Nanoporous Gold Nanocomposites as a Versatile Platform for Plasmonic Engineering and Sensing.

Plasmonic metal nanostructures have shown great potential in sensing applications. Among various materials and structures, monolithic nanoporous gold disks (NPGD) have several unique features such as three-dimensional (3D) porous network, large surface area, tunable plasmonic resonance, high-density hot-spots, and excellent architectural integrity and environmental stability. They exhibit a great potential in surface-enhanced spectroscopy, photothermal conversion, and plasmonic sensing. In this work, interactions between smaller colloidal gold nanoparticles (AuNP) and individual NPGDs are studied. Specifically, colloidal gold nanoparticles with different sizes are loaded onto NPGD substrates to form NPG hybrid nanocomposites with tunable plasmonic resonance peaks in the near-infrared spectral range. Newly formed plasmonic hot-spots due to the coupling between individual nanoparticles and NPG disk have been identified in the nanocomposites, which have been experimentally studied using extinction and surface-enhanced Raman scattering. Numerical modeling and simulations have been employed to further unravel various coupling scenarios between AuNP and NPGDs.

Reagent- and separation-free measurements of urine creatinine concentration using stamping surface enhanced Raman scattering (S-SERS).

We report a novel reagent- and separation-free method for urine creatinine concentration measurement using stamping surface enhanced Raman scattering (S-SERS) technique with nanoporous gold disk (NPGD) plasmonic substrates, a label-free, multiplexed molecular sensing and imaging technique recently developed by us. The performance of this new technology is evaluated by the detection and quantification of creatinine spiked in three different liquids: creatinine in water, mixture of creatinine and urea in water, and creatinine in artificial urine within physiologically relevant concentration ranges. Moreover, the potential application of our method is demonstrated by creatinine concentration measurements in urine samples collected from a mouse model of nephritis. The limit of detection of creatinine was 13.2 nM (0.15 µg/dl) and 0.68 mg/dl in water and urine, respectively. Our method would provide an alternative tool for rapid, cost-effective, and reliable urine analysis for non-invasive diagnosis and monitoring of renal function.

Label-free, zeptomole cancer biomarker detection by surface-enhanced fluorescence on nanoporous gold disk plasmonic nanoparticles.

We experimentally demonstrate a label-free biosensor for the ERBB2 cancer gene DNA target based on the distance-dependent detection of surface-enhanced fluorescence (SEF) on nanoporous gold disk (NPGD) plasmonic nanoparticles. We achieve detection of 2.4 zeptomole of DNA target on the NPGD substrate with an upper concentration detection limit of 1 nM. Without the use of molecular spacers, the NPGD substrate as an SEF platform was shown to provide higher net fluorescence for visible and NIR fluorophores compared to glass and non-porous gold substrates. The enhanced fluorescence signals in patterned nanoporous gold nanoparticles make NPGD a viable material for further reducing detection limits for biomolecular targets used in clinical assays. With patterned nanoporous gold disk (NPGD) plasmonic nanoparticles, a label-free biosensor that makes use of distance-dependent detection of surface-enhanced fluorescence (SEF) is constructed and tested for zeptomole detection of ERBB2 cancer gene DNA targets.

Laser rapid thermal annealing enables tunable plasmonics in nanoporous gold nanoparticles.

A novel laser rapid thermal annealing (LRTA) technique is reported to tune the plasmonic resonance of disk-shaped nanoporous gold (NPG) nanoparticles for the first time. LRTA alters both the external and internal geometrical parameters of NPG nanoparticles at temperatures significantly lower than the melting temperature of bulk gold or non-porous gold nanoparticles. With increasing annealing laser intensity, the average pore size increases, while the mean disk diameter decreases. These morphological changes lead to blueshifting of the localized surface plasmon resonance (LSPR), which subsequently fine-tunes the SERS performance by better aligning the excitation laser and Raman scattering wavelengths with the LSPR peak. This technique can provide an effective means to optimize NPG nanoparticles for various plasmonic applications such as photothermal conversion, light-gated molecular release, and molecular sensing.

