Liposome-based immunostrip for the rapid detection of Salmonella

Abstract

Salmonellae are ubiquitous human pathogens, which pose a danger to the elderly and children. Due to the increased number of outbreaks of human illness associated with the consumption of contaminated products in the USA and many other countries, there is an urgent need to develop rapid assays to detect common food-borne pathogens. This study demonstrates the feasibility of using a detectable label comprising methyl blue (MB), a visible dye, entrapped inside liposomes. Immunoliposomes tagged with anti-Salmonella common structural antigens (CSA) antibody encapsulating MB dye were prepared and used as the signal amplifier for the development of a field-portable colorimetric immunoassay to detect Salmonellae. Tapping mode atomic force microscopy (TMAFM), a scanning probe technique, was utilized to demonstrate the presence of anti-Salmonella antibody at the thus-prepared liposome. A plastic-backed nitrocellulose strip with two immobilized zones formed the basis of a sandwich assay. The first zone was the antigen capture zone (AC zone), used in a sandwich (noncompetitive) assay format; the other was the biotin capture zone (BC zone), used as a quality control index for the strip assay. During the capillary migration of the wicking reagent containing 80 μL of immunoliposomes and 40 μL of the test sample (heat-killed S. typhimurium), sample pathogens with surface-bound immunoliposomes were captured at the AC zone, while the unbound immunoliposomes continued to migrate and bind to the anti-biotin antibodies coated on the BC zone. The color density of the AC zone was directly proportional to the number of Salmonella typhimurium in the test sample. The detection limit of the current assay with heat-killed Salmonella typhimurium was 1,680 cells. The cross-reactivity of the proposed immunoassay was also investigated, and pathogens including E. coli O157:H7 and Listeria genus specific caused no interference with the detection of Salmonella typhimurium.

Nanoparticle-based lateral flow biosensors

“…There are some reports about the use of liposomes on LFBs (Ho and Wauchope, 2002;Baeumner et al, 2004aBaeumner et al, , 2004bWen et al, 2005;Edwards and Baeumner, 2006;Ho et al, 2008;Khreich et al, 2008;Shukla et al, 2011;Leem et al, 2014) with good levels of sensitivity due to the high quantities of dye that can be loaded inside the liposomes. Nevertheless, the synthesis of liposomes is often a long procedure, with difficult size-control, so the reproducibility of the test could be affected if the protocol is not well controlled.…”

Lateral flow (immuno)assay: its strengths, weaknesses, opportunities and threats. A literature survey

“…Labels are made of coloured or fluorescent nanoparticles with sizes of 15-800 nm, allowing an unobstructed flow through the membrane. They are often made of colloidal gold [1,[17][18][19][20] or latex [21], less often selenium [22], carbon [2,23] or liposomes [24][25][26][27][28][29] are used. Latex nanoparticles are coloured [21] for optical detection.…”

Development and characterisation of integrated microfluidics on waveguide-based photonic platforms fabricated from hybrid materials

“…Wide channels containing micropillars arrays (of defined radius and separation) were also designed. Micropillars have two important roles in microfluidic channel operation: firstly, they prevent the PDMS cap layer from bonding to the bottom surface of the channel, which was a problem for wide channels which did not feature micropillars; secondly, they encourage fluid flow within a wide channel by means of capillary wicking as is observed in lateral flow platforms (Ho et al 2008). …”