Shengli Zou

• University of Central Florida

The synthesis of high-purity gold nano bipyramids (Au NBPs) with a narrow size distribution and tunable plasmon resonances is of great significance for plasmon resonance-related applications. However, the synthesis Au NBP approach involves multiple steps with many parameters that can affect the purity of the final product. In this work, we were dev...

Photoexcited nonthermal electrons and holes in metallic nanoparticles, known as hot carriers, can be judiciously harnessed to drive interesting photocatalytic molecule-transforming processes on nanoparticle surfaces. Interband hot carriers are generated upon direct photoexcitation of electronic transitions between different electronic bands, wherea...

The double-slit experiment has long been pivotal in understanding matter’s wave–particle duality. A central question revolves around Born’s interpretation of wavefunction whether a single photon demonstrates a 50% probability of passing through each slit individually as particles or simultaneously traverses both as waves. Experimentally, once the p...

UV–vis spectrophotometry and spectrofluorometry are indispensable tools in education, research, and industrial process controls with widespread applications in nanoscience encompassing diverse nanomaterials and fields. Nevertheless, the prevailing spectroscopic interpretations and analyses often exhibit ambiguity and errors, particularly evident in...

Different cuprous oxide (Cu2O) particle forms, including the octahedron, truncated octahedron, cube, and star-like forms, are synthesized through chemical reduction under different reaction conditions. The correlation between the morphology and the catalytic activity of hydrogen evolution reactions (HERs) is investigated. It is discovered that the...

Cascading optical processes involve sequential photon-matter interactions triggered by the same individual excitation photons. Parts I and II of this series explored cascading optical processes in scattering-only solutions (Part I) and solutions with light scatterers and absorbers but no emitters (Part II). The current work (Part III) focuses on th...

This work examines the roles played by wall thickness in determining the plasmonic properties of gold-silver (Ag-Au) nanocages. Ag-Au cages with different wall thicknesses, but the same void or outer size, shape, and elemental composition, were designed as a model platform. The experimental findings were understood with theoretical calculations. Th...

In Part I of the three companion articles, we reported the effects of light scattering on experimental quantification of scattering extinction, intensity, and depolarization in solutions that contain only scatterers with no significant absorption and photoluminescence activities. The present work (Part II) studies the effects of light scattering an...

Light scattering is a universal matter property that is especially prominent in nanoscale or larger materials. However, the effects of scattering-based cascading optical processes on experimental quantification of sample absorption, scattering, and emission intensities, as well as scattering and emission depolarization, have not been adequately add...

Using the undetermined coefficients method, we obtained the exact solution of Schrodinger equation of a three-body system, H2⁺ ion, in a restricted form. We found that its ground state energy when the nuclear distance becomes zero can be the same as that of a He⁺ ion. However, its radial wavefunction is e-r while the corresponding wavefunction is e...

Linear light-absorbing nanomaterials are ideal for film-based solar harvesting applications as they form porous structures that can maximize the absorption and minimize the reflection of the solar light. Conventional 1D nanochains of plasmonic nanoparticle assemblies can achieve significantly broadened optical absorption through surface plasmon cou...

Current methods for tuning the plasmonic properties of metallic nanoparticles typically rely on alternating the morphology (i.e., size and/or shape) of nanoparticles. The variation of morphology of plasmonic nanoparticles oftentimes impairs their performance in certain applications. In this study, we report an effective approach based on the contro...

Strong coupling of plasmon and exciton could occur in a hybrid metal-dye/semiconductor structure, where the fast energy exchange between plasmons and excitons leads to two new eigenmodes of the system, known as Rabi splitting. Not only new optical features emerge from Rabi splitting, strong plasmon-exciton coupling has the potential to alter the ch...

Reliable quantification of the optical properties of fluorescent quantum dots (QDs) is critical for their photo-chemical, -physical, and -biological applications. Presented herein is the experimental quantification of photon scattering, absorption, and on-resonance-fluorescence (ORF) activities of CdSe/CdS core/shell fluorescent QDs as a function o...

