Described herein is an approach using inexpensive, disposable chemical sensor probes that can be mounted on a small unmanned aerial vehicles (UAVs) and used to analyze a site (such as one known or suspected to contain explosive residue, spilled material or contaminated soil) without the need for a person to conduct ground operations at the site. The method involves contacting a soil or a surface with a filter paper wetted with a solvent, then subjecting the filter paper to spectroscopy, thus detecting a possible variation indicative of one or more analytes, wherein the solvent is a deep eutectic solvents consisting of a mixture of ethylene glycol and choline chloride.