Preparation of RIGS kit.
A novel format (Fig. 1) was designed for RIGS kit, so that it enables the detection of TSWV on a single strip.
The colloidal-gold-conjugated solution of antisera raised against TSWV was mixed in equal quantities and applied on 26 × 1.7 cm conjugate pads (Standard 14) and dried under dry air for 10-15 min. TSWV IgG-BSA conjugate was diluted in 20 mM sodium phosphate buffer, (pH 8.0) containing 1% sucrose to a final concentration of 2 mg/ml and applied as a 0.5 mm thick, 26 cm line, centrally at 1.25 cm from the top and bottom ends on one side of a 2.5 × 26 cm nitrocellulose plastic backed membrane strip, using a locally fabricated airbrush device (Innovative Biosciences, India). Nitrocellulose membrane was cut into sections (2.5 cm × 26 cm).
Test line was coated with TSWV-IgG conjugate, which was applied to each membrane in 150 μg/ml TSWV using TLC conjugate sampler.
The distance between the test line and control line was 6 mm. The test strips were dried at 37°C for 30 min. TSWV IgGBSA conjugate was diluted in 1 mM Tris-HCl buffer (pH 8.0) containing containing 1% sucrose to a final concentration of 3 μg/ml and applied as a 1 mm thick, 26 cm line, at 0.5 cm from the top end of the membrane. The membrane was dried at 3°C under a dry wind blower for 10-15 min and blocked with 10 mM potassium phosphate buffer (pH 7.5) containing 0.25% BSA and 1.0% sucrose.
The membrane was dried at 37°C under a dry wind blower for 10-15 min and washed twice with 10 mM, sodium phosphate buffer (pH 7.2) before drying it for 10–15 min at 50°C.
A polyethylene plastic sheet (26 × 8 cm) of 0.2 mm thickness was coated with acrylic adhesive on one side and the 2.5 cm wide membrane was placed centrally at a spacing of 1.5 cm from the top and 4 cm from the bottom end of the sheet.
The conjugate coated glass-fiber pad was placed on the lower end of the membrane, so as to overlap 2 mm on it. A filter pad was placed to overlap 2mm on the lower end of the conjugate release pad to act as sample pad and another pad (CF4) was placed to overlap 2 mm on the upper end of the membrane to act as absorbent pad. The assembly was cold-laminated using an 8 cm wide transparent adhesive tape. The laminated 26 × 8 cm assembly was cut into lateral-flow strips of 8 × 0.4 cm.
The strips were stored in an airtight plastic bottle containing a desiccant pack.