Effect of Etching Time Variation on Porous Si of SERS Substrate for NS1 Detection

Dengue is a major international public health issue. Since 2015, approximately more than 100,000 reported cases with roughly 200 fatal cases are reported yearly in Malaysia. Early detection of infection during the first five days is crucial for monitoring patients to help in reducing the fatality rate. Dengue virus nonstructural 1 (DENV NS1) protein has gained a lot of interest as an early biomarker for diagnosis of DENV infection. Currently, the presence of NS1 is detected through enzyme-linked immunosorbent assay (ELISA) and immuno-chromatographic (ICT) rapid test kit using patients' blood samples which is invasive and prone to blood infection risks. Interestingly, NS1 is also discovered in saliva but at much lower sensitivity performance at ∼64.7% due to its low concentration. In this study, an ultra-sensitive and specific technique known as Surface-Enhanced Raman Spectroscopy (SERS) is proposed for the detection of low concentration of NS1 in saliva. However, SERS performance is highly dependent on the SERS substrate to be used. In this study, electro-chemical etching technique is employed to fabricate porous silicon (porous Si) with variation in structural features served as the SERS substrate base. The focus of this paper is to report on the structural variation of porous Si due to the different etching time duration. Surface characterization of the sample is investigated through the Field Emission Scanning Electron Microscope (FESEM) and energy-dispersive X-ray spectroscopy (EDX). From the top-view, cross-shaped structures are observed, while from the cross-sectional view, triangle-shaped structures are observed. The size of the formed structure increases as etching time increases. However, at the etching time of 30 min, the constructed structure starts to connect with the neighboring structure producing uneven porous Si.