SERS SLIPS Ahead
Can a new slippery surface for Raman scattering open the door to routine single molecule detection?
Tak Sing Wong |
Surface-enhanced Raman scattering (SERS) has high molecular specificity and high sensitivity, but its applicability is limited by a reliance on aqueous solvents for extraction and poor performance in heavily diluted solutions. Now, researchers from Pennsylvania State University have combined SERS with slippery liquid-infused porous surfaces (SLIPS) to create... You guessed it: SLIPSERS (1). We spoke with Tak Sing Wong, Assistant Professor of Mechanical Engineering and lead author of the study, to find out how they’re addressing the limitations of SERS.
Why focus on SERS?
SERS is a very powerful platform for molecular diagnostics and analysis. However, there are two important roadblocks that limit its practical application. First, SERS detection in liquid media relies on highly statistical binding of analytes to the SERS-sensitive regions (or “hot spots”) because of the diffusive nature of the analytes. As a result, it is very challenging to achieve single-molecule detection in highly diluted solutions. Second, many real-life analytes may be dispersed in liquid or gas phases or may be bound to solid substrates (for example, soil), which may require the use of non-aqueous solvents for extraction.
My postdoctoral researcher – Shikuan Yang – and I have come up with a solution to these problems. By allowing a non-aqueous/aqueous droplet containing the extracted analytes and the SERS substrates to shrink in an isotropic manner onto a solid surface, we can bring all the analytes to close proximity of the SERS hot spots. SLIPS is the perfect solid surface to achieve this because it can be designed to repel both aqueous and non-aqueous liquids.
What exactly is SLIPS?
SLIPS is formed by infusing a liquid lubricant on a functionalized micro/nanotextured solid surface. Once the SLIPS is prepared, we can place a liquid droplet that contains the targeted analytes and SERS substrates (for example, gold nanoparticles) onto the surface. By allowing the liquid droplet to fully evaporate, the SERS substrates and analytes will self-assemble into a microscopic aggregate, which can then be used for SERS analysis.
And how is SLIPSERS performing?
By using the SLIPSERS platform, we found that we can achieve limits of detection down to subfemtomolar level in both aqueous and non-aqueous liquids. This limit of detection level, particularly within non-aqueous liquid, is very challenging to achieve using conventional detection methods. In addition, the flexibility on the choice of extraction solvents also allows us to perform ultrasensitive detection of analytes from gaseous, liquid or solid samples.
How do you see SLIPSERS being applied?
In the future, we hope to see SLIPSERS technology used for ultrasensitive molecular detection in applications related to analytical chemistry, medical diagnostics, environmental monitoring and national security. The ability to detect single molecules of any kind would revolutionize disease diagnostics and environmental monitoring.
- S Yang et al., “Ultrasensitive surface-enhanced Raman scattering detection in common fluids”, Proc Natl Acad Sci USA, 113, 2, 268-73 (2016). PMID: 26719413.