Ratiometric Photoluminescence Research Articles

Ratiometric Imaging Detection of Amyloid-β Fibrils by a Dual-Emissive Tris-Heteroleptic Ruthenium Complex.

Two dual fluorescent/phosphorescent tris-heteroleptic mononuclear Ru(ΙΙ) complexes (2 and 3) were designed and applied in amyloid-β (Aβ) sensing. These complexes have a general formula of [Ru(phen)(dppz)(L)](PF6)2, where L is (2-pyrazinyl)(2-pyridyl)(methyl)amine (H-L) with different substituents (-OMe for 2, -H for 3), phen is 1,10-phenanthroline, and dppz is dipyridophenazine, respectively. Compared with the previously reported ratiometric probe 1 with a di(pyrid-2-yl)(methyl)amine ligand, complex 2 can be employed for not only ratiometric emissive detection of Aβ aggregation but also ratiometric imaging detection of Aβ fibrils. In ratiometric emissive detection, as the incubation time of the Aβ sample (Aβ40 and Aβ42) was prolonged, a new phosphorescence emission band appeared with gradual enhancement of the emission intensity, while the fluorescence emission was basically unchanged, which could be treated as an intrinsic internal reference signal. In comparison, a larger ratiometric photoluminescence enhancement (I640/I440) was observed for Aβ40 aggregation with respect to Aβ42. In ratiometric imaging detection, the imaging signals obtained from the phosphorescence emission are much brighter than the fluorescence emission in both Aβ40 and Aβ42 fibrils. As indicated by molecular docking results, stronger interactions were found between complex 2 with Aβ40 fibrils, which included π/π, π/C-H, and π/H interactions between bidentate ligands dppz and phen with amino acid residues. Moreover, computational calculations were carried out to assist the interpretation of these experimental findings.

Fluorimetric ratiometric tryptophan detection based on dual-ultraviolet-emission fluorine-doped carbon nanodots

In this work, strong electronegativity fluorine-doped carbon nanodots (FCDs) with distinctive dual-ultraviolet-emission characteristics was easily synthesized by a simple solvothermal approach using 4-fluorophenethylamine as the only precursor. Experimental results demonstrate that the FCDs exhibits dual-ultraviolet luminous peaks at 286 and 386 nm due to the participation of fluorine and nitrogen atoms, under 265 nm excitation. Next, the FCDs can be further served as an efficacious ratiometric photoluminescence (PL) probe for tryptophan (Trp) analysis based on the energy/electron transfer of the inner filter effect mechanism between FCDs and Trp. Under optimized experimental conditions, a wide linear relationship obtained between the PL386nm/PL286nm ratio of FCDs and the concentrations of Trp in the range of 0–200.0 μM, with the limit of detection of 0.31 µM (3σ/k). Moreover, the developed ratiometric probe was smoothly applied for estimating Trp in serum samples, revealing promising application opportunities in biological fluids. This work further demonstrates the importance of heteroatom species in regulating the physicochemical properties of carbon materials.

Immobilization of europium and terbium ions with tunable ratios on a dispersible two-dimensional metal-organic framework for ratiometric photoluminescence detection of D2O.

A two-dimensional zirconium-based metal-organic framework (2D Zr-MOF), ZrBTB (BTB = 1,3,5-tri(4-carboxyphenyl)benzene), is used as a platform to simultaneously immobilize terbium ions and europium ions with tunable ratios on its hexa-zirconium nodes by a post-synthetic modification. The crystallinity, morphology, porosity and photoluminescence (PL) properties of the obtained 2D Zr-MOFs with various europium-to-terbium ratios are investigated. With the energy transfer from the excited BTB linker to the installed terbium ions and the energy transfer from terbium ions to europium ions, a low loading of immobilized europium ions and a high loading of surrounding terbium ions in the 2D Zr-MOF result in the optimal PL emission intensities of europium; this phenomenon is not observable for the physical mixture of both terbium-installed ZrBTB and europium-installed ZrBTB. The role of installed terbium ions as efficient mediators for the energy transfer from the excited BTB linker to the installed europium ion is confirmed by quantifying PL quantum yields. As a demonstration, these materials with modulable PL characteristics are applied for the ratiometric detection of D2O in water, with the use of the stable emission from the BTB linker as the reference. With the strong emission of immobilized europium ions and the good dispersity in aqueous solutions, the optimal bimetal-installed ZrBTB, Eu-Tb-ZrBTB(1 : 10), can achieve the sensing performance outperforming those of the terbium-installed ZrBTB, europium-installed ZrBTB and the physical mixture of both.

