An optofluidic sensor from nanochannel arrays and laser interferometry

L.N. ACQUAROLI, R. URTEAGA, C.L.A. BERLI, R.R. KOROPECKI

Heidelberg

Congreso; Microfluidics 2012; 2012

European Molecular Biology Laboratory (EMLB)

The integration of optics and microfluidics is a rapid developing field of research and applications are continuously growing, notably in chemical and biological sensing. In this framework, we present the implementation of an optical technique to follow the spontaneous filling of nanochannels driven by capillary forces in nanoporous substrates, such as anodized alumina and silicon membranes. The experiments consist in measuring reflectance variations in time produced by variations of the optical path thickness due to liquid imbibition into the substrate. The method exploits the fact that nanochannel radii are small compared to light wavelength, therefore the thickness of the layers can be measured by laser interferometry along the fluid flow direction. Accordingly, the refractive index can be computed by using an effective medium theory, and a simple optical scheme is used to analyze the interference pattern. A fluid dynamic model is proposed to describe the liquid penetration in the nanoporous matrix as a function of time. The technique can be used as nanofluidic sensor to determine fluid properties such as viscosity and surface tension of a small sample of liquid, as well as to investigate the internal structure of nanoporous materials. In particular, since nanopore radius is comparable to the molecular size of large biomolecules (DNA, proteins), anodized alumina and silicon membranes provide attractive functionalities to be used in optofluidic biosensing.