Dithiosulfindene (DTS) is a model molecule for dithiolethiones, a class of biomedically important sulfur-rich compounds with a general formula R1-S-S-C(=S)-R2. Reported herein is a combined experimental and computational study of DTS interactions with plasmonic gold nanoparticles (AuNPs) in water. DTS adsorptions and reactions on AuNPs were investi...

Optical excitation of plasmonic electron oscillations confined by metallic nanoparticles provides a unique means of driving unconventional photocatalytic transformations of molecular adsorbates on the nanoparticle surfaces. Photothermal heating, local-field enhancement, and hot carrier generation have been identified as three major plasmon-induced...

Optical properties of fluorescent materials including their UV-vis absorption, scattering, and on-resonance fluorescence activities are strongly wavelength-dependent. Reported herein is a divide-and-conquer strategy for experimental quantification of fundamental optical constants of fluorescent nanomaterials including their UV-vis absorption, scatt...

The electromagnetically induced transparency (EIT) phenomenon is of great importance for plenty of applications, such as slow light, nonlinear effect, nanosensing, and metamaterials. The linewidth is a key factor to evaluate the characteristic of EIT, because the drastic change in dispersion in the narrow spectra can make good control of light. How...

Hexachlorobenzene (HCB), like many chlorinated organic compounds, has accumulated in the environment from agricultural and industrial activity. Because of its health risks and adverse impact on various ecosystems, remediation of this contaminant is of vital concern. The objective of this study is to evaluate the proficiency of activated magnesium m...

Recently, surface-enhanced Raman scattering nanoprobes have shown tremendous potential in oncological imaging owing to the high sensitivity and specificity of their fingerprint-like spectra. As current Raman scanners rely on a slow, point-by-point spectrum acquisition, there is an unmet need for faster imaging to cover a clinically relevant area in...

The compound 3,5,6-trichloro-2-pyridinol (TCPy), a metabolite of the broad-spectrum organophosphorus insecticide chlorpyrifos, is both more persistent and more water soluble than its parent compound. This difference, which allows TCPy to more readily leach into surface water and groundwater, has led to widespread contamination of TCPy in soils and...

Anisotropy and depolarization are two interconvertible parameters in fluorescence and light scattering spectroscopy that describe the polarization distribution of emitted and scattered photons generated with linearly polarized excitation light. Whereas anisotropy is more frequently used in fluorescence literature for studying association/dissociati...

Chlorinated alkanes were heavily used in a wide range of industrial applications including as degreasers, paint strippers, chemical intermediates, and soil fumigants. These compounds are an environmental concern due to the adverse health effects associated with them and have been detected in environmental matrices including soils and groundwater. C...

We formally prove that Schrödinger equation with Coulomb potential has no nontrivial exact solutions for three or more unrestrained particles. New potentials are needed to solve this issue. This is the subject of an ongoing project. The proof technique is to logically embed three loops of mathematical induction into each other. Our work is an expan...

Hybrid nanostructures comprised of metal nanoparticles (MNPs) and quantum dots (QDs) have been found to exhibit unique, new optical properties due to the interaction that occurs between the MNPs and QDs. The aim of this work is to understand how the exciton-plasmon interaction in these systems is dependent on the excitation wavelength. The nanoasse...

Localized surface plasmon resonance (LSPR) of metal nanoparticles has been proven to be sensitive to their dielecric enviroment and molecular binding, but less is known about the cpability of LSPR towards differentiating homogeneous versus segregated molecular distribution on the nanoparticle surface. Using silica on Au nanospheres to mimic the die...

Graphitic substrates with different curvatures (i.e. carbon nanotubes, carbon nanofibers and graphene) are used to induce the crystallization of poly(3-hexylthiophene) (P3HT) on the surfaces. The effect of P3HT molecular weight (Mn) and the surface curvature on P3HT crystal structures is investigated. P3HTs with an Mn above the chain folding thresh...

With the objective of developing new near-infrared fluorescent probes and understanding the effect molecular structure exerts on physical properties, a series of aniline-based squaraine dyes with different number and position of methoxy substituents adjacent to the squaraine core was synthesized and investigated. Using both computational and experi...

