Rapid detection of microalgae cells based on upconversion nanoprobes.

The quantification of microalgae cells is crucial for the treatment of ships' ballast water. However, achieving rapid detection of microalgae cells remains a substantial challenge. Here, we develop a new method for rapid and effective detection of microalgae concentration by utilizing upconversion nanoprobes (UCNPs) of NaYF4:Er3+,Tm3+. Three ligands, carboxylated methoxypolyethylene glycols with 5000 and 2000 molecular weights (mPEG-COOH-5, mPEG-COOH-2) and D-gluconic acid sodium salt (DGAS), were used to convert hydrophobic UCNPs into a hydrophilic state through modification. The results show that the mPEG-COOH-5 modified UCNPs present the highest stability in an aqueous solution. Fourier Transform Infrared Spectroscopy (FTIR) measurements reveal the presence of a significant number of -COOH functional groups on UCNPs after the mPEG-COOH-5 modification. These -COOH groups enhance the hydrophilicity and biocompatibility of UCNPs. The soluble UCNPs were directly mixed with microalgae, and the upconversion luminescence (UCL) spectra of the UCNPs were recorded immediately after thorough shaking. This greatly reduces the measurement time and could realize rapid onboard detection. In this sensing procedure, the UCNPs with red UCL functioned as energy donors, while microalgae with red absorption served as an energy acceptor. The UCL gradually diminishes with an increase in microalgae concentration based on the inner filter effect, thus establishing a relationship between UCL and microalgae concentration. The accuracy of the detection is further validated through the traditional microscope counting method. These findings pave the way for a novel rapid strategy to assess microalgae concentration using UCNPs.

Color-reversible fluorescence tracking for the dynamic interaction of SO2 with Hg2+ in living cells.

Mercury ion (Hg2+) is one of the most threatening substances to human health, and the mercury poisoning can damage physiological homeostasis severely in human, even cause death. Intriguingly, Sulfur dioxide (SO2), a gas signal molecule in human, can specifically interact with Hg2+ for relieving mercury poisoning. However, the dynamic interaction of Hg2+ with SO2 at the tempospatial level and the correlation between Hg2+ and SO2 in the pathological process of mercury poisoning are still elusive. Herein, we rationally designed a reversible and dual color fluorescent probe (CCS) for dynamically visualizing Hg2+ and SO2 and deciphering their interrelationship in mercury poisoning. CCS held good sensitivity, selectivity and reversibility to Hg2+ and SO2, that enabled CCS to specifically detect SO2 and Hg2+ via cyan fluorescence channel (centered around 485 nm) and red fluorescence channel (centered around 679 nm), respectively. Notably, the separate fluorescence signal changes of CCS realized the dynamic tracing of Hg2+ and SO2 in living cells, and presented the potential for exploring the correlation between SO2 and Hg2+ in mercury poisoning.

Promising lanthanide-doped double molybdates KYb(MoO4)2 phosphors for highly efficient upconversion luminescence and temperature sensing.

Here we report the highly efficient upconversion luminescence (UCL) and optical temperature sensing based on the novel host of KYb(MoO4)2 doped with trivalent lanthanide (Ln3+) ions at 980 nm excitation. The high Yb3+ concentration and unique ordered layer structure in KYb(MoO4)2 host are beneficial for the enhancement of UCL efficiency by improving the absorption and the negative migration of excitation energy. Ho3+, Er3+, and Tm3+ ions were selected to singly dope the KYb(MoO4)2 host, achieving three primary colors of red, green, blue UCL, respectively. At the optimal doping concentration, the blue upconversion quantum yield (UCQY) of the KYb(MoO4)2: 1.0%Tm3+ phosphor reaches 0.13%, which is rare for the Tm3+-doped oxides. By leveraging the efficient blue light, we achieved high-brightness white UCL by co-doping Ho3+ in KYb(MoO4)2: Tm3+. Furthermore, the temperature sensing performance of the KYb(MoO4)2: Tm3+, Ho3+ phosphors operating within the first biological window (BW-I) was evaluated based on a thermo-responsive fluorescence intensity ratio (FIR) of far-red to near-infrared (NIR) emission from completely separated 3F2,3/3H4 → 3H6 transitions of Tm3+. At the excitation of 980 nm, the maximum absolute and relative sensitivities were determined as 0.25 × 10-3 K-1 at 673 K and 2.84% K-1 at 303 K, respectively. These results indicate that the double alkali-rare-earth molybdate KYb(MoO4)2 can be used as a promising host to achieve highly efficient UCL and temperature sensing, suggesting potential applications in the fields of anti-counterfeiting, displays, and non-contact temperature sensors.

