Surface-Enhanced Raman Spectroscopy for the Detection of a Metabolic Product in the Headspace Above Live Bacterial Cultures

Fraud detection in crude palm oil using SERS combined with chemometrics

Edible crude palm oil (CPO) is a vital oil utilized in various industries, including food, pharmaceuticals, and domestic cooking. Unfortunately, reports of CPO adulteration with harmful Sudan dyes have surfaced over the years. Surface-enhanced Raman spectroscopy (SERS) and chemometrics were employed to detect Sudan dyes adulteration in CPO within 900 - 1800 cm^{- 1} Raman peak. The concentration of Sudan dyes detected in CPO samples ranged between 0.005 and 4 ppm. The principal component analysis (PCA) model detected Sudan II and Sudan IV in CPO with 99.88 and 99.90% accuracy. Linear discriminant analysis (LDA) and K-Nearest Neighbors (KNN) also recorded high detection rates of Sudan II and IV dyes in CPO. Sudan II and IV dyes could be detected at 0.0028 ppm and 0.0019 ppm by this sensor. The performance of the Au@Ag SERS sensor was comparable to that of HPLC. This study proved SERS and chemometrics can be used to authenticate edible CPO.

Quantitative Analysis of Salmonella typhimurium Based on Elemental-Tags Laser-Induced Breakdown Spectroscopy

Current rapid bacterial detection methods are dedicated to the classification and identification of bacteria. However, there is still a lack of a method for specific quantitative analysis of certain bacteria. In this work, a method based on elemental-tags laser-induced breakdown spectroscopy (ETLIBS) was developed for the rapid and specific quantitative analysis of Salmonella typhimurium (S. ty). Elemental tags were first synthesized by assembling copper nanoparticles (CuNPs) with poly(thymine) (poly-T) template that linked with the aptamer sequence. Under the specific recognition of the aptamer, S. ty can be fully combined with the elemental tags within 30 min to achieve labeling. Afterward, the silicon nanowires (SiNWs) array modified with Au@Ag nanoparticles (SiNWs-Au@Ag) was employed to capture S. ty in 30 min. Attributed to the rapid analysis superiority of ETLIBS mapping, 100 spectra of SiNWs-Au@Ag/S. ty/CuNPs can be obtained in 5 min. It was found that the peak area of the Cu(I) atomic emission line at 324.75 nm fitted by the Voigt profile was linearly related to the bacterial concentration in the range of 10²-10⁶ CFU/mL(R² = 0.978). Furthermore, ETLIBS mapping achieved a low limit of detection (LOD) of 61 CFU/mL and showed good selectivity to S. ty compared with other bacteria. Besides, the method exhibited preeminent detection performance in spiked samples with the recoveries of 87-113%. With the advantages of rapidity, high efficiency, and specificity, the proposed method is expected to be a powerful tool for bacterial detection.

Ta@Ag Porous Array with High Stability and Biocompatibility for SERS Sensing of Bacteria

The reliable sensing of bacteria by surface-enhanced Raman scattering (SERS) technology necessitates a rational design of a substrate with high sensitivity, stability, and minimal invasion. Hence, a bimetallic Ta@Ag film with a porous array is developed by the magnetron sputtering technique and the structure could be controlled by a Ta dopant. A porous array connected by ligaments with compact granular nanoprotrusions is a fascinating substrate for SERS sensing. It makes steady SERS signals even in harsh chemical environments due to its high structural and chemical stability. The configuration of binary Ta@Ag has higher surface free energy than that of pure Ag, and the strong bactericidal activity of Ag is suppressed efficiently. Using E. coli as a model pathogen, the Ta@Ag porous film could maintain the long-term survival rate of E. coli up to 95% and a limit of SERS detection of E. coli down to 10² CFU/mL, which is measured by the standard colony-counting method. In sum, this work provides a promising strategy to fabricate a corrosion-resistant and biocompatible bimetallic Ta@Ag film with a porous array for the SERS sensing of microbial cells.

Present and Future of Surface-Enhanced Raman Scattering

The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.