In this study, we aim to investigate the change in photon emission statistics of single CdSe/CdS core/shell quantum dots (QDs) on dielectric modified gold nanoparticle (NP) substrates as a function of excitation wavelength. Photons emitted from single QDs are typically “anti-bunched” and are independent of excitation wavelength. However, when QDs a...

Using the recent polarized resonance synchronous spectroscopic (PRS2) technique, we reported the quantification of photon extinction, absorption, scattering cross-section spectra and scattering depolarization spectra for AuNPs of different sizes and shapes. The effects of the solvent composition, ligand functionalization, and nanoparticle aggregati...

The Cl-initiated atmospheric oxidation mechanism of methyl isopropenyl ketone (MIK) has been investigated at the CCSD(T)/6-311++G(d,p)//MP2/6-311G(d,p) level of theory. Two reaction types initiated from Cl-addition and H-abstraction, respectively, and the key intermediates involved, IM1, IM2 (obtained from Cl-addition) and IM6 (obtained from H-abst...

Rayleigh scattering is a universal material property because all material has nonzero polarizability. Reliable quantification of material light scattering cross-section in liquid phase and their depolarization spectra is however, challenging due to a host of sample and instrument issues. Using the recently developed polarized resonance synchronous...

An important challenge in molecular assembly and hierarchical molecular engineering is to control and program the chiral directional self-assembly. Here, we present a versatile DNA surface adapter that can be programmed to self-assemble into various chiral supramolecular architectures, thereby regulating the chiral directional "bonding" of gold nan...

An important challenge in molecular assembly and hierarchical molecular engineering is to control and program the chiral directional self-assembly. Here, we present a versatile DNA surface adapter that can be programmed to self-assemble into various chiral supramolecular architectures, thereby regulating the chiral directional "bonding" of gold nan...

Fluorophores are important but optically complicated photonic materials as they are simultaneous photon absorbers, emitters, and scatterers. Existing studies on fluorophore optical properties have been focused almost exclusively on its photon absorption and Stokes-shifted fluorescence (SSF) with scant information on the fluorophore photon scatterin...

Galvanic replacement reaction (GRR) has been shown to be an effective method to fine tune the structure of monometallic nanoparticles by controlling the precursor concentration and surface ligands. However, the structural evolution of nanoparticles is not well understood in multimetallic systems, where along with oxidation, dealloying and diffusion...

Polychlorinated biphenyls (PCBs) are banned in the U.S. but are persistent in the environment; current regulations provide an urgent need to remediate PCBs in a cost-effective way. In prior work, a novel method of degradation of PCBs via hydrodehalogenation with ball milled zero-valent magnesium and activated carbon showed promising results even wi...

Using numerical approaches, two different mechanisms leading to enhanced transmission in a sandwiched nanofilm are demonstrated. The film is composed of a flat silver layer and two layers of silver prisms arrays on its both sides. The central flat silver layer is coated with glass substrates on its both sides and the silver prisms arrays are deposi...

This article reports the observation of electrical modulation of localized surface plasmon around self-assembled monolayer (SAM) modified gold nanoparticles, and the establishment of a new spectroscopy technique, i.e., dynamic electro-optical spectroscopy (DEOS). The gold nanoparticles are deposited onto a transparent conductive substrate, and an e...

The gas-phase degradation mechanisms of β-ionone with O3 are investigated using density functional theory (DFT). Possible reaction pathways are presented and discussed. The calculated results show that O3 addition to the double bond in the side chain is favored over that in the ring in the initial steps. The experimentally observed products of 2-ox...

Localized surface plasmon resonance (LSPR) arises when light interacts with metallic nanoparticles (NPs). When nanoparticles (NPs) assemble together, the plasmon coupling effect between the NPs often leads to new features in the LSPR of the assembled structure. Understanding the plasmon coupling in the complex assemblies will greatly benefit the de...

Existing studies on molecular fluorescence have almost exclusively been focused on Stokes-shifted fluorescence spectroscopy (SSF) in which the emitted photon is detected at the wavelengths longer than that for the excitation photons. Information on fluorophore on-resonance fluorescence (ORF) and resonance Rayleigh scattering (RRS) is limited and of...

