A simple drop‐and‐detect method using porous alumina ceramics as platforms for rapid surface‐enhanced Raman spectroscopy

Abstract

We propose a simple and rapid surface‐enhanced Raman spectroscopy (SERS) method based on the dropping and detection of a sample droplet on a porous alumina ceramic platform (ACP). The SERS versatility of the proposed drop‐and‐detect method was demonstrated by using well‐studied water‐soluble melamine and ethanol‐soluble 4‐mercaptobenzoic acid as Raman probes. Colloidal silver nanoparticles were used as SERS substrates. Because of the fast permeation of the sample droplet by using ACPs, reproducible SERS measurements could be performed within a minute after the dropping of the sample solution. In comparison with its counterpart quartz plate, the cost‐effective ACP made the uniformity of the distribution pattern of the dried droplet improved by an order of magnitude. The measurement sensitivity was also greatly improved by using ACPs due to their enrichment functions. The lowest detectable concentrations achieved for melamine and 4‐mercaptobenzoic acid were 2.5 µg/l and 2.5 × 10−8 mol/l, respectively. The proposed drop‐and‐detect method was also demonstrated by quantitative detection of trace level melamine in liquid milk achieving a lowest detectable concentration of 0.1 mg/l, indicating its advantages of simplicity and efficiency for practical SERS applications. Copyright © 2016 John Wiley & Sons, Ltd.

Porous alumina aerogel with tunable pore structure for facile, ultrasensitive, and reproducible SERS platform

“…Similar with the effect of PEG addition, the increase of the gelation temperature also leads to form larger sheet‐like particles with larger pore size as shown in Figures d and e. For a comparison, ACP was also used as platform. As shown in Figure f, ACP is agglomerated by spheroidal‐like particles and mainly consisting of microscale pores (>1 μm).…”

“…Besides, 2D nanostructured materials deposited with noble metal NPs, such as anodic aluminum oxide layer, polymer thin films, filter paper, and porous silicon layer, are also prepared as SERS substrates. Furthermore, 3D porous structures embedded with Ag or Au NPs have also been exploited as efficient SERS substrate, such as porous polymers, porous silicon, porous alumina membranes and ceramics, and porous glass ceramics . Compared with colloid and 2D SERS substrate, it is recognized that 3D substrate can provide 3D spatial structure and larger specific surface area (SSA) for fast permeation and binding of more target analytes to form more hot spots within the laser‐illumination area, resulting in better SERS performance .…”

“…After heated at 1200°C, the alumina aerogel has a robust mesoporous skeleton, pore diameter mainly ranging from 2 to 50 nm, and a high surface area . Compared with porous alumina membranes and porous alumina ceramics, alumina aerogel platform has higher porosity, larger SSA, and smaller pore size for the better filtration and adsorption of metal NPs and target analytes.…”

“…The pore structure and surface morphology of monolithic alumina aerogel from sol–gel method were tuned by adding PEG‐400 and varying the gelation temperature. Macroporous alumina ceramic platform (ACP) reported in literature was also used for comparison. The effects of surface morphology and pore size of alumina aerogel platform on SERS performance were investigated.…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XII

“…Lou et al described a simple drop‐and‐detect method using porous alumina ceramics as platforms for rapid SERS spectroscopy. Their proposed drop‐and‐detect method was demonstrated in relevant way by the quantitative detection of trace levels of melamine in liquid milk achieving a lowest detectable concentration of 0.1 mg/L, indicating its advantages of simplicity and efficiency for practical SERS applications . Nicolson et al described through barrier detection of ethanol using handheld Raman with conventional Raman (CR) versus spatially offset Raman spectroscopy (SORS).…”