Efficient single cell monitoring of pathogenic bacteria using bimetallic nanostructures embedded in gradient porous silicon

Plasmonics silver and palladium bimetallic alloy nanoparticles ((Ag@Pd)NPs) within gradient porosity silicon (GPSi) layer were prepared and investigated successfully as an efficient surface enhanced Raman scattering (SERS) active substrates. The GPSi was fabricated by dynamic etching process using CW, 405 nm, laser diode with a steady decrease of the etching current density from 80 mA/cm(2 )to 10 mA/cm(2) with eight steps for an etching period of 2 min per step. Bimetallic alloy nanoparticles were prepared by ion reduction process. This was attained by immersing the GPSi in a salt solution containing AgNO3 and PdCl2; mixed at equal ratio for immersing time about 60, 120, 180, and 240 s. The bimetallic alloy SERS active substrates for bacterial detection as a function of immersion time were explored by using Field emission scanning electron microscopy, X-Ray diffraction and Fourier transform infrared spectroscopies and Raman measurements. Efficient SERS active substrates were achieved with a uniform and dense aggregation of nanoparticles on bacterial cells by controlling the immersion times. Aggregated bimetallic alloy nanoparticles into GPSi achieved a SERS enhancement factor (EF) 2.1 x 10(3) , 8.6 x 10(4) , 2.3 x 10(5) , and 5.4 x 10(4) with 60, 120, 180, and 240 s immersion time, respectively for detecting an ultra-low concentration of about 1 Cfu/ml.