Noninvasive measurement of the 308 nm LED‐based UVB protection factor of sunscreens

The current method for determining the sun protection factor (SPF) requires erythema formation. Noninvasive alternatives have recently been suggested by several groups. Our group previously developed a functional sensor based on diffuse reflectance measurements with one UVB LED, which was previously evaluated on pig ear skin. Here we present the results of a systematic in vivo study using 12 sunscreens on 10 volunteers (skin types [ST] I-III). The relationship of the UVB-LED reflectance of unprotected skin and melanin index was determined for each ST. The spatial variation of the reflectance signal of different positions was analyzed and seems to be mainly influenced by sample inhomogeneity except for high-protection factors (PFs) where signal levels are close to detection noise. Despite the low-signal levels, a correlation of the measured LED-based UVB PF with SPF reference values from test institutes with R-2 = 0.57 is obtained, suggesting a strong relationship of SPF and LED-based UVB-PF. Measured PFs tend to be lower for increasing skin pigmentation. The sensor design seems to be suitable for investigations where a fast measurement of relative changes of PFs, such as due to inhomogeneous application, bathing and sweating, is of interest

Energy-Energy Correlations in Square and Cubic Ising Models

Cluster-Monte-Carlo simulations are used to calculate the structure factors associated with order-parameter and energy correlations for square and cubic Ising models, from which the corresponding correlation lengths $\xi$ and $\xi_{\rm E}$, respectively, are determined. The amplitude ratio $X_{\rm E}\equiv \xi_{\rm E}^2 /\xi^2$ is asymptotically universal but strongly influenced by the crossover from mean-field behavior. The numerically determined $X_{\rm E}$ therefore does not reach its universal asymptotic value but agrees well with $\varepsilon$-expansion predictions including corrections to scaling. The consequences for experiments on near-critical fluids and colloidal systems are briefly discussed

Energy-Energy Correlations in Square and Cubic Ising Models

Cluster-Monte-Carlo simulations are used to calculate the structure factors associated with order-parameter and energy correlations for square and cubic Ising models, from which the corresponding correlation lengths $\xi$ and $\xi_{\rm E}$, respectively, are determined. The amplitude ratio $X_{\rm E}\equiv \xi_{\rm E}^2 /\xi^2$ is asymptotically universal but strongly influenced by the crossover from mean-field behavior. The numerically determined $X_{\rm E}$ therefore does not reach its universal asymptotic value but agrees well with $\varepsilon$-expansion predictions including corrections to scaling. The consequences for experiments on near-critical fluids and colloidal systems are briefly discussed

Fibre-optic IR-spectroscopy for biomedical diagnostics

Abstract. The use of microscopy is a valuable means of gaining vital information for medical diagnostics. Due to a number of recent technological developments advances have been made in IR microscopy and in particular, rapid detection methods. Microscopic examination methods usually involve sampling followed by a method of sample purification or preparation. The advantages of the IR analytical method are that it is based on a direct, non-destructive measurement of sample material and that the resulting IR spectra provide extensive and specific information about the sample composition and structure. The course of a disease can lead to either formation or loss of organic compounds in metabolism as well as changes within the biological matrix. Corresponding changes can also be expected in the IR-signature in view to the grading of alteration. Our preliminary IR microscopic investigations compared diseased and healthy tissue samples individually and basic information was obtained about the tissue specific spectral signature, taking account of biological variance. Human tissue samples taken from the colon were used for these studies. Given the number of endoscopic applications used in minimally invasive medicine, we hope to establish the IR fibre based procedure as an optical biopsy method for tissue diagnostics. The aqueous environment as well as the IR radiation source, signal detection and the flexible wave guide type will be a limiting factor for an IR system. The hygiene requirements are particularly high for a fibre based system to be used for in vivo applications. First experiments were used to check the transmission of the IR microspectroscopic data. Fibre supported measurements were made in ATR and remission. High powered IR laser diodes were tested in subsequent trials for application in biomedicine. First results are presented on the way to an IR-endo-spectroscopic system

