A near-infrared fluorescent dye (aza-bodipy or azaBDPBA) functionalized with boronic acid groups was synthesized for the preparation of optodes to measure glucose in 40-fold diluted whole blood. Boronic acid groups as an electron deficient group on aza-bodipy was reacted with hydrogen peroxide into an electron-rich phenolic group leading to the red-shift of emission wavelength from 682 to 724 nm. The emission in near-infrared region offered a low level of background interference from whole blood. Also, the dual-wavelength emission guaranteed our probe to measure glucose in whole blood accurately after the conversion of glucose into hydrogen peroxide using glucose oxidase. The measuring range of glucose from 0.2 to 200 mM in the buffer was achieved with high selectivity. To facilitate the blood test, the probe was immobilized into thin hydrophobic polymer films to prepare the disposal glucose optode, which could detect glucose in the solution from 60 μM to 100 mM. The concentration of glucose in 40-fold diluted whole blood was determined using our optode and the reference method, respectively. The consistence in the concentration obtained from these two assays revealed that our azaBDPBA-based optodes were promising for the clinic assay of glucose in the whole blood.Keywords: aza-bodipy; dual-wavelength emission; fluorescence optode; glucose; near-infrared; whole blood;

A class of squaramide-based tripodal molecules was employed as new ionophores for highly sensitive and selective sulfate-selective sensors. Compared with the reported tripodal ionophore with urea, squaramide groups as superior hydrogen bonding donor were introduced into the tripodal structure to obtain new ionophores leading to better electrode performance. Three derivatives with unsubstituted (I), p-carbon trifluoride (II), and p-nitro (III) phenyl groups were attached to squaramide groups for the optimization of ionophore based sensors. Electron withdrawing p-nitrophenyl groups gave a greater enhancement of the hydrogen bond donor ability of squaramide so that Ionophore III was chosen as the best candidate for sulfate ion recognition. Such a membrane with 30 mol% TDMACl exhibited a Nernstian slope of −30.2 mV per decade to sulfate ions with a linear range from 1 μM to 100 mM in potentiometric measurement. The selectivity coefficients of the proposed sensor over H2PO4−, Cl−, Br−, NO3−, SCN−, I− and ClO4− were −4.3, −3.4, −2.5, −0.6, +3.1, +3.4 and +5.9, respectively, which were much better than the existing sulfate-selective sensors. The new sensors with high selectivity were successfully applied for the quantification of sulfate in cell lysates and drinking water with good recoveries.

A highly stable, long wavelength polarity sensitive probe, 8-nitrophenyl-3,5-dipiperidine-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (NPBDP), was developed for living cell imaging of intracellular lipid droplets by fluorescence microscopy.

We proposed here a potassium selective optode incorporating NaYF4:Er,Yb upconverting nanorods and chromoionophore ETH 5294 together in hydrophobic polymer matrixes and the response of the optode is based on changes in the upconverting luminescence intensity induced from the absorption change of the proton sensitive chromoionophore. The optode was used for determination of the potassium content in the whole blood sample for the first time. Because the excitation source of 980 nm, as well as the emission wavelength, lies in the near-infrared region, the background absorption and autofluorescence of the biological sample could be eliminated, and ensure the sensitivity and selectivity of the sensor. The potassium levels of sheep plasma and whole blood samples obtained by the optode were comparable with the results obtained by ICPMS and ISE methods, providing possibilities for further application in clinical diagnosis.

By employing dipalladium corners [(bpy)2Pd2(NO3)2](NO3)2 or [(phen)2Pd2(NO3)2](NO3)2 (where bpy = 2,2′-bipyridine and phen = 1,10-phenanthroline) to bridge ferrocene-based dipyrazole ligand (L11) and m-phenylene-based dipyrazole ligands (L2–32–3) in aqueous solution, a series of positively-charged [M4L2]4+ metallomacrocycles were obtained. Their structures were characterized by 1H NMR, electrospray ionization mass spectrometry (ESI-MS), elemental analysis, and single crystal X-ray diffraction analysis for 1·4NO3 ({[(bpy)Pd]4L112}(NO3)4) and 4·4NO3 ({[(phen)Pd]4L222}(NO3)4). In their single crystal structures, NO3− anions are located at the dipalladium corners by C–H⋯O hydrogen bonds. Importantly, the anion-sensing properties of ferrocene functionalized [Pd4Fe2] hetero-metallomacrocycle 1 were investigated in acetonitrile by SWV, CV and NMR analysis, showing promise for Br− sensing.

In this study, BODIPY-appended calix[4]arene was chosen as a fluorescent probe for intracellular pH. The compound with cell permeability can monitor the minor pH change near neutrality inside the cell and is the first BODIPY-derived probe reported for cytosolic pH. Owing to a high level of cell retention and minor cytotoxicity of the probe, stable fluorescence is provided in the cells for 24 h, facilitating the precise observation of intracellular pH. A model of cell apoptosis was designed by exposure of the cells to a low concentration of hydrogen peroxide. An increase in the fluorescence of the cells confirmed that BODIPY-appended calix[4]arene sensed the fluctuation of the cellular pH during early cell apoptosis. The developed fluorescent pH probe will be useful for the study of cell apoptosis.