Organothiol binding to gold nanoparticles (AuNPs) in water proceeds through a deprotonation pathway in which the sulfur-bound hydrogen (RS-H) atoms are released to solution as protons and the organothiol attach to AuNPs as negatively charged thiolate. The missing puzzle pieces in this mechanism are (i) the significance of electrostatic repulsion am...

Using an array of rectangular silver prisms, we numerically demonstrated that close to 100% transmission and reflection of the electromagnetic wave can be switched by slightly changing the incident wavelengths of less than 10 nm. The calculations showed that the resonance wavelengths are associated with the coherent dipole coupling among nanopartic...

Carbon-carbon bond is one of the most ubiquitous molecular building blocks for natural and man-made materials. Rotational isomerization is fundamentally important for understanding the structure and reactivity of chemical and biological molecules. Reported herein is the first demonstration that a single C-C bond does not rotate in water. The two di...

Demonstrated herein is a UV-vis Ratiometric Resonance Synchronous Spectroscopic (R2S2, pronounced as “R-two-S-two” for simplicity) technique where the R2S2 spectrum is obtained by dividing the resonance synchronous spectrum of a NP-containing solution by the solvent resonance synchronous spectrum. Combined with conventional UV-vis measurements, thi...

The Raman scattering of a molecule will be enhanced when it is placed near a metal nanoparticle and the enhancement factor was believed to be proportional to the enhanced local electric field |E|2 at both excitation and scattering wavelengths. The original prediction was derived based on spherical particles but was popularly applied to different co...

Ion-pairing, the association of oppositely-charged ionic species in solution and at liquid/solid interfaces has been proposed as a key factor for a wide range of physicochemical phenomena. However, experimental observations of ion pairing at the ligand/solid interfaces is challenging due to difficulties in differentiating ion species in electrical...

Single particle level study of the bimetallic nanoparticle growth provides valuable information that is usually hidden in ensemble measurements, helping to improve the understanding of reaction mechanism and overcome the synthetic challenges. In this study, we use single particle spectroscopy to monitor the changes in the scattering spectra of Au-C...

Organodithiols with two distal thiols have been used extensively in gold and silver nanoparticle (AuNP and AgNP) applications. However, understanding the structures and conformations of organodithiols on these nanoparticles is challenging. Reported in this work is a combined surface enhanced Raman spectroscopy (SERS), transmission electron microsco...

Au nanorods are optically tunable anisotropic nanoparticles with built-in catalytic activities. The state-of-the-art seed-mediated nanorod synthesis offers excellent control over the aspect ratios of cylindrical Au nanorods, which enables fine-tuning of plasmon resonances over a broad spectral range. However, facet control of Au nanorods with atomi...

In this work, we systematically investigated the plasmonic effect on blinking, photon antibunching behavior and biexciton emission of single CdSe/CdS core/shell quantum dots (QDs) near gold nanoparticles (NPs) with a silica shell (Au@SiO2). In order to obtain a strong interaction between the plasmons and excitons, the Au@SiO2 NPs and CdSe/CdS QDs o...

In this work, we investigated how the blinking statistics and the photon antibunching behavior of single CdSe/CdS core/shell quantum dots(QDs) get modified in the presence of gold nanoparticles(Au NPs) overcoated with a silica shell of varying thickness.(Au@SiO2). The Au@SiO2 NPs have distinct plasmon resonance peaks which overlap with the absorpti...

Gold nanoparticles (AuNPs) have been used extensively as surface enhanced Raman spectroscopic (SERS) substrates for their large SERS enhancements and widely believed chemical stability. Presented is the finding that iodide can rapidly reduce the SERS intensity of the ligands, including organothiols adsorbed on plasmonic AuNPs through both iodide-in...

In this work, we develop a simple method to produce highly uniform localized surface plasmon resonance (LSPR) substrates based on self-assembly of colloidal gold nanoparticles onto pretreated glass substrates. The LSPR wavelength of the gold nanoparticle arrays is blue-shifted from that of the gold nanoparticles in solution and the single gold nano...

Dispersion stability, ligand structure and conformation, and SERS activities of 1-alkanethiol (CnH2n+1SH, n = 214) functionalized gold and silver nanoparticles (AuNPs and AgNPs) were studied as a function of alkanethiol carbon chain length and nanoparticle (NP) type and size. The dispersion stability of alkanethiol functionalized NPs in water incre...

