One of our goal in prototypes building was to try them for both arsenic and bacteria detection thanks to fluorescence method. Arsenic detection is in progress. But we stagnate for bacteria because of material needs especially the 280 nm LED cost used in excitation part.
280 nm is the limit wavelength between UV-B (315 – 280 nm) and UV-C (280 – 100 nm). UVs are emitted by the sun but almost all UVs that arrive on earth are UV-A (315 – 400nm). UV-B and -C are filtered by the ozone layer. 280 nm is a wavelength included in a range usually used for medical imagery and protein analysis in laboratory, forensic science (black light used as drug detection), barcode readers or optical scanners and some disinfection technic. We are interested in 280 nm wavelength because it excites the tryptophan and tyrosine at the RecA C-terminal domain of E.coli (Energy transfer of aromatic amino acids in photosystem 2 core antenna complexes CP43 and CP47).
This wavelength is shorter than visible light thus more complex to produce. On the market we find deep UV LEDs that have range included 280 nm. But these LEDs need difficult materials handling and the market share is too small for mass production this is why it is so expansive.
On some sites we found UV LEDs price lists. We have to spend 100 to 400 euros for 265 to 340 nm LED while for 355 to 400 nm LED the price range is less than 1 to 15 euros. Particularly the 280 nm LED are between 100 and 200 euros.
Digikey (an electronic device dealer) has a nice article about today LEDs! They say: “In 2011, LEDs continued to be sold mostly in the UV-A/B spectrum (especially in upper wavelengths, between 365 to 400 nm).” That shows us the small deep UV LED market share.
Therefore we have to abort the bacteria part because of prices, leading time but also because of our project time lasting…