactant replacements and lung surfactant components. However, the commercially available PBS is not able to dynamically track bubble size and shape. The PBS therefore does not account for bubble growth or elliptical bubble shape that frequently occur during device use. More importantly, the oscillatory volume changes of the pulsating bubble are different than those assumed by the software of the commercial unit. This leads to errors in both surface area and surface tension measurements. We have modified a commercial PBS through the addition of an image-acquisition system, allowing real-time determination of bubble size and shape and hence the accurate tracking of surface area and surface tension. Compression-expansion loops obtained with the commercially available PBS software were compared with those provided by the image-analysis system for dipalmitoylphosphatidylcholine, Infasurf, and Tanaka lipids (dipalmitoylphosphatidylcholine-palmitoyloleoylphosphatidylglycerol-palmitic acid, 68:22:9) at concentrations of 0.1 and 1.0 mg/ml and at frequencies of 1 and 20 cycles/min. Whereas minimum surface tension as determined by the image-analysis system is similar to that measured by the commercially available software, the maximum surface tension and the shapes of the interfacial area-surface tension loops are quite different. Differences are attributable to bubble drift, nonsinusoidal volume changes, and variable volume excursions seen with the modified system but neglected by the original system. Image analysis reveals that the extent of loop hysteresis is greatly overestimated by the commercial device and that an apparent, rapid increase in surface tension upon film expansion seen in PBS loops is not observed with the image-analysis system. The modified PBS system reveals new dynamic characteristics of lung surfactant preparations that have not previously been reported. [ABSTRACT FROM AUTHOR]

Liquid can be instilled into the pulmonary airways during medical procedures such as surfactant replacement therapy, partial liquid ventilation, and pulmonary drug delivery. For all cases, understanding the dynamics of liquid distribution in the lung will increase the efficacy of treatment. A recently developed imaging technique for the study of real-time liquid transport dynamics in the pulmonary airways was used to investigate the effect of respiratory rate on the distribution of an instilled liquid, surfactant, in a rat lung. Twelve excised rat lungs were suspended vertically, and a single bolus (0.05 ml) of exogenous surfactant (Survanta, Ross Laboratories, Columbus, OH) mixed with radiopaque tracer was instilled as a plug into the trachea. The lungs were ventilated with a 4-ml tidal volume for 20 breaths at one of two respiratory rates: 20 or 60 breaths/min. The motion of radio-dense surfactant was imaged at 30 frames/s with a microfocal X-ray source and an image intensifier. Dynamics of surfactant distribution were quantified for each image by use of distribution statistics and a homogeneity index. We found that the liquid distribution depended on the time to liquid plug rupture, which depends on ventilation rate. At 20 breaths/min, liquid was localized in the gravity-dependent region of the lung. At 60 breaths/min, the liquid coated the airways, providing a more vertically uniform liquid distribution. [ABSTRACT FROM AUTHOR]

The Center for Innovation in Point-of-Care Technologies for HIV/AIDS at Northwestern University (C-THAN) is a partner in the Point-of-Care Technologies Research Network (POCTRN) of the National Institutes of Biomedical Imaging and Bioengineering. POCTRN's mission is to drive the development of appropriate point-of-care (POC) diagnostic technologies through collaboration that merges scientific and technological capabilities with clinical need. C-THAN develops POC technologies for improved management of HIV/AIDS in low- and middle-income countries with a focus on sub-Saharan Africa. C-THAN incorporates clinical and user needs with technology expertise and resources to address commercialization and implementation barriers through: 1) assessment of unmet clinical needs in POC testing for HIV/AIDS and its comorbidities; 2) collaborations with physicians, researchers and engineers; 3) development of technical, clinical, industrial and regulatory partnerships; 4) clinical testing of prototype devices; and 5) creation of training opportunities for technology developers, evaluators, and other stakeholders. Technologies supported include tests for detection and monitoring of HIV/AIDS and its common comorbidities including tuberculosis, non-tuberculous mycobacteria, viral hepatitis and HIV-related malignancies. CTHAN relies on collaborations established by Northwestern University in Nigeria, South Africa, Mali and Tanzania, to have impact on the prevention and clinical management of HIV/AIDS.

