Clemens Burda

Publications (62)399.62 Total impact

• Article: Photophysics of Silicon Phthalocyanines in Aqueous Media.

  Tennyson L Doane, Chi-Hung Chuang, Andrew Chomas, Clemens Burda
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  ABSTRACT: Phthalocyanines have been used as photodynamic therapy (PDT) agents because of their uniquely favorable optical properties and high photostability. They have been shown to be highly successful for the treatment of cancer through efficient singlet-oxygen ((1) O(2) ) production. However, due to their hydrophobic properties, the considerations of solubility and cellular location have made understanding their photophysics in vitro and in vivo difficult. Indeed, many quantitative assessments of PDT reagents are undertaken in purely organic solvents, presenting challenges for interpreting observations during practical application in vivo. With steady-state and time-resolved laser spectroscopy, we show that for axial ligated silicon phthalocyanines in aqueous media, both the water:lipophile ratio and the pH have drastic effects on their photophysics, and ultimately dictate their functionality as PDT drugs. We suggest that considering the presented photophysics for PDT drugs in aqueous solutions leads to guidelines for a next generation of even more potent PDT agents.
  ChemPhysChem 01/2013; · 3.41 Impact Factor
• Article: Nanoparticles for imaging and treating brain cancer.

  Joseph D Meyers, Tennyson Doane, Clemens Burda, James P Basilion
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  ABSTRACT: Brain cancer tumors cause disruption of the selective properties of vascular endothelia, even causing disruptions in the very selective blood-brain barrier, which are collectively referred to as the blood-brain-tumor barrier. Nanoparticles (NPs) have previously shown great promise in taking advantage of this increased vascular permeability in other cancers, which results in increased accumulation in these cancers over time due to the accompanying loss of an effective lymph system. NPs have therefore attracted increased attention for treating brain cancer. While this research is just beginning, there have been many successes demonstrated thus far in both the laboratory and clinical setting. This review serves to present the reader with an overview of NPs for treating brain cancer and to provide an outlook on what may come in the future. For NPs, just like the blood-brain-tumor barrier, the future is wide open.
  Nanomedicine 01/2013; 8(1):123-43. · 5.05 Impact Factor
• Article: Ultrafast Photoinduced Electron Transfer between an Incarcerated Donor and a Free Acceptor in Aqueous Solution.

  Mintu Porel, Chi-Hung Chuang, Clemens Burda, Vaidhyanathan Ramamurthy
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  ABSTRACT: Supramolecular photoinduced electron transfer dynamics between coumarin 153 (C153) and 4,4'-dimethyl viologen dichloride (MV(2+)) across the molecular barrier of a host molecule, octa acid (OA), has been investigated with femtosecond time resolution. The ultrafast electron transfer from C153 to MV(2+) followed excitation with 150 fs laser pulses at a wavelength of 390 nm despite the fact that C153 was incarcerated within an OA(2) capsule. As a result, the photoexcited coumarin did not show any of the typical relaxation dynamics that is usually observed in free solution. Instead, the excited electron was transferred across the molecular wall of the capsuleplex within 20 ps. Likewise, the lifetime of the charge transfer state was short (724 ps), and electron back-transfer reestablished the ground state of the system within 1 ns, showing strong electronic coupling among the excited electron donor, host, and acceptor. When the donor was encapsulated into the host molecule, the electron transfer process showed significantly accelerated dynamics and essentially no solvent relaxation compared with that in free solution. The study was also extended to N-methylpyridinium iodide as the acceptor with similar results.
  Journal of the American Chemical Society 08/2012; 134(36):14718-21. · 9.91 Impact Factor
• Article: The unique role of nanoparticles in nanomedicine: imaging, drug delivery and therapy.

