This project explored novel optical and surface enhanced raman spectroscopy methods to detect, identify and characterise airborne organophosphates. This is a classic multidisciplinary project and exemplifies the diverse services of Platform Kinetics. This project incorporates - optical design, electronics, software, microfluidics and surface and electro chemistry. The project started out using conventional NIR surface enhanced raman spectroscopy via a laser and NIR spectrometer as a benchmark proof of concept. The goal being to automate the sample preparation and sensing using a MEMs Digital microMirror Device (DMD).
Stage 1 - Assessment of Substrates
Two of the key requirements were that the sample preparation could be automated and that the cost per sample was low. We investigated different surface enhanced substrates which would meet these requirements.
We investigated: -
Stage 2 - Raman Set-up & Microfluidic Platform
The basic Raman apparatus consisted of a 500mW 780nm laser, an Ocean Optics QE-Pro spectrometer and an Inphotonics Raman Probe. The apparatus featured a thermoelectric controller on which the microfluidic cartridge was placed (this cannot be shown).
The airborne sample entered the microfluidic and condensed onto the surface enhanced substrate, where the measurement was performed. A sequence of cleaning then took place to clean and replenish the substrate ready for the next sample/measurement.
Stage 3 - Signal Processing & Characterisation
The system would eventually be characterised using organophosphates, however, here we present the results on the compound BPE.
The left image shows the raman 'fingerprint' for a serial dilution of BPE vs a clean electrode.
The right image shows the 'raw' signal of a library compound and the measured compound. Using continuous wavelet transform a method called 'semblance' can be derived which determines how likely a match of the compound is compared to each 'known' compound in the library.
Stage 4 - Prototype Embedded System
The embedded system was then developed based on the DMD technology. This allowed for a fully integrated and deployable system containing the spectrometer, laser, condensor, storage fluids & microfluidic cartridge.