This paper presents the latest progress on quantitative, in vivo, transcutaneous glucose sensing using surface enhanced spatially offset Raman spectroscopy (SESORS). Silver film over nanosphere (AgFON) surfaces were functionalized with a mixed self-assembled monolayer (SAM) and implanted subcutaneously in Sprague-Dawley rats. The glucose concentration was monitored in the interstitial fluid of six separate rats. The results demonstrated excellent accuracy and consistency. Remarkably, the root-mean-square error of calibration (RMSEC) (3.6 mg/dL) and the root-mean-square error of prediction (RMSEP) (13.7 mg/dL) for low glucose concentration (<80 mg/dL) is lower than the current International Organization Standard (ISO/DIS 15197) requirements. Additionally, our sensor demonstrated functionality up 17 days after implantation, including 12 days under the laser safety level for human skin exposure with only one time calibration. Therefore, our SERS based sensor shows promise for the challenge of reliable continuous glucose sensing systems for optimal glycemic control.

Inferences need to be drawn in biological systems using experimental multivariate data. The number of samples collected in many such experiments is small, and the data are noisy. We present and study the performance of a robust optimization (RO) model for such situations. We adapt this model to generate a minimum and a maximum estimation of analyte concentration for a given sample, producing a prediction range. The calibration model was applied to sets of Raman spectra. In particular we used normal Raman measurements of pyridine/deuterated pyridine mixtures and spectra from a more complex glucose detection system based on surface-enhanced Raman spectroscopy. The results from the RO model were compared with prediction intervals estimated from partial least squares (PLS) method. We find that the RO prediction ranges included the actual concentration value of the sample more consistently than the 99% prediction intervals built with PLS methods.

Background: In this report, we detail our current work towards developing a surface-enhanced Raman spectroscopy (SERS) based sensor for in vivo glucose detection. Despite years of innovations in the development of blood glucose monitors, there remains a need for accurate continuous glucose sensors to provide care to rising numbers of diagnosed diabetes patients and mitigate secondary health complications associated with this metabolic disorder., Methods: SERS is a highly specific and sensitive optical technique suitable for direct detection of glucose. The SERS effect is highly distance dependent, thus the glucose molecules need to be within a few nanometers or adsorbed to an SERS-active surface. In our sensor, this is achieved with a self-assembled monolayer (SAM) that facilitates reversible interactions between glucose molecules and the surface. The amount of glucose near the surface is proportional to its concentration in the surrounding environment., Results: We determined that the SAM-functionalized surface is stable for at least 10 days and provides rapid, reversible partitioning. In vitro experiments in bovine plasma as well as in vivo experiments in rats demonstrated quantitative detection., Conclusions: We show successful use of the SERS glucose sensor in rats, making it the first in vivo SERS sensor. Furthermore, we demonstrate free space transdermal detection of a SERS signal through the rat's skin as an initial step toward developing a transcutaneous sensor.

Purpose: Oxidative stress has been implicated in a variety of diseases of the eye. In several other tissues, keratinocyte growth factor (KGF) has been shown to prevent negative cellular changes associated with oxidative insult, such as permeability increases and nuclear DNA damage. In this study, we looked at whether KGF provided these same protective effects to cultured human retinal pigmented epithelial (RPE) cells (ARPE-19)., Methods: Reverse transcriptase-polymerase chain reaction (RT-PCR) using a published primer pair sequence followed by restriction endonuclease digestion with AvaI and HincII was used to look for the KGF receptor message in ARPE-19 cells. Cellular response to KGF was verified through proliferation assays and Western blot analysis for mitogen-activated protein kinase (MAPK). Single-cell gel electrophoresis was used to assess DNA damage, Western blot analysis was used to assay actin cytoskeletal changes, and electrical resistance and tracer experiments with Transwell tissue plates were used to assess permeability changes. Immunostaining was used to verify the existence of the tight junction protein occludin., Results: It was verified through RT-PCR that the ARPE-19 cell line exhibited the message for FGFR2-IIIb, otherwise known as KGFR. KGF was also shown to increase cellular proliferation and activated the MAPK p44/p42 cascade. KGF ameliorated nuclear DNA damage and cytoskeletal rearrangement caused by oxidative stress through the addition of exogenous hydrogen peroxide but was unable to prevent permeability changes., Conclusions: KGF was shown to significantly reduce DNA damage and cytoskeletal rearrangement caused by oxidative stress in cultured ARPE-19 cells. This result may be useful in targeting future therapies to combat a multitude of diseases of the eye that result from increases in reactive oxygen species.