Gold microflowers greatly enhance SERS signals from molecules

Warsaw, Poland--To obtain strong enhancement of electromagnetic radiation emitted by single molecules using surface-enhanced Raman spectroscopy (SERS), the sample being analyzed must be placed on an appropriately shaped substrate; unfortunately, the lack of cost-effective and user-friendly substrates limits the application of the SERS spectroscopy method. But researchers at the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS; www.ichf.edu.pl) may have developed a breakthrough: flower-like micrometer-sized gold aggregates that enhance SERS signals ten million times compared to other substrates.

Marcin Fiałkowski, associate professor at IPC PAS says that the microflowers (to be distinguished from nanoflowers) resemble peaked mountains (with peak heights measured in nanometers) covered with a layer of gold. The substrates are fabricated by depositing spherical, strongly ragged gold structures precipitating from solution, on a slide surface. When observed under electron microscope, these micrometer-sized spheres resemble flower buds composed of many gold petals.

The highest enhancement of a SERS signal occurs when a molecule is placed in the meeting area of two "peaks" of the substrate. The effect can be hardly reached with existing mountain-like surfaces, as the peaks there are distinctly separated. The situation on the substrates made with gold flowers is different: the ragged microflowers form thick, complex 3D structures with numerous meeting areas between the petals, enhancing the signals emitted from the flower substrates by ten million times that of other substrates.

Equally crucial as the enhancement is the repeatability of signals obtained from a specific substrate, which is excellent for the gold microflowers. The signals originating from molecules of the same type that are placed at different locations on the same substrate are very similar to each other, and this is not always the case for surfaces obtained with other methods.

The fabrication of substrates using gold flowers is fast, simple, cheap, and does not require a robot or clean room. The reaction mixture contains only a gold salt and a reducing agent, mixed in an appropriate mixing ratio, with the role of the reducing agent to reduce gold cations to metallic gold. The deposition of gold flowers is usually completed within one hour, and the substrate is ready for use on the next day.

SOURCE: Polish Academy of Sciences; www.english.pan.pl/index.php?option=com_content&view=article&id=369:gold-microflowers-to-enhance-signals-from-molecules&catid=15:news