All polymeric material show some autofluorescence. If you do not see a signal it might be due to the intensity of signal being very small. There is a useful paper which studied autofluorescence of some plastics including PMMA:

The autofluorescence of plastic materials and chips measured under laser

irradiation

Aigars Piruska,Irena Nikcevic, Se Hwan Lee, Chong Ahn, William R. Heineman, Patrick A. Limbacha and Carl J. Seliskar

a

Received 13th June 2005, Accepted 10th October 2005

First published as an Advance Article on the web 1st November 2005

DOI: 10.1039/b508288a

Lab Chip, 2005, 5, 1348–1354

Thank you Menekse for the reference. It helps a bit, although there is no emission spectrum of the PMMA autofluorescence. I'm using tight bandpass filter centered at around 655 nm and I'm wondering is it possible that i do detect some of the matrix autofluorescence together with the samples emission. In the said paper is no information given about the spectral position of the autofluorescence peak as only dichroic mirrors were used to filter out the excitation.

In general autofluorescence is seen as a small signal over a wide spectrum so if you use a longpass filter you are able collect the cumulative signal over a large portion of the spectrum and signal becomes large enough so that the detector can capture. In case of yours, using a band pass filter (with a very tight band around 655 nm) and unless you are using a specifically high sensitive detector (most CCD's are not that sensitive and very few PMT's are able to capture signals that weak) you probably will not be able to capture any emission. If you are using a fluorometer you can use bulk as a blank to subtract from the emission even if there practically exists none or if you are using a fluorescent microscopy technique (especially confocal) you can make a line scan which gives you the signal intensities as a histogram and give your data from fluorophore loaded films in correlation with the bulk histograms to show that there is no/negligible amount of emission from the polymer matrix itself.

Hi Nikodem,

for a non known material usually on should check a zero order measurements. You may use a broad band filter starting just below your excitation wavelentgt (e.g. OG450 nm glas filter.). And if you are using a monochromator you should open the slit and chouse zero-order (That mean 0 position of Monochromator), of course with a broad band filter. Another point is that your excitation does not excite properly or there is no luminescence of this material under this excitation.

It is years ago that I studied the photophysics of aromatics in PMMA, but I remeber that the "blank" PMMA did not show luminescence at the most optimum conditions as described by the other contributors above. And in case you find some emission at the conditions mentioned thay would interfere with solute emissons when you limit the sensitivity anyhow?!

Correction of typo in previous entry: it should read:

...at the conditions mentioned (small detection bandwidth) this would NOT interfere with the emisson of your target dye

Even in single molecule spectroscopy when the dye concentration is well below nanomolar?

When the questioneer is not able to measure any photons for "pure" PMMA at his detection conditions then that is the blank value. Whatever he adds to the PMMa he will or will not detect depending on his sensitivity for the detection conditions. My reamrk is why would one do the blank at a much more sensitive setting by using a cut-off filter ofr a broad detection bandwidth

I am able to measure photons from 'pure' PMMA film and that is why I am asking the question. I would like to check the overlap between PMMA emission spectrum and used filters.

Nikodem,

you can find pure PMMA emission spectrum under excitation at 355 nm in Fig 2b of the paper by Molard et al. in Chemistry - A European Journal, Volume 16, Issue 19, pages 5613–5619, 2010 (full text: http://onlinelibrary.wiley.com/doi/10.1002/chem.200902131/pdf ). The spectrum exhibits a maximum at about 450 nm. The long wave edge of the absorption spectrum is also plotted in the same figure. I suspect that the single photon technique can easily detect some fluorescence from pure PMMA at 655 nm even under anti-Stokes excitation at 405 nm.

Nikodem and Aleksander

A.: The publication is behind a paywall; can you post the spectrum

Then a question Nikodem: what bandwidth do you use in detection and what is your exciation source? Are you sure that it is emission from PMMA or an impurity or a photochemically induced impurity made at a possibly very intense source? Single photon counting, by the way also existed in "my" time (seventies), by the way

I use various bandpass filters, from 10 nm to 40 nm wide centered in the region 650..670 nm. I use an EM CCD camera for detection so it is sensitive enough to see some background luminescence - PMMA, glass etc. ( I elimitaed glass coverslips in my setup and exchanged them with quartz).

Thank you prof. Balter for the paper. Spectrum that I have found inside is exactly the thing I was asking for.

Nikodem

I just noticed: you and Aleksander are colleagues and communicate via Researchgate? You did not talk this over during a coffee-break?

We used Ar ion as the excitation source and did not find a blank value, but then we used a monochromator with a much smaller detection bandwidth

pure PMMA does not have any emission when excited at 400 nm or at a longer wavelength. Anything you or someone saw was luminescence of impurities. I am doing single molecules spectroscopy in PMMA matrices, for us it is very importnat to have no luminescence at all from the PMMA film only. Impurities can come from PMMA itself or from the solvent used to dissolve it, or from any other contamination in the lab.

I agree with Ivan G.Scheblukin answer. It should be noted that commercial PMMA samples sometime contain luminescent impurities as stabilizator

Does anyone know commercial sources of PMMA that has no/low luminescence/autofluorescence?