Multifunctional Roles of Dihydrotetrazine-Decorated Zr-MOFs in Photoluminescence and Colorimetrism for Discrimination of Arsenate and Phosphate Ions in Water.

The high chemical and structural stabilities of zirconium (Zr)-based metal-organic frameworks (MOFs) in aquatic media make them ideal candidates for wastewater treatment. Rational decoration or Zr-MOFs with functional groups can significantly extend their application in this area. In this work, two well-known Zr-MOFs, UiO-66 and MIL-140-A, were functionalized with dihydrotetrazine function to increase their capability in water treatment. Investigations reveal that these two dihydrotetrazine (DHTZ)-functionalized MOFs, namely UiO-66(Zr)-DHTZ and MIL-140(Zr)-DHTZ, can be applied as a two-component array for highly selective and sensitive discrimination of arsenate (AsO43-) and phosphate (PO43-) ions in water in the presence of other anions. Photoluminescence (PL) tests using UiO-66(Zr)-DHTZ show that this MOF can detect these two anions via a ratiometric response, 1.74 for arsenate and 1.84 for phosphate at 2 μM, with superior detection limits (7.2 × 10-8 M for AsO43- and 4.3 × 10-8 M for PO43-). The ratiometric PL response of UiO-66(Zr)-DHTZ toward arsenate and phosphate anions arises possibly from the arsenate-dihydrotetrazine hydrogen bonding. In the next step, colorimetric tests using MIL-140(Zr)-DHTZ were conducted to discriminate the arsenate from phosphate with a very low detection limit at nanomolar level. This MOF undergoes a yellow-to-pink color change in the presence of arsenate ions, while no color change is observed in the presence of phosphate. This color change is observed through conversion of dihydrotetrazine sites inside the pores of MIL-140(Zr)-DHTZ into tetrazine. Altogether, the PL response of UiO-66(Zr)-DHTZ is originated from the hydrogen bond-donating/accepting character of DHTZ function, while the colorimetric response of MIL-140(Zr)-DHTZ is based on the chemical conversion of DHTZ function. This work clearly shows that the decoration of Zr-based MOFs with multicharacter functional groups can develop their application in wastewater treatment as multipurpose platforms.

Nitrogen-doped carbon dots as a highly selective and sensitive fluorescent probe for sensing Mg2+ ions in aqueous solution, and their application in the detection and imaging of intracellular Mg2+ ions

The magnesium (Mg2+) ion is the second most abundant intracellular cation after potassium, and it is involved in a variety of biological processes and physiological functions. Because of the different effects which are dependent on Mg2+ ion concentration, it is critical to monitor Mg2+ ion levels in biological systems. Here, we report the hydrothermal synthesis of photoluminescent N-doped carbon dots (NCDs) using 4-Hydroxybenzaldehyde and 1, 2, 4, 5-benzenetetramine tetrahydrochloride as carbon and nitrogen sources, respectively. The as-synthesized NCDs demonstrated excitation dependent photoluminescence (PL) with a quantum yield of 16.2%. Because of water dispersibility and chelating functional groups, NCDs were used for highly selective detection of Mg2+ ions using ratiometric PL enhancement with a detection limit of 60 μM. Following that, based on highly biocompatibility and sensing of Mg2+ ions in aqueous solutions, NCDs were employed as photoluminescent probe to detect the Mg2+ ions of mammalian cell lines such as J774, HeLa, and Hek293T, which is most likely due to effective complex formation between NCDs and the intracellular Mg2+ ions. As far as we could possibly know, this is the first report of aqueous solution dispersed carbon dots for intracellular sensing and imaging of Mg2+ ions based solely on an increase in NCDs PL intensity.

