Dave stoft's challenge:

"To qualify (for this challenge) the application concept needs 1) some detail about the degree of oil detection (it must be better than detecting oil at a level far below that which I can already detect it by sight and smell) and 2) details showing the measurement concept has a viable technique of acquiring reproducible data.."

For the specific concept of oil detection, fluorescence has been shown to exist with oil .... but it also appears with detergents -- and detection and discrimination between oil and detergent using a PLab device (or some other simple spectrometer) has not yet been demonstrated.

For absorption, as related to oil detection, absorption is one component .... but a specific relationship to oil, vs any other substance, has not been demonstrated using a PLab device (or evidence from some other simple spectrometer).

So, finding that evidence would be the next step toward identifying a spectrometer-based oil-detection application which qualifies as a potential, real-world use for a PLab device.