Photostability of luminescent ruthenium(II) complexes in polymers and in solution

[Ru(dpp)3 ]Cl2 -Embedded Oxygen Nano Polymeric Sensors: A Promising Tool for Monitoring Intracellular and Intratumoral Oxygen Gradients with High Quantum Yield and Long Lifetime

Unraveling the intricacies between oxygen dynamics and cellular processes in the tumor microenvironment (TME) hinges upon precise monitoring of intracellular and intratumoral oxygen levels, which holds paramount significance. The majority of these reported oxygen nanoprobes suffer compromised lifetime and quantum yield when exposed to the robust ROS activities prevalent in TME, limiting their prolonged in vitro usability. Herein, the ruthenium-embedded oxygen nano polymeric sensor (Ru-ONPS) is proposed for precise oxygen gradient monitoring within the cellular environment and TME. Ru-ONPS (≈64±7 nm) incorporates [Ru(dpp)3 ]Cl2 dye into F-127 and crosslinks it with urea and paraformaldehyde, ensuring a prolonged lifetime (5.4 µs), high quantum yield (66.65 ± 2.43% in N2 and 49.80 ± 3.14% in O2 ), superior photostability (>30 min), and excellent stability in diverse environmental conditions. Based on the Stern-Volmer plot, the Ru-ONPS shows complete linearity for a wide dynamic range (0-23 mg L-1 ), with a detection limit of 10 µg mL-1 . Confocal imaging reveals Ru-ONPS cellular uptake and intratumoral distribution. After 72 h, HCT-8 cells show 5.20±1.03% oxygen levels, while NIH3T3 cells have 7.07±1.90%. Co-culture spheroids display declining oxygen levels of 17.90±0.88%, 10.90±0.88%, and 5.10±1.18%, at 48, 120, and 216 h, respectively. Ru-ONPS advances cellular oxygen measurement and facilitates hypoxia-dependent metastatic research and therapeutic target identification.

Supramolecular porphyrin as an improved photocatalyst for chloroform decomposition

In this work, the outlying decoration of the free-base meso-(4-tetra) pyridyl porphyrin (H₂TPyP) with the RuCl(dppb)(5,5'-Me-bipy) ruthenium complex (here named Supra-H₂TPyP) is observed as an improved molecular photocatalyst for dye-mediated chloroform (CHCl₃) decomposition via one-photon absorption operating in the visible spectral range (532 nm and 645 nm). Supra-H₂TPyP offers a better option for CHCl₃ photodecomposition when compared to the same process mediated by pristine H₂TPyP, which requires either excited-state- or UV absorption. The chloroform photodecomposition rates for Supra-H₂TPyP as well as its excitation mechanisms are explored as a function of distinct laser irradiation conditions.

A background-subtraction strategy leads to ratiometric sensing of oxygen without recalibration

Luminescence-quenching based optical oxygen sensors have wide applications in many fields, which have already replaced almost 40% of the commercial market share dominated previously by the Clark oxygen electrode. The majority of optical oxygen sensors are based on lifetime measurement, which are precise, but are relatively expensive, and require high-speed electronics and detecting circuits. Alternatively, oxygen concentration can be measured via a luminescence intensity change, which is a referenced approach according to the Stern-Volmer equation. However, luminescence intensity based measurement tends to be highly influenced by background light. At a given sensor composition, different instrumentation setups, sensor surface roughnesses and thicknesses, and environmental light will result in significantly different calibration curves and sensitivities. This makes luminescence-intensity based optical sensors almost impossible to use practically, because each sensor needs to be recalibrated before use, and the calibration curve each time is quite different. We have solved this problem by introducing a new background-subtraction strategy. After background subtraction, oxygen sensors with different probe concentrations, instrumentation setups, surface roughnesses, supporting matrixes, and at different temperatures present identical calibration curves. This could greatly reduce the calibration task during practical use. Combined with the advantages of low price and a simple optical configuration, the new method will significantly promote wider applications of optical oxygen sensors.