Upconversion nanoparticles@single-walled carbon nanotubes composites as efficient self-monitored photo-thermal agents.

Conventional photothermal therapy (PTT) usually relies on a macroscopic heat source to raise the temperature of tissues to 41-45 °C, which not only kills the pathological cells but causes severe side effects on nearby normal tissues, thus reducing the accuracy of PTT. Here we successfully fabricated nanocomposites of NaYF4:Yb3+,Tm3+@NaYF4:Yb3+@SiO2-SWCNTs, in which the upconversion nanoparticles (UCNPs) serve as real-time temperature-feedback moiety and the single-walled carbon nanotubes (SWCNTs) serve as efficient nano-heaters. The sample displays an excellent photothermal conversion capacity, i.e., the temperature of the aqueous dispersion increases from 23.3 °C up to 60.1 °C under 980 nm excitation due to the intense absorption and highly efficient heat generation of SWCNTs. Meanwhile, the temperature of the nanocomposites is monitored in real time based on the fluorescent intensity ratio of UCNPs. The in-vitro experiments demonstrate that the temperature of the nanocomposites at tissue injection of 1 mm can reach PTT temperature of 42.2 °C with a facile surrounding temperature of 36.2 °C under moderate laser power (980 nm, 2.0 W cm-2). These results provide a novel design for multifunctional nanocomposites that enable safe and controlled PTT.

Investigating the AIE and water sensing properties of a concise naphthalimide fluorophore.

A simple naphthalimide fluorophore NAP-H2O was designed and synthesized. Basic photophysical properties were investigated, especially found that the probe showed robust green fluorescence in water compared with that in various organic solvents, and the specific mechanism was conformed to be the aggregation induced emission (AIE) through dynamic light scattering (DLS) analysis, solid-state luminescence and fluorescence imaging. Accordingly, the capability of NAP-H2O for water sensing was examined, and good linear relationships between fluorescence intensities at the green emission band and the water content were obtained, enabling quantitative detection of water in organic solvents. The detection limits were calculated to be 0.004 % (v/v) in ACN, 0.117 % (v/v) in 1,4-dioxane, 0.028 % (v/v) in THF, 0.022 % (v/v) in DMF and 0.146 % (v/v) in DMSO, respectively. In addition, the probe presented fast response time within 5 s to water and good photostability. Furthermore, the probe was successfully applied for fast and naked-eye detection of water in organic solvents via test papers. This work provides a rapid, sensitive and naked-eye method for trace amount detection of water in organic solvents and has potential for practical applications.

Engineering Er3+-sensitized nanocrystals to enhance NIR II-responsive upconversion luminescence.

An Er3+-sensitized system with a high response to 1550 nm radiation in the second near-infrared window (NIR II) has been considered for a new class of potential candidates for applications in bio-imaging and advanced anti-counterfeiting, yet the achievement of highly efficient upconversion emission still remains a challenge. Here, we constructed a novel Er3+-sensitized core-shell-shell upconversion nanostructure with a Yb3+-enriched core as the emitting layer. This designed nanostructure allows the Yb3+ emitting layer to more efficiently trap and lock excitation energy by combining the interfacial energy transfer (IET) from the shell (Er3+) to the core (Yb3+), high activator Yb3+ content, and minimized energy back-transfer. As a result, the NIR II emission at 1000 nm is remarkably enhanced with a high quantum yield (QY) of 11.5%. Based on this trap and lock-in effect of the excitation energy in the Yb3+-enriched core, highly efficient 1550 nm-responsive visible and NIR upconversion emissions are also achieved by co-doping with other activator ions (e.g., Ho3+ and Tm3+). Our research provides a new functional design for improving NIR II-responsive upconversion luminescence, which is significant for developing practical applications.

Near-infrared-emitting upconverting BiVO4 nanoprobes for in vivo fluorescent imaging.

