Jingyi Chen | University of Arkansas (original) (raw)

Papers by Jingyi Chen

Chemical Society Reviews, 2006

The surface plasmon resonance peaks of gold nanostructures can be tuned from the visible to the n... more The surface plasmon resonance peaks of gold nanostructures can be tuned from the visible to the near infrared region by controlling the shape and structure (solid vs. hollow). In this tutorial review we highlight this concept by comparing four typical examples: nanospheres, nanorods, nanoshells, and nanocages. A combination of this optical tunability with the inertness of gold makes gold nanostructures well suited for various biomedical applications.

Nano Letters, 2004

... (c, d, g, h) Models showing that the growth of Pt nanoparticle (see the HRTEM image immediate... more ... (c, d, g, h) Models showing that the growth of Pt nanoparticle (see the HRTEM image immediately ... This article has been cited by 47 ACS Journal articles (5 most recent appear below). ... Synthesis of Porous Single-Crystalline Platinum Nanocubes Composed of Nanoparticles. ...

Journal of The American Chemical Society, 2006

Gold-silver alloy nanocages with controllable pores on the surface have been synthesized via galv... more Gold-silver alloy nanocages with controllable pores on the surface have been synthesized via galvanic replacement reaction between truncated Ag nanocubes and aqueous HAuCl4. Unlike in the previous studies, the initiation of replacement reaction started in a controllable way, simultaneously from eight corners of the truncated Ag nanocubes where {111} facets were exposed. The formation of cubic nanocages with pores at all the corners was determined by the capping agent, poly(vinyl pyrrolidone) (PVP), which preferentially covered the {100} facets of a truncated Ag nanocube.

Angewandte Chemie-international Edition, 2005

Optics Letters, 2007

We demonstrate a self-aligned balanced cross-correlator based on a single type-II phase-matched P... more We demonstrate a self-aligned balanced cross-correlator based on a single type-II phase-matched PPKTP crystal. The birefringence of the crystal generates a walk-off between the two orthogonally polarized pulses. This enables the balancing of the cross-correlator with input pulses at the same center wavelength. As a first application of this single-crystal balanced crosscorrelator, we stabilized a 310-meter long optical fiber link for timing distribution with long-term stable 10-fs precision.

Accounts of Chemical Research, 2008

Noble-metal nanocages represent a novel class of nanostructures with hollow interiors and porous ... more Noble-metal nanocages represent a novel class of nanostructures with hollow interiors and porous walls. They are prepared using the remarkably simple galvanic replacement reaction between solutions containing metal precursor salts and Ag nanostructures prepared by polyol reduction. The electrochemical potential difference between the two species drives the reaction, with the reduced metal depositing on the surface of the Ag nanostructure. In our most studied example involving HAuCl 4 as the metal precursor, the resultant Au epitaxially deposits on the surface of the Ag nanocubes, adopting their cubic structure. Concurrent with this deposition, the interior Ag is oxidized and removed, together with alloying and dealloying, to produce hollow and eventually porous structures that we commonly refer to as Au nanocages. This approach has proven versatile, with a wide range of morphologies -including nanorings, prism-shaped nanoboxes, nanotubes, and multiple-walled nanoshells or nanotubes -being produced by changing the shape of the initial Ag template. Besides Au-based structures, Pt-and Pd-containing hollow nanostructures have been prepared by switching the metal salt precursors

Journal of The American Chemical Society, 2004

Platinum nanowires of approximately 100 nm in length and approximately 5 nm in diameter have been... more Platinum nanowires of approximately 100 nm in length and approximately 5 nm in diameter have been synthesized by reducing H(2)PtCl(6) with ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) and a trace amount of Fe(3+) or Fe(2+). The wires were generated at the final stage of the synthesis, which involved the formation of several intermediate species. The Fe(3+) or Fe(2+) ions had dual functions in the synthesis: they induced aggregation of Pt nanoparticles into larger structures that served as the nucleation sites, and they greatly reduced the reaction rate and supersaturation level to induce anisotropic growth. The reaction mechanism was studied by X-ray photoelectron spectroscopy (XPS) and UV-vis spectral analysis. The Pt nanowires could be readily separated from the surfaces of the agglomerates by sonication and obtained as pure samples by centrifugation.

