Methylene Blue-Loaded Upconverting Hydrogel Nanocomposite: Potential Material for Near-Infrared Light-Triggered Photodynamic Therapy Application

The property of upconverting nanoparticles to convert the low-energy near-infrared (NIR) light into high-energy visible light has made them a potential candidate for various biomedical applications including photodynamic therapy (PDT). In this work, we show how a surface functionalization approach on the nanoparticle can be used to develop a nanocomposite hydrogel which can be of potential use for the PDT application. The upconverting hydrogel nanocomposite was synthesized by reacting 10-undecenoic acid-capped Yb3+/Er3+-doped NaYF4 nanoparticles with the thermosensitive N-isopropylacrylamide monomer. The formation of hydrogel was completed within 15 min and hydrogel nanocomposites showed strong enhancement in the visible light emission compared to the emission obtained from 10-undecenoic acid-capped Yb3+/Er3+-doped NaYF4 nanoparticles via the upconversion process (under 980 nm laser excitation). The upconverting hydrogel nanocomposites displayed high swelling behavior in water because of their porous nature. The porous structure ensured a higher loading of methylene blue dye (∼78% in 1 h) into the upconverting hydrogel, which was achieved via the swelling diffusion phenomenon. Upon excitation with the NIR light, the visible light emitted from the hydrogel activated the photosensitizer methylene blue which generated reactive oxygen species. Our results were able to show that the methylene blue-loaded composite hydrogel can be a potential platform for the future of NIR-triggered PDT in skin cancer treatment

A Luminescent Nanocrystal Marker for the Selective and Ultrasensitive Detection of Explosives

We developed a luminescent probe for the selective and sensitive detection of an explosive, i.e., picric acid (PA), based on the luminescence quenching of CeIII and TbIII co-doped Sr2GdF7 nanocrystals. A new colloidal synthesis route at low temperature (80 °C) was developed to synthesize the luminescent nanocrystals host matrix Sr2GdF7. The nanocrystals showed strong green emission under UV excitation (290 nm) by efficient energy transfer from CeIII to TbIII ions. The functionalization of the nanocrystals with l-cysteine (Cys) rendered the luminescent probe water dispersible. The presence of the −NH2 groups of Cys allowed the selective interaction of the probe with PA among other nitro explosives. This caused a 92 % reduction of the photoluminescence intensity of TbIII in the Sr2GdF7 nanocrystals, and led to the selective detection of PA with an unprecedented limit of detection (LOD) of approx. 4 nm

Methyl Oleate-Capped Upconverting Nanocrystals: A Simple and General Ligand Exchange Strategy To Render Nanocrystals Dispersible in Aqueous and Organic Medium

We report a simple and general ligand exchange strategy to functionalize the nanocrystals with both hydrophobic and hydrophilic ligands. This is achieved by first capping the Er/Yb-doped NaYF₄ nanocrystals with a weak ligand such as methyl oleate and subsequently ligand exchanged with various organic ligands which can strongly coordinate to the surface of the nanocrystals. The method involves only a simple stirring or sonication of the nanocrystals dispersion with the ligands of interest. Dicarboxylic acids such as sebacic acid, adipic acid, succinic acid, and malonic acid-functionalized nanocrystals which are difficult to achieve via thermal decomposition method were easily prepared by this ligand exchange strategy. In addition, low boiling point ligands like hexanoic acid can easily be coated over the surface of the Er/Yb-doped NaYF₄ nanocrystals. Both size and shape of the nanocrystals were preserved after the ligand exchange process. The methyl oleate-capped Er/Yb-doped NaYF₄ nanocrystals display strong upconversion emission after ligand exchanged with hydrophobic and hydrophilic molecules. The high stability of the nanocrystals after ligand exchange process is verified by performing time-dependent luminescent measurements at different pH, buffers, etc

Directed self-assembly of functionalized silica nanoparticles on molecular printboards through multivalent supramolecular interactions

