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A new method for the determination of oxytetracycline (OTC) has been established by coupling the catalytic amplification reaction of copper nanoclusters (CuNCs) with the aptamer reaction. CuNCs prepared by a wet chemical method have the catalytic activity for the formation of gold nanoparticles (AuNPs) resulting from a HAuCl4-ethanol (En) reaction. The experimental results showed that OTC aptamer (Apt) can be adsorbed on the surface of CuNCs in a non-specific way, thus inhibiting its catalytic activity. When OTC was added to the solution, the OTC-Apt complex was generated by a specific reaction, which made the CuNCs desorb and restore their catalytic activity. With the increase of OTC, the recovery of the catalytic activity of CuNCs is strengthened, the reaction speed is accelerated, and the number of AuNPs is increased. The generated AuNPs exhibited surface enhanced Raman scattering (SERS) signals at 1615 cm−1 in the presence of Vitoria blue 4R (VB4R) molecular probes, and a resonance Rayleigh scattering (RRS) peak at 586 nm. There is a good linear relationship between the intensities of SERS, or RRS, and OTC concentration at the range of 37.5–300 ng/L or 37.5–225 ng/L, respectively. A new SERS and RRS assay for the determination of trace OTC based on the regulation of CuNCs catalysis was established. [ABSTRACT FROM AUTHOR]

Carbon monoxide (CO) is a commonly poisonous gas. It is important to detect CO in daily life. Herein, a new and sensitive surface enhanced Raman scattering (SERS) and resonance Rayleigh scattering (RRS) coupled di-mode method was developed for CO, based on gold nano-enzyme catalysis and gold nanoprobes. CO can react with HAuCl4 to generate gold nanoparticles (AuNPs) in pH 5.2 HAc-NaAc buffer. The generated AuNPs exhibited SERS activity at 1620 cm−1 in the presence of Vitoria blue B (VBB) molecular probes, and an RRS peak at 290 nm. Based on the AuNP bifunctional probes, the increased SERS and RRS intensities respond linearly with the concentration of CO in the range of 100–1500 ng/mL and 30–5230 ng/mL, respectively. To improve the sensitivity, the produced AuNPs were used as nano-enzyme catalysts for the new indicator reaction of HAuCl4-ethanol (En) to amplify the signal. The sensitive SERS method was coupled with the accurate RRS method to develop a sensitive and accurate SERS/RRS di-mode method for determination of 3.0–413 ng/mL CO, based on the AuNP-HAuCl4-En nanocatalytic reaction and its product of AuNPs as SERS and RRS bifunctional probes. [ABSTRACT FROM AUTHOR]

Highlights • CD Ca exhibited strong catalysis of nanogold reaction between HAuCl 4 and H 2 O 2. • PA binds with CD Ca to inhibit its nanocatalysis. • The intensity of the SERS peak at 1615 cm−1 is increased linearly with Na+ concentration increasing. • The SERS quantitative analysis method for Na+ has high sensitivity. Abstract The Ca-doped carbon dots (CD Ca) exhibited strong catalysis of HAuCl 4 -H 2 O 2 reaction to produce gold nanoparticle (AuNP), using Vitoria blue 4R (VB4r) as molecular probe, it appeared a strong surface enhanced Raman scattering (SERS) peak at 1615 cm−1 in the AuNP nanosol substrate. When catalyst CD Ca increased, the SERS peak enhanced linearly owing to AuNPs increasing, that is, the AuNP concentration is linear to SERS signal. Potassium pyroantimonate (PA) ligand can adsorb on CD Ca surface to inhibit the catalysis and cause the SERS peak decreasing. The analyte of Na+ reacts with PA to produce the stable precipitate of [Na 2 (PA)] and free CD Ca catalyst. The more Na+, the more CD Ca released, and the stronger SERS signal due to more AuNP substrate. Accordingly, a SERS quantitative analysis method for Na+ was developed based on CD Ca catalytic SERS reaction, with a linear range of 0.004–0.043 μmol/L, and a detection limit of 0.0019 μmol/L Na. [ABSTRACT FROM AUTHOR]

• A COF of MaBd was prepared by melamine (Ma) and p -benzaldehyde (Bd). • MaBd can strongly catalyze the GC-HAuCl 4 nanoreaction. • A SERS quantitative method was constructed coupled aptamer with nanoreaction. • The method has high sensitivity and selectivity, and low blank. A highly catalytic and stable covalent organic frameworks (COFs) of MaBd were prepared by the polycondensation of melamine (Ma) and p -benzaldehyde (Bd), and characterized by molecular spectra and electron microscopy. MaBd strongly catalyze the new indicator reaction between glycol (GC) and chloroauric acid to generate gold nanoparticles (AuNP) with strong RRS effect at 370 nm and surface enhanced Raman scattering (SERS) effect at 1617 cm−1 using Vitoria blue B (VBB) as molecular probes. Combining the MaBd nanocatalytic amplification reaction with highly selective aptamer (Apt) of glyphosate (GLY), a new, simple and highly sensitive SERS method was developed with a linear range of 0.003−0.07 nmol/L, and the detection limit of 0.002 nmol/L GLY. GLY in soil samples were analyzed by this SERS method, with relative standard deviation of 4.78–5.71 % and recovery of 92.3–105.3 %. [ABSTRACT FROM AUTHOR]

• Highly catalytic N-doped carbon dots (N-CDs) were prepared by microwave irradiation. • The N-CDs catalytic nano-reaction was utilized to amplify SERS signal. • The N-CDs nanocatalytic reaction was coupled with the affinity reaction. • A highly sensitive and selective SERS quantitative method was developed for biotin. Highly catalytic and stable N-doped carbon dots (N-CDs) were prepared rapidly by microwave procedure using glucose as precursor and ammonium sulfite as N-dopant. The reduction of AgNO 3 by trisodium citrate (TCA) was slow to form nanosilver (AgNP), and the N-CDs exhibited strong catalysis of the AgNP reaction. The formed AgNPs were used as indicator in the presence of Vitoria blue B (VBB) molecule probe with a SERS peak at 1615 cm−1. With the increase of nancatalyst N-CDs concentration, the AgNP reaction speed up, and the SERS peak of VBB enhanced linearly due to formation of more AgNPs as substrate. In the presence of avidin (Ad), the SERS peak weakened. Upon addition of biotin, the SERS peak enhanced due to turn on the indicator nanoreaction. The enhanced SERS signal had a good linear relationship with the biotin concentration in range of 0.0006–0.021 ng/mL, with a detection limit of 0.3 pg/mL. [ABSTRACT FROM AUTHOR]