Sensitive Cylindrical SERS Substrate Array for Rapid Microanalysis of Nucleobases

In this work, a cylindrical-substrate array for surface-enhanced Raman scattering (SERS) measurements was developed to enable analysis of nucleobases in a few microliters of liquid. To eliminate uncertainties associated with SERS detection of aqueous samples, a new type of cylindrical SERS substrate was designed to confine the aqueous sample at the tip of the SERS probe. Poly­(methyl methacrylate) (PMMA) optical fibers in a series of different diameters were used as the basic substrate. A solution of poly­(vinylidene fluoride)/dimethylformamide (PVDF/DMF) was used to coat the tip of each fiber to increase the surface roughness and facilitate adsorption of silver nanoparticles (AgNPs) for enhancing Raman signals. A chemical reduction method was used to form AgNPs in and on the PVDF coating layer. The reagents and reaction conditions were systematically examined with the aim of estimating the optimum parameters. Unlike the spreading of aqueous sample on most SERS substrates, particularly flat ones, the new SERS substrates showed enough hydrophobicity to restrict aqueous sample to the tip area, thus enabling quantitative analysis. The required volume of sample could be as low as 1 μL with no need for a drying step in the procedure. By aligning the cylindrical SERS substrates into a solid holder, an array of cylindrical substrates was produced for mass analysis of aqueous samples. This new substrate improves both reproducibility and sensitivity for detection in aqueous samples. The enhancement factor approaches 7 orders in magnitude with a relative standard error close to 8%. Using the optimized conditions, nucleobases of adenine, cytosine, thymine, and uracil could be detected with limits approaching a few hundreds nanomolar in only a few microliters of solution

Silver Nanoparticle-Decorated Shape-Memory Polystyrene Sheets as Highly Sensitive Surface-Enhanced Raman Scattering Substrates with a Thermally Inducible Hot Spot Effect

In this study, an active surface-enhanced Raman scattering (SERS) substrate with a thermally inducible hot spot effect for sensitive measurement of Raman-active molecules was successfully fabricated from silver nanoparticle (AgNP)-decorated shape-memory polystyrene (SMP) sheets. To prepare the SERS substrate, SMP sheets were first pretreated with <i>n</i>-octylamine for effective decoration with AgNPs. By varying the formulation and condition of the reduction reaction, AgNP-decorated SMP (Ag@SMP) substrates were successfully prepared with optimized particle gaps to produce inducible hot spot effects on thermal shrink. High-quality SERS spectra were easily obtained with enhancement factors higher than 10⁸ by probing with aromatic thiols. Several Ag@SMP substrates produced under different reaction conditions were explored for the creation of inducible hot spot effects. The results indicated that AgNP spacing is crucial for strong hot spot effects. The suitability of Ag@SMP substrates for quantification was also evaluated according to the detection of adenine. Results confirmed that prepared Ag@SMP substrates were highly suitable for quantitative analysis because they yielded an estimated limit of detection as low as 120 pg/cm², a linear range of up to 7 ng/cm², and a regression coefficient (<i>R</i>²) of 0.9959. Ag@SMP substrates were highly reproducible; the average relative standard deviation for all measurements was less than 10%

Rhenium-Based Molecular Trap as an Evanescent Wave Infrared Chemical Sensing Medium for the Selective Determination of Amines in Air

An evanescent wave infrared chemical sensor was developed to selectively detect volatile amines with heterocyclic or phenyl ring. To achieve this goal, a rhenium-based metallacycle with a “molecular-trap” structure was designed and synthesized as host molecules to selectively trap amines with heterocyclic or phenyl ring through Re–amine and π–π interactions. To explore the trapping properties of the material, a synthesized Re-based molecular trap was treated on an IR sensing element, and wide varieties of volatile organic compounds (VOCs) were examined to establish the selectivity for detection of amines. Based on the observed IR intensities, the Re-based molecular trap favors interaction with amines as evidenced by the variation of absorption bands of the Re molecular trap. With extra π–π interaction force, molecules, such as pyridine and benzylamine, could be detected. After optimization of the parameters for IR sensing, a rapid response in the detection of pyridine was observed, and the linear ranges were generally up to 10 mg/L with a detection limit around 5.7 μg/L. In the presence of other VOCs, the recoveries in detection of pyridine were all close to 100%

Single-Step Preparation of Silver-Doped Magnetic Hybrid Nanoparticles for the Catalytic Reduction of Nitroarenes

This study adopts a simple but facile process for preparing silver-doped magnetic nanoparticles by the spontaneous oxidation–reduction/coprecipitation method. The preparation can be achieved in one pot with a single step, and the prepared silver-doped magnetic nanoparticles were utilized as nanocatalysts for the reduction of <i>o</i>-nitroaniline. Utilizing the magnetic characteristics of the prepared nanoparticles, the catalytic reactions can be carried out under quasi-homogeneous condition and the nanocatalysts can be easily collected after the conversion is achieved. It can be revealed from the results that the morphologies and the composition of the prepared silver-doped magnetic nanoparticles can be adjusted by changing the conditions during the production, which affects the efficacy of the catalysis. In addition, the catalysis efficiency is also controlled by the pH, temperature, and the amounts of nanocatalysts used during the catalytic reaction. Finally, the silver-doped magnetic nanocatalysts prepared in this study own the advantages of easy preparation, room-temperature catalysis, high conversion ability, and recyclability, which make them more applicable in real utilities