Silica nanoparticles functionalized with -cyclodextrin (CD) host molecules (5) have been prepared by reacting carboxylic active ester-terminated silica nanoparticles (4) with CD heptamine. Silica nanoparticles functionalized with glucosamine (6), having similar surface properties as 5 but lacking the host-guest recognition motif, were used to perform blank experiments. The CD-functionalized silica nanoparticles 5 were determined by TEM to be 55 ± 6 nm in size. They exhibited pH-dependent aggregation, which is explained by the presence of free amino and carboxylic acid groups on the particle surface, which was corroborated by zeta potential measurements. The functionalization with CD was further confirmed by host-guest studies in solution and at CD-functionalized silicon substrates. The addition of an adamantyl-terminated dendrimer, capable of multivalent host-guest binding with CD, led to strong aggregation of the CD particles 5, but not of the glucosamine-functionalized 6. Furthermore, 5 gave strong adsorption to CD monolayers on silicon onto which adamantyl-terminated dendrimers were adsorbed, whereas 6 did not. The good discrimination between dendrimer-covered and uncovered areas of the CD monolayer substrates allowed the directed self-assembly of the silica particles 5 onto dendrimer-patterned areas created by microcontact printing

3,5-Dinitrobenzoic Acid-Capped Upconverting Nanocrystals for the Selective Detection of Melamine

In this Research Article, we report for the first time the use of upconverting nanoparticles to detect melamine up to nanomolar concentration. Detection of melamine is important as it is one of the adulterant in protein rich food products due to its high nitrogen content. In this work, we have shown how the electron deficient 3,5-dinitrobenzoic acid (DNB)-coated Er/Yb-NaYF₄ nanocrystals can specifically bind to electron rich melamine and alter the upconverting property of the nanocrystals. This selective binding led to the quenching of the upconversion emission from the nanocrystals. The high selectivity is verified by the addition of various analytes similar in structure with that of melamine. In addition, the selective quenching of the upconversion emission is reversible with the addition of dilute acid. This process has been repeated for more than five cycles with only a slight decrease in the sensing ability. The study was also extended to real milk samples, where the milk adulterated with melamine quenches the emission intensity of the DNB coated NaYF₄:Er/Yb nanocrystals, whereas hardly any change is noted for the unadulterated milk sample. The high robustness and the sharp emission peaks make Er³⁺/Yb³⁺-doped NaYF₄ nanocrystals a potential melamine sensing material over other organic fluorophores and nanocrystals possessing broad emissions

Host-guest and electrostatic interactions in supramolecular nanoparticle clusters

The influence of the charge, structure, and host–guest interactions of different soft polymeric components on their assembly with negatively charged inorganic gold and up-converting nanoparticles (NPs) functionalized with cyclodextrins (CD-AuNPs and CD-UCNPs) was studied. The inter-/intramolecular interplay was evaluated by changing the morphology and the charge of the polymeric component. Use of a linear, anionic guest-functionalized polymer resulted in the formation of thin coating layers around the CD-AuNPs and CD-UCNPs without further NP aggregation. When the branched cationic polymer poly(ethylene imine) (PEI) was used instead, small clusters were obtained before the electrostatic neutralization point, whereas large NP aggregates were obtained above the neutralization point. When branched cationic guest-functionalized dendrimers were used, clusters were obtained at a 1:1 host/guest stoichiometry. In this case, self-assembly occurred when still far away from the neutrality point, indicating that this cluster formation is driven by supramolecular host–guest interactions. The luminescence of the CD-UCNPs with the linear polymer was quenched due to C–H vibrational modes of the guest polymer, whereas in the case of electrostatic cluster formation by PEI the luminescence of CD-UCNPs was enhanced after the neutralization point, due to the formation of densely packed NP assemblies. These findings should be useful for the design of hybrid polymeric–inorganic assemblies for sensing and biomedical applications

Phosphorus-Induced One-Step Synthesis of NiCo₂S₄ Electrode Material for Efficient Hydrazine-Assisted Hydrogen Production

