Week 6 Update: Getting a clearer picture

So far in my research, getting an intuitive feel for what our scans and blinking traces of EY on TiO2 should and do look like has been a bit of an ongoing challenge. Building intuition with anything takes time and exposure, though – at the end of this week, I feel as though the time I have put into my project is starting to pay off not only in the results of my research but also in my knowledge of and confidence in them. For example, I know that scans of EY on TiO2 in air show more localized spots than their counterparts on a glass substrate (see Figure 1), and I know that the blinking traces in air show much fewer events on a TiO2 substrate than on glass (Figure 2). Once all of our data has been collected and analyzed, we’ll be able to get a better idea of where this difference arises from.

[Read more…]

Week 5 Update!

My last post detailed our recent battles with contamination – something in the oven that we use to sinter our slides was showing up on our scans of supposedly blank TiO2. Cranking the oven up to 1000°C and leaving it there all day did the trick for our slides for most of the week, but this past Wednesday, we noticed that contamination had come back. Fortunately, turning the oven up again for a couple hours Wednesday afternoon seemed to get rid of the issue, and our Thursday slides came out clean. It seems like this step will be something to add to our TiO2 slide protocol for the rest of the summer, just to be safe. I’m definitely glad that we caught the contamination early on this time!

[Read more…]

Week 4 Update: Confrontation with contamination

At the beginning of week 4 we thought we had everything we needed to move forward – a reliable method for discerning the presence of TiO2, strong laser power settings – all I can say is, thank goodness we decided to look at a blank slide. We began the day Tuesday by running a pretty routine control test, pointing the laser at our blank substrate to find what intensity we can consider to be blank glass, or blank TiO2, in analyzing the data we collect. However, scan after scan, big bright spots that looked like molecules kept showing up on what should have been a blank slide. This raised a lot of questions: Are our slides contaminated? Where is the contamination coming from? How can we know for sure? So that day consisted of a lot of scans of a lot of different types of blank slides (sintered and unsintered, glass and TiO2, old and brand new), as well as searching the TiO2 manufacturer’s website to ensure that we were using our stock solution correctly.

[Read more…]

Week 3: With great power comes great density

Last week I mentioned that it’s harder to see single eosin Y dye molecules on TiO2 (our current substrate) than on glass (the old substrate). This is due to TiO2’s status as a semiconductor – the dye can inject an electron into TiO2 once excited rather than emitting a photon, so it won’t necessarily fluoresce as much, and fluorescence is what gives us our images. So it follows that when we started doing single-molecule scans of EY on TiO2 this past week and late the week before, we weren’t seeing as many molecules at a time as we were used to, a lower spot density.

[Read more…]

Week 2 Update: Seeing the difference between TiO2 and glass

We began this past week by making new TiO2 slides and trying to find some way to ensure our slides really had TiO2 on them – this is an important step to take because if we end up collecting data on blank glass, that’s information that our lab already knows, not quite relevant to this project. However, making sure that TiO2 is there is harder than you may think, since there’s no difference between TiO2 on glass and blank glass to the naked eye. We spent a day scanning TiO2 slides and glass slides with the laser, without any dye on the slides, hoping to find significantly different average intensities for each. At the end of the day, however, while TiO2 had a higher mean intensity, its standard deviation was so large that a slide within one standard deviation of the mean would be indistinguishable from glass. This could mean that we need more data points for this test, or that we weren’t seeing TiO2 at all on the slides we were scanning – at some point, we had to make the assumption that TiO2 was there to determine a threshold for future batches. Today, however, we made a new batch of TiO2 slides and spin coated them with a higher concentration than normal of eosin Y. Comparing their intensities with the same dye concentration on glass, we found that the TiO2 slides gave us much lower counts – this means that rather than fluorescing, EY is injecting electrons into TiO2, which is exactly what we want to see. This procedure should be a reliable way to determine if we have the right substrate going forward.

[Read more…]