Showing papers by "Xingde Li published in 2005"

Gold nanocages: bioconjugation and their potential use as optical imaging contrast agents.

Abstract: Gold nanocages of <40 nm in dimension have been synthesized using the galvanic replacement reaction between Ag nanocubes and HAuCl4 in an aqueous solution. By controlling the molar ratio between Ag and HAuCl4, 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 m2 but a very large absorption cross-section of ∼7.26 × 10-15 m2, 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.

Gold Nanocages: Engineering Their Structure for Biomedical Applications

Abstract: The galvanic replacement reaction between a Ag template and HAuCl4 in an aqueous solution transforms 30-200 mn Ag nanocubes into Au nanoboxes and nanocages (nanoboxes with porous walls). By controlling the molar ratio of Ag to HAuCl4, the extinction peak of resultant structures can be continuously tuned from the blue (400 nm) to the near-infrared (1200 nm) region of the electromagnetic spectrum. These hollow An nanostructures are characterized by extraordinarily large cross sections for both absorption and scattering. Optical coherence tomography measurements indicate that the 36 nm nanocage has a scattering cross-section of similar to 0.8 X 10(-15) m(2) and an absorption cross-section of similar to 7.3 X 10(-15) m(2). The absorption cross-section is more than five orders of magnitude larger than those of conventional organic dyes. Exposure of Au nanocages to a camera flash resulted in the melting and conversion of Au nanocages into spherical particles due to photothermal heating. Discrete-di poleapproximation calculations suggest that the magnitudes of both scattering and absorption cross-sections of An nanocages can be tailored by controlling their dimensions, as well as the thickness and porosity of their walls. This novel class of hollow nanostructures is expected to find use as both a contrast agent for optical imaging in early stage tumor detection and as a therapeutic agent for photothermal cancer treatment.

Shape-Controlled Synthesis of Silver and Gold Nanostructures

Abstract: This article provides a brief account of solution-phase methods that generate silver and gold nanostructures with well-controlled shapes. It is organized into five sections: The first section discusses the nucleation and formation of seeds from which nanostructures grow. The next two sections explain how seeds with fairly isotropic shapes can grow anisotropically into distinct morphologies. Polyol synthesis is selected as an example to illustrate this concept. Specifically, we discuss the growth of silver nanocubes (with and without truncated corners), nanowires, and triangular nanoplates. In the fourth section, we show that silver nanostructures can be transformed into hollow gold nanostructures through a galvanic replacement reaction. Examples include nanoboxes, nanocages, nanotubes (both single- and multi-walled), and nanorattles. The fifth section briefly outlines a potential medical application for gold nanocages.We conclude with some perspectives on areas for future work.

Optical fiber scanner for performing multimodal optical imaging

Abstract: An optical fiber scanner is used for multiphoton excitation imaging, optical coherence tomography, or for confocal imaging in which transverse scans are carried out at a plurality of successively different depths within tissue The optical fiber scanner is implemented as a scanning endoscope using a cantilevered optical fiber that is driven into resonance or near resonance by an actuator The actuator is energized with drive signals that cause the optical fiber to scan in a desired pattern at successively different depths as the depth of the focal point is changed Various techniques can be employed for depth focus tracking at a rate that is much slower than the transverse scanning carried out by the vibrating optical fiber The optical fiber scanner can be used for confocal imaging, multiphoton fluorescence imaging, nonlinear harmonic generation imaging, or in an OCT system that includes a phase or frequency modulator and delay line

Gold nanocages as contrast agents for spectroscopic optical coherence tomography.

Abstract: 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.

High-resolution optical coherence tomographic imaging of osteoarthritic cartilage during open knee surgery.

Abstract: This study demonstrates the first real-time imaging in vivo of human cartilage in normal and osteoarthritic knee joints at a resolution of micrometers, using optical coherence tomography (OCT). This recently developed high-resolution imaging technology is analogous to B-mode ultrasound except that it uses infrared light rather than sound. Real-time imaging with 11-μm resolution at four frames per second was performed on six patients using a portable OCT system with a handheld imaging probe during open knee surgery. Tissue registration was achieved by marking sites before imaging, and then histologic processing was performed. Structural changes including cartilage thinning, fissures, and fibrillations were observed at a resolution substantially higher than is achieved with any current clinical imaging technology. The structural features detected with OCT were evident in the corresponding histology. In addition to changes in architectural morphology, changes in the birefringent or the polarization properties of the articular cartilage were observed with OCT, suggesting collagen disorganization, an early indicator of osteoarthritis. Furthermore, this study supports the hypothesis that polarization-sensitive OCT may allow osteoarthritis to be diagnosed before cartilage thinning. This study illustrates that OCT, which can eventually be developed for use in offices or through an arthroscope, has considerable potential for assessing early osteoarthritic cartilage and monitoring therapeutic effects for cartilage repair with resolution in real time on a scale of micrometers.