Osmium(II) polypyridyl polyarginine conjugate as a probe for live cell imaging; a comparison of uptake, localization and cytotoxicity with its ruthenium(II) analogue

A first investigation into the application of a luminescent osmium(ii) bipyridine complex to live cell imaging is presented. Osmium(ii) (bis-2,2-bipyridyl)-2(4-carboxylphenyl) imidazo[4,5f][1,10]phenanthroline was prepared and conjugated to octaarginine, a cell penetrating peptide. The photophysics, cell uptake and cytotoxicity of this osmium complex conjugate were performed and compared with its ruthenium analogue. Cell uptake and distribution of both ruthenium and osmium conjugates were very similar with rapid transmembrane transport of the osmium probe (complete within approx. 20 min) and dispersion throughout the cytoplasm and organelles. The near-infrared (NIR) emission of the osmium complex (λmax 726 nm) coincides well with the biological optical window and this facilitated luminescent and luminescence lifetime imaging of the cell which was well resolved from cell autofluorescence. The large Stokes shift of the emission also permitted resonance Raman mapping of the dye within CHO cells. Rather surprisingly, the osmium conjugate exhibited very low cytotoxicity when incubated both in the dark and under visible irradiation. This was attributed to the remarkable stability of this complex which was reflected by the complete absence of photo-bleaching of the complex even under extended continuous irradiation. In addition, when compared to its ruthenium analogue its luminescence was short-lived in water therefore rendering it insensitive to O2.

A multi-imaging approach to study the root-soil interface

BACKGROUND AND AIMS

Dynamic processes occurring at the soil-root interface crucially influence soil physical, chemical and biological properties at a local scale around the roots, and are technically challenging to capture in situ. This study presents a novel multi-imaging approach combining fluorescence and neutron radiography that is able to simultaneously monitor root growth, water content distribution, root respiration and root exudation.

METHODS

Germinated seeds of white lupins (Lupinus albus) were planted in boron-free glass rhizotrons. After 11 d, the rhizotrons were wetted from the bottom and time series of fluorescence and neutron images were taken during the subsequent day and night cycles for 13 d. The following day (i.e. 25 d after planting) the rhizotrons were again wetted from the bottom and the measurements were repeated. Fluorescence sensor foils were attached to the inner sides of the glass and measurements of oxygen and pH were made on the basis of fluorescence intensity. The experimental set-up allowed for simultaneous fluorescence imaging and neutron radiography.

KEY RESULTS

The interrelated patterns of root growth and distribution in the soil, root respiration, exudation and water uptake could all be studied non-destructively and at high temporal and spatial resolution. The older parts of the root system with greater root-length density were associated with fast decreases of water content and rapid changes in oxygen concentration. pH values around the roots located in areas with low soil water content were significantly lower than the rest of the root system.

CONCLUSIONS

The results suggest that the combined imaging set-up developed here, incorporating fluorescence intensity measurements, is able to map important biogeochemical parameters in the soil around living plants with a spatial resolution that is sufficiently high enough to relate the patterns observed to the root system.

Optical methods for sensing and imaging oxygen: materials, spectroscopies and applications

We review the current state of optical methods for sensing oxygen. These have become powerful alternatives to electrochemical detection and in the process of replacing the Clark electrode in many fields. The article (with 694 references) is divided into main sections on direct spectroscopic sensing of oxygen, on absorptiometric and luminescent probes, on polymeric matrices and supports, on additives and related materials, on spectroscopic schemes for read-out and imaging, and on sensing formats (such as waveguide sensing, sensor arrays, multiple sensors and nanosensors). We finally discuss future trends and applications and summarize the properties of the most often used indicator probes and polymers. The ESI† (with 385 references) gives a selection of specific applications of such sensors in medicine, biology, marine and geosciences, intracellular sensing, aerodynamics, industry and biotechnology, among others.

