Two-photon cross-sections of the photosensitizers m-THPC and m-THPP in the 1.05–1.45μm range

The two-photon absorption of the photosensitizers 5,10,15,20-tetrakis(m-hydroxyphenyl) porphyrin and the corresponding chlorin has been studied in the near infrared (IR) range using open-aperture z-scan technique. We found cross sections of 10–40 GM in the Q-band region, comparable to values in the Soret-band. Both photosensitizers are promising candidates for IR two-photon photodynamic therapy given the better penetration of IR light into tissue

An alternative evolutionary strategy to optimize photoreaction quantum yields

Photoisomerization of a protein bound chromophore is the basis of light sensing of many photoreceptors. We tracked Z-to-E photoisomerization of Cph1 phytochrome chromophore PCB in the Pr form in real-time. Two different phycocyanobilin (PCB) ground state geometries with different ring D orientations have been identified. The pre-twisted and hydrogen bonded PCBa geometry exhibits a time constant of 30 ps and a quantum yield of photoproduct formation of 29%, about six times slower and ten times higher than that for the non-hydrogen bonded PCBb geometry. This new mechanism of pre-twisting the chromophore by protein-cofactor interaction optimizes yields of slow photoreactions and provides a scaffold for photoreceptor engineering

An angle balanced polarization resolved femtosecond VIS pump–IR probe study

Photoisomerization of biliverdin (BV) chromophore triggers the photoresponse in native Agp1 bacteriophytochrome. We discuss heterogeneity in phytochrome Pr form to account for the shape of the absorption profile. We investigated different regions of the absorption profile by angle balanced polarization resolved femtosecond VIS pump–IR probe spectroscopy. We studied the Pr form of Agp1 with its natural chromophore and with a sterically locked 18Et-BV (locked Agp1). We followed the dynamics and orientations of the carbonyl stretching vibrations of ring D and ring A in their ground and electronically excited states. Photoisomerization of ring D is reflected by strong signals of the ring D carbonyl vibration. In contrast, orientational data on ring A show no rotation of ring A upon photoexcitation. Orientational data allow excluding a ZZZasa geometry and corroborates a nontwisted ZZZssa geometry of the chromophore. We found no proof for heterogeneity but identified a new, to our knowledge, electronic transition in the absorption profile at 644 nm (S0→S2). Excitation of the S0→S2 transition will introduce a more complex photodynamics compared with S0→S1 transition. Our approach provides fundamental information on disentanglement of absorption profiles, identification of chromophore structures, and determination of molecular groups involved in the photoisomerization process of photoreceptors

CO2 Gas Temperature Sensing near Room Temperature by a Quantum Cascade Laser in Inter Pulse Mode

A non-invasive CO2 gas temperature sensing technique at or close to the room temperature range based on quantum cascade laser absorption spectroscopy is presented. The method probes thermally populated ground state and hot-band rotational-vibrational transitions of CO2 in the frequency range from 2349 to 2351 cm−1 from which the gas temperature is obtained from Boltzmann statistics. Transmission spectra are recorded by injection-current driven frequency-scans, the so-called inter pulse mode, of a pulsed distributed feedback quantum cascade laser. The statistical uncertainty (1σ) in temperature for single frequency scans with time resolution of 10 ms is 4 K and can be further reduced down to ∼50 mK by long-time averaging of about 1 min. The technique is evaluated with particular emphasis on implementation, data acquisition, data analysis and potential improvements

Fast Simultaneous CO2 Gas Temperature and Concentration Measurements by Quantum Cascade Laser Absorption Spectroscopy

A quantum cascade laser-based sensing technique is presented which allows for in situ high-precision temperature and/or CO2 concentration measurements of gases in the room temperature regime with sampling rates up to about 40 kHz. The method is based on Boltzmann-like thermally populated fundamental and hot-band rovibrational transitions of CO2 with opposite temperature dependence. Single absorption spectra at about 2350 to 2352 cm−1 are recorded by a nanosecond frequency down chirped IR pulse of a pulsed distributed feedback quantum cascade laser (intrapulse mode). The statistical uncertainty (1σ) in the temperature measurement within one laser pulse is about 1 K and can be further reduced down to about 0.1 K by time averaging over 100 ms. Online temperature and CO2 concentration measurements on a breath simulator controlled gas flow were performed to demonstrate response-time and sensitivity for an application-driven test system

CO₂ Gas Temperature Sensing near Room Temperature by a Quantum Cascade Laser in Inter Pulse Mode

A non-invasive CO2 gas temperature sensing technique at or close to the room temperature range based on quantum cascade laser absorption spectroscopy is presented. The method probes thermally populated ground state and hot-band rotational-vibrational transitions of CO2 in the frequency range from 2349 to 2351 cm−1 from which the gas temperature is obtained from Boltzmann statistics. Transmission spectra are recorded by injection-current driven frequency-scans, the so-called inter pulse mode, of a pulsed distributed feedback quantum cascade laser. The statistical uncertainty (1σ) in temperature for single frequency scans with time resolution of 10 ms is 4 K and can be further reduced down to ∼50 mK by long-time averaging of about 1 min. The technique is evaluated with particular emphasis on implementation, data acquisition, data analysis and potential improvements