Journal of The American Chemical Society, 2005

. UV-vis spectra of solutions taken at different reaction stages. The inset depicts the time depe... more . UV-vis spectra of solutions taken at different reaction stages. The inset depicts the time dependence of the absorbance at ∼245 nm, which is directly proportional to the concentration of the [PdCl4] 2species.

Optics Letters, 2005

We describe gold nanocages as a new class of potential contrast agent for spectroscopic optical c... more We describe gold nanocages as a new class of potential contrast agent for spectroscopic optical coherence tomography (OCT). Monodispersed gold nanocages of an approximately 35 nm edge length exhibit strong optical resonance, with the peak wavelength tunable in the near-infrared range. We characterized the optical properties of the nanocage by using OCT experiments along with numerical calculations, revealing an absorption cross section approximately 5 orders of magnitude larger than conventional dyes. Experiments with tissue phantoms demonstrated that the nanocages provide enhanced contrast for spectroscopic as well as conventional intensity-based OCT imaging.

Gold nanocages of different sizes synthesized via galvanic replacement reaction have been studied... more Gold nanocages of different sizes synthesized via galvanic replacement reaction have been studied by ultrafast time-resolved spectroscopy. The vibrational phonon modes were excited and the periods of these modes increase with the size of the gold nanocages. For a specific size of nanocage, experiments with different excitation powers of the pump laser were performed (from 2 μJ to 20 μJ), we found that the period of the vibrational mode increased with the laser intensity. This was compared to experiments on spherical gold nanoparticles, which allow us to roughly estimate the temperature of the nanocages when the electrons and the phonons reach the equilibrium. The temperature of the nanocages can increase up to 1000 K, near the melting point of the bulk metal, while the particles maintain their integrity. This makes the nanocages potentially useful for photothermal therapy applications. The heat dissipation rate for the nanocages was also studied in these experiments, and was found to have the similar trend as spherical nanoparticles, i.e., larger particles stay hot for longer times than smaller particles.

Nano Letters, 2007

Gold nanocages with a relatively small size (e.g., ~45 nm in edge length) have been developed, an... more Gold nanocages with a relatively small size (e.g., ~45 nm in edge length) have been developed, and the structure of these nanocages was tailored to achieve strong absorption in the near infrared (NIR) region for photothermal cancer treatment. Numerical calculations show that the nanocage has a large absorption cross-section of 3.48×10 −14 m 2 , facilitating conversion of NIR irradiation into heat. The gold nanocages were conjugated with monoclonal antibodies (anti-HER2) to target epidermal growth factor receptors (EGFR) that are over-expressed on the surface of breast cancer cells (SK-BR-3). Our preliminary photothermal results show that the nanocages strongly absorb light in the NIR region, with an intensity threshold of 1.5 W/cm 2 to induce thermal destruction to the cancer cells. In the intensity range of 1.5-4.7 W/cm 2 , the circular area of damaged cells increased linearly with the irradiation power density. These results suggest that this new class of bioconjugated gold nanostructures -immuno gold nanocages -can potentially serve as an effective photothermal therapeutic agent for cancer treatment.

Materials Letters, 2014

ABSTRACT The centrifugation method was proposed to extract Au nanocages (AuNCs) from a mixture of... more ABSTRACT The centrifugation method was proposed to extract Au nanocages (AuNCs) from a mixture of the bimetallic Au and Ag alloyed nanocages, Ag and Au core-shell structure, and Au-pitted silver nanocubes. The DDA simulation was found to be a powerful tool to characterize a colloidal dispersion of the plasmonic nanoparticles. The effect of the irregularity of Au hollow cages and presence of the polymer shells around the cages on the surface plasmon resonance spectra (SPR) had been suggested based on the DDA simulations.

