Electrochemistry shows great potential for biosensing due to its easy-operation (typically with a three-electrode system) and rapid measuring, particularly for portable substrates so they can be integrated as electrode conveniently with the system. The electrical and physical properties make metallic nanoparticles suitable materials for electrochemical biosensors. Metallic nanoparticles can not only facilitate electron transfer with high conductivity but also immobilize molecules of interest. Among metals, silver is the best conductor and silver nanoparticles (AgNPs) can be easily obtained through chemical synthesis. Conductive carbon tapes are a good candidate for deposition of metallic nanoparticles. They can not only make the substrates flexible and portable but also provide good conductivity during electrochemical measurements. They can be self-assembled with metallic nanoparticles. Therefore, in this work, double-sided adhesive carbon tapes coated with AgNPs are fabricated in a simple way. With the prepared conductive substrate as working electrode in a three-electrode system, urea and other proteins at low concentration were measured with cyclic voltammetry (CV). The results showed that carbon tapes coated with AgNPs were able to detect urea with strong signals and that different proteins on the substrates can also be identified. Moreover, urea can be distinguished from proteins or other samples such as plasma including several components on this substrate via EC biosensing.
Surface-enhanced Raman Scattering (SERS) is a promising technique for biosensing due to its high sensitivity at low concentration of analytes of interest. Via this technique, Raman signals of detected molecules are significantly enhanced on the surface of metal or metallic nanostructures. Metallic nanoparticles are widely used for biosensors based on SERS due to their optical and physical properties, generating high enhancement factor. The enhancement factor of SERS is not only dependent on the materials but also dependent on the size, shape and architecture of the substrates. Biosilica diatoms make good candidates that are attractive for plasmonic composite since they show natural nanostructures with a great diversity, which lead to their unique mechanical and optical properties. Therefore, in this work, diatoms and metallic nanoparticles are combined as a novel biocomposite material for potential applications as biosensors. Silver nanoparticles (AgNPs) were self-assembled with diatoms and then deposited on adhesive office tapes. With the prepared substrate, bacteria and proteins at low concentration were measured with Raman spectroscopy. The results indicated although the substrate based the nanocomposite consisting of AgNPs, diatoms and office tapes is particularly suitable for biological particles at nano- to micro-meter scale, showing better performance on identifying different types or strains of bacteria from each other compared to protein identification due to their larger sizes.