Rational control of the reaction parameters is highly important for synthesizing active electrocatalysts. NiCo2S4 is an excellent spinel-based electrocatalyst that is usually prepared through a two-step synthesis. Herein, a one-step hydrothermal route is reported to synthesize P-incorporated NiCo2S4. We discovered that the inclusion of P caused formation of the NiCo2S4 phase in a single step. Computational studies were performed to comprehend the mechanism of phase formation and to examine the energetics of lattice formation. Upon incorporation of the optimum amount of P, the stability of the NiCo2S4 lattice was found to increase steadily. In addition, the Bader charges on both the metal atoms Co and Ni in NiCo2S4 and P-incorporated NiCo2S4 were compared. The results show that replacing S with the optimal amount of P leads to a reduction in charge on both metal atoms, which can contribute to a more stable lattice formation. Further, the electrochemical performance of the as-synthesized materials was evaluated. Among the as-synthesized nickel cobalt sulfides, P-incorporated NiCo2S4 exhibits excellent activity toward hydrazine oxidation with an onset potential of 0.15 V vs RHE without the assistance of electrochemically active substrates like Ni or Co foam. In addition to the facile synthesis method, P-incorporated NiCo2S4 requires a very low cell voltage of 0.24 V to attain a current density of 10 mA cm–2 for hydrazine-assisted hydrogen production in a two-electrode cell. The free energy profile of the stepwise HzOR has been investigated in detail. The computational results suggested that HzOR on P-incorporated NiCo2S4 was more feasible than HzOR on NiCo2S4, and these findings corroborate the experimental evidence

A Highly Efficient UV–Vis–NIR Active Ln³⁺-Doped BiPO₄/BiVO₄ Nanocomposite for Photocatalysis Application

In this Article, we report the synthesis of Ln³⁺ (Yb³⁺, Tm³⁺)-doped BiPO₄/BiVO₄ nanocomposite photocatalyst that shows efficient photocatalytic activity under UV–visible–near-infrared (UV–vis–NIR) illumination. Incorporation of upconverting Ln³⁺ ion pairs in BiPO₄ nanocrystals resulted in strong emission in the visible region upon excitation with a NIR laser (980 nm). A composite of BiPO₄ nanocrystals and vanadate was prepared by the addition of vanadate source to BiPO₄ nanocrystals. In the nanocomposite, the strong blue emission from Tm³⁺ ions via upconversion is nonradiatively transferred to BiVO₄, resulting in the production of excitons. This in turn generates reactive oxygen species and efficiently degrades methylene blue dye in aqueous medium. The nanocomposite also shows high photocatalytic activity both under the visible region (0.010 min^–1) and under the full solar spectrum (0.047 min^–1). The results suggest that the photocatalytic activity of the nanocomposite under both NIR as well as full solar irradiation is better compared to other reported nanocomposite photocatalysts. The choice of BiPO₄ as the matrix for Ln³⁺ ions has been discussed in detail, as it plays an important role in the superior NIR photocatalytic activity of the nanocomposite photocatalyst

Highly Selective and Sensitive Detection of Cu²⁺ Ions Using Ce(III)/Tb(III)-Doped SrF₂ Nanocrystals as Fluorescent Probe

We report a green synthetic approach to the synthesis of water dispersible Ce³⁺/Tb³⁺-doped SrF₂ nanocrystals, carried out using environment friendly microwave irradiation with water as solvent. The nanocrystals display strong green emission due to energy transfer from Ce³⁺ to Tb³⁺ ions. This strong green emission from Tb³⁺ ions is selectively quenched upon addition of Cu²⁺ ions, thus making the nanocrystals a potential Cu²⁺ ions sensing material. There is barely any interference by other metal ions on the detection of Cu²⁺ ions and the detection limit is as low as 2 nM. This sensing ability is highly reversible by the addition of ethylenediaminetetraacetic acid (EDTA) with the recovery of almost 90% of the original luminescence. The luminescence quenching and recovery cycle was repeated multiple times without much effect on the sensitivity. The study was extended to real world water samples and obtained similar results. In addition to the sensing, we strongly predict the small size and high luminescence of the Ce³⁺/Tb³⁺-doped SrF₂ nanocrystals can be used for bioimaging applications