Switchable Luminescent Probe for Trace-Level Detection of the Spodoptera litura Nuclear Polyhedrosis Virus via a Color-Changing Response

Abstract

A luminescent ruthenium(II) polypyridyl complex has been designed for ratiometric optical sensing of Spodoptera litura nuclear polyhedrosis virus (SLNPV) both in aqueous medium and in commercial samples. The detailed spectroscopic studies indicate that the ruthenium(II) complex can electrostatically bind to the negatively charged outer protein (polyhedron) layer of SLNPV and renders a change in the luminescence color from red (λem ∼ 605 nm) to blue (λem ∼ 487 nm). The linear variation in luminescence color (ratiometric response) over a wide concentration range of occlusion bodies (OBs) (0–1.3 × 107 POBs/mL) ensures the quantitative estimation of SLNPV even in unknown samples. The detection limit for SLNPV was found to be 5.6 × 103 POBs/mL. In addition to discriminating the freshly prepared/active SLNPV from its storage old/less reactive analogue, the system presented here can distinguish SLNPV from other commercially available NPV pesticides, such as Helicoverpa armigera nuclear polyhedrosis virus (HaNPV). In addition, the dye-coated paper strips were developed for rapid, on-field estimation of SLNPV in commercial formulations and aqueous extracts of agricultural crops. This method can be successfully utilized to detect SLNPV in complex biological media such as leaf extracts (more than 20 different agricultural crops were screened). This sustainable strategy of detecting biopesticides is one of a kind and will surely add a new dimension to the improved management of S. litura in agriculture to minimize the extent of crop loss.