Multidrug-resistant Staphylococcus aureus (MRSA) has become one of the major causes of various infections, leading to morbidity in both healthy and immune-compromised populations worldwide. Herein, we report a novel type of hybrid photosensitizer based on amphiphilic block copolymer-functionalized gold nanoparticles. The design of the nanoparticles provides a facile means to incorporate hydrophobic photosensitizing molecules for use in aqueous media. The hybrid photosensitizers display greatly enhanced singlet oxygen generation and outstanding photodynamic inactivation (PDI) efficacy against MRSA under light illumination. These hybrid photosensitizers greatly improve the effectiveness of PDI against MRSA while not involving antibiotics.Topics: Bacteria; Photosensitizers; Photosensitizers;

•Nanoparticle-based method to perform magnetic relaxation for detection of analytes.•Magnetic relaxation-based quantification of phosphate ion in aqueous media.•Magnetic relaxation-based detection of phosphate in fertilizer without separation.We report a novel magnetic relaxation-based sensing method for sensitive and selective detection of phosphate ions in aqueous media using paramagnetic nanoparticles. The method can detect phosphate ions at physiological pH quantitatively with high selectivity, even in a commercial fertilizer without separation.

In recent years, multidrug-resistant Staphylococcus aureus (MRSA) has become one of the main bacteria associated with serious diseases in both hospital and the community. Herein we report that a type of hybrid photosensitizers consisting of silver nanoparticles and photosensitizing molecules display outstanding photodynamic inactivation capability against MRSA, with an enhanced killing efficacy of up to ∼6 orders of magnitude under the experimental conditions. The results support that such hybrid photosensitizers can be used for photodynamic inactivation of MRSA without involving antibiotics.

We report the development of a type of novel hybrid photosensitizers for photodynamic inactivation of broad-spectrum bacteria. A thiol-modified amphiphilic block copolymer, poly(N-isopropylacrylamide-block-styrene), was synthesized and characterized. Subsequently, silver nanoparticles stabilized by poly(N-isopropylacrylamide-block-styrene) were synthesized and used to entrap hydrophobic photosensitizing molecules (such as hematoporphyrin). The resulting water-dispersible hybrid photosensitizers demonstrated enhanced singlet oxygen generation with a broadened excitation profile, as compared to the pristine hematoporphyrin molecules. Photodynamic inactivation of Staphylococcus epidermidis and Escherichia coli by the hybrid photosensitizer showed significantly enhanced killing efficacy, up to ∼5 orders of magnitude, under both white light and red/near-infrared light illuminations. The hybrid photosensitizers at the concentration used in the photodynamic inactivation assays displayed low cytotoxicity to Hela cells under ambient light conditions. These results demonstrate the great potential of such hybrid photosensitizers for photodynamic inactivation and photodynamic therapy applications.

We report a quantitative SERS measurement scheme based on the magnetic microsphere–Ag nanoparticles to detect target DNA. The quantitative SERS measurements can quantify the target DNA concentration down to 10 nM.

We report an investigation of triplet–triplet annihilation upconversion (TTA-UC) based on polymeric emitters with tunable inter-chromophore distances. Poly[(9-anthrylmethyl methacrylate)-co-(methyl methacrylate)] (poly(AnMMA-co-MMA)) with different percentages of AnMMA was synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization, and used as an emitter in association with platinum octaethylporphyrin as a sensitizer to form TTA-UC systems. It is observed that the TTA-UC intensity first increases with increasing AnMMA percentage in the polymers then decreases, and ultimately disappears, upon further increasing the AnMMA percentage. The results shed light on the key factors affecting TTA-UC in polymers, and have implications for the design of polymer-based TTA-UC systems.

We report a new NMR relaxation time-based method for sensitive and selective dopamine detection using paramagnetic nanoparticles. The Fe3+ species in the nanoparticles serves as both the contrast agent and the target recognition element. The results demonstrate that paramagnetic nanoparticles, similar to the more widely used superparamagnetic nanoparticles, can be integrated into relaxation based detection schemes while avoiding the aggregation problem commonly associated with superparamagnetic nanoparticles.