A thermal-assisted electrochemical strategy to synthesize carbon dots with bimodal photoluminescence emission

Although several groups have reported bimodal emissive carbon dots (B-CDs) and paid considerable attention to their ratiometric fluorescent sensing application in recent years, the establishment of convenient yet robust strategies that can generate B-CDs from various low-cost and extensive carbon sources is still required. Here a novel thermal-assisted electrochemical strategy for preparing B-CDs from low-cost carbon sources, including graphite and raw coal, is reported. The as-prepared B-CDs exhibit bimodal photoluminescence (PL) emission at 415 and 510 nm under single-wavelength excitation. Furthermore, the origination of the bimodal emissive characteristics of the as-prepared B-CDs was investigated in detail. Under thermal induction, the carbonyl-related surface state PL centers are generated at the surface of B-CDs, and the co-existence of the carbonyl-related surface state and core state PL centers results in bimodal PL emission. Finally, to demonstrate its practical application, a ratiometric PL nanoprobe was developed to sense pH. This thermal-assisted electrochemical strategy is versatile and potentially suitable to a wide range of low-cost carbon sources.

Internal Referencing Photoluminescence Probes for Simultaneous Sensing of O2 Gas and Temperature Based on Mn:MAPb(Br/Cl)3 Perovskite

The ratiometric photoluminescence (PL)‐based O2 sensitive probes provide built‐in self‐calibration for the correction of various target‐independent influencing factors. They attract particular attention to be used for O2 gas sensing and imaging. Herein, internal referencing ratiometric PL probes are fabricated that not only detect O2 concentration and temperature simultaneously but also remove the destructive effect of temperature on O2 sensing. A dual‐emission thin film of Mn‐doped halide perovskite nanocrystals (PNCs) (Mn:MAPb(Br/Cl)3) with a 50% PL quantum yield is used as the sensing layer, which is synthesized in situ. Through the sensing process, excitonic PL and the PL caused by Mn are used for detecting temperature and O2 partial pressures, respectively. Remarkably, the Mn PL intensity shows 40% decrement with increasing O2 partial pressures from 0% to 20%, while for the excitonic PL, intensity changes are less than 5%. As the temperature undesirably affects the sensing quantity, the O2 PL is used as an internal reference signal to achieve good accuracy and selectivity. Furthermore, the temperature variation is determined by measuring PL peak intensity change and wavelength shift. In addition to the O2 gas sensitivity of 1.55, a relative temperature sensitivity of −9.36% K−1 is also achieved.

An “on-off” ratio photoluminescence sensor based on catalytically induced PET effect by Fe3O4 NPs for the determination of coumarin

Herein, using Fe3O4 nanoparticles (Fe3O4 NPs) as a magnetic artificial peroxidase, an “on–off” ratiometric photoluminescence sensor with high-sensitivity and high-selectivity for coumarin was constructed based on photoinduced electron transfer (PET) between 7-hydroxycoumarin and rhodamine B (RB). The results showed that Fe3O4 NPs catalyzed H2O2 to generate nucleophilic group ·OH, which attacked the active site of coumarin and produced strong fluorescent 7-hydroxycoumarin molecules. Then, the fluorescence of RB was quenched with 7-hydroxycoumarin through the PET effect. The ratio signal generated in the above process was used for the quantitative detection of coumarin. Under optimized conditions, the linear range 0.5–25 mg/L was acquired for coumarin with the detection limit of 0.016 mg/L. This method had excellent selectivity and the recovery rate was 81.8%−106.8% with the relative standard deviation less than 5.6%, so it can be used for the quantitative analysis of coumarin in complex matrix samples.

