Luminescence Lifetime-Based Sensing Platform Based on Cyclometalated Iridium(III) Complexes for the Detection of Perfluorooctanoic Acid in Aqueous Samples.

Luminescence lifetimes are an attractive analytical method for detection due to its high sensitivity and stability. Iridium probes exhibit luminescence with long excited-state lifetimes, which are sensitive to the local environment. Perfluorooctanoic acid (PFOA) is listed as a chemical of high concern regarding its toxicity and is classified as a "forever chemical". In addition to strict limits on the presence of PFOA in drinking water, environmental contamination from industrial effluent or chemical spills requires rapid, simple, accurate, and cost-effective analysis in order to aid containment. Herein, we report the fabrication and function of a novel and facile luminescence sensor for PFOA based on iridium modified on gold surfaces. These surfaces were modified with lipophilic iridium complexes bearing alkyl chains, namely, IrC6 and IrC12, and Zonyl-FSA surfactant. Upon addition of PFOA, the modified surfaces IrC6-FSA@Au and IrC12-FSA @Au show the largest change in the red luminescence signal with changes in the luminescence lifetime that allow monitoring of PFOA concentrations in aqueous solutions. The platform was tested for the measurement of PFOA in aqueous samples spiked with known concentrations of PFOA and demonstrated the capacity to determine PFOA at concentrations >100 µg/L (240 nM).

Luminescence-Based Infrared Thermal Sensors: Comprehensive Insights.

Recent chronological breakthroughs in materials innovation, their fabrication, and structural designs for disparate applications have paved transformational ways to subversively digitalize infrared (IR) thermal imaging sensors from traditional to smart. The noninvasive IR thermal imaging sensors are at the cutting edge of developments, exploiting the abilities of nanomaterials to acquire arbitrary, targeted, and tunable responses suitable for integration with host materials and devices, intimately disintegrate variegated signals from the target onto depiction without any discomfort, eliminating motional artifacts and collects precise physiological and physiochemical information in natural contexts. Highlighting several typical examples from recent literature, this review article summarizes an accessible, critical, and authoritative summary of an emerging class of advancement in the modalities of nano and micro-scale materials and devices, their fabrication designs and applications in infrared thermal sensors. Introduction is begun covering the importance of IR sensors, followed by a survey on sensing capabilities of various nano and micro structural materials, their design architects, and then culminating an overview of their diverse application swaths. The review concludes with a stimulating frontier debate on the opportunities, difficulties, and future approaches in the vibrant sector of infrared thermal imaging sensors.

Chelating silica nanoparticles for efficient antibiotic delivery and particle imaging in Gram-negative bacteria.

The inefficacy of antibiotics against Gram-negative bacteria is a major challenge for treatment of many clinically important bacterial infections. The complex structure of the double cell membrane of Gram-negative bacteria makes it inaccessible to many key antibiotics such as vancomycin and also presents a major challenge for drug development. In this study we design of a novel hybrid silica nanoparticle system bearing membrane targeting groups with the antibiotic encapsulated together with a ruthenium luminescent tracking agent, for optical detection of the nanoparticle delivery in the bacterial cell. The hybrid system shows delivery of vancomycin and efficacy against a library of Gram negative bacterial species. Evidence of penetration of nanoparticles in bacteria cells is achieved via luminescence of the ruthenium signal. Our studies show that nanoparticles modified with aminopolycarboxylate chelating groups are an effective delivery system in bacterial growth inhibition in species whereas the molecular antibiotic is ineffective. This design provides a new platform for delivery of antibiotics that cannot alone penetrate the bacterial membrane.

Photo- and Electrochemical Dual-Responsive Iridium Probe for Saccharide Detection.

Dual detection systems are of interest for rapid, accurate data collection in sensing systems and in vitro testing. We introduce an IrIII complex with a boronic acid receptor site attached to the 2-phenylpyridine ligand as an ideal probe with photo- and electrochemical signals that is sensitive to monosaccharide binding in aqueous solution. The complex displays orange luminescence at 618 nm, which is reduced by 70 and 40 % upon binding of fructose and glucose, respectively. The electro-chemiluminescent signal of the complex also shows a direct response to monosaccharide binding. The IrIII complex shows the same response upon incorporation into hydrogel matrices as in solution, thus demonstrating the potential of its integration into a device, as a nontoxic, simple-to-use tool to observe sugar binding over physiologically relevant pH ranges and saccharide concentrations. Moreover, the complex's luminescence is responsive to monosaccharide presence in cancer cells.

