Embodiments of the present invention are generally directed to the remote detection of explosives and other harmful materials. In some such embodiments, such remote detection involves the use of semiconducting nanoparticles. In some or other such embodiments, such remote detection involves the use of photoacoustic detection and/or spectroscopy. In some such latter embodiments, the photoacoustic system comprises a light source 201 that passes through a chopper 202 and into a photoacoustic cell 203 comprising the analyte gas. Pressure waves within the cell are detected as sound waves by microphones 204. The signal produced by the microphones can then be amplified and transmitted to a remote location, typically via a wireless means.