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Example Minute Paper

Minute Paper #1 (09/04/2007) - Christy L. Haynes

Title: In Vivo Detection of Gold-Imidazole Self-Assembly Complexes: NIR-SERS Signal Reporters
By: G. R. Souza et al.
Journal: Analytical Chemistry

In this paper, the authors attempt to control aggregation of Au nanoparticles by adding imidazole in order to shift the nanoparticle optical properties so that high surface-enhanced Raman scattering (SERS) enhancement factors can be achieved with near-IR laser excitation. The techniques used in this work include: nanoparticle synthesis, UV-vis extinction spectroscopy, transmission electron microscopy, dynamic light scattering, and near-IR SERS.

The authors claim that adding specific concentrations of imidazole (with 2 available nitrogens for covalent attachment to Au) to Au nanoparticles generates nanoparticle aggregates with discrete sizes and optical properties. Individual Au nanoparticles absorb and scatter light at 520 nm; however, the authors need the optical properties to shift to the NIR in order to achieve large SERS enhancement factors in the "water window" (700 - 900 nm) for biological imaging. SERS enhancement factors are largest when the laser excitation wavelength matches the surface-enhancing substrate's optical properties. After aggregating the nanoparticles, the authors calculate their SERS enhancement factors to be as large as 10^9. This is a much larger than expected enhancement factor for spherical gold nanoparticles. The authors then inject the nanoparticle aggregates into mouse tumors and demonstrate that they can collect SERS spectra through the skin of the mouse.

The authors leave many questions unanswered in this work. In figure 1a, you see that the normal Raman scattering and SERS spectra are very different. This is expected because normal Raman scattering reports the vibrational structure of the bulk imidazole in solution while the SERS spectrum reveals the molecules covalently bound to the Au surface. In figure 1b, you can not see the red-shift in the optical properties very easily because the post-aggregation spectrum has very low intensity. This suggests that the nanoparticles are aggregating to the point where they precipitate out of solution. Also, the authors continually report the nanoparticles extinction at 520 nm (the absorption band for the original unaggregated Au nanoparticle solution) even though the most useful information would be the extinction efficiency at 785 nm (since this is the laser excitation they plan to use). Further, the calculated enhancement factors seem way too high based on previous literature precedent - this leads me to believe that their molecular coverage calculations are not correct. They should do a quantitative coverage measurement in order to conclusively demonstrate the claimed enhancement factor. Finally, while the authors show that you can collect SERS spectra through skin, the signals are very small and they do not explain how this will be used in actual biological imaging.

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Sarah Gruba
Minute Paper #1 9/7/12
Title: Aptamer-Guided Silver-Gold Bimetallic Nanostructures with Highly Active Surface-Enhanced Raman Scattering for Specific Detection and Near-Infrared Photothermal Therapy of Human Breast Cancer Cells

Authors: Ping Wu, Yang Gao, Hui Zhang, and Chenxin Cai

Journal: Analytical Chemistry

Due to the high rate of human breast cancer and success rate of treating and killing the MCF-7 (breast cancer cell) if detected early enough, these researchers saw a need for a way in which to detect very small traces of MCF-7 before it is even noticeable through other standard means. In order to accomplish this, researchers noticed that the MCF-7 cells had a 10 fold increase in MUC1 mucin compared to regular cells. Using the S2.2 aptamer (that specifically binds to MUC1)attached to Ag-Au nanoparticles (collectively called nanostructures) and bound to Rh6G, they were able to obtain a surface enhanced Raman spectra with known peaks associated with Rh6G. In order to confirm that this is the only positive control, they looked at SERS of the nanostructures attached to the MCF-7 cells with non bound Rh6G and SERS on other cells with the nanostructures and Rh6G. All three of these were negative for the known peaks.

In order to confirm that all the steps in making the nanostructures had worked, they used several other techniques. The first was looking at the UV absorption spectra to see if the aptamer was being changed as they added the silver and gold. They also used TEM to look at the nanostructures and to see if the nanostructures were attaching to the MCF-7 cells.

Finally, they wanted to see if they could kill the cancer cells attached to the nanostructures using near inferred radation(NIR) and Trypan Blue which stains the nucleus of dead cells blue. As they increased the radiation, the MCF-7 cells died off; however the non MCF-7 cells did not turn blue. This meant that the Ag-Au nanostructures attached to the MCF-7 cells were causing local heating which killed the cells. A final study to show that it was the nanostructures that were heating and killing the MCF-7 cells was done by putting only MCF-7 cells under the NIR and seeing if they could stay alive.

Since it was shown that these bind only to breast cancer cells, I think one of the next steps the researchers might take with these nanostructures is trying to see if they can load them with drugs that could fight the cancer similar to what Katie Hurley and Sam Eggert are doing in the Haynes Lab with nanoparticles. With the ability to only bind to certain sites, the medication can be directly delivered to the cancer cells and along with NIR treatment it would be more likely to kill the cancerous cells. The other study they will want to do is a degradation study to see how long they would last in the body or if there are any long term effects.

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