Photoswitching of bis-spiropyran using near-infrared excited upconverting nanoparticles

Bis-spiropryran molecules were grafted onto the surface of upconverting nanoparticles. Fluorescence resonance energy transfer from the upconverting nanoparticles to the surface bis-spiropyran molecules triggered the transformation of the ring-closed bis-spiropyran to the ring-open bis-merocyanine forms.     

Multimodal fluorescence modulation using molecular photoswitches and upconverting nanoparticles

The intensity and colour of the light emitted from upconverting nanoparticles is controlled by the state of photoresponsive dithienylethene ligands decorated onto the surface of the nanoparticles. By selectively activating one or both ligands in a mixed, 3-component system, a multimodal read-out of the emitted light is achieved.     

Near-infrared light-triggered dissociation of block copolymer micelles using upconverting nanoparticles

We demonstrate a novel strategy enabling the use of a continuous-wave diode near-infrared (NIR) laser to disrupt block copolymer (BCP) micelles and trigger the release of their "payloads". By encapsulating NaYF(4):TmYb upconverting nanoparticles (UCNPs) inside micelles of poly(ethylene oxide)-block-poly(4,5-dimethoxy-2-nitrobenzyl methacrylate) and exposing the micellar solution to 980 nm light, photons in the UV region are emitted by the UCNPs, which in turn are absorbed by o-nitrobenzyl groups on the micelle core-forming block, activating the photocleavage reaction and leading to the dissociation of BCP micelles and release of co-loaded hydrophobic species. Our strategy of using UCNPs as an internal UV or visible light source upon NIR light excitation represents a general and efficient method to circumvent the need for UV or visible light excitation that is a common drawback for light-responsive polymeric systems developed for potential biomedical applications.     

Multiplexed near-infrared in vivo imaging complementarily using quantum dots and upconverting NaYF4:Yb3+,Tm3+ nanoparticles

A new multiplexed NIR in vivo imaging is showcased by using quantum dots and NaYF(4):Yb(3+),Tm(3+) nanoparticles. The 'temporal' multiplexing is demonstrated by alternating the excitation wavelengths and unmixing the emissions of different probes. Multiplexed cellular imaging and the cellular trafficking in animal models are shown.     

Quenching of the luminescence of upconverting luminescent nanoparticles by heavy metal ions

We report that the luminescence of upconverting luminescent nanoparticles (UCLNPs) is quenched by heavy metal ions and halide ions in aqueous solution. The UCLNPs consist of hexagonal NaYF₄ nanocrystals doped with trivalent rare earth ions and were synthesized by both the oleic acid (solvothermal) method and the ethylenediaminetetraacetic acid (co‐precipitation) method. Quenching was studied for the Cu^II, Hg^II, Pb^II, Cd^II, Co^II, Ag^I, Fe^III, Zn^II, bromide, and iodide ions and is found to be particularly strong for Hg^II. Stern–Volmer plots are virtually linear up to quencher concentrations of 10–25 mM , but deviate from linearity at higher quencher concentrations, because static quenching causes an additional effect. The UCLNPs display two main emission bands (blue, green, red or near‐infrared), and the quenching efficiencies for these are found to be different. The effect seems to be generally associated with UCLNPs because it was observed for all UCLNPs doped with trivalent lanthanide ions including Yb^III, Er^III, Ho^III, and Tm^III. The results are discussed in terms of quenching mechanisms and with respect to potential applications such as optical sensing.     

Reversible two-photon photoswitching and two-photon imaging of immunofunctionalized nanoparticles targeted to cancer cells

Both photoswitchable fluorescent nanoparticles and photoactivatable fluorescent proteins have been used for super-resolution far-field imaging on the nanometer scale, but the photoactivating wavelength for such photochemical events generally falls in the near-UV (NUV) region (<420 nm), which is not preferred in cellular imaging. However, using two near-IR (NIR) photons that are lower in energy, we can circumvent such problems and replace NUV single-photon excitations (e.g., 390 nm) with NIR two-photon excitations (e.g., 780 nm). Thus, we have demonstrated that alternating 780 nm NIR two-photon and 488 nm single-photon excitations induces reversible on-off fluorescence switching of immunotargeted nanoparticles in the human breast cancer cell line SK-BR-3. Herein, two-photon absorption not only caused spiropyran-merocyanine photoisomerization within the particles but also imparted red fluorescence. In comparison with single-photon NUV excitations, two-photon NIR laser excitations can potentially reduce absorption-related photodamage to living systems because cellular systems absorb much more weakly in the NIR.     

