A novel format (Fig. 2) was designed for RIGS kit, so that it enables the detection of TBSV on a single strip. Thecolloidal-gold-conjugated solution of antisera raised against TBSV 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. TBSV IgG–ovalbumin conjugate was diluted in 0.02 M sodium phosphate buffer, (pH8.0) 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 TBSV-IgG conjugate, which was applied to each membrane in 1 g/L TBSV using TLC conjugate sampler (Sambrook
et al., 1989). The distance between the test line and control line was 6 mm. The test strips were dried at 37oC for 30 min. TBSV IgG–ovalbumin conjugate was diluted in 0.02 M sodium phosphate buffer (pH8.0) containing 1% sucrose to a final concentration of 3 μg/mL and applied as a 1mm thick, 26 cm line, at 0.5 cm from the top end of the membrane. The membrane was dried at 50oC under a dry wind blower for 10 - 15 min and blocked with PBS containing 2% ovalbumin and 1.5% sucrose. The membrane was dried at 50oC under a dry
wind blower for 10-15 min and washed twice with 0.01 M, sodium phosphate buffer, pH7.2 before drying it for 10 - 15 min at 50oC. 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 4cm 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 2mm on it. A filter pad was placed to overlap 2 mm 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. Extraction of TBSV-infected tomato Tomato leaf tissues infected by TBSV were extracted with 5 mL of 0.5X PBS (pH7.4) solution using tissue grinder (Agdia, USA). Then the crude sap was precipitated briefly and the supernatant was used for specificity of RIGS kit.