Dual-functional nano-photosensitizers: Eosin-Y decorated gold nanorods for plasmon-enhanced fluorescence and singlet oxygen generation.

Photosensitizer (PS) with enhanced fluorescence is attractive for image-guided photodynamic therapy (PDT) due to its dual functional role in Singlet Oxygen Generation (SOG) and producing high fluorescence signals. Here, Eosin-Y (Ey) decorated polymer coated gold nanorods (GNRs) of different aspect ratios are synthesized and introduced as novel plasmon-enhanced nano-photosensitizers for this purpose. We show, upon excitation at 519 nm, simultaneous enhancement in fluorescence and SOG was achieved for the hybrid nanostructure. The best enhancement factors of 110 and 18 for metal-enhanced fluorescence and metal-enhanced SOG, respectively, are obtained with GNRs of length 133 nm and width 45 nm, where Ey is positioned at 12.6 nm from the metal core using layer-by-layer assembly of oppositely charged polymers. The observed plasmonic effect is critically analysed by comparing the near field damping rate along with decay length, far field scattering and nonradiative energy transfer of the nanohybrids.

Ag-Au-Cu Trimetallic Alloy Microflower: A Highly Sensitive SERS Substrate for Detection of Low Raman Scattering Cross-Section Thiols.

Trimetallic Ag-Au-Cu alloy microflowers (MFs) with various surface compositions were synthesized on a glass coverslip and used as efficient surface-enhanced Raman spectroscopy (SERS) substrates for highly sensitive label-free detection of smaller Raman scattering cross-section molecules, namely, L-cysteine and toxic thiophenols. MFs of different compositions were synthesized via appropriate mixing of metal-alkyl ammonium halide precursors followed by a single-step thermolysis at 350 °C. While the Ag percentage was kept constant at 90% for all the substrates, the composition of Au and Cu was varied between 1 and 9% sequentially. The synthesized MFs were thoroughly characterized by using field emission scanning electron microscopy (FE-SEM), wide-angle X-ray scattering, X-ray photoelectron spectroscopy (XPS), and X-ray fluorescence techniques. FE-SEM studies revealed that the MFs were present throughout the substrate, and the average size varied from 20 to 40 µm. XPS studies showed that the top surface of the alloy substrates was rich in either Au or Cu atoms, while Ag remained underneath. The performance of the trimetallic MFs as SERS substrates was evaluated using Rhodamine 6G as a probe molecule, which showed that the MFs with Ag-Au-Cu compositions 90-7-3 and 90-3-7 were found to be the best and of equal SERS efficiency. The SERS enhancement factor (EF) of both these MFs was found to be the same, approximately 9 × 107, when calculated using 1,2,3-benzatriazole as the probe molecule. Between the two, the trimetallic substrate with a higher Au percentage (Ag-Au-Cu as 90-7-3) was used for the sensitive SERS-based detection of thiols to exploit the strong Au-S binding interaction. By virtue of the high EF of the substrate, the inherently low Raman scattering cross-sections of the probe molecules were greatly enhanced in SERS mode. The 'limit of quantification (LOQ)' values were found to be 1 nM for aliphatic L-Cysteine and 1-0.1 pM for aromatic thiols using the trimetallic SERS sensor.

Designing a nanothermometer using gel-to-liquid phase transition property of hybrid niosome.

The gel-to-liquid phase transition property of a hybrid niosome, which is made with a non-ionic surfactant, span 60 (S60), and triblock copolymer L64, is effectively utilized to design a nanothermometer for temperature sensing in the physiological range (20 °C to 50 °C). The fluorescence signal of a polarity-sensitive probe, Coumarin 153, loaded into the niosome, is used as an indicator for temperature sensing. Due to its excellent temperature sensitivity and resolution, the sensor is capable of sensing temperature inside FaDu cells.