•A new methodology to perform quantitative SERS measurements of analytes using internal reference.•SERS-based quantification of Toluidine Blue O as a proof-of-concept study.•SERS-based quantification of melamine in milk.Analytical applications of SERS are often more associated with qualitative than quantitative analysis, because of the difficulty in obtaining quantitative SERS results. In this paper we introduce a new strategy to quantitatively measure the SERS signals of analytes based on Au-core/Ag-shell nanoparticles with embedded 4-aminothiophenol as the internal reference. Successful detections of two analytes, Toluidine Blue O in aqueous solution (detection limit of 0.1 μM) and melamine in milk (detection limit of ∼5 μM), are demonstrated. The improvement in the linear fitting illustrates that the use of internal reference significantly improves the accuracy of the quantitative SERS measurements. The successful detection of melamine in milk illustrates the versatility of this detection scheme for a wide variety of analytes.

We report the investigation of surface plasmon induced enhancement of homogeneous and heterogeneous triplet–triplet annihilation (TTA) by gold nanoparticles (AuNPs). Results show that AuNPs enhance the overall efficiency in both cases. Excitation rate and intersystem crossing efficiency of the sensitizer, and efficiency of energy transfer between sensitizer and acceptor are believed to be enhanced by the surface plasmon of AuNPs, leading to the enhancement of overall TTA efficiency.

In this study a one-pot synthesis of hydrophilic, amine-functionalized NaYF4(Yb,Er) upconversion nanoparticles is demonstrated. A photosensitizing molecule, chlorin e6, is deposited onto the nanoparticle surface to form a hybrid photosensitizer, which can generate singlet oxygen under both near-infrared and visible light excitations. Effects of beef tissue in the light path under both excitations are investigated and compared.

Conjugated polymer nanodots are shown to have great potential as probe for fluorescence-based biosensing and bioimaging applications. Yet the need to functionalize these polymer nanodots is hindering their uses in many applications. Here, we report the preparation and encapsulation of fluorescent polymer nanodots inside silica nanoparticles. The facile, template-assisted method has little effect on the fluorescent properties of polymer nanodots. The resulting nanodot-embedded silica nanoparticles can be easily functionalized for downstream applications.

Surface Enhanced Raman Spectroscopy (SERS) is an excellent tool that provides information about the vibrational modes of molecules. However, quantitative analysis using SERS has remained a challenge largely because of the difficulty in reproducing the SERS substrates. We report a facile synthesis method of Ag–Fe3O4 nanocomposites that can be used as SERS substrates in solutions. Quantitative SERS measurements using the Ag–Fe3O4 nanocomposites are successfully demonstrated with 4-aminothiophenol and dopamine as analytes. The inclusion of an internal reference significantly improves the reliability and quality of quantification of the analytes. The scheme is versatile and has the potential for the detection of a wide range of analytes.

We demonstrate a methodology to prepare Au-core–Ag-shell nanoparticles displaying both SERS and surface-enhanced fluorescence (SEF) activities simultaneously by embedding dye molecules between the core and the shell. Polyelectrolytes are used to adjust the spacing and the dye position between the core and the shell. Layer-by-layer polyelectrolyte deposition can serve as an effective and flexible way to introduce various types of dye molecules into the nanostructures. Results from the spectral measurements shed light on the intricacy between SERS and SEF.

The most common BRAF mutation, V600E, accounts for a variety of cancers. Here we report a highly specific and sensitive method for the detection of the V600E mutation. The detection scheme is based on luminescence resonance energy transfer (LRET) between upconversion nanoparticles (UCNPs) and an intercalating dye, SYBR Green I. Target DNA serves as the template for two DNA probes, one of them covalently attached to UCNPs, to be ligated into a hairpin-forming DNA strand, which brings SYBR Green I close to the upconversion nanoparticles. The number of the resulting DNA strand is amplified through thermal cycling. The degree of LRET is correlated to the amount of the initial DNA targets. Factors affecting the detection specificity and sensitivity, including ligation temperature, amount of ligase, and number of thermal cycles, have been investigated to optimize the performance of the detection method. The method can easily differentiate the V600E mutation from the wild-type sequence with a mutant-to-wild-type ratio of 1:1000. A detection limit of 1 femtomole BRAF V600E mutation is achieved.