Langmuir, 2007

We review recent developments in our group regarding the solution-phase synthesis of one-dimensio... more We review recent developments in our group regarding the solution-phase synthesis of one-dimensional nanostructures of metals. The synthetic approaches include solution-liquid-solid growth for nanowires of low-melting-point metals such as Pb; seed-directed growth for Ag nanowires, nanobeams, and nanobelts; kinetically controlled growth for Pt nanorods, nanowires, and multipods; and galvanic replacement for nanotubes of Au, Pt, and Pd. Both characterization and mechanistic studies are presented for each nanostructure. Finally, we highlight the electrical and plasmonic properties of these metal nanostructures and discuss their potential applications in nanoscale devices. (1) Xia, Y.; Yang, P.; Sun, Y.; Wu, Y.; Mayers, B.; Gates, B.; Yin, Y.; Kim, F.; Yan, H. Alekseeva, A. V.; Bogatyrev, V. A.; Dykman, L. A.; Khlebtsov, B. N.; Trachuk, L. A.; Melnikov, A. G.; Khlebtsov, N.

Chemical Physics Letters, 2006

This Letter describes the fastest route to monodispersed silver nanocubes. By adding a trace amou... more This Letter describes the fastest route to monodispersed silver nanocubes. By adding a trace amount of sodium sulfide (Na2S) or sodium hydrosulfide (NaHS) to the conventional polyol synthesis, the reaction time was significantly shortened from 16–26 h to 3–8 min. By merely adjusting the reaction time, monodispersed silver nanocubes of 25–45 nm in edge length were rapidly and routinely produced on relatively large scales. These small nanocubes are of great interest for biomedical applications by way of generating gold nanocages with plasmon resonance peaks tunable to the near-infrared region through a galvanic replacement reaction.This Letter describes the fastest route to 25–45 nm monodispersed silver nanocubes rapidly and routinely produced on relatively large scales. By adding a trace amount of sodium sulfide (Na2S) or sodium hydrosulfide (NaHS) to the conventional polyol synthesis, the reaction time was significantly shortened to 3–8 min.■

Journal of Agricultural and Food Chemistry, 2013

Nano Letters, 2005

Pd nanocubes between 8 and 50 nm in size were synthesized at the same concentration of Na 2 PdCl ... more Pd nanocubes between 8 and 50 nm in size were synthesized at the same concentration of Na 2 PdCl 4 precursor by controlling the number of seeds formed in the nucleation stage. Increasing the concentration of FeCl 3 , an oxidative etchant for Pd, reduced the number of seeds and led to formation of larger Pd nanocubes. The larger nanocubes exhibited surface plasmon resonance peaks in the visible region, the locations of which matched with the results of the discrete dipole approximation calculation. While the nanocubes of 25 and 50 nm in size oxidized in air to form Pd@PdO core−shell structures, the 8-nm nanocubes were stable in air for over 90 days.

Journal of The American Chemical Society, 2005

The rapid reduction of Na2PdCl4 by ethylene glycol in the presence of poly(vinyl pyrrolidone) (PV... more The rapid reduction of Na2PdCl4 by ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) has recently been demonstrated as a convenient method of generating Pd cubooctahedra and twinned nanoparticles. Here we describe a new procedure where Pd triangular or hexagonal nanoplates could be selectively synthesized by manipulating the reduction kinetics of the polyol process. More specifically, the reduction rate was substantially reduced through the introduction of Fe(III) species and the O 2/Clpair, two wet etchants for Pd(0). The etching power of the O2/Clpair could be further enhanced by adding an acid to lower the pH of the reaction solution. Unlike the previously reported synthesis of Ag and Au nanoplates, light was found to have no indispensable role in the formation of Pd nanoplates. Both triangular and hexagonal nanoplates of Pd exhibited surface plasmon resonance (SPR) peaks in the visible region, and their positions matched with the results of discrete dipole approximation (DDA) calculation. Thanks to their sharp corners and edges, these Pd nanoplates could serve as active substrates for surface-enhanced Raman scattering (SERS).

