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Oxygen sensing capabilities of a series of luminescent zirconium-based porphyrinic metal–organic frameworks (MOFs) (PCN-222, PCN-223, and PCN-224) have been investigated. Design of experiments allowed identification of the most sensitive material, a PCN-224 MOF. In this material, luminescence in air is quenched by up to 7.3-fold with a bimolecular quenching constant kq of 56,000 Pa–1 s–1, which is significantly above the previously reported benchmark material of the same MOF type (kq of 34,000 Pa–1 s–1). The oxygen sensitivity increases in the order PCN-222 < PCN-223 < PCN-224 with effective Stern–Volmer (SV) constants in the range of 0.13 kPa–1 for PCN-222, 0.18 kPa–1 for PCN-223 and up to 0.45 kPa–1 for PCN-224-type materials. This effect is attributed to the increase in the porphyrin–porphyrin separation in these nanostructured materials that results in the increase in the fluorescence decay time and thus the probability of the quenching event. Defects in the nanostructure also are important and explain variations in the sensitivity within the MOFs of the same type. Among the investigated materials, those belonging to the PCN-223 type were found to be the most robust in terms of oxygen sensing capabilities with only little variation in the SV constants. The analogues of the PCN MOFs that utilize a Pt-(II) porphyrin as a building block were also prepared. It is shown that the same synthetic protocols established for the metal-free systems can be used for the metal complex. Analogous to the MOFs based on the metal-free porphyrin, the oxygen sensitivity increases from Pt-(II)-PCN-222 (KSV 30 kPa–1) via Pt-(II)-PCN-223 (KSV 40 kPa–1) to Pt-(II)-PCN-224 (KSV up to 87 kPa–1). [ABSTRACT FROM AUTHOR]

Phosphors based on magnesium titanate activated with Mn4+ ions are of great interest because, when excited with blue light, they display a strong red-emitting luminescence. They are characterized by a luminescence decay which is strongly temperature dependent in the range from -50 °C to 150 °C, making these materials very promising for temperature sensing in the biochemical field. In this work, the optical and thermal properties of the luminescence of Mg2TiO4 are investigated for different Mn4+ doping concentrations. The potential of this material for temperature sensing is demonstrated by fabricating a fiber optic temperature microsensor and by comparing its performance against a standard resistance thermometer. The response of the fiber optic sensor is exceptionally fast, with a response time below 1 s in the liquid phase and below 1.1 s in the gas phase. [ABSTRACT FROM AUTHOR]

Highlights: [•] A robust referencing schema for colorimetric indicators is proposed. [•] Time-resolved ratiometric read-out is realized. [•] (Photo)chemically stable inorganic phosphors are used. [•] The new method enables simple and low cost read-out set-up. [•] Application of the schema for sensing pH or carbon dioxide is demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: Cooled black-and-white CCD-cameras are well-established devices to monitor the signal response of probes and sensors in imaging applications. When two (or even three) analytes are considered, the signals of interest have to be separated from each other. Generally, this is accomplished by using filter wheels or, in case of fluorescence lifetime imaging, by evaluating the different luminescent decay times of the indicators. Here we present a novel approach for signal separation of multiple sensors. It utilizes the basic setup of color CCD and CMOS cameras. The principle of color cameras is based on the application of three different types of pixels or layers, each of them sensitive towards different wavelength ranges. These detectors can be used to record and separate multiple sensor signals. With this new approach the sensor response of dual or even triple sensors can be monitored in a very straightforward manner. The only precondition is that the applied indicators emit at separable wavelengths. The applicability is demonstrated by means of a dual sensor based on luminescent probes for carbon dioxide and temperature incorporated in different polymer matrices. [Copyright &y& Elsevier]

Abstract: Nanosensors for pH are prepared by staining poly(styrene-block-vinylpyrrolidone) nanobeads with lipophilic pH indicators based on fluoresceins and 1-hydroxypyrene-3,6,8-trisulfonate. Fine tuning of the pH-sensing properties is achieved by varying substituents on the pH indicator. Fluoresceins based on octadecylester- and 5(6)-N-alkyl-carboxamido derivatives show significantly different sensing properties due to lactonization occurring in the latter. The nanobeads show pK a values varying from 5.6 to 7.7, possess low cross-sensitivity to the ionic strength, and are potentially suitable for application in biology, biotechnology, marine science, and other fields. [Copyright &y& Elsevier]