Microfluidic surface-enhanced Raman scattering sensor with monolithically integrated nanoporous gold disk arrays for rapid and label-free biomolecular detection.

We present a microfluidic surface-enhanced Raman scattering (SERS) sensor for rapid and label-free biomolecular detection. Our sensor design mitigates a common limiting factor in microfluidic SERS sensors that utilize integrated nanostructures: low-efficiency transport of biomolecules to nanostructured surface which adversely impacts sensitivity. Our strategy is to increase the total usable nanostructured surface area, which provides more adsorption sites for biomolecules. Specifically, a nanoporous gold disk (NPGD) array, a highly effective SERS substrate, has been monolithically integrated inside a microfluidic chip. Individual NPGD is known to feature an order of magnitude larger surface area than its projected disk area. The increased surface area arises from nanoscale pores and ligaments three-dimensionally distributed in the NPGD, which manifest themselves as high-density SERS hot-spots. High-density NPGD arrays further guarantee large coverage of these hot-spots on the microchannel floor. The sensor performance has been demonstrated using Rhodamine 6G to quantify spatial uniformity and determine the shortest detection time. Next, the sensor is applied to detect two biomolecules, dopamine and urea, with unprecedented detection limit and speed compared to other existing microfluidic SERS sensors. The sensor holds great promise in point-of-care applications for various biomolecular detections.

Analysis of ethyl and methyl centralite vibrational spectra for mapping organic gunshot residues.

Detection of ethyl and methyl centralites in gunshot residues is important in forensic science due to their limited contamination from environmental sources compared to other organic residues. However, the vibrational frequencies of centralites are little explored and their frequency assignments are incomplete. Herein, we investigated vibrational frequencies of centralites based on Density functional theory (DFT) to understand their vibrations. The simulated frequencies exhibit excellent agreement with the experimental data, and the detailed assignments are comprehensively elaborated. We also demonstrate that centralite particles could be detected through Raman imaging based on their fingerprints. This work is very important for the further vibrational studies in detecting and tracing centralites in gunshot residues.

Label-free, in situ SERS monitoring of individual DNA hybridization in microfluidics.

We present label-free, in situ monitoring of individual DNA hybridization in microfluidics. By immobilizing molecular sentinel probes on nanoporous gold disks, we demonstrate sensitivity approaching the single-molecule limit via surface-enhanced Raman scattering which provides robust signals without photobleaching for more than an hour. We further demonstrate that a target concentration as low as 20 pM can be detected within 10 min under diffusion-limited transport.

Monolithic NPG nanoparticles with large surface area, tunable plasmonics, and high-density internal hot-spots.

Plasmonic metal nanostructures have shown great potential in sensing, photovoltaics, imaging and biomedicine, principally due to the enhancement of local electric field by light-excited surface plasmons, i.e., collective oscillation of conduction band electrons. Thin films of nanoporous gold have received a great deal of interest due to the unique 3-dimensional bicontinuous nanostructures with high specific surface area. However, in the form of semi-infinite thin films, nanoporous gold exhibits weak plasmonic extinction and little tunability in the plasmon resonance, because the pore size is much smaller than the wavelength of light. Here we show that by making nanoporous gold in the form of disks of sub-wavelength diameter and sub-100 nm thickness, these limitations can be overcome. Nanoporous gold disks not only possess large specific surface area but also high-density, internal plasmonic "hot-spots" with impressive electric field enhancement, which greatly promotes plasmon-matter interactions as evidenced by spectral shifts in the surface plasmon resonance. In addition, the plasmonic resonance of nanoporous gold disks can be easily tuned from 900 to 1850 nm by changing the disk diameter from 300 to 700 nm. Furthermore, nanoporous gold disks can be fabricated as either bound on a surface or as non-aggregating colloidal suspension with high stability.

Stamping surface-enhanced Raman spectroscopy for label-free, multiplexed, molecular sensing and imaging.