Langmuir, 2006

Poly(vinyl pyrrolidone) (PVP) has been extensively used in the solution-phase synthesis of many t... more Poly(vinyl pyrrolidone) (PVP) has been extensively used in the solution-phase synthesis of many types of colloidal particles, where it is mainly considered as a steric stabilizer or capping agent with a major role to protect the product from agglomeration. In a recent study, we discovered that the hydroxyl end groups of PVP could also serve as a very mild reductant for kinetically controlled synthesis of Ag nanoplates with yields as high as 75%. Here we further demonstrate that hydroxyl-terminated PVP is also a well-suited reductant for the aqueous synthesis of circular, triangular, and hexagonal nanoplates made of other noble metals including Pd, Au, and Pt. The reduction kinetics of a metal salt by the hydroxyl end groups of PVP can be maneuvered in at least two different ways to facilitate the evolution of plate morphology: (i) by adjusting the molar ratio of PVP to the salt precursor and (ii) by altering the molecular weight of PVP. Unlike previously reported studies of Ag and Au thin plates, light was found to have a negligible role in the present synthesis.

Nano Letters, 2005

Gold nanocages of <40 nm in dimension have been synthesized using the galvanic replacement reacti... more Gold nanocages of <40 nm in dimension have been synthesized using the galvanic replacement reaction between Ag nanocubes and HAuCl 4 in an aqueous solution. By controlling the molar ratio between Ag and HAuCl 4 , the gold nanocages could be tuned to display surface plasmon resonance peaks around 800 nm, a wavelength commonly used in optical coherence tomography (OCT) imaging. OCT measurements on phantom samples indicate that these gold nanocages have a moderate scattering cross-section of ∼8.10 × 10 -16 m 2 but a very large absorption cross-section of ∼7.26 × 10 -15 m 2 , suggesting their potential use as a new class of contrast agents for optical imaging. When bioconjugated with antibodies, the gold nanocages have also been demonstrated for specific targeting of breast cancer cells.

Chemical Society Reviews, 2006

The surface plasmon resonance peaks of gold nanostructures can be tuned from the visible to the n... more The surface plasmon resonance peaks of gold nanostructures can be tuned from the visible to the near infrared region by controlling the shape and structure (solid vs. hollow). In this tutorial review we highlight this concept by comparing four typical examples: nanospheres, nanorods, nanoshells, and nanocages. A combination of this optical tunability with the inertness of gold makes gold nanostructures well suited for various biomedical applications.

Nano Letters, 2004

... (c, d, g, h) Models showing that the growth of Pt nanoparticle (see the HRTEM image immediate... more ... (c, d, g, h) Models showing that the growth of Pt nanoparticle (see the HRTEM image immediately ... This article has been cited by 47 ACS Journal articles (5 most recent appear below). ... Synthesis of Porous Single-Crystalline Platinum Nanocubes Composed of Nanoparticles. ...

Journal of The American Chemical Society, 2006

Gold-silver alloy nanocages with controllable pores on the surface have been synthesized via galv... more Gold-silver alloy nanocages with controllable pores on the surface have been synthesized via galvanic replacement reaction between truncated Ag nanocubes and aqueous HAuCl4. Unlike in the previous studies, the initiation of replacement reaction started in a controllable way, simultaneously from eight corners of the truncated Ag nanocubes where {111} facets were exposed. The formation of cubic nanocages with pores at all the corners was determined by the capping agent, poly(vinyl pyrrolidone) (PVP), which preferentially covered the {100} facets of a truncated Ag nanocube.

Angewandte Chemie-international Edition, 2005

Optics Letters, 2007

We demonstrate a self-aligned balanced cross-correlator based on a single type-II phase-matched P... more We demonstrate a self-aligned balanced cross-correlator based on a single type-II phase-matched PPKTP crystal. The birefringence of the crystal generates a walk-off between the two orthogonally polarized pulses. This enables the balancing of the cross-correlator with input pulses at the same center wavelength. As a first application of this single-crystal balanced crosscorrelator, we stabilized a 310-meter long optical fiber link for timing distribution with long-term stable 10-fs precision.