Controllable FRET Behaviors of Supramolecular Host-Guest Systems as Ratiometric Aluminum Ion Sensors Manipulated by Tetraphenylethylene-Functionalized Macrocyclic Host Donor and Multistimuli-Responsive Fluorescein-Based Guest Acceptor.

The novel multistimuli-responsive monofluorophoric supramolecular polymer Poly(TPE-DBC)/FL-DBA and pseudo[3]rotaxane TPE-DBC/FL-DBA consisted of the closed form of nonemissive fluorescein guest FL-DBA along with TPE-based main-chain macrocyclic polymer Poly(TPE-DBC) and TPE-functionalized macrocycle TPE-DBC hosts, respectively. By the combination of various external stimuli, these fluorescent supramolecular host-guest systems could reveal interesting photoluminescence (PL) properties in DMF/H2O (1:1, v/v) solutions, including bifluorophoric host-guest systems after the complexation of Al3+ ion, i.e., TPE-DBC/FL-DBA-Al3+ and Poly(TPE-DBC)/FL-DBA-Al3+ with their corresponding open form of fluorescein guest FL-DBA-Al3+. Importantly, the Förster resonance energy transfer (FRET) processes occurred in both bifluorophoric host-guest systems between blue-emissive TPE donors (λem = 470 nm) and green-emissive fluorescein acceptors (λem = 527 nm) after aluminum detection, which were further verified by time-resolved photoluminescence (TRPL) measurements to acquire their FRET efficiencies of 40.4 and 31.1%, respectively. Both supramolecular host-guest systems exhibited stronger green fluorescein emissions as well as appealing ratiometric PL behaviors within the desirable donor-acceptor distances of FRET processes in comparison with their detached analogous mixtures. Regarding the pH effects, the optimum green fluorescein emissions with effective FRET processes of all compounds and host-guest systems were sustained in the range pH = 7-10. Interestingly, both host-guest systems TPE-DBC/FL-DBA and Poly(TPE-DBC)/FL-DBA possessed high sensitivities and selectivities toward aluminum ion to display their strong green emissions via FRET-ON behaviors due to the chelation-induced ring opening of spirolactam moieties to become green-emissive guest acceptor FL-DBA-Al3+, which offered excellent limit of detection (LOD) values of 50.61 and 38.59 nM, respectively, to be further applied for the fabrication of facile test strips toward aluminum detection. Accordingly, the inventive ratiometric PL and FRET sensor approaches of supramolecular host-guest systems toward aluminum ion with prominent sensitivities and selectivities were well-established in this study.

FRET processes of bi-fluorophoric sensor material containing tetraphenylethylene donor and optical-switchable merocyanine acceptor for lead ion (Pb2+) detection in semi-aqueous media

A novel aggregation-induced emission (AIE) structure containing a tetraphenylethene (TPE) unit covalently linked with a spiropyran (SP) unit was synthesized and investigated in semi-aqueous solutions with 90% water fraction. The open-form structure of red-emissive merocyanine (MC) unit combined with TPE unit was utilized as a bi-fluorophoric sensor to detect lead(II) ion, which could be transformed from the close-form structure of non-emissive SP unit upon UV exposure. Moreover, the TPE unit as an energy donor with the blue-green photoluminescence (PL) emission at 480 nm was combined with the MC unit as an energy acceptor with the red PL emission at 635 nm. Due to the Förster resonance energy transfer (FRET) processes, the bi-fluorophoric sensor produced more efficient ratiometric PL behavior to induce a stronger red PL emission than that of the mono-fluorophoric MC unit. Hence, the PL sensor responses of the AIE bi-fluorophoric structure toward lead(II) ion could be further amplified via the FRET-OFF processes to turn off red PL emission of the coordinated MC acceptor and to recover blue-green PL emission of the TPE donor. Accordingly, the best LOD value for the AIE sensor detection toward Pb2+ was 0.27 μM. The highest red MC emission with the optimum FRET process of AIE sensor could be utilized in cell viability tests to prove the non-toxic and remarkable bio-marker of AIE sensor to detect lead(II) ion in live cells. The developed FRET-OFF processes with ratiometric PL behavior of the bi-fluorophoric AIE sensor can be utilized for future chemo- and bio-sensor applications.