Near-infrared (NIR) emitting BiVO4:Yb3+,Tm3+ nanoparticles are synthesized by a new solvothermal strategy using solvents of oleic acid and methanol. The obtained BiVO4:Yb3+,Tm3+ samples show an average particle size of ≈164 nm and exhibit an asymmetry monoclinic crystal structure of BiVO4. At NIR excitation of 980 nm, the BiVO4:Yb3+,Tm3+ sample exhibits a nearly single NIR emission at ≈796 nm with extremely weak blue emissions from Tm3+ ions. These high-energy visible emissions are absorbed by the semiconducting host of BiVO4 that possesses a bandgap of ≈2.2 eV. Therefore, the NIR excitation to a single intense NIR emission fluorescent BiVO4 materials could be a potential ideal probe for deep-tissue high-resolution bioimaging. To validate the ability of BiVO4 materials for bio-applications, we conduct the cytotoxicity experiments. The results show that the cytotoxicity of HeLa cells is negligible at a concentration of 0.2 mg/ml of BiVO4:Yb3+,Tm3+ , and the cell viability approaches 90% at a high dosage of 0.5 mg/ml. The Daphnia magna and Zebrafish treated with nanoparticles (0.5 mg/ml) display bright NIR emission without any background, indicating the excellent in vivo fluorescent imaging capacity of BiVO4:Yb3+,Tm3+ nanoparticles. Our findings offer an environment-friendly strategy to synthesize BiVO4 UCL nanophosphors and provide a promising new class of fluorescent probes for biological applications.

Inhibition of Amyloid Aggregation and Toxicity with Janus Iron Oxide Nanoparticles.

Amyloid aggregation is a ubiquitous form of protein misfolding underlying the pathologies of Alzheimer's disease (AD), Parkinson's disease (PD) and type 2 diabetes (T2D), three primary forms of human amyloid diseases. While much has been learned about the origin, diagnosis and management of these neurological and metabolic disorders, no cure is currently available due in part to the dynamic and heterogeneous nature of the toxic oligomers induced by amyloid aggregation. Here we synthesized beta casein-coated iron oxide nanoparticles (ßCas IONPs) via a BPA-P(OEGA-b-DBM) block copolymer linker. Using a thioflavin T kinetic assay, transmission electron microscopy, Fourier transform infrared spectroscopy, discrete molecular dynamics simulations and cell viability assays, we examined the Janus characteristics and the inhibition potential of ßCas IONPs against the aggregation of amyloid beta (Aß), alpha synuclein (αS) and human islet amyloid polypeptide (IAPP) which are implicated in the pathologies of AD, PD and T2D. Incubation of zebrafish embryos with the amyloid proteins largely inhibited hatching and elicited reactive oxygen species, which were effectively rescued by the inhibitor. Furthermore, Aß-induced damage to mouse brain was mitigated in vivo with the inhibitor. This study revealed the potential of Janus nanoparticles as a new nanomedicine against a diverse range of amyloid diseases.

A thiocarbonate-caged fluorescent probe for specific visualization of peroxynitrite in living cells and zebrafish.

Peroxynitrite (ONOO-), a highly reactive oxygen species (ROS), is implicated with many physiological and pathological processes including cancer, neurodegenerative diseases and inflammation. In this regard, developing effective tools for highly selective tracking of ONOO- is urgently needed. Herein, we constructed a concise and specific fluorescent probe NA-ONOO for sensing ONOO- by conjugating an ONOO--specific recognition group ((4-methoxyphenylthio)carbonyl, a thiocarbonate derivative) with a naphthalene fluorophore. The probe, NA-ONOO, was in a dark state because the high electrophilicity of (4-methoxyphenylthio)carbonyl disturbs the intramolecular charge transfer (ICT) in the fluorophore. Upon treatment with ONOO-, the fluorescent emission was sharply boosted (quantum yield Φ: 3% to 56.6%) owing to an ONOO- triggered release of (4-methoxyphenylthio)carbonyl from NA-ONOO. Optical analyses showed that NA-ONOO presented high selectivity and sensitivity toward ONOO-. With good cell permeability and biocompatibility, the NA-ONOO probe was successfully applied to imaging and tracing exogenous and endogenous ONOO- in living cells and zebrafish. The probe NA-ONOO presents a new recognition group and a promising method for further investigating ONOO- in living systems.

Engineering Organic/Inorganic Nanohybrids through RAFT Polymerization for Biomedical Applications.