Accounts of Chemical Research, 2008

Noble-metal nanocages represent a novel class of nanostructures with hollow interiors and porous ... more Noble-metal nanocages represent a novel class of nanostructures with hollow interiors and porous walls. They are prepared using the remarkably simple galvanic replacement reaction between solutions containing metal precursor salts and Ag nanostructures prepared by polyol reduction. The electrochemical potential difference between the two species drives the reaction, with the reduced metal depositing on the surface of the Ag nanostructure. In our most studied example involving HAuCl 4 as the metal precursor, the resultant Au epitaxially deposits on the surface of the Ag nanocubes, adopting their cubic structure. Concurrent with this deposition, the interior Ag is oxidized and removed, together with alloying and dealloying, to produce hollow and eventually porous structures that we commonly refer to as Au nanocages. This approach has proven versatile, with a wide range of morphologies -including nanorings, prism-shaped nanoboxes, nanotubes, and multiple-walled nanoshells or nanotubes -being produced by changing the shape of the initial Ag template. Besides Au-based structures, Pt-and Pd-containing hollow nanostructures have been prepared by switching the metal salt precursors

Journal of The American Chemical Society, 2004

Platinum nanowires of approximately 100 nm in length and approximately 5 nm in diameter have been... more Platinum nanowires of approximately 100 nm in length and approximately 5 nm in diameter have been synthesized by reducing H(2)PtCl(6) with ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) and a trace amount of Fe(3+) or Fe(2+). The wires were generated at the final stage of the synthesis, which involved the formation of several intermediate species. The Fe(3+) or Fe(2+) ions had dual functions in the synthesis: they induced aggregation of Pt nanoparticles into larger structures that served as the nucleation sites, and they greatly reduced the reaction rate and supersaturation level to induce anisotropic growth. The reaction mechanism was studied by X-ray photoelectron spectroscopy (XPS) and UV-vis spectral analysis. The Pt nanowires could be readily separated from the surfaces of the agglomerates by sonication and obtained as pure samples by centrifugation.

Journal of The American Chemical Society, 2005

. UV-vis spectra of solutions taken at different reaction stages. The inset depicts the time depe... more . UV-vis spectra of solutions taken at different reaction stages. The inset depicts the time dependence of the absorbance at ∼245 nm, which is directly proportional to the concentration of the [PdCl4] 2species.

Optics Letters, 2005

We describe gold nanocages as a new class of potential contrast agent for spectroscopic optical c... more We describe gold nanocages as a new class of potential contrast agent for spectroscopic optical coherence tomography (OCT). Monodispersed gold nanocages of an approximately 35 nm edge length exhibit strong optical resonance, with the peak wavelength tunable in the near-infrared range. We characterized the optical properties of the nanocage by using OCT experiments along with numerical calculations, revealing an absorption cross section approximately 5 orders of magnitude larger than conventional dyes. Experiments with tissue phantoms demonstrated that the nanocages provide enhanced contrast for spectroscopic as well as conventional intensity-based OCT imaging.

Gold nanocages of different sizes synthesized via galvanic replacement reaction have been studied... more Gold nanocages of different sizes synthesized via galvanic replacement reaction have been studied by ultrafast time-resolved spectroscopy. The vibrational phonon modes were excited and the periods of these modes increase with the size of the gold nanocages. For a specific size of nanocage, experiments with different excitation powers of the pump laser were performed (from 2 μJ to 20 μJ), we found that the period of the vibrational mode increased with the laser intensity. This was compared to experiments on spherical gold nanoparticles, which allow us to roughly estimate the temperature of the nanocages when the electrons and the phonons reach the equilibrium. The temperature of the nanocages can increase up to 1000 K, near the melting point of the bulk metal, while the particles maintain their integrity. This makes the nanocages potentially useful for photothermal therapy applications. The heat dissipation rate for the nanocages was also studied in these experiments, and was found to have the similar trend as spherical nanoparticles, i.e., larger particles stay hot for longer times than smaller particles.

