Microbial detection article having a water-absorbent filter assembly
A microbial detection article and methods of using the same, the article comprising: a base member comprising a self-supporting water impervious substrate with first and second generally opposed major surfaces; a filter assembly defining a filter assembly aperture therein, and having a composite filter body mounted across the filter assembly aperture; wherein the composite filter body comprises: a microporous membrane, and a water-absorbent layer in fluid communication with the microporous membrane; and a cover sheet.
1. A microbial detection article comprising:
a base member comprising a self-supporting water impervious substrate with a first major surface and a second major surface that is generally opposed to the first major surface;
a filter assembly defining a filter assembly aperture therein, and having a composite filter body mounted across the filter assembly aperture; wherein the composite filter body comprises:
1) a filter support layer having the filter assembly aperture,
2) a microporous membrane positioned on a first side of the filter support, wherein the microporous membrane overlays the filter assembly aperture and extends beyond the perimeter of the filter assembly aperture, and
3) a water-absorbent layer positioned on a second side of the filter support opposite the microporous membrane, wherein the water absorbent layer is positioned under the filter assembly aperture, is in fluid communication with the microporous membrane, and extends beyond the perimeter of the filter assembly aperture, wherein the water absorbent layer comprises a fibrous substrate functionalized with a grafted hydrogel polymer; and
a cover sheet;
wherein
the filter assembly is positioned between the cover sheet and the base member;
the filter assembly is coupled to the cover sheet, to the base member, or to both; and the water-absorbent layer is positioned between the microporous membrane and the base member.
2. The article of claim 1 , further comprising a spacer layer defining a spacer aperture therein, wherein the spacer layer faces the first major surface of the substrate, and wherein the spacer aperture is in fluid communication with the filter assembly aperture.
3. The article of claim 1 , wherein the filter assembly is attached to the base member, and wherein the cover sheet is attached to the base member.
4. The article of claim 1 , wherein the cover sheet further comprises at least one of a water-soluble gelling agent, a nutrient medium, or a detection reagent.
5. The article of claim 1 , wherein the microporous membrane comprises a material selected from the group consisting of polyethersulfone, nylon, polycarbonate, polyester, cellulose acetate, mixed cellulose esters, polyvinylidene fluoride, nitrocellulose, a ceramic, a derivative of any of the foregoing, and any combination of these.
6. The article of claim 1 , wherein the water-absorbent layer comprises a nonwoven substrate having:
an average fiber size in a range from 0.7 micrometer to 15 micrometers;
a void volume in a range from 50% to 95%; and
a hydrogel polymer comprising grafting monomer units grafted to a surface of the nonwoven substrate, wherein the grafting monomer units are selected from the group consisting of ionic grafting monomer units, non-ionic hydrophilic grafting monomer units, and mixtures thereof.
7. The article of claim 6 , wherein the ionic grafting monomer units comprise cationic monomer units.
8. The article of claim 6 , wherein the ionic grafting monomer units comprise anionic monomer units.
9. The article of claim 6 , wherein the non-ionic hydrophilic monomer units are selected from the group consisting of dimethylacrylamide and 2-hydroxyethyl(meth)acrylate.
10. The article of claim 6 , wherein the nonwoven substrate has a surface area in a range from 15 square meters per square meter of nonwoven substrate to 50 square meters per square meter of nonwoven substrate.
11. The article of claim 6 , wherein the nonwoven substrate has a mean pore size in a range from 1 micrometer to 40 micrometers.
12. The article of claim 6 , wherein a weight of the hydrogel polymer comprising the monomer units grafted to the surface of the nonwoven substrate is in a range from 0.5 to 5 times a weight of the nonwoven substrate.
13. The article of claim 6 , wherein the nonwoven substrate is a hydrophilic thermoplastic polymer substrate.
14. The article of claim 6 , wherein nonwoven substrate is a polyamide nonwoven substrate.
15. The article of claim 6 , wherein the nonwoven substrate is a nylon nonwoven substrate having an average effective fiber diameter of not greater than 1 micrometer.
16. The article of claim 6 , wherein the water-absorbent layer has a Water Absorption Capacity Ratio in a range of from 0.5 to 30.
17. A method of testing for the presence of a microorganism in an aqueous sample, the method comprising:
providing the microbial detection article of claim 1 ;
providing an aqueous sample;
passing the aqueous sample firstly through the microporous membrane and secondly through the water-absorbent layer, wherein the water absorbent layer retains an aliquot of water from the aqueous sample;
incubating the microbial detection article for an incubation period, wherein at least a portion of the aliquot of water contacts the microporous membrane throughout the incubation period; and
observing an indication of the presence or absence of microbial growth.
18. The method of claim 17 , wherein the incubation period is less than 24 hours.
19. The method of claim 17 , further comprising:
providing a filtration apparatus, the filtration apparatus comprising a filter seat comprising a filter support surface and defining a filter seat inlet and a filter seat outlet; and
placing the water-absorbent layer of the filter plate article against the filter support surface prior to passing the aqueous sample firstly through the microporous membrane and secondly through the water-absorbent layer.
20. A filtration apparatus for use with a microbial detection article of claim 1 , the filtration apparatus comprising:
(a) a filtration assembly comprising:
(i) a filter seat comprising a filter support surface and defining a filter seat inlet, a filter seat outlet; and
(ii) a sample head defining a sample head inlet and a sample head outlet;
wherein the filter seat is slidably engageable with the sample head to define an insertion gap between the filter support surface and the sample head outlet; and
(b) a guide assembly comprising a first guide member and a second guide member, wherein the first guide member and the second guide member are arranged parallel to each other on opposing sides of the filtration assembly to define an insertion path, thereby to guide the filter membrane layer of the filter article into the insertion gap.