Luminescent Yb3+,Er3+-Doped α-La(IO3)3 Nanocrystals for Neuronal Network Bio-Imaging and Nanothermometry.

Dual-light emitting Yb3+,Er3+-codoped α-La(IO3)3 nanocrystals, known to exhibit both second harmonic signal and photoluminescence (PL), are evaluated as optical nanoprobes and thermal sensors using both conventional microscopes and a more sophisticated micro-PL setup. When loaded in cortical and hippocampal neurons for a few hours at a concentration of 0.01 mg/mL, a visible PL signal arising from the nanocrystals can be clearly detected using an epifluorescent conventional microscope, enabling to localize the nanocrystals along the stained neurons and to record PL variation with temperature of 0.5% K−1. No signal of cytotoxicity, associated with the presence of nanocrystals, is observed during the few hours of the experiment. Alternatively, a micro-PL setup can be used to discriminate the different PL lines. From ratiometric PL measurements, a relative thermal sensitivity of 1.2% K−1 was measured.

B- and N-Embedded π-Conjugation Units Tuning Intermolecular Interactions and Optical Properties of Platinum(II) Complexes.

A new series of neutral and cationic platinum(II) complexes containing a B- or N-embedded π-conjugation unit has been prepared. Notably, significantly different intermolecular interactions (Pt-Pt, π-π, head to tail, and head to head) and interesting optical properties exist in these complexes, which can be attributed to the difference in spatial structures and π-electron properties between B- and N-embedded π-conjugation units. Unexpectedly, under a hypoxic atmosphere, N-embedded neutral complex PtNacac can display a distinct dual-emission with both fluorescence and phosphorescence, whereas only a single fluorescence emission was observed in the air, which is different from the B-embedded neutral complex PtBacac with only a single phosphorescence emission at any atmosphere, as well confirmed by lifetime measurement and oxygen sensing experiments. DFT calculations reveal that unusual ligand-to-metal charge transfer (LMCT) excited state character and low spin orbit coupling (SOC) elements can be found in N-embedded complexes due to the strong electron-donating ability of the N-embedded unit. Based on this, as a novel ratiometric oxygen probe with a simple structure, PtNacac can be successfully used to examine intracellular oxygen levels by monitoring both fluorescence and phosphorescence signals via ratiometric photoluminescence imaging and time-resolved luminescence imaging (TRLI) technology. This work provides a completely new idea for designing fluorescence/phosphorescence dual-emissive complexes.

Efficient FRET Approaches toward Copper(II) and Cyanide Detections via Host-Guest Interactions of Photo-Switchable [2]Pseudo-Rotaxane Polymers Containing Naphthalimide and Merocyanine Moieties.