Bimetallic Ag-Cu Alloy SERS Substrates as Label-Free Biomedical Sensors: Femtomolar Detection of Anticancer Drug Mitoxantrone with Multiplexing.

Surface-enhanced Raman spectroscopy (SERS) has been recognized as a promising label-free technology for clinical monitoring due to its high sensitivity and multiplexing ability, which should accelerate the screening of important drugs in the blood and plasma of cancer patients in a simpler, faster, and less-expensive manner. In this work, bimetallic Ag-Au and Ag-Cu alloy microflowers (MFs) with tunable surface compositions were fabricated on a glass cover slip by simple thermolysis of a metal alkyl ammonium halide precursor and used as SERS substrates for the sensitive detection of anticancer drug mitoxantrone (MTO). Two different laser excitation sources, 532 and 632.8 nm, were used to explore the possibility of surface-enhanced resonance Raman scattering. The Ag-Cu substrate showed superior detection capability over Ag-Au, whereby the sensor recorded a noteworthy "limit of detection" value of 1 fM for MTO. Theoretical electromagnetic field maps were simulated on appropriately chosen plasmonic systems to compare the electromagnetic field enhancements with the experimental SERS efficiencies of the substrates. Further, using a 10% Ag-Cu substrate, efficient multiplexing detection of MTO was demonstrated with another anticancer drug doxorubicin (DOX) in water and mouse blood plasma.

Development of low-cost copper nanoclusters for highly selective "turn-on" sensing of Hg2+ ions.

The development of low-cost earth abundant metal based fluorescent sensors for a rapid and selective nanomolar level detection of Hg2+ is essential due to the increasing world-wide concern of its detrimental effect on humans as well as the environment. Herein, we present a perylene tetracarboxylic acid functionalized copper nanoclusters (CuNCs) based "turn-on" fluorescence probe for highly selective detection of toxic Hg2+ ions. The fabricated CuNCs exhibited high photostability with emission maximum centered at 532 nm (λex = 480 nm). The fluorescence intensity of CuNCs was remarkably enhanced upon the addition of Hg2+ over other competing ions and neutral analytes. Notably, the 'turn-on' fluorescence response exhibits highly sensitive detection limit as low as 15.9 nM (S/N âˆ¼ 3). The time resolved fluorescence spectroscopy suggested the energy transfer between CuNCs and Hg2+ ions following either inhibited fluorescence resonance energy transfer (FRET) or surface modification of CuNCs during Hg2+ sensing. This study offers the systematic design and development of new fluorescent 'turn-on' nanoprobes for rapid and selective recognition of heavy metal ions.

Bimetallic Ag-Cu Alloy Microflowers as SERS Substrates with Single-Molecule Detection Limit.

Bimetallic Ag-Cu alloy microflowers with tunable surface compositions were fabricated as surface-enhanced Raman spectroscopy (SERS) substrates with a limit of detection in the zeptomolar range for the analyte molecule rhodamine 6G (R6G). The substrates were prepared on a glass coverslip through a bottom-up strategy by simple thermolysis of metal-alkyl ammonium halide precursors. The reaction temperature and composition of the alloy were varied sequentially to find out the maximum SERS efficiency from the substrates. While UV-vis spectroscopy was employed to characterize the optical properties of the substrates, the bulk and surface compositions of the microflowers were determined using energy-dispersive X-ray fluorescence (ED-XRF) and X-ray photoelectron spectroscopy (XPS) techniques, respectively. Also, the structural and morphological characterizations of the substrates were performed by X-ray diffraction and scanning electron microscope (SEM), respectively. For alloys, the ED-XRF studies confirmed that the bulk compositions matched with the feed ratio, while the surface compositions were found to be rich in copper in the form of both elementary copper and copper oxide, as revealed by XPS studies. From the efficiency studies for different compositions prepared, it was found that 10% Ag-Cu alloy microflowers produced the maximum SERS intensity for resonant R6G molecules as probes. In fact, R6G evidences a 50-fold enhancement in SERS spectra with 10% alloy microflowers as against pure Ag microflowers. Using 1, 2, 3-benzotriazole as a nonresonant Raman probe, uniform enhancement factors on the order of ≈108 were achieved from different parts of the 10% Ag-Cu alloy microflower. The same substrate showed excellent Raman response for detecting R6G at very low concentrations such as 10 zM, leading to detection and analysis of SERS spectra from a single R6G molecule.

A metal-enhanced fluorescence sensing platform for selective detection of picric acid in aqueous medium.

Apart from national security and military purposes, it is also of great importance to detect picric acid (PA) in aqueous solution for pollution control. Herein, we report a gold nanoparticle (AuNP)-based sensor for detection of PA in aqueous condition, based on metal-enhanced fluorescence (MEF) of poly(allylamine)hydrochloride (PAH). Notable enhancement in fluorescence intensity is observed when PAH is incubated with Au@SiO2 nanoparticles, where silica shell controls the distance between gold core and PAH. Almost ∼280 fold enhancement is recorded when PAH is incubated with ∼45 nm diameter Au nanoparticles. A significant reduction in excited state lifetime followed the enhancement in fluorescence intensity, identifying the mechanism to be primarily obtained from the intrinsic radiative decay rate enhancement of PAH. The MEF sensor shows excellent selectivity for detection of PA in water, among similar electron deficient compounds via fluorescence quenching. The detection limit of the sensor is calculated to be 79 nM, in the linear range. Detection of PA is demonstrated in simulated water samples, where matrix effects are taken into account to assess the efficacy of the sensor.

Red-Emitting Carbon Dots as a Dual Sensor for In3+ and Pd2+ in Water.

We have demonstrated the synthesis, characterization, and application of nitrogen-doped red-emitting carbon dots (NRCDs) for dual sensing of indium (In3+) and palladium (Pd2+) in water. The detection of In3+ was associated with "turn-on" fluorescence response with a red shift, while in the presence of Pd2+, the fluorescence intensity of NRCDs was quenched to show a "turn-off" response. The interaction of NRCDs with the metal ions was investigated using 1H nuclear magnetic resonance and Fourier-transform infrared spectroscopy studies. The synthesized nanoprobes possessed good biocompatibility and photostability and were found to be suitable candidates for bioimaging due to their emission profiles in the near-infrared (NIR) window. Applicability of the as-prepared NRCDs was demonstrated in the NIR region when they were loaded in vesicle membranes with and without cations and subjected to confocal imaging successfully.

Synthesis, Detailed Characterization, and Dual Drug Delivery Application of BSA Loaded Aquasomes.

Aquasomes (AQ) are self-assembled nanostructures, made up of a spherical hydroxyapatite core and a carbohydrate layer on top, for delivering bioactive molecules like proteins, peptides, etc., which are adsorbed on the carbohydrate layer. This is the first report of its kind demonstrating AQ as an efficient dual drug delivery system, capable of releasing bioactive molecule and a hydrophobic drug together. The synthesized AQ before and after adsorption of the bioactive molecule are characterized using dynamic light scattering, scanning electron microscopy, X-ray diffraction, small-angle X-ray scattering, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and Raman spectroscopy. BSA (bovine serum albumin) protein is used as the model bioactive molecule for the in vitro dual release studies along with representative hydrophobic drugs Coumarin 153 (C153), Warfarin (WAR), and Ibuprofen (IBU). The release behaviors of the hydrophobic drugs are explained by studying their binding interactions with BSA. The binding interactions of the drugs with BSA are analyzed by carrying out fluorescence quenching experiment of BSA, site marking competition experiment, anisotropy, and ET (30) studies. Further, in vitro biocompatibility studies are performed for dually loaded AQ by using hemolysis assay. The hemolysis assay do not show any lysing of the red blood cells, suggesting the formulations to be clinically capable for administration.