Metallic nanoparticle inks - colloidal suspensions of silver or gold nanoparticles in water or other organic solvents - can
be sintered at relatively low temperatures (70 - 200°C). With appropriate thermal treatment the sintering can be
controlled to fabricate nanoparticle substrates with a distribution of clusters sizes and interparticle distances. Such
substrates exhibit relatively high (108 - 109) surface enhanced Raman scattering (SERS) amplification factors (AFs). The high AFs in such substrates arise from several mechanisms. The 'dimers' - two nanoparticles separated by a nanometersize
gap - are known to produce amplification of the local electric field orders of magnitude larger than at the surface of
an isolated single nanoparticle due to surface plasmon resonance. Furthermore, the lack of translational symmetry in the
clusters leads to localizations of electromagnetic excitations to very small regions that can create SERS hot spots. Here
we report that microwave absorption (~ 10 GHz) as a function of thermal annealing in dry-drop substrates can be used to
monitor the sintering process in metallic nanoparticle inks. The predominant contribution to microwave absorption comes from electrically resistive weak links that are formed between nanoparticles as a result of the thermal treatment. Just before the creation of these weak links, such nanoparticle pairs are also the ones that make a major contribution to the SERS AFs. This leads to a correlation between the observed microwave absorption and the SERS signal intensities. We also present a simple model that describes the microwave absorption as a function of the isothermal annealing treatment.
Surface enhanced Raman scattering (SERS) is now a well-established technique to greatly amplify the normally weak
Raman scattering signals. The amplification is achieved by using SERS substrates - specially structured metallic
substrates with nano-scale morphological features. One of the most widely used methods for SERS amplification
employs nanoparticles of silver or gold either in colloidal suspension or in dry-drop form. In such substrates SERS
amplification factors (AF) exceeding 1012 have been reported. The reproducibility of the colloid-based substrates,
however, is a problem. The lack of reproducibility can be caused by a variety of factors that can change the interparticle
distances. In this paper we show that thermal annealing of SERS substrates fabricated using commercially available
nano-particle inks can be used to create thermally stable substrates with high reproducibility. It appears that thermal
annealing destroys the unstable hot-spots with very high AF's but still leaves the sample with high AF sites yielding
spatially averaged substrate AF's exceeding 108.
Raman spectroscopy is now a well-established analytical tool for obtaining rapid and compound specific
information for chemical analysis. However, Raman scattering - inelastic scattering of photons - cross
sections are typically of the order of 10-30 cm2 per molecule and thus Raman signals are usually weak. In
Surface Enhanced Raman Scattering (SERS) the signals can be greatly amplified by using specially
structured metallic (usually Ag, Au, and Cu) substrates. SERS substrates can be fabricated by a variety of
methods. Here, we report a method for fabricating SERS substrates from commercially available silver
nanoparticle based printing inks. For dilute inks (~ 1-2% Ag by weight) the method involves the
airbrushing of inks on heated (~100oC) quartz or polymer substrates followed by heating at 170oC for about
20 minutes. The heating treatment removes the polymer coating used to prevent aggregation of Ag
particles in the colloidal suspension and allows partial sintering of particles. More concentrated inks (~ 20
- 30% Ag by weight) can be applied to various substrates at room temperature followed by the thermal
treatment. SERS spectra of Rhodamine 6G, and β-carotene molecules are reported. SERS amplification
factors of more than 106 can be easily obtained reproducibly.
Artificially pigmented hTERT-RPE1 cells were exposed to a mode-locked or continuous wave (CW) laser at 458 nm for one hour in a modified culture incubator. Exposure conditions were selected to give greatest likelihood of damage due to a photochemical mechanism, with interest in possible differences between CW and mode-locked damage thresholds. After post-exposure-recovery (PER) for either 1-hour or 24-hour, cells were concurrently stained with annexin V and 6-CFDA to determine if they had undergone necrosis or apoptosis. Alternatively, cells were stained with Ethidium Homodimer (EthD-1) and Calcein AM to determine if they had undergone necrosis following 1-hour and 24-hours PER. Preliminary results indicate that laser exposure induced some apoptosis following 1-hour PER, with irradiance required for apoptosis being lower than that for necrosis with mode-locked exposure conditions. Probit analysis yielded necrosis thresholds for cell culture following 1-hour PER using data compiled from both dye sets. CW exposures resulted in a lower threshold than mode-locked exposures for necrosis following 1-hour PER. A thermal model provided the predicted temperature rise in cell culture due to laser exposure. The thermal model validates our choice of laser parameters to obtain photochemical damage. Data following 24-hours PER were inconclusive. Considerations of cell migration are included in the interpretation of data and further improvements to methods when using live cell assays are recommended.
The reflectance and absorption of the skin plays a vital role in determining how much radiation will be absorbed by human tissue. Any substance covering the skin would change the way radiation is reflected and absorbed and thus the extent of thermal injury. Hairless guinea pigs (cavia porcellus) in vivo were used to evaluate how the minimum visible lesion threshold for single-pulse laser exposure is changed with a topical agent applied to the skin. The ED50 for visible lesions due to an Er: glass laser at 1540-nm with a pulse width of 50-ns was determined, and the results were compared with model predictions using a skin thermal model. The ED50 is compared with the damage threshold of skin coated with a highly absorbing topical cream at 1540 nm to determine its effect on damage pathology and threshold. The ED50 for the guinea pig was then compared to similar studies using Yucatan minipigs and Yorkshire pigs at 1540-nm and nanosecond pulse duration.1,2 The damage threshold at 24-hours of a Yorkshire pig for a 2.5-3.5-mm diameter beam for 100 ns was 3.2 Jcm-2; very similar to our ED50 of 3.00 Jcm-2 for the hairless guinea pigs.
An optical phantom was designed to physically and optically resemble human tissue, in an effort to provide an alternative for detecting visual damage resulting from inadvertent exposure to infrared lasers. The phantom was exposed to a 1540-nm, Erbium:Glass, Q-switched laser with a beam diameter of 5 mm for 30 ns at varying power levels. Various materials were tested for use in the phantom; including agar, ballistic media, and silicone rubber. The samples were analyzed for damage lesions immediately after exposure and the Minimum Visible Lesion - Estimated Dose 50% (MVL-ED50 ) thresholds were determined from the data. In addition, any visible damage was evaluated for similarity to human tissue damage to determine if the phantom tissue would be a suitable substitute for in vivo exposures.
Purpose: the purpose of these experiments was to evaluate the temperature and predicted cell kill distribution during LITT of breast tissue phantoms at 940nm and compare with the results of previous experiments ar 830 nm and 980 nm. Material and Methods: A Dornier Medilas D Skinpulse 940 nm diode lase system coupled to a Dornier D-6111-T2 fiber (Dornier Surgical Products, Phoenix, AZ) was used to irradiate the porcine tissue three times at approximately 5 W for 10 minutes. Results: The initial rate of temperature increase at 940 nm for locations 5, 10, and 15 mm from the fiber axis ranged from 0.076 to 0.142 °C/s, 0.027 to 0.041 °C/s, and 0.008 to 0.013 °C/s, respectively, wile the maximum temperature increase ranged from 37.8 to 46.9 °C, 19.3 to 26.1 °C, 8.6 to 13.0 °C, respectively, temperature curves hed lower slopes at 940 nm than at 830 nm and 980 nm. the maximum temperature increase was higher at 940 nm than at 830 nm. Predicted area of 100% cell kill was approximately 2 cm by 2 cm Conclusion: Results of experiments at 940 nm were more comparable to those at 980 nm than at 830 nm.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.