Photothermomechanical Nanopump: A Flow-Through Plasmonic Sensor at the Fiber Tip

Optical fibers equipped with plasmonic flow sensors at their tips are fabricated and investigated as photothermomechanical nanopumps for the active transport of target analytes to the sensor surface. The nanopumps are prepared using a bottom-up strategy: i.e., by sequentially stacking a monolayer of a thermoresponsive polymer and a plasmonic nanohole array on an optical fiber tip. The temperature-dependent collapse and swelling of the polymer is used to create a flow-through pumping mechanism. The heat required for pumping is generated by exploiting the photothermal effect in the plasmonic nanohole array upon irradiation with laser light (405 nm). Simultaneous detection of analytes by the plasmonic sensor is achieved by monitoring changes in its optical response at longer wavelengths (∼500–800 nm). Active mass transport by pumping through the holes of the plasmonic nanohole array is visualized by particle imaging velocimetry. Finally, the performance of the photothermomechanical nanopumps is investigated for two types of analytes, namely nanoscale objects (gold nanoparticles) and molecules (11-mercaptoundecanoic acid). In the presence of the pumping mechanism, a 4-fold increase in sensitivity was observed compared to the purely photothermal effect, demonstrating the potential of the presented photothermomechanical nanopumps for sensing applications

Photothermomechanical Nanopump: A Flow-Through Plasmonic Sensor at the Fiber Tip

Optical fibers equipped with plasmonic flow sensors at their tips are fabricated and investigated as photothermomechanical nanopumps for the active transport of target analytes to the sensor surface. The nanopumps are prepared using a bottom-up strategy: i.e., by sequentially stacking a monolayer of a thermoresponsive polymer and a plasmonic nanohole array on an optical fiber tip. The temperature-dependent collapse and swelling of the polymer is used to create a flow-through pumping mechanism. The heat required for pumping is generated by exploiting the photothermal effect in the plasmonic nanohole array upon irradiation with laser light (405 nm). Simultaneous detection of analytes by the plasmonic sensor is achieved by monitoring changes in its optical response at longer wavelengths (∼500–800 nm). Active mass transport by pumping through the holes of the plasmonic nanohole array is visualized by particle imaging velocimetry. Finally, the performance of the photothermomechanical nanopumps is investigated for two types of analytes, namely nanoscale objects (gold nanoparticles) and molecules (11-mercaptoundecanoic acid). In the presence of the pumping mechanism, a 4-fold increase in sensitivity was observed compared to the purely photothermal effect, demonstrating the potential of the presented photothermomechanical nanopumps for sensing applications

Photothermomechanical Nanopump: A Flow-Through Plasmonic Sensor at the Fiber Tip

Optical fibers equipped with plasmonic flow sensors at their tips are fabricated and investigated as photothermomechanical nanopumps for the active transport of target analytes to the sensor surface. The nanopumps are prepared using a bottom-up strategy: i.e., by sequentially stacking a monolayer of a thermoresponsive polymer and a plasmonic nanohole array on an optical fiber tip. The temperature-dependent collapse and swelling of the polymer is used to create a flow-through pumping mechanism. The heat required for pumping is generated by exploiting the photothermal effect in the plasmonic nanohole array upon irradiation with laser light (405 nm). Simultaneous detection of analytes by the plasmonic sensor is achieved by monitoring changes in its optical response at longer wavelengths (∼500–800 nm). Active mass transport by pumping through the holes of the plasmonic nanohole array is visualized by particle imaging velocimetry. Finally, the performance of the photothermomechanical nanopumps is investigated for two types of analytes, namely nanoscale objects (gold nanoparticles) and molecules (11-mercaptoundecanoic acid). In the presence of the pumping mechanism, a 4-fold increase in sensitivity was observed compared to the purely photothermal effect, demonstrating the potential of the presented photothermomechanical nanopumps for sensing applications