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A selective and ultrasensitive surface-enhanced Raman spectroscopy (SERS) method was developed for the determination of formaldehyde (HCHO) in environmental waters and food samples. It is based on derivatization of HCHO with 4-amino-5-hydrazino-3-mercapto-1,2,4-triazole (AHMT) with HCHO. One of the products of the derivative reaction, 6-mercapto-5-triazolo[4,3-b]-s-tetrazine (MTT), can be quantified by SERS at 832 cm using silver nanoparticles (AgNPs) as substrates. The incubation time for derivatization, the volume of reagents and the mixing times were optimized. The peak areas of the SERS are linearly related to the concentration of HCHO in the 1 − 1,000 μg L range, the limit of detection is 0.15 μg L, and the limit of quantification is 0.45 μg L. Recoveries obtained by analyzing two spiked samples of environmental water and two spiked food samples were in the range between 91.0 and 108.7 %. There is no significant difference between the results obtained by the present method and the liquid chromatographic method (Chinese industrial standard method, SN/T 1547-2011). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We have developed a SERS method for the determination of o-phenylenediamine (OPD) in water. It is based on the chemical cyclization reaction of OPD with nitrite in acidic medium. Benzotriazole (BTAH), one of the products of the reaction, can be determined by SERS with high sensitivity when using silver nanoparticles decorated with α-cyclodextrin (α-CD-AgNPs) as a substrate. The acidity of the medium, nitrite concentration, reaction time and mixing time for solutions of analytes and SERS substrates were optimized. The enhancement factors of the optimal SERS substrates (even if stored for a few months) range from 2.17 × 10 to 2.52 × 10 when utilizing the SERS peak at 1,602 cm. Other figures of merit include (a) a linear analytical range from 0.10 to 1.0 μmol L, (b) a detection limit of 30 nmol L, and (c) a quantification limit at 100 nmol L. The high selectivity for OPD was confirmed by studies on the potentially interfering species m- and p-phenylenediamine, aniline, and 1-naphthylamine. Recoveries of OPD from spiked real water samples ranged from 97.8 to 104.5 %, with relative standard deviations of less than 4 %. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We have developed a surface-enhanced Raman scattering (SERS) probe for the determination of mercury(II) using methimazole-functionalized and cyclodextrin-coated silver nanoparticles (AgNPs). These AgNPs in pH 10 solution containing sodium chloride exhibit strong SERS at 502 cm. Its intensity strongly decreases in the presence of Hg(II). This effect serves as the basis for a new method for the rapid, fast and selective determination of trace Hg(II). The analytical range is from 0.50 μg L to 150 μg L, and the limit of detection is 0.10 μg L. The influence of 11 metal ions commonly encountered in environmental water samples was found to be quite small. The method was applied to the determination of Hg(II) in spiked water samples and gave recoveries ranging from 98.5 to 105.2 % and with relative standard deviations of <3.5 % ( n = 5). The total analysis time is <10 min for a single sample. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A reversible off-on-type probe for pH sensing with fluorescence and surface-enhanced Raman scattering (SERS) dual-signal output, Rhodamine–phenanthroline (RGP), was designed and synthesized from Rhodamine 6G and 1,10-phenanthroline. Due to the molecular structure transformation between spirocyclic and ring-open forms, RGP exhibits varying fluorescence and SERS activities at different pH levels. The values of acidity constants ( pK a ) and fluorescence quantum yield ( Φ ) of RGP were 2.43 (±0.14) and 0.48, respectively. The fluorescence change of RGP was reversible and took place mainly within the pH range from 1.0 to 4.0. The SERS signals of RGP could be stable more than 3 h under room temperature and with little loss of efficiency after the pH of the sample solution was switched between 3.29 and 6.09 for 5 times. Most of the common inorganic ions and polycyclic aromatic hydrocarbons (PAHs) in water samples have little influence on the analytical performance of the probe. The present probe is simple and easy-to-use for the pH sensing in acidic media. [ABSTRACT FROM AUTHOR]