Fabrication of flexible, cost-effective, and scalable silver substrates for efficient surface enhanced Raman spectroscopy based trace detection

Optimization of Paper-Based Alveolar-Mimicking SERS Sensor for High-Sensitivity Detection of Antifungal Agent

Crystal violet (CV) is a disinfectant and antifungal agent used in aquaculture that plays a vital role in treating aquatic diseases and sterilizing water. However, its potential for strong toxicity, including carcinogenicity and mutagenicity, upon accumulation in the body raises concerns regarding its safe use. Therefore, there is a growing need for the quantitative detection of CV in its early application stages to ensure human safety. Recently, Raman spectroscopy-based surface-enhanced Raman scattering (SERS) detection research has been actively conducted; consequently, an alveolar-mimicking SERS paper (AMSP) inspired by the structure of the human lungs was developed. The AMSP was optimized through various factors, including paper type, reducing agent, reducing agent concentration, and reaction time. This optimization enhanced the surface area of interaction with the target substances and promoted hotspot formation, resulting in enhanced SERS performance. The substrate exhibited exceptional uniformity, reproducibility, and reliability. CV was successfully detected at a concentration of 1 nM in laboratory settings. Furthermore, the AMSP detected CV at 1 nM in real-world environmental samples, including fish farm water and human serum, confirming its potential as a practical detection and monitoring platform for CV in real-world samples.

Plasmonic nanoparticle sensors: current progress, challenges, and future prospects

Plasmonic nanoparticles (NPs) have played a significant role in the evolution of modern nanoscience and nanotechnology in terms of colloidal synthesis, general understanding of nanocrystal growth mechanisms, and their impact in a wide range of applications. They exhibit strong visible colors due to localized surface plasmon resonance (LSPR) that depends on their size, shape, composition, and the surrounding dielectric environment. Under resonant excitation, the LSPR of plasmonic NPs leads to a strong field enhancement near their surfaces and thus enhances various light-matter interactions. These unique optical properties of plasmonic NPs have been used to design chemical and biological sensors. Over the last few decades, colloidal plasmonic NPs have been greatly exploited in sensing applications through LSPR shifts (colorimetry), surface-enhanced Raman scattering, surface-enhanced fluorescence, and chiroptical activity. Although colloidal plasmonic NPs have emerged at the forefront of nanobiosensors, there are still several important challenges to be addressed for the realization of plasmonic NP-based sensor kits for routine use in daily life. In this comprehensive review, researchers of different disciplines (colloidal and analytical chemistry, biology, physics, and medicine) have joined together to summarize the past, present, and future of plasmonic NP-based sensors in terms of different sensing platforms, understanding of the sensing mechanisms, different chemical and biological analytes, and the expected future technologies. This review is expected to guide the researchers currently working in this field and inspire future generations of scientists to join this compelling research field and its branches.

Machine learning-based exosome profiling of multi-receptor SERS sensors for differentiating adenocarcinoma in situ from early-stage invasive adenocarcinoma

Exosomes, extracellular vesicles released by cells, hold potential as diagnostic markers for the early detection of lung cancer. Despite their clinical promise, current technologies lack rapid and effective means to discriminate between exosomes derived from adenocarcinoma in situ (AIS) and early-stage invasive adenocarcinoma (IAC). This challenge arises from the intrinsic structural heterogeneity of exosomes, necessitating the development of advanced methodologies for precise differentiation. Here, we demonstrate a novel approach for plasma exosome detection utilizing multi-receptor surface-enhanced Raman spectroscopy (SERS) technology to differentiate between AIS and early-stage IAC. To accomplish this, we synthesized a stable and uniform two-dimensional SERS substrate (BC/Au NPs film) by fabricating gold nanoparticles onto bacterial cellulose. We then enhanced its capabilities by introducing multi-receptor SERS functionality via modifying the substrate with both low-specificity and physicochemical-selective molecules. Furthermore, by strategically combining all capturer-exosome SERS spectra, comprehensive "combined-SERS spectra" are reconstructed to enhance spectral variations of the exosome. Combining these features with partial least squares regression-discriminant analysis (PLS-DA) modeling significantly improved discriminatory accuracy, achieving 90% sensitivity and 95% specificity in distinguishing AIS from early-stage IAC. Our developed SERS sensor provides an effective method for early detection of lung cancer, thereby paving a new way for innovative advancements in diagnosing lung cancer.

Au-NP-Decorated Cotton Swabs as a Facile SERS Substrate for Food-Safety-Related Molecule Detection

Recently, food safety has received considerable attention, and various analytical techniques have been employed to monitor food quality. One of the promising techniques in this domain is the surface-enhanced Raman scattering (SERS) technique. This study developed a facile, cost-effective SERS method by supporting a wipe-type substrate with a small-head cotton swab. We fabricated Au-nanoparticle (NP)-decorated cotton swabs (CS-Au NP) via the dropwise addition of gold colloid on the cotton fibers. These swabs exhibit reduced gold colloid consumption and a compact fiber structure, allowing for the uniform distribution of Au NPs and easy capture of molecular signals. Experiments were conducted to obtain a CS-Au NP wiper performance optimized for cotton swab selection, NaCl concentration, and Au NP layers. The Raman reporter molecule 4-mercaptopyridine was detected at a concentration of 1 × 10^-8 M and a relative standard deviation of ≤10%. The proposed SERS platform enables the facile and reliable detection of food-safety-related molecules such as malachite green on the surface of fruits and vegetables. This paper describes the development of an easy, cost-effective, and environment-friendly method of detecting food-safety-related molecules on various food surfaces through SERS.

Low-cost and flexible paper-based plasmonic nanostructure for a highly sensitive SERS substrate

The application of a noble-metal-based plasmon-enhanced substrate to detect low-concentration analytes has attracted extensive attention. Most of the substrates used in recently reported researches are based on two-dimensional structures. Hence, we prepared a higher efficiency Raman activity substrate with a filter paper structure, which not only provides more plasmonic "hot spots," but also facilitates analyte extraction and detection due to the flexibility of the paper. The preparation of the plasmonic paper substrate adopted centrifugation to deposit the alloy nanoparticles onto the paper base. The optimal particle deposition condition was found by adjusting the centrifugal force and centrifugation time. Then, the surface-enhanced Raman spectroscopy (SERS) performance of the substrate was enhanced by altering the plasmon resonance peak on the surface of the nanoparticles. The enhancement factor of this paper-based substrate was 1.55×10⁷, with high detection uniformity (10^-6 M, rhodamine 6G) and a low detection limit (10^-11 M, rhodamine 6G). Then, we applied the SERS substrate to pesticide detection; the detection limit of the thiram reached 10^-6 M. As a result, the simple and cost-effective paper-based SERS substrate obtained in this way has high detection performance for pesticides and can be used for rapid detection in the field, which is beneficial to food safety and environmental safety.