Single photon counting fluorescence lifetime detection of pericellular oxygen concentrations

Fluorescence lifetime imaging microscopy offers a non-invasive method for quantifying local oxygen concentrations. However, existing methods are either invasive, require custom-made systems, or show limited spatial resolution. Therefore, these methods are unsuitable for investigation of pericellular oxygen concentrations. This study describes an adaptation of commercially available equipment which has been optimized for quantitative extracellular oxygen detection with high lifetime accuracy and spatial resolution while avoiding systematic photon pile-up. The oxygen sensitive fluorescent dye, tris(2,2'-bipyridyl)ruthenium(II) chloride hexahydrate [Ru(bipy)(3)](2+), was excited using a two-photon excitation laser. Lifetime was measured using a Becker & Hickl time-correlated single photon counting, which will be referred to as a TCSPC card. [Ru(bipy)(3)](2+) characterization studies quantified the influences of temperature, pH, cellular culture media and oxygen on the fluorescence lifetime measurements. This provided a precisely calibrated and accurate system for quantification of pericellular oxygen concentration based on measured lifetimes. Using this technique, quantification of oxygen concentrations around isolated viable chondrocytes, seeded in three-dimensional agarose gel, revealed a subpopulation of cells that exhibited significant spatial oxygen gradients such that oxygen concentration reduced with increasing proximity to the cell. This technique provides a powerful tool for quantifying spatial oxygen gradients within three-dimensional cellular models.

Potent and selective photo-inactivation of proteins with peptoid-ruthenium conjugates

Advances in high-throughput screening now enable the rapid discovery of bioactive small molecules, but these primary hits almost always exhibit modest potency. We report a strategy for the transformation of these hits into much more potent inhibitors without compound optimization. Appending a derivative of Ru(II)(tris-bipyridyl)²⁺, an efficient photosensitizer of singlet oxygen production, to synthetic protein-binding compounds results in highly potent and specific target protein inactivation upon irradiation with visible light.

On the factors influencing the performance of solar reactors for water disinfection with photosensitized singlet oxygen

Two solar reactors based on compound parabolic collectors (CPCs) were optimized for water disinfection by photosensitized singlet oxygen (1O2) production in the heterogeneous phase. Sensitizing materials containing Ru(II) complexes immobilized on porous silicone were produced, photochemically characterized, and successfully tested for the inactivation of up to 10(4) CFU mL(-1) of waterborne Escherichia coli (gram-negative) or Enterococcus faecalis (gram-positive) bacteria. The main factors determining the performance of the solar reactors are the type of photosensitizing material, the sensitizer loading, the CPC collector geometry (fin- vs coaxial-type), the fluid rheology, and the balance between concurrent photothermal--photolytic and 1O2 effects on the microorganisms' inactivation. In this way, at the 40 degrees N latitude of Spain, water can be disinfected on a sunny day (0.6-0.8 MJ m(-2) L(-1) accumulated solar radiation dose in the 360-700 nm range, typically 5-6 h of sunlight) with a fin-type reactor containing 0.6 m2 of photosensitizing material saturated with tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) (ca. 2.0 g m(-2)). The optimum rheological conditions require laminar-to-transitional water flow in both prototypes. The fin-type system showed better inactivation efficiency than the coaxial reactor due to a more important photolytic contribution. The durability of the sensitizing materials was tested and the operational lifetime of the photocatalyst is at least three months without any reduction in the bacteria inactivation efficiency. Solar water disinfection with 1O2-generating films is demonstrated to be an effective technique for use in isolated regions of developing countries with high yearly average sunshine.

Enzymatic fluorescent microsphere glucose sensors:evaluation of response under dynamic conditions

Most previous attempts at the development of a "smart tattoo" for glucose monitoring in diabetes--implantable fluorescent microspheres that can be implanted intradermally and interrogated transdermally using light--have focused on the encapsulation of a competitive binding assay for glucose within hydrogel microspheres or polyelectrolyte microcapsules. We recently reported on the development of a microsphere sensor based on an enzymatic scheme, combined with an oxygen-quenched fluorescent reporter element. A novel feature of this design is the use of polyelectrolyte multilayer nanofilms, which are assembled stepwise on the surface of the microspheres, for modulation of glucose and oxygen mass transport, allowing them to be designed for sensitive and safe operation within the "oxygen deficit" present in the skin. In this work, a flow-through sensor testing apparatus was used to demonstrate the reversible response of the sensors under controlled, dynamic conditions. The sensors were shown to be sensitive over at least 0-140 mg/dL glucose, with a response time of less than 2 min. This report also identifies some current problems with the approach, and gives potential solutions towards the development of a practical implantable sensor for glucose monitoring in diabetes.