The wavelength-dependent correlations between UV-vis intensities and surface enhanced Raman spectroscopic (SERS) enhancement factors (EFs) of aggregated gold and silver nanoparticles (AgNPs and AuNPs) were investigated using two experimental approaches. The first is to study the time-resolved SERS EFs under three fixed excitation wavelengths (532,...

Nanoparticle self-assembly is fundamentally important for bottom-up functional device fabrication. Currently, most nanoparticle self-assembly have been achieved with gold nanoparticles (AuNPs) functionalized with surfactants, polymeric materials, or cross-linkers. Reported herein is a facile synthesis of gold and silver nanoparticle (AgNP) films as...

The dependence of quantum dot (QD) fluorescent emission on the proximity of 30 nm gold nanoparticles (AuNPs) was studied with controlled inter-particle distances ranging from 15-70 nm. This was achieved by co-assembling DNA-conjugated QDs and AuNPs in a 1:1 ratio at precise positions on a triangular shaped DNA origami platform. A profound, long ran...

In this paper, we present an experimental and theoretical study of the plasmonic properties of single Ag nanospheres and the plasmon interactions in assemblies of Ag nanosphere dimers and trimers. High-quality Ag nanospheres with small size distribution are synthesized by etching prefabricated Ag nanocubes. We perform a 360° polarization-resolved s...

Previous researchers proposed that thiolated poly(ethylene glycol) (PEG-SH) adopts a “mushroom-like” conformation on gold nanoparticles (AuNPs) in water. However, information regarding the size and permeability of the PEG-SH mushroom caps and surface area passivated by the PEG-SH mushroom stems are unavailable. Reported herein is our finding that A...

We recently reported that a wide range of ligands, including organothiols (OTs), can be completely desorbed from gold nanoparticles (AuNPs) by NaBH4 in water. In addition, NaBH4 induces desulfurization of 2-mercaptobenzimidazole (2-MBI) and 6-thioguanine (6-TG) on AuNPs. Reported herein is a systematic investigation of treating ligands adsorbed ont...

Using electrodynamics theory, we numerically demonstrated that when the incident light polarization direction is parallel to a silver rod axis, the modes that are forbidden in a fully illuminated silver rod can be excited when the rod is partially illuminated. The modes are excited due to the symmetry breaking of the rod when it is partially illumi...

The present invention relates to compositions, devices and methods for detecting microorganisms (e.g., anthrax). In particular, the present invention provides portable, surface-enhanced Raman biosensors, and associated substrates, and methods of using the same, for use in rapidly detecting and identifying microorganisms (e.g., anthrax).

Organothiol (R-SH) (OT) adsorption onto silver nanoparticles (AgNPs) in water was studied for a series of aromatic OTs including p-methylbenzenethiol (p-MBT), p-benzenedithiol (p-BDT), and 2-mercaptobenzimidazole (2-MBI). Unlike the common view that OT forms monolayer adsorption on AgNPs, we found that these aromatic OTs continuously reacted with A...

Using the discrete dipole approximation (DDA) method, we investigated the propagation of light within the visible wavelength region for a two-layer silver film with periodic angled holes. The perforation of the holes at an angle of 45° allows light to propagate selectively along different directions at two resonance wavelengths. The Poynting vector...

Confinement and propagation of light under the diffraction limit is a substantial challenge for the development of waveguides as components in subwavelength optical devices. Light confinement and propagation at optical frequencies in a two-layer silver film with a periodic array of holes is investigated in a numerical study using the discrete dipol...

A generalized electrodynamics model is proposed to describe the enhancement and quenching of the fluorescence signal of a dye molecule placed near a metal nanoparticle (NP). Both the size of the NP and quantum yield of the dye molecule are crucial in determining the emission intensity of the molecule. Changing the size of the metal NP will alter th...