  Tennyson L Doane, Clemens Burda
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  ABSTRACT: This critical review will present the role of nanoparticles (NPs) in the directions that are vital to the new field of nanomedicine, including imaging and drug delivery. We reflect on the physical properties that make NPs advantageous for in vivo efficacy, and review recent advances in major NP based biomedical applications. Critical questions of transport, uptake, and clearance will be discussed and illustrated through the success and opportunities of NP imaging and therapy on a photodynamic therapy (PDT) based NP system that has been developed in our lab over the past decade (540 references).
  Chemical Society Reviews 01/2012; 41(7):2885-911. · 28.76 Impact Factor
• Article: Nanoparticle ζ -potentials.

  Tennyson L Doane, Chi-Hung Chuang, Reghan J Hill, Clemens Burda
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  ABSTRACT: For over half a century, alternating electric fields have been used to induce particle transport, furnishing the ζ-potential of analytes with sizes ranging from a few nanometers to several micrometers. Concurrent advances in nanotechnology have provided new materials for catalysis, self-assembly, and biomedical applications, all of which benefit from a thorough understanding of particle surface charge. Therefore, the measurement of the ζ-potential via electrophoretic light scattering (ELS) has become essential for nanoparticle (NP) research. However, the interpretation of NP electrophoretic mobility, especially that of ligand-coated NPs, can be a complex undertaking. Despite the inherent intricacy of these data, key concepts from colloidal science can help to distill valuable information from ELS. In this Account, we adopt PEGylated Au NPs as an illustrative example to explore extensions of the classical theories of Smoluchowski, Hückel, and Henry to more contemporary theories for ligand-coated NP systems such as those from Ohshima, and Hill, Saville, and Russel. First, we review the basic experimental considerations necessary to understand NP electrophoretic mobility, identifying when O'Brien and White's numerical solution of the standard electrokinetic model should be adopted over Henry's closed-form analytical approximation. Next, we explore recent developments in the theory of ligand-coated particle electrophoresis, and how one can furnish accurate and meaningful relationships between measured NP mobility, ζ-potential, and surface charge. By identifying key ligand-coated NP parameters (e.g., coating thickness, permeability, molecular mass, and hydrodynamic segment size), we present a systematic method for quantitatively interpreting NP electrophoretic mobility. In addition to reviewing theoretical foundations, we describe our recent results that examine how the unique surface curvature of NPs alters and controls their properties. These data provide guidelines that can expedite the rational design of NPs for advanced uses, such as heterogeneous catalysis and in vivo drug delivery. As a practical demonstration of these concepts, we apply the ligand-coated theory to a recently developed noncovalent PEGylated Au NP drug-delivery system. Our analysis suggests that anion adsorption on the Au NP core may enhance the stability of these NP-drug conjugates in solution. In addition to providing useful nanochemistry insights, the information in this Account will be useful to biomedical and materials engineers, who use ELS and ζ-potentials for understanding NP dynamics.
  Accounts of Chemical Research 11/2011; 45(3):317-26. · 21.64 Impact Factor
• Article: Measuring electron and hole transfer in core/shell nanoheterostructures.

  Chi-Hung Chuang, Tennyson L Doane, Shun S Lo, Gregory D Scholes, Clemens Burda
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  ABSTRACT: Using femtosecond transient absorption and time-resolved photoluminescence spectroscopy, we studied the electron versus hole dynamics in photoexcited quasi-type-II heterostructured nanocrystals with fixed CdTe core radii and varying CdSe shell coverage. By choosing the pump wavelength in resonance with the core or the shell states, respectively, we were able to measure the excited electron and hole dynamics selectively. Both, the core- and the shell-excited CdTe/CdSe nanocrystals showed the same spectral emission and photoluminescence lifetimes, indicating that ultrafast electron and hole transfer across the core/shell interface resulted in the identical long-lived charge transfer state. Both charge carriers have subpicosecond transfer rates through the interface, but the subsequent relaxation rates of the hole (τ(dec) ∼ 800 ps) and electron (τ(avg) ∼ 8 ps) are extremely different. On the basis of the presented transient absorption measurements and fitting of the steady-state spectra, we find that the electron transfer occurs in the Marcus inverted region and mixing between the CdTe exciton and charge transfer states takes place and therefore needs to be considered in the analysis.
  ACS Nano 06/2011; 5(7):6016-24. · 10.77 Impact Factor
• Article: Addressing Brain Tumors with Targeted Gold Nanoparticles: A New Gold Standard for Hydrophobic Drug Delivery?