An azido-bridged [FeII4] grid-like molecule showing spin crossover behaviour.

The supramolecular self-assembly synthetic strategy provides a valid tool to obtain polynuclear Fe(II) complexes having effective communication between the metal centres and distinct spin crossover behaviour. Despite the great success in constructing various magnetic molecules, progress has not been made in SCO complexes based on azido bridges. In this article, the coordination-driven supramolecular assembly based on 3,6-substituted pyridazine and azide is presented to afford two Fe(II) grid-like complexes: [(L)4FeII4(N3)4][BPh4]4·sol (1, L = 3,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)pyridazine and 2, L = 3,6-di(pyridin-2-yl)pyridazine). The substitution of pyridinyl groups in 2 instead of pyrazolyl ones in 1 led to the only example exhibiting spin-crossover behaviour (T1/2 = 230 K) among the azido-bridged complexes. In addition, a temperature-dependent photoluminescence study of 2 demonstrates a visible synergetic effect between the SCO event and the luminescence.

Alginate-based microparticles coated with HPMCP/AS cellulose-derivatives enable the Ctx(Ile21)-Ha antimicrobial peptide application as a feed additive.

Microencapsulation is a potential biotechnological tool, which can overcome antimicrobial peptides (AMP) instabilities and reduce toxic side effects. Thus, this study evaluates the antibacterial activities of the Ctx(Ile21)-Ha AMP against multidrug-resistant (MDR) and non-resistant bacteria and develop and characterize peptide-loaded microparticles coated with the enteric polymers hydroxypropylmethylcellulose acetate succinate (HPMCAS) and hydroxypropylmethylcellulose phthalate (HPMCP). Ctx(Ile21)-Ha was obtained by solid phase peptide synthesis (SPPS) method, purified and characterized by HPLC and Mass Spectrometry. The peptide exhibited potent antibiotic activities against Salmonella enteritidis, Salmonella typhimurium, Pseudomonas aeruginosa (MDR), Acinetobacter baumannii (MDR), and Staphylococcus aureus (MDR). Ctx(Ile21)-Ha microencapsulation was performed by ionic gelation with high efficiency, maintaining the physical-chemical stability. Ctx(Ile21)-Ha coated-microparticles were characterized by DSC, TGA, FTIR-Raman, XRD and SEM. Hemolytic activity assay demonstrated that hemolysis was decreased up to 95% compared to single molecule. In addition, in vitro release control profile simulating different portions of gastrointestinal tract was performed and showed the microcapsules' ability to protect the peptide and release it in the intestine, aiming pathogen's location, mainly by Salmonella sp. Therefore, use of microencapsulated Ctx(Ile21)-Ha can be allowed as an antimicrobial controller in monogastric animal production as an oral feed additive (antimicrobial controller), being a valuable option for molecules with low therapeutic indexes or high hemolytic rates.

Strong Coupling and Slow Relaxation of the Magnetization for an Air-Stable [Co4] Square with Both Tetrazine Radicals and Azido Bridges.

Introducing both tetrazine radical and azido bridges afforded two air-stable square complexes [MII4(bpztz•-)4(N3)4] (MII = Zn2+, 1; Co2+, 2; bpztz = 3,6-bis(3,5-dimethylpyrazolyl)-1,2,4,5-tetrazine), where the metal ions are cobridged by µ1,1-azido bridges and tetrazine radicals. Magnetic studies revealed strong antiferromagnetic metal-radical interaction with a coupling constant of -64.7 cm-1 in the 2J formalism in 2. Remarkably, 2 exhibits slow relaxation of magnetization with an effective barrier for spin reverse of 96 K at zero applied field.

Quantification by Luminescence Tracking of Red Emissive Gold Nanoparticles in Cells.