Nano Letters, 2007

Gold nanocages with a relatively small size (e.g., ~45 nm in edge length) have been developed, an... more Gold nanocages with a relatively small size (e.g., ~45 nm in edge length) have been developed, and the structure of these nanocages was tailored to achieve strong absorption in the near infrared (NIR) region for photothermal cancer treatment. Numerical calculations show that the nanocage has a large absorption cross-section of 3.48×10 −14 m 2 , facilitating conversion of NIR irradiation into heat. The gold nanocages were conjugated with monoclonal antibodies (anti-HER2) to target epidermal growth factor receptors (EGFR) that are over-expressed on the surface of breast cancer cells (SK-BR-3). Our preliminary photothermal results show that the nanocages strongly absorb light in the NIR region, with an intensity threshold of 1.5 W/cm 2 to induce thermal destruction to the cancer cells. In the intensity range of 1.5-4.7 W/cm 2 , the circular area of damaged cells increased linearly with the irradiation power density. These results suggest that this new class of bioconjugated gold nanostructures -immuno gold nanocages -can potentially serve as an effective photothermal therapeutic agent for cancer treatment.

Materials Letters, 2014

ABSTRACT The centrifugation method was proposed to extract Au nanocages (AuNCs) from a mixture of... more ABSTRACT The centrifugation method was proposed to extract Au nanocages (AuNCs) from a mixture of the bimetallic Au and Ag alloyed nanocages, Ag and Au core-shell structure, and Au-pitted silver nanocubes. The DDA simulation was found to be a powerful tool to characterize a colloidal dispersion of the plasmonic nanoparticles. The effect of the irregularity of Au hollow cages and presence of the polymer shells around the cages on the surface plasmon resonance spectra (SPR) had been suggested based on the DDA simulations.

Langmuir, 2007

We review recent developments in our group regarding the solution-phase synthesis of one-dimensio... more We review recent developments in our group regarding the solution-phase synthesis of one-dimensional nanostructures of metals. The synthetic approaches include solution-liquid-solid growth for nanowires of low-melting-point metals such as Pb; seed-directed growth for Ag nanowires, nanobeams, and nanobelts; kinetically controlled growth for Pt nanorods, nanowires, and multipods; and galvanic replacement for nanotubes of Au, Pt, and Pd. Both characterization and mechanistic studies are presented for each nanostructure. Finally, we highlight the electrical and plasmonic properties of these metal nanostructures and discuss their potential applications in nanoscale devices. (1) Xia, Y.; Yang, P.; Sun, Y.; Wu, Y.; Mayers, B.; Gates, B.; Yin, Y.; Kim, F.; Yan, H. Alekseeva, A. V.; Bogatyrev, V. A.; Dykman, L. A.; Khlebtsov, B. N.; Trachuk, L. A.; Melnikov, A. G.; Khlebtsov, N.

Chemical Physics Letters, 2006

This Letter describes the fastest route to monodispersed silver nanocubes. By adding a trace amou... more This Letter describes the fastest route to monodispersed silver nanocubes. By adding a trace amount of sodium sulfide (Na2S) or sodium hydrosulfide (NaHS) to the conventional polyol synthesis, the reaction time was significantly shortened from 16–26 h to 3–8 min. By merely adjusting the reaction time, monodispersed silver nanocubes of 25–45 nm in edge length were rapidly and routinely produced on relatively large scales. These small nanocubes are of great interest for biomedical applications by way of generating gold nanocages with plasmon resonance peaks tunable to the near-infrared region through a galvanic replacement reaction.This Letter describes the fastest route to 25–45 nm monodispersed silver nanocubes rapidly and routinely produced on relatively large scales. By adding a trace amount of sodium sulfide (Na2S) or sodium hydrosulfide (NaHS) to the conventional polyol synthesis, the reaction time was significantly shortened to 3–8 min.■