  Yu Cheng, Joseph D Meyers, Richard S Agnes, Tennyson L Doane, Malcolm E Kenney, Ann-Marie Broome, Clemens Burda, James P Basilion
  Small 06/2011; · 8.35 Impact Factor
• Article: Synthesis and Photophysical Properties of Ternary I–III–VI AgInS2 Nanocrystals: Intrinsic versus Surface States

  Baodong Mao, Chi-Hung Chuang, Junwei Wang, Clemens Burda
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  ABSTRACT: Ternary I–III–VI AgInS2 (AIS) semiconductor nanocrystals (NCs) with strong photoluminescence (PL) were synthesized using a one-pot reaction at low temperature. UV–vis absorption and PL spectra red shifted as the AIS NCs grew. Both steady-state and time-resolved PL spectroscopies were used to investigate the influence of surface and intrinsic trap states on the PL behaviors of the prepared AIS NCs. PL lifetimes at different wavelengths in the full spectrum range were measured using a streak camera for each sample toward a systematic kinetic study. We found PL lifetime components that were short-lived from surface states and long-lived from intrinsic states. Surface trap emissions were wavelength- and size-dependent. Besides these PL studies, we report the first measurements using femtosecond transient absorption spectroscopy to investigate the exciton dynamics of the AIS NCs. Because of the abundant intrinsic trap states, these ternary AIS NCs have long-lived excitons, which may provide potential applications in photocatalysis and photovoltaics.
  04/2011;
• Source

  Available from: zhugroup-nju.com

  Article: Rapid sonochemical synthesis of highly luminescent non-toxic AuNCs and Au@AgNCs and Cu (II) sensing.

  Hongying Liu, Xiang Zhang, Ximei Wu, Liping Jiang, Clemens Burda, Jun-Jie Zhu
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  ABSTRACT: Highly fluorescent and water-soluble gold nanoclusters (AuNCs) with near-infrared-emission and Au@AgNCs with yellow-emission were successfully prepared via a rapid sonochemical approach, and the as-prepared AuNCs could be applied in the determination of Cu(2+) with a wider detection range and lower detection limit.
  Chemical Communications 02/2011; 47(14):4237-9. · 6.17 Impact Factor
• Article: Deep penetration of a PDT drug into tumors by noncovalent drug-gold nanoparticle conjugates.

  Yu Cheng, Joseph D Meyers, Ann-Marie Broome, Malcolm E Kenney, James P Basilion, Clemens Burda
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  ABSTRACT: Efficient drug delivery to tumors is of ever-increasing importance. Single-visit diagnosis and treatment sessions are the goal of future theranostics. In this work, a noncovalent PDT cancer drug-gold nanoparticle (Au NP) conjugate system performed a rapid drug release and deep penetration of the drug into tumors within hours. The drug delivery mechanism of the PDT drug through Au NPs into tumors by passive accumulation was investigated via fluorescence imaging, elemental analysis, and histological staining. The pharmacokinetics of the conjugates over a 7-day test period showed rapid drug excretion, as monitored via the fluorescence of the drug in urine. Moreover, the biodistribution of Au NPs in this study period indicated clearance of the NPs from the mice. This study suggests that noncovalent delivery via Au NPs provides an attractive approach for cancer drugs to penetrate deep into the center of tumors.
  Journal of the American Chemical Society 02/2011; 133(8):2583-91. · 9.91 Impact Factor
• Article: Emergent properties resulting from type-II band alignment in semiconductor nanoheterostructures.