Organosulfur compounds are known to poison metallic nanoparticle catalysts. Herein NaBH4 is shown to desorb and desulfurize 2-mercaptobenzimidazole (2-MBI) and 6-thioguanine (6-TG) adsorbed on 10, 15, and 50 nm diameter gold nanoparticles (AuNPs). The desulfurization rates decrease significantly with increasing AuNP sizes. Isotope labeling experime...

Plasmonic nanostructures can profoundly affect the optical properties of light absorbers and emitters. Using quantum dot-modified-atomic force microscopy (AFM) tips as a nanoscale light source, the topological features of a Ag nanowire and its effect on the fluorescence intensity and lifetime of the QDs can be simultaneously imaged with AFM spatial...

A novel chamber-channel system is proposed to achieve the bending of light at a 90 deg angle with relatively high transmission efficiencies. An ultrathin film is introduced into the chamber to couple more light into the system, which makes the chamber as a light absorber, while the channel serves as an output pathway to guide the light through the...

We used DNA origami as a platform to coassemble a 20 nm gold nanoparticle (AuNP) and an organic fluorophore (TAMRA) and studied the distance-dependent plasmonic interactions between the particle and the dye using steady state fluorescence and lifetime measurements. Greater fluorescence quenching was found at smaller dye-particle distances, which wa...

Recent research has demonstrated that the nanoparticle (NP) surface enhanced Raman spectroscopy (SERS) substrate modifies an analyte’s Raman signal through two competitive mechanisms, SERS enhancement and NP inner filter effect, instead of SERS enhancement alone as commonly believed. Using a combination of time-resolved Raman spectroscopy and a sol...

Mechanism of sodium borohydride removal of organothiols from gold nanoparticles (AuNPs) was studied using an experimental investigation and computational modeling. Organothiols, and other AuNP surface adsorbates such as thiophene, adenine, Rhodamine, small anions (Br- and I-), and a polymer (PVP, poly(N-vinylpyrrolidone)) can all be rapidly and com...

Presented herein is a combined experimental and computational study of the gold nanoparticle (AuNP) inner filter effect on surface enhanced Raman spectroscopic (SERS) measurements. Using a bianalyte strategy in which dithiopurine (DTP) and ethanol were employed as the model analytes, we demonstrated that AuNPs enhance DTP's Raman signal but attenua...

Hot electron relaxation and coherent vibrational oscillations of gold nanostars (AuNS) were studied using femtosecond laser spectroscopy. Transient profiles feature a fast decay attributed to electron–phonon interaction and a slower decay due to phonon relaxation. Superimposed on the slow decay are oscillations attributed to coherent vibrations of...

This article describes a low cost method of generating silicon nanowire arrays that have similar structure and light trapping ability as moth-eye for matrix-free laser desorption/ionization mass spectrometry analysis of small molecules without matrix peak interference. The nanowire array is produced by combining low cost nanosphere lithography and...

This article describes a low cost method of generating silicon nanowire arrays that have similar structure and light trapping ability as moth-eye for matrix-free laser desorption/ionization mass spectrometry analysis of small molecules without matrix peak interference. The nanowire array is produced by combining low cost nanosphere lithography and...

Herein we report the formation of the second-ring Diels–Alder adduct together with the central-ring adduct in a reaction of pentacene and tetracyanoethylene at room temperature. DFT calculations showed that the difference between the free energy of the two isomers is about 3.9 kcal/mol. Photo- and thermal-induced isomerization between the central-r...

Studying the correlation between the molecular structures of SERS-active analytes and their SERS enhancement factors is important to our fundamental understanding of SERS chemical enhancement. Using a common internal reference method, we quantitatively compared the Raman activities, SERS activities, and SERS enhancement factors for a series of orga...

Using theoretical tools, we numerically demonstrated Fano line shapes in the scattering spectra of silver rods resulting from different mechanisms. One of the Fano line shapes is due to the coupling of an in-plane quadrupole and a dipole mode in a single rod. Two nodes were observed at the resonance wavelength, each of which is located at a quarter...

Programmable positioning of one-dimensional (1D) gold nanorods (AuNRs) was achieved by DNA directed self-assembly. AuNR dimer structures with various predetermined inter-rod angles and relative distances were constructed with high efficiency. These discrete anisotropic metallic nanostructures exhibit unique plasmonic properties, as measured experim...