In this paper we report a highly specific and sensitive method for the detection of T790M mutation in epidermal growth factor receptor (EGFR). This detection scheme is based on luminescent resonance energy transfer between upconversion nanoparticles and the intercalating dye, SYBR Green I. Target DNA serves as a template for two DNA probes, one of them covalently attached to upconversion nanoparticles, to be joined into a long, hairpin-forming DNA by ligase. The number of the resulting DNA strand, which brings SYBR Green I close to the upconversion nanoparticles, is amplified by thermal cycling. A number of factors affecting the detection specificity and sensitivity, including probe design, ligation temperature, type and amount of ligase, and number of thermal cycles, have been considered and investigated to optimize the performance of the method. The method can easily differentiate the T790M mutation from the wild-type sequence with a mutant-to-wild-type ratio of 1:100. The results show that 0.01 pmole of EGFR T790M mutant can be readily detected.

We report a new strategy to engineer versatile SERS-active nanoparticles by embedding Raman reporter molecules inside Au-core/Ag-shell nanoparticles through layer-by-layer deposition of polyelectrolytes. The results demonstrate a class of core–shell nanoparticles that can find use as SERS-tags for Raman-based assays and imaging with strong SERS signals, versatility and simplicity in synthesis, and good stability. The strategy may also be useful to the preparation of plasmonic nanostructures for other purposes.

A novel ligase-assisted signal-amplifiable DNA detection scheme is demonstrated based on upconversion nanoparticles. Target DNA serves as a template for two designed DNA probes, one of which covalently attached to upconversion nanoparticles, to be joined into a single DNA strand by ligase. The resulting long DNA is able to form a hairpin loop structure, the number of which is amplified by thermal cycling. Energy transfer occurs between the upconversion nanoparticles and the intercalating dyes residing in the stem portion of the hairpin loop, and is monitored to quantify the amount of the initial target DNA. The method displays high sensitivity and specificity for DNA detection.

We report the development of a highly sensitive and selective colorimetric detection method for glutathione (GSH) over cysteine (Cys) or homocysteine (Hcy) using gold nanoparticles (AuNPs). The detection scheme is based on the quasi-stable state of AuNPs in the presence of sodium nitrate and GSH. The significant differences in interparticle forces and the assembly process of AuNPs enable the discrimination of GSH over Cys and Hcy. The presence of GSH can be detected by the naked eye and its concentration determined by UV/Vis spectrometry.

Sialic acid reduced and stabilized gold nanoparticles (d=20.1±1.8 nm) were synthesized by a simple one-pot, green method without chemically modifying sialic acid for colorimetric detection of influenza virus. The gold nanoparticles showed target-specific aggregation with viral particles via hemagglutinin–sialic acid binding. A linear correlation was observed between the change in optical density and dilution of chemically inactivated influenza B/Victoria and influenza B/Yamagata. Virus dilution (hemagglutination assay titer, 512) of 0.156 vol% was readily detected. The upper limit of the linearity can be extended with the use of more sialic acid–gold nanoparticles.

Here we report the observation of significantly enhanced fluorescence from molecules placed inside a silver nanocavity, as compared to those without the silver coating.