  Shun S Lo, Tihana Mirkovic, Chi-Hung Chuang, Clemens Burda, Gregory D Scholes
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  ABSTRACT: The development of elegant synthetic methodologies for the preparation of monocomponent nanocrystalline particles has opened many possibilities for the preparation of heterostructured semiconductor nanostructures. Each of the integrated nanodomains is characterized by its individual physical properties, surface chemistry, and morphology, yet, these multicomponent hybrid particles present ideal systems for the investigation of the synergetic properties that arise from the material combination in a non-additive fashion. Of particular interest are type-II heterostructures, where the relative band alignment of their constituent semiconductor materials promotes a spatial separation of the electron and hole following photoexcitation, a highly desirable property for photovoltaic applications. This article highlights recent progress in both synthetic strategies, which allow for material and architectural modulation of novel nanoheterostructures, as well as the experimental work that provides insight into the photophysical properties of type-II heterostructures. The effects of external factors, such as electric fields, temperature, and solvent are explored in conjunction with exciton and multiexciton dynamics and charge transfer processes typical for type-II semiconductor heterostructures.
  Advanced Materials 11/2010; 23(2):180-97. · 13.88 Impact Factor
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  Available from: zhugroup-nju.com

  Article: Solar-light photoamperometric and photocatalytic properties of quasi-transparent TiO2 nanoporous thin films.

  Yajun Ji, Keng-Chu Lin, Hegen Zheng, Chung-Chiun Liu, Laurie Dudik, Junjie Zhu, Clemens Burda
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  ABSTRACT: Transparent photocatalytic surfaces are of ever increasing importance for many applications on self-cleaning windows and tiles in everyday applications. Here, we report the formation and photocatalytic testing of a quasi-transparent thin and nanoporous titania films deposited on glass plates. Sputtered Ti thin films were anodized in fluoride-ion-containing neutral electrolytes to form optically semitransparent nanoporous films, which transformed to be completely transparent after thermal annealing. The nanoporous films were studied at different stages, such as before and after anodization, as well as after thermal annealing using scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-vis and Raman spectroscopy. It was observed that anodization at 20 V of high-temperature deposited titanium films resulted in regular nanopore films with pore diameters of 30 nm. Structural investigations on the transparent nanopore arrays reveal the presence of anatase phase TiO(2) even after annealing at 500 °C, which was confirmed by XRD and Raman spectroscopy measurements. The solar-light induced photocatalytic decomposition of stearic acid and photoconductivity characteristics of these nanoporous thin films are also presented.
  ACS Applied Materials & Interfaces 10/2010; 2(11):3075-82. · 4.53 Impact Factor
• Article: Electrophoretic mobilities of PEGylated gold NPs.

  Tennyson L Doane, Yu Cheng, Amir Babar, Reghan J Hill, Clemens Burda
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  ABSTRACT: Electromigration of nanoparticles (NPs) is relevant to many technological and biological applications. We correlate the experimentally observed electromigration of Au NPs with a closed-form theoretical model that furnishes key NP characteristics, including the previously unknown values of Au NP core ζ-potential, PEG-corona permeability, and particle-hydrogel friction coefficient. More generally, the theory furnishes new understanding of NP electromigration in complex environments, establishing a robust and predictive model to guide the design and characterization of functionalized NPs.
  Journal of the American Chemical Society 10/2010; 132(44):15624-31. · 9.91 Impact Factor
• Article: Visible-light-driven reversible and switchable hydrophobic to hydrophilic nitrogen-doped titania surfaces: correlation with photocatalysis.