Gold Nanocages: Engineering Their Structure for Biomedical Applications

Abstract: The galvanic replacement reaction between a Ag template and HAuCl4 in an aqueous solution transforms 30-200 mn Ag nanocubes into Au nanoboxes and nanocages (nanoboxes with porous walls). By controlling the molar ratio of Ag to HAuCl4, the extinction peak of resultant structures can be continuously tuned from the blue (400 nm) to the near-infrared (1200 nm) region of the electromagnetic spectrum. These hollow An nanostructures are characterized by extraordinarily large cross sections for both absorption and scattering. Optical coherence tomography measurements indicate that the 36 nm nanocage has a scattering cross-section of similar to 0.8 X 10(-15) m(2) and an absorption cross-section of similar to 7.3 X 10(-15) m(2). The absorption cross-section is more than five orders of magnitude larger than those of conventional organic dyes. Exposure of Au nanocages to a camera flash resulted in the melting and conversion of Au nanocages into spherical particles due to photothermal heating. Discrete-di poleapproximation calculations suggest that the magnitudes of both scattering and absorption cross-sections of An nanocages can be tailored by controlling their dimensions, as well as the thickness and porosity of their walls. This novel class of hollow nanostructures is expected to find use as both a contrast agent for optical imaging in early stage tumor detection and as a therapeutic agent for photothermal cancer treatment.

Continuous focus tracking for real-time optical coherence tomography.

Abstract: We report an approach to achieving continuous focus tracking and a depth-independent transverse resolution for real-time optical coherence tomography (OCT) imaging. Continuous real-time focus tracking is permitted by use of a lateral-priority image acquisition sequence in which the depth-scanning rate is equivalent to the imaging frame rate. Real-time OCT imaging with continuous focus tracking is performed at 1? frame?s by reciprocal translation of a rapid lateral-scanning miniature imaging probe (e.g., an endoscope). The optical path length in the reference arm is scanned synchronously to ensure that the coherence gate coincides with the imaging beam focus. The image quality improvement is experimentally demonstrated by imaging a tissue phantom embedded with polystyrene microspheres and rabbit esophageal tissues.

High-resolution optical coherence tomographic imaging of osteoarthritic cartilage during open knee surgery

Abstract: National Institutes of Health (U.S.) (Contract R01-AR44812) (Contract R01-EB000419) (Contract R01 AR46996) (Contract R01-HL55686) (Contract R01-EB002638) (Contract NIH-RO1-HL63953) (Contract NIH-1-R29-HL55686) (Contract NIH- 9-RO1-EY11289) (Contract NIH-1-RO1-CA75289)

Optimization of optical spectral throughput of acousto-optic modulators for high-speed optical coherence tomography.

Abstract: We describe a generic method to optimize the optical spectral throughput of a pair of acousto-optic modulators (AOM) which can be used for introducing a frequency shift in ultrahigh-resolution heterodyne optical coherence tomography. Systematic and quantitative analysis of a pair of AOMs indicates that a configuration with a spectral bandwidth of more than 200 nm at a center wavelength of 825 nm (tunable) can be achieved. Using a pair of AOMs in conjunction with a broadband low coherence light source, real-time imaging of biological tissues with an axial resolution ~3 μm (in air) has been experimentally demonstrated with a high-speed OCT system.

Using optical coherence tomography to guide articular cartilage ablation.

Abstract: Current clinical imaging technologies are not capable of accurately resolving the microscopic components of articular cartilage. Optical coherence tomography (OCT) is a recently developed imaging modality analogous to ultrasound--OCT measures backreflection of infrared light instead of sound. In the study reported here, we wanted to determine the efficacy of OCT for monitoring cartilage laser ablation. Real-time imaging was conducted on bovine cartilage ablated by an argon laser in vitro. Image sequences were generated illustrating the extent of tissue degradation postablation. The images accurately correlated with histology. These results indicate that current ablation procedures could benefit from OCT guidance.

Bioconjugated Au/Ag nanocages as a novel optical imaging contrast and thermal therapeutic agent

Abstract: We have synthesized 40-nm Au/Ag nanocages and explored their use as an optical imaging/spectroscopy contrast agent and potentially a thermal therapeutic agent. Cancer cell specific targeting by antibody-conjugated nanocages has also been demonstrated.

Real-time ultrahigh-resolution lateral-priority OCT imaging with a broad spectrum throughput acousto-optic modulation

Abstract: We describe a generic method to optimize the optical spectrum throughput of acousto-optic modulators for performing real-time lateral-priority OCT imaging with an axial resolution of /spl sim/2.3 /spl mu/m. Ultrahigh-resolution imaging of biological tissues is demonstrated.