Methods and systems for physical expansion and imaging of biological samples
Methods and systems for physical expansion and imaging of biological samples are described herein. In one aspect of the disclosure, a method for preparing a biological sample for the purpose of generating images of its ultrastructure with an imaging instrument includes a) physically expanding the sample by at least a factor of two in at least one dimension; and b) bulk labeling a plurality of components of the sample with at least one reagent to introduce contrast.
1 . A method for preparing a biological sample, the method comprising:
(a) fixing the sample with a fixative molecule;
(b) embedding the biological sample in a swellable polymer containing fixative-modifying monomers;
(c) disrupting chemical bonds within the biological sample;
(d) expanding the sample in a solvent to generate an expanded sample; and
(e) labeling the expanded sample with at least one bulk label and expanding the sample in another solvent, wherein the at least one bulk label labels multiple portions of non-identical molecules in the biological sample.
2 . The method of claim 1 , wherein fixative molecule comprises an amine-reactive fixative and the swellable polymer contains at least one amine-functionalized monomer.
3 . The method of claim 1 , wherein fixative molecule comprises a thiol-cleavable fixative and the swellable polymer contains at least one thiol-reactive monomer.
4 . The method of claim 2 , wherein the amine-reactive fixative comprises:
A) a heat-reversible fixative, a base-cleavable fixative, or a combination thereof; or B) formaldehyde (FA), dimethyl suberimidate (DMS), dimethyl pimelimidate (DMP) dimethyl adipimidate (DMA), or a combination thereof.
5 . The method of claim 2 , wherein the at least one amine-functionalized monomer is acrylamide (AAm), allylamine (ADP), 2-vinylpyridine (2-VP), N-(2-Aminoethyl) acrylamide hydrochloride, 2-aminoethyl methacrylate hydrochloride, or a combination thereof.
6 . The method of claim 3 , wherein the thiol-cleavable fixative is dithiobis (succinimidyl propionate) (DSP), 1,5-difluoro-2,4-dinitrobenzene (DFDNB), succinimidyl 3-(2-pyridyldithio) propionate (SPDP), succinimidyl 6-(3(2-pyridyldithio) propionamido) hexanoate (LC-SPDP), or 4-succinimidyloxycarbonyl-alpha-methyl-α(2-pyridyldithio) toluene (SMPT), or a combination thereof.
7 . The method of claim 3 , wherein the at least one thiol-reactive monomer is pyridyl disulfide ethyl methacrylate (PDSMA), pyridyl disulfide ethyl acrylamide (PDSAAm), or a combination thereof.
8 . The method of claim 1 , wherein the swellable hydrogel is crosslinked with piperazine diacrylamide with concentrations between 0.001% and 0.2%.
9 . The method of claim 1 , wherein prior to step (b) and/or step (c), the sample is denatured with
(A) anionic detergents or chaotropic reagents, or
(B) sodium dodecyl sulfate, urea, guanidine hydrochloride, or a combination thereof.
10 . A method for preparing a biological sample, the method comprising:
(a) fixing the sample;
(b) embedding the sample in a polymer network containing fixative-modifying monomers;
(c) disrupting chemical bonds within the sample;
(d) modifying the polymer network by inserting additional molecules into the polymer network to increase its size; and
(e) labeling the sample with at least one bulk label and expanding the sample in a solvent.
11 . The method of claim 10 , wherein the polymer network of step (b) is swellable.
12 . The method of claim 10 , wherein:
the polymer network of step (b) comprises at least one insertion site;
the inserting of the additional molecules in step (d) comprises:
in situ polymerization of monomer inserts at the insertion site of the polymer network to form an in situ-formed polymer; or
insertion of a bifunctional linear polymer at the insertion site of the polymer network to form an inserted bifunctional linear polymer; and
the in situ-formed polymer or inserted bifunctional linear polymer contains at least one additional monomer or polymer insertion site, the additional monomer or polymer insertion site permitting insertion of additional in situ-formed polymer or bifunctional linear polymer through at least one successive round of in situ polymerization or bifunctional linear polymer insertion, or a combination thereof.
13 . The method of claim 12 , wherein the in situ-formed or inserted bifunctional linear polymer chains are swellable.
14 . The method of claim 10 , wherein step (d) occurs before step (c) or after step (e).
15 . The method of claim 12 , wherein the in situ polymerization comprises reversible addition-fragmentation chain-transfer (RAFT) polymerization of hydrophilic monomers.
16 . The method of claim 15 , wherein the polymer chains are grown by RAFT photopolymerization of a thiocarbonate-crosslinked polymer network in the presence of hydrophilic monomers, a photocatalyst, and a light source.
17 . The method of claim 10 , wherein the polymer network of step (b) is synthesized with cleavable crosslinkers.
18 . The method of claim 12 , wherein the at least one insertion site comprises a monomer insertion site, crosslinker insertion site, polymer insertion site, or a combination thereof.
19 . The method of claim 18 , wherein the insertion site is a polymerizable molecule enabling in situ polymerization of monomer inserts.
20 . The method of claim 18 , wherein the insertion site is conjugated to a bifunctional linear polymer.