  Junwei Wang, Baodong Mao, James L Gole, Clemens Burda
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  ABSTRACT: Visible-light-responsive nitrogen-doped titanium dioxide nanorods have been synthesized by a hydrothermal method at low temperature. X-Ray diffraction, scanning electron microscopy, UV-vis spectroscopy, and contact angle measurements were used to obtain the crystal structures, morphologies, visible-light absorbance, and hydrophobicity, respectively, of the prepared nanorods. The surface wettability of the samples could be reversibly tuned from hydrophobic to hydrophilic upon visible-light illumination. This switchable surface wettability is crucial since the photocatalytic activity of this nanoscaled catalyst for the decomposition of organic molecules exhibits a strong dependence on the surface wettability.
  Nanoscale 10/2010; 2(10):2257-61. · 5.91 Impact Factor
• Article: Charge Separation and Recombination in CdTe/CdSe Core/Shell Nanocrystals as a Function of Shell Coverage: Probing the Onset of the Quasi Type-II Regime

  Chi-Hung Chuang, Shun S. Lo, Gregory D. Scholes, Clemens Burda
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  ABSTRACT: Femtosecond transient absorption (TA) is used to investigate population dynamics of electronic states in CdTe/CdSe core/shell nanocrystals (NCs) with varying CdSe shell coverage. Upon CdSe shell growth, the CdTe/CdSe NCs show a gradual evolution of surface passivation toward a quasi-type-II charge separation regime. Our results indicate that ultrafast electron transfer (ET) through the interface of CdTe/CdSe NCs becomes measurable as the CdSe shell approaches the quasi-type-II regime which we experimentally determined to be at 0.4 nm (shell) for a 3.4 nm CdTe core. This work reports the first measurement using femtosecond TA to study the electronic states in CdTe/CdSe NCs and spectroscopically observe the evolution of an ultrafast charge transfer (CT) in such a core/shell system. Time-resolved photoluminescence (PL) spectroscopy is used to study the radiative lifetimes of the CdTe/CdSe NCs. One monolayer CdSe coverage leads to longer-lived PL, which is red-shifted by 140 nm compared to the CdTe core PL. It is concluded that this is due to greater electron−hole separation providing a longer-lived CT state.Keywords (keywords): charge separation; electron transfer; core−shell; femtosecond transient absorption; quasi-type-II heterostructure
  08/2010;
• Article: Study of concentration-dependent cobalt ion doping of TiO2 and TiO(2-x)Nx at the nanoscale.

  James L Gole, Sharka M Prokes, O J Glembocki, Junwei Wang, Xiaofeng Qiu, Clemens Burda
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  ABSTRACT: Experiments with a porous sol-gel generated TiO(2) nanocolloid and its corresponding oxynitride TiO(2-x)N(x) are carried out to evaluate those transformations which accompany additional doping with transition metals. In this study, doping with cobalt (Co(ii)) ions is evaluated using a combination of core level and VB-photoelectron and optical spectroscopy, complementing data obtained from Raman spectroscopy. Raman spectroscopy suggests that cobalt doping of porous sol-gel generated anatase TiO(2) and nitridated TiO(2-x)N(x) introduces a spinel-like structure into the TiO(2) and TiO(2-x)N(x) lattices. TEM and XPS data complemented by valence band-photoelectron spectra demonstrate that metallic cobalt clusters are not formed even at high doping levels. As evidenced by Raman spectroscopy, the creation of a spinel-like structure is commensurate with the room temperature conversion of the oxide and its oxynitride from the anatase to the rutile form. The onset of this kinetically driven process correlates with the formation of spinel sites within the TiO(2) and TiO(2-x)N(x) particles. Despite their visible light absorption, the photocatalytic activity of these cobalt seeded systems is diminished relative to the oxynitride TiO(2-x)N(x).
  Nanoscale 07/2010; 2(7):1134-40. · 5.91 Impact Factor
• Article: Improving Thermoelectric Properties of Chemically Synthesized Bi2Te3-Based Nanocrystals by Annealing