Liquid Crystals, the Visual System and Polarization Sensitivity

We have examined the vertebrate visual system from a liquid crystalline perspective, with the aim of understanding the mechanisms responsible for polarization vision in vertebrates. Using a technique called micro-spectrophotometry (MSP), we show that the different types of light-sensitive cells in the retina absorb polarized light differently. Based on these measured geometries of absorbance, analytic solutions to Maxwell's equations using a 4×4 matrix technique demonstrate the possibility of intrinsic linear dichroism under axial illumination in those photoreceptors sensitive to polarized light. This provides a new mechanism for axial polarization sensitivity in vertebrate photoreceptors

Visual pigment composition in zebrafish: Evidence for a rhodopsin–porphyropsin interchange system

Numerous reports have concluded that zebrafish (Danio rerio) possesses A1-based visual pigments in their rod and cone photoreceptors. In the present study, we investigated the possibility that zebrafish have a paired visual pigment system. We measured the spectral absorption characteristics of photoreceptors from zebrafish maintained in different temperature regimes and those treated with exogenous thyroid hormone using CCD-based microspectrophotometry. Rods from fish housed at 15°C and 28°C were not significantly different, having [lambda]max values of 503 ± 5 nm (n = 106) and 504 ± 6 nm (n = 88), respectively. Thyroid hormone treatment (held at 28°C), however, significantly shifted the [lambda]max of rods from 503 ± 5 nm (n = 194) to 527 ± 8 nm (n = 212). Cone photoreceptors in fish housed at 28°C (without thyroid hormone treatment) had [lambda]max values of 361 ± 3 nm (n = 2) for ultraviolet-, 411 ± 5 nm (n = 18) for short-, 482 ± 6 nm (n = 9) for medium-, and 565 ± 10 nm (n = 14) for long-wavelength sensitive cones. Thyroid hormone treatment of fish held at 28°C significantly shifted the [lambda]max of long-wavelength sensitive cones to 613 ± 11 nm (n = 20), substantially beyond that of the [lambda]max of the longest possible A1-based visual pigment ([similar]580 nm). Thyroid hormone treatment produced smaller shifts of [lambda]max in other cone types and increased the half-band width. All shifts in photoreceptor [lambda]max values resulting from thyroid hormone treatment matched predictions for an A1- to A2-based visual pigment system. We therefore conclude that zebrafish possess a rhodopsin–porphyropsin interchange system that functions to spectrally tune rod and cone photoreceptors. We believe that these observations should be carefully considered during analysis of zebrafish spectral sensitivity

Liver Status Assessment by Spectrally and Time Resolved IR Detection of Drug Induced Breath Gas Changes

The actual metabolic capacity of the liver is crucial for disease identification, liver therapy, and liver tumor resection. By combining induced drug metabolism and high sensitivity IR spectroscopy of exhaled air, we provide a method for quantitative liver assessment at bedside within 20 to 60 min. Fast administration of 13C-labelled methacetin induces a fast response of liver metabolism and is tracked in real-time by the increase of 13CO2 in exhaled air. The 13CO2 concentration increase in exhaled air allows the determination of the metabolic liver capacity (LiMAx-test). Fluctuations in CO2 concentration, pressure and temperature are minimized by special gas handling, and tracking of several spectrally resolved CO2 absorption bands with a quantum cascade laser. Absorption measurement of different 12CO2 and 13CO2 rotation-vibration transitions in the same time window allows for multiple referencing and reduction of systematic errors. This FLIP (Fast liver investigation package) setup is being successfully used to plan operations and determine the liver status of patients

Fast Simultaneous CO2 Gas Temperature and Concentration Measurements by Quantum Cascade Laser Absorption Spectroscopy

A quantum cascade laser-based sensing technique is presented which allows for in situ high-precision temperature and/or CO2 concentration measurements of gases in the room temperature regime with sampling rates up to about 40 kHz. The method is based on Boltzmann-like thermally populated fundamental and hot-band rovibrational transitions of CO2 with opposite temperature dependence. Single absorption spectra at about 2350 to 2352 cm−1 are recorded by a nanosecond frequency down chirped IR pulse of a pulsed distributed feedback quantum cascade laser (intrapulse mode). The statistical uncertainty (1σ) in the temperature measurement within one laser pulse is about 1 K and can be further reduced down to about 0.1 K by time averaging over 100 ms. Online temperature and CO2 concentration measurements on a breath simulator controlled gas flow were performed to demonstrate response-time and sensitivity for an application-driven test system