The storage buffer used in qEV columns is changing, due to ProClin's notable benefits compared with sodium azide.
Following thorough consideration and in-house studies conducted in 2023, we have decided to transition from sodium azide buffer to ProClin 200 buffer for qEV column storage. This change is due to ProClin's notable benefits compared with sodium azide, including its broad-spectrum action and improved health & environmental hazard profile.
ProClin 200 is an existing, widely used biocide in in vitro diagnostics. It is an aqueous mixture of chloromethylisothiazolinone (CMIT) and methylisothiazolinone (MIT), allowing for broad spectrum antimicrobial properties. CMIT and MIT act on gram-positive & gram-negative bacteria and fungi. This is a key improvement, as sodium azide is ineffective against gram-positive bacteria, resulting in a diminished antimicrobial effect in the presence of gram-positive bacteria.
The qEV column flushing protocol will remain unchanged.
Note: Once flushing is completed, the columns are no longer protected by ProClin 200's antimicrobial properties. If storing for future use, follow the cleaning and flushing instructions found in your qEV user manual, and store in PBS containing a bactericide or bacteriostatic agent (e.g., 0.05% w/v sodium azide or 0.05% ProClin 200), or 20% ethanol.
In-house studies highlighting the benefit of ProClin 200
In one in-house microbial challenge study, 4 different wildtype colonies were plated and incubated on control (PBS- only), PBS + 0.1% sodium azide, and PBS + 0.1% ProClin 200. PBS-only and sodium azide-treated plates had no antimicrobial effects on the 4 wildtype strains, while all concentrations of ProClin 200 strongly inhibited bacterial growth at room temperature and at 30 °C, indicating strong antimicrobial properties (Table 1). This supports the transition to ProClin 200, as the bacterial growth present with sodium azide suggests that there were gram-positive bacteria or even the potential for sodium azide resistant strains. ProClin 200 addresses these potential sodium azide-related drawbacks.
Table 1. ProClin versus sodium azide microbial challenge
|
Test Solution |
Inoculation (CFU/mL) |
14-day count |
|
PBS-only |
3.2 x 10^8 |
TMTC |
|
PBS with 0.1% sodium azide |
3.2 x 10^8 |
TMTC |
|
PBS with 15 ppm (0.1%) ProClin 200 |
3.2 x 10^8 |
< 10 |
Stated measured values were the same when plates were incubated at 30°C and room temperature.
TMTC – Too many to count. CFU – Colony-forming units.
In an additional in-house study, the microbial challenge was repeated to test a range of ProClin 200 concentrations (1 ppm, 3 ppm, 7.5 ppm and 15 ppm). 1 ppm ProClin 200 (0.007%) was shown to be just as effective as 15 ppm ProClin 200 (0.1%) in preventing microbial growth (Table 2).
Table 2. ProClin concentration microbial challenge
|
Test Solution |
Inoculation (CFU/mL) |
7-day count |
|
PBS-only |
2.6 x 10^10 |
TMTC |
|
PBS with 15 ppm ProClin 200 |
2.6 x 10^10 |
0 |
|
PBS with 7 ppm ProClin 200 |
2.6 x 10^10 |
0 |
|
PBS with 3.5 ppm ProClin 200 |
2.6 x 10^10 |
0 |
|
PBS with 1 ppm ProClin 200 |
2.6 x 10^10 |
0 |
Plates incubated at 30°C
TMTC – Too many to count. CFU – Colony-forming units.
In-house testing shows that ProClin 200 does not affect qEV column performance. EV isolates from plasma samples passed through qEV columns (qEVoriginal / 70 nm Gen 2) stored in either ProClin 200 (0.1%) or sodium azide (0.05%) showed no difference in the mean or median particle diameter. Furthermore, elution profiles did not differ by storage buffer, and showed no significant difference in EV concentration, or the percentage of protein eluting in later volumes between ProClin 200 and sodium azide.
These columns were sent to an independent lab, to test for the presence of aerobic bacteria in eluted samples. No bacteria of any description were evident in columns stored in either ProClin 200 (0.1%) or sodium azide (0.05%).
Related article: Does my qEV column contain sodium azide or ProClin?