• New fluorescent sensors for potassium are prepared and characterized. • Systematic tuning of the sensitivity via variation of the matrix polymer and additives becomes possible. • The sensitivity is enhanced in more hydrophilic polymers and polymers containing negatively-charged groups. • Materials with improved sensitivity are promising for potassium monitoring in whole blood. Optical sensors were prepared via immobilization of K+ fluoroionophore (K+FI) into different hydrophilic polymers and their properties (luminescence brightness, stability, sensitivity, cross talk to sodium, dynamic range, response time) were investigated. Depending on the character of the used polymeric matrix, the fluorescence quantum yields for the K+-fluoroionophore complex (500 mM K+) span from 44 % in commercial polyurethane hydrogel D1 to 18 % in poly(2-hydroxyethyl methacrylate). Dynamic intensity measurements show reversibility of the sensors and response times (t 90) below 1 min for most of the materials. Blending of poly(2-hydroxyethyl methacrylate) with polyurethane hydrogels is necessary to ensure compatibility of the indicator and the matrix. Comparison of dissociation constants (K d) reveals moderate sensitivity enhancement in more hydrophilic polyurethane hydrogel D1 (K d 51.8 mM) and much stronger enhancement in poly(2-hydroxyethyl methacrylate) (K d 15.4 mM) compared to previously used hydrogel D4 (K d 60.4 mM). Drastic increase in the sensitivity upon addition of negatively-charged aliphatic sulfonates is observed (K d < 3 mM). In case of the latter, the enhancement in the sensitivity is significantly lower in presence of sodium ions. Modification of a commercially available polyurethane hydrogel with sulfonate groups enables preparation of stable sensors with improved binding ability (K d 11.1 mM). This study demonstrates the fundamental role of the polymer matrix in characteristics of the solid-state optical potassium sensors and provides the guidelines for general design of ion sensors with improved characteristics. [ABSTRACT FROM AUTHOR]

A novel sensing concept for the selective detection of ammonia over amines is introduced. For the first time, the reversible fluorescence-based NH 3 sensor makes use of an ammonium-sensitive fluoroionophore instead of commonly utilized pH indicators. NH 3 diffuses into the sensor where a buffered internal electrolyte generates the corresponding ammonium ion, which is then detected by an ion selective NIR fluoroionophore. [ABSTRACT FROM AUTHOR]

Six new BODIPY dyes have been synthesized exhibiting fluorescence emission in the far red part of the electromagnetic spectrum. The compounds were prepared via an acid catalyzed reaction of rigidified pyrroles with benzaldehyde derivatives. This reaction tolerates a variety of aldehydes and therefore analyte responsive parts can be easily introduced. As an example, indicators with a crown ether receptor, sensitive for potassium, and a pH sensitive group for the determination of CO 2 , were obtained via modification of a BODIPY bearing a carbazole motif. Apart from the bathochromic shift of the absorption and emission spectra (about 130–200 nm compared to 4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza- s -indacene) most of the new dyes possess excellent photophysical properties, such as high molar absorption coefficients (130 000–230 000 M−1 cm−1), sharp absorption and emission bands as well as high quantum yields (0.48–0.95). In case of the potassium fluoroionophore both fluorescence intensity and decay time are enhanced in presence of the analyte making it potentially suitable for the self-referenced read-out. Image 1 • New BODIPY dyes with conjugated fluorene and carbazole motifs are prepared. • The dyes feature far-red emission and high brightness. • A fluoroionophore for potassium shows response in fluorescence intensity and decay time. • Modification of the chromophores with a phenolic receptor enables carbon dioxide sensing. [ABSTRACT FROM AUTHOR]

Abstract Continuous monitoring of dissolved oxygen, pH and carbon dioxide are of great importance in oceanography. Sensors are the optimal tools for in situ measurements from mobile platforms, like A utonomous U nderwater V ehicles (AUVs) or Argo profiling floats, and for shipboard deployments. A validation study of small, versatile, easy-to-use, stand-alone optodes is presented. Each analyte can be read out with the identical optoelectronics which greatly minimizes the costs of the hardware needed. Several deployments were performed to evaluate the applicability of the sensors. The deployments varied in terms of duration (profiling, long-term monitoring 5 days to 8 weeks) and environmental conditions (salinity: 6–33 PSS; temperature: 9–25 °C). A set of sensors was successfully deployed at a mooring buoy, in an aquaculture facility and in the Monterey Bay Aquarium Open Sea Exhibition. They were also integrated in an AUV and a profiling float. The performance of the optodes was evaluated in comparison with commercially available sensors for dissolved oxygen (Aanderaa Data Instruments AS, Sea-Bird Scientific, OxyGuard®), pH (Hach, Satlantic) and carbon dioxide (Turner design). The data collected by our optodes and the commercially available sensors is generally in good agreement showing that the new, compact sensor device in combination with sensor foils (pO 2 , pH, pCO 2) can be a valuable tool for many applications in oceanography. The data also revealed the importance of the calibration strategy since inappropriate calibration resulted in an offset in the measured parameter. The efficiency of simple biofouling protection strategy (copper guard) for prolong measurements in highly dynamic environments was also demonstrated. Highlights • New optodes for oxygen, pH and carbon dioxide are deployed in various marine environments • Compact and low cost autonomous device is used in combination with interchangeable sensing caps for each analyte • The data collected by the optodes are in good agreement with the values obtained with commercial reference systems • Anti-biofouling strategy with copper guard is shown to be efficient for long term monitoring in highly active environments [ABSTRACT FROM AUTHOR]