We report stamping surface-enhanced Raman spectroscopy (S-SERS) for label-free, multiplexed, molecular sensing and large-area, high-resolution molecular imaging on a flexible, nonplasmonic surface without solution-phase molecule transfer. In this technique, a polydimethylsiloxane (PDMS) thin film and nanoporous gold disk SERS substrate play the roles as molecule carrier and Raman signal enhancer, respectively. After stamping the SERS substrate onto the PDMS film, SERS measurements can be directly taken from the "sandwiched" target molecules. The performance of S-SERS is evaluated by the detection of Rhodamine 6G, urea, and its mixture with acetaminophen, in a physiologically relevant concentration range, along with the corresponding SERS spectroscopic maps. S-SERS features simple sample preparation, low cost, and high reproducibility, which could lead to SERS-based sensing and imaging for point-of-care and forensics applications.

Characterization of nanoporous gold disks for photothermal light harvesting and light-gated molecular release.

Nanoporous gold disks (NPGDs) with 400 nm diameter, 75 nm thickness, and 13 nm pores exhibit large specific surface area and effective photothermal light harvesting capability with a conversion efficiency of 56%. A potential application is demonstrated by light-gated, multi-step molecular release of the pre-adsorbed R6G fluorescent dye on arrayed NPGDs.

In situ surface-enhanced Raman spectroscopic studies of nafion adsorption on Au and Pt electrodes.

Understanding interactions between Nafion (perfluorosulfonic acid) and Pt catalysts is important for the development and deployment of proton exchange membrane fuel cells. However, study of such interactions is challenging and Nafion/Pt interfacial structure remains elusive. In this study, adsorption of Nafion ionomer on Au and Pt surfaces was investigated for the first time by in situ surface-enhanced Raman spectroscopy. The study is made possible by the use of uniform SiO(2)@Au core-shell particle arrays which provides very strong enhancement of Raman scattering. The high surface sensitivity offered by this approach yields insightful information on interfacial Nafion structure. Through spectral comparison of several model compounds, vibration assignments of SERS bands were made. The SER spectra suggest the direct interaction of sulfonate group with the metal surfaces, in accord with cyclic voltammetric results. Comparison of present SERS results with previous IR spectra was briefly made.

Three-dimensional colloidal crystal-assisted lithography for two-dimensional patterned arrays.

In this paper, we report our recent work on preparing two-dimensional patterned microstructure arrays using three-dimensional colloidal crystals as templates, namely, colloidal crystal-assisted lithography. Two alternative processes are described and involved in colloidal crystal-assisted lithography. One is based upon imprinting the polymer films with three-dimensional silica colloidal crystals, and the other is based upon chemically depositing Ag microstructures on Au substrates covered by polymer colloidal crystals. By varying the experimental conditions in the colloidal crystal-assisted lithography process, we can intentionally control the morphologies of the resulting microstructures. The resultant Ag-coated Au substrates can be used as surface-enhanced Raman scattering substrates, and they would provide an ideal system for the mechanism study of surface-enhanced Raman scattering. We expect that colloidal crystal-assisted lithography will be a versatile approach which can be applied to patterning other materials such as functional molecules, polymers, oxides, and metals.

Polytrauma with thoracic and/or abdominal injuries: experience in 1 540 cases.

OBJECTIVE: To investigate the early diagnosis and treatment of polytrauma patients with thoracic and/or abdominal injuries. METHODS: The data of all polytrauma patients with thoracic and/or abdominal injuries during the past 10 years were studied retrospectively. RESULTS: In the present study, there were 1 540 polytrauma patients, accounting for 65.0% of all 2 368 trauma patients. Of these patients, 62.4% were in shock state on admission. The operative rates were 15.0% (181/1 206) and 79.9% (612/766) in patients with thoracic and abdominal injury (P<0.01), 5.2% (39/758) and 31.7% (142/448) in patients with blunt and penetrating chest trauma (P<0.01), and 72.45% (359/496) and 93.7% (253/270) in patients with blunt and penetrating abdominal injuries (P<0.01), respectively. To deal with abdominal injury, angioembolization was performed in 43 cases, with 42 cured. The overall mortality rate was 6.2%. And in the blunt and penetrating subgroups, the mortalities were 7.9% (75/950) and 3.6% (21/590), respectively (P<0.01). Most patients died from exsanguination. CONCLUSIONS: The first "golden hour" after trauma should be grasped, since the treatment in this hour can determine greatly whether the critically-injured victim could survive. Prompt diagnosis and proper treatment contribute more greatly to the survival of the victim than the severity of injury.