Identification of a Quenching Species in Ruthenium Tris-Bipyridine Electroluminescent Devices

We have used matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry and micro-Raman spectroscopy to identify a quenching species that is formed during operation of [Ru(bpy)3]2+ electroluminescent devices. We identify this performance-degrading product to be the oxo-bridged dimer [(bpy)2(H2O)RuORu(OH2)(bpy)2]4+ and show this dimer to be an effective quencher of device luminescence. This work is the first to detect a specific chemical degradation product formed during iTMC OLED operation.

Synthesis and Assembly with Mesoporous Silica MCM-48 of Platinum(II) Porphyrin Complexes Bearing Carbazyl Groups: Spectroscopic and Oxygen Sensing Properties

The synthesis and spectroscopic characterization of a series of luminescent platinum meso-tetrakis{3,5-di[(N-carbazyl)n-alkyloxyphenyl]}porphyrin (Pt-8Cn-TPP, n-alkyl = (CH2)n, n = 4, 6, and 8) are presented. The protonated platinum porphyrins ([Pt-8Cn-TPPH8]8+) were assembled with mesoporous silica MCM-48 resulting in the assembly materials [Pt-8Cn-TPPH8]8+/MCM-48. The luminescence of [Pt-8Cn-TPPH8]8+/MCM-48 can be extremely quenched by molecular oxygen with very high sensitivity (I0/I100 > 5000) and rapid response time (0.04 s) suggesting that the [Pt-8Cn-TPPH8]8+/MCM-48 system can be employed to develop high performance oxygen sensors. Among this assembly system, [Pt-8C8-TPPH8]8+/MCM-48 exhibits the highest sensitivity. Even if the concentration of oxygen is 0.1%, the luminescence intensity of [Pt-8C8-TPPH8]8+/MCM-48 can be quenched by 86%.

Structurally integrated organic light emitting device-based sensors for gas phase and dissolved oxygen

A compact photoluminescence (PL)-based O2 sensor utilizing an organic light emitting device (OLED) as the light source is described. The sensor device is structurally integrated. That is, the sensing element and the light source, both typically thin films that are fabricated on separate glass substrates, are attached back-to-back. The sensing elements are based on the oxygen-sensitive dyes Pt- or Pd-octaethylporphyrin (PtOEP or PdOEP, respectively), which are embedded in a polystyrene (PS) matrix, or dissolved in solution. Their performance is compared to that of a sensing element based on tris(4,7-diphenyl-l,10-phenanthroline) Ru II (Ru(dpp)) embedded in a sol-gel film. A green OLED light source, based on tris(8-hydroxy quinoline Al (Alq3), was used to excite the porphyrin dyes; a blue OLED, based on 4,4'-bis(2,2'-diphenylviny1)-1,1'-biphenyl, was used to excite the Ru(dpp)-based sensing element. The O2 level was monitored in the gas phase and in water, ethanol, and toluene solutions by measuring changes in the PL lifetime tau of the O2-sensitive dyes. The sensor performance was evaluated in terms of the detection sensitivity, dynamic range, gas flow rate, and temperature effect, including the temperature dependence of tau in pure Ar and O2 atmospheres. The dependence of the sensitivity on the preparation procedure of the sensing film and on the PS and dye concentrations in the sensing element, whether a solid matrix or solution, were also evaluated. Typical values of the detection sensitivity in the gas phase, S(g) identical with tau(0% O2)/tau(100% O2), at 23 degrees C, were approximately 35 to approximately 50 for the [Alq3 OLED[/[PtOEP dye] pair; S(g) exceeded 200 for the Alq3/PdOEP sensor. For dissolved oxygen (DO) in water and ethanol, S(DO) (defined as the ratio of tau in de-oxygenated and oxygen-saturated solutions) was approximately 9.5 and approximately 11, respectively, using the PtOEP-based film sensor. The oxygen level in toluene was measured with PtOEP dissolved directly in the solution. That sensor exhibited a high sensitivity, but a limited dynamic range. Effects of aggregation of dye molecules, sensing film porosity, and the use of the OLED-based sensor arrays for O2 and multianalyte detection are also discussed.

