Shell-Isolated Nanoparticle-Enhanced Luminescence of Metallic Nanoclusters.

Metallic nanoclusters (NCs) have molecular-like structures and unique physical and chemical properties, making them an interesting new class of luminescent nanomaterials with various applications in chemical sensing, bioimaging, optoelectronics, light-emitting diodes (LEDs), etc. However, weak photoluminescence (PL) limits the practical applications of NCs. Herein, an effective and facile strategy of enhancing the PL of NCs was developed using Ag shell-isolated nanoparticle (Ag SHIN)-enhanced luminescence platforms with tuned SHINs shell thicknesses. 3D-FDTD theoretical calculations along with femtosecond transient absorption and fluorescence decay measurements were performed to elucidate the enhancement mechanisms. Maximum enhancements of up to 231-fold for the [Au7Ag8(C≡CtBu)12]+ cluster and 126-fold for DNA-templated Ag NCs (DNA-Ag NCs) were achieved. We evidenced a novel and versatile method of achieving large PL enhancements with NCs with potential for practical biosensing applications for identifying target DNA in ultrasensitive surface analysis.

Background-Free Quantitative Surface Enhanced Raman Spectroscopy Analysis Using Core-Shell Nanoparticles with an Inherent Internal Standard.

Surface enhanced Raman spectroscopy (SERS) is an ultrasensitive label-free analytical technique that can provide unique chemical and structural fingerprint information. However, gaining reliable quantitative analysis with SERS remains a huge challenge because of poor reproducibility and the instability of nanostructured SERS active surfaces. Herein, an effective strategy of coating Au nanoparticles (NPs) with ultrathin and uniform Prussian blue (PB) shell (Au@PB NPs) was developed for quantitative detection of dopamine (DA) concentrations in blood serum and crystal violet (CV) contaminants in lake water. The only intense PB Raman signal at 2155 cm-1 served as an ideal and interference-free internal standard (IS) for correcting fluctuations in the Raman intensities of analytes. Also, the stability of Au@PB NPs was investigated, exhibiting good functionality in strong acid solutions and thermal stability at 100 °C. This work demonstrates a convenient and fast quantitative SERS technique for detecting analyte concentrations in complex systems and has a great number of potential applications for use in analytical chemistry.

Rapid and Quantitative Detection of Aflatoxin B1 in Grain by Portable Raman Spectrometer.

Many foodstuffs are extremely susceptible to contamination with aflatoxins, in which aflatoxin B1 is highly toxic and carcinogenic. Therefore, it is crucial to develop a rapid and effective analytical method for detecting and monitoring aflatoxin B1 in food. Herein, a surface-enhanced Raman spectroscopic (SERS) method combined with QuEChERS (quick, easy, cheap-effective, rugged, safe) sample pretreatment technique was used to detect aflatoxin B1. Sample preparation was optimized into a one-step extraction method using an Au nanoparticle-based solution (Au sol) as the SERS detection substrate. An affordable portable Raman spectrometer was then used for rapid, label-free, quantitative detection of aflatoxin B1 levels in foodstuffs. This method showed a good linear log relationship between the Raman signal intensity of aflatoxin B1 in the 1-1000 µg L-1 concentration range with a limit of detection of 0.85 µg kg-1 and a correlation coefficient of 0.9836. Rapid aflatoxin B1 detection times of ∼10 min for wheat, corn, and protein feed powder samples were also achieved. This method has high sensitivity, strong specificity, excellent stability, is simple to use, economical, and is suitable for on-site detection, with good prospects for practical application in the field of food safety.

Rapid and low-cost quantitative detection of creatinine in human urine with a portable Raman spectrometer.

The creatinine concentration of human urine is closely related to human kidney health and its rapid, quantitative, and low-cost detection has always been demanded. Herein, a surface-enhanced Raman spectroscopic (SERS) method for rapid and cost-effective quantification of creatinine concentrations in human urine was developed. A Au nanoparticle solution (Au sol) was used as a SERS substrate and the influence of different agglomerating salts on its sensitivity toward detecting creatinine concentrations was studied and optimized, as well as the effect of both the salt and Au sol concentrations. The variation in creatinine spectra over time on different substrates was also examined, demonstrating reproducible quantitative analysis of creatinine concentrations in solution. By adjusting the pH, a simple liquid-liquid solvent extraction procedure, which extracted creatinine from human urine, was used to increase the SERS detection selectivity toward creatinine in complex matrices. The quantitative results were compared to those obtained with a clinically validated enzymatic "creatinine kit (CK)." The limit of detection (LOD) for the SERS technique was 1.45 mg L-1, compared with 3.4 mg L-1 for the CK method. Furthermore, cross-comparing the results from the two methods, the average difference was 5.84% and the whole SERS detection process could be completed within 2 min compared with 11 min for the CK, indicating the practicality of the quantitative SERS technique. This novel quantitative technique shows promises as a high-throughput platform for relevant clinical and forensic analysis.

Different behaviors in the transformation of PATP adsorbed on Ag or Au nanoparticles investigated by surface-enhanced Raman spectroscopy - a study of the effects from laser energy and annealing.

In order to explore the key role of surface plasmon resonance (SPR) and active (3)O2 for the chemical transformation to 4,4-dimercaptoazobenzene (DMAB) from p-aminothiophenol (PATP) adsorbed on Ag or Au NPs, we systematically investigated the laser wavelength and temperature dependent surface-enhanced Raman spectra of PATP capped Ag and Au NPs. DMAB can be easily observed at the 514.5nm laser for Ag NPs but at the 632.8nm laser for Au NPs, indicating that a suitable energy level is necessary for the formation of DMAB. The tendency is consistent with the wavelength dependent SPR properties of Ag or Au NPs accordingly. With the energy provided by annealing, the transformation of PATP to DMAB is much easier on Ag NPs at a lower temperature, and more DMAB can be observed at the same temperature, compared to the case of Au NPs under the same condition. It is mainly due to the active (3)O2 on Ag surfaces could be more easily formed than that on Au surfaces.