A supramolecular [2]pseudo-rotaxane containing a naphthalimide-based pillararene host and a spiropyran-based imidazole guest was synthesized and investigated in a semiaqueous solution with 90% water fraction. Upon UV exposure, the close-form structure of nonemissive spiropyran guest could be transformed into the open-form structure of red-emissive merocyanine guest reversibly, which was utilized as a monofluorophoric sensor to detect copper(II) and cyanide ions. Moreover, the naphthalimide host as an energy donor with green photoluminescence (PL) emission at 505 nm was complexed with the merocyanine guest as an energy acceptor with red PL emission at 650 nm in 1:1 molar ratio to generate a [2]pseudo-rotaxane polymer, which was further verified by the diffusion coefficients of DOSY nuclear magnetic resonance (NMR) measurements. Due to the Förster resonance energy transfer (FRET) processes, the bifluorophoric [2]pseudo-rotaxane produced more efficient ratiometric PL behavior to induce a stronger red PL emission than that of the monofluorophoric guest; therefore, the PL sensor responses of the supramolecular [2]pseudo-rotaxane toward copper(II) and cyanide ions could be further amplified via the FRET-OFF processes to turn off red PL emission of the reacted merocyanine acceptor and to recover green PL emission of the naphthalimide donor. Accordingly, the best and prominent values of the limit of detection (LOD) for the host-guest detections toward Cu2+ and CN- were 0.53 and 1.34 μM, respectively. The highest red MC emission with the optimum FRET processes of [2]pseudo-rotaxane was maintained around room temperature (20-40 °C) in wide pH conditions (pH = 3-13), which can be utilized in the cell viability tests to prove the nontoxic and remarkable biomarker of [2]pseudo-rotaxane to detect Cu2+ and CN- in living cells. The developed FRET-OFF processes with ratiometric PL behavior of the bifluorophoric supramolecular [2]pseudo-rotaxane polymer will open a new avenue to the future applications of chemo- and biosensors.

Carbon dots and ruthenium doped oxygen sensitive nanofibrous membranes for monitoring the respiration of agricultural products

During the storage of agricultural products, the oxygen concentration in the packages represents the level of food respiration and hence indicates its freshness. Herein, self-referenced photoluminescent oxygen sensitive fibrous membranes were prepared, with the inclusion of an oxygen-sensitive probe, i.e. tris (4,7-diphenyl-1,10-phenanthroline) ruthenium (II) dichloride (RuDPP), with an oxygen-insensitive luminophore, i.e. silane-functionalized carbon dots (SiCDs). Silicone was selected as the matrix, obtained via sol-gel process, and was electrospun to get nanofibers containing mesoporous microstructure and with high oxygen permeability. The as-prepared RuDPP@SiCDs/SiO2 fibrous membranes possessed hydrophobicity and exhibited ideal oxygen sensitivity, which realized a remote evaluation of the freshness of packaged fruits, through ratiometric photoluminescence imaging on the concentration change of environmental oxygen. The results indicate that such kind of oxygen-sensitive fiber membranes are capable as an optical oxygen sensor for agricultural applications.

A QDs Nanocomposites-Based Photoluminescence Ratiometric Method for Selective and Visual Cadmium Detection Combining with Smartphone-Based PL E-Eye

Photoluminescence (PL) sensors based on quantum dots (QDs) are difficult to achieve exact detection in sample waters. In this paper, polyvinyl alcohol (PVA) based CdTe/ZnS/CdS QDs and fluorescein isothiocyanate (FITC) fluorophores were used to build a ratiometric PL sensor. Combining with the homemade smartphone-based PL E-eye, the Cd2+ exact detection can be achieved. PVA was used to connect QDs and FITC fluorophores without unnecessary ligand exchange and purification. For QDs fluorophore, ethylenediaminetetraaceticacid (EDTA) was used on the surface to induce the specifically Cd2+ recognition site. For FITC fluorophore, the PL remains unchanged in this experiment. Thus, the ratio of two fluorophores can be used to provide a built-in correction. The PL changes with the increase of Cd2+ concentrations could be displayed as a visual color change on the smartphone. Further quantitative analysis could be carried out by the RGB value of the picture through the App in less than 1 min The ratio of R/G is linear to Cd2+ concentration in the range of 1–2000 μg l−1 with a low LOD of 0.057 μg l−1 (S/N). Compared with traditional analysis methods, the PL ratiometric method with PL E-eye is portable, rapid, visible and highly selective especially in discriminate Cd2+ from Zn2+.

Highly Efficient Förster Resonance Energy Transfer Modulations of Dual-AIEgens between a Tetraphenylethylene Donor and a Merocyanine Acceptor in Photo-Switchable [2]Rotaxanes and Reversible Photo-Patterning Applications.

