Long time monitoring of the respiratory activity of isolated mitochondria.

We have investigated the ability of optical oxygen sensors incorporated in a microplate to determine the respiratory activity of cell fractions. Different cell fractions were monitored, in particular to evaluate the long term functionality of isolated mitochondria. It is possible to continuously sense respiratory activity of isolated mitochondria over time. We found that they are functional for three hours but stop respiring at a critical limit of 20% air saturation in the system. Furthermore, inhibition and enhancement of respiratory activity were detected. In conclusion, oxygen sensors are a powerful tool to evaluate the functionality of isolated mitochondria.

Referenced dual pressure- and temperature-sensitive paint for digital color camera read out.

The first fluorescent material for the referenced simultaneous RGB (red green blue) imaging of barometric pressure (oxygen partial pressure) and temperature is presented. This sensitive coating consists of two platinum(II) complexes as indicators and a reference dye, each of which is incorporated in appropriate polymer nanoparticles. These particles are dispersed in a polyurethane hydrogel and spread onto a solid support. The emission of the (oxygen) pressure indicator, PtTFPP, matches the red channel of a RGB color camera, whilst the emission of the temperature indicator [Pt(II) (Br-thq)(acac)] matches the green channel. The reference dye, 9,10-diphenylanthracene, emits in the blue channel. In contrast to other dual-sensitive materials, this new coating allows for the simultaneous imaging of both indicator signals, as well as the reference signal, in one RGB color picture without having to separate the signals with additional optical filters. All of these dyes are excitable with a 405 nm light-emitting diode (LED). With this new composite material, barometric pressure can be determined with a resolution of 22 mbar; the temperature can be determined with a resolution of 4.3 °C.

Multiple fluorescent chemical sensing and imaging.

Optical sensors, unlike most others, enable multiple sensing of (bio)chemical species by making use of probes whose signals can be differentiated by spectral and/or temporal resolution. Multiple sensors are of substantial interest for continuous monitoring of chemical parameters in complex samples such as blood, bioreactor fluids, in the chemical industry, aerodynamic research, and when monitoring food quality control, to mention typical examples. Moreover, such sensors enable non-invasive, non-toxic and online detection. We discuss in this critical review the state of the art in terms of spectroscopic principles, materials (mainly indicator probes and polymers), and give selected examples for dual and triple sensors along with a look into the future (109 references).

Upconverting nanoparticles for nanoscale thermometry.

Upconverting materials are capable of absorbing near-infrared light and converting it into short-wavelength luminescence. The efficiency of this remarkable effect is highly temperature dependent and thus can be used for temperature determination (thermometry) on a nanometer scale. All the upconverting materials discovered so far display several (mainly two) narrow emission bands, each of which has its own temperature dependence. The ratio of the intensity of two of these bands provides a referenced signal for optical sensing of temperature, for example inside cells.

Dual sensing of pO(2) and temperature using a water-based and sprayable fluorescent paint.

Core-shell particles (CSPs) composed of a polystyrene core and a poly(vinyl pyrrolidone) shell were dyed with a luminescent platinum(ii) porphyrin probe for oxygen. In parallel, microparticles were dyed with a luminescent iridium(ii) complex acting as a probe for temperature. The particles were deposited (by spraying) on a surface to enable continuous imaging of the distribution of oxygen (and thus of barometric pressure) and temperature. Unlike most previous paints of this kind, a binder polymer is not needed and water can be used as a dispersant. This makes the paint environmentally friendly and reduces costs in terms of occupational health, clean-up, and disposal. Both indicator probes in the sensor paint can be excited at 405 nm using LEDs or diode lasers, whilst their emission maxima are spectrally separated by about 130 nm. Thus, two independent optical signals are obtained that allow for fluorescent imaging of barometric pressure (in fact oxygen partial pressure) and of temperature, and also to correct the oxygen signal for effects of temperature. The paint was calibrated at air pressures ranging from 50 mbar to 2000 mbar and at temperatures between 1 degrees C and 50 degrees C.

Red- and green-emitting iridium(III) complexes for a dual barometric and temperature-sensitive paint.

A new dual luminescent sensitive paint for barometric pressure and temperature (T) is presented. The green-emitting iridium(III) complex [Ir(ppy)(2)(carbac)] (ppy=2-phenylpyridine; carbac=1-(9H-carbazol-9-yl)-5,5-dimethylhexane-2,4-dione) was applied as a novel probe for T along with the red-emitting complex [Ir(btpy)(3)], (btpy=2-(benzo[b]thiophene-2-yl)pyridine) which functions as a barometric (in fact oxygen-sensitive) probe. Both iridium complexes were dissolved in different polymer materials to achieve optimal responses. The probe [Ir(ppy)(2)(carbac)] was dispersed in gas-blocking poly(acrylonitrile) microparticles in order to suppress any quenching of its luminescence by oxygen. The barometric probe [Ir(btpy)(3)], in turn, was incorporated in a cellulose acetate butyrate film which exhibits good permeability for oxygen. The effects of temperature on the response of the oxygen probe can be corrected by simultaneous optical determination of T, as the poly(acrylonitrile) microparticles containing the temperature indicator are incorporated into the film. The phosphorescent signals of the probes for T and barometric pressure, respectively, can be separated by optical filters due to the approximately 75 nm difference in their emission maxima. The dual sensor is applicable to luminescence lifetime imaging of T and barometric pressure. It is the first luminescent dual sensor material for barometric pressure/T based exclusively on the use of Ir(III) complexes in combination with luminescence lifetime imaging.

Photon upconverting nanoparticles for luminescent sensing of temperature.

Photon upconverting nanoparticles convert near-infrared into visible light (anti-Stokes emission), which strongly reduces the background of autofluorescence and light scattering in biological materials. Hexagonal NaYF(4) nanocrystals doped with Yb(3+) as the sensitizer and Er(3+)/Ho(3+)/Tm(3+) as the activator display at least two emission lines that respond differently to temperature changes. The ratio of the main emission line intensities enables a self-referenced optical readout of the temperature in the physiologically relevant range from 20 to 45 °C. Upconverting nanoparticles of the type NaYF(4):Yb, Er covered by an inactive shell of NaYF(4) are bright and allow for resolving temperature differences of less than 0.5 °C in the physiological range. The optical readout of this nanoparticle-based thermometer offers many options for imaging the two-dimensional distribution of temperature.

Oxygen and temperature sensitivity of blue to green to yellow light-emitting Pt(II) complexes.

The synthesis and photophysical properties of a series of yellow-green to blue-green emitting heteroleptic, cyclometalated Pt(II)(acac) complexes based on substituted phenylpyridine and tetrahydroquinoline ligands is reported. The luminescence intensities and lifetimes of these compounds were also studied in poly(styrene) films with respect to their responses to oxygen and temperature. Particularly, due to the insensitivity to oxygen quenching, these complexes are promising candidates as inert reference dyes in optical sensors. On the other hand, the Pt(II) complex with 2-(4-bromophenyl)-5,6,7,8-tetrahydroquinoline as C^N ligand, displays a strong temperature quenching effect. The distinct response to temperature was additionally calibrated after incorporation in poly(vinylidene chloride-co-acrylonitrile) serving as oxygen-blocking matrix copolymer. The resulting yellow-green-emitting temperature sensor signifies an interesting alternative to the available mostly red emitting temperature-sensitive probes.