Optical microscopy techniques are ideal for live cell imaging for real-time nanoparticle tracking of nanoparticle localization. However, the quantification of nanoparticle uptake is usually evaluated by analytical methods that require cell isolation. Luminescent labeling of gold nanoparticles with transition metal probes yields particles with attractive photophysical properties, enabling cellular tracking using confocal and time-resolved microscopies. In the current study, gold nanoparticles coated with a red-luminescent ruthenium transition metal complex are used to quantify and track particle uptake and localization. Analysis of the red-luminescence signal from particles is used as a metric of cellular uptake, which correlates to total cellular gold and ruthenium content, independently measured and correlated by inductively coupled plasma mass spectrometry. Tracking of the luminescence signal provides evidence of direct diffusion of the nanoparticles across the cytoplasmic membrane with particles observed in the cytoplasm and mitochondria as nonclustered "free" nanoparticles. Electron microscopy and inhibition studies identified macropinocytosis of clusters of particles into endosomes as the major mechanism of uptake. Nanoparticles were tracked inside GFP-tagged cells by following the red-luminescence signal of the ruthenium complex. Tracking of the particles demonstrates their initial location in early endosomes and, later, in lysosomes and autophagosomes. Colocalization was quantified by calculating the Pearson's correlation coefficient between red and green luminescence signals and confirmed by electron microscopy. Accumulation of particles in autophagosomes correlated with biochemical evidence of active autophagy, but there was no evidence of detachment of the luminescent label or breakup of the gold core. Instead, accumulation of particles in autophagosomes caused organelle swelling, breakdown of the surrounding membranes, and endosomal release of the nanoparticles into the cytoplasm. The phenomenon of endosomal release has important consequences for the toxicity, cellular targeting, and therapeutic future applications of gold nanoparticles.

Two azido-bridged [2×2] cobalt(ii) grids featuring single-molecule magnet behaviour.

The self-assembly of Co(ii) salts, pyridazine derivatives and azides afforded two azido-bridged [2×2] grid-type complexes {[(L)4CoII4(N3)4][BPh4]4}·sol (1, L = 3,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)pyridazine (pzdz) and sol = 4CH3CN·3CHCl3·2CH3OH and 2, L = 3,6-di(pyridin-2-yl)pyridazine (pydz) and sol = 4CH3CN). Upon comparison with other related grid-like complexes, the incorporation of end-on azido-bridges resulted in overall intramolecular ferromagnetic couplings, and thus endowed complexes 1 and 2 single molecule magnet behaviour with field-induced slow magnetic relaxation.

Cost-Efficient Printing of Graphene Nanostructures on Smart Contact Lenses.

Smart contact lenses have been put forward for years, but there is still no commercial product in the market; the high cost due to expensive fabrication techniques could be one of the reasons. In this paper, first, a cost-efficient and reliable route to fabricate graphene grating on contact lens was designed and demonstrated based on the direct laser interference patterning graphene film on commercial contact lenses using an Nd:YAG laser. The thickness of the film and the interference angle have been taken into consideration. Optical characterization and simulation have been applied to evaluate the quality of our final achieved grating patterns with a grating size from 0.92 to 3.04 µm. Two-dimensional (2D) patterns could also be obtained through double-time laser interference. Contact angles for samples with different interference angles were presented considering the service environment of smart contact lenses. Of course, the conductivity of the samples was evaluated using a four-probe method. The most conductive sample had the sheet resistance lower than 30 Ω/sq. This research study highlighted the possibility of patterning graphene with the laser ablation method and provided a candidate solution for the fabrication of smart contact lenses under controlled cost.

Imidodiphosphonate Ligands for Enhanced Sensitization and Shielding of Visible and Near-Infrared Lanthanides.

The design of coordination sites around lanthanide ions has a strong impact on the sensitization of their luminescent signal. An imidodiphosphonate anionic binding site is attractive as it can be functionalized with "remote" sensitizer units, such as phenoxy moieties, namely, HtpOp, accompanied by an increased distance of the lanthanide from the ligand high-energy stretching vibrations which quench the luminescence signal, hence providing flexible shielding of the lanthanide. We report the formation and isolation of Ln(tpOp)3 complexes where Ln = Er, Gd, Tb, Dy, Eu, and Yb and the Y(tpOp)3 diamagnetic analogue. The complexes are formed from reaction of KtpOp and the corresponding LnCl3·6H2O salt either by titration and in situ formation or by mixing and isolation. All complexes are seven-coordinated by three tpOp ligand plus one ethanol molecule, except for Yb(tpOp)3 which has no solvent coordinated. Phosphorus NMR shows characteristic shifts to support the coordination of the lanthanide complexes. The complexes display visible and near-infrared luminescence with long lifetimes even for the near-infrared complexes which range from 3.3 µs for Nd(tpOp)3 to 20 µs for Yb(tpOp)3. The ligand shows more efficient sensitization than the imidodiphosphinate analogues for all lanthanide complexes with a notable quantum yield of the Tb(tpOp)3 complex at 45%. We attribute this to the properties of the remote sensitizer unit and its positioning further away from the lanthanide, eliminating quenching of high energy C-H vibrations from the ligand shell. Calculations of the ligand shielding support the photophysical properties of the complexes. These results suggest that these binding sites are promising in the further development of the lanthanide complexes in optoelectronic devices for telecommunications and new light emitting materials.

