Early Detection of Ovarian Cancer Cells using Silica Nanowires and CA125 Biomarkers

In this work, an electrochemical bio-sensor using aligned silica nanowires in a micro-fluidic platform is proposed for sensitive and specific estimation of targeted species namely CA125 antigens essential for the early detection of ovarian cancer. The silica nanowires were grown selectively on the Si-wafer using the novel approach of ion implantation (Pd) induced VLS growth. 1 This particular approach not only helps to control the specific site but also size and distribution of nanowires, which could be further improved by controlled annealing during or after ion implantation. Further, silica nanowires were modified with OC125 antibody for specific cancer associated CA125 antigen detection. Consequently, the corresponding change in the electronic properties as a result of selective binding is measured using square wave voltammetry (SWV), already established in our group. The antibody receptor modified silica nanowires serves as a working electrode, while counter electrode was fabricated in Pt, accomplished using photolithography, subsequent e-beam evaporation and lift-off of Ti/Pt electrodes, also a double junction Ag/AgCl reference electrode was deposited on the Si chip. A 60 µm tall micro-fluidic chamber was fabricated in SU-8 (Microchem Corp. Newton, MA) to hold the reagents. Special care was taken to prevent any outgassing or contamination by hard baking the SU-8 chamber at 180 0 C for 3 m. The directed assembly/alignment of the nanowires was achieved using electrophoresis technique. Figure 1 shows the SEM images of the assynthesised silica nanowires. The nanowires grow with diameters ranging from about 15 to 90 nm and length was observed to vary up to about 50 µm corresponding to an aspect ratio of up to ~3000.