SERS swabs and dipsticks from inkjet-printed paper

SERS-active paper swabs and dipsticks have been produced by inkjet printing for the cheap and simple on-site sampling of liquids and surfaces in a variety of settings, including forensics and homeland security. Ian White and Wei Yu from the University of Maryland described in Analyst how they used a low-cost commercial inkjet printer to transfer silver nanoparticles onto untreated chromatography paper where they formed clusters in the cellulose matrix to introduce the SERS enhancement. The paper was then cut into dipsticks or swabs.

When the dipsticks were dipped into a solution, the sample was drawn into the paper by capillary action and a natural lateral flow concentrated the analytes at the narrow tip of the paper, thereby increasing the SERS signal intensity. Swabs dampened with a solvent like methanol were used to wipe surfaces before dipping into a solvent to concentrate the analytes, again by lateral flow capillary action.

Using these devices, SERS detection limits of 95 fg for rhodamine 6G, 413 pg for malathion, 15 ng for cocaine and 9 ng for heroin were achieved. These are comparable to those reported for other SERS substrates but there is room for improvement by optimising the paper porosity and thickness and tuning the plasmonic resonance of the silver aggregates to that of the laser excitation wavelength.

The swabs and dipsticks have several advantages over microfluidic devices, including high speed, low cost, simplicity of production and use, and the absence of any pump. The swabs can be used for surface testing operations like the on-site detection of illicit drugs, chemical warfare agents, and pesticides on food surfaces. The dipsticks can be used for environmental testing of pollutants in water or contaminants in liquid foods.