No isolation method gives pure vesicles, so the honest description of any preparation is the method plus what was measured on it. A precipitation kit is fast and co-precipitates protein; size exclusion is gentle and dilute; ultracentrifugation is the old reference and shears. The field's reporting guidance asks for the method, a particle count and at least one positive and one negative marker.
A tsg101 exosome marker and the panel it belongs to
A tsg101 exosome preparation is evidenced by markers rather than by the kit: an endosomal protein such as TSG101 or a tetraspanin as positive, a cytosolic or nuclear protein as the negative that shows cells were not lysed into the pellet. A single positive band proves the least interesting part. Because the markers are low abundance, the load is much higher than a cell lysate blot and a recombinant standard helps.
exosome detection, and what each instrument counts
exosome detection by nanoparticle tracking counts particles and sizes them but cannot tell a vesicle from an aggregate or a lipoprotein; single vesicle flow methods can label and count; electron microscopy shows morphology on very few objects. Every count is instrument dependent, so a particle number without the instrument and its dilution is not comparable between papers.
An exosome purification kit against a column or a rotor
An exosome purification kit based on polymer precipitation recovers the most material and the most contaminating protein, so it suits a downstream measurement that tolerates that. Size exclusion columns give cleaner preparations at lower yield and in a larger volume. Density gradient work separates by buoyancy and is what a claim about a specific subpopulation needs. The choice is a purity against yield decision written into the method.
An exosome kit for medium against one for plasma
An exosome kit is validated for a starting material, and plasma is the hard one: lipoproteins outnumber vesicles by orders of magnitude and co-isolate with every chemistry. Conditioned medium is easier but is only as good as the serum used to make it. Volume matters too, since a kit built for a millilitre of medium does not scale linearly to a hundred.
ev depleted fbs and why the serum matters
Serum carries its own vesicles, so ev depleted fbs is used when the vesicles measured must come from the cells rather than the medium, and depletion is by ultracentrifugation or filtration with a stated residual particle count. Depletion also removes growth factors, so cells behave differently and a conditioning period is part of the protocol rather than an inconvenience.
exosome depleted fbs, and the same product under another name
exosome depleted fbs and vesicle depleted serum describe the same reagent, and the specification to compare is the residual particle concentration and the method used to reach it, not the word in the catalogue. Lot to lot variation is real, so a long study buys one lot and reserves it. Cells grown in it often need a longer adaptation before an experiment starts.
exosome quantification, and what a number means
exosome quantification is reported either as particles by a counting instrument, as protein by an assay, or as a lipid or marker signal, and the three do not agree because each counts a different thing. A ratio of particles to protein is the usual purity indicator. Whatever the unit, it is reported per volume of starting material rather than per volume of preparation.
exosome proteomics and the contamination it exposes
exosome proteomics is the measurement that shows how impure a preparation is, since serum albumin and lipoprotein proteins appear in any list from a precipitated sample. That makes the depletion and the isolation method part of the interpretation. Sample amount is the practical limit, so pooled preparations and a stated number of biological replicates are what make a protein list believable.
Questions people ask about exosome isolation kit
Does a kit alone prove I isolated exosomes?
No. The evidence is the method plus a particle count and at least one positive and one negative marker.
Why is plasma harder than medium?
Lipoproteins outnumber vesicles by orders of magnitude and co-isolate with every chemistry.
Why use depleted serum?
Serum carries its own vesicles. Depletion also removes growth factors, so cells need an adaptation period.