Silicon Sensors

Biosensors and Biointerfaces Group - Research Projects

Porous silicon photonic crystals as sensors (with Dr. Peter Reece in Physics and Prof. Katharina Gaus in Medicine at UNSW)

 

Figure 1: Porous silicon photonic crystals each engineered to reflect a different wavelength of light.

The project focuses on detecting the release of enzymes from cell. Such devices can be used for personalised medicine, drug testing and toxicology. Porous silicon (PSi) is electrochemically etched crystalline silicon comprising of nanostructured holes such that the silicon will reflect well-defined wavelengths of light. To use it as a sensor relies on the fact that reflectance of light from these optical structures is sensitive to the changes in the average refractive index of the crystal. Therefore, any binding event in the internal pore space of this nanoporous material results in a shift in the optical signature of the crystal. For PSi to act as a biosensor, the group has developed surface chemistries to (1) prevent surface oxidation thereby stabilising PSi in physiological media and (2) to present functional moieties for the attachment of appropriate biological species allowing for the monitoring of the biological activity. The research using PSi as a biosensor is divided into 3 subcategories:


Development of single cell sensors

The goal of this project is to develop a cellular microarray platform using chemically functionalised PSi crystals to achieve in vitro monitoring of biochemical species released by single live cells and to understand the differences between a single cell and a bulk tissue response. The group has developed these PSi based microarray systems using photolithography. These arrays have been chemically patterned facilitating the adhesion of either a single or a few cells on the surface.

 

Figure 2: A microscopic image showing the localisation of a single or multiple cells in the patterned regions of a microfabricated PSi chip.

 

Enzymatic profiling using PSi

The PSi microarray platform can be used to profile different types of enzymes released by cells. This can be achieved by modifying the pore space of the PSi sensors with different peptide sequences which can act as substrates for different enzymes yielding useful information about their activity and kinetics. Additionally, the use of a microarray will allow for multiplex and rapid assessment of the specificity of the peptide for the enzyme.

Figure 3: A schematic showing the illumination of one of the spots on a microfabricated PSi array. The degradation of the peptides by the enzymes inside the pores results in a blue shift in the optical reflectivity of the PSi (shown on right).

 

Development of implantable PSi based microsensors

PSi has shown to be biocompatible and biodegradable material and as a result has been used as an implantable/injectable nanomaterial. The research work going in this area is to develop PSi microsensors to monitor protease activity in vivo. Currently, the work involves the modification of PSi microsensors with specific surface chemistries to make these sensors respond to particular proteases upregulated in an ocular inflammatory disease. Once the microsensors are injected into the vitreal cavity, the amounts of proteases present inside the cavity can be estimated by measuring the changes in the optical spectra of the injected particles.

 

Figure 4. A photograph showing the presence of PSi microsensors that were injected inside the vitreal cavity of an animal eye.

For more information on PSi sensors see:

  • Kilian, K. A., Böcking, T., Gaus, K., Gal, M. and Gooding, J. J. Peptide-Modified Optical Filters for Detecting Protease Activity. ACS Nano 1 355-361 (2007). DOI:10.1021/nn700141n
  • Kilian, K. A. et al. Smart Tissue Culture: in Situ Monitoring of the Activity of Protease Enzymes Secreted from Live Cells Using Nanostructured Photonic Crystals. Nano Letters 9 2021-2025 (2009). DOI:10.1021/nl900283j
  • Soeriyadi, A. H., Gupta, B., Reece, P. J. and Gooding, J. J. Optimising the enzyme response of a porous silicon photonic crystal via the modular design of enzyme sensitive polymers. Polymer Chemistry 5 2333-2341 (2014). DOI:10.1039/C3PY01638B
  • Zhu, Y., Soeriyadi, A. H., Parker, S. G., Reece, P. J. and Gooding, J. J. Chemical patterning on preformed porous silicon photonic crystals: towards multiplex detection of protease activity at precise positions. Journal of Materials Chemistry B 2 3582-3588 (2014). doi:10.1039/C4TB00281D