Journal of Agricultural and Food Chemistry, 2013

Nano Letters, 2005

Pd nanocubes between 8 and 50 nm in size were synthesized at the same concentration of Na 2 PdCl ... more Pd nanocubes between 8 and 50 nm in size were synthesized at the same concentration of Na 2 PdCl 4 precursor by controlling the number of seeds formed in the nucleation stage. Increasing the concentration of FeCl 3 , an oxidative etchant for Pd, reduced the number of seeds and led to formation of larger Pd nanocubes. The larger nanocubes exhibited surface plasmon resonance peaks in the visible region, the locations of which matched with the results of the discrete dipole approximation calculation. While the nanocubes of 25 and 50 nm in size oxidized in air to form Pd@PdO core−shell structures, the 8-nm nanocubes were stable in air for over 90 days.

Journal of The American Chemical Society, 2005

The rapid reduction of Na2PdCl4 by ethylene glycol in the presence of poly(vinyl pyrrolidone) (PV... more The rapid reduction of Na2PdCl4 by ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) has recently been demonstrated as a convenient method of generating Pd cubooctahedra and twinned nanoparticles. Here we describe a new procedure where Pd triangular or hexagonal nanoplates could be selectively synthesized by manipulating the reduction kinetics of the polyol process. More specifically, the reduction rate was substantially reduced through the introduction of Fe(III) species and the O 2/Clpair, two wet etchants for Pd(0). The etching power of the O2/Clpair could be further enhanced by adding an acid to lower the pH of the reaction solution. Unlike the previously reported synthesis of Ag and Au nanoplates, light was found to have no indispensable role in the formation of Pd nanoplates. Both triangular and hexagonal nanoplates of Pd exhibited surface plasmon resonance (SPR) peaks in the visible region, and their positions matched with the results of discrete dipole approximation (DDA) calculation. Thanks to their sharp corners and edges, these Pd nanoplates could serve as active substrates for surface-enhanced Raman scattering (SERS).

Langmuir, 2006

Poly(vinyl pyrrolidone) (PVP) has been extensively used in the solution-phase synthesis of many t... more Poly(vinyl pyrrolidone) (PVP) has been extensively used in the solution-phase synthesis of many types of colloidal particles, where it is mainly considered as a steric stabilizer or capping agent with a major role to protect the product from agglomeration. In a recent study, we discovered that the hydroxyl end groups of PVP could also serve as a very mild reductant for kinetically controlled synthesis of Ag nanoplates with yields as high as 75%. Here we further demonstrate that hydroxyl-terminated PVP is also a well-suited reductant for the aqueous synthesis of circular, triangular, and hexagonal nanoplates made of other noble metals including Pd, Au, and Pt. The reduction kinetics of a metal salt by the hydroxyl end groups of PVP can be maneuvered in at least two different ways to facilitate the evolution of plate morphology: (i) by adjusting the molar ratio of PVP to the salt precursor and (ii) by altering the molecular weight of PVP. Unlike previously reported studies of Ag and Au thin plates, light was found to have a negligible role in the present synthesis.

Nano Letters, 2005

Gold nanocages of <40 nm in dimension have been synthesized using the galvanic replacement reacti... more Gold nanocages of <40 nm in dimension have been synthesized using the galvanic replacement reaction between Ag nanocubes and HAuCl 4 in an aqueous solution. By controlling the molar ratio between Ag and HAuCl 4 , the gold nanocages could be tuned to display surface plasmon resonance peaks around 800 nm, a wavelength commonly used in optical coherence tomography (OCT) imaging. OCT measurements on phantom samples indicate that these gold nanocages have a moderate scattering cross-section of ∼8.10 × 10 -16 m 2 but a very large absorption cross-section of ∼7.26 × 10 -15 m 2 , suggesting their potential use as a new class of contrast agents for optical imaging. When bioconjugated with antibodies, the gold nanocages have also been demonstrated for specific targeting of breast cancer cells.