Paper-based plasmon-enhanced protein sensing by controlled nucleation of silver nanoparticles on cellulose

Cheap, disposable bio-diagnostic devices are becoming increasingly prevalent in the field of biosensing. Earlier we had reported the ability of cellulosic surface to control the nucleation of plasmonic silver nanoparticles and in this report we utilize this nucleation controlling property to demonstrate a new plasmonic sensing mechanism based on paper substrates to quantitatively detect proteins. On contrary to conventional paper based diagnostic devices which use the cellulosic part of paper as a support structure, the proposed method takes advantage of cellulose as nucleation controller during silver nanoparticle formation. Reduction of silver ions interacting competitively with nucleation controlling cellulosic surface and reduction suppressing amino acids of protein (via complexation) resulted in silver nanoparticles whose size-shape dependent plasmonic property quantitatively reflected the concentration of protein on paper, characterized using UV-Vis and surface-enhanced Raman spectroscopies. As a proof-of-concept, bovine serum albumin (BSA) was tested as the target analyte. UV-Vis spectroscopy based BSA quantification was sensitive in the concentration range 10-60 mg ml(-1) while that for surface enhanced Raman spectroscopy extended well below 10 mg ml(-1), thus demonstrating the potential of this simple method to quantitatively detect a wide range of proteins relevant to the field of biodiagnostics.