Abstract
Diatomite consists of fossilized remains of ancient diatoms and is a type of naturally abundant photonic crystal biosilica with multiple unique physical and chemical functionalities. In this paper, we explored the fluidic properties of diatomite as the matrix for on-chip chromatography and, simultaneously, the photonic crystal effects to enhance the plasmonic resonances of metallic nanoparticles for surface-enhanced Raman scattering (SERS) biosensing. The plasmonic nanoparticle-decorated diatomite biosilica provides a lab-on-a-chip capability to separate and detect small molecules from mixture samples with ultra-high detection sensitivity down to 1 ppm. We demonstrate the significant potential for biomedical applications by screening toxins in real biofluid, achieving simultaneous label-free biosensing of phenethylamine and miR21cDNA in human plasma with unprecedented sensitivity and specificity. To the best of our knowledge, this is the first time demonstration to detect target molecules from real biofluids by on-chip chromatography-SERS techniques.