diff --git a/README.md b/README.md
index 4aa2f9ac39897124ec715b993cd8dc4c2c2a53f3..1cfc9ac6ac171a07b84174f59d03e6bc0fd931c2 100644
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+++ b/README.md
@@ -86,6 +86,8 @@ also, I tried measuring evaporated solution on a few microscope slides and the s
 but can see the particles in the Olympus microscope 
 ![](100nm_gold_particles.jpg)
 
+### spectrophotometer
+Implen NP80 nanophotometer picks up 100 nm Au particles! simplest relative measuring technique 
 
 ### Resources
 [^DIYmask]: University of Cambridge [DIY mask efficacy testing](https://www.researchgate.net/publication/258525804_Testing_the_Efficacy_of_Homemade_Masks_Would_They_Protect_in_an_Influenza_Pandemic)