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.

A sensitive and simple method for detecting Cu²⁺ in the water source was proposed by using surface-enhanced Raman scattering spectroscopy (SERS) based on the Ag@SiO₂/Au core–shell composite. The Ag@SiO₂ SERS tag was synthesized by a simple approach, in which Ag nanoparticles were first embedded with Raman reporter PATP and next coated with a SiO₂ shell. The Ag@SiO₂ nanoparticles had strong stability even in a high-concentration salty solution, and there were no changes to their properties and appearance within one month. The Ag@SiO₂/Au composite was fabricated through a controllable self-assemble process. L-cysteine was decorated on the surface of a functionalized Ag@SiO₂/Au composite, as the amino and carboxyl groups of it can form coordinate covalent bond with Cu²⁺, which shows that the Ag@SiO₂/Au composite labelled with L-cysteine has excellent performance for the detection of Cu²⁺ in aqueous media. In this study, the SERS detection of Cu²⁺ was carried out using Ag@SiO₂ nanoparticles, and the limit of detection (LOD) as low as 0.1 mg/L was achieved.

Developing efficient synthetic strategies to construct luminescent MOF materials combined triazolate and tetracarboxylate linkers are still great challenges. In this work, by employing a mixed ligand strategy, a new luminescent Zn-MOF based on mixed carboxylate-azolate ligands was synthesized through a DMF/DMSO system, namely, {Zn₆(ABTC)₂(TRZ)₄(H₂O)₄(DMSO)₂} (MOF1) (ABTC^4- = 3,3′,5,5′-azobenzenetetracarboxylate, TRZ⁻ = 1,2,4-triazole). In this framework, two types of inorganic SBUs and two different conformations of ABTC⁴⁻ ligands assemble into a 3D framework with three different types of open channels. More importantly, MOF1 exhibits a strong blue luminescence property in the solid state at room temperature. Graphical Abstract A rare Zn-MOF based on mixed carboxylate-azolate ligands have been designed and synthesized by utilizing the powerful solvent system of DMF/DMSO, exhibiting a strong blue luminescence property in the solid state at room temperature.