Despite many early accomplishments in nanomaterial design and synthesis, there remains a significant requirement for novel inorganic and organic nanohybrids with the potential to act as efficacious molecular imaging agents and theranostic vectors. The functionalization of surfactant-coated inorganic nanoparticles with polymer shells represents one of the most suitable and popular methods to synthesize polymer/inorganic nanohybrids for theranostic applications. Key requirements for effective imaging agent design include water dispersibility, biocompatibility and functionality to enable enhanced contrast magnetic resonance imaging (MRI), positron-emission tomography (PET), computed tomography (CT), or ultrasound modalities. In this Perspective, we highlight recent advances in the fabrication of organic/inorganic nanohybrids exploiting functionalized polymers prepared using reversible addition-fragmentation chain transfer (RAFT) polymerization. The polymer shells can imbue favorable traits to the nanoparticles such as stealth, image enhancement, storage (and release) of therapeutics, and sensitivity to biological stimuli. In this Perspective, we discuss the design and synthesis of hybrid nanoparticles and discuss current trends and future opportunities.

Fluorescence imaging of lysosomal hydrogen selenide under oxygen-controlled conditions.

Hydrogen selenide (H2Se), a central metabolite of Se supplements, displays critical biological functions in many physiological and pathological processes. To better understand its comprehensive function, especially those exerted in subcellular organelles, the development of specific assays is urgently needed. However, the methodology to detect H2Se is poorly developed. Here, we present a concise design strategy to obtain an activatable fluorescent probe (Se-1) for H2Se by utilizing an intramolecular photoinduced electron transfer (PET) process to switch the fluorescence. The probe is able to selectively react with H2Se without interference from intracellular reactive species, and has been successfully used to image the H2Se content in lysosomes. Additionally, with the aid of Se-1, we demonstrated that lysosomal H2Se can be generated and can gradually accumulate in HepG2 cells under hypoxic conditions. These applications make Se-1 a potential new candidate for deciphering the biological effects of H2Se on lysosomes in biology and pathology.

A two-photon fluorescent probe for basal formaldehyde imaging in zebrafish and visualization of mitochondrial damage induced by FA stress.

The detection of mitochondrial formaldehyde (FA) is of great significance because FA is generated through a one-carbon formaldehyde cycle in mitochondria, and abnormal elevations in FA levels can damage mitochondria by decreasing the mitochondrial membrane potential and inhibiting mitochondrial respiration. Herein, a mitochondria-targetable two-photon probe (Mito-FA-FP) has been well demonstrated. Mito-FA-FP is conjugated with hydrazine as the FA-reactive site and a pyridine derivate as the mitochondria-targetable moiety. After reacting with FA, Mito-FA-FP exhibits dramatic fluorescence enhancement (12-fold) due to suppression of the PET process in the probe and presents good selectivity as well as high sensitivity (LOD: 12.4 µM). Moreover, Mito-FA-FP can be utilized to monitor endogenous FA in mitochondria and evaluate mitochondrial damage caused by FA stress through observing mitochondrial morphology changes. With good two-photon absorption cross-section and high two-photon fluorescence contrast, Mito-FA-FP has been successfully employed for the two-photon fluorescence imaging of basal FA in zebrafish.

A lysosome targetable versatile fluorescent probe for imaging viscosity and peroxynitrite with different fluorescence signals in living cells.

The lysosome, which acts as the cellular recycling centre, is filled with numerous hydrolases that can degrade most cellular macromolecules. The abnormalities of the lysosome are closely associated with diseases, such as Hermanský-Pudlák syndrome, Griscelli syndrome and Chédiak-Higashi syndrome. Studies have shown that abnormal viscosity and the accumulation of reactive oxygen species (ROS) in the lysosome will disorder the normal function of the lysosome. In this research, a versatile fluorescent probe Lyso-NA has been developed for the multi-channel imaging of lysosomal viscosity and peroxynitrite (ONOO-). When excited at 550 nm, the Lyso-NA exhibited about a 50-fold increase in fluorescence at 610 nm and also with the increasing viscosity from 1.0 cP to 1410 cP, and about a 3.5-fold increase in fluorescence at 510 nm (excitation at 440 nm) together with the increasing ONOO-. These satisfactory response properties make it possible to use Lyso-NA to monitor changes in both viscosity and ONOO- inside the lysosome. To achieve its practical application, it was further demonstrated that Lyso-NA exhibits low cytotoxicity, and good cell permeability, and could be used to monitor lysosomal viscosity and ONOO- in living cells.