Surface-enhanced Raman activity and stability study of silver films prepared by reduction of Ag+ ions in N,N-dimethylformamide.

A new SERS-active silver film prepared by directly depositing silver nanoparticles on glass is reported. The spontaneous reduction of Ag+ ions in N,N-dimethylformamide (DMF) (in the absence of a protecting agent) leads to the deposition of silver nanoparticles on clean glass surfaces in contact with the solution. The observed optical micrographs and AFM images show that the arrangement of the nanoparticles is inhomogeneous and the particles appear to be closely packed. These films are shown to be excellent substrates for SERS measurements, demonstrating significant enhancement, good stability, and trace detection capability. The SERS enhancement of the silver films with different deposition times was compared and found that the 8-h film gives the largest enhancement ability with an enhancement factor estimated at about 10(9). It is also found that the silver films stored for 80 days in air show no significant degradation in their sensitivity.

Management of severe pelvic fracture associated with injuries of adjacent viscera.

OBJECTIVE: To investigate the approach of emergency management for severe pelvic fracture associated with injuries of adjacent viscera and evaluate the therapeutic effect. METHODS: The data of 79 patients with severe pelvic fracture associated with injuries of adjacent viscera were retrospectively studied, and the study covered a period of 14 years. RESULTS: To cease massive bleeding due to pelvic fracture, ligation of internal iliac arteries was performed on 33 cases, and angioembolization on 8. Of 42 patients with cystic or/and urethral injury, 35 underwent cystostomy and delayed reconstruction, and 7 received a primary realignment. All of 17 patients with injury of retroperitoneal rectum underwent diverting colostomy of the proximal end of sigmoid with presacral drainage, but 4 received primary repair without colostomy. In 22 patients with intraperitoneal colorectal injury, 19 were managed with primary repair or anastomosis while 3 received a colostomy. The overall mortality rate was 8.86% (7/79); the main causes were hemorrhagic shock and associated injury. The complications included urethro-rectal fistula in 4 cases, thrombosis of right common iliac artery in 1, ARDS following chest trauma in 1, and paraplegia in 1. Except the patient with paraplegia, all of them were cured. CONCLUSIONS: Prompt diagnosis and proper treatment are the key to success. Devascularization of internal iliac arteries with external fixation cage of the pelvis, cystostomy and proximal sigmoidostomy are effective procedures in emergency treatment of the critical patients.

Epidemiological characteristics and preventive strategies for fall injury.

OBJECTIVE: To elucidate the epidemiological characteristics and to define some preventive strategies for fall injury (FI). METHODS: The medical records of patients admitted following a fall from a certain height between August 1996 and July 1997 were analyzed retrospectively. RESULTS: A total of 138 patients were assessed, with a mortality of 31.2%. The male-to-female ratio was 3.5:1. The persons between 20 and 59 years old were the main victims (81.8%), of which 52.2% were related with their work altitude. The remaining adults fall because of, accidents in daily life, suicide attempts, drug abuse, alcohol, or criminal behavior. There were significant differences between the death group and the survival group in the Revised Trauma Score (RTS) and the Injury Severity Score (ISS) value (P<0.05 and P<0.01, respectively). Six children fall from balconies, open windows or roofs. There were significant differences for the height of fall and RTS value in aged group than those in children, adolescents, and adults (P<0.001, 0.005, 0.05; and P<0.05, 0.01, 0.05, respectively). The mortality of FI was significantly correlated to the height of fall (r=0.897, P<0.005). CONCLUSIONS: Male adults are the main victims, especially the workers at high altitudes. The mortality of FI is significantly correlated to the height of fall. The preventive strategies developed through analyzing the risk factors of fall in different age groups might reduce the injuries and deaths following fall.