Study highlights potential use of algae for biochemical sensing applications

Gary Boas

Unicellular algae known as diatoms could contribute to a range of biochemical-sensing applications, based on changes to their photoluminescence properties caused by adsorption of particular gases, for example. To this end, investigators have explored the sensitivity of the photoluminescence properties for a specific type of diatom by exposing it to different types of volatile solvents. However, the findings of this study were only qualitative; quantitative analysis is needed if the algae are to be developed for application in optochemical gas detection.

Researchers with Università di Napoli Federico II and Consiglio Nazionale delle Ricerche, both in Naples, Italy, recently performed a study in which they characterized the optochemical response to three importing polluting gases: nitrogen dioxide, methane and carbon monoxide. What they found could help to advance a variety of applications. “Diatoms are very intriguing, since their microshells have very different micro- and nano-structured morphologies,” said Luca De Stefano, the principal investigator of the study. “They can be used as natural-made templates for realizing nanocomposites or directly used as optical transducers, since they show photoluminescence when UV-irradiated.”

Researchers have characterized the optochemical response of unicellular algae known as diatoms to various gases. The diatoms’ walls contain pores called frustules; the scientists found that the frustules from diverse species of diatoms exhibit different optical gas-sensing photoluminescence properties. Their findings could contribute to significant improvements in gas-sensing applications based on detection of photoluminescence.

The researchers measured the photoluminescence spectra from three diatoms’ cultures: Thalassiosira rotula Meunier, Coscinodiscus wailesii and Cocconeis scutellum. They obtained the spectra using a 325-nm continuous-wave He-Cd laser for excitation and a Peltier CCD camera for detection, and they correlated the spectra with the various sizes and densities of the pores found on the diatoms’ cage walls (called frustules); the frustules are lined with three-dimensional distributions of pores, with diameters ranging from tenths of nanometers to a few micrometers, and they knew that any variation in these might affect the photoluminescence.

The experiments confirmed that the frustules from different species of diatoms exhibited different optical gas-sensing photoluminescence properties and revealed surface signatures of the associated processes. Thus, the frustules can be exploited for sensing applications. The investigators noted that, because there are so many dimensions, porosities and surface morphologies of the frustules in nature, diatoms can significantly improve the selectivity of gas sensing based on detection of photoluminescence.

The researchers continue to investigate diatoms’ frustules for biosensing applications. “We have chemically modified the porous silica microshells of diatoms in order to link some bioprobes on their surfaces and use them as optical biosensors,” De Stefano said. “Their reduced dimensions and their biocompatibility open [them] to other utilizations, such as cancer targeting or medical imaging.”

Applied Physics Letters, July 30, 2007, 051921.