Converting Capsules to Sensors for Nondestructive Analysis: From Cargo-Responsive Self-Sensing to Functional Characterization.

A general concept of converting capsules into sensors is reported. Such simple conversion enables instantaneous nondestructive analysis for applications such as controlled release and energy storage among others. Converted capsule sensors are responsive in emission colors to varying core cargos via the incorporation of a solvatochromic fluorophore under excitation. Such cargo-responsive self-sensing abilities facilitate their application in capsule-level analysis such as cargo retention-leakage detection and release implications, as well as defect identification. The versatile concept is shown as an auxiliary tool in thermal energy storage to visualize phase transition, exhibiting promising potentials in application-level characterization.

Assisted delivery of anti-tumour platinum drugs using DNA-coiling gold nanoparticles bearing lumophores and intercalators: towards a new generation of multimodal nanocarriers with enhanced action.

New gold and lipoic based nanocarriers for the delivery of platinum(ii) and platinum(iv) drugs are developed, which allow enhanced loading of the drug on the surface of the nanocarriers and release in a pH-dependent fashion, with superior release at lower pHs which are associated with many tumours. The conjugate nanoparticles and their conjugates enter cells rapidly (within 3 hours). They tend to cluster in vesicles and are also observed by light and electron microscopies in the cytoplasm, endoplasmic reticulum and nucleus. We further incorporate aminoanthraquinone units that are both fluorophores and DNA intercalators. This results in nanocarriers that after drug release will remain surface decorated with DNA-binders challenging the conventional design of the nanocarrier as an inert component. The outcome is nanocarriers that themselves have distinctive, remarkable and unusual DNA binding properties being able to bind and wrap DNA (despite their anionic charge) and provide enhanced cytotoxic activity beyond that conferred by the platinum agents they release. DNA coiling is usually associated with polycations which can disrupt cell membranes; anionic nanoparticles that can cause novel and dramatic effects on DNA may have fascinating potential for new approaches to in-cell nucleic acid recognition. Our findings have implications for the understanding and interpretation of the biological activities of nanoparticles used to deliver other DNA-binding drugs including clinical drug doxorubicin and its formulations.

Iridium Nanoparticles for Multichannel Luminescence Lifetime Imaging, Mapping Localization in Live Cancer Cells.

The development of long-lived luminescent nanoparticles for lifetime imaging is of wide interest as luminescence lifetime is environmentally sensitive detection independent of probe concentration. We report novel iridium-coated gold nanoparticles as probes for multiphoton lifetime imaging with characteristic long luminescent lifetimes based on iridium luminescence in the range of hundreds of nanoseconds and a short signal on the scale of picoseconds based on gold allowing multichannel detection. The tailor-made IrC6 complex forms stable, water-soluble gold nanoparticles (AuNPs) of 13, 25, and 100 nm, bearing 1400, 3200, and 22 000 IrC6 complexes per AuNP, respectively. The sensitivity of the iridium signal on the environment of the cell is evidenced with an observed variation of lifetimes. Clusters of iridium nanoparticles show lifetimes from 450 to 590 ns while lifetimes of 660 and 740 ns are an average of different points in the cytoplasm and nucleus. Independent luminescence lifetime studies of the nanoparticles in different media and under aggregation conditions postulate that the unusual long lifetimes observed can be attributed to interaction with proteins rather than nanoparticle aggregation. Total internal reflection fluorescence microscopy (TIRF), confocal microscopy studies and 3D luminescence lifetime stacks confirm the presence of bright, nonaggregated nanoparticles inside the cell. Inductively coupled plasma mass spectrometry (ICPMS) analysis further supports the presence of the nanoparticles in cells. The iridium-coated nanoparticles provide new nanoprobes for lifetime detection with dual channel monitoring. The combination of the sensitivity of the iridium signal to the cell environment together with the nanoscaffold to guide delivery offer opportunities for iridium nanoparticles for targeting and tracking in in vivo models.

Tailoring iridium luminescence and gold nanoparticle size for imaging of microvascular blood flow.

