[Answer]-Why can't Django find an object contains unicode like this?

This part make me think that You are storing not string itself but representation of dict containing this string or json dump of it.

>>> models.Samples.objects.filter(description__contains=u' rosiglitazone / 0.1% DMSO for 1 hour')[0].description
u'{"source name": "3T3-L1 adipocytes (Day 7)", "treatment": "1 \\u03bcM rosiglitazone / 0.1% DMSO for 1 hour", "cell type": "3T3-L1 adipocytes", "chip antibody": "anti-CBP (sc-369; Santa Cruz)"}'

In this case Unicode character will be present in database as \u03bcM but not utf-8 character

To search using this string one should process it same way (json dump or repr)

I find a hacking to solve this problem

from _json import encode_basestring_ascii as c_encode_basestring_ascii

>>> c_encode_basestring_ascii(a)
'"1 \\u03bcM rosiglitazone / 0.1% DMSO for 1 hour"'

Then the query can return the right result..