Synthesis and Unexpected Reactivity of Iron Tris(bipyridine) Complexes with Poly(ethylene glycol) Macroligands

High molecular weight poly(ethylene glycol) (PEG) derivatized iron tris(bipyridine) complexes, presenting hydroxyl end groups for further modification as bioconjugates, copolymers, or cross-linking agents, were synthesized via ring-opening anionic polymerization of ethylene oxide from hydroxyl-functionalized bipyridine (bpy) initiators and subsequent chelation to iron(II). Bpy-centered PEG macroligands (bpyPEG(2)) with molecular weights ranging from 4,000 to 17,000 and low polydispersity indices (<1.1) were obtained. Chelation of the bpyPEG(2) macroligands to iron(II) sulfate was studied in aqueous solution by titration and kinetics experiments, which revealed unexpected air sensitivity compared to nonpolymeric iron tris(bipyridine) complexes. Red-violet aqueous solutions of [Fe(bpyPEG(2))(3)](2+) begin to bleach within hours when exposed to air. Enhanced polymer degradation and gel formation of acrylate-modified bpyPEG(2) in the presence of Fe(2+) suggest that radicals may be involved. Under argon, the chromophores are stable. Polymeric iron complexes are slower to form and faster to degrade in air with increasing bpyPEG(2) molecular weight. These studies demonstrate the influence of molecular weight in polymeric iron tris(bipyridine) complex coordination chemistry and reactivity.

Nanoscale internally referenced oxygen sensors produced from self-assembled nanofilms on fluorescent nanoparticles

A novel sensor fabrication concept using indicators trapped in nanoengineered ultrathin films deposited on fluorescent nanoparticles is demonstrated for oxygen sensing. The nanoscale systems are based on the quenching of tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) immobilized within polyelectrolyte multilayers deposited on the surface of nanoparticle templates. The ionically bound nanofilms create a porous scaffold into which controlled precipitation of the chromophore is achieved using a combination of electrostatic attraction and dye insolubility in water. The fluorescent nanoparticles act as physical scaffolds and also provide a complementary spectral signature for use as an internal intensity reference. Oxygen sensors created on 100-nm yellow-green fluorescent particles exhibit a linear Stern-Volmer behavior with a quenching constant of 1.06 mM and sensitivity of 60%, which demonstrates that the dye is still partially accessible to oxygen following immobilization. To demonstrate the feasibility of intracellular metabolic monitoring with such nanoprobes, the oxygen sensors were chemically delivered into human dermal fibroblasts with no apparent loss in cell viability. The results prove that the approach to sensor production is facile and leads to sensitive systems that can be further optimized for improved response, and these findings support the further development of similar self-referenced probes toward quantitative intracellular analysis.

Metalloinitiation Routes to Biocompatible Poly(lactic acid) and Poly(acrylic acid) Stars with Luminescent Ruthenium Tris(bipyridine) Cores

Poly(lactic acid) (PLA) and poly(acrylic acid) (PAA) biomaterials with luminescent ruthenium tris(bipyridine) centers couple drug delivery and imaging functions. Hydrophobic [Ru(bpyPLA2)3](PF6)2 (1) was generated from [Ru[bpy(CH2OH)2]3](PF6)2 in bulk monomer using 4-(dimethylamino)pyridine as the catalyst. The bromoesters, [Ru[bpy(CH2OR)2]3](PF6)2, [Ru[bpy(C13H27)2][bpy(CH2OR]2](PF6)2 (4), and [Ru[bpy(PLAOR)2]3]2+ (9) (R=COCBr(CH3)2), served as initiators for tert-butyl acrylate (tBA) polymerization. Conversion of PtBA to PAA via hydrolysis affords water soluble materials, [Ru(bpyPAA2)3]2+ (7) and [Ru[bpy(C13H27)2](bpyPAA2)2]2+ (8) and the amphiphilic star polymer [Ru[bpy(PLA-PAA)2]3)](PF6)2 (11), which is soluble in a H2O/CH3CN (1:1) mixture. Luminescence excitation and emission spectra of the Ru polymers were in agreement with the parent [Ru(bpy)3]2+ chromophore (lambdaex=468, lambdaem=621 nm). Lifetimes of tau approximately 700 ns in both air and nitrogen atmospheres are typical for most materials; however, the amphiphilic star block copolymer 11 is quenched by oxygen to some degree. Thermal analysis shows the expected glass transitions for the polymeric ruthenium complex materials.