Well, it's been nearly a year since I updated this. The work has carried on in the background, and the microscope is now completed, and I've been using it to look at sunscreens.
The idea was that could I build a microscope that would work in the visible, UVA and UVB regions to allow me to look at the structures in topical sunscreen products (creams, lotions etc). The structure of a product and the distribution of the sun filters influences how it spreads and how efficient it is as blocking the UV. A few days ago, I presented some initial images from it at the 15th Sun Protection Conference in London as part of my UV imaging talk, and wanted to share them here too. My talk at the conference won an award from the International Journal of Cosmetic Science - no money for that, but they will cover the open access fees for a paper on this, which will allow me to reach a wider audience with the work when I publish it as a paper. The images are not as good as most of what is posted on here, but the unusual part is being able to image in the UVB, so might be of interest to some.
For these images I took two different creams - both oil in water emulsions (like cream) one with a UVA absorbing filter in the oil phase, the other with a UVB absorbing filter in the oil phase. I then dispersed both of these in water, and mixed the two dispersions together. The end result is a mix of oil drops from the two products suspended in a water phase. A droplet of this mixed dispersion was then placed on a fused silica slide and a fused silica coverslip placed on top.
First, how the dispersion looks in visible light (mainly 546nm from a filtered mercury xenon lamp).
In normal visible light, you can see the oil droplets in the water phase. Droplet size around a 3 micron and smaller (this was done with a 32x Zeiss Ultrafluar objective). The droplets all look similar as would be expected based on how they were produced and their optical properties in visible light.
Now the same sample in UVA (filtered 365nm).
In UVA some of the oil droplets now look black, while others remain clear. The black ones are the ones containing the UVA absorbing filter.
And finally, in UVB (313nm).
In the 313nm image, the droplets which are black were clear at 356nm and vice versa.
It's early days, and there is still plenty of work to do with it. These are sample images I've got permission to share, as I'm working on a publication of a larger data set with a client. Movement of the samples is an issue - the droplets absorb quite a lot of light in the UV and warm up, and Brownian motion becomes a real problem limiting the shutter speed. I can't stack images for the same reason, as there is too much random movement, so these were single images with a 32x objective.
The build is based on an Olympus BHB, and I've extensively modified it to remove any glass and replace it with fused silica. I'm currently able to image in the visible light and at 365nm and 313nm, although the microscope itself should be good down to around 250nm (with different light source, filters and camera). At the moment it is using a monochrome converted SLR, which is not ideal especially at higher magnifications, but in future I hope to get hold of a different camera for it. It was a lot more complicated to build than I thought it would be, but then to be honest I knew nothing about microscopy when I started it.
The aim is to use this for helping product development of sunscreens. Skin cancers are on the rise unfortunately, so there is a real need to develop better products, but also to communicate their benefits in a way that consumer can visualise and understand. This is where UV imaging really can help, so is the approach I am taking.