Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Towards defining reference materials for extracellular vesicle size,
  concentration, refractive index and epitope abundance   Accurate characterization of extracellular vesicles (EVs) is critical to
explore their diagnostic and therapeutic applications. As the EV research field
has developed, so too have the techniques used to characterize them. The
development of reference materials is required for the standardization of these
techniques. This work, initiated from the ISEV 2017 Biomarker Workshop in
Birmingham, UK, and with further discussion during the ISEV 2019
Standardization Workshop in Ghent, Belgium, sets out to elucidate which
reference materials are required and which are currently available to
standardize commonly used analysis platforms for characterizing EV size,
concentration, refractive index, and epitope expression. Due to their
predominant use, a particular focus is placed on the optical methods
nanoparticle tracking analysis and flow cytometry.

9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th
8
The categories of this paper are: hep-ex
13
The categories of this paper are: quant-ph
5
The categories of this paper are: gr-qc
7
The categories of this paper are: hep-th
3
The categories of this paper are: physics
23
The categories of this paper are: solv-int
22
The categories of this paper are: chao-dyn
28
The categories of this paper are: alg-geom
29
The categories of this paper are: funct-an
16
The categories of this paper are: stat
14
The categories of this paper are: math-ph
19
The categories of this paper are: eess
6
The categories of this paper are: astro-ph
34
The categories of this paper are: chem-ph