AIM: Imaging of blood flow in narrow channels and close to vessel walls is important in cardiovascular research for understanding pathogenesis. Our aim was to provide novel nanoprobes with visible emission and long lifetimes as trackers of flow. MATERIALS & METHODS: Gold nanoparticles coated with an iridium complex were prepared. Luminescence imaging was used to monitor their flows in different hematocrit blood and in murine tissues. RESULTS: The velocities are independent of hematocrit level and the nanoparticles entering blood circulation can be clearly detected in vessels in lungs, mesentery and the skeletal muscle. CONCLUSION: The work introduces for the first time iridium-based yellow-green luminescence with nanoparticle size of 100 nm for visualizing and monitoring flows with much higher resolution than conventional alternatives.

Fluorescent Block Copolymer Micelles That Can Self-Report on Their Assembly and Small Molecule Encapsulation.

Block copolymer micelles have been prepared with a dithiomaleimide (DTM) fluorophore located in either the core or shell. Poly(triethylene glycol acrylate)-b-poly(tert-butyl acrylate) (P(TEGA)-b-P(tBA)) was synthesized by RAFT polymerization, with a DTM-functional acrylate monomer copolymerized into either the core forming P(tBA) block or the shell forming P(TEGA) block. Self-assembly by direct dissolution afforded spherical micelles with Rh of ca. 35 nm. Core-labeled micelles (CLMs) displayed bright emission (Φf = 17%) due to good protection of the fluorophore, whereas shell-labeled micelles (SLMs) had lower efficiency emission due to collisional quenching in the solvated corona. The transition from micelles to polymer unimers upon dilution could be detected by measuring the emission intensity of the solutions. For the core-labeled micelles, the fluorescence lifetime was also responsive to the supramolecular state, the lifetime being significantly longer for the micelles (τAv,I = 19 ns) than for the polymer unimers (τAv,I = 9 ns). The core-labeled micelles could also self-report on the presence of a fluorescent hydrophobic guest molecule (Nile Red) as a result of Förster resonance energy transfer (FRET) between the DTM fluorophore and the guest. The sensitivity of the DTM fluorophore to its environment therefore provides a simple handle to obtain detailed structural information for the labeled polymer micelles. A case will also be made for the application superiority of core-labeled micelles over shell-labeled micelles for the DTM fluorophore.

Highly luminescent gold nanoparticles: effect of ruthenium distance for nanoprobes with enhanced lifetimes.

The photophysical properties of gold nanoparticles, AuNPs, with sizes of 13, 50 and 100 nm in diameter, coated with surface-active ruthenium complexes have been studied to investigate the effect of the distance of the ruthenium luminescent centre from the gold surface. Luminescence lifetimes of the three ruthenium probes, RuS1, RuS6 and RuS12, with different length spacer units between the surface active groups and the ruthenium centre were taken. The metal complexes were attached to AuNP13, AuNP50 and AuNP100 via thiol groups using a method of precoating the nanoparticles with a fluorinated surfactant. The luminescence lifetime of the longer spacer unit complex, RuS12, was enhanced by 70% upon attachment to the AuNP when compared to the increase of the short and medium linker unit complexes, RuS1 (20%) and (RuS6 40%) respectively. The effect of the surfactant in the lifetime increase of the ruthenium coated AuNPs was shown to be larger for the medium spacer probe, RuS6. There was no effect of the change of the size of the AuNPs from 13 to 50 or 100 nm.

Alginate-Iron Speciation and Its Effect on In Vitro Cellular Iron Metabolism.

Alginates are a class of biopolymers with known iron binding properties which are routinely used in the fabrication of iron-oxide nanoparticles. In addition, alginates have been implicated in influencing human iron absorption. However, the synthesis of iron oxide nanoparticles employs non-physiological pH conditions and whether nanoparticle formation in vivo is responsible for influencing cellular iron metabolism is unclear. Thus the aims of this study were to determine how alginate and iron interact at gastric-comparable pH conditions and how this influences iron metabolism. Employing a range of spectroscopic techniques under physiological conditions alginate-iron complexation was confirmed and, in conjunction with aberration corrected scanning transmission electron microscopy, nanoparticles were observed. The results infer a nucleation-type model of iron binding whereby alginate is templating the condensation of iron-hydroxide complexes to form iron oxide centred nanoparticles. The interaction of alginate and iron at a cellular level was found to decrease cellular iron acquisition by 37% (p < 0.05) and in combination with confocal microscopy the alginate inhibits cellular iron transport through extracellular iron chelation with the resulting complexes not internalised. These results infer alginate as being useful in the chelation of excess iron, especially in the context of inflammatory bowel disease and colorectal cancer where excess unabsorbed luminal iron is thought to be a driver of disease.