'''Single Particle Extinction and Scattering (SPES)''' is a technique in [[physics]] that is used to characterise micro and [[nanoparticle]]s suspended in a fluid through two independent parameters, the diameter and the [[refractive index|effective refractive index]].<ref>{{Cite web |url=https://www.ncbi.nlm.nih.gov/pubmed/28756089journal |title=Single particle extinction and scattering optical method unveils in real time the influence of the blood components on polymeric nanoparticles |last=Sanvitojournal |first=Tiziano|last2=Bigini |first2=Paolo |date=November 2017 |website=Nanomedicine: Nanotechnology, Biology, and Medicine|publishervolume =[[NationalCenter13|issue for= Biotechnology8|last1=Sanvito Information]],|first1=Tiziano [[U.S.|last2=Bigini National|first2=Paolo Library|date=November of Medicine]]2017 |pages=2597–2603 |doi=10.1016/j.nano.2017.07.008 |pmid=28756089 |access-date=16 June 2019 |last3=Cavanna |first3=Maria V. |last4=Fiordaliso |first4=Fabio |last5=Violatto |first5=Martina B. |last6=Talamini |first6=Laura |last7=Salmona |first7=Mario |last8=Milani |first8=Paolo |last9=Potenza |first9=Marco A. C.}}</ref><ref>{{Cite web |url=https://pubs.rsc.org/en/content/articlelanding/2017/nr/c6nr08977ajournal |title=Detecting the shape of anisotropic gold nanoparticles in dispersion with single particle extinction and scattering |lastlast1=Dawson |firstfirst1=K. A. |last2=Milani |first2=P. |date=2017-02-23 |websitejournal=Nanoscale |publishervolume=[[Royal Society of Chemistry]]9 |___locationissue=United Kingdom8 |pages=2778–2784 |language=en |publication-place=United Kingdom |doi=10.1039/C6NR08977A |access-date=2019-06-16 |last3=Castagnola |first3=V. |last4=Boselli |first4=L. |last5=Cella |first5=C. |last6=Araújo |first6=J. M. de |last7=Monopoli |first7=M. |last8=Cai |first8=Q. |last9=Sanvito |first9=T.|pmid=28155930 |doi-access=free |hdl=2434/701388 |hdl-access=free }}</ref>
A [[laser]] generates a [[gaussian beam]] which focuses inside a flow cell. A particle that passes through the focal region generates an interference in the beam, which is collected with a sensor. Through this signal it is possible to derive the real part and the imaginary part of the forward scattering field from each particle.
The technique was developed to measure aerosols in air<ref>https://{{Cite journal |doi.org/ = 10.1007/s11051-017-3995-3|title = Single Particle Extinction and Scattering allows novel optical characterization of aerosols|journal = Journal of Nanoparticle Research|volume = 19|issue = 8|pages = 291|year = 2017|last1 = Mariani|first1 = Federico|last2 = Bernardoni|first2 = Vera|last3 = Riccobono|first3 = Francesco|last4 = Vecchi|first4 = Roberta|last5 = Valli|first5 = Gianluigi|last6 = Sanvito|first6 = Tiziano|last7 = Paroli|first7 = Bruno|last8 = Pullia|first8 = Alberto|last9 = Potenza|first9 = Marco A. C.|bibcode = 2017JNR....19..291M|s2cid = 139469999}}</ref> and particles in liquid.<ref>{{Cite web |url=https://www.nature.com/articles/srep18228journal |title=Single particle optical extinction and scattering allows real time quantitative characterization of drug payload and degradation of polymeric nanoparticles |lastlast1=Milani |firstfirst1=P. |last2=Lenardi |first2=C. |date=2015-12-15 |websitejournal=Scientific Reports |publishervolume=[[Nature5 (journal)]] |pages=18228 |doi=10.1038/srep18228 |access-datepmid=2019-06-1626667064 |last3=Paroli |first3=B. |last4=Cella |first4=C. |last5=Argentiere |first5=S. |last6=Sanvito |first6=T. |last7=Potenza |first7=M. a. C.|bibcode=2015NatSR...518228P |pmc=4678328 }}</ref>
