Binding interactions in dipstick assays

A dipstick for testing for the presence of target nucleic acid in a sample solution which comprises:

• a chromatographic strip having a contact end for contacting the sample solution;
• a capture moiety, immobilised at a capture zone remote from the contact end, the capture moiety being capable of binding directly or indirectly to the target nucleic acid;
• and
• a detection probe, releasably immobilised at a probe zone located between the contact end and the capture zone, the detection probe being capable of hybridising to the target nucleic acid and the detection probe being coupled to a label allowing direct detection of the target nucleic acid utilising the detection probe, or the detection probe being coupled to a detection ligand allowing indirect detection of the target nucleic acid utilising the detection probe,
• wherein the label or the detection ligand is linked to a detection probe spacer and the detection probe spacer is linked to the detection probe, thereby coupling the label or the detection ligand to the detection probe and spacing the label or the detection ligand from the detection probe.

A kit for testing for the presence of target nucleic acid in a sample solution which comprises:

• i) a dipstick comprising a chromatographic strip having a contact end for contacting the sample solution and a capture moiety immobilised at a capture zone of the chromatographic strip remote from the contact end, the capture moiety being capable of binding directly or indirectly to the target nucleic acid;
• ii) a capture probe capable of hybridising to the target nucleic acid, or to a hook capture probe bound to the target nucleic acid, wherein the capture probe is coupled to a capture ligand which can be bound by the capture moiety;
• and
• iii) a detection probe capable of hybridising to the target nucleic acid, the detection probe being coupled to a label allowing direct detection of the target nucleic acid utilising the detection probe, or the detection probe being coupled to a detection ligand allowing indirect detection of the target nucleic acid utilising the detection probe, wherein the label or the detection ligand is linked to a detection probe spacer and the detection probe spacer is linked to the detection probe thereby coupling the label or the detection ligand to the detection probe and spacing the label or the detection ligand from the detection probe.

A kit for testing for the presence of target nucleic acid in a sample solution which comprises:

• i) a dipstick comprising a chromatographic strip having a contact end for contacting the sample solution and a capture moiety immobilised at a capture zone of the chromatographic strip remote from the contact end;
• ii) a capture probe capable of hybridising to the target nucleic acid, or to a hook capture probe bound to the target nucleic acid, wherein the capture probe is linked to a capture probe spacer and the capture probe spacer is linked to a capture ligand thereby coupling the capture ligand to the capture probe and spacing the capture ligand from the capture probe;
• and
• iii) a detection probe capable of hybridising to the target is nucleic acid, the detection probe being coupled to a label allowing direct detection of the target nucleic acid utilising the detection probe, or the detection probe being coupled to a detection ligand allowing indirect detection of the target nucleic acid utilising the detection probe.