Triblock copolymer polystyrene-block-polybutadiene-block-polystyrene (PS-PB-PS, SBS) and its composites with ionic liquid have been applied for preparing solid contact ion-selective potentiometric sensors for the first time. Both types of materials form hydrophobic membranes with excellent mechanical properties. The proposed sensors containing ionophore and ion-exchanger exhibited the fast and Nernstian response to the primary ions and good selectivity over various interfering ions. The self-plasticizing property of triblock SBS enables the fabrication of completely solvent-free ion sensors. Such membranes showed much improved lifetime than the ones containing ionic liquid as plasticizer because the leaching of the ionic liquid has been eliminated. The SBS membrane is more hydrophobic than traditional plasticized poly vinyl chloride membrane, which prevents the formation of the water layer between the metal electrode substrate and the sensing membrane.

Optical thin films incorporating NaYF4:Er,Yb upconverting nanorods and chromoionophore ETH 5418 in hydrophobic polymer matrixes have been developed for the first time to measure pH and metal ions based on the ion-exchange mechanism. The absorption spectra of protonated and unprotonated ETH 5418 overlap the two emission peaks of upconverting material, respectively, which makes the inert nanorods ion-sensitive. Optodes for pH and metal ions (Na+, K+, Ca2+, and Cu2+) were investigated and exhibited excellent sensitivity, selectivity, and reproducibility. Because of excitation by the 980 nm laser source, detection in the near-infrared region at 656 nm, and high quantum yield of the nanorods in hydrophobic membrane, the proposed sensors have been successfully used in whole blood measurements with minimized background absorption and sample autofluorescence.

Fluorescent probes based on boron dipyrromethene functionalized with a phenylboronic acid group (BODIPY–PBAs) were synthesized in high yield for the first time by Suzuki coupling of bis(pinacolato)diboron and 8-(4-bromophenyl)-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY). Wavelength tuning of the fluorophores was achieved by attaching an auxochromic substituent to the 5-position of the BODIPY core structure through Knoevenagel condensation. The emission intensity of fluorophores increases when binding to the analytes with diol groups and forming boronic esters at fixed pH. These compounds can detect monosaccharides in the concentration range of 0.1–100 mM. Whereas glycogen was found to quench the fluorescence of BODIPY–PBAs in an aqueous solution due to the self-quenching of the fluorophores after attaching in the extensively branched and compact glucose polymer, further addition of d-fructose to the solution can release the fluorophores from the polymer and the fluorescence regains. The BODIPY–PBA fluorophore has been applied in polymeric optodes containing anion exchangers to perform repetitive measurement. Such sensors respond to different monosaccharides in the range of 0.1–100 mM and demonstrate an improved selectivity toward d-fructose over other saccharides, compared to the results obtained from homogeneous assay.

Highly stable near infrared fluorescent (NIRF) boron-dipyrromethene (BODIPY) derivatives have been utilized as chromoionophores in ion-selective optodes for the first time. The pKa values of the chromoionophores are tuned by using different substituted aniline groups. The derivative with dimethyl aniline group has pKa value of 2.5 in plasticized poly (vinyl chloride) membrane, while the more basic piperidine group gives larger pKa value of 5.4. Ion optodes prepared with NIRF chromoionophores and cation exchanger are pH sensitive and exhibited fully reversible response. With additional ionophore such optodes can measure the concentration of metal ion based on ion exchange mechanism and exhibited comparable dynamic range and selectivity to the optodes containing traditional ETH types of chromoionophores. Fluorescence measurements in near infrared region between 700 and 900 nm minimize the influence of autofluoresence and background absorption, resulting in more sensitive and precise detection. The proposed optodes had been applied for pH measurement in blood samples.

A new near infrared (NIR) fluorescent 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dye with dual functionality was synthesized and characterized. The compound 1 responds to copper ion in NIR region with high selectivity through a photo-induced electron transfer process established between the substituted benzene group in the meso position and the BODIPY core when Cu2+ binds with the four oxygen atoms in the structure, and results in the quenching of the fluorescence. The response range to copper ions was from 10 to 50 μM, and other metal ions including Li+, Na+, K+, Mg2+, Ca2+, Pb2+, Fe3+, Ag+, Hg2+, Co2+, Zn2+, Mn2+, Cd2+, Ni2+ and Al3+ had no interference. When excited at 520 nm, a new emission peak at 568 nm of compound 1 was used to detect Al3+ selectively from 30 μM to 110 μM without any interference from other metal ions including copper ions.

