Xiu-Tao Lou

Rapid and sensitive SERS method for determination of Rhodamine B in chili powder with paper-based substrates

Surface-enhanced Raman spectroscopy (SERS) was used for detecting Rhodamine B (RB) which is often added illegally to chili powder. Based on density functional theory, the Raman spectrum of RB was calculated and characteristic peaks of RB were assigned to the corresponding vibrational modes. RB was detected utilizing paper-based SERS substrates which were fabricated via a liquid–liquid interface-mediated self-assembly technique. Meanwhile, with simple sample pretreatment, the detection limit could reach 10−6 g g−1 for RB in chili powder (5 × 10−7 g mL−1 in extraction agent). Within the concentration range from 10−2 g g−1 to 10−6 g g−1, Raman intensity follows a certain function in relation to the concentration of RB. The recovery of this method ranges from 96.4% to 108.9%, which gives rapid and reliable quantitative detection of RB in chili powder. Therefore, the proposed SERS method is suitable for on-site detection and analysis of RB in chili powder.

Rapid fabrication of self-assembled interfacial film decorated filter paper as an excellent surface-enhanced Raman scattering substrate

An excellent paper-based SERS substrate was easily fabricated by utilizing interfacial films formed in the mixture of Ag colloid and CH2Cl2. This interfacial film coating method significantly improves the fabrication efficiency of SERS substrates. The substrate has a high coverage of silver nanoparticles (Ag NPs) and can be tailored to arbitrary shapes. The SERS substrate exhibits high sensitivity (EF ∼ 4 × 107) and gives uniform SERS signals with a relative standard deviation (RSD) of 8.08% (spot-to-spot) and 8.65% (batch-to-batch) using 4-mercaptobenzoic acid (4-MBA) as a Raman probe. In addition, this SERS substrate with excellent stability can be stored for more than 30 days. The limit of detection was found to be 10−8 M for 4-MBA. In general, this SERS substrate is qualified for rapid and simple trace detection of various analytes.

Droplet detection: simplification and optimization of detecting conditions towards high sensitivity quantitative determination of melamine in milk without any pretreatment

A new droplet configuration was developed to simplify and optimize the SERS detecting condition using silver colloid as SERS substrate. Samples were measured in solution to improve the evenness of SERS response. The influences of the reflectivity of substrates and height of sample solution on Raman intensity have been studied systematically. Aluminum tape was employed as the supporting platform for SERS detection. Based on the high reflectivity and hydrophobicity of aluminum tape, this configuration is both highly efficient and convenient. The detection limit of melamine is 10−2 ppb in water and the distribution of SERS intensity is regular over the droplet profile with good reproducibility. Under this configuration, melamine in milk can be quantitatively detected without any sample pretreatment in a special order of agent addition. A good linear relationship was obtained at concentrations ranging from 0.05 to 10 ppm (R2 = 0.9963). Our scheme has advantages such as simplicity, improved reproducibility, less time and good accuracy over other methods, which offers tremendous potential for the on-site examination of trace melamine in three types of milk (pasteurized milk, skimmed milk, sweet milk).

A reproducible gold SERS substrate assisted by silver nanoparticles without using extra aggregation agents

Because of excellent molecular specificity, great success in chemical detection using surface-enhanced Raman scattering (SERS) has been achieved. However, the preparation of a simple and reproducible SERS substrate with good enhancement performance is still a challenge. Here we found that a silver-assisted gold SERS substrate can achieve very excellent reproducibility and high enhancement. Owing to the combined utilization of Au NPs and Ag NPs, the substrate can achieve high enhancement without using extra aggregation agents. Because hot-spots are created only by analyte molecules themselves, the adsorption of analytes on the surface of nanoparticles generating hot-spots is more stable and uniform. For colloids substrate, some problems such as random adsorption, large conglomeration are avoided. Thus the excellent reproducibility can be obtained. Besides, interference between analyte molecule and aggregation agent may occur. Thus, elimination of extra aggregation agents is desirable. The relative standard deviation of <3.7% and the enhancement factor of ∼1.5 × 107 are reached. The preparation of the substrate is achieved only by mixing Au colloids with Ag colloids at a certain volume ratio. By SERS measurement of Rhodamine 6G, the performance of the silver-assisted gold SERS substrate is demonstrated.

Direct and quantitative detection of dicyandiamide (DCD) in milk using surface-enhanced Raman spectroscopy

Dicyandiamide (DCD) is a contaminant found in New Zealands milk supply, which needs to be examined for security. In this study, the feasibility of using a SERS technique to detect DCD in milk was evaluated. Assignments of the DCD vibrational spectra have been conducted by DFT calculations. The influences of different aggregating agents and pH have been investigated in terms of their efficiency for detecting DCD. Two detection modes were established for detecting DCD in an aqueous solution. Among the three ions, SO42− provides the best performance in both acidic and alkaline conditions, and the limit of detection in alkaline conditions (with an enhancement factor of 2.88 × 105) is lower than that under acidic conditions. For real milk samples, based on a particular order of agent addition, DCD can be quantitatively detected without any sample pretreatment through an internal standard method. The linear coefficient is 0.99747 at a concentration range from 1 × 10−4 to 1 × 10−3 g mL−1. By exploiting the multi-component detection ability and high sensitivity of SERS, our scheme has advantages such as simplicity, reduced time and good accuracy over other methods, which shows a great promise for the on-site screening of DCD in milk products.

Rapid and simple detection of pethidine hydrochloride injection using surface-enhanced Raman spectroscopy based on silver aggregates

A portable Raman spectrometer was used for the rapid detection using surface-enhanced Raman spectroscopy (SERS) of pethidine hydrochloride injection by employing a silver colloid as the SERS active substrate. Different substrates and aggregation agents were investigated in order to explore the optimum conditions for the SERS detection of pethidine hydrochloride injection. Under the optimum experimental conditions, excellent reproducibility and stability of SERS detection was guaranteed. In addition, the limit of detection (LOD) for pethidine hydrochloride injection in water was low at 0.1 μg mL−1 with an analytical enhancement factor of 5.3 × 104, which is extremely far below typical administered dosages (50 mg mL−1). Finally, a good linear relationship between the Raman intensity and concentration was obtained for pethidine hydrochloride injection in water at a concentration range from 0.1 to 10 μg mL−1 (R2 = 0.999), which lays a favourable foundation for the semi-quantitative analysis of the concentration of pethidine hydrochloride injection. In general, the capabilities reported here demonstrate that the SERS method is convenient, rapid and efficient, and has good potential in clinical applications for point-of-care detection and real-time monitoring.