  Yixin Zhao, Jeffrey S. Dyck, Brett M. Hernandez, Clemens Burda
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  ABSTRACT: The power factors of chemically synthesized Bi2Te3 and Bi0.5Sb1.5Te3 nanocrystals (NCs) were improved up to 2.4 and 7.8 μW cm−1 K−2, respectively, which are significantly higher than previously reported values for chemically synthesized Bi2Te3 NCs and even comparable to the recently reported highest power factor of 5 μW cm−1 K−2 for Bi2Te3 NCs consolidated by spark plasma sintering. This improvement was achieved by annealing the NCs under argon protection, and the crystal structures and morphologies of these annealed NCs were characterized via XRD, SEM, and TEM measurements. The temperature-dependent thermoelectric properties of these modified NCs were explored on cold-pressed pellets of NCs. Improvement of the thermoelectric performances of the pellets resulted primarily from an increase in electrical conductivity (σ), while only weakly increasing the lattice thermal conductivity (κL), which was still kept lower than bulk values. Hall carrier concentration studies suggest that the improvement of the electrical conductivity is caused primarily by modification of the charge carrier mobility rather than the carrier concentration. A mechanism is proposed to explain a large increase of electrical conductivity by annealing related to a decrease of activation energy for the mobility after the removal of organic capping ligands through annealing.
  06/2010;
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  Available from: zhugroup-nju.com

  Article: Fabrication of near-infrared-emitting CdSeTe/ZnS core/shell quantum dots and their electrogenerated chemiluminescence.

  Guo-Xi Liang, Ling-Ling Li, Hong-Yin Liu, Jian-Rong Zhang, Clemens Burda, Jun-Jie Zhu
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  ABSTRACT: New water-soluble CdSeTe/ZnS core-shell quantum dots with excellent near-infrared emission were synthesized via an aqueous solution method; they showed strong electrogenerated chemiluminescence and favorable biocompatibility.
  Chemical Communications 05/2010; 46(17):2974-6. · 6.17 Impact Factor
• Article: Enhancing thermoelectric performance of ternary nanocrystals through adjusting carrier concentration.

  Yixin Zhao, Jeffrey S Dyck, Brett M Hernandez, Clemens Burda
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  ABSTRACT: The carrier concentration of chemically synthesized Bi(2)Te(3)-based nanocrystals (NCs) is for the first time reported to be adjusted by forming ternary Bi(2-x)Sb(x)Te(3) NCs (x = 0.02, 0.05, 0.10, 0.20, 0.50, and 1.50) through partial substitution of Bi with Sb. Carrier concentrations of ternary Bi(2-x)Sb(x)Te(3) NCs were successfully adjusted by a factor of more than 10 controlled by the stoichiometric partial Sb/Bi substitution level. The power factors of the stoichiometric ternary Bi(2-x)Sb(x)Te(3) NCs improved three times compared to the parent Bi(2)Te(3) due to the carrier concentration adjustment.
  Journal of the American Chemical Society 03/2010; 132(14):4982-3. · 9.91 Impact Factor
• Article: Improvement of the thermoelectric power factor through anisotropic growth of nanostructured PbSe thin films.

  Xiaofeng Qiu, Yixin Zhao, Ian M Steward, Jeffrey S Dyck, Clemens Burda
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  ABSTRACT: Nanostructured PbSe films with different (200)/(111) grain size ratios were prepared by anisotropic growth on glass substrates. Although face centered cubic bulk PbSe is an isotropic material, the thermopower (S), electrical conductivity (sigma) and hole mobility of the prepared nanostructured PbSe films show an obvious dependence on the anisotropic parameter, (200)/(111) grain size ratio. The thermoelectric power factor (S(2)sigma) of the nanostructured films is improved with higher (200)/(111) grain size ratio. Temperature-dependent transport measurements suggest that grain boundary scattering dominates in these nanostructured films. Subtle changes in the microstructure are discussed in the light of the effect on grain boundary activation energy (barrier height). A 20% enhancement of the room temperature thermopower (S) at given carrier concentrations is demonstrated for the CBD-grown nanostructured PbSe films compared to single crystal bulk PbSe.
  Dalton Transactions 01/2010; 39(4):1095-100. · 3.84 Impact Factor