A series of novel photo-switchable [2]rotaxanes (i.e., Rot-A-SP and Rot-B-SP before and after shuttling controlled by acid-base, respectively) containing one spiropyran (SP) unit (as a photochromic stopper) on the axle and two tetraphenylethylene (TPE) units on the macrocycle were synthesized via click reaction. Upon UV/visible light exposure, both mono-fluorophoric rotaxanes Rot-A-SP and Rot-B-SP with the closed form (i.e., non-emissive SP unit) could be transformed into the open form (i.e., red-emissive merocyanine (MC) unit) to acquire their respective bi-fluorophoric Rot-A-MC and Rot-B-MC reversibly. The aggregation-induced emission (AIE) properties of bi-fluorophoric TPE combined with MC AIEgens of these designed rotaxanes and mixtures in semi-aqueous solutions induced interesting ratiometric photoluminescence (PL) and Förster resonance energy transfer (FRET) behaviors, which were further investigated and verified by dynamic light scattering (DLS), X-ray diffraction (XRD), and time-resolved photoluminescence (TRPL) measurements along with theoretical studies. Accordingly, in contrast to the model axle (Axle-MC) and the analogous mixture (Mixture-MC, containing the axle and macrocycle components in a 1:1 molar ratio), more efficient FRET behaviors and stronger red PL emissions were obtained from dual-AIEgens between a blue-emissive TPE donor (PL emission at 468 nm) and a red-emissive MC acceptor (PL emission at 668 nm) in both novel photo-switchable [2]rotaxanes Rot-A-MC and Rot-B-MC under various external modulations, including water content, UV/Vis irradiation, pH value, and temperature. Furthermore, the reversible fluorescent photo-patterning applications of Rot-A-SP in a powder form and a solid film with excellent photochromic and fluorescent behaviors are first investigated in this report.

Y0.4Gd1.6O2S: Eu nanocrystals for ratiometric Pb2+ ions sensing via selectively non-radiative relaxation

Toxic divalent lead ions are broadly chosen for famous perovskite systems with great optoelectronic performances, which motivates us to explore a novel strategy for its determination with high sensitivity. In this work, lanthanide doped inorganic oxysulfide nanocrystals (NCs) are verified to be excellent candidates for ratiometric Pb2+ ions sensing. Specifically, the photoluminescence (PL) intensity of Eu3+ ions in Y0.4Gd1.6O2S NCs decreases gradually with the increase of Pb2+ ions concentration under the excitation of 254 nm, while its intensity keep unchanged under 311 nm excitation. In this occasion, a ratiometric PL sensing route for Pb2+ ions is obtained through using I311 as intrinsic reference. The detection limit for Pb2+ ions is 7.1 nM. This work provides a new ratiometric PL sensing route for Pb2+ ions via selectively non-radiative relaxation.

Photoluminescence and Electrochemiluminescence Dual-Signaling Sensors for Selective Detection of Cysteine Based on Iridium(III) Complexes.

Cysteine (Cys) is important in biosynthesis, detoxification, and metabolism. The selective detection of Cys over structurally similar homocysteine (Hcy) or glutathione (GSH) remains an immense challenge. Although there are many methods for detecting Cys, photoluminescence (PL) and electrochemiluminescence (ECL) techniques are well-suited for clinical diagnostics and analytical technology because of their high sensitivities. Herein, we report PL and ECL dual-channel sensors using cyclometalated iridium(III) complexes for the discrimination of Cys from Hcy and GSH. The sensors react with cysteine preferentially because of kinetic differences in intramolecular conjugate addition/cyclization, enabling phosphorescence enhancement and ECL decrease in the blue-shifted region. Sensor 1 shows ratiometric PL turn-on and ECL turn-off for Cys. In addition, unique ECL-enhancing behavior of sensor 1 toward GSH enables discrimination between Cys and GSH. Sensor 1 was successfully applied to the detection of Cys in human serum by the ECL method. We demonstrate the first case of a Cys-selective PL and ECL dual-channel chemodosimetric sensor based on cyclometalated iridium(III) complexes and expect that the rational design of efficient PL and ECL dual-channel sensors will be useful in diagnostic technology.