Synthesis of branched Au nanoparticles with tunable near-infrared LSPR using a zwitterionic surfactant

Asymmetric branched gold nanoparticles are obtained using for the first time in the seed-growth approach a zwitterionic surfactant, laurylsulfobetaine, whose concentration in the growth solution allows to control both the length to base-width ratio of the branches and the LSPR position, that can be tuned in the 700-1100 nm near infrared range.     

Anomalous phase behavior in a model fluid with only one type of local structure

We present evidence that the concurrent existence of two populations of particles with different effective diameters is not a prerequisite for the occurrence of anomalous phase behaviors in systems of particles interacting through spherically symmetric unbounded potentials. Our results show that an extremely weak softening of the interparticle repulsion, which yields a single nearest-neighbor separation, is able to originate a wide spectrum of unconventional features including reentrant melting, solid polymorphism, as well as thermodynamic, dynamic, and structural anomalies. These findings extend the possibility of anomalous phase behavior to a class of systems much broader than currently assumed.     

Glucose detection at attomole levels using dynamic light scattering and gold nanoparticles

Glucose is directly related to brain activity and to diabetes.Therefore,developing a rapid and sensitive method for glucose detection is essential.Here,label-free glucose detection at attomole levels was realized by detecting the average diameter change of gold nanoparticles(AuNPs)utilizing dynamic light scattering(DLS).Single-strand DNA(ssDNA)adsorbed into the AuNPs’surfaces and prevented them from aggregating in solution that contained NaCl.However,ssDNA cleaved onto ssDNA fragments upon addition of glucose,and these fragments could not adsorb onto the AuNPs’surfaces.Therefore,in high-salt solution,AuNPs would aggregate and their average diameter would increase.Based on monitoring the average diameter of AuNPs with DLS,glucose could be detected in the range from 15 pmol/L to 2.0 nmol/L,with a detection limit of 8.3 pmol/L.Satisfactory results were also obtained when the proposed method was applied in human serum glucose detection.     

Preparation of peptide-functionalized gold nanoparticles using one pot EDC/sulfo-NHS coupling

Although carbodiimides and succinimides are broadly employed for the formation of amide bonds (i.e., in amino acid coupling), their use in the coupling of peptides to water-soluble carboxylic-terminated colloidal gold nanoparticles remains challenging. In this article, we present an optimization study for the successful coupling of the KPQPRPLS peptide to spherical and rodlike colloidal gold nanoparticles. We show that the concentration, reaction time, and chemical environment are all critical to achieving the formation of robust, peptide-coated colloidal nanoparticles. Agarose gel electrophoresis was used for the characterization of conjugates.     

Multi-element analysis by energy-dispersive X-ray fluorescence using a simple calibration procedure, requiring only one or two standards

Summary A reliable method for the determination of the slopes of calibration curves by interpolation is described for multi-element analysis by energy-dispersive X-ray fluorescence. The method is based on normalizing theoretically calculated curves of slope vs. atomic number, with the aid of one or two standards. It is applied to the analysis of powdered samples, using correction via the Comptonscattering peak to compensate for small matrix effects.

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Multielementanalyse durch energiedispersive Röntgenfluorescenz mit einem einfachen Eichverfahren, das nur ein oder zwei Standards erfordert

Zusammenfassung Eine zuverlässige Methode für die Bestimmung der Steigungen der Eichkurven für die Multielementanalyse durch energiedispersive Röntgenfluorescenz wird beschrieben. Die Methode basiert auf der Normierung theoretisch berechneter Kurven für die Abhängigkeit der Steigung von der Ordnungszahl mit Hilfe von ein oder zwei Standards. Sie wird angewendet auf die Analyse von Pulverproben unter Benutzung der Compton-Streupeak-Korrektur zum Ausgleich kleinerer Matrixeffekte.