An ESIPT based naphthalimide chemosensor for visualizing endogenous ONOO- in living cells.

Based on ESIPT, we designed and synthesized a naphthalimide chemosensor N-CBT for selectively visualizing endo/exogenous peroxynitrite (ONOO-) in living cells. The incorporation of 2-benzothiazoleacetonitrile offers N-CBT a rare pre-existing eight-membered ring hydrogen bonding configuration, which is able to generate two types of emission of naphthalimide. Confirmed by calculation results, fast proton transfer from the hydroxyl group to the carbonyl group occurs along with excited-state energy transfer via the intramolecular H-bond, leading to a tautomeric transformation from the excited enol form to the excited keto form. In aqueous solution, the formation of intermolecular hydrogen bonding with water perturbs ESIPT and destroys the stable planar construction. By breaking the cyano carbon-carbon double bond in the presence of ONOO-, green fluorescence can be regenerated efficiently. As a result, 34-fold fluorescence enhancement at 518 nm was observed in response, and it showed a good linear relationship in the range of 1 to 14 µM with a detection limit of 37 nM. Subsequently, N-CBT was applied in visualizing cellular ONOO-, and it demonstrated great potential in selectively visualizing endo/exogenous peroxynitrite (ONOO-) in living cells.

An ultrafast responsive BODIPY-based fluorescent probe for the detection of endogenous hypochlorite in live cells.

Hypochlorite plays a significant role in various physiological and pathological processes; however, its role is still less clear than the role of other reactive oxygen species. Herein, we report an ultrafast responsive (<0.2 s) and highly selective probe B-Ts for hypochlorite with high sensitivity and a detection limit as low as 7.5 nM. The probe was compatible in a wide pH range of 4-13. More importantly, experiments in live cells showed that the probe could penetrate the cell membrane easily and was capable of imaging endogenous and exogenous hypochlorite specifically with a fast response.

Ratiometric fluorescence imaging of endogenous selenocysteine in cancer cell matrix.

Monitoring intracellular selenocysteine (Sec) is of significant interest for studying Sec metabolism and disease-relevant changes in Sec homeostasis. Herein, we rationally designed an ICT-based ratiometric probe (Rat-Sec) for selectively discriminating endogenous Sec in a live cell matrix. By utilizing an acrylate moiety, Rat-Sec manifested significantly ratiometric and red-shifted (∼117 nm) fluorescence signals within 1 min, and concomitantly demonstrated apparent color alteration from colorless to faint yellow in the presence of Sec. When applied to quantitatively detect Sec under physiological conditions, Rat-Sec gives a detection limit of 12 nM. Offering great advantages due to its ratiometric nature and high specificity and selectivity, Rat-Sec provides reliable fluorescence quantification and rapid tracking of exogenous and endogenous Sec in living cells.

UV-assisted synthesis of long-wavelength Si-pyronine fluorescent dyes for real-time and dynamic imaging of glutathione fluctuation in living cells.

Changes in intracellular glutathione (GSH) concentration are closely linked with various cellular physiological and pathological mechanisms. In the present work, four long-wavelength Si-pyronine (SiP) fluorescent dyes are readily synthesized via a UV-assisted aromatization reaction, and used for real-time, dynamic and reversible monitoring of GSH changes in vitro and in living cells. Based on the mechanism that Si atom incorporation greatly increases the pyronine affinity towards sulfhydryl (-SH), SiPs can undergo ultrafast and reversible Michael addition with biological thiols, leading to fluctuations in fluorescence intensity due to the interruption and restoration of their π-conjugation. Relying on the unique reactivity of SiPs with GSH under physiological conditions, the fluorescence intensity of SiPs responds to GSH changes with high sensitivity. SiPs also exhibit excellent photophysical properties including deep-red to near-infrared excitation wavelength (>600 nm), a high fluorescence efficiency (0.20-0.41) in aqueous media, suitable water-solubility and membrane permeability. Using SiP-Pr to incubate with HeLa cells, we achieved real-time, dynamic and repeated imaging of fluctuations in intracellular GSH homeostasis under N-ethylmaleimide stimulation.