Quantum Ensembles of Silicon Nanoparticles: Discrimination of Static and Dynamic Photoluminescence Quenching Processes.

Porous silicon photoluminescence is characterized by a broad emission band that displays unusually long (tens to hundreds of micro-seconds), wavelength-dependent emissive lifetimes. The photoluminescence is associated with quantum confinement of excitons in silicon nanocrystallites contained within the porous matrix, and the broad emission spectrum derives from the wide distribution of nanocrystallite sizes in the material. The longer emissive lifetimes in the ensemble of quantum-confined emitters correspond to the larger nanocrystallites, with their longer wavelengths of emission. The quenching of this photoluminescence by aromatic, redox-active molecules aminochrome (AMC), dopamine, adrenochrome, sodium anthraquinone-2-sulfonate, benzyl viologen dichloride, methyl viologen dichloride hydrate, and ethyl viologen dibromide is studied, and dynamic and static quenching mechanisms are distinguished by the emission lifetime analysis. Because of the dependence of the emission lifetime on emission wavelength from the silicon nanocrystallite ensemble, a pronounced blue shift is observed in the steady-state emission spectrum upon exposure to dynamic-type quenchers. Conversely, static-type quenching systems show uniform quenching across all emission wavelengths. Thus, the difference between static and dynamic quenching mechanisms is readily distinguished by ratiometric photoluminescence spectroscopy. The application of this concept to imaging of AMC, the oxidized form of the neurotransmitter dopamine that is of interest for its role in neurodegenerative diseases, is demonstrated. It is found that static electron acceptors result in no ratiometric contrast, while AMC shows a strong contrast, allowing ready visualization in a 2-D imaging experiment.

Monocycloplatinated Solvento Complex Displays Turn-on Ratiometric Phosphorescence Responses to Histamine.

The study of biological histamine (HA) requires probes capable of ratiometric photoluminescence detection of HA. We discovered that a monocycloplatinated complex having two solvento ligands ([Pt(2-(2-naphthyl)quinolinate)(NCCH3)2]ClO4) could produce ratiometric phosphorescence responses to HA in aerated aqueous solutions buffered to pH 7.4. The HA response was characterized with a hypsochromic shift of an emission peak wavelength from 635 to 567 nm. The corresponding phosphorescence intensity ratio (i.e., I567 nm/ I635 nm) increased from 0.26 to 1.90. Spectroscopic and spectrometric investigations indicated an occurrence of spontaneous displacement of the labile CH3CN ligands with HA. An independently prepared HA adduct supported this notion. The ratiometric phosphorescence responses to HA were highly tolerant to other biological stimuli, including changes in pH and the presence of biometals and biological Lewis bases such as amino acids, nucleosides, biothiols, neurotransmitters, and small molecular metabolites. Of note was the high selectivity toward HA over common biological ligands, including histidine, cysteine, and homocysteine, which was ascribed to tighter HA binding. Our phosphorescence measurements employing Boc-protected derivatives of HA suggested that the bis-chelate motif involving imidazolyl and terminal amino groups was crucial for eliciting the ratiometric phosphorescence signaling. Finally, the bioimaging utility of the HA probe was validated using RAW 264.7 macrophages that were exogenously supplemented with HA or stimulated with thapsigargin to enrich intracellular HA. Ratiometric phosphorescence imaging microscopy experiments demonstrated the ability of the probe for monitoring intracellular HA uptake. In addition, photoluminescence lifetime imaging microscopy techniques could be applied for visualization of HA within the RAW 264.7 cells, because the HA binding elongated the photoluminescence lifetime. Our study demonstrated the promising utility of inner-sphere interactions of phosphorescent Pt(II) complexes for detection of biological HA.