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On leave from Rand Afrikaans University, Johannesburg, Republic of South Africa     

Free-radical polymerization upon near-infrared light irradiation,merging photochemical and photothermal initiating methods

Polymerization of (meth)acrylate resins upon near-infrared (NIR) light remains a huge challenge. In this study, a new photoinduced method of polymerization of methacrylic monomers is presented, originally merging a photochemical and a photothermal pathway. A four-component system is proposed comprising an NIR dye combined with an iodonium salt, a phosphine, and a thermal initiator. A selection of dyes is suggested regarding electron transfer properties and/or light-to-heat conversion abilities. Several thermal initiators are studied: an alkoxyamine (BlocBuilder MA), an azo derivative, and a peroxide. For the first time, an NIR absorbing dye is used in photopolymerization using both its capacities of light-to-heat conversion and its ability to initiate an electron transfer reaction. Three wavelengths of irradiation will be presented here: 785, 940, and 1064 nm. These long wavelengths are challenging because the energy of photons is extremely low but these wavelengths offer significant advantages in term of light penetration (e.g., for the access to composites through photopolymerization processes). The different systems presented here exhibit high and rapid conversions of methacrylate functions. The underlying chemical mechanism will be fully depicted by real-time Fourier transform infrared spectroscopy and thermal imaging measurements. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 300–308     

Hydrothermal synthesis of Nd-doped orthoborate nanoparticles that emit in the near-infrared

The Y_1−xBO₃:Nd_x nanoparticles have been prepared by a mild hydrothermal method and luminescence properties in the NIR of Y_1−xBO₃:Nd_x nanoparticles have been investigated. The Y_1−xBO₃:Nd_x nanoparticles with 0-15 mol% Nd³⁺ were found to be isostructural with YBO₃ crystal. The preferential nucleation and growth of Y_1−xBO₃:Nd_x nanoparticles along a certain plane can be observed and the dopants of Nd³⁺ ions would help to weaken the selectivity of the growth of Y_1−xBO₃:Nd_x nanoparticles. The emission spectrum in the NIR of Y_1−xBO₃:Nd_x nanoparticles consisted of a few narrow, sharp lines corresponding to the and transitions of Nd³⁺ ions when pumped with 800 nm laser radiation. The luminescence intensity of Y_1−xBO₃:Nd_x nanoparticles increased remarkably with the increase in the doping concentration of Nd³⁺ ions and reached a maximum at approximately 10 mol%.     

Optimization of silver nanoparticles for surface enhanced Raman spectroscopy of structurally diverse analytes using visible and near-infrared excitation

Several experimental parameters affecting surface enhanced Raman (SER) signals using 488, 785 and 1064 nm excitation for eight diverse analytes are reported. Citrate reduced silver colloids having average diameters ranging from 40 ± 10 to 100 ± 20 nm were synthesized. The nanoparticles were characterized by transmission electron microscopy, dynamic light scattering and absorbance spectrophotometry before and after inducing nanoparticle aggregation with 0.99% v/v 0.5 M magnesium chloride. The nanoparticle aggregates and SERS signal were stable between 30 and 90 minutes after inducing aggregation. For the analytes 4-mercaptopyridine, 4-methylthiobenzoic acid and the dipeptide phenylalanine-cysteine using all three excitation wavelengths, the highest surface area adjusted SER signal was obtained using 70 ± 20 nm nanoparticles, which generated 290 ± 40 nm aggregates with the addition of magnesium chloride. The decrease in the SER signal using non-optimum colloids was 12 to 42% using 488 nm excitation and larger decreases in signal, up to 92%, were observed using near infrared excitation wavelengths. In contrast, pyridine, benzoic acid, and phenylalanine required 220 ± 30 nm aggregates for the highest SER signal with 785 or 1064 nm excitation, but larger aggregates (290 ± 40 nm) were required with 488 nm excitation. The optimum experimental conditions measured with the small molecule analytes held for a 10 amino acid peptide and hemoglobin. Reproducible SERS measurements with 2 to 9% RSD have been obtained by considering nanoparticle size, aggregation conditions, excitation wavelength and the nature of the analyte-silver interaction.     

Immunoassay for serum alpha-fetoprotein using silver nanoparticles and detection via resonance light scattering

The assay for alpha-fetoprotein (AFP) is based on the use of immobilized anti-AFP labeled with silver nanoparticles (AgNPs). The immunoreaction between the labeled antibody against AFP and free AFP takes place in pH 6.0 solution and leads to the formation of the respective immunocomplex which displays enhanced resonance light scattering (RLS) intensity at 480 nm. Under the optimal conditions, the intensity of the enhanced RLS is proportional to the concentration of AFP in the range from 0.10 to 50 ng mL^?1, with a detection limit of 40 pg mL^?1. The characteristics of RLS, the immunocomplex, the immuno response, and the optimum conditions of the immunoreaction have been investigated. The concentration of AFP in 20 serum specimens was determined by the new assay, and results are consistent with those obtained with a commercially available ELISA kit.