Hydrophobic room temperature ionic liquid (RTIL), trihexyltetradecyl phosphonium bis(2,4,4-trimethylpentyl)phosphinate [THTDP][TMPP] as plasticizer for bulk ion optode membranes was studied. Chromoionophore ETH 5294 was incorporated into the PVC–[THTDP][TMPP] optode for detecting inorganic acids, including HCl, H2SO4, HNO3 and HClO4 based on the coextraction response mechanism. Compared to the optodes prepared with conventional plasticizers, PVC–IL based ones exhibited enhanced selectivity and much improved stability for hydrophilic anions. The leaching of ETH 5294 from polymeric film into HCl and H2SO4 solutions was eliminated when ionic liquid has been used as plasticizer.

A novel magnesium-selective ion-channel mimetic sensor based on a well-known calcium ionophore, ETH 5234, was demonstrated. Due to different stoichiometry of the ionophore with Mg2+ and Ca2+, the sensor exhibits high selectivity to Mg2+ by controlling ionophore concentration on the electrode surface, which allows the measurement of Mg2+ in a 1 mM Ca2+ background solution.

By employing diimine ligands coordinated dimetallic clips ([(bpy)2Pd2(NO3)2](NO3)2 or [(phen)2Pd2(NO3)2](NO3)2, where bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline) as the corner and anthracene-, naphthalene-, and benzene-based dipyrazolate dianions as the linker, a series of positively charged metallomacrocycles ([M4L2]4+ or [M8L4]8+) have been synthesized through a directed self-assembly method in aqueous solution. Every macrocycle has a cavity to bind solvent molecules or anions. The structures were characterized by elemental analysis, 1H and 13C NMR, electrospray ionization mass spectrometry, and single crystal X-ray diffraction analysis for compound 1·4PF6¯ (1 = {[(bpy)Pd]4L12}4+), 3·4PF6¯·8CH3CN·H2O (3 = {[(bpy)Pd]4L22}4+), and 7·4PF6¯·6H2O (7 = {[(bpy)Pd]4L52}4+). The 1:1 host−guest complexation for anthracene-based dipyrazolate-bridged macrocycles with aromatic guests was investigated via UV−vis and fluorescent titration.

We developed the highly sensitive bulk optodes with new synthesized rhodamine type of fluorescent chromoionophore. The fluorescent turn-on through spirolactam ring-opening of rhodamine dye inside the hydrophobic polymer phase can only be obtained by incorporating cation exchanger into the sensing membrane. The rhodamine-based optode containing copper ionophore exhibited nanomolar detection limit to copper ion at pH 5.5. By introducing an inert BODIPY derivative B as the reference dye, a fluorescence resonance energy transfer (FRET) process is established between the chromoionophore and the reference dye to allow the ratiometric fluorescence measurement. The discrimination between metal ions has been achieved by simply introducing different kinds of commercially available ionophores into the membrane. The proposed optodes exhibited wide response range, excellent reproducibility and fast response time.

Single-piece all-solid-state ion-selective electrode was fabricated with polymer–carbon nanotube composites. The ion-sensing cocktail containing plasticizer, poly(vinyl chloride) (PVC) and multi-wall carbon nanotube (MWCNTs) in polymeric dispersant is drop cast directly on a solid substrate to form the electrode. Polymeric dispersants with MWCNTs showed good compatibility in plasticized PVC matrix. The introduction of 0.2–0.5 wt% carbon nanotubes as ion-to-electron transducer has much improved the potential stability of the solid-contact electrode. It also makes an essential role to enhance the hydrophobicity of the membrane, which contributes to the more stable potential signal by elimination of undesirable water layer at the interface. The single-piece solid-state sensors with different ionophores were easily fabricated. Such electrodes exhibited excellent sensing properties comparable to the corresponding liquid-contact electrodes.

This paper presents the simplest method so far to prepare all solid-state ion-selective sensors with excellent potential stability and sensing properties. With the aid of block polymer PEO-PPO-PEO (F127) multi-wall carbon nanotubes (MWCNTs) facilitating the ion-to-electron transfer can be well-dispersed in different polymer matrices including plasticized poly vinyl chloride, plasticizer-free methacrylate copolymer and PVC-ionic liquid, which leads to a general approach to prepare all solid-state ion-selective sensors by simple one-step drop casting method.

By employing dipalladium corners [(bpy)2Pd2(NO3)2](NO3)2 or [(phen)2Pd2(NO3)2](NO3)2 (where bpy = 2,2′-bipyridine and phen = 1,10-phenanthroline) to bridge ferrocene-based dipyrazole ligand (L11) and m-phenylene-based dipyrazole ligands (L2–32–3) in aqueous solution, a series of positively-charged [M4L2]4+ metallomacrocycles were obtained. Their structures were characterized by 1H NMR, electrospray ionization mass spectrometry (ESI-MS), elemental analysis, and single crystal X-ray diffraction analysis for 1·4NO3 ({[(bpy)Pd]4L112}(NO3)4) and 4·4NO3 ({[(phen)Pd]4L222}(NO3)4). In their single crystal structures, NO3− anions are located at the dipalladium corners by C–H⋯O hydrogen bonds. Importantly, the anion-sensing properties of ferrocene functionalized [Pd4Fe2] hetero-metallomacrocycle 1 were investigated in acetonitrile by SWV, CV and NMR analysis, showing promise for Br− sensing.