Abstract
Diatomaceous earth—otherwise called diatomite—is essentially composed of hydrated biosilica with periodic nanopores. Diatomite is derived from fossilized remains of diatom frustules and possesses photonic-crystal features. In this paper, diatomite simultaneously functions as the matrix of the chromatography plate and the substrate for surface-enhanced Raman scattering (SERS), by which the photonic crystal-features could enhance the optical field intensity. The on-chip separation performance of the device was confirmed by separating and detecting industrial dye (Sudan I) in an artificial aqueous mixture containing 4-mercaptobenzoic acid (MBA), where concentrated plasmonic Au colloid was casted onto the analyte spot for SERS measurement. The plasmonic-photonic hybrid mode between the Au nanoparticles (NP) and the diatomite layer could supply nearly 10 times the increment of SERS signal (MBA) intensity compared to the common silica gel chromatography plate. Furthermore, this lab-on-a-chip photonic crystal device was employed for food safety sensing in real samples and successfully monitored histamine in salmon and tuna. This on-chip food sensor can be used as a cheap, robust, and portable sensing platform for monitoring for histamine or other harmful ingredients at trace levels in food products.
Highlights
Diatom frustules are single-celled algae that possess a biogenic silica shell with periodic nanopores on the surface [1,2]
We report the progress of using diatomite photonic crystals as a robust lab-on-a-chip platform for separating and detecting harmful chemicals in complex real food samples
A 100× objective lens focused onto a single diatomite frustule, and a Halogen lamp was used as the light source
Summary
Diatom frustules are single-celled algae that possess a biogenic silica shell with periodic nanopores on the surface [1,2]. Hybrid photonic-plasmonic modes were formed between the diatom photonic biosilica and plasmonic nanoparticles, which could enhance the local optical field near the plasmonic NPs and additional SERS enhancement was obtained [16,17,18,19,20,21] These biosensors were employed for TNT and mouse IgG sensing, in which the sensitivity was achieved to 10−10 M and 10 pg/mL, respectively. The TLC chips were fabricated using diatomite photonic crystal biosilica and used for identification of several kinds of harmful compounds (Sudan I and histamine) in food samples. The diatomite photonic crystal plate enhanced with plasmonic nanoparticles produced in this study could achieve nearly 10 times the increment of the intensity of SERS spectra than a normal TLC chip with silica gel layers. We successfully demonstrated on-chip detection of histamine from mixed salmon samples and from real spoiled tuna using a TLC-SERS method without any sample pretreatment
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