One-step assay for detecting influenza virus using dynamic light scattering and gold nanoparticles

Herein we detail the development of a simple, rapid, and sensitive method for quantitative detection of influenza A virus using dynamic light scattering (DLS) and gold nanoparticle (AuNP) labels. Influenza-specific antibodies are conjugated to AuNPs, and aggregation of the AuNP probes is induced upon addition of the target virus. DLS is used to measure the extent of aggregation and the mean hydrodynamic diameter is correlated to virus concentration. The effects of nanoparticle concentration and size on the analytical performance of the assay were systematically investigated. It was determined that decreasing the AuNP probe concentration improves the detection limit while the effect of changing the AuNP size is minimal. Optimization of the assay provided a detection limit of <100 TCID(50)/mL which is 1-2 orders of magnitude improved over commercial diagnostic kits without increasing the assay time or complexity. Additionally, this assay was demonstrated to perform equivalently for influenza virus prepared in different biological matrices.     

Experimental and theoretical studies of the optimisation of fluorescence from near-infrared dye-doped silica nanoparticles

There is substantial interest in the development of near-infrared dye-doped nanoparticles (NPs) for a range of applications including immunocytochemistry, immunosorbent assays, flow cytometry, and DNA/protein microarray analysis. The main motivation for this work is the significant increase in NP fluorescence that may be obtained compared with a single dye label, for example Cy5. Dye-doped NPs were synthesised and a reduction in fluorescence as a function of dye concentration was correlated with the occurrence of homo-Förster resonance energy transfer (HFRET) in the NP. Using standard analytical expressions describing HFRET, we modelled the fluorescence of NPs as a function of dye loading. The results confirmed the occurrence of HFRET which arises from the small Stokes shift of near-infrared dyes and provided a simple method for predicting the optimum dye loading in NPs for maximum fluorescence. We used the inverse micelle method to prepare monodispersed silica NPs. The NPs were characterised using dynamic light scattering, UV spectroscopy, and transmission electron microscopy (TEM). The quantum efficiency of the dye inside the NPs, as a function of dye loading, was also determined. The fluorescent NPs were measured to be approximately 165 times brighter than the free dye, at an optimal loading of 2% (w/w). These experimental results were in good agreement with model predictions.

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Figure The change in nanoparticle fluorescence versus increased dye loading modelled using homo-Förster resonance energy transfer.

     

Fabrication of acrylate monolith using photopolymerization: Effect of light intensity on electrochromatographic performance

A hexyl acrylate monolith was prepared via photopolymerization into a cyclic olefin copolymer micro-device for reversed-phase electrochromatography purposes. This work deals with the influence of the irradiation conditions (irradiation time and light intensity) used during synthesis on the electrochromatographic performances of the monolithic column obtained. Up to day, the monolith structure was often controlled by means of irradiation time at constant light intensity, but the effect of light intensity (irradiance) on the monolith structure was scarcely considered. This study shows a strong effect of light intensity on electrochromatographic efficiency. Using an optimal light intensity of 4.7 mW/cm(2) and an irradiation time of a few minutes allows obtaining heights equivalent to a theoretical plate reaching down to 5 μm for the reversed-phase separation of six polycyclic aromatic hydrocarbons.     

Selective imaging and killing of cancer cells with protein-activated near-infrared fluorescing nanoparticles

We present a general approach for the selective imaging and killing of cancer cells using protein-activated near-infrared emitting and cytotoxic oxygen generating nanoparticles. Poly(propargyl acrylate) (PA) particles were surface modified through the copper-catalyzed azide/alkyne cycloaddition of azide-terminated indocyanine green (azICG), a near-infrared emitter, and poly(ethylene glycol) (azPEG) chains of various molecular weights. The placement of azICG onto the surface of the particles allowed for the chromophores to complex with bovine serum albumin when dispersed in PBS that resulted in an enhancement of the dye emission. In addition, the inclusion of azPEG with the chromophores onto the particle surface resulted in a synergistic ninefold enhancement of the fluorescence intensity, with azPEGs of increasing molecular weight amplifying the response. Human liver carcinoma cells (HepG2) overexpress albumin proteins and could be employed to activate the fluorescence of the nanoparticles. Preliminary PDT studies with HepG2 cells combined with the modified particles indicated that a minor exposure of 780 nm radiation resulted in a statistically significant reduction in cell growth.