The buzz around trace-level detection

Ocean Optics has shown how highly sensitive, trace-level Raman spectroscopy measurements can detect concentrations of insecticide that are less than a fiftieth of the level judged harmful to honeybees.

Using a real-world example related to the problem of honeybee population decline, the company demonstrated the power of Ram-Sers-SP Surface-Enhanced Raman Spectroscopy substrates’ gold-silver nanosponge alloy.

By comparing the ability of new gold-silver substrates with that of traditional substrates to detect imidacloprid, an insecticide suspected to be dangerous to bee colonies, Ocean Optics scientists were able to demonstrate the enhanced sensitivity that Ram-Sers-SP substrates bring to Raman measurements.

Sers substrates amplify very weak Raman signals by many orders of magnitude, with measurements of Sers-active analytes possible at even parts-per-trillion levels.

Silver-only Sers substrates work best with 532nm Raman excitation, while gold substrates are better suited to 785nm Raman systems.

By combining the silver and gold on one substrate the new Sers nanosponge substrates perform well with either wavelength.

When used with 638nm Raman excitation, the nanosponge substrates are enhanced to an even higher level of sensitivity.

In the USA, recent increasing rates of honeybee loss have been investigated by government regulators and other researchers.

According to ongoing US Environmental Protection Agency (EPA) studies, the insecticide imidacloprid has been identified as a threat to commercial honeybee colonies, with the agency citing traces at concentration levels greater than 25 ppb as likely harmful to honeybees.

To test the effectiveness of Ocean Optics substrates in detecting imidacloprid at these harmful trace levels, the company’s scientists set up a lab experiment using its gold nanoparticle and gold-silver nanosponge Sers substrates.

They made a series of measurements using the gold nanoparticle substrates, in a setup with 785nm Raman laser excitation, and a series of measurements using the gold-silver nanosponge substrates, in a setup with 638nm Raman excitation.

In the test, the gold-silver nanosponge Sers substrates delivered the best results, detecting imidacloprid concentrations as low as 0.4 ppb (well within the 25 ppb concentration rate cited by the EPA as harmful to bees).

The substrates’ high sensitivity and low background noise made it easier to discern Raman peaks at these very low-concentration levels.

Raman is a useful technique for fast, non-destructive analysis, with the enhanced sensitivity provided by Sers substrates allowing detection of trace levels of samples such as insecticides. 

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