A new group of optical CO 2 sensors based on red-emitting pH-sensitive zinc azaphthalocyanine (Zn-AzaPc) indicators embedded into polyurethane polymeric matrices is presented. The effects of particular Zn-AzaPc indicator, type of a polymeric matrix and a base on sensing properties are investigated. All the indicators are virtually non-fluorescent in the deprotonated form (in the absence of CO 2 ) and are “switched on” in presence of the analyte. Zn-AzaPc without any phenolate moiety is used as a positive control (always-ON state). Among the indicators with one, two and four phenolate receptors, the dye with one receptor is the most suitable due to brightest emission in ON state. Sufficient water content is found to be particularly important in case of the hydrophobic Zn-AzaPc indicators and leads to the necessity of employing hydrophilic HydroThane™ matrices instead of conventional ethylcellulose matrix. Among them HydroThane™ 25 showed the most promising results with the highest increase in fluorescence intensity between OFF/ON states (12×), reasonably high fluorescence quantum yields in ON state (0.071) and the most reliable and reproducible response to CO 2 in sensing range 0–95 kPa pCO 2 with the limited temperature-dependency in the range 15–35 °C. Importantly, sensitivity significantly increased with shortening of the alkyl chains of a base, i.e. in order TOAOH < TBAOH < TEAOH that gives us a nice tool for tuning the dynamic range of CO 2 sensors for different applications. Finally, fiber-optic sensors compatible with a commercially available compact phase fluorometer as well as materials for 2-wavelength sensing and imaging are prepared and possibility of a referenced read-out is demonstrated. [ABSTRACT FROM AUTHOR]

New robust optical pH sensors rely on a combination of a photochemically stable NIR colorimetric aza-BODIPY dye and inorganic phosphors. Inner-filter effect is utilized to convert the colorimetric changes into a luminescence response. Chromium(III)-activated gadolinium aluminium borate and Egyptian Blue were used as inert reference phosphors, enabling two-wavelength ratiometric read-out in the emission and excitation mode, respectively. Additionally, we synthetized dually-emitting upconverting particles (UCPs) based on lanthanide-doped molybdates (NaCaY 1− x La x (MoO 4 ) 3 , La = Yb(III), Ho(III) and Tm(III)) featuring anti-Stokes emission peaks in the red/NIR spectral region (645/800 nm). Upon NIR excitation (980 nm) the NIR emission of the upconverting particles is modulated by the pH indicator, whereas the red emission serves as a reference. Importantly, the spectral properties of the pH sensor based on UCPs are fully compatible with the biological optical window. [ABSTRACT FROM AUTHOR]

• New fluorescent BODIPY dyes cover green to far red part of electromagnetic spectrum. • The red emitting dyes feature unmatched photostability. • Phenol receptors render dyes pH sensitive and suitable for sensing applications. • Optical plastic carbon dioxide sensors are prepared upon immobilization of the indicators into ethyl cellulose. • Tuneability of sensing properties and suitability for referenced ratiometric read-outs are demonstrated. Several new BODIPY pH indicators are prepared and tested as transducers in polymer-based optical carbon dioxide sensors. Apart from classical BODIPY chromophore absorbing at around 505 nm, π-extended analogs showing absorption maxima at around 635 and 665 nm are prepared. All the dyes possess excellent brightness due to combination of high molar absorption coefficients and fluorescence quantum yields. Additionally, the π-extended BODIPYs show unmatched photostability whereas the classical 1,3,5,7-tetramethyl-8-aryl-4,4-difluoroboradiazaindacene is found to be photolabile. The phenol receptors render BODIPY dyes pH sensitive inducing fluorescence quenching in the phenolate form. Carbon dioxide sensors are prepared via immobilization of the dyes into ethyl cellulose along with tetraoctylammonium hydrogencarbonate. The sensitivity of these sensors is mainly guided by the nature of the receptor and to a smaller extent by the nature of the chromophore, and can be tuned over a very wide range covering all important applications. Introduction of the receptor bearing carboxylic group in the o-position towards OH group of the receptor enables highly sensitive sensors resolving ambient CO 2 levels (LOD 0.009 hPa). Sensors based on other indicators show optimal response from 0.2 to 60 hPa and from 20 to 400 hPa, making them attractive for medical and food packaging applications, respectively. Materials for referenced sensing with phase fluorometry and ratiometric imaging with RGB cameras have also been prepared. [ABSTRACT FROM AUTHOR]