We report the development of Raman reporter-embedded TiO2 nanoparticles coated with mixed Ag and Au shells, showing enormous ensemble surface-enhanced Raman scattering (SERS) enhancement factors (up to 1010). Effects of shell composition on the enhancement are investigated both experimentally and theoretically. Colloidal TiO2 nanoparticles are first tagged with meso-tetra(4-carboxyphenyl)porphine or tris(2,2′-bipyridyl)ruthenium(II) chloride, used as reporter molecules. They are subsequently coated with either a Ag shell or a mixed Au−Ag shell with different compositions. The resulting nanostructures are characterized by UV−visible spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, particle size analyzer, and Raman spectroscopy. These Raman reporter-embedded TiO2 core−metal shell nanoparticles exhibit reproducible SERS signals of the reporter molecules with very high average enhancement factors. Interestingly, depending on the excitation wavelength, bimetallic Au−Ag shell nanostructures with proper Au/Ag ratios display higher enhancement factors than Ag-only shell. Simulation results based on equivalent dielectric functions show a very good match with the experimental observations.

Here we report the observation of significantly enhanced fluorescence from molecules placed inside a silver nanocavity, as compared to those without the silver coating.

Surface Enhanced Raman Spectroscopy (SERS) is an excellent tool that provides information about the vibrational modes of molecules. However, quantitative analysis using SERS has remained a challenge largely because of the difficulty in reproducing the SERS substrates. We report a facile synthesis method of Ag–Fe3O4 nanocomposites that can be used as SERS substrates in solutions. Quantitative SERS measurements using the Ag–Fe3O4 nanocomposites are successfully demonstrated with 4-aminothiophenol and dopamine as analytes. The inclusion of an internal reference significantly improves the reliability and quality of quantification of the analytes. The scheme is versatile and has the potential for the detection of a wide range of analytes.

We report a new strategy to engineer versatile SERS-active nanoparticles by embedding Raman reporter molecules inside Au-core/Ag-shell nanoparticles through layer-by-layer deposition of polyelectrolytes. The results demonstrate a class of core–shell nanoparticles that can find use as SERS-tags for Raman-based assays and imaging with strong SERS signals, versatility and simplicity in synthesis, and good stability. The strategy may also be useful to the preparation of plasmonic nanostructures for other purposes.

We report the investigation of surface plasmon induced enhancement of homogeneous and heterogeneous triplet–triplet annihilation (TTA) by gold nanoparticles (AuNPs). Results show that AuNPs enhance the overall efficiency in both cases. Excitation rate and intersystem crossing efficiency of the sensitizer, and efficiency of energy transfer between sensitizer and acceptor are believed to be enhanced by the surface plasmon of AuNPs, leading to the enhancement of overall TTA efficiency.

We report a quantitative SERS measurement scheme based on the magnetic microsphere–Ag nanoparticles to detect target DNA. The quantitative SERS measurements can quantify the target DNA concentration down to 10 nM.

We report a new NMR relaxation time-based method for sensitive and selective dopamine detection using paramagnetic nanoparticles. The Fe3+ species in the nanoparticles serves as both the contrast agent and the target recognition element. The results demonstrate that paramagnetic nanoparticles, similar to the more widely used superparamagnetic nanoparticles, can be integrated into relaxation based detection schemes while avoiding the aggregation problem commonly associated with superparamagnetic nanoparticles.

We demonstrate a methodology to prepare Au-core–Ag-shell nanoparticles displaying both SERS and surface-enhanced fluorescence (SEF) activities simultaneously by embedding dye molecules between the core and the shell. Polyelectrolytes are used to adjust the spacing and the dye position between the core and the shell. Layer-by-layer polyelectrolyte deposition can serve as an effective and flexible way to introduce various types of dye molecules into the nanostructures. Results from the spectral measurements shed light on the intricacy between SERS and SEF.

We report an investigation of triplet–triplet annihilation upconversion (TTA-UC) based on polymeric emitters with tunable inter-chromophore distances. Poly[(9-anthrylmethyl methacrylate)-co-(methyl methacrylate)] (poly(AnMMA-co-MMA)) with different percentages of AnMMA was synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization, and used as an emitter in association with platinum octaethylporphyrin as a sensitizer to form TTA-UC systems. It is observed that the TTA-UC intensity first increases with increasing AnMMA percentage in the polymers then decreases, and ultimately disappears, upon further increasing the AnMMA percentage. The results shed light on the key factors affecting TTA-UC in polymers, and have implications for the design of polymer-based TTA-UC systems.