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September 26, 2012

Lenses Tutorial

A student in a previous year's course suggested that I share this link about lenses with everyone in the class: http://paws.kettering.edu/~drussell/Demos/RayTrace/Lenses.html. She found it useful as she was performing the first problem set and preparing for the first midterm exam.

Minute Papers Due 09/28/2012

Please post this week's minute papers as "comments" to this post. Minute papers should be posted by 5 pm on Friday. Feel free to read your classmate's posts.

September 22, 2012

Availability on Exam Day

Before coming to class on Monday, please take a look at your calendar to see if you are available for an extended class session on 10/24, starting at 8 am and ending at 9:55 am.

Lecture 6 Notes

Most of Monday's class will focus on the notes from Friday; here are the next set of notes:

Download the ppt file.
Download the pdf file.

September 21, 2012

Rayleigh Equation

This slide includes the equation for Rayleigh scattering intensity and cross-section.

September 20, 2012

Lecture 5 Notes

After finishing Wednesday's activity, we'll begin with the notes below:

Download the ppt file.
Download the pdf file.

September 19, 2012

Problem Set 1 - Due 09/28/2012

Download problem set #1.


**Please turn your assignment in via email, or to my Chemistry Department mailbox (A14) by 5 pm. **

September 18, 2012

Minute Papers Due 09/21/2012

Please post this week's minute papers as "comments" to this post. Minute papers should be posted by 5 pm on Friday. Feel free to read your classmate's posts.

September 17, 2012

Lasers

Before Wednesday's class, please read this perspective on lasers in analytical chemistry: "25 years of lasers and analytical chemistry: A reluctant pairing with a promising future" by Ben Smith. After reading, explore how one of the following methods work (according to the first letter of your last name): laser induced breakdown spectroscopy (A-H), laser ablation sampling (I-Q), or laser ionization mass spectrometry (R-Z).

**There will be no new notes for Wednesday's lecture - we will just finish the notes posted for Monday.

September 15, 2012

Lecture 4 Notes

After finishing the notes from last Wednesday's class, we will continue on with the notes below.

Download lecture 4 ppt file.
Download lecture 4 pdf file.

September 11, 2012

Minute Papers Due 09/14/2012

Please post this week's minute papers as "comments" to this post. Minute papers should be posted by 5 pm on Friday. Feel free to read your classmate's posts.

September 7, 2012

Lecture 3 Notes

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Download the pdf file.

Lecture 2 Notes

We'll continue Monday's lecture with the remaining slides from the first day of class. Then, we will start the material below:

Download the powerpoint file.
Download the pdf file.

September 6, 2012

Minute Papers Due 09/07/2012

Please post this week's minute papers as "comments" to this post. Minute papers should be posted by 5 pm on Friday (though they may not appear on the blog immediately). Feel free to read your classmate's posts.

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.

Science Writing Lecture Notes

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We will use this paper in class to practice writing minute papers.

September 4, 2012

Lecture 1 Notes

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Download the ppt file.

**Please bring a scientific calculator with you to each class.**