Hollow Gold Nanosphere Templated Synthesis of PEGylated Hollow Gold Nanostars and Use for SERS Detection of Amyloid Beta in Solution.

Hollow gold nanospheres (HGNs) have been used as the template for seed-mediated growth of multibranched hollow gold nanostars (HNS). The HGNs were synthesized via anerobic reduction of cobalt chloride to cobalt nanoparticles and then formation of a gold shell via galvanic replacement followed by the oxidation of the cobalt core. We obtained control of the inner core size of the HGNs by increasing the size of the sacrificial cobalt core and by varying the ratio of B(OH)3/BH4 using boric acid rather than 48 h aged borohydride. We synthesized the HNS by reducing Au3+ ions in the presence of Ag+ ions using ascorbic acid, creating a spiky morphology that varied with the Au3+/Ag+ ratio. A broadly tunable localized surface plasmon resonance was achieved through control of both the inner core and the spike length. Amyloid beta (Aß) was conjugated to the HNS by using a heterobifunctional PEG linker and identified by the vibrational modes associated with the conjugated ring phenylalanine side chain. A bicinchoninic acid assay was used to determine the concentration of Aß conjugated to HNS as 20 nM, which is below the level of Aß that negatively affects long-term potentiation. Both the core size and spike length were shown to affect the optical properties of the resulting nanostructures. This HGN templated method introduced a new parameter for enhancing the plasmonic properties of gold nanostars, namely, the addition of a hollow core. Hollow gold nanostars are highly desirable for a wide range of applications, including high sensitivity disease detection and monitoring.

Spatiotemporal Temperature and Pressure in Thermoplasmonic Gold Nanosphere-Water Systems.

We offer a detailed investigation of the photophysical properties of plasmonic solid and hollow gold nanospheres suspended in water by combining ultrafast transient absorption (TA) spectroscopy with molecular dynamics (MD) simulations. TA reveals that hollow gold nanospheres (HGNs) exhibit faster excited state relaxation and larger amplitude acoustic phonon modes than solid gold nanoparticles of the same outer diameter. MD simulation carried out on full scale nanoparticle-water models (over 10 million atoms) to simulate the temporal evolution (0-100 ps) of the thermally excited particles (1000 or 1250 K) provides atomic-scale resolution of the spatiotemporal temperature and pressure maps, as well as visualization of the lattice vibrational modes. For the 1000 K HGN, temperatures upward of 500 K in the vicinity of the shell surface were observed, along with pressures up to several hundred MPa in the inner cavity, revealing potential use as a photoinduced nanoreactor. Our approach of combining TA and MD provides a path to better understanding how thermal-structural properties (such as expansion and contraction) and thermal-optical properties (such as modulated dielectrics) manifest themselves as TA signatures. The detailed picture of heat transfer at interfaces should help guide nanoparticle design for a wide range of applications that rely on photothermal conversion, including photothermal coupling agents for nanoparticle-mediated photothermal therapy and photocatalysts for light-driven chemical reactions.

Synergistic Surface Passivation of CH3 NH3 PbBr3 Perovskite Quantum Dots with Phosphonic Acid and (3-Aminopropyl)triethoxysilane.

CH3 NH3 PbBr3 perovskite quantum dots (PQDs) are synthesized by using four different linear alkyl phosphonic acids (PAs) in conjunction with (3-aminopropyl)triethoxysilane (APTES) as capping ligands. The resultant PQDs are characterized by means of XRD, TEM, Raman spectroscopy, FTIR spectroscopy, UV/Vis, photoluminescence (PL), time-resolved PL, and X-ray photoelectron spectroscopy (XPS). PA chain length is shown to control the PQD size (ca. 2.9-4.2 nm) and excitonic absorption band positions (λ=488-525 nm), with shorter chain lengths corresponding to smaller sizes and bluer absorptions. All samples show a high PL quantum yield (ca. 46-83 %) and high PL stability; this is indicative of a low density of band gap trap states and effective surface passivation. Stability is higher for smaller PQDs; this is attributed to better passivation due to better solubility and less steric hindrance of the shorter PA ligands. Based on the FTIR, Raman, and XPS results, it is proposed that Pb2+ and CH3 NH3 + surface defects are passivated by R-PO3 2- or R-PO2 (OH)- , whereas Br- surface defects are passivated by R-NH3 + moieties. This study establishes the combination of PA and APTES ligands as a highly effective dual passivation system for the synergistic passivation of multiple surface defects of PQDs through primarily ionic bonding.

Highly Tunable Hollow Gold Nanospheres: Gaining Size Control and Uniform Galvanic Exchange of Sacrificial Cobalt Boride Scaffolds.

In principle, the diameter and surface plasmon resonance (SPR) frequency of hollow metal nanostructures can be independently adjusted, allowing the formation of targeted photoactivated structures of specific size and optical functionality. Although tunable SPRs have been reported for various systems, the shift in SPR is usually concomitant with a change in particle size. As such, more advanced tunability, including constant diameter with varying SPR or constant SPR with varying diameter, has not been properly achieved experimentally. Herein, we demonstrate this advanced tunability with hollow gold nanospheres (HGNs). HGNs were synthesized through galvanic exchange using cobalt-based nanoparticles (NPs) as sacrificial scaffolds. Co2B NP scaffolds were prepared by sodium borohydride nucleation of aqueous cobalt chloride and characterized using UV-vis, dynamic light scattering, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Careful control over the size of the Co2B scaffold and its galvanic conversion is essential to realize fine control of the resultant HGN diameter and shell thickness. In pursuit of size control, we introduce B(OH)4- (the final product of NaBH4 hydrolysis) as a growth agent to obtain hydrodynamic diameters ranging from ∼17-85 nm with relative standard deviation <3%. The highly monodisperse Co2B NPs were then used as scaffolds for the formation of HGNs. In controlling HGN shell thickness and uniformity, environmental oxygen was shown to affect both the structural and optical properties of the resultant gold shells. With careful control of these key factors, we demonstrate an HGN synthesis that enables independent variation of diameter and shell thickness, and thereby SPR, with unprecedented uniformity. The new synthesis method creates a truly tunable plasmonic nanostructure platform highly desirable for a wide range of applications, including sensing, catalysis, and photothermal therapy.

Towards understanding the unusual photoluminescence intensity variation of ultrasmall colloidal PbS quantum dots with the formation of a thin CdS shell.

In this study, we report anomalous size-dependent photoluminescence (PL) intensity variation of PbS quantum dots (QDs) with the formation of a thin CdS shell via a microwave-assisted cation exchange approach. Thin shell formation has been established as an effective strategy for increasing the PL of QDs. Nonetheless, herein we observed an unusual PL decrease in ultrasmall QDs upon shell formation. We attempted to understand this abnormal phenomenon from the perspective of trap density variation and the probability of electrons and holes reaching surface defects. To this end, the quantum yield (QY) and PL lifetime (on the ns-µs time scales) of pristine PbS QDs and PbS/CdS core/shell QDs were measured and the radiative and non-radiative recombination rates were derived and compared. Moreover, transient absorption (TA) analysis (on the fs-ns time scale) was performed to better understand exciton dynamics at early times that lead to and affect longer time dynamics and optical properties such as PL. These experimental results, in conjunction with theoretical calculations of electron and hole wave functions, provide a complete picture of the photophysics governing the core/shell system. A model was proposed to explain the size-dependent optical and dynamic properties observed.

Organolead Halide Perovskite Nanocrystals: Branched Capping Ligands Control Crystal Size and Stability.

CH3 NH3 PbBr3 perovskite nanocrystals (PNCs) of different sizes (ca. 2.5-100 nm) with high photoluminescence (PL) quantum yield (QY; ca. 15-55 %) and product yield have been synthesized using the branched molecules, APTES and NH2 -POSS, as capping ligands. These ligands are sterically hindered, resulting in a uniform size of PNCs. The different capping effects resulting from branched versus straight-chain capping ligands were compared and a possible mechanism proposed to explain the dissolution-precipitation process, which affects the growth and aggregation of PNCs, and thereby their overall stability. Unlike conventional PNCs capped with straight-chain ligands, APTES-capped PNCs show high stability in protic solvents as a result of the strong steric hindrance and propensity for hydrolysis of APTES, which prevent such molecules from reaching and reacting with the core of PNCs.

Tunable Photoluminescent Core/Shell Cu(+)-Doped ZnSe/ZnS Quantum Dots Codoped with Al(3+), Ga(3+), or In(3+).

Semiconductor quantum dots (QDs) with stable, oxidation resistant, and tunable photoluminescence (PL) are highly desired for various applications including solid-state lighting and biological labeling. However, many current systems for visible light emission involve the use of toxic Cd. Here, we report the synthesis and characterization of a series of codoped core/shell ZnSe/ZnS QDs with tunable PL maxima spanning 430-570 nm (average full width at half-maximum of 80 nm) and broad emission extending to 700 nm, through the use of Cu(+) as the primary dopant and trivalent cations (Al(3+), Ga(3+), and In(3+)) as codopants. Furthermore, we developed a unique thiol-based bidentate ligand that significantly improved PL intensity, long-term stability, and resilience to postsynthetic processing. Through comprehensive experimental and computational studies based on steady-state and time-resolved spectroscopy, electron microscopy, and density functional theory (DFT), we show that the tunable PL of this system is the result of energy level modification to donor and/or acceptor recombination pathways. By incorporating these findings with local structure information obtained from extended X-ray absorption fine structure (EXAFS) studies, we generate a complete energetic model accounting for the photophysical processes in these unique QDs. With the understanding of optical, structural, and electronic properties we gain in this study, this successful codoping strategy may be applied to other QD or related systems to tune the optical properties of semiconductors while maintaining low toxicity.

Physical and photoelectrochemical properties of Zr-doped hematite nanorod arrays.

This work examines the effect of Zr(4+) ions on the physical and photoelectrochemical (PEC) properties of hematite (α-Fe2O3) nanorod arrays grown in an aqueous solution containing zirconyl nitrate (ZrO(NO3)2) as a dopant precursor. The concentration of ZrO(NO3)2 in the precursor solution influenced both the film thickness and the Zr(4+) concentration in the resulting films. Zr doping was found to enhance the photocurrent for water splitting; the highest photocurrent at 1.0 V vs. Ag/AgCl (0.33 mA cm(-2)) for the Zr-doped α-Fe2O3 film was approximately 7.2 times higher than that for the undoped film (0.045 mA cm(-2)). Additionally, the incident photon to current efficiency (IPCE) at 360 nm and 1.23 V vs. the reversible hydrogen electrode (RHE) increased from 3.8% to 13.6%. Ultrafast transient absorption spectroscopy suggests that Zr